Marine and Freshwater Resources Institute
O Box 114 Queenscliff Victoria 3225 Australia
1. THE SPECIES Galeorhinus galeus
1.1 Taxonomy
The species is currently classified in the order Carcharhiniformes, family Triakide, genus Galeorhinus, species Galeorhinus galeus (Linnaeus 1758). Taxonomic synonyms adopted at various times are Squalus rhinophanes Peron 1807; Galeus vulgaris Fleming 1828; Galeus canis Bonaparte 1834; Galeus nilssoni Bonaparte 1846; Galeus communis Owen 1853; Galeus linnei Malm 1877; Galeus australis Macleay 1881; Galeus zyopterus Jordan & Gilbert 1883; Galeus chilensis Perez Canto 1886; Galeus molinae Philippi 1887; Carcharhinus cyrano Whitley 1930; and Galeorhinus vitaminicus de Buen 1950. Other scientific names used recently are Galeorhinus australis (Macleay 1881); Galeorhinus zyopterus (Jordan & Gilbert 1883); are Galeorhinus chilensis (Perez Canto 1886).
Common names adopted for Galeorhinus galeus vary depending on region. In English speaking countries it is called ‘school shark’ in Australia and New Zealand, ‘soupfin’ in the US, ‘tope’ in the north-eastern Atlantic, and ‘soupfin’ or ‘vaalhaai’ in South Africa. It is referred to as ‘cazón’, ‘tiburón vitamínico’ (vitamin shark) or ‘tiburón trompa de cristal’ (glass-snouted shark) in Argentina and Uruguay, ‘çãcao-bico-de-cristal’ (glass-snouted shark) in Brazil, and ‘requin-hâ’ in French speaking countries of the North East Atlantic.
1.2 Distribution
G. galeus is found in temperate waters of the North East and South West Atlantic, eastern North and South Pacific, off South Africa, southern Australia and New Zealand (Compagno 1984). In the North East Atlantic, it ranges from 23°N off Mauritania (Maurin and Bonnet 1970) to 70°N north of Iceland (Stevens 1990), into the Mediterranean and 1000 nautical miles (nm) offshore to the Azores (Fitzmaurice 1979), and from shallow water to 475m depth (Maurin and Bonnet 1970). In the South West Atlantic, it occurs off Argentina to about 43°S (Van Der Molen et al. 1998) and possibly to 45°S (Menni and Gozstonyi 1982) north through Uruguay and into southern Brazil to 30°S during winter with the influx of the cold Malvinas bottom current. Peres and Vooren (1991) record it to 375m depth off Brazil. In the North East Pacific, G. galeus ranges from central Baja California at 27°N to 55°N in Hecate Strait, northern British Columbia (Hart 1973) and to a depth of 411m (Eschmeyer et al. 1983). Compagno (1984) gives its distribution in the South East Pacific as about 10°S in Peru to 55°S in Chile. Off southern Africa, G. galeus is found from southern Namibia (28°S) to East London (36°S) and from shallow bays to 300m depth (Compagno et al. 1991); Van der Elst and Vermeulen (1986) cite its presence in depths to 450m. In Australasia, G. galeus has been recorded from about 30°S to 45°S in southern Australia through the Tasman Sea to all coasts of New Zealand where it has been caught to a depth of 800m.
1.3 Stock structure
The only detailed information on stock structure of G. galeus is from Australasia. Tagging studies in Australia were carried out in the 1940s and 1950s by (Oísen 1953; Oísen 1954) and in the 1970s and 1990s by Waiker et al. (1997b), Stevens and West (1997) and H. Williams (Pers. Comm.). In New Zealand, G. galeus have been tagged from 1985 to the present (McGregor 1994). A genetic study employing allozyme and mitochondrial DNA techniques examined material from different regions in southern Australia, New Zealand, South Africa, Argentina, and England (Ward and Gardner 1997). A total of 29 allozyme loci were screened of which only two were polymorphic (degree of polymorphism 0.069; degree of heterozygosity 0.019); since there was little variation allozymes are of very limited use for population comparisons. The limited allozyme data using the PEPS-2 locus showed a significant difference between Australia (pooled samples) and New Zealand (p = 0.04) and between Australia and South Africa (p < 0.001).
Ten restriction enzymes were screened for mitochondrial DNA analysis of which one (Hind 111) showed sufficient variation for comparative purposes. Using Hind 111, samples from Argentina and England were differentiated from all other samples, with South Africa differentiated from Australian samples. There was no significant difference between samples from South Australia, Victoria and Tasmania. When the Australian samples were pooled and compared with New Zealand; limited differentiation was evident (p = 0.052).
Results from the various tagging studies show mixing across all regions of the species Australian range. A number of trans-Tasman tag recaptures show there is also mixing between Australia and New Zealand (Coutin et al. 1992). Combined with the genetic data, this suggests mixing of Australian and New Zealand populations on common feeding grounds, but little evidence of inter-breeding. In the North East Atlantic, tagging studies (Holden and Harrod 1979; Fitzmaurice 1979; Stevens 1990) show mixing throughout the species' range with tagged fish recaptures in England coming from as far as north of Iceland, the Azores and Canary Islands. In the North West Pacific, limited tagging (Herald and Ripley 1951) has shown mixing across the range of the stock from southern California to British Columbia.
2. THE FISHERIES FOR G. galeus
2.1 Origins and evolution of the catch
The histories of the fisheries for G. galeus in southern Australasia, South Africa, the west coast of North America in the North East Pacific and east coast of South America in the South West Atlantic are similar. Only the history of the fishery for this species in the North East Atlantic differs as G. galeus has been taken mainly as bycatch. The earliest recorded harvest of G. galeus by settlers in southern Australia and New Zealand was for fertiliser and shark-fin soup during the late nineteenth or early twentieth centuries. In south-eastern Australia, the harvest of the species for shark meat began in the 1920s using bottom-set longlines. By the 1930s, the species was also being taken for its meat and fins in South Africa and California. Catches in all these fisheries and in southern Brazil, Uruguay and northern Argentina increased dramatically during World War II as the market for shark liver-oil increased. Catches rose rapidly in response to the demand for shark liver-oil as a source of vitamin A to replace cod liver-oil when the cod fleets stopped fishing during the war. The demand for liver oil declined rapidly after the war, initially in response to cod liver-oil resuming as the traditional source of vitamin A, and subsequently to the development of synthetic vitamin A during the 1950s. Markets for G. galeus were subsequently affected during the 1970s and 1980s because of high mercury concentrations in the meat. Hence, G. galeus have been fished commercially in most parts of its range.
Catch data, where available, have been collated from the literature for southern Australia, New Zealand, the Southwest Atlantic and Northeast Pacific (Figure 1). Where necessary catch landing data have been converted from carcass weight to whole weight by multiplying by 1.5; this was done for data presented by Cailliet et al. (1993) and (Walker et al. 1998b). Data from only one fishing port are available from each of Uruguay and Brazil and are therefore incomplete for these two countries. Gaps in the time series of catches imply the data are not available and there are insufficient data from South Africa and the North East Atlantic to present trends. Some of these trends have contributed to the commonly held view that shark fisheries are ‘boom and bust’ fisheries. The Californian G. galeus fishery is one of the most cited examples of a collapsed shark fishery.
Figure 1
Galeorhinus galeus catch trends for four regions of the world
(There are insufficient data to present trends for South Africa and North East Atlantic; sources are presented on figures; and gaps imply no data.)
In addition to the remarkable similarities in the development of the G. galeus fisheries, there are interesting similarities between the species mix of species of temperate-water demersal and semi-pelagic sharks inhabiting the continental shelf and slopes taken commercially with G. galeus by bottom-set gill-net and bottom-set longline methods. Some of the other species taken include large quantities of one or two species of Mustelus, and small quantities of bronze whaler (Carcharhinus brachyurus), broadnose sevengill shark (Notorynchus cepedianus) and one or two species of the genera Callorhinchus, Squalus and Squatina.
2.2 Southern Australia
G. galeus, along with other species of shark, were used as fertiliser for Tasmanian orchards between 1875 and the early 1920s (Tenison-Woods 1882) and small quantities of shark have been taken since European settlement for liver-oil, fins, bait, and leather. Olsen (1959) dates the start of the shark fishery of southern Australia as 1927 when the Melbourne Fish Market recorded a throughput of 4t carcass weight. The fishery in oceanic waters was initiated by rock lobster fishers in Victoria who caught sharks with hooks for southern rock lobster (Jasus edwardsii) bait. Because of transportation and storage difficulties the fishery was restricted to central and eastern Bass Strait waters closest to the Melbourne Fish Market. By the mid-1930s annual catches were around 400– 500t.
When World War II created a national demand for greater food production and demand for vitamin A from shark liver-oil, the fishery expanded rapidly to include, with the exception of the west coast, most regions around Tasmania and south-eastern region of South Australia (Figure 2). Demand for liver-oil after the war continued and between 1944 and 1949, when liver-oil prices peaked, the fleet in Victoria alone grew from 35 to 62 vessels (excluding those working from Lakes Entrance) and the fishery rapidly spread to central and western South Australia. The overall catch reached approximately 2000t.
Initially, fishers used bottom-set longlines with several hundred baited hooks to target large mature G. galeus over the summer months as they entered shallow waters to give birth. Large mature gummy sharks (Mustelus antarcticus) were often taken as a non-targeted catch. As the abundance of adult sharks in shallow water declined shark fishers targeted sub-adult sharks offshore to the shelf break. For vessels working out of Stanley, north-west Tasmania, during the 1940s, Olsen (1959) recorded that catch rates for G. galeus declined by 70% and distances of trips increased from 3 to 24nm. By 1943 vessels working off the Victorian coast were fishing 40 – 60nm south and seaward of their home ports and between 1944 and 1956 catch rates of Victorian vessels fell by more than half. In the absence of effort control the catch of juvenile G. galeus in Port Phillip Bay declined by around 80% between 1942 and 1955.
The price of shark liver-oil collapsed in 1949 and the fishery for sub-adults in Victoria became uneconomic as their livers have a lower oil content and attracted lower prices. Many Victorian fishers changed fisheries and moved west to South Australia (around Robe and Port Lincoln), or south to Tasmania where large mature sharks could be targeted. Through the 1950s catches from Victoria and Tasmania fell by more than 50% while South Australian catches doubled. Overall catches remained around the 1940s level. Olsen (1959) noted the same pattern of development in the new fishing grounds of South Australia; initially large adult sharks were targeted inshore during spring then the fishery targeted smaller sub-adults on the shelf as adult stocks declined.
There was no further growth in the fishery until the early 1960s as the demand for shark meat grew in Victoria. During 1964 the Victorian fishers introduced gill-nets into the fishery and by the early 1970s most of the catch was taken by this method. Production rose rapidly during the 1960s and peaked in 1969 at 3756t untrimmed carcass weight, consisting of mainly G. galeus. During the 1970s, production declined initially in response to declining stocks of G. galeus, and fell sharply in 1972 when the 1972–85 ban on the sale of large G. galeus was adopted because of their mercury content. For the rest of the 1970s, M. antarcticus replaced G. galeus as the predominant species, then during 1980–87 G. galeus was again the predominant species but since 1988 the G. galeus catch has fallen rapidly while the M. antarcticus catch has remained high. After reaching a second peak in 1986, the combined catch of the two species subsequently declined, partly in response to restrictions on the use of gill-nets and partly to a decline in the abundance of G. galeus (Figure 1).
Figure 2
Region of southern Australian Galeorhinus galeus fishery
The transition from targeting G. galeus to targeting M. antarcticus that occurred in Bass Strait during the early 1970s occurred later in South Australia, around St Vincent Gulf, Kangaroo Island and the Coorong during the late 1970s and early 1980s, when the annual M. antarcticus landings rose from about 100 to 400t. In southern and western Tasmania, and west of Port Lincoln the fishery has remained a fishery targeting G. galeus although there is some evidence that the fishery around Port Lincoln is now beginning the same transition.
In Western Australia, longline and gill-net fishing for shark species developed rapidly during the 1980s. There has been a recent trend of increased targeting of G. galeus in deeper water on the south coast of Western Australia but this appears to have reversed. Annual catches during 1991–97 were 82, 105, 95, 41, 55, 35 and 37t. Off New South Wales the narrowness of the continental shelf limits the habitat area suitable for G. galeus and the stocks support only a few longline vessels. Monofilament gill-nets are banned off New South Wales and most sharks are taken as a bycatch in trawl and inshore teleost fisheries. Demersal trawl vessels operating in southern Australia catch only small quantities of G. galeus.
Operators throughout the fishery principally target M. antarcticus and G. galeus. During 1970–97, these two species provided 47% and 41% of the weight of the catch respectively. The remaining 12% comprised saw shark (Pristiophorus nudipinnis and P. cirratus) (7%), elephant fish (Callorhinchus milii) (2%), and several other species of shark (3%) (Walker et al. 1998b). Whiskery shark (Furgaleus macki) and dusky shark (Carcharhinus obscurus) are important in Western Australia and are taken in small quantities off South Australia. Other less important species taken in the fishery include broadnose sevengill shark (Notorynchus cepedianus), blue shark (Prionace glauca), bronze whaler (Carcharhinus brachyurus), mako shark (Isurus oxyrinchus), and angel shark (Squatina australis). In recent years several fishers have begun using gill-nets on the continental slope to target southern dogfish (Centrophorus uyato), and greeneye spurdog (Squalus mitsukurii), and to a lesser extent endeavour dogfish (Centrophrorus moluccensis) and Harrison's dogfish (Centrophorus harrisoni) for liver-oil. Along with other species of dogfish, these four species are taken as part of the bycatch in the South East Fishery demersal trawl and drop-line fisheries on the continental slope. Total production of dogfish is several hundred tonnes a year but precise estimates are not available because catches of the species are often recorded as ‘dogfish’ or ‘other shark’ or ‘other species’ on logbook returns from the South East Fishery (Walker et al. 1997b).
Bycatch from the fishery is low. Small catches of silver trevally (Pseudocaranx dentex), longsnout boarfish (Pentaceropsis recurvirostris), nannygai (Centroberyx affinis), blue warehou (Seriolella brama), spotted warehou (Seriolella punctata) and John Dory (Zeus faber) are marketed. Draughtboard shark (Cephaloscyllium laticeps) and Port Jackson shark (Heterodontus portusjacksoni) are discarded live.
2.3 New Zealand
In New Zealand, G. galeus, referred to as ‘kapeta’, provided for an important traditional fishery and food source for Maori. The flesh was dried for storage and the liver-oil was used in cosmetics, traditional ceremonies and mixed with pigments for painting canoes, houses and carvings (Paul 1988). Francis (1998) outlines the development of the commercial fishery for G. galeus. A shark processing factory operated north of Auckland. Liver-oil was used as a food additive for calves and the carcasses were used as farm fertiliser for several years at the beginning of the 1900s.
When World War II interrupted imports of halibut and cod liver-oil, liver processing factories were established in Auckland in 1942 and in Wellington in 1943. Annual catch estimates based on the quantity of livers processed indicate a peak of roughly 2500t and the fishery collapsed during the early 1950s when synthetic vitamin A became available. During the late 1950s, an export market for G. galeus meat to Australia developed and annual catch rose to 300–600t between 1957 and 1971. But during 1972 the catch dropped in response to import restrictions when Australia adopted a limit of 0.5 parts of mercury per million parts of meat, wet weight, for all imported fish products, and, in Victoria where most shark meat in Australia is consumed, a legal maximum length of shark was enforced because the mercury concentration in large animals of G. galeus the exceeded the new health standard.
Until 1979 G. galeus were targeted with handlines and longlines with some bycatch (mostly juveniles) taken by trawlers, but during 1979–84, bottom-set monofilament gill-nets were phased in and the catch rose rapidly from 500 to 5000t. The rapid increase was partly in response to Australia relaxing its import restrictions but as a result of fishers establishing ‘catch histories’ before the introduction of a quota management system. The sharks were caught mainly during spring and summer when large sharks, particularly pregnant females, moved into shallow coastal waters. In October 1986, the Total Allowable Commercial Catch was set at 2590t but this was revised to 3106t by 1995–96. Landings have usually been below these set levels.
Longlines, hand-lines and gill-nets used for catching G. galeus also take rig (Mustelus lenticulatus), elephant fish (Callorhinchus milii), C. brachyurus, spiny dogfish (Squalus acanthias) and several other species. These and many other species such as the seal shark (Dalatias licha), shovelnose dogfish (Deania calcea), dark ghost shark (Hydrolagus novaezealandiae), pale ghost shark (Hydrolagus sp.), rough skate (Raja nasuta) and smooth skate (R.. innominata) are taken in the New Zealand trawl fishery (Francis 1998).
2.4 South Africa
Sharks were landed for their meat, fins and skins as early as 1930 in South Africa (Figure 3). The shark fishery expanded rapidly in the South Western Cape region from about 1941 in response to the demand for vitamin A. G. galeus were targeted because they occurred in large numbers, were accessible to inshore vessels and had high levels of vitamin A in the liver-oils. The catch records during World War II were poor and the first estimate of catch was not until about 1947 when a rough figure of 3750t, live weight, was calculated from 250 000 sharks landed in Gans Baai with an estimated mean weight of 15kg. Demand for liver-oil declined rapidly after 1948 and by 1952 when synthetic vitamin A became available the fishery had ceased (Freer 1992). Sharks were initially caught with hand-lines but later with bottom-set gill-nets and short longlines. Catches of up to 1500 sharks could be made during a one-week trip. Following concern about the high catches and high proportion of pregnant females in the catch, a minimum mesh-size of 9 inches (229 mm) was implemented in 1948 (Kroese et al. 1995).
Figure 3
Region of South African Galeorhinus galeus fishery
The G. galeus fishery expanded again in the 1950s as markets for dried and later frozen shark meat developed. Dried meat was exported to Central America and frozen meat was exported to Europe, the Far East and Australia. With the development of markets for frozen shark meat, catches increased to about 2000t until 1967. By 1973, reported landings were ˜ 145 000 sharks; however, high mercury concentrations in G. galeus meat severely restricted export markets for several years. During 1968–1977, catches were generally low as a result of low market price, but the market recovered in the 1980s and 1990s to ~ 1000t/yr.
Hand-line fishers targeting sharks (usually G. galeus or Mustelus spp.) or teleost species (mainly Thyrsites atun, Argyrosomus spp. or Seriola lalandii) take a range of elasmobranch bycatch species that are either landed or discarded (notably Carcharhinus obscurus, C. brachyurus, Triukis megalopterus, Poroderma spp., and various species from the Alopiidae, Hexanchidae, Squalidae and Dasyatidae). Apart from large sharks which break the line most discarded sharks are killed (Kroese et al. 1995).
2.5 South West Atlantic
On the east coast of South America (Figure 4), G galeus is harvested in Argentina, Uruguay and southern Brazil. A liver-oil industry developed rapidly during the 1940s and declined during the 1950s due to market factors as has been described for Argentina (de Buen 1952; Chiaramonte 1998) and Uruguay (de Buen 1952; Praderi 1990), but not for southern Brazil. In a review of shark fisheries of Argentina, Chiaramonte (1998) quoting Siccardi (1950) notes that 45 factories were registered by 1943 to process shark liver-oil. The liver-oil was first exported to the US and later to the UK, Italy, Sweden, Switzerland and some Latin American countries. G. galeus has been landed in ports in the south-central zone of the Buenos Aires province and in northern Patagonia. According to de Buen (1952) most of the catch was landed in Mar del Plata, Quequén-Necochea and Madryn-Rawson during August-November and reached a peak of 10 303t in 1944 and 8 327t in 1945. These are presumably whole weights and include small quantities of the smoothhound Mustelus schmitti. Nevertheless, they represent the highest annual catches for G. galeus anywhere in the world. De Buen (1952) showed that for 1949 the catch was predominantly males during August-September and predominantly females during October-December.
In Argentina during the 1980s, G. galeus again became an important target species and today Mar del Plata and Necochea are the most important ports landing G. galeus. During 1993–96 when the annual catch was 1707–2255t, 80% of the catch was landed in Mar del Plata, 15% in Necochea and 5% in other ports. Also, during 1990–96 when the annual catch was 1707–4381t, the largest catches were taken during November (25% of annual catch) and December (11%); other seasonal peaks occur during May (8%), June (9%) and August (12%) (Argentine oficial sources, unpublished data).
The coastal trawlers targeting mainly false halibut (‘lenguado’ - Paralichthys spp.) and “snails” (‘caracol’ or ‘voluta’ - Adelomelon spp.) take small quantities of G. galeus as bycatch. Most of these sharks are small but they catch large animals migrating south during September-December and north during March-April. Records from a fish processor in Necochea indicate the mean live weight of G. galeus was ~ 2.5kg from trawling during most of the year and 9kg from gill-netting during November-December. During these periods, when G. galeus migrate, many demersal trawlers replace their trawl nets with gill-nets to target G. galeus. In other fishing ports in the Province of Buenos Aries, such as Mar del Plata, Claromecó, Monte Hermoso, Pehuencó, Puerto Rosales and Bahia San Blas, some fishers also use gill-nets during the shark fishing season. At some of these locations, the vessels are launched off the beaches. Artisanal fishers use 100–105mm mesh nets to take M. schmitti (known locally ‘gatuzo’) and several species of teleosts. Some fishers occasionally use 120mm mesh nets to target large M. schmitti which takes a bycatch of G. galeus. Artsanal fishers hand-lining from Monte Hermoso report catching G. galeus of 2–3kg but these were larger towards the end of the year. A bycatch of G. galeus is also taken further south in the Patagonian coastal trawl fisheries where the main target species is hake (Merluccius hubbsi) (Van Der Molen et al. 1998).
Figure 4
Region of South West Atlantic Galeorhinus galeus fishery
About 35 species of sharks and 34 species of rays inhabit the continental shelves of Argentina and Uruguay. Of these only three species are targeted with bottom-set gill-nets: G. galeus, Mustelus schmitti and Carcharhinus brachyurus. Other commercially important species include Squatina argentina, S. guggeheim, Notorynchus cepedianus, Mustelus canis and several species of skates and rays. C. brachyurus and C. taurus are caught by recreational fishers (Chiaramonte 1998). Van Der Molen et al. (1998), analysing bycatches of sharks in Patagonian coastal trawl fisheries, found seven species of shark in the following order of importance: M. schmitti, Squatina argentina, G. galeus, Squalus acanthias, Schroederichtys bivius, Notorynchus cepedianus and Cetorhinus maximus (a single specimen).
The fishery in Uruguay began in 1940 with artisanal fishers in 4.5m row boats setting 600m long cotton-filament gill-nets (‘trasmallos’) 1–2nm from shore in depths of 10–13m. The nets were set parallel to coast and coastal current. During 1950–55, larger boats (8m OAL) were used and were gradually fitted with small deck-houses and outboard motors. Fishing for G. galeus and other sharks (principally Mustelus schmitti and Carcharhinus brachyurus) continued, albeit at a reduced level after the demand for liver-oil ceased, to satisfy a growing demand for fresh and salted (‘bacalao’) shark meat. By 1974, the fishery had contracted to Punta del Diablo with 14 vessels fishing all year round and by 1979 had contracted further because of rising fishing costs. At this time expansion of the trawl fishery in La Paloma exacerbated these problems by taking bycatches of shark and reducing the productivity of the inshore grounds and by damaging the shark gill-nets (Praderi 1990). Praderi (1990) estimated that the artisanal fleet caught 54–140t whole weight annually during 1981–89. Praderi (1990) estimated that there was an incidental kill of 3008 Franciscana dolphins (Pontoporia blainvillei) (50% in the Punta del Diablo region) from bottom-set gill-nets, particularly from the larger mesh-sizes, during 1974–89.
There appear to be no records of a liver-oil fishery for G. galeus in southern Brazil during the 1940s and 1950s. For example, in a detailed description of the fishery in Uruguay and Argentina, de Buen (1952) does not mention southern Brazil. Similarly, in a historical review, Giulietti and de Assumpção (1995) say the fishing industry is one of the oldest in Brazil but make no mention of a shark liver-oil industry during the 1940s or 1950s.
Demersal otter trawl surveys undertaken by the University of Rio Grande during 1980–86 show G. galeus are seasonally abundant at depths of 40–350m (most abundant 40–100m) between latitudes 32°S and 34°30'S; the species is scarce further north. The species is most abundant during June-September and either scarce or absent for the rest of the year (Peres and Vooren 1991). These authors characterise the species as a seasonal migrant entering southern Brazil during autumn, attaining a peak abundance during winter and leaving to travel south during spring. During April-May mainly adolescent and adult pregnant females are present but during June-September individuals of both sexes and all sizes are present. Small sharks (<70cm) are present only during June-August (Ferreira and Vooren 1991).
G. galeus are fished on the continental shelf of southern Brazil at depths from 40 to 200m by otter trawl, pair trawl and bottom-set gill-net from the ports of Rio Grande and Itajaí. Landing statistics refer to ‘cações’, which for these two ports comprises mainly G. galeus with Mustelus schmitti. During 1973–82 catches of cações increased from 1414 to 3217t (Vooren 1990). Catches of cações consist of adults and large juveniles of both sexes, and are landed as headed and gutted carcasses. Annual landings of shark rose from 1414t in 1973 to 3839t in 1987, then declined to 2791t in 1992. Over this period there has been increased targeting and less discarding of shark and while catches from trawlers have dropped with falling CPUE, total landings increased due to a rapid increase of gill-net effort; the latter produced 85% of demersal shark landings in 1992. At present, 60 vessels operate bottom gillnets of 10km average length, landing 85% of total demersal shark landings. Fishing trips last 10–15 days and catches are stored on ice. In 1995, 21 boats fished with gillnets of mostly 8–12km length of monofilament nylon with an average mesh-size of ~140mm, designed for targeting whitemouth croaker (‘corvina blanca’) (Micropogonias furnieri) (C. M. Vooren, pers. comm.. When targeting G. galeus gill-net mesh sizes of 200–220mm are used.
2.6 North East Pacific
In California (Figure 5), G. galeus must have been caught as bycatch in small quantities since the introduction of the demersal trawl fishery in 1876 (Jow 1993) and trammel nets in the 1880s for catching California halibut (Paralichthys californicus) and sharks (Barsky 1993). The trammel nets were constructed of cotton multifilament webbing. Shark landings during 1930–36 were low and stable at about 270t/yr; G. galeus comprised a high percentage of the catch and were landed whole; the fins were removed, dried and sold as soup stock; fillets were sold to consumers as ‘grayfish’, fillet of sole or swordfish (Byers 1940).
The fishery rapidly expanded southward following a new market starting in Monterey and San Francisco for liver-oil during January 1937 and experimental fishing even extended into the waters of Mexico and the Gulf of California where Ensenada and Guaymas were the principal ports. The sharks were landed whole; livers were removed and rest of the shark was processed in to fishmeal (80% protein) for stock food (Byers 1940). Catches expanded rapidly, peaking at 4185t in 1939 and the fishery took on the aspects of a bonanza (Ripley 1946). About 75–80% of the catch comprised G. galeus while the rest was a mixture of spiny dogfish (Squalus acanthias), broadnose sevengill shark (Notorynchus cepedianus), leopard shark (Triakis seminifasciata) and blue shark (Prionace glauca). Prices rose from about $50/t in 1937 to $2000/t in 1941. G. galeus landings were recorded specifically from 1941; they declined from 2172t in 1941 to 287t in 1944. Ripley (1946) reported CPUE in one region declined from 55.4 fish/1000 fathom of gill-net fished for 20 h in 1942, to 7.7 in 1945 and noted that this trend was probably indicative for the whole coast. While the fishery was intensive and expanded rapidly it only lasted eight years. Bottom-set trammel nets, 8–81/2 inch mesh-size monofilament gill-nets (Diamond and Vojkovich 1993; Miller 1993) and longlines have continued to be used to target California halibut and other species such as the Pacific angel shark (Squatina californica) and demersal trawl nets continue to take a small bycatch of G. galeus. More than 50 years later the G. galeus stocks often are assumed not to have recovered despite there being no fisheries specifically targeting them.
Figure 5
Californian region of North East Pacific Galeorhinus galeus fishery
During 1939–44, 11% of the catch was landed in the northern region of California, principally through Eureka (8%) and Fort Bragg (3%); 73% in the central region, principally San Francisco (42%) and Monterey (9%); and 26% in the southern region, principally through Santa Barbara (14%), Newport (4%),and San Diego (3%) (Ripley 1946).
Following collapse of the Californian G. galeus liver-oil fishery in the 1940s, sharks were viewed as of little value. However, in the late 1970s, a growing market demand for shark meat in the US stimulated the growth of shark fisheries on the east, west and gulf coasts. On the west coast, the spiny dogfish (Squalus acanthias) provides by far the largest portion of the shark catch, followed by the common thresher (Alopias vulpinis), shortfin mako (Isurus oxyrinchus), Pacific angel (Squatina californica), blue (Prionace glauca), G. galeus and leopard (Triakis semifasciata) sharks (Cailliet et al. 1993).
Catches of G. galeus off the US West Coast varied during 1976–94, between 100–380t, whole weight; calculated by multiplying dressed weights presented by (Cailliet et al. 1993) by 1.5. Data presented by these authors for 1987–89 indicate 94% of the catch was landed in California, 4% in Oregon and 2% in Washington. In British Columbia, bottom-set gill-nets were used to target G. galeus during the 1940s off the west coast of Vancouver Island and in Hecate Strait, but more recently catches have been negligible (Hart 1973). Of catches landed in California during 1987–94, 36% was landed in Santa Barbara, 26% in San Diego, 20% in Los Angeles, 8% in Monterey, 7% in San Francisco and 3% in Eureka. During 1994, 80% of the catch of this species in California was reported taken by gill-nets, 2% by hook and line, 6% by demersal trawl and 12% by unspecified methods (California Department of Fish and Game, unpublished data).
Although the fishery for G. galeus collapsed during the 1940s, it seems unlikely the stock collapsed. Mainly G. galeus of a relatively large size were caught in California and because the small juveniles, which would take several years to recruit to the fishery, were only lightly fished it is likely the stocks should have recovered after fishing ceased.
Since the fishery collapse there has never been an economic incentive for fishers to target G. galeus. Because of the schooling and highly migratory characteristics of G. galeus, fishers need considerable experience and skill to successfully find and catch this species and today there is little economic incentive to do so. During 1994, for example, the mean price received by the fishers was $1.88/kg for G. galeus, compared with $3.14/kg for A. vulpinis and $2.62/kg for I. oxyrinchus Nevertheless, several fishers occasionally target G. galeus; for example, one fisher operating from Long Beach, Los Angeles, reported catching 0–13 sharks per set in bottom-set gill-nets of total length 2200m and of mesh-size 73/4 inches (197 mm) set 26–36 hours in depths 160–170m during May 1995 (California Department of Fish and Game, unpublished data).
2.7 North East Atlantic
Bonfil (1994) states that G. galeus comprised 6% of the shark landings and is the third most important shark species. Muñoz-Chápuli et al. (1993) report that G. galeus landings have decreased steadily from about 1100t in 1982 to 225t in 1992. The species is exported to Italy where there are problems with mercury in the meat (Anon. 1989). Management comprises limited entry, legal minimum lengths of shark, gear controls restricting effort in the net and hook sectors, closure of nursery areas and some inshore waters, restrictions on mesh-size, and plans for a government buy-back to further reduce effort in the fishery.
2.8 Fleet characteristics, evolution of the fleet and fishing effort
Only in southern Australia has there been a steady evolution of the fleet and fishing effort. Elsewhere the fleets have entered and left the fishery depending on demand. In most regions where G. galeus occur, for much of the history of the fishery, many of the vessels have been engaged on a short-term or part-time basis.
In California, the first vessels to target G. galeus had been engaged in trolling for salmon (Oncorhynchus spp.) and albacore (Thunnus alalunga) from Monterey and San Francisco. These vessels of 6–11m OAL were referred to as ‘market fishing boats’ and had a small deckhouse, clipper bow and short bowsprit. Larger vessels (12–18m OAL) from the northern California halibut fleet soon followed in 1938 and were capable of working with large amounts of longline fishing gear. Several large vessels were built and began operating further afield but these were not as profitable as many of the small vessels already established in other fisheries which could be equipped for shark fishing at little cost. By 1939, an assortment of about 600 vessels were fishing for G. galeus along the entire coast of California (Byers 1940) but most had stopped by 1945 (Ripley 1946).
No details of the vessels targeting G. galeus in South Africa during the 1940s are available. At present, a large number of small vessels (mostly <10m OAL) take small quantities of G. galeus by hand-line. A total of 31 permits have been issued for larger vessels to target sharks with longlines. In addition, about 30 inshore trawlers operate in depths less than 120m and 60 larger offshore trawlers operate in depths >110m off the south and west coasts and take a bycatch of G. galeus (Kroese et al. 1995).
On the east coast of South America there is a large number of vessels with a wide size range taking G. galeus, mainly as bycatch, but they occasionally target the species. Large industrial trawlers (and also pair trawlers) operate out of Itajaí and Rio Grande in southern Brazil, Montevideo in Uruguay, and Mar del Plata, Puerto Quequén-Necochea and Rawson in Argentina. Large gill-net vessels (>20 m) also operate out of Itajaí. Vessels deploying bottom-set gill-nets and longlines out of the southerly Brazilian port of Rio Grande and ports in Uruguay and Argentina tend to be smaller. For example, in the Argentine port of Necochea, which has the largest number of vessels targeting G. galeus, the number of vessels operating varied from 5 to 33 during 1984–96 and peaked in 1992. These coastal wooden vessels varied from 10 to 21m OAL (Chiaramonte 1998). Small artisanal vessels take G. galeus with bottom-set gill-nets and longlines operate out of several ports in Uruguay (e.g. Barra del Chuy, Cabo Polonio, Valizas, Coronilla and Punta del Este) and Argentina. Small vessels are launched of the beaches in ports such Punta del Diablo (6–8m) and Piriapolis (<4m) in Uruguay and Claromecó in Argentina.
In southern Australia, when the target fishery for G. galeus began in the mid-1920s, shark fishing was undertaken from small wooden ‘couta’ boats fitted with sails but these were soon replaced by larger wooden vessels powered by diesel engines as fishers moved further offshore and remained at sea for several days. Since the 1960s there has been a trend to replace the wooden vessels with steel vessels.
During the early stages of the fishery the boats were engaged primarily in the rock lobster fishery taking southern rock lobsters (Jasus edwardsii) and shark fishing was done on a part-time basis. Later, as the fishery developed there was a trend towards specialisation, but even today most of the catch is taken by a relatively small number of specialist vessels. A large number of vessels take small quantities of shark but are primarily engaged in the inshore scale fish and rock lobster fisheries, with a few engaged in commercial scallop (Pecten fumatus) and trawl fisheries.
There were 301 vessels with an Australian Commonwealth Fishing Boat Licence that reported shark catches at least once a month during the period October 1981 to September 1984. Of these, 175 vessels took the majority of their catch using gill-nets and 126 using longlines. In addition, several hundred vessels took small quantities of shark within state waters, some with shark monofilament gill-nets or shark longlines but also as a bycatch using other types of gear in other fisheries (Walker et al. 1997b). The 301 vessels with Commonwealth Fishing Boat Licences had a mean length of 14.5m and ranged from 5 to 32m with the majority (86%) from 10 to 20m. The vessels remaining at sea for several days possess ‘ice-holds’, ‘refrigerated-holds’ or ‘brine-tanks’ for storing the catch, whereas smaller vessels returning to port daily tend to carry the catch either on the deck without ice, in an ‘ice-hold’, or ‘wet-well’.
Estimates of fishing effort are not available for the period before 1973. Nominal ‘equivalent gill-net effort’ peaked during 1987 at 120 000 km-lifts. This was determined by weighting up the nominal total gill-net effort of 99 000 km-lifts during 1987 from the gill-net catch to the combined gill-net and longline catch. This peak followed an increase from 25 000 km-lifts (21% of peak effort) during 1973 and was subsequently followed by a decline to 56 000 km-lifts (47% of peak effort) during 1996. This returned to 66 000 km-lifts during 1997. The G. galeus catch taken by longline was 31% during 1973–81 and 23% during 1982–95, and by 1997 had declined to 8% (Walker et al. 1998b).
2.9 The harvest processes
2.9.1 Bottom-set longline fishing
Bottom-set longlines were more important during the early phases of the various G. galeus fisheries. Most of these fisheries then switched to bottom-set gill-nets. Longline fishing has several advantages over gill-net fishing: (a) longlines can be readily set in deep water on the continental slope where there is the highest risk of losing gill-nets, (b) longlines can be set in strong tidal currents where gill-nets cannot be used effectively, (c) the sharks are usually captured live and therefore less likely to be damaged as a result of being eaten by ‘sea-lice’ (mainly isopods and copepods) or other fish, and (d) longline fishing gear and appropriate hauling equipment is cheaper to purchase and maintain than gill-net fishing gear. An important development in longlining is the use of automatic baiting and attachment of snoods to the main-line when setting the gear. It also facilitates removal of the snoods when hauling the gear. This increases the number of hooks set and the period a vessel can operate each day.
In southern Australia longline fishing is the original method for catching shark but was largely replaced by gill-net fishing during the second half of the 1960s and early 1970s. The longline consists of a sinking main line constructed of 6–8mm dia. synthetic rope (traditionally manilla or sisal rope) with snoods about 1m long attached every 6–10m. Each snood carries a 10/O short-shank (with monol wire trace) or 11/O long-shank Mustad hook (without trace) at one end and was attached to the main-line at the other permanently until the late 1960s and then by means of a ‘snood clip’.
This gear is divided into a number of ‘sets’, each of up to 300 hooks. The hooks together with the main-line and an anchor weight at each end are placed on the seabed. Until adoption in Commonwealth waters of a 2000-hook limit, more than 2000 hooks were commonly used during a single fishing operation; however, the average was less than half this number. Common baits are eel, barracouta and squid. Fresh bait is more effective than frozen bait. A buoy and dahn pole with flag are attached by way of buoy-line to the main-line at each end for retrieval of the gear. The main-line is hauled into a large box by a line hauler from one end over a roller mounted on the gunnels, usually situated in the mid-section of the vessel. The snoods are stored separately.
In New Zealand until 1979 most G. galeus were taken with longlines. By the mid-1980s much of the catch was taken by gill-nets and demersal trawl; about one-third of the catch was taken by longline. No recent analyses have been made of the proportion of the landings taken by method. In South Africa, bottom-set longlining was the main method used during World War II particularly by larger vessels. Following this phase, small vessels operating in shallow water (<9m) caught smaller G. galeus (44–70cm total length (TL)) (Freer 1992). During 1983–90, up to 15 vessels initially issued with experimental permits to target hake (Merluccius spp.) but which subsequently targeted kingclip (Genypterus capensis) took a bycatch of G. galeus. At present 31 vessels with permits first issued during 1991–94, target sharks with longlines. The fishers use up to 3000 hooks to target G. galeus or Mustelus spp. in shallower waters or Isurus oxyrinchus and the vessels operate over depths of 50– 450m. The average CPUE during 1992–94 was 787 kg/1000 hooks (weight of headed, gutted and finned carcass) (Kroese et al. 1995). Skippers operating form Gans Baai currently report using salted mullet as bait. They tend to catch large G. galeus (>15kg carcass weight) in deep water (>100m) and smaller G. galeus (<10kg carcass weight) inshore. About two-thirds of the longline catch is landed in Gans Baai but some catch is landed in most ports in the South Western Cape region, particularly Kalk Baai, Saldanha Baai and Laaiplek (Freer 1992).
In California, bottom-set longlines were the first used for shark fishing. When the northern California halibut fleet entered the fishery in 1938 they started using the California halibut longline gear for targeting G. galeus. In Monterey and San Francisco for targeting large G. galeus longlines were constructed with a main-line of tarred manilla rope (4mm diameter) with ~1m long snoods set 4m apart. Up to 10 separate sets, each with about 70 long-shanked 11/O–14/O hooks were baited with sardines and mackerel or, if these were not available, anchovies and herring. At times lighter gear with 6/O–9/O hooks were used in the San Francisco area to catch small G. galeus. The dahn poles were constructed of 3–5m bamboo poles fitted with a red flag and sometimes a small electric bulb fastened at the tip to enable night fishing (Byers 1940). By 1946 longlining was phased out in favour of bottom-set gill-nets (Ripley 1946).
The description by de Buen (1952) of the longlines ‘palangres’ used in Uruguay during the 1940s applies equally to those used today. Artisanal vessels are equipped with the same round shallow 45cm diameter flat-bottom baskets for holding coils of main-line, snoods and baited hooks. The snoods (~1m long), fixed about 1–2m apart on the main-line are much lighter than those used in Australia and South Africa. Each basket can hold a coil with up to 100 Mustad 4/O hooks and it is not uncommon for small vessels to set ˜6000 hooks a day. A catch typically consists of a mix of Brazilian menhaden (‘lacha’) (Brevoortia aurea), sea trout (‘pescadilla’) (Cynoscion striatus), Brazilian cod (‘brótola’) (Urophysis brasiliensis), ‘gatuzo’ (Mustelus schmitti) and ‘trompo de cristal’ (G. galeus) (Gustavo Chiaramonte, Museo Argentino, Buenos Aires, pers. comm.). In Argentina, a small amount of longline fishing for hake (Merluccius hubbsi) occurs in the Gulf of San Matias and takes a bycatch of medium- and large-sized (>100cm TL) G. galeus (Raúl González, Pers. Comm.).
2.9.2 Hand-line fishing
Hand-line fishing for G. galeus was important in New Zealand until 1979. Hand-lines are occasionally used by a small number of artisanal fishers in Argentina to catch G. galeus and Mustelus antarcticus. In South Africa, hand-lines have been used for the entire history of the fishery, however catches by this method have declined since about 1978 when a maximum G. galeus catch of 800t was so taken (Freer 1992). At present the majority of the targeted catch is taken by hand-lines (Kroese and Sauer 1998); G. galeus are targeted when teleost catches are low (Freer 1992). The hand-line method is usually undertaken from a large number of small vessels (>3000 registered) mostly <10m LOA (Kroese et al. 1995) with large crews of artisanal fishers generally operating in depths <50m and within ˜15nm of port. Initially, sharks were caught on cord lines using a fixed 450g sinker with a 6– 8cm chain trace and a single 11/O or larger Mustad hook. More recently, heavy gauge monofilament nylon of 100kg weight breaking strain and hook-size down to 8/O Mustad is used (Freer 1992).
2.9.3 Surface-set longline fishing
G. galeus can be caught in small numbers on surface-set longlines well off the continental shelf and offshore. Occasional offshore bycatches of G. galeus have been reported by observers on vessels fishing for southern bluefin tuna (Thunnus maccoyii) in the EEZs off southern Australia (Walker et al. 1997b) and New Zealand (Annala et al. 1998). Although there are no documented reports, it is likely that they are occasionally caught off the continental shelfs of South Africa, the east coast of South America, and west coast of North America. Large vessels targeting tuna and tuna-like species off the continental shelf of South Africa (currently 120 permits available) (Kroese and Sauer 1998), southern Brazil (Amorim et al. 1998), Uruguay (Marin et al. 1998) and Argentina (Chiaramonte 1998) have not been reported to catch G. galeus. In southern California during 1988– 91, 6–10 vessels were authorised under experimental permits to use surface-set longlines to catch shortfin mako (Isurus oxyrinchus) and blue shark (Prionace glauca). These vessels were authorised to use 5nm of line during 1988 and then subsequently 4nm of longline. During the first two years of the fishery there were on-board observers during 19% of the operations but no G. galeus catches were reported (O'Brien and Sunada 1994). Since 1980 there have been no foreign fishing longline fleets operating in the EEZ of the US (Rose 1998).
2.9.4 Bottom-set gill-net fishing
Apart from the North East Atlantic, bottom-set gill-nets are an important method for catching G. galeus and in most fisheries have largely replaced bottom-set longlines. Gill-nets have the advantage that bait is unnecessary and less labour is needed than for longlines. Also, apart from areas of strong tidal flow, bottom-set gill-netting can be designed to catch a particular size range of sharks. Gill-nets are highly length-selective as small sharks can swim through them and large sharks are deflected unless they roll up in the gill-nets (Kirkwood and Walker 1986; McLoughlin and Stevens 1994; Simpfendorfer and Unsworth 1998). Details on the design, construction and deployment of gill nets in Australian shark fisheries are given in Walker (1999).
In New Zealand, when bottom-set monofilament gill-nets were phased in the late 1970s, the catch rose rapidly and since 1983, bottom-set gill-nets became the dominant gear; about half the catch is taken by this method, although this varies with region (Paul 1988). In South Africa, bottom-set gill-nets were used extensively during the early stages of the G. galeus fishery, but following a legal minimum mesh-size of 9 inches (230 mm) adopted in 1948 and subsequent restrictions on their use, gill-nets have not been used to target G. galeus. However, 780 vessels with permits to use gill-nets for targeting southern mullet (Liza richardsoni) and St Joseph elephant fish (Callorhincus capensis) inshore take a small bycatch of G. galeus (Kroese et al. 1995).
In the South West Atlantic, a range of mesh-sizes are used in southern Brazil, Uruguay and the Province of Buenos Aires, Argentina. The mesh-sizes adopted depends on the species of shark or teleosts targeted by the fishers. Surface-set gill-nets (drift-nets) of mainly 340–400mm mesh-size are used in the Brazilian states of São Paulo and Santa Catarina to target the scalloped hammerhead shark (Sphyrna lewini) and other pelagic sharks. In addition, bottom-set gill-nets of 400mm mesh-size is used to target large angel sharks (Squatina argentina, S. guggenheim and S. occulta). G. galeus are not reported as part of the catch because these mesh-sizes are too large to enmesh the species and, the drift-nets are usually set north of their range. Bottom-set gill-nets of 120–150mm mesh-sizes of monofilament webbing are used for targeting the whitemouth croaker (Micropogonias furnieri) but catch G. galeus, M. schmitti, and several other species of shark (Kotas et al. 1995). Further south-in Uruguay and Argentina-mesh-sizes of ~300mm are used for catching bronze whaler (Carcharhinus brachyurus), ~200mm for G. galeus and ~100mm for M. schmitti.
In Uruguay, Praderi (1990) describes bottom-set gill-nets used by the artisanal fleet from 8m vessels during 1973 as constructed of monofilament webbing in panels 60m long by 3–5m deep (‘vagas’) with mesh-sizes-ranging from 200 to 220mm when targeting G. galeus, 300–340mm when targeting large sharks such as C. brachyurus, and 100–120mm when targeting M. schmitti or teleosts. Floats (50–70mm dia.) were spaced about 1.3m along the head-line and lead weights (50–70g) were spaced about 0.2m along the foot-line. Vessels operating from La Paloma (3 vessels), Cabo Polonio (3), Punta del Diablo (9) and La Coronilla (2) carried 20–28 panels and usually fished 20–30nm from port in depths of 20–30m. Vessels (3) operating from Valizas fished 5–l0nm from port in depths 6– 15m. Operating with a 3–4 crew, the gill-nets were set in the one position for 15–20 days hauled periodically in the morning and early afternoon by hand. G. galeus were usually targeted during July-October.
Chiaramonte (1998) explains that in the Necochea area of Buenos Aires Province, Argentina, bottom-set gill-nets of 185–210mm mesh-size are set perpendicular to the coastal current. The webbing consists of five twisted filaments of polyethylene (0.30mm dia.) which together are 2–3mm thick, or, for some since 1995, polyamide monofilament (0.6–0.8mm thick). The panels of net (locally called paño) are usually 56–60m long, but up to 80m in Necochea and 100m in Claromecó, and 2.2–4.3m high. The panels are joined to form a continuous net but have spaces of 5–10m every three or four panels. The mean number of panels used by a vessel varied from 40–60 during 1988–96. Corcuera et al. (1994) estimated that at the height of the season in 1990 a total length 60–80km of gill-nets was set by the fleet. The gear is hauled and reset in the same position each day or every second day.
In California, most of the first bottom-set gill-nets were of 8-inch (203mm) mesh-size but by 1941 these were increased to 10 inch (254mm) mesh-size, varying from 9 inch (229mm) to 11 inch (279mm) mesh-size, hung from 15 to 30 meshes deep. They were made of 18 to 30 thread cotton twine webbing. The head-lines and foot-lines were made from manila or sisal rope. Cork floats (75– 125mm diameter) were attached to the head-lines and lead weights to the foot-lines. Panels, referred to as ‘shackles’ or ‘shots’ at the time, 46–92m long were joined together in groups of 2–8 and constructed with a bridle at each end which were attached to 20–34kg anchors and buoy-lines. These nets were initially hauled by hand; later mechanical winches were introduced that allowed the fishers to operate in deeper water; the gear was rarely set >150m. Surface-set drift-nets were introduced in 1943 and by 1944 were widely used. By 1946, most of the gear used for targeting G. galeus was either bottom-set gill-nets or surface-set gill-nets (Ripley 1946).
Since the collapse of the Californian fishery, G. galeus has not been targeted with gill-nets, but there has been a small bycatch of G. galeus in the ongoing 8 – 81/2 inch mesh-size trammel-net and set-net fishery for Pacific halibut (Paralichthys californicus) (Barsky 1993) and, since 1978 for Pacific angel shark (Squatina californica) near Santa Barbara within one mile of shore (Cailliet et al. 1993). Vessels targeting Pacific angel sharks during the winter and spring soon increased the mesh-size to 12–16 inches until the fishery effectively ended in 1994 when bottom-set gill-nets were prohibited within Californian State waters (i.e. within the 3 mile limit).
2.9.5 Surface-set gill-net fishing (drift-nets)
Small quantities of G. galeus have been caught in surface-set drift-nets off California and, as noted, possibly off southern Brazil; there are no reports of the species taken by this method in other areas. Drifts-nets are not as effective as bottom-set gill-nets for catching G. galeus and are currently banned in Australia, New Zealand and South Africa. In California, ~80m long drift-nets, 45–46 meshes deep, of 8 inch (203mm) mesh-size were used during the late 1930s. These were buoyed through use of 10cm long cork floats and were sunk by adding 57g lead-weights to the foot-line. Drift-nets were set before dusk to fish overnight and were hauled in the morning (Byers 1940). In 1940, heavier bottom-set gill-nets of larger mesh-size were introduced and by 1941 most of the larger vessels adopted these nets (Ripley 1946).
Much later, small quantities of G. galeus were taken as bycatch in the Californian drift-net fishery. This fishery developed rapidly during the late 1970s off southern California and gradually expanded to Oregon and Washington and further offshore. The fishery initially targeted the common thresher (Alopias vulpinis), but swordfish (Xiphias gladius) and shortfin mako (Isurus oxyrinchus) soon became important components of the catch. Drift-nets used in the fishery are 1500–1800m long and 50–100 meshes deep and constructed with webbing of 3-strand twisted nylon and mesh-size 13– 19 inches (330–483mm); they are set 5–8m under the surface. G. galeus bycatch gradually declined from 13t during 1981/82 to one tonne during 1990/91 (Hanan et al. 1993). The decline in the G. galeus catch was a reflection of a decline in fishing effort (from 11 000 sets during 1986/87 to 4000 during 1990/91), rising mesh-size and legislative requirements for the fleet to operate progressively further offshore.
2.9.6 Demersal trawling
Demersal trawling occurs in all regions of fisheries for G. galeus. There are major demersal trawl fisheries in southern Australia, New Zealand, South Africa, California, eastern South America, and North West Atlantic and all take a bycatch of G. galeus.
Trawling began in California in 1876 when a demersal pair-trawl net ‘paranzella’ was first towed by a pair of sail boats in San Francisco Bay. By 1880, the fishery expanded to the ocean and sail power was gradually replaced by steam, gasoline and finally diesel engines. Pair trawling was replaced by single vessel otter board trawling in the 1940s. The current fleet of 141 trawlers operates between southern California and southern Oregon from nearshore to depths >900m (Jow 1993).
In South Africa, early research trawls indicated that G. galeus provided 5% of the trawl catch in the 180–360m depth-range south-west of Cape Agulhas during October-December 1947. About 30 inshore trawlers operate within depths <120m, mainly on the Agulhas Bank, and 60 offshore trawlers operate at depths >110m off the south and west coasts (Kroese et al. 1995). During 1982–87, 31–44% of the catch over all species of shark was taken by demersal trawl and consisted of a mixture of Squalus spp., Mustelus spp. and G. galeus (Freer 1992). The results from 12 cruises of the FRV Africana between 1986 and 1990 on the west coast of southern Africa between 23°S and 36°S over the depth range 33–1016m provide data on geographic and bathymetric distribution of G. galeus. A total of 92 G. galeus were caught at 869 fishing stations between 28°S and 35°S over the depth-range 50–500m (Compagno et al. 1991).
In southern Australia, the annual catch of G. galeus and Mustelus antarcticus from all types of trawlers reported in the trawl logbooks during 1986–93 varied from 19 to 57t. There is likely to be additional bycatch of these species reported in the logbooks as ‘other shark’ or ‘other species’ which includes sharks. In New Zealand, the large trawl fleet has always taken a bycatch of G. galeus, but the catch has been relatively small compared with the longline and demersal gill-net catch. During 1983–86, about 15% of the shark catch was taken by trawl (Paul 1988).
2.9.7 Recreational fisheries
In general, G. galeus is not a shark species targeted by recreational fishers, but the species forms a minor component of the recreational shark catch in all regions where commercial fisheries occur. In southern Australia, it is known that recreational fishers take small quantities of G. galeus from beaches, rocky shores and small boats. Tag recaptures suggest the recreational catch is negligible. No attempt has been made to estimate the recreational catch.
In New Zealand, surveys undertaken during 1991–94 indicate the annual catch was ~58 000 which is of the order of 175t. The survey consisted of (a) a random telephone survey of 35 115 households (3%) to identify those containing recreational fishers, (b) the completion of fishing diaries over 12 months by a sub-sample of 4579 identified recreational fishers, (c) aerial and boat ramp surveys to verify catch estimates, and (d) boat ramp surveys to obtain mean weight estimates (Francis and Shallard 1999; Teirney et al. 1997).
In South Africa, an estimated 400 000 recreational shore anglers and ski-boat anglers operating 10 000 ski-boats (4–8m OAL) (Kroese et al. 1995) catch small quantities of G. galeus and bronze whaler (Carcharhinus brachyurus).
In the US, a Marine Recreational Fisheries Statistics Survey estimated the Pacific coast recreational catch of all species of shark averaged 182t during 1984–89, of which G. galeus was a minor species. The main species are spiny dogfish (Squalus acanthias) (Rose 1998) and shortfin mako (Isurus oxyrinchus) (Cailliet et al. 1993). Reports of shark catches from a derby in San Francisco Bay with 1406 registered fishers on one day during September 1950 showed that of 926 sharks caught, 60 (6.5%) were G. galeus (Herald and Ripley 1951).
In Argentina, C. brachyurus and C. taurus are the main recreational species (Chiaramonte 1998), but G. galeus are occasionally caught. In the UK, G. galeus are taken as part of the recreational fishery, but no estimates of the catch have been made (Fleming and Papageorgiou 1996).
2.10 The markets for G. galeus
In southern Australia, prices of G. galeus and M. antarcticus, as a headed and gutted carcass with fins attached, varied between A$5.50–8.50/kg during 1994 with an average price ~A$7.00/kg. Larger shark received about 10%/kg less than those 4–6kg. Most of the catch landed in Victoria is auctioned as carcasses on the Melbourne Fish Market where it is sold fresh to fish and chip shops, the retail sector and through restaurants as ‘flake’. Sharks landed in Tasmania, South Australia and Western Australia are often first sold to local processors before being sold locally or in Victoria. Prices for shark are generally higher for product sold directly on the Melbourne Fish Market than those sold to local processors in Tasmania, South Australia and Western Australia. This pattern of distribution and pricing has persisted for much of the history of the fishery. Shark meat is often imported but rarely exported.
In New Zealand, interpreting data presented by (Hayes 1996), Francis and Shallard (1999) using a fillet weight to whole weight of 2.30 estimate 31–49% of the G. galeus catch is exported. Most of the G. galeus fillets are exported to Australia. Shark fins, liver-oil and cartilage are exported but there is little information available on the destinations and quantities. Francis and Shallard (1999) provides estimates of the total price paid to fishers for the catch of NZ$3.1m and NZ$3.3m during 1994 and 1995, respectively.
In South Africa, shark fins, cartilage and frozen shark meat are exported but there is little information available on the destinations and quantities. Small quantities of the shark meat is exported to Australia and Argentina. Much of the shark meat, some of which is salted, is sold for domestic consumption.
In California, during 1930–36 there was a small domestic market for fresh shark meat and there was an export market for dried fins. Prices for G. galeus liver-oil rose from some $50/t in 1937 to $2000/t in 1941 (Ripley 1946).
In Uruguay, a G. galeus weighing 10kg whole produces ~2kg of salted dried meat (‘bacalao’). In April 1990, fishers received $ 1.80–2.20/kg which sold in markets at ~$4.00/kg (Praderi 1990).
In the North East Atlantic, there is a demand for shark meat although preferences vary among the countries of the European Community (EC). The majority of shark exports from EC countries are to other EC members. G. galeus is consumed in several countries. France consumes part of its G. galeus catch but much of it is exported to Italy. In Spain it is sometimes referred to as ‘bienmesabe’ (good taste) and sold in markets for $4.90 during April 1996 (Fleming and Papageorgiou 1996).
3. THE BIOLOGY OF G. galeus
3.1 Population structure
The maximum size for G. galeus varies considerably between regions with the smallest sizes recorded in the South West Atlantic and the largest in the North East Atlantic and North East Pacific. Off Brazil, the largest of 904 females examined by Peres and Vooren (1991) was 155cm TL and the largest of 644 males was 148cm. In a smaller sample from Tunisia in the Mediterranean (42 males and 60 females), Capapé and Mellinger (1988) recorded males up to 158cm and females up to 200cm. In the more northern parts of their North East Atlantic range Wheeler (1969) gives the maximum size as 150cm and 32kg, although angling records suggest a somewhat larger size of 180cm and 35kg in weight. In the North East Pacific, Ripley (1946) notes males up to 185cm and females to 195cm. Maximum sizes from South Africa and Australasia are similar.
Freer (1992) records males to about 170cm and females to 173cm and 30.5kg from South Africa, while in Australia males attain 171cm and females 174cm (Moulton et al. 1992; Olsen 1954). Weight-length relationships are available for Australia (Olsen 1954; Punt and Walker 1998), South Africa (Freer 1992), California (Ripley 1946), Ireland (Fitzmaurice 1979), Argentina (Chiaramonte and Corcuera 1995) and, for eviscerated weight, Brazil (Peres and Vooren 1991)..
Spatial and temporal variations in size structure and sex ratio are apparent for various populations of G. galeus. Marked differences in the sex ratio of the catches in California are evident from the data presented by (Ripley 1946). In northern California, where catches are essentially restricted to October-December, 98% of the landings were males and this was consistent over the depth range of the fishery (20–200m). Off central California, catches of the sexes were about equal while in the southern part of the fishery catches were highest from April–July and 98% of the catches were female and were essentially restricted to depths less than 60m. In the Santa Barbara region, there appears to be a concentration of males during June and July in deeper water (100–240m). Variations in size structure in the Californian fishery are influenced by the selectivity of the predominantly 10 inch mesh-size of the gill-nets for the larger sharks. The distribution of juvenile fish was biased to areas using other gears which would catch these fish. However, there was a trend for the proportion of mature female sharks to increase to the south while the opposite trend was apparent for males with larger more mature fish to the north (Ripley 1946).
In southern Australia, small juveniles are concentrated in inshore bays and estuaries of Victoria and Tasmania. The proportion of larger mature fish is higher in Western Australia (Walker 1995a), South Australia (Walker 1995a; Walker and Hudson 1995; Walker et al. 1989a) and Tasmania (Walker 1995a) while the waters of Bass Strait (Olsen 1954; Walker et al. 1989a) comprise mainly larger juveniles and sub-adults. Concentrations of mature females have been noted in South Australian waters from June to October and in Victoria and Tasmania during November to January while schools of adult males are common during June-August on the west coast of Tasmania.
In South Africa, Freer (1992) reports that sexually segregated schooling only occurs after sexual maturity has been attained. Mature females were never caught in schools with mature males and appeared to be absent from the area during winter. Males were caught during winter and summer resulting in a marked seasonal sex ratio. Juveniles are found in mixed schools, and sub-adult females occasionally occur with sexually mature male schools. Mature female schools appear to migrate out of the commercial fishing areas during the winter. During February-April the number of males and females caught are about even but during May-September the catch is mostly males and during October–January the catch is mostly females (Freer 1992).
In Argentina in the region of Mar del Plata and Necochea during 1949 the catch was shown to be predominantly males during August-September but predominantly females during October-December (de Buen 1952). More recently, further south, G. galeus caught in Golfo San Matias tend to be large for both the demersal trawl (Guillermo Caille, pers. comm.) and longline fisheries. Data collected by Consejo Nacional de Investigaciónes Cientficas y Tecnicas, Centro Nacional Patagonico of length-frequency for longline caught G. galeus from Golfo Neuvo had a range of 105–150cm TL (mean 132cm TL) and were predominantly males (A. E. Gozstonyi and Enes Elias, pers. comm.). These data were consistent with those data held by the Instituto de Biologia Marina y Pesquera Almorante Storni for experimental longline fishing for M. hubbsi caught G. galeus from Golfo Neuvo (Raúl González, pers. comm.).
In the North East Atlantic, tagging studies show that females are more prevalent in the North Sea and English Channel while males dominate the catches on the west coast of England, particularly around Wales (Holden and Harrod 1979; Stevens 1990). Muñoz-Chápuli (1984) identify different zones with marked differences in the sex ratio in the southern part of their range in the Northeast Atlantic.
3.2 Reproductive biology
3.2.1 Size at maturity
There are differences in the size at maturity among regions and different maximum sizes. Peres and Vooren (1991) showed that males matured at 107–117cm TL with 50% mature by 111cm; females matured between 118–128cm TL with 50% mature by 123cm. Olsen (1954) determined that maturity in Australian G. galeus was attained from 120–132cm TL for males and that first maturity in females was reached at 135cm TL. Similar minimum sizes at maturity were reported by Freer (1992) for South Africa with males maturing at 128cm and females at 134cm. Larger maximum sizes in the North East Pacific are reflected in a larger size at maturity with males attaining first maturity at 135cm and about 87% of males being mature by 155cm (Ripley 1946). Females first mature at 150cm with about 50% mature by 158cm (Ripley 1946). In the Mediterranean, off Tunisia, Capapé and Mellinger (1988) note minimum sizes at maturity of 125cm for males and 140cm for females.
3.2.2 Fecundity
G. galeus is ovoviviparous giving birth to an average of 20–35 pups in most areas. Ripley (1946) recorded litter sizes of 6–52 from California with an average of 35. In Australia, Olsen (1954, 1984) reported litter sizes varying from 17–41 with an average of 28 while Walker et al. (1989b) noted a range of 14–43. Whitley (1940) mentions 50 young from a South Australian specimen. Peres and Vooren (1991) recorded 4–41 pups in Brazilian G. galeus, with an average of 23. Similar data were reported from Tunisia by Capapé and Mellinger (1988) with an average litter size of 30 and a range of 10–41. Litter sizes in South Africa may be smaller as Freer (1992) gives a range of 8–20, although the sample size was not given. Several authors have described an increase in fecundity with increasing female size, but the correlation between number of in utero embryos and maternal length is weak (Ripley 1946; Olsen 1954; Capapé and Mellinger 1988; Freer 1992; Peres and Vooren 1991).
3.2.3 Size and sex ratio at birth
The size at birth is about 30–35 cm from all areas. Ripley gives the average size at birth for Californian specimens as 35–37cm and Capapé and Mellinger (1988) also give birth size from Tunisia as about 37cm. Olsen (1954) gave the size range of normal full-term embryos as 26–35cm, with a mode at 30cm. Freer (1992) notes that pups from 29.8cm appear ready for birth and that mean size at birth is 30.7cm in South Africa. A similar average size at birth of 30–31 cm was given by Peres and Vooren (1991) for Brazilian sharks.
In California, Ripley (1946) noted that the embryos in the posterior part of the uterus were of larger size than those in the anterior portion giving an example of a female in which the embryos varied from 52–75mm in the left uterus and 53–79mm in the right uterus. Olsen (1954) could find only a small difference of about a 1mm decrease in length for every fourth embryo from the posterior to the anterior of the uterus in Australian sharks. He also found no difference in lengths of full-term embryos from the left or right uterus of each parent or between male and female pups. He did, however, find more male than female embryos in the litters and noted that this sex ratio was also evident in free-swimming pups soon after birth (54 males to 46 females). Olsen (1954) found that this ratio changed with increasing time after birth until it was the reverse (54 females to 46 males) about 12 months after parturition; Olsen (1954) suggested this might reflect a higher natural mortality of males. Peres and Vooren (1991) found that the sex ratio of embryos of Brazilian G. galeus did not differ from unity; they did however, note that embryos at the posterior of the uterus were 2–4cm larger than those in the anterior of the uterus. In South Africa, Freer (1992) reported the sex ratio of embryos was about unity and that there was a slight increase in pup size toward the posterior of the uterus, with a maximum range of 8mm.
3.2.4 Reproductive cycle
There are some differences in the reproductive cycle of G. galeus reported from different regions. This may reflect population differences or may be due to the difficulties of interpreting data from a species that shows marked temporal and spatial sexual and size segregation and makes extensive movements. There is general consensus that ovulation and parturition is seasonal with birth occurring in late spring or early summer and that the gestation period is about 12 months. However, reported breeding frequency of individual females varies from every year to every third year.
In California, Ripley (1946) noted that ovulation and fertilisation of the eggs occurred in spring and that by following the seasonal growth of embryos found that gestation took about 12 months with birth occurring from May to July. Between May and October, 94–99% of 3233 females over 160cm length were to be pregnant and while Ripley (1946) referred to the ‘annual cycle of females’, presumably meaning that individual females bred each year, he also cautioned that the high pregnancy rate could be influenced by emigration and immigration of females in different stages of development.
Olsen (1954) determined that Australian G. galeus gave birth mainly in December, that about half of the adult females were pregnant in a given year and that full-term pregnant females had only small ova in their ovaries. From these data, together with observations on ova size and ‘male ripeness’ (fullness of seminal vesicles) which he interpreted as indicating mating and ovulation in May - June, Olsen (1954) thought that gestation took about six months. However, subsequent data from Australia (T.I. Walker, J. D. Stevens, unpublished data) indicates that the ovulation period is October - January giving at least a 12 month gestation.
Peres and Vooren (1991) postulated a three year female reproductive cycle for G. galeus in Brazilian waters. Within the study area pregnant females contained small (<10mm) white ova which did not increase in diameter over the seven months the fish were present in the area. Two groups of non-pregnant fish were also present, those with light yellow ova averaging 5–25mm in diameter which showed no increase in size and those with golden-yellow ova averaging 35–55mm diameter which increased some 13mm over the four months they were in the area. Peres and Vooren (1991) interpreted these data as follows. During the first 12 months after parturition the uterus is in a resting stage and vitellogenesis is slow. During the next 12 months large mature ova are produced and the uteri and nidamental glands are prepared for ovulation which occurs in November-December. Gestation lasts 12 months during which there is no vitellogenesis, and birth occurs in November-December. These authors thought that males had an annual reproductive cycle and, based on the presence of sperm in the nidamental glands of females in July, that copulation could precede ovulation by at least five months.
Data on the reproductive cycle from South Africa are sparse. Freer (1992) suggests that copulation occurs in May based on gonadosomatic index, however, the data are unconvincing and show little seasonal trend; birth occurs in late December and January in the Gans Baai area. Little information is also available on the reproductive cycle in the North East Atlantic and Mediterranean. Capapé and Mellinger (1988) provide the most data from Tunisia where, based on a small sample size, they suggest that birth, mating and ovulation occur from April to June. Since near-term pregnant females contained large ova (sample size 4) they thought that vitellogenesis proceeded in parallel with gestation and that consequently females had an annual cycle. In more northern waters, birth occurs from June-September on the French coast and Wheeler (1969) similarly reports birth occurring during summer, presumably referring to British waters.
3.2.5 Nursery areas
The location of possible nursery areas for the different populations has received little attention outside Australia. Olsen (1954, 1984) reported that there was an inshore migration of pregnant females to waters of Victoria and Tasmania to give birth during November-January and that these nursery areas were characterised by low energy protected bays and estuaries. New-born and small juveniles remained in these nursery areas during summer but moved into deeper water during late summer. In the following spring, the majority return to their original nurseries while others move to adjacent estuaries and bays. Juveniles start to leave the nursery areas from about age two. Olsen (1984) noted that no known nursery areas occurred in South Australia. Olsen (1959, 1984) reported a decline in abundance of juveniles in two Tasmanian nursery areas sampled regularly over a five year period. He attributed this decline to fishing pressure on pregnant females during their pupping migration and to intensified fishing of juveniles in inshore areas such as Port Phillip Bay during the period 1940–50. Between 1943–45, in Port Phillip Bay 60 000 juveniles averaging 0.9kg, were caught annually. A continuation of this sampling in the 1990s (Stevens and West 1997) showed a substantial further reduction in abundance of G. galeus pups and small juveniles in Tasmanian and Victorian embayments and estuaries. Since the abundance of pups sampled in these areas seems insufficient to account for the current adult stock size it is probable that other pupping areas exist, either outside Victoria and Tasmania, or more likely, close inshore along ocean beach coastlines.
Authors from other areas have made only passing reference to the location of nursery areas. Ripley (1946) mentions evidence of nursery areas in San Francisco Bay and Tomales Bay close to latitude 38°N and near Point Conception and Ventura, between latitudes 34°N and 35°N, for the Northwest Pacific population in southern California based on the high proportion of pregnant females found and the capture of small juveniles in that region. Herald and Ripley (1951) mention that pupping occurs in San Francisco Bay. The nursery areas for the South West Atlantic stock appear to be inshore embayments of Bahia Blanca, Samborombon, San Blas and Gulf of San Matias in Argentina (G.E. Chiaramonte, pers. comm.). While near-term pregnant females are present in southern Brazilian waters as late as November-December, which is the birth period, pupping does not appear to occur in Brazilian waters (C.M. Vooren, Rio Grande, Brazil, pers. comm.).
Freer (1992) mentions that in South African waters juveniles are caught in shallow embayments including Struis, St. Helena, Walker and False Bay. Nursery areas have been reported in inshore embayments of New Zealand such as Kaipara Harbour. Muñoz-Chápuli (1984) thought that in the North East Atlantic, nursery areas may exist between 37–40°N off the Portuguese coast and between 27–31°N around the Canary Islands, as these were the only areas south of 40°N where pregnant females were captured. Large females have been reported from very shallow water in southern England during summer and free-swimming 0+ fish have recently been captured in the Bristol Channel , suggesting births occur in this area (J.R. Ellis, pers. comm.).
3.3 Migrations
Tagging studies on G. galeus were done in Australia during the 1940s and 1950s (Olsen 1953; Olsen 1954), 1970s (Walker 1989a) and 1990s (H. Williams, pers. comm.), (Walker et al. 1997a; Stevens and West 1997). In total, 9638 sharks were tagged resulting in 1011 returns. Of 301 reported tag recaptures from 2505 releases during 1990–96, 65% of displacements were >500km for large females (>104cm TL), and 20 recaptures for the sexes combined had displacements >1000km. The mean distance between release and recapture positions was 415 km (Walker et al. 1997a). The longest recorded displacement is 3016km for a female (156cm TL at release) released in the Great Australia Bight and recaptured near the south east coast of New Zealand's South Island after 1033 days. Olsen (1984) proposed a generalised movement pattern based on his tagging data. The adults tend to move inshore in summer and offshore at the start of winter, others move to warmer waters in New South Wales and South Australia before returning south in late spring. Pregnant females move into nursery areas in Victoria and Tasmania during late spring and summer to give birth. After parturition, the females move out into deeper water. Juveniles spend the summer in inshore nursery areas before moving into adjacent deeper water for their first winter, often returning in the following spring. Older juveniles (2+ years) move towards eastern Bass Strait or to warmer waters in winter. Tagging carried out in the 1990s in nursery areas confirmed Olsen's observations in relation to these movements of juveniles. Developments in the fishery and scientific data collected since Olsen (1954; 1962) generally support this theory. One exception is the absence of significant catches of G. galeus from the east coast longline fishery which suggests only a small component of the stock occurs off New South Wales (Walker et al. 1997b).
There is stronger evidence for the movement of pregnant sharks to waters off South Australia, particularly the great Australian Bight, where they remain for the period of gestation, returning to eastern Bass Strait and Tasmania to give birth (Walker 1995a). Recently a movement model has been developed (Taylor 1997; Xiao 1996) to quantify mixing rates between different areas of the fishery. Tagging in New Zealand has been carried out opportunistically since the 1970s; of 3950 G. galeus tagged and released during 1985–97, 208 (5%) have been recaptured and reported (R. Hurst, pers. comm.). Movements have not been analysed in detail but indicate south-north movements along the east coast of South Island. During 1991–98, 24 G. galeus tagged in New Zealand have been recaptured in Australia while five sharks made the reverse migration. Prior to 1991 no trans-Tasman movements had been reported. These returns provide further evidence that the distribution of G. galeus, at least in some areas, extends into the near-oceanic zone. Recently, ‘archival’ tags have been attached to animals in the Australian population and they should provide further information on their depth distribution, vertical movements in the water column and offshore distribution. Five recaptures confirm movements on and off the continental shelf and vertical movement. Three of the five sharks showed dramatic diving behaviour; the deep dives lasted for one to two weeks, before the pattern became shallower. The sharks remained in deep water during daylight and moved to the surface at night during November-February, except at times of full moon. During late February and March, this pattern changed and the sharks appeared to remain on the bottom (Anon. 1997, 1998b).
Tagging studies on G. galeus in the North East Atlantic (Fitzmaurice 1979; Holden and Harrod 1979; Stevens 1990) have also demonstrated extensive movements. Fish tagged in England and Ireland were recaptured as far away as north of Iceland (2461km), the Canary Islands (2526km) and the Azores. Results from three studies do not show any clear seasonal movement pattern. North of 45°N, recaptures were made in all months, but were highest in December. Most returns from south of 45°N were made in April and May, but the data were spread between March and December. The majority of fish tagged around the UK probably remain in the area, moving into deeper water during the coldest months and returning inshore in spring. A proportion of the fish may move south in winter, some as far as the Canary Islands and Azores, not necessarily returning as far north the following spring. These southerly migrations may be associated with reproduction. Muñoz-Chápuli (1984) postulated the existence of separate stocks of G. galeus in the North East Atlantic based on catch data. He suggested that apparent differences in the maximum lengths between northern and southern latitudes (i.e. Britain and Tunisia), and their extensive distribution relative to their capacity for movement, supported this hypothesis. However, the results from tagging show that there is mixing throughout the North East Atlantic distribution.
Information on the movement patterns of the North West Pacific population is limited. Only 136 individuals were tagged (Herald and Ripley 1951); two recaptures of Californian tagged sharks were made in British Columbia (1609km) while four other recaptures were made between 121– 306km from their tagging site. These limited results suggest mixing across the range of the North West Pacific population.
3.4 Age and growth
The first studies of age and growth of G. galeus were done by Olsen (1954) using modal analysis of length-frequency data on juvenile sharks, and tag-recapture data for older fish in Australia. Olsen (1954) produced a growth curve suggesting a longevity of about 22 years with males reaching sexual maturity at about eight years and females at ten or eleven. Annual growth increments decreased from 13cm/yr in 0+ fish to about 3cm/yr for 11+ individuals. Above age group 12 (140cm), Olsen (1954) could not distinguish modal increases in the length data. Grant et al. (1979) used tag data from Olsen (1954) to calculate growth parameters using the method of Fabens (1965). Their growth curve indicated a longevity of up to 40 years. Subsequently, a number of recent tag returns from sharks surviving for up to 40 years from the original study by Olsen (1953, 1954) suggest that G. galeus may have a longevity approaching 60 years. Moulton et al. (1992) used a whole vertebral ageing technique counting bands on the centra faces as well as analysing tag-recapture data from the 1970s tagging experiment and re-analysing the earlier tag data. While the growth curves derived from the tag-recapture data were similar, the vertebral method gave a maximum age estimate of 20 years for a recaptured tagged shark calculated to have an age exceeding 45 years! Thus, vertebral ageing is believed to underestimate the age of fish larger than about 130cm and older than 11 years and the ages of the oldest sharks in the population will be severely underestimated using the whole vertebral ageing technique.
Ferreira and Vooren (1991) used a microradiograph technique for enhancing rings on the vertebral centra of G. galeus from Brazil. Their growth curve suggests that males mature at about 10 years, females at 15 years and that longevity is about 40 years. Francis and Mulligan (1998) also using a microradiographic technique estimated males matured at about 12–17 years and females at about 13–15 years; their oldest age estimate is 25 years.
Freer (1992) used vertebral ageing to produce a growth curve for South African G. galeus. Their data suggest that males reach maturity at 8–9 years and females at 10 years with longevity in the region of 25 years. Given their small sample size and the likely problems of underestimating age in the older fish using their technique, their growth curve and age estimates for the larger fish are probably unreliable. Stevens (1990) examined growth data from a limited number of North East Atlantic tag returns to suggest that there is good agreement between observed growth and that predicted from an Australian growth curve.
3.5 Diet
The diet of G. galeus consists mainly of teleost fish, particularly demersal species, and cephalopods. Juveniles in inshore nursery areas take a greater proportion of cephalopods, crustaceans, gastropods and annelids. Olsen (1954) examined the diet of 600 G. galeus of all sizes from southern Australia of which 74% contained food; 92% of those containing food had preyed on fish, octopus or squid. A total of 17 species of fish were identified in the diet of which the main ones were barracouta (Thyrsites atun) and jack mackerel (Trachurus declivis); the other species were mostly bottom feeders and often restricted to reefs. Olsen (1954) noted that the type of habitat had a marked influence on the diet of juveniles in nursery areas and that the fish and cephalopod component was lower in juveniles (88%) than in adults (98%). Crabs, annelids, shrimps and gastropods were frequently preyed on by juveniles. An analysis by Coleman and Mobley (1984) of G. galeus stomach contents showed that cephalopods comprised 80% of the diet by weight, most being arrow squid (Nototodarus gouldi) and octopus (Octopus pallidus). Walker (1989b) also examined the diet of Australian G. galeus and found that teleosts comprised 47% and cephalopods 37% of the diet by weight. Teleosts were mainly barracouta (Thyrsites atun), jack mackerel (Trachurus declivis) and leatherjackets (Monacanthidae) and cephalopods were mainly Octopus spp., arrow squid and calamari (Sepioteuthis australis). In 0+ sharks examined from Tasmanian nursery areas (mainly Pittwater) by the CSIRO Marine Laboratory more recently, fish, cephalopods and crustaceans were of similar importance while in 2+ sharks crustaceans were a negligible component of the diet. The cephalopod component in the diet also declined with increasing age class but this was mainly a reflection of relatively high predation of 0+ sharks on the inshore loliginid Loliola noctiluca in Pittwater (John Stevens, CSIRO, Hobart, pers. comm.).
Ripley (1946) reported some qualitative observations on stomach contents of G. galeus from California. Teleost fish were the most frequent prey with flatfish, midshipman (Porichthys), sardine, mackerel and rockfish the most common. Squid were taken relatively frequently but octopus were infrequent in the stomachs. Ripley (1946) noted that the seasonal abundance and availability of various prey types were reflected in the stomach contents of the sharks. Since both demersal (rockfish and midshipmen) and pelagic (sardines and squid) prey were present. Ripley (1946) thought that G. galeus did not confine itself to feeding on the bottom and cited the success of floating drift-nets in capturing G. galeus as evidence for their pelagic mode in search of food.
Freer (1992) examined the stomach contents of 375 G. galeus from South Africa of which 24.5% were empty. Teleosts comprised 57%, cephalopods 40%, crayfish 0.8% and sharks 1.9% of stomach contents by weight; the most commonly occurring fish were silver (Argyrozona argyrozona) pilchard (Sardinops ocellata), harder (Liza sp) and hottentot (Pachymetopon blochii). Cephalopods, both octopus and squid, were well represented in the stomachs. The diet of juveniles (<90cm) was similar but the species were smaller and more characteristic of sheltered embayments with Sufflogobius bibarbatus the most common prey. Bass et al. (1975) recorded mostly bottom-living teleosts such as soles (Soleidae) and hake (Merluccius capensis), as well small cephalopods from the few specimens they examined from South African waters.
Ellis et al. (1996) examined the stomach contents of 46 G. galeus from the Irish Sea, of which 4% were empty. Teleosts occurred most frequently in the stomachs (78% of the diet) with mackerel (Scomber scombrus), gadoids, herring (Clupea harengus) and dragonets (Callionymus spp.) most common. Cepahalopods were the next most important prey group (19%) with octopus (Elledone cirrhosa) the most important.
3.6 Predation, mortality and survival
Little is known about predators of G. galeus. The broadnose sevengill shark (Notorynchus Cepedianus) is the most likely predator of juvenile G. galeus in Victorian and Tasmanian nursery areas and probably in nursery areas in other parts of the species range such as California, Argentina and South Africa. Freer (1992) mentions that small G. galeus (450–700mm TL) are caught on hooks with N. cepedianus in the Laaiplek area. In more open waters there may be some predation on juveniles by large teleosts such as Serranids but other shark species (such as Notorynchus cepedianus) are the most likely predators on adult G. galeus. Mortality estimates are only available from the Australian population (Kesteven 1966; Walker 1970; Grant et al. 1979; Dow 1986). Kesteven (1966) applied the methods of Gulland (1955) and Jones (1966) to the tag-recapture data to estimate instantaneous fishing mortality and natural mortality to be 0.045 and 0.310, respectively. Walker (1970) applied the method of Gulland (1969) to the same data set to provide estimates of 0.020 and 0.123, respectively. Grant et al. (1979) used the Paulik (1963) method also on the tag-recapture information. They found fishing mortality to be 0.018, and natural mortality 0.101 (there was no significant difference between the sexes). Dow (1986) estimated natural mortality to be 0.26 by applying the Kirkwood (1984) method to tag release-recapture data from the 1970s.
3.7 Vitamin A in liver-oil
Methods used to extract liver-oil from the livers varied from heating minced livers in open tubs and skimming the oil off the surface, to processing involving either coagulation and pressing, oil solvent extraction or thawing, grinding and centrifuging (Byers 1940). In California, studies of the liver-oil content of livers and the vitamin A content of the liver-oil were carried out on specimens of G. galeus collected during 1943 and 1944. These studies showed that the percentage of oil in livers and the concentration of vitamin A in liver-oil tend to rise with increasing size of G. galeus. These trends imply that the concentration of vitamin A in the liver and the total yield of vitamin A from livers also rise with increasing size of shark. The vitamin A yields from livers of males of TL <155cm and females <165cm were too low for commercial use.
These Californian studies also showed that there is a marked difference in percentage of oil in livers between mature males (60%) and mature females in various reproductive condition. Mature females with enlarged ova that were either not pregnant or pregnant with only in utero eggs had higher percentages of liver oil (75%), but much lower concentrations of vitamin A in the oil, than mature females that were pregnant with full term embryos or females that had recently pupped. The concentration of vitamin A in liver-oil of males is three times that of females (Ripley and Bolomey 1946).
In South Africa, data on the vitamin A concentration in the liver-oil of G. galeus for the 31/2-year period during January 1944-June 1947 from six sites from Table Bay, Cape Town, to Algoa Bay, Port Elizabeth, have a general trend of increasing from west to east. There are no data on sex composition or size composition of the catch during this period, but the trend in vitamin A concentration suggests a trend of increasing size, or perhaps increasing male:female ratio, from west to east (Archer 1948).
3.8 Mercury content of meat
G. galeus off south-eastern Australia were found to have mercury concentrations in the axial muscle ranging from 0.01 to 4.9μg g-1 wet weight (Walker 1988). Males had higher concentrations than females and concentrations tended to increase with size. The estimated overall mean concentration in the Victorian landed catch was 0.90μg g-1 in 1971 (Walker 1976). At that time, Victoria and Australia had food standards for mercury in fish and fish products based on a statutory limit of 0.5μg g-1 such that most of the domestic catch and imported G. galeus was illegal. Later, the Victorian and Australian standards were revised to a mean of 1.0μg g-1 for sharks and other predatory fish as recommended by the United Nations World Health Organization. This revision made the G. galeus catch, as a whole, conform to the food standard.
