Organization of this work
The first section examines official statistics worldwide to describe the scale of global elasmobranch fishing. The section consists of an overview of the catch statistics by FAO major fishing areas including short–term projected catches and an overview of the trends in the most important fisheries for elasmobranchs in the world on a country basis. In the next two sections a more detailed analysis of elasmobranch fisheries is given. For this review, countries with reported elasmobranch catches of 10 000t/yr or more are called “major” elasmobranch–fishing countries.
The second and third sections deal with the major fisheries for elasmobranchs, the by catches and their discards at sea. Although it is difficult to distinguish between directed and incidental fisheries, especially when dealing with fishes that are seldom targeted and/or caught alone as is the case of sharks and rays, these two main divisions of elasmobranch commercial fisheries are used. Directed fisheries are taken as those that target elasmobranchs, together with coastal or small scale multispecies fisheries which catch elasmobranchs incidentally. Typically, the catches from these two sources are mixed together in the official statistics of most countries and it becomes necessary to treat them together. But, there is a group of large–scale long–range fisheries that mainly target high value species such as tunas which catch elasmobranchs incidentally and which mostly discard them for various reasons. These fisheries comprise an essentially different category in which the elasmobranch resource is not only wasted, but the actual numbers of elasmobranchs caught are also poorly known and usually do not form part of reported fisheries statistics. Most cases in this category are high seas large scale fisheries with driftnets and longlines, carried out by a few countries and targeting very specific resources such as tunas, billfishes, salmonids and squid. These fisheries are suspected of causing substantial mortalities of elasmobranchs, mainly sharks. This has raised concern over the conservation of these fishes, though it is secondary to concern over marine mammals, which are also frequently taken as by catch. Depending on the amount of information available in each case, the species, catches, gears, fishing units, localities, levels of exploitation and existing management or conservation measures, are summarized.
The data used in this analysis was taken from official fishery statistics of each country. The first source was the compilation of Compagno (1990) who analyzed FAO data for the period 1947–1985. FAO figures since 1970 have been updated using their Fisheries Yearbooks for 1988–1991 (FAO 1990–1993 and data provided directly from the FAO statistical database (David Die, FAO, pers. comm. August 2, 1993). Additional sources are: Fishery Statistical Bulletins for the South China Sea Area years 1976–1990 (SEAFDEC 1977–1993, appendix 1), the Fisheries Yearbook of Taiwan Area for 1970 and 1988–1990 and the Mexican Fishery Statistical Yearbooks 1976–1990 (Secretaria de Pesca 1979–1992, appendix 1). After the review of FAO data by Compagno (1990), the information is updated here and expanded, including, in particular, the catches of Taiwan (Prov. of China).
Total world elasmobranch catches reported for the period 1947–1991 (Figure 2.1) grew to a record 704 000t in 1991. Roughly four periods with different trends can be identified. Poor growth in catches between 1947 and 1954, a sustained increase of production during 1955–1973 followed by a period of sluggish production for most of the 70's and finally renewed growth in catches during the last years 1984–1991.
Catches by major FAO Fishing Areas from 1967 to 1991 are summarized in Table 2.1. An attempt is made to rank these areas according to their catch. Because the sizes, coastline lengths and human populations of each area vary notably, a rough index of relative production was devised for comparison. This index is defined as the average total elasmobranch catch of each area divided by the square root of the surface of the area in km2. A better index might have been the size of the continental shelf for each area but it was not possible to obtain these data. Arbitrarily, values of the index below 5 were considered indicative of low relative production, those between 5 and 10 intermediate and those of more than 10. as high. Additionally, the trend in catches during the last 10 years recorded for each area is expressed as the slope of a least squares linear regression.
In the Western Atlantic Ocean, all the areas have fairly high increasing trends, especially Area 21 (North West Atlantic) which has the most rapidly increasing trend in the world. All three areas show strong variations in their catches. Area 21 had the highest variability with recent years apparently recovering production from a dramatic drop suffered in the late 70's following high yields in the early 70's. Area 21 had a marginally higher index of relative production (IRP), but considering that a good part of this area includes arctic waters practically void for fishing, a much higher future IRP should not be expected from this area. In the Western Central Atlantic (Area 31) there was of a moderate increase in catch trend while the IRP indicated a low elasmobranch yield. This agrees with Stevenson (1982) who suggested that elasmobranch resources in this area could have been under–utilized. Perhaps there is still potential for expansion of catches, mainly for countries of the Caribbean region. For Area 41 (South Western Atlantic), elasmobranch catches also show a moderate increasing trend after variable catches in the 60's. Average catch of elasmobranchs in Area 41 is the highest in the Western Atlantic but this is also the largest area. Thus it has only an intermediate IRP. Small increases in catches might still be possible here in the future. Catches in Area 31 have been the lowest in the Western Atlantic while in the first half of the period and during the last two years, Area 21 had the highest yields.
For the Eastern Atlantic Ocean, Area 27 (the North Eastern Atlantic) had by far the largest catches in the Atlantic as well as the third largest and the second least variable catches in the world. According to the IRP this area has the highest production of elasmobranchs worldwide but further expansions in the catches should probably not be expected. In fact, the catch trend hardly increased as production has fallen since 1988, perhaps showing that the high levels of exploitation in this area are not sustainable. The Central Eastern Atlantic (Area 34) shows a medium variation in elasmobranch production. This area increased its catches during the early 1970s but the recent trend is of a slow decline. This is an area with an intermediate IRP, thus a good recovery in catches could be possible. For the Mediterranean Sea (Area 37), production was relatively variable during the period examined. The recent trend of declining catches is the steepest in the world. Because of the small size and the high density of human settlements of this Area, fishing is intense and the IRP for elasmobranchs is the second highest in the Atlantic Ocean. Very likely, elasmobranchs stocks here are close to full exploitation. In Area 47 (South Eastern Atlantic) catches have been fairly variable. It has the second smallest mean catch of elasmobranchs and the lowest IRP in the world, showing the most possibilities for increased exploitation of elasmobranchs in the future. For the four areas of the Eastern Atlantic, Area 27 dominated the catches producing more than the other three areas together.
|F A O Major Fishing Areas||Area Million Km2||Mean Catch '000 t||Coefficient Of variation||I.R.P. Avg Catch/Sqrt Area||Trend 82–91 '000t/y|
|27 NE Atlantic Ocean||16.9||94.8||12%||23.07||0.26|
|61 NW Pacific Ocean||20.5||102.3||10%||22.60||-0.29|
|51 W Indian Ocean||30.2||97.6||19%||17.75||1.16|
|21 NW Atlantic Ocean||5.2||26.5||57%||11.61||5.48|
|37 Mediterranean & Black Seas||3.0||18.2||29%||10.50||-0.76|
|71 W Central Pacific Ocean||33.2||59.1||38%||10.26||5.00|
|41 SW Atlantic Ocean||17.6||34.2||30%||8.15||0.60|
|57 E Indian Ocean||29.8||42.9||32%||7.87||1.34|
|34 E Central Atlantic Ocean||14.0||28.6||29%||7.63||-0.65|
|87 SE Pacific Ocean||16.6||21.4||32%||5.24||-0.39|
|31 W Central Atlantic Ocean||14.7||17.4||47%||4.54||0.77|
|77 E Central Pacific Ocean||57.5||21.1||34%||2.79||0.08|
|81 SW Pacific Ocean||33.2||10.4||47%||1.81||0.55|
|67 NE Pacific Ocean||7.5||4.8||60%||1.74||0.20|
|47 SE Atlantic Ocean||18.6||6.6||42%||1.53||0.07|
Figure 2.1 World reported catch of elasmobranch fishes 1947–1991 (Data from FAO and SEAFDEC, Fishery Yearbooks for Taiwan Area, and Scretaria de Pesca).
There are only two FAO areas in the Indian Ocean. The Western Indian Ocean (Area 51) has the second highest average yield in the world. This area has shown reasonably low variability in catches but a decreasing trend in recent production. Catches increased steadily up to the early 1970s but fell dramatically during 1983. Judging from the recent increasing trend in production, the situation seems to be recovering but catches have not yet reached previous levels. The IRP of Area 51 is the third highest in the world. Most of the catches in this area are taken in the northern region by Pakistan, India and Sri Lanka. Stocks in the northern region might be close to over-exploitation but given the large extension of this area and the low catches from its southern portion it might present some possibilities for increasing elasmobranch exploitation especially those of oceanic species. Area 57 (Eastern Indian Ocean) shows more variable catches with a growing trend. It has an intermediate IRP and higher yields are expected here. In the Indian Ocean, Area 51 produces, on average, more than double the catches of Area 57.
In the Western Pacific Ocean, Area 61 (North Eastern Pacific) had a decreasing trend for recent catches and the lowest variability of elasmobranch catches in the world. This area had the highest average yields in the world and the IRP was accordingly very high, marginally second to the North Eastern Atlantic. Therefore, stocks in this area might not provide any substantial increases in the future and may even be over-exploited. Area 71 (Central Western Pacific) showed the second highest trend of increase in catches reaching in the last few years five times those of the mid-1960s. The IRP in this area is relatively high and may indicate that yields could probably not be expanded much more. In the South Eastern Pacific (Area 81) catches have varied substantially with a low positive trend of recent catches. Average catches and therefore the IRP are very low. One possible reason for this is the relatively small extension of coastline inside this area together with correspondingly few human settlements. The potential of this area for significantly increased catches will depend mainly on the abilities of the stocks of oceanic and deep water elasmobranch species to sustain fisheries. Of the three areas of the Western Pacific, Area 61 is the most important for elasmobranchs having produced on average almost twice the catch of Area 71 and about ten times that of Area 81.
For the three areas of the Eastern Pacific, Area 67 (North Easter Pacific) has the smallest average catch and the highest variation in the world. The IRP is the second smallest in the world and the trend of recent catches is moderately positive. Larger catches might be obtained here in the future. Area 77 (Central Eastern Pacific) has variable catches with a low increasing trend and low IRP. Area 77 is the largest in the world but its low population density might account for the low IRP. The potential for increasing catches here is probably good especially in Central American countries and in the vast oceanic waters. The South Eastern Pacific (Area 87) is the only area of the East Pacific with a negative trend in catches and has an intermediate IRP. Further increases in the catches should be possible. Of the whole Eastern Pacific, Areas 77 and 87 have almost the same average catch during this period amounting to about four times those of Area 67.
Assuming that recent trends will continue without major changes in each of the FAO fishing areas, reported catches of elasmobranchs in the world can be expected to reach between 755 000t and 827 000t by the year 2000. These forecasts are based on “jackknife” linear regression analyses of elasmobranch catches since 1967 in each FAO major fishing area using a step of 5 years.
Data by countries for the period 1947–1991 indicate that 26 countries presently harvest, or have recently harvested, more than 10 000t/yr of elasmobranch fishes. These countries are often referred to as “major elasmobranch-fishing countries”. The elasmobranch catches of the People's Republic of China, although not available, also surpass 10 000t/yr and China is included as one of these 26 countries.
Catch statistics for the 25 major elasmobranch fishing countries for which data are available are shown in Table 2.2. Japan has traditionally been the overall major fisher of elasmobranchs in the world with average catches of 65 000t/yr. Indonesia, India, Taiwan (Prov. of China) and Pakistan follow with catches between 33 000t/yr and 43 000t/yr. France, the UK, the former USSR and Norway, recorded between 21 000t/yr and 27 000t/yr. Mexico, Brazil, South Korea, Nigeria, Philippines, Sri-Lanka and Peru caught between 11 000t/yr and 18 000t/yr. A large group formed by Spain, USA, Malaysia, Argentina, Thailand, Australia, Italy, New Zealand and Ireland followed with average catches between 4 000 and 10 000t/yr.
Even though there is great variability in the development of individual elasmobranch fisheries some patterns can be identified. About one third of the major elasmobranch fishing countries show recent levelling in their catches, probably signalling full exploitation of their resources. Seven countries show falling trends while nine others have a definite rise in catches (Figure 2.2).
Elasmobranch production is specially high in Indonesia where catches have soared since the early 1970s with no sign of a slow-down. Taiwan (Prov. of China), the USA, Spain and India are other countries with increasing landings of sharks and rays. Japan, historically the leader in elasmobranch fishing, has a clear trend of decreasing catches. Norway showed a clear increasing trend until the early 60's but catches have since sharply decreased. The same is true for the former USSR catches which grew from the early 60's to the mid-1970s but have since substantially decreased with no recovery. Catches in the UK have a very slight decreasing trend. Pakistan had a strong increasing trend in catch until the late 1970s, but dramatically dropped in the early 80's to be followed by a slow but sustained comeback. The range of causes for these decreasing trends is not easy to find in all cases but possible explanations for some cases follow.
The reported statistics indicate that during the last 15 years sharks have been slightly more important in catches than other elasmobranchs. The average reported catch of sharks and batoids is 285 433t/yr and 180 196t/yr respectively with an additional 190 159t reported as “various elasmobranchs”. After reallocating catches wrongly reported as “various elasmobranchs” to either sharks or rays with the help of ancillary information and splitting the remaining 94 139t/yr of “various elasmobranchs” in equal parts, a total of 393 741t/yr (about 59.5% of total elasmobranchs) can be attributed to sharks whereas 262 046t/yr are skates and rays (about 39.5%). Less than 1% are quimaeras and elephant fishes.
Two main sources provided the information in this section. First, literature on the subject was consulted for each case as extensively as possible. Much information probably remains in the form of unpublished reports from different governmental offices. Second, in an attempt to fill in some of the many gaps of information, a questionnaire was sent to officers or scientists in all major elasmobranch fishing countries. However, the success of this approach was poor. The extent of published work on elasmobranchs in each country and the level of response to the questionnaire is reflected in the quantity of information that is presented under each country's account.
Figure 2.2. Historical catches of elasmobranchs for the 25 major elasmobranch fishing countries arranged by geographical area
|YEAR||T.W.F.||T.W.CUPL||T.ELAS||EL/FISH %||CUPL/FISH %||USA||MEX (p)||BRA||PERU||ARG||USSR||UK||EIRE||NORW|
|% of worldwide elasmobranch catch, 1987–1991||3.57||4.88||3.69||2.71||2.54||1.75||3.31||1.03||1.21|
|% importance of elasmobranchs in country, 1987–1991||0.42||2.36||3.00||0.29||3.19||0.11||2.63||3.03||0.44|
|SPAIN||ITALY||FRA||NIG||PKST||INDIA||SRILK||THAI||MALAY||INDONE||S KOR||JAPAN||PHILIPP||TAIWAN||AUST||N ZEL|
(p) data from Secretaria de Pesca (Appendix 1)
(s) data from SEAFDEC (Appendix 1)
(s/f) data from SEAFDEC and FAO (Appendix 1)
(t/f) data from Fishery Yearbooks for Taiwan Area and FAO
While the USA is one of the few countries with reasonably detailed information on elasmobranch fisheries no comprehensive account of these fisheries on a national basis could be located. Main fisheries for elasmobranchs in the USA have traditionally been centred on sharks, although batoids have also been fished. Rays and skates were recorded in commercial catches as early as 1916 (Martin and Zorzi, 1993) mainly as by catch of more important fisheries. However, the first directed fisheries for elasmobranchs in the USA seem to have been for the tope shark, Galeorhinus galeus (then zyopterus), in California and for large sharks off Salerno in Florida. Both flourished as a consequence of the high demand for shark liver oil in the 1940s-50s and stopped mainly because of laboratory synthesis of vitamin A in 1950.
According to FAO statistics, until recently, the commercial catches of elasmobranchs in the USA were, together with those of Argentina, the least important among major elasmobranch-fishing countries in America. However, this has changed since the early 1990s. Elasmobranch production has varied considerably for the last 40 years oscillating around 10 000t/yr until the late 80's. Two periods of very low catches were 1952–1956 and 1970–1977, while 1958–1960 saw some of the highest yields. Since 1988 the post-war peak of 17 000t has been exceeded (Figure 2.2). Catches rapidly increased during the mid 1970s and soared in the mid-80's. Still, elasmobranchs are only a minor fishery as catches during 1987–1991 averaged only 0.42 % of the total fisheries production of the USA while representing 3.57% of the total reported elasmobranch catch in the world (Table 2.2).
According to Compagno (1990), the recent rise in catches might reflect a change in consumer preference that has made shark meat fashionable and acceptable to the public as a direct result of the infamous “Jaws” films. This would have prompted a whole new group of fisheries directed to sharks in the USA. According to Cook (1990), very recent changes in international shark-fin markets have further increased the demand for sharks in the USA. Amongst these new fisheries, those for the thresher shark, Alopias vulpinus, the Pacific angelshark Squatina californica and the shortfin mako Isurus oxyrinchus, are the most important in the West Coast. For the Gulf of Mexico and East Coast of the U.S.A, most of the recently increasing shark fisheries take a diverse catch of coastal sharks, reported as unclassified sharks. This difference in detail of the reported catches between the two coasts of the USA is probably because on the west coast there are different markets and prices for many species of elasmobranchs whereas on the east coast (NOAA 1991) only mako sharks attain a price different from the remaining “unclassified sharks”.
Data from FAO shows that until 1980 elasmobranch catches in the USA were about evenly distributed on both coasts. Since 1981, the east coast has contributed the bulk of the catches as a result of a large expansion of fisheries for sharks and rays (Figure 2.3). This new growth led to the recent implementation management of large shark fisheries in the east coast. Overall, the two most important elasmobranch groups in the fisheries of the USA are the dogfishes (mainly Squalus acanthias) and the skates. Dogfish and skate catches from the waters within FAO Area 21 (roughly corresponding to the New England and Mid-Atlantic regions of the National Marine Fisheries Service of the USA) and dogfish catches in FAO Area 67 (roughly corresponding to the coasts of Washington and Oregon) have dominated the elasmobranch production of the country until recently.
Dogfish catches from the Northeast USA (Area 21) were the major part of total elasmobranch catches during 1979–1983, fell in 1984 and have slowly recovered since 1985. Skate catches in this region have increased tremendously since 1983. This made them the second most important group in 1989 with almost one third of the total elasmobranch catches of the country (Figures 2.3 and 2.4). Dogfish catches off the northwest USA (taken mainly in Washington) had fairly variable yields, and declining during the mid 80's, partially recovered in 1986–1987 only to subsequently fall. Most of the dogfish on the east coast and skates on both sides of the country are taken by trawlers while dogfish in the northwest coast are apparently harvested with gillnets and trawl nets. Although both rays and dogfish are low priced resources when compared with some other elasmobranchs (eg, mako or thresher sharks) they are available in such large quantities that they become profitable for fishing companies. There are apparently no management regimes specifically directed at the dogfish and ray resources of the USA. At most, some stocks are included in general management schemes for ground fish resources. Grulich and DuPaul (1987) estimate that the piked dogfish stocks of the US east coast could support a harvest of about 24 000t/yr in the mid-80's. However, recent studies suggest that the biomass of the Squalus acanthias stock sustaining most of this fishery, although increasing recently, is highly variable from year to year (Silva 1993). This could mean that high levels of exploitation are not sustainable and consequently supplies for a large market would be unreliable.
The East Coast
Throughout this century, the single most important fishery for sharks in the East Coast of USA was that for large sharks of Salerno Florida during the period 1935–1950 (major accounts are given in Springer 1951, 1960). The fishery depended on production of vitamin A from shark liver oil and failed when industrial synthesis of vitamin A began. The fins and hides were also utilized. The fleet was based at Salerno but during the summer it usually extended operations west to the Mississippi river and after 1945 expanded to include boats in the Carolinas, the Florida keys and the Gulf coast of Florida. The Caribbean and West Indies also provided catches to the company based at Salerno. In the later years approximately half of the catch came from the Gulf of Mexico. Up to 16 boats of 12–15.5m operated concurrently, fishing with two bottom longlines of at least 200 hooks in depths up to 90m. Floating longlines and bottom gillnets were also occasionally used. Sandbar sharks, Carcharhinus plumbeus, composed most of the catches, which peaked at 10 514 sharks in 1947.
In recent times, the second most important elasmobranch fisheries in the USA after dogfish and rays have been the growing fisheries for large sharks in the Gulf of Mexico and South Atlantic. While catches of large sharks have remained practically unchanged in the Mid-Atlantic and New England regions, shark catches in the Gulf of Mexico and South Atlantic regions underwent radical changes with an eightfold increase in yield from 1984 to 1989 (Figure 2.4). This trend, caused mainly by the development of a stable market, began in 1985 when fishermen began to target sharks with gillnets and longlines. The landing of previously discarded shark by catches from other fisheries also became profitable.
According to NOAA (1991), directed fisheries for sharks in the east coast include: a monofilament 18–64cm mesh driftnet fishery apparently targeted on schooling blacktip sharks in Florida; a May-November gillnet fishery in the east coast of Florida catching mostly Carcharhinus spp.; a driftnet fishery for tunas, billfishes and sharks in the Atlantic, Gulf of Mexico and Caribbean; pelagic longlines for tunas, billfishes and sharks in the Atlantic, Caribbean and Gulf of Mexico (this fishery deploys gear in a mechanized operation involving large vessels and thousands of hooks); a recent fishery for sharks with bottom longlines sets manually with up to 100 hooks from each small boat; and a pelagic hook and line fishery for tunas, billfishes and sharks in the Gulf of Marine, South New England and the Mid Atlantic.
Figure 2.3. Elasmobranch catches of the USA by major groups and regions as reported by FAO during 1977-1991.
Figure 2.4. Elasmobranch catches from the east coast of the USA during 1980-1989. Bars represent shark fisheries. (Data from FAO and Hoff 1990).
Lawlor and Cook (1987) report that the seasonal East Florida longline fishery for sharks is carried out from boats 11–15.5 m long with 2–4 fishermen using bottom and/or surface longlines for periods of 1–2 days. The mainline varies from 1.6 to 10km in length and is made of 4.8–6.4 hard-lay tarred nylon, from which 300–500 ganglions of 3.6 m long multistrand steel cable fall, with 3/0 or 3.5/0 shark hooks each. Buoys are attached to the mainline on 28–30 m leaders for bottom longlines and for pelagic longlines with 10–30 m leaders. Bluefish, bonito, mackerel, mullet and squid are the most common bait. Apparently, about 110 boats work full-time and year-round in this fishery following migrating sharks along the coast. NOAA (1991) indicate that 124 vessels target sharks in the US east coast with longliner catches during 1989 adding up to 6140t while gillnetters caught 62lt.
Some sharks in the east coast of USA are also landed as by catch from the following fisheries: the Gulf of Mexico tuna fisheries; the Gulf of Mexico and south Atlantic coast snappergrouper bottom longline fishery; swordfish gillnet fishery of Massachussets and Rhode Island (up to 15 vessels) and the gillnet fisheries of Maine, Virginia, New York and New Jersey. The main species caught in the South Atlantic and Gulf of Mexico with gillnets are Carcharhinus plumbeus, C. limbatus, C. leucas, C. altimus, C. brevipinna, Galeocerdo cuvier, Carcharias taurus, Negaprion brevirostris, Sphyrna lewini and S. mokarran. Those captured with longlines are mainly C. plumbeus, C. limbatus, C. isodon, C. acronotus, C. leucas, C. brevipinna, C. obscurus, Rhizoprionodon terraenovae, Carcharias taurus and Sphyrna lewini(Hoff 1990; NOAA 1991). Russell (1993) reports C. limbatus, Mustelus canis and Rhizoprionodon terraenovae as the most common species caught by shark longliners in the northern Gulf of Mexico. Data from NOAA (1991) shows that ex-vessel prices for sharks in the Gulf of Mexico and southeast USA almost doubled from an average price in constant $US of $0.57/kg in 1979 to $1.12/kg in 1986, the average since 1983 being approximately $1.00/kg. Meanwhile, the prices for fins have risen nearly an order of magnitude since 1985. In general, higher prices are paid for dressed carcasses and for sharks fished in waters more than 3 miles from the coast as opposed to those caught inside the 3-mile state waters limit. The mako shark attains a higher price than the rest of the species which are treated as “unclassified shark”.
Hoff (1990) stresses that important by catches of several species of sharks are taken regularly by the shrimp trawl fisheries in the northern Gulf of Mexico. Unfortunately, most of the catch is discarded as there is no market (GMFMC 1980). NOAA (1991) estimate that the incidental catch of sharks in the Gulf of Mexico shrimp fishery is of about 2800t/yr. Most individuals are juveniles from nursery areas and this catch might represent an important threat for recruitment to future breeding stocks. Escapement of larger specimens will probably increase if the regulations for the mandatory use of turtle excluder devices (TED) are approved. Overall, total yearly discards of sharks in all fisheries of the east coast of USA averaged 16 000t (NOAA 1991).
The great increase in shark exploitation both by commercial and recreational fishermen on the east coast of the USA led to catch quotas and bag limits in April 1993. This management took 10+ years to implement due to, among other things, lack of appropriate data for assessment regarding abundance, biology, distribution, life history and catches of shark. Given concerns about possible overexploitation of shark stocks during the late 80's, an assessment was performed with the available information. The estimated levels of long-term production are about 3400t for large coastal sharks and about 3600t for small coastal sharks (Parrack 1990, NOAA 1991). The species considered in each of the management units are listed in Table 2.3. A number of management measures aimed at rebuilding stocks in effect since April 1993 include: 1993 commercial quotas (in dressed weights) of 2436t for large coastal species and 580t for pelagic species; recreational bag limits of four sharks/vessel/trip for large coastal and pelagic sharks combined and five sharks/person/day for small coastal species; commercial fishing only by permit; fins landed in proportion to carcasses; release of shark by catches ensuring maximum probability of survival; compulsory submission of sales receipts and logbooks from selected commercial and recreational operators; presence of observers in selected commercial boats; and banning of shark catches for foreign vessels in US waters (NMFS 1993).
The West Coast
Holts (1988) and Cailliet et al. (1993) review the shark fisheries of the west coast of the USA. Aside from the piked dogfish fisheries which dominate the catches, an important group of directed fisheries for sharks suddenly arose in California at the end of the 70's. but some of have declined during the following decade. These fisheries arose mainly as a response to changes of trends in consumer preference which increased demand and prices for some species. Total catches (excluding dogfish) increased through the late 70's to a peak of about 1 800t in 1982 but have since varied with a decreasing trend (Table 2.4). Cailliet et al. (1993) consider market fluctuations and susceptibility to overexploitation of some stocks as the main reasons for diminishing catches.
The first species whose landings increased was the thresher shark (Alopias vulpinus) fishery centred between San Diego and Cape Mendocino. Operations started with 15 large-mesh driftnet vessels in 1977. Ex-vessel prices for this species increased from US$0.64/kg in 1977 to US$3.52/kg in 1986. The thresher shark fishery was soon displaced by the more valuable swordfish fishery and the thresher shark. This lead to social problems and poor management of the fishery and resulted in the loss of the thresher populations (see Bedford 1987 for a detailed account). Catches peaked in 1982 at 1083t when more than 200 vessels were operating, but slowly declined until 1986 when limited area and season legislation was passed. Catches further declined as a result of these regulations until the directed fishery for this species was banned in October 1990. At present only incidental catches are permitted which and they account for almost 300t/y (pers. comm., Holts, NMFS Southwest Fisheries Center) in the swordfish fishery. Throughout most of the fishery catches were composed mainly of young sharks 1–2 years old a few A. superciliosus and A. pelagicus are also included. Bedford (1987) reports that market sampling data showed decreasing modal sizes with time along with declining CPUE indices since the mid-80's. Unpublished data (Holts, pers. comm. op. cit.) shows the mean length of fish caught clearly declined during the same period.
Another recent development on the west coast was the fishery for Pacific angelshark (Squatina californica). This began as a localized operation in Santa Barbara in 1977 (166kg landed), underwent a great expansion in 1981 (158t landed), reached a peak in 1986 (563t landed) and steadily declined in the following three years (121t in 1989, Table 2.4; Cailliet et al. 1993). Ex-vessel prices climbed from US$0.33/kg in 1978 to US$0.99/kg in 1984 (Holts 1988). Pacific angelsharks were taken initially as by catch of the Pacific halibut fishery with bottom set trammel nets. As markets and demand expanded, they began to be targeted with single-walled nylon twine (No. 24 to No.30) gillnets, 366–549m long and 13 meshes deep (mesh sizes between 30.5 and 40.6cm) (Richards 1987). Vessels were usually from the halibut fishery and used hydraulic gear retrievers. Operations were centred in the Santa Barbara-Ventura region and the Channel Islands in waters less than 20m deep, less than 1.6km offshore. In the opinion of Cailliet et al. (1993) the drop in catches since 1986 is due to a combination of declining availability of the species and changes in the market as cheaper imports of shark meat became available. The only regulations applied to this fishery are those pertaining to the set-net fishery for halibut in California. These neglect the need for separate management of the elasmobranch resources.
A shortfin mako (Isurus oxyrinchus) fishery in California also started as a valuable by catch of the driftnet fishery for swordfish and thresher shark in the late 70's. Catches increased steadily from 1977 through 1982 when they reached 239t then underwent a period of lower levels possibly owing to changes in fishing strategy or environmental conditions (Holts 1988) but peaked again in 1987 at 277t. Since then, catches have declined once more (Table 2.4). The bycatch of makos in the driftnet fishery is low and since 1988 a closely controlled experimental fishery was started with longlines targeting this species. Under this regime, 6 vessels using 4.8-8.2km stainless steel cable longlines near the surface are allowed to fish subject to time/area closures and away from sport fishing grounds. Additionally, a TAC has been established at 80t and a market for the substantial blue shark by catch must be developed to utilize this resource. By catches of shortfin mako in the driftnet fishery are also allowed. Although the shortfin mako fishery is mainly sustained by very young sharks averaging 9–14kg dressed weight, there is no apparent decline in the mean size of the catches. Populations look healthy and even might be relatively lightly exploited (Holts 1988, Cailliet et al. 1993).
|FAO Common Name||Scientific Name|
|Large Coastal Sharks||Sandbar||Carcharhinus plumbeus|
|Caribbean reef||Carcharhinus perezi|
|Bigeye sand tiger||Odontaspis noronhai|
|Scalloped hammerhead||Sphyrna lewini|
|Great hammerhead||Sphyrna mokarran|
|Smooth hammerhead||Sphyrna zygaena|
|Great White||Carcharodon carcharias|
|Small Coastal Sharks||Atlantic sharpnose||Rhizoprionodon terraenovae|
|Carribbean sharpnose||Rhizoprionodon porosus|
|Sand devil||Squatina dumeril|
|Pelagic Sharks||Shortfin mako||Isurus oxyrinchus|
|Longfin mako||Isurus paucus|
|Bigeye thresher||Alopias superciliosus|
|Oceanic whitetip||Carcharhinus longimanus|
|Sharpnose sevengill||Heptranchias perlo|
|Bluntnose sixgill||Hexanchus griseus|
|Bigeye sixgill||Hexanchus vitulus|
|BIGEYE THRESHER SHARK||4,507||0||0||0||4,922||4,786||16,466||48,354||33,945||54,313||20,968||11,488||5,463||10,030|
|GREAT WHITE SHARK||0||0||0||1,030||754||19||3,656||288||2,770||1,299||419||610||997||596|
|PELAGIC THRESHER SHARK||0||0||0||0||0||0||0||4,959||0||291||106||1,041||350||113|
|BROADNOSE SEVENGLL SHARK||0||0||38||0||247||1,550||927||788||128||405||25||77||10||6|
|BLUNTNOSE SIXGILL SHARK||0||0||0||9||5||144||0||58||44||2||0||25||9||61|
|TOTAL EXCLUDING DOGFISH||381,084||453,790||592,440||956,460||1,671,892||1,637,808||1,793,021||1,401,102||1,569,852||1,662,863||1,535,097||1,285,347||860,009||732,055|
* includes catches from Canadian waters (approx. 50% during 1983-89)
In addition to these three fisheries which constitute the main “new” shark fisheries in the last 15 years on the west coast, many other elasmobranchs are also taken commercially, mainly as a by catch of other fisheries. Martin and Zorzi (1993) review the skate fisheries of California. Skates (mainly Raja binoculata, R inornata and R. rhina) have been fished in California since at least 1916, averaging 96t/yr and 11.8% of total commercial elasmobranch catches in California. San Francisco and Monterey are the main landing ports receiving 70% of the total. There are technical constraints in the processing marketable skates of sizes up to one kilogram and most of the landings of R. binoculata and R. rhina consist of immature individuals. Roedel and Ripley (1950) suggest that the skate resource might be underutilized, but it also seems to be presently misutilized. A market for larger skates should be developed if this resource is to be properly used and managed.
Another species of interest is the blue shark (Prionace glauca). Holts (1988) and Cailliet et al. (1993) summarize the available information. The blue shark is a major incidental catch of the driftnet fishery of California and a minor by catch of the set-net fisheries for halibut and angel sharks. Mortality estimates for the driftnet fishery were 15 000–20 000 (300t) sharks annually in the early period, although changes in gear design have reduced this mortality. The experimental longline fishery for mako sharks also takes incidental catches of blue sharks at a rate of four blue sharks for each mako. Nevertheless, a conservation programme of enforced rapid release of live sharks is expected to decrease this mortality. A small experimental longline fishery with one vessel occurred during 1980–1982 and catches of blue sharks peaked around 90t in 1980 and 1981 (Table 2.4). The main constraint for the development of a large scale fishery for blue sharks is the lack of markets. Blue shark meat is reportedly less palatable than that of other elasmobranchs. Attempts to start a fishery for salmon sharks Lamna ditropis in Alaskan waters was reported (Paust 1987) but no other records were found.
The single most important fishery for elasmobranchs off the west coast of the USA was that developed in California for tope shark Galeorhinus galeus during the 1930's–1940's. Ripley (1946) gives a detailed description of this fishery. Stimulated by the discovery in 1937 that the tope sharks of that area were the richest source of high potency vitamin A in the world, the subsequent 4 years saw increases in catches that reached over eight times those of pre-boom levels and averaged approximately 3400t/yr. Vessels from the northern halibut fishery switched to shark fishing and in a short period all sorts of vessels modified their operations and joined the fishery totalling about 600 boats by 1939. Swift changes in gears from drift and set gillnets to machine-handled halibut longlines and back to “diver” gillnets and the posterior mechanization of their operation occurred in a period of less than 3 years (detailed description of gears used are given in Roedel and Ripley 1950). Northern California was the main fishing area with more than 70% of the catches although fishing occurred along the entire coast, mostly within 7.8 km of shore in waters up to 144m deep. After 1941, catches plummeted and never recovered their former levels. The discovery of synthetic vitamin A prevented efforts to revive this fishery, although a small fishery has continued to present times. Catches since 1976 fluctuated between 66 and 253t/yr (Table 2.3). Activities are now centred around San Diego and Orange counties (Holts 1988) apparently as an incidental consequence of net fisheries for halibut and angel shark. Only general regulations for the latter fisheries “protect” tope shark populations. Holden (1977) estimates the north Pacific unexploited stock size at 29 400t, but it appears that stocks have not yet recovered to former levels (Holts 1988). However, no recent assessments have been done for this species. Finally, a short lived small-scale harpoon fishery for basking sharks (Cetorhinus maximus) existed during the late 40's in Pismo Beach (Roedel and Ripley 1950) but also ceased as a consequence of the fall of the liver oil industry.
Since the mid-70's, Mexican elasmobranch fisheries have been the largest in America (Figure 2.2). FAO statistics show that there has been a general trend of increased catches of elasmobranchs in Mexico, from the typical 5 000t/yr of the 50's to recent levels of varying around 30 000t/yr since the early 80's. Judging from the trend of the last ten years, Mexican fisheries for sharks and rays have attained relative stability. Elasmobranchs are a relatively important resource in Mexico, comprising 2.36% of the national catches during 1987–1991. This figure is comparable with other major elasmobranch-fishing countries but is substantially higher than the 0.8% contribution of elasmobranchs to world fisheries in the last 10 years. Elasmobranch exploitation in Mexico can be traced back to at least the 1930's, but detailed statistics are difficult to find before the mid–-1970's. Walford (1935) reports “several tons” of shark fins from the west coast of Mexico being imported to California each year and Ripley (1946) refers to Mexican fisheries supplying shark liver oil to the USA industry. Mazatlan and Guaymas were the main ports in the west coast shark fishery. Catches peaked at 9 000t in 1944 but declined to 480t in 1953 after the fall of the shark liver oil industry (Castillo 1990). On the east coast during the 40's, a fleet based at Progreso, Yucatan targeted sharks had characteristics similar to the fleet of Salerno, Florida, and caught up to 3200/yr since 1950 (GMFMC 1980).
Mexican fisheries for elasmobranchs are targeted on sharks. Batoids are seldom exploited but considerable (and unknown) amounts are discarded in the extensive trawling operations for shrimp fisheries. According to data from the Mexican Ministry of Fisheries yearbooks for 1977-1991, sharks account for 94.8% (29 036t/yr) of elasmobranch catches while batoids only represent 4.2% (1272t/yr).
Because of its larger coastal extension, the Pacific coast contributes 60% of total shark catches while the remaining 40% comes from the Gulf of Mexico and Caribbean. No data on catches by species are available. Only small sharks (those measuring less than 1.5m total length (TL) when caught and are know locally as cazón) and large sharks (those larger than 1.5m TL) are recorded in the statistics. Large sharks comprise 60% of total shark catches and 2/3 of these are caught in the Pacific while only 1/3 are caught in the Gulf of Mexico and Caribbean. The remaining 40% of the total shark catches are small sharks, 64% come from the Pacific and 36% from the east coasts. There is some variability in the catches of large and small sharks from each coast, but overall, Mexican fisheries seem to have reached an equilibrium during the last 10 years (Figure 2.5). Meanwhile, batoid catches are slowly and steadily expanding.
Mexican shark fisheries are largely artisanal, multispecies, multigear fisheries. Bonfil et al. (1990), Castillo (1990) and Bonfil (in press) summarize most of the available information on elasmobranch fisheries in Mexico. They estimate that about 1/3 of the shark catch is taken by small-scale fisheries. Vessels are generally made of fibreglass, 7–9 m with outboard motors using either gillnets or longlines depending on the regional customs. Some vessels of 14-20 m are also used whereas only a few vessels in excess of 20 m take part in the fishery. Significant quantities of sharks and rays are also taken as incidental catches of large-scale trawl fisheries for shrimp or demersal fishes in both coasts. Large scale fisheries for tunas and billfishes in both coasts also contribute to the total catches. Sharks and rays are traditionally used for food in Mexico, either fresh, frozen or more commonly, salt-dried. Shark fins and hides are also exported and most offal is reduced to fish meal.
The main fishing grounds in the Pacific are centred in the Gulf of California in the north and the Gulf of Tehuantepec in the south. However, most of the available information about these fisheries comes from the northern area. Apart from the total catch, little is know about the shark fisheries in the Gulf of Tehuantepec. In the northern part, sharks are mainly caught with monofilament longlines of 1–2 km and approximately 350 hooks, although smaller quantities are taken with gillnets of up to 2 km long. Some 17 vessels, 44 m long and using longlines of up to 2000 hooks targeted sharks and billfishes on the Pacific coast during 1987. It is unknown if these vessels are still operating. A similar number of Japanese-Mexican joint venture longliners caught 234t/yr of sharks in Baja California during 1981–1983 (Holts 1988).
Fishing grounds span the entire east coast. During 1976–1988, Veracruz and Campeche shared 58% of the total shark catch and Tamaulipas and Yucatán 30%. Longlines are utilized mostly in the state of Veracruz and presumably also in Tamaulipas. Gillnets from 11–40cm mesh size are the main fishing gear in the Bank of Campeche. There is a substantial by catch of mainly juvenile sharks in the semi-industrialized longline fisheries for red grouper and red snapper on the Campeche Bank but no estimates of this catch are available.
Information about the species caught in the different regions of the Mexican coast and the composition of the catches is incomplete. Most of the available research has been done in the mouth of the Gulf of California on the west coast and in the southern States of Campeche, Yucatan and Quintana Roo on the east coast. Important landings also occur in other areas of both coasts but have been poorly documented.
At least 44 species of shark are reported in the commercial catches of Mexico and 12 are the most important in the catches in the area of La Paz, Baja California and Sinaloa whereas 15 are the main species in the Gulf of Mexico and Caribbean (Table 2.5). Most of the large sharks caught consist of Carcharhinus spp, Sphyrna spp and other carcharhinids, while the small shark catches are a mixture of mainly Mustelus spp. and Rhizoprionodon spp., with juveniles of the large sharks sometimes contributing an important part of the total. Along the Sinaloa coast in the central Pacific Rhizoprionodon longgurio, Sphyrna lewini, Nasolamia velox, Carcharhinus limbatus, C. falciformis, C. leucas and Galeocerdo cuvier, are the most important species. Galván-Magaña et al. (1989) report that Mustelus lunulatus, Heterodontus mexicanus and Sphyrna lewini are the most important sharks in the area of La Paz, B.C.. Experimental catches of longliners in the Pacific caught mainly pre-adult and adult Alopias vulpinus and Carcharhinus limbatus (Velez et al. 1989). For the east coast, the most important species are Carcharhinus falciformis, C leucas, C. obscurus, C. plumbeus, C. limbatus, Rhizoprionodon terraenovae, Sphyrna tiburo, Mustelus canis, C. brevipinna, Negaprion brevirostris, Sphyrna mokarran, Sphyrna lewini, Galeocerdo cuvier and Ginglymostoma cirratum. With the exceptions of C. obscurus and Ginglymostoma cirratum, all the important species of the east coast are known to be heavily exploited as juveniles and sometimes even as newborns, atg least in some part of their range.
|FAMILY||SPECIES||PACIFIC||GULF OF MEXICO/CARIBBEAN|
|19||Mustelus sp. ?||X|
* Main species in the commercial catches
Figure 2.5. Elasmobranch catches in the pacific and Gulf of Mexico/Caribbean coasts of Mexico during 1977–1991. (sh = sharks). (Data from Secretaria de Pesca, Mexico).
A few isolated preliminary assessments of the status of some shark stocks exist for the east coast. Alvarez (1988) reports that surplus production models show that the stocks of Sphyrna tiburo and Rhizoprionodon terraenovae in Yucatan are close to optimal exploitation levels; results of the yield-per-recruit model suggest exploitation of Sphyrna tiburo is at the optimum level whereas Rhizoprionodon terraenovae seems to be already overexploited. For the production models, catch and effort were estimated in a very rough way and for the dynamic model, growth and mortality were estimated via length frequency analysis. Bonfil(1990), estimated growth via vertebrae readings and using the yield-per-recruit model found growth overfishing for the Carcharhinus falciformis stock of the Campeche Bank. This results mainly from the high catches of newborns and juveniles of this species in the local red grouper fishery.
There have been several permanent research programmes for shark fisheries in Mexico since the early 80's. Despite this, to date Mexico has no specific management for elasmobranch fisheries. A number of concerns have been expressed about undesirable practices in the fisheries. At least, Carcharhinus falciformis, C. acronotus, Rhizoprionodon terraenovae and Sphyrna tiburo are heavily exploited as juveniles in Campeche and Yucatan, hence raising the possibility of a future collapse of their stocks. Further, there are indications that large decreases in the abundance of juveniles of C. leucas, C. limbatus, C. acronotus, C. perezi and Negaprion brevirostris have occured in some coastal lagoons of the Yucatan Peninsula as a direct consequence of heavy fishing with set nets (Bonfil in press). It is likely that this is commonplace in most coastal lagoons along the coast of Mexico. Further, the killing of large numbers of pregnant female Rhizoprionodon longurio in Sinaloa, on the west coast is another concern. Although information is poor it is likely that many stocks in the Gulf of California and Tehuantepec are close to their optimum level of exploitation or are even overfished. However, no assessments are known to date. Limited or non-existent information about the size of the stocks and about the actual levels of mortality makes an adequate appraisal of the status of Mexican shark fisheries difficult.
As in other countries, socio-economic and health problems related to the fisheries complicate the management of elasmobranchs in Mexico. The chances of curtailing the fishing of juvenile sharks in Mexico is constrained by the problems of the artisanal nature of many of the fishing fleets (loss of income for large numbers of fishermen) and the high demand for small sharks. The higher concentration of heavy metals generally found in older sharks also makes the harvesting of juveniles preferable.
From the mid-sixties until recently, the elasmobranch catches of Peru were the third largest in America and contributed 2.71% to the world elasmobranch catch. Nevertheless, elasmobranchs are of minor importance in Peru and represent only 0.29% of the total fishery production (Table 2.2). Their elasmobranch fisheries had a fairly steady trend of slow development in the 50's and early 60's. Since the mid-1960s catches have oscillated around 18 000t, peaking at more than 30 000t in 1984 and crashing in 1990–1991 (Figure 2.2). There may be a link between recently declining elasmobranch catches and the eruption of cholera in Peru during 1990.
Elasmobranch production in Peru is strongly dominated by smoothhounds. During the period 1977–1991, smooth-hounds of the genus Mustelus were the most important species in the elasmobranch catch making 5% (10 219t/yr) of the total and accounted for 25 000t in 1984 when record elasmobranch catches of 34 400t were taken, (Figure 2.6). Unspecified rays comprise 25% (4640t/yr) of the total catches. Their landings have increased significantly since 1984, making them the second most important elasmobranch group. Rhinobatos planiceps and angel sharks, Squatina spp., are also important species with average catches of 10% (1908t/yr) and 3% (560t/yr) respectively. The yields of these two groups showed variable trends in this period. An assorted group of elasmobranchs comprise the remaining 6% (1133t/yr). Apart from FAO statistics, nothing else is known about the elasmobranch fisheries of Peru.
The Americas Brazilian elasmobranch catches follow those of Mexico and the USA, in size. It appears that Brazilian elasmobranch fisheries have attained a good degree of stability. After a slow but steady start through the sixties and a brief fall in the 70's, the catches of sharks and rays from Brazil underwent a major leap in the early 80's. Yields have since varied up to a maximum of 30 000t (Figure 2.2). Sharks and rays contributed 3% to the total catch during 1987–1991 making 4.0% of the world catches of elasmobranchs (Table 2.2).
Statistics do not differentiate elasmobranchs by species in Brazil. At least 30 elasmobranchs are common in the commercial catches in the southeast, but most of the landings are dressed and without head or fins making it difficult to distinguish species (Tomas 1987). Some of the species mentioned in commercial catches are: Mustelus schmitti, Galeorhinus galeus Prionace glauca, Isurus oxyrinchus, Squatina guggenheim, Squatina sp, Pristis spp., Rhinobatos percellens, R. horkelii, Dasyatis spp, Gymnura spp and Myliobatisspp.
According to FAO data Brazilian landings during the period 1977 – 1991 have been dominated by an assorted group of species corresponding to 72% (17 919t/yr) of the elasmobranch catches. Yields for this group of elasmobranchs grew rapidly from less than 1 000t in 1978 to more than 23 000t in 1982 and have remained close to 20 000t/yr since then (Figure 2.7). All the sharks known to occur in Brazilian catches are included in this group. According to Batista (1988) landings of Galeorhinus galeus have increased since 1970 due to increased trawling in south east Brazil. The second most important group during this period were the skates and rays comprising 17% (4254t/yr) of the catches. Landings of this group, as well as those of guitarfishes Rhinobatos spp. which averaged 7% (1683t/yr) of the total elasmobranch catch, expanded slowly. Small catches of sawfishes Pristis sp. have been steadily landed averaging 4% (1014t/yr) of the catch.
Vooren and Betito (1987) report on at least 25 species of small sharks and 24 of batoids found in waters less than 100m deep in the southeastern continental shelf. Swept area biomass estimates indicate that 20 000t are available in winter and 13 000t in summer. Of these 90% consist of 16 small sharks and 8 batoid species of commercial value. Apparently the only traditional use for elasmobranchs in Brazil has been for food, but Göcks (987) and Jacinto (1987) note some efforts to use the hides and other parts.
At least two kinds of fisheries land elasmobranchs in the north of Brazil (R. Lessa, pers. comm). An industrial longline fishery for tunas with up to 50% bycatches of sharks, takes mainly Prionace glauca, Carcharhinus longimanus, Carcharhinus spp., Sphyrnaspp., Isurusspp. Alopias spp., Pseudocarcharias kamoharai and Galeocerdo cuvier. This fishery landed an average of 144t/yr of sharks between 1985–1990. About 60% of these were sharks less than 1.5m TL. Artisanal fisheries to catch Cynoscium acoula and Scomberomorus spp. catch Carcharhinus porosus, Rhizoprionodon spp., Sphyrna spp., Isogomphodon oxyrhynchus and Pristis peroretti. There is a high incidence of juveniles in this fishery which uses small driftnets about 1km long and 6m deep. Along the north shore between the Amazon river and Recife elasmobranch catches comprise up to 60% of the total catch. Incidental catches of small sharks and rays in the Brachyplatystoma, shrimp and snapper fisheries in the north of Brazil are reported by Evangelista (1987). Apparently most of the bycatches were formerly discarded but are now beginning to be used.
Vooren et al. (1990) summarize information on demersal fisheries for elasmobranchs during 1973–1986 on the continental shelf off the southern port of Rio Grande. Elasmobranchs account for 7.3% of the total catches, 13.1% of the trawl catches, 7.1% of the paired trawl catches and 5.4% of small-scale fisheries catches. Trawling is done with 440–480 HP boats of 11-13 day trips in depths between 40–100m while paired trawling is done by 340–370 HP boats of 9–11 day trips in depths less than 40m. Small-scale fisheries include beach seining and trammel nets used in waters less than 10m deep and gillnetting by 11–16m boats with 100–130 HP motors in waters 8–40m deep. Small sharks average 46.3% of elasmobranch catches while angel sharks, guitar fishes and rays account for 24.85%, 24.5% and 5%, respectively, of the catch. Mustelus schmitti and Galeorhinus galeus comprise most of the catches of “caçoes” or small sharks, and show increased landings, from 1414t in 1973 to 3217t in 1986, but,according to SUDEPE (1990), landings to 2023t in 1989. The proportion of small sharks in the catches of the small-scale and pair-trawler fishery increased during this period but decreased in the trawl fishery. This resulted in almost equal landings by each but fishery in 1983–1986. CPUE of small sharks for both types of trawlers tended to increase throughout the study period. Angel sharks (Squatina guggenheim and Squatina sp.) landings increased from 822t in 1973 to 1777t in 1986. As with the small sharks, the proportion of catches contributed by small-scale fisheries and pair trawlers increased while that of the trawl fishery decreased. Still, about 50% of the total landings of angel sharks came from the latter. While CPUE of angel sharks from trawlers showed an overall increase, paired trawlers' CPUE increased until 1983 and decreased afterwards. Landings of guitar fish, Rhinobatos horkelii, varied between 600 and 1925t. Most of this came from the small scale fisheries (50%) and paired trawlers (32%), while trawlers contributed very small catches (13%). Data of CPUE showed a slight decrease until 1982 for both types of trawlers, increasing to 1984 and then falling. Landings of rays, mainly of Dasyatis spp. and Gymnura spp., and to a lesser extent, Myliobatis, grew from 36t in 1973 to 484t in 1986. Small-scale fisheries averaged 18% of these catches, paired trawling 53% and otter trawling 34%. CPUE for rays in trawl fisheries were variable with an increasing trend.
Figure 2.6. Elasmobranch catches if Peru, by species groups, during 1977-1991 (Data from FAO).
Figure 2.7. Elasmobranch catches of Brazil, by species groups, during 1977-1991 (Data from FAO).
The apparent decline of some of these populations in the last period of the above study seems to be confirmed by a switch from trawling to bottom longlines and gillnets (the latter specifically aimed at Squatina and Galeorhinus) which started in 1986 due to decreasing CPUE. This switch was coupled with additional fishing for angel sharks by shrimp trawlers from other areas during the off-season for shrimp (Pers.comm., C.M. Vooren, Universidad de Rio Grande, 1991).
Amorim and Arfelli (1987) and Arfelli et al. (1987) report some bycatches of large sharks in southern and southeastern waters by tuna longliners. Prionace glauca accounted for 33% of total catches of this fleet in 1985 and Isurus oxyrinchus accounted for 3.2% of total catches during 1971–1985. They are caught mainly during April-July and May-November. Landings of blue sharks consist mainly of carcasses of 20-40kg dressed weight(no head, fins or guts) which accounted for 553t and 462t in 1984 and 1985 respectively. Blue shark CPUE has varied from 0.4 kg/100 hooks in 1971 (when their capture was avoided) to 27.6kg/100 hooks in 1985. Shortfin mako catches varied between 21t (1971) and 73t (1981), their mean weight in the catch varying between 42kg and 60kg throughout 1985. They are the most valued of elasmobranchs in Brazil and are consumed locally and exported to the USA.
Much research on elasmobranchs in done by Brazilian Universities, governmental and non-governmental organizations. However, according to Lessa (pers.comm.,op.cit.), at present there are no management measures for elasmobranchs in Brazil although some local groups intend to raise governmental concern about the status of these fisheries. There are plans to report landings by species and her communication notes that elasmobranch stocks exploited by the north coast artisanal fishery are thought to be underexploited, those utilized by the tuna longline fishery are sustainably exploited and the south Brazil demersal stocks are overexploited.
Elasmobranch catches of Argentina are one of the few expanding major elasmobranchfishing countries in America. After a temporary drop in the late 40's, attributed to the collapse of shark liver oil fisheries, shark and ray production had a slow but steady growth from the early 1950s to the mid 1960s (Figure 2.2). Since 1967, yields have fluctuated around 10 000t and have increased since 1981. Despite the relatively low catches, which accounted only for 2.54% of the world elasmobranch catch during 1987–1991,elasmobranchs are reasonably important for Argentinean fisheries contributing 3.19% of the total yield during this period. This is the highest relative importance of elasmobranchs in major American elasmobranch fishing countries.
During 1977 – 1991 the most important species in the elasmobranch catches were: stat. Mustelus schmitti which averaged 49% (6790t/yr) of the total elasmobranch catch; several rays at 20% (2722t/yr), unclassified elasmobranchs at 23% (3160t/yr) and elephant fishes (Callorhinchus sp.) at 8% (1048t/yr). Of these groups, catches of smooth-hounds and “various elasmobranchs” had an increasing trend while elephant fishes and rays had a decreasing tendency. Argentina is one of the few countries in the world, with important catches of chimaeriformes (Figure 2.8).
Crespo and Corcuera (1990) give a detailed description of the fisheries for sharks off Claromeco and Necochea, Buenos Aires Province. In this northern Argentine fishery, gillnets are used to catch Galeorhinus galeus, Mustelus schmitti, Carcharias taurus and Squatina argentina. About 23 vessels, from 8 – 44.9m in length prosecute this fishery. They use nylon monofilament gillnets (2-3mm twine) with 19 – 21cm mesh, 55-71m long, 3.8m deep and 8-25 panels. These gillnets are set on the bottom between 0.5 and 25nm from the coast in depths from 2 – 70m. Usual catch per panel is 6-15 Squatina argentina and 1 – 20 of the other sharks species. Ex-vessel prices are US$3-4/kg for undamaged Galeorhinus destined for export (mainly to Italy) and US$1-2.5/kg for damaged ones that are consumed salt-dried in the local market. These authors report extensive damage to shark catches by marine mammals. Sea lions bite out the belly of entangled sharks and eat the liver.
Menni et al. (1986) note the presence of more sharks in the catch in northern Argentina. In addition to the species mentioned above, they report Mustelus canis, M. fasciatus, Squalus blainvillei, S. cubensis and Notorhynchus cepedianus in the commercial catches of Buenos Aires province. Mustelus schmitti accounted for 92% of their shark samples at commercial landing sites. The remaining species are less than 1% of the shark catch except S. cubensis which made up 2%. Government statistics of shark landings at Mar del Plata port averaged 5890t during 1971–1980. This is about ¥ of the average total elasmobranch catch of Argentina during that period. About 93% of this catch is made of ‘gatuzos’ (predominantly Mustelus schmitti, with some quantities of M. canis and some small numbers of M. asciatus)). Cazones, (mainly Galeorhinus galeus but including some large M. canis) contributed the remaining 7%. Apparently, the remaining species are not recorded in the statistics.