Eubalaena glacialis Right whale
The whaling maps of Townsend (1935) show that large concentrations of this whale were to be found between 30 and 40°S, west of the Cape of Good Hope. Another, smaller ground, the Woolwich Bay Ground, was found off the coast of Namibia, presumably a breeding area. The Report of the IWC Right Whale Workshop (1983) indicates a possible Southern African population in 1980–82 of 478–614 whales. This species does not consume fish (Tomilin 1967), but entanglement in coastal fishing gear is a potential problem, of which at least one instance is already known (Report of the Right Whale Workshop, IWC 1983).
Caperea marginata Pygmy right whale
Ross et al (1975) found 71 recorded individuals of this species by 1975, and there do not appear to be any other indications as to the possible size of the population. Best (1977) records the incidental capture of 3 animals in beach seining operations, fishing for mullet, but states that this practice has probably stopped now. Ross et al also report the incidental capture of 2 individuals in beach nets. The food is thought to consist mostly of copepods (Ivashin et al 1972), and no other interactions with fisheries are likely.
Balaenoptera physalus Fin whale
This species is known to migrate from Antarctic waters to the coasts of South Africa and Namibia to breed in the winter (Tomilin 1967). Best (1967) found about 36% of fin whales in South African whaling grounds were feeding, 94% of the diet was euphasiids, and the rest copepods and amphipods. No fish were found. There is no clear indication of the numbers of fin whales to be found in area 47, but this is presumably in the low tens of thousands.
Balaenoptera musculus Blue whale
The blue whale also migrates to area 47 to breed from Antarctic waters, but again in unknown numbers, presumably in the hundreds or low thousands. Blue whales do not consume fish in the southern hemisphere, and do not feed at all in the winter months (Nemoto 1959, Mackintosh 1965), so there are unlikely to be any interactions with fisheries.
Balaenoptera acutorostrata Minke whale
Hershkovitz (1966) states that the minke whale occurs from the Cape of Good Hope, south to the Antarctic Ice Shelf, but it is presumably found north of the Cape also. Best et al (1983) saw three off the South African coast in a sightings cruise in 1983, and Tomilin (1967) states that minke whales are also found in tropical waters, although rarely. Tomilin adds that the diet is mostly pelagic crustacea in the southern Oceans. There is no clear indication of the likely numbers of minke whales which migrate into area 47, but this may be in the hundreds of thousands. Interactions with fisheries are unlikey, due to the diet of crustacea.
Balaenoptera borealis Sei whale
In common with other baleen species, the sei whale migrates to the coastal waters of south western Africa in the winter months. Again, population estimates are crude, but between a few thousand and a few tens of thousands of animals are probably involved. Although known to eat fish elsewhere, Best (1967) found that, of the whales he examined, about 50% were feeding; of these about 70% of the food was euphasiids, and about 30% copepods. Only about 0.2% of the diet (by volume) was found to be fish.
Balaenoptera edeni Bryde's whale
Bryde's whale is less inclined to wander southward to the Antarctic in this area, and may be found throughout the year in South African waters, apparently not straying further south than around 40°S (NCC 1980). Two stocks of this species, an inshore and an offshore form, are recognised around South Africa, (Best 1977a). Best (1967) found that overall, Bryde's whales in South African waters consumed 47% fish and 53% euphasiids. Of the fish, most was Engraulis and Trachurus, with some Sardinops ocellata and Lestidium sp.. Best (1977a) suggests that the inshore form eats mainly fish, especially Engraulis capensis, Trachurus capensis and Sardinops ocellata, but also some euphausiids, and that the offshore form prefers euphausiids, but eats some fish. Best et al (1983) suggest that the inshore stock may total around 500 animals. There do not appear to be any estimates of the offshore stock. Due to the intensive purse-seine fishery for anchovy and other pelagice species in this area, the distribution and abundance of the inshore stock could be influenced by changes in the fish stocks.
Megaptera novaeangliae Humpback whale
Known to migrate to waters off the coast of Angola (Tomilin 1967), Townsend's (1935) whaling maps clearly show a dense distribution of catches in that area. Tomilin (1967) states that the diet of this species in southern oceans consists of Krill, but that in winter some individuals may feed on the pelagic decapod Munida gregaria. Mackintosh (1965) suggests that winter feeding in humpbacks is negligible. The population size in this area is unknown at present, but unlikely to exceed a very few thousand at most.
Berardius arnuxii Arnoux's beaked whale
Confined to waters further south than 30°, (McCann 1975). Very little is known about its biology or population size. It is thought to feed on squid, and is very unlikely to come into conflict with fisheries.
Mesoplodon densirostris Blainville's beaked whale
Ross (1979) records this species from South Africa. Interactions with fisheries are unlikely.
Mesoplodon layardii Strap-toothed whale
Recorded by Leatherwood and Reeves (1983) from South Africa, little more information than this is available. Interactions with fisheries are unlikely.
Mesoplodon hectori Hector's beaked whale
Again recorded by Leatherwood and Reeves (1983) from South Africa, very little is known of this species and the likelihood of interactions with fisheries is very small.
Mesoplodon grayi Gray's beaked whale
As with the two previous species, this whale is recorded from South Africa by Leatherwood and Reeves (1983) and interactions with fisheries are unlikely.
Mesoplodon mirus True's beaked whale
Individuals are known from South Africa (Leatherwood and Reeves 1983), but the distribution of this species remains unclear. There may be a separate stock here or else the species may range over much of the Atlantic. No interactions with fisheries are likely.
Ziphius cavirostris Cuvier's beaked whale
Another little known species, Mitchell (1975) refers to strandings as far south as the Cape of Good Hope. There is no indication of population size in this area, nor of the diet, which may be presumed to be squid or deepwater fish. No interactions with fisheries are likely.
Hyperoodon planifrons Southern bottlenose whale
Recorded from South Africa (Mitchell 1975), but apparently confined to more southerly regions, little is known of this species, and interactions with fisheries are unlikely.
Physeter macrocephalus Sperm whale
An extensive year round concentration of sperm whales appears on Townsend's (1935) whaling maps (the Carroll Ground) off the coast of Angola, and a smaller ground around Tristan da Cunha. The current numbers of sperm whales in area 47 are unknown, but may be in the hundreds of thousands. Feeding is almost exclusively on squid, and no biological interactions with fisheries are likely.
Kogia breviceps Pygmy sperm whale
Tomilin (1967) suggests that this species is mainly a warm water species, but that its range extends down as far as the Cape of Good Hope. Records are scarce however, and knowledge of the diet scanty, but this is presumed to consist mostly of squid. Interactions with fisheries are unlikely.
Kogia simus Dwarf sperm whale
Ross (1979) records this species in South Africa. It is uncommon worldwide and interactions with fisheries seem unlikely.
Steno bredanensis Rough-toothed dolphin
Few data have been published on this species, but it is known from strandings in South Africa (Leatherwood and Reeves 1983). Mitchell (1975) suggests that food, in general, is likely to be fish, although some of the few data available show a diet of cephalopods (Layne 1965, Cadenet 1959). There are no feeding or abundance data published on this species in area 47 and no interactions with fisheries are likely.
Sousa chinensis Indo-Pacific hump-backed dolphin
Distributed from near the Cape of Good Hope up the east African coast (Mitchell 1975), the population size is unknown. Saayman and Taylor (1973) state that Sousa is a fairly solitary species, feeding over reefs and rocky outcrops, often near breaking waves, and that the population is dispersed. There does not seem to be any published data on feeding, although there is some suspicion that in area 51 this species is caught in shark nets while following pilchard schools (IWC 1982 p207–208), otherwise food species might be expected to include rocky bottom species of this area. There do not appear to be any records of interactions between this species and commercial fisheries in the southern limits of its distribution as yet.
Sousa teuszii Atlantic hump-backed dolphin
The Atlantic humpbacked dolphin is thought to extend to the coastal waters of Angola, (Mitchell 1975), although its main area of distribution is further north. The population in area 47 is therefore presumably small, and although no interactions with fisheries are reported, the artisanal coastal fisheries of Angola (FAO 1981a) make some such interactions probable. Food is unknown in this region.
Peponocephala electra Melon-headed whale
Not a common species in this area, it may normally be confined to an area north of 10°S (NCC 1980), one individual however has been recorded in South African Waters (IWC 1978). Almost nothing is known of their feeding anywhere and there are no likely interactions with fisheries in this area.
Feresa attenuata Pygmy killer whale
This species has been recorded infrequently from South Africa (Caldwell & Caldwell 1971a), and nothing is known of its diet or population size in this area. Interactions with fisheries would seem unlikely at present.
Pseudorca crassidens False killer whale
Tomilin (1967) states that South Africa represents the southern limit of the distribution of this species, and Mitchell (1975) adds that it prefers offshore waters. There are no population estimates for this species, nor feeding data in this area, although it is generally known to eat fish. No interactions with fisheries are apparent at present, but this situation could change as commercial species (Carangids) are known to be included in the diet elsewhere.
Orcinus orca Killer whale
Widespread and relatively common worldwide, there are nevertheless no abundance estimates for area 47. Budylenko (1981) suggests that the diet of the killer whale in the South Atlantic is predominantly dolphins and fish. Interestingly, despite fairly heavy fishing operations in area 47, killer whales do not seem to have been reported in any interactions with fisheries here. Best (pers. comm.) however reports some interaction with tuna fishermen, both sport and commercial, off the Western Cape Province.
Globicephala melaena Long-finned pilot whale
Mitchell (1975) states that this species occurs from the Antarctic convergence, north with the Benguela current. There are no population estimates of this species in this area. The diet is known to consist of cephalopods almost everywhere it has been studied. There appear to be no reported interactions with fisheries, nor would any seem likely.
Globicephala macrorhynchus Short-finned pilot whale
Mitchell (1975) describes the distribution of this species as extending down as far as 15°S on the Angolan coast. Ross (1979), also records it from the south east coast of South Africa. There do not appear to be any data on feeding habits nor population size in this area however, and no records of interactions with fisheries either.
Lagenorhynchus obscurus Dusky dolphin
Distributed throughout the cooler and temperate waters of this area, the dusky dolphin is said to prefer inshore waters (Mitchell 1975). There are no abundance estimates, although during a 3 week cruise in 1983, Best et al (1983) report sighting of 94 individuals. Food of this species is uncertain, but Best (1977) reports that it is caught incidentally in the purse seine fishery for Engraulis capensis and Trachurus capensis which may indicate something as regards diet. Best suggests that around 100 animals of possibly 4 cetacean species are caught in these purse seine fisheries per annum. Lagenorhynchus species elsewhere are also known to feed on schooling pelagic commercial fish species, and these are possibly amongst the marine mammals most likely to be affected by interaction with commercial fisheries. No further data on the problem exist however.
Lagenorhynchus cruciger Hourglass dolphin
A pelagic species, confined to colder waters, little is known about the population or diet of this species, and there do not appear to be any records of interactions with fisheries.
Lagenodelphis hosei Fraser's dolphin
Ross (1979) has recorded this species from the south eastern coast of South Africa, but there seem to be no records of interactions with fisheries.
Tursiops truncatus Bottlenose dolphin
Apparently fairly common throughout the area, Best et al 1983 report sighting 56 individuals during a 3 week cruise of South African inshore waters. However, no estimates of abundance are available for this area. Best (1977) reports the probable incidental capture of this species in the purse seine fisheries for anchovy and horse mackerel in area 47, which appears to be the only indication of feeding or of interactions with fisheries for this area. It would seem likely that other incidental captures occur, but as yet have not been reported.
Grampus griseus Risso's dolphin
Found in warm and temperate waters as far south as South Africa (Tamilin 1967), this is not a particularly common species anywhere. Nevertheless, Best et al (1983) report seeing 143 individuals in a 3 week cruise in inshore South African waters. There do not appear to be any reports of incidental captures of this species in this area yet, and predatory interactions are unlikely if the food is primarily cephalopods (Mitchell 1975).
Stenella longirostris Spinner dolphin
Reported to be present from Senegal to the Cape of Good Hope (Mitchell 1975), there are no indications of population abundance or of any interactions with fisheries in this region. Food could presumably be small mesopelagic fish and epipelagic and mesopelagic squids as described by Perrin et al (1973), in which case, in the absence of incidental captures in tuna seining operations, there may be no liklihood of any immediate interactions.
Stenella coeruleoalba Striped dolphin
The striped dolphin is apparently more common in South African waters than the spinner in the summer at least; Best et al (1983), report sighting 100 individuals of this species in a 3 week cruise in the coastal waters of South Africa, and none of the previous species. The food in this area is unknown, but may be small mesopelagic fish as elsewhere (Miyazaki et al 1973). There are no reported interactions with fisheries at present.
Stenella attenuata Spotted dolphin
Again there are no estimates of population abundance or feeding of these species in this area. There are no interactions with fisheries at present, which for these species generally means no dolphin-associated tuna purse seining in the area.
Delphinus delphis Common dolphin
This species appears to be very abundant in this area, being the species most commonly sighted by Best et al (1983); 1 585 individuals were counted in a 3 week period in inshore waters of South Africa. Food of this species is often small pelagic fish, frequently commercial species, so it is not surprising therefore that Best (1977) reports D. delphis as an incidental catch in the purse seine fishery for anchovy, and for horse mackerel. Best estimates less than 100 are killed in purse seines per year in this manner. There are no further data on any other interactions with fisheries, but these may be considered possible.
Lissodelphis peronii Southern right whale dolphin
Cruickshank and Brown (1981) and Brown (1982) give details of 8 sightings of this species in the waters around South Africa. It is a pelagic species, not often observed, and there are no population estimates. Food is unknown, but Cruickshank and Brown (1981) found lantern fish, euphausiids, and small squids were abundant in the same region as the rightwhale dolphins. No interactions with fisheries are reported from this area, and are not likely to be significant.
Cephalorhynchus heavisidii Heaviside's dolphin
Confined to the coastal seas of South Africa and Namibia, from Cape Town to Cape Cross (Mitchell 1975). The population size is unknown, but Best et al (1983) report sighting 38 in a 3 week cruise of inshore waters. Food is also unknown, but thought to be squids and bottom dwelling fish (Mitchell 1975). Best (1977) reports that some of this species may be caught incidentally in the anchovy and horse mackerel fisheries of the region. The South African Progress Report to the IWC (1979) also states that 2 individuals were caught by a Portuguese stern trawler. The extent of interactions between this species and commercial fisheries is therefore unknown, but some possibly significant interaction does occur.
Arctocephalus pusillus Cape fur seal.
The African subspecies breeds on offshore islands and along the coasts of Namibia and South Africa, from 11°S on the west coast to 33°S on the south east coast. Definite migrations are not known, but individuals have been recorded up to 100 nm out at sea (Shaughnessy 1979, 1984 in press). The total population has been estimated at 944 000 individuals, and is thought to be still increasing (Shaughnessy 1984 in press). There is a cull which amounts to around 78 000 pups and 2 200 bulls (Shaughnessy 1979). Market conditions forced a substantial drop in this in 1983 (Best, pers. comm.). There is some considerable interaction between this species and commercial fisheries of the region. The situation is described in detail by Shaughnessy (1984 in press). There is some damage to fishing gear, trawl nets and possible seine nets too, but Shaughnessy suggests that this does not amount to much. A more major problem comes with interference in purse seining operations, where hundreds of seals may move into the encircling net to eat the fish, causing a nuisance and consuming catch. There is some disturbance in trawl nets and hand line fisheries too; Shaughnessy & Payne (1979 cited in Shaughnessy in press) estimate that around 4 000 seals are killed in trawls, and Shaughnessy (in press) suggests an indeterminate number are also killed by seining operations. Rand (1959) also noted the habit that fur seals have of eating fish protruding from trawl nets, and occasionally becoming trapped in the cod end as the trawl is raised to the surface. Such seals are killed when the net is shot away again, or when they come on board. Fur seals will follow fishing boats, and are often attracted by the fish offal discarded over the side. Rand (1959) found that schooling fish, notably Sardinops ocellata, Trachurus trachurus and Scomber japonicus made up 80% by volume of the fish food. Fish formed 60% of the diet, with crustaceans and cephalopods making up the remainder. Anchovy was found to comprise only 2% by volume of the diet. Rand noted year to year fluctuations in the relative quantities of the different species eaten. Shaughnessy, however, found that the main food items in 1975 were the bearded goby (a non commercial species) and horse mackerel, whilst anchovy was also fairly common but pilchard rarer. The change in diet, Shaughnessy suggests, may be due to a shift in species composition under the influence of commercial fishing. The effect that the fisheries have on the seal population in this area may not, therefore, be significant in terms of loss of food; whether the same can be said of the effect of seals on fisheries remains to be seen.
Arctocephalus tropicalis Subantarctic fur seal
The population in area 47 breeds at the Tristan da Cunha - Gough Island group, and may have numbered around 13 000 animals in the 1950s (Swales 1956, cited in Shaughnessy 1979); Shaughnessy (1979) suggests the population may have increased since then, Rand (1956) also showed that the food of this species is largely Nothothenid fish, cephalopods, and euphausiids. There do not appear to be any interactions with fisheries, which are not very active in these regions, and there is no culling of this stock.
(Hydrurga leptonyx Leopard seal
Occasionally straggling northwards to this area (Hofman 1979), there are no interactions with fisheries.)
Trichechus senegalensis West African manatee
Occurring as far south as Angola, this species is found only in the very north of area 47 (Husar 1978). As in the rest of its range, accidental capture in fishing nets is likely to cause some additional mortality to an already depleted stock, but no data are available for this (See also area 34).
Of the 40 or so species of marine mammal found in this area, only a few are involved in any interactions with fisheries. 6 species of baleen whale do not consume fish in this area. The seventh species is known to eat some commercial fish, including pilchards, anchovies and horse mackerel. At least another 9 species are not well enough known to establish their diet in this area and at least 12 more species feed wholly or mostly on cephalopods. The diets of the remaining 12 species are not all well known either.
The dolphins of the genus Stenella and the subantarcic fur seal are thought to feed on small non-commercial fish species and squids, as is the right whale dolphin; the killer whale is thought to feed on marine mammals. The only other species with any information on their diets in this area are the Indo-Pacific hump-backed dolphin, which may eat pilchards, the few delphinid species which might be assumed to eat anchovies and pilchards, such as the common dolphin and the dusky dolphin and possibly the bottlenose dolphin too, and the fur seal and manatee, the former of which eats gobies and horse mackerel, and the latter only plant matter.
DEMERSAL FISH RESOURCES
The principle stocks of demersal species in this area are hakes, which make up the bulk of the catch, and a few other species such as kinglip (Genypterus) and seabreams (Sparidae), but the number of species caught is relatively few. The total catch of demersal species in 1981 totalled 450 000 tonnes. This represents a considerable drop from the peak of approaching 1 million tonnes in 1976, due largely to the over-exploitation of hake. Demersal fish are not apparently important in the natural diet of any species of marine mammal in this area.
GADIDAE
Merluccius capensis and M. paradoxus
A trawl fishery for these species includes large long-range vessels from a number of foreign fleets. Several stocks may exist in the area, but the stock relationships are not yet entirely clear (ICSEAF 1982). Gulland (1983) states that the stocks are heavily fished, with effort currently exceeding that which would produce an MSY by a wide margin, current catches totalling around 300 000 tonnes (in 1981), a drop from 800 000 tonnes in 1976 (FAO 1983).
There are some reported by-catches of marine mammals in trawl nets, 2 Cephalorynchus heavisidii having been reported in 1979 (S. Af. Prog. Report to IWC, 1979), and fur seals are also known to get caught in trawl nets (see above). It would seem probable that other incidental catches may occur, but go unreported. There seem to be no records of marine mammals eating hake, apart from the fur seals, so that an overexploited stock may not be having any great impact on marine mammal feeding.
Other stocks.
Other stocks of demersal fish in the area produce, by comparison, very small catches. In the more northerly regions off Namibia and Angola, hakes are replaced by grunts, croakers and basses, the largest catches being less than 10 000 tonnes for any one species. Most of these appear to be taken by small scale inshore fisheries (FAO 1981a) and their status is unclear.
PELAGIC FISH RESOURCES
The total pelagic catch in 1981 slightly exceeded 1.7 million tonnes. The number of species of importance exceeds those in the demersal fishery, with pilchard, horse mackerel, anchovy and sardinellas all being important components.
CARANGIDAE
Trachurus capensis and Trachurus trecae horse mackerels Trawlers from a number of foreign countries as well as local purse seiners take more than half a million tonnes a year of these species. Stocks are distributed around the coast from Natal to southern Angola. Catches may be approaching or exceeding the MSY at present, and the decline of the pilchard stocks may have been one factor causing the recent increase in horse mackerel stocks (FAO 1981a). Best (1977) suggests horse mackerel purse seiners may take around 100 small cetaceans a year, incidental to the catch. Horse mackerels are known to be eaten by cape fur seals.
CLUPEIDAE
Sardinella spp Sardinella
Distributed mainly in more northerly coastal waters, the sardinella yielded around 160 000 tonnes in 1981, (FAO 1983), down on the previous two years, but the total potential and state of the stocks are unknown.
Sardinops ocellata Pilchard
Under 100 000 tonnes were taken in 1981, following the collapse of the Namibian stock in the 1970's (FAO 1983). Distributed mainly off Namibia and the west coast of South Africa, this species still remains an important part of the local purse seine fishery.
Engraulis capensis Anchovy
Catches in excess of half a million tonnes have been reported in the late 1970's, but in 1981 the catch fell to 490 000 tonnes (FAO 1983). The anchovy stocks appear to have benefitted from the collapse of the pilchard stocks. Best (1977) referred to the incidental capture of a few small cetaceans in this fishery. This species, and the preceding one may feature in the diet of a number of dolphin species
Other Stocks
Other important fisheries include a hand line fishery for snoek (Thyrsites atun), which is known to be hindered by fur seals occasionally, and which took 25 000 tonnes in 1981. There are also other species involved in the purse seine fishery, including mackerel (Scomber japonicus) of which 24 000 tonnes were taken in 1981 (FAO 1983). Tuna are also important, although no interactions with dolphins have been reported here yet.
INVERTEBRATE RESOURCES
CEPHALOPODS
The total catch of all species is just over 8 000 tonnes in 1981, most of which were loligonids and ommastrephids, Voss (1973) refers to Rand's assessment of squid stocks of the region and suggests that a figure of several hundred thousand tonnes potential yield may not be unreasonable.
The lobster fishery should also be mentioned as an important commercial operation (7 000 tonnes in 1981), but one which does not appear to have any direct impact on marine mammals, or vice versa, at present.
Newman (1977) has reviewed the fisheries of the region, while Shaughnessy (1984 in press) has discussed their relation to marine mammals. Rather more than half the catch is taken by large foreign trawlers, fishing mainly for hake, horse mackerel and sardinella. Since the period reviewed by Newman, most foreign vessels have left South African waters, following the extension of the limits, though foreign fleets still fish off Namibia and, by arrangement, off Angola.
Locally based fisheries employ trawlers (mostly for hake and kinglip), and purse seiners (for pilchard and anchovy), as well as a variety of other gears from small vessels off South Africa and Angola.
Operational interactions
Gear conflicts as reported are limited in the number of marine mammal species involved. The most dramatic is that of the fur seals which cause severe nuisance in purse seine fisheries, and in trawl and handline fisheries.
Pygmy right whales have been reported in beach nets.
Dusky dolphins, common and Heaviside's dolphins have all been reported in seine or trawl nets in small numbers.
Bottlenose dolphins are thought likely to be caught in similar cases, though there appear to be no records at present.
Fur seals cause the most dramatic nuisance to fishermen by invading purse seine nets, and taking fish from trawls.
Biological interactions
There has been some criticism of fur seals in this respect, but Shaughnessy (1984 in press) suggests that there may have been a change in the diet of these species to reflect the change in fish species abundance. Undoubtedly, however, some commercial fish are still eaten, and this may still be seen as a problem in some quarters.
Potential problems exist in the number of marine mammals which feed on squid, a resource which is at present greatly under-utilized in this area. Any increase in the size of the Bryde's whale stocks in inshore waters around South Africa may also lead to some conflict as this species is known to consume commercial species. Finally some of the dolphin
species could also be affected by the reduction in biomass of some of the stocks of small clupeids. The common dolphin in particular, which appears to live up to its name in this area, could also be seen as a competitor with commercial fisheries in this respect.
Eubalaena glacialis Right whale
Townsend's (1935) whaling maps show three or four whaling grounds for this species in the south of area 51, and Marcuzzi and Pilleri (1971) show the range extending as far north as Mozambique on the East African coast. No data are available on the size of the population in area 51, but this may number in the hundreds. No interactions with fisheries are likely.
Caperea marginata Pygmy right whale
Ross et al (1975) describe the distribution of this species, which includes area 51, south of about 31°S. Sightings of this species are sparse, and although it has turned up in nets in South Africa (see area 47), interactions with fisheries are unlikely.
Balaenoptera physalus Fin whale
Tomilin (1967) states that fin whales migrate from the Antarctic to Madagascar, but that bones of fin whales have also been found in the Red Sea. Keller et al (1982) also found fin whales present around the Seychelles and give other records from the Indian Ocean. There are no reliable population estimates of this species in area 51, and no data on feeding. However, the population could be in the thousands or tens of thousands, and feeding on anything other than swarming crustacea is unlikely. No interactions with fisheries are recorded or likely.
Balaenoptera musculus Blue whale
Observed as far north as the Gulf of Aden (Yukov, 1969 cited in Keller et al 1982), Tomilin (1967) states that part of the Antarctic population moves north to Madagascar in winter. The population size is unknown, but is possibly in the thousands. There are no known interactions with fisheries in area 51 and none seem likely.
Balaenoptera acutorostrata Minke whale
Tomilin (1967) states that this species is rare in the tropics but has been found in Ceylon. Gambell et al (1975) also record minke whales in this area. The population size is unknown but may number in the tens or even hundreds of thousands. Feeding in this area is also unknown; Tomilin (1967) and Nemoto (1970) both characterise the minke whale
in Antarctic waters as a euphausiid eater, but it is unclear whether there is any feeding in more northerly waters. There are no records of interactions with fisheries in area 51.
Balaenoptera borealis Sei whale
Budylenko (1978) summarizes information on this species in the Indian Ocean. Sei whales are widespread throughout the area, and have been observed throughout the year. Feeding is presumably confined to swarming crustacea such as Calanus (Budylenko 1978). There are no estimates of the population size in this area but this may be in the thousands. No interactions are recorded or likely.
Balaenoptera edeni Bryde's whale
Present in tropical and temperate waters throughout the Indian Ocean, Ohsumi's (1981) analysis suggests a population size in area 57 in excess of 10 000 animals. The diet is known to include small fish and so some interaction with fisheries is probable, though as yet unreported. Leatherwood et al (1983) report one individual feeding on a school of fish, presumed to be mackerel.
Megaptera novaeangliae Humpback whale
Marcuzzi and Pilleri (1971) give breeding sites of this species, including areas of Mozambique and Madagascar. Humpbacks are also known from the Gulf of Aden (Yukov, 1969 cited in Keller et al 1982). The current population size is unknown but may only number in the hundreds in this area. There are no records of fish consumption, nor any interactions with fisheries.
Berardius arnuxii Arnoux's beaked whale
Leatherwood and Reeves (1983) describe the distribution of this species as almost certainly including the Southern Indian Ocean. Other references to area 51, seem to be very sparse. The population size is certainly unknown, and interactions with fisheries unlikely.
Mesoplodon pacificus Longman's beaked whale
Possibly the least known cetacean species. One of the two known specimens comes from Somalia (Azzaroli, 1968) so the distribution is inferred to include area 51. Keller et al (1982) publish a photograph which shows 4 beaked whales, possibly of this species. Gambell et al (1975) explain the difficulty in obtaining observations of this genus in general. No population estimates are possible, and interactions with fisheries are unlikely.
Mesoplodon densirostris Blainville's beaked whale
Widely distributed throughout the world, and recorded from the Seychelles (Hershkovitz 1966), this species is still rarely seen, and no population estimates are possible. No interactions with fisheries are likely.
(Mesoplodon layardii Strap-toothed whale
Leatherwood and Reeves (1983) suggest the probable existence of this species in area 51, although there are apparently no records of it here. No interactions with fisheries can be foreseen).
Mesoplodon grayi Gray's beaked whale
Leatherwood and Reeves (1983) state that sighting frequency suggest that this species may be common south and east of Madagascar in deep water. Keller et al (1982) suggest a further possible sighting in the Seychelles. No population estimates are available. No interactions with fisheries are likely.
Mesoplodon ginkgodens Ginkgo-toothed beaked whale
Recorded from this area only in Ceylon (Hershkovitz 1966). Again no interactions with fisheries are likely.
Ziphius cavirostris Cuvier's beaked whale
Sighted by Keller et al (1982) around the Seychelles, the distribution of this species is presumed to include all oceans. Pelagic and not commonly observed, no interactions with fisheries are foreseen at present.
Hyperoodon planifrons Southern bottlenose whale
A cold water species which, although generally presumed to inhabit the southern Indian Ocean, does not appear to have been sighted in area 51 (NCC 1980). No population estimates can be made for this area, and no interactions with fisheries are likely at present.
Physeter macrocephalus Sperm whale
Townsend's (1935) maps show a patchy distribution of catches throughout area 51, right up to the southern Arabian coast. No current population estimates are available for area 51, but this could be in the hundreds of thousands. No interactions with fisheries would seem likely at present as very little squid is caught in this area.
Kogia breviceps Pygmy sperm whale
Marcuzzi and Pilleri (1971) include the west Indian Ocean in the distribution of this species. Records from Africa are even more scarce than from other areas (Handley 1966), so this species must be considered uncommon here, as elsewhere. No interactions with fisheries are predictable, as even the diet is unclear.
(Kogia simus Dwarf sperm whale
Generally presumed to inhabit all warm waters, records from the Indian Ocean are very sparse. No interactions in area 51 are likely.)
Steno bredanensis Rough-toothed dolphin
Reported from the Seychelles (Keller et al 1982) and from the Zambezi Coast and Aden district (Best 1971 cited in Keller et al 1982). The status is unclear, but this species is rarely recorded. There is no information on feeding in area 51, and there are no records of interactions with fisheries in this area either.
Sousa chinensis Indo-Pacific hump-backed dolphin
Recorded from Ceylon to the Suez Canal, to South Africa and in the central Indian Ocean (Marcuzzi and Pilleri 1971, NCC 1980). The number of records of this species might indicate that it is quite common in this area, but this may be because it frequents shallow coastal waters and is easily seen. There are a number of records of this speces being trapped accidentally in shark nets in Natal, and these are recorded in the South African Progress Reports to the IWC. Such mortalities may have considerable local impact on populations. The 1982 report suggests that these individuals may have been following a sardine run when they became trapped. Saayman and Tayler (1973) suggest that Sousa is a solitary species feeding on rocky outcrops and reefs near to the shore. There is no data on food species, but for an inshore species such as this, which Mitchell (1975) states ‘seems to feed on fish’, it would seem likely that some commercial species are taken. Given the artisanal nature of much of the fisheries in this area, incidental catches are also likely to occur, especially if synthetic fibre gill nets are employed in this area. So far very little such catch has been reported: Mitchell (1975a), citing Al-Robaae (1970) gives one example of a fisherman catching one specimen in the Arabian Gulf, Howell and Pearson (1977) record 4 more such events and Jones (1976) records Sotalia fluviatilis, presumably this species, in Indian coastal fisheries.
Peponocephala electra Melon-headed whale
The status of the population is unknown. The diet in this area is also unknown, and so nothing may be said about biological interactions with fisheries. There are no indications of operational interactions either.
Feresa attenuata Pygmy killer whale
There appears to be only one record of this species in area 51, that of Racey and Nicoll, cited in Keller et al (1982), in the Seychelles. It is very rarely recorded worldwide, which may imply that this is a rare species. The diet in area 51 is not known and there have been no records of interactions with fisheries in this area.
Psuedorca crassidens False killer whale
Keller et al (1982) do not record this species from the Seychelles, but Hershkovitz (1966) records it from Ceylon, Gambell et al (1975) from the Natal coast and Frazier (1983) from Zanzibar. The status of this species is unknown in this area and the diet is not clear anywhere but may include squid and fish. Mitchell (1975) states that this species damages fish on longlines worldwide, but there are no obvious records of this in area 51. Other interactions with fisheries are not predictable.
Orcinus orca Killer whale
Keller et al (1982) recorded this species in the waters around the Seychelles, and Gambell et al (1975) also record it in area 51, southeast of Madagascar. The killer whale does not appear to be particularly rare in any of the world's seas, but there are no population estimates for the Indian Ocean. The food may include other cetaceans (IWC 1982 SC/33/Rep 4) but there has been little published information. Elsewhere the diet is known to include fish, and Sivasubramanian (1964) states that in the period 1955 to 1963 Orcinus presence during tuna longlining operations in the Indian Ocean increased from 4% to 9.6%, in parallel to the increase in fishing. He suggests that around 4% of the catch may be lost to killer whales and sharks, adding that the crews state killer whale presence may increase or depress catch rates, depending on whether the fish are frightened onto or off the bait. He also states that Orcinus is widely distributed throughout the Indian Ocean. There does not appear to be any more recent information on this interaction however.
Globicephala macrorhynchus Short-finned pilot whale
Keller et al (1982) record a pilot whale from the Seychelles, and Leatherwood and Reeves (1983) state that it probably occurs in most of the warm waters of the Indian Ocean. There are no indications of abundance, but this species does not appear to be rare. Jones (1976a) summarises information on this species in the Indian Ocean. The diet is unknown, but if squid is important, then interactions with fisheries are likely to be small.
(Lagenorhyncus cruciger Hourglass dolphin
Although not yet recorded in this area, it is found in other southern oceans, where it may be quite common. There would not seem to be much chance for interactions with fisheries at present.)
Lagenodelphis hosei Fraser's dolphin
Perrin et al (1973) suggest a continuous high seas distribution throughout the area. Gambell et al (1975) report sighting this species regularly off the Natal coast; its status is unclear. There are no data on feeding, and no interactions with fisheries yet recorded in this area, although incidental catches in pelagic fisheries have occurred elsewhere.
Tursiops truncatus Bottlenose dolphin
No population estimates are available, but Mitchell (1975a) refers to it as abundant in temperate and tropical inshore waters. There is little published information on diet in this area, but this species is known to get caught in shark nets off Natal, where some have been drowned, apparently following sardine shoals (IWC 1982). At least 13 were killed in this way in 1981. The effect of this on the population is unknown. Mitchell (1975a) states that off Ceylon this species is regarded as vermin as it damages gill nets and catch, and that some animals are killed in beach seines. Jones (1976a) adds that Tursiops is also taken occasionally in Indian coastal fisheries. Presumably similar problems exist in other parts of this area, but data are lacking.
Grampus griseus Risso's dolphin
Gambell et al (1975) report sighting this species in the south of area 51, and Keller et al (1982) give details of other sightings around the Seychelles, and in the Red Sea. This species is widespread but not particularly abundant anywhere in its range. No interactions with fisheries are known or likely without an expanded squid fishery.
Stenella longirostris Spinner dolphin
Hershkovitz (1966) records this species from Ceylon; Leatherwood et al (1983) report spinning dolphins from the Seychelles, and Howell and Pearson (1977) record the species from Tanzania. There is no indication of its rarity except that Keller et al (1982) did not observe any during their survey around the Seychelles. Records of interactions with fisheries are limited to that of Howell and Pearson, who record a possible incidental capture in Tanzania. Jones (1976) who records this species occasionally in the Indian coastal fisheries, and Leatherwood et al (1983) who state that fishermen take tuna from under ‘spinning dolphins’ around the Seychelles. The association with tuna raises the potential problem of incidental captures, but as yet there are no reports of dolphin mortality associated with tuna seining.
Stenella coeruleoalba Striped dolphin
Rice and Scheffer (1968) describe this species as widely distributed in temperate and tropical waters around the world. Gambell et al (1975) report hundreds of this species from waters around Madagascar and Watson (1981) reports seeing large schools east of the Seychelles. There is no other information relating to population sizes or feeding in this area, so the potential for interaction with fisheries is unclear.
Stenella attenuata Spotted dolphin
Rice and Scheffer (1968) report this species from the Indian Ocean, chiefly near coastal areas or islands. Keller et al (1982) tentatively describe spotted dolphins from the Seychelles, and Gambell et al (1975) describe them from the waters around Madagascar. There is no information on abundance and interactions with fisheries. Presumably a potential exists for incidental capture in purse seining operations, but this has not been reported yet.
Delphinus delphis Common dolphin
Leatherwood and Reeves (1983) describe this species as very widely distributed, occurring in all temperate and tropical seas, including the Indian Ocean. Jones (1976) describes this as one of the more common species in the seas around India, but Keller et al (1982) do not record it from the Seychelles. Jones (1976) describes fishing operations in Indian coastal waters, which include shore seines, boat seines, drift nets and fixed gill nets fishing for mackerel, sardines, anchovies and black tuna. Common dolphins are said to be caught in such nets often. The South African Progress Report to the IWC also reports a number of common dolphins trapped in shark nets off Natal. In 1981, at least 89 were trapped, apparently having followed sardine shoals into the nets. It would seem likely that this species is frequently caught as a by-catch throughout the area. The diet is elsewhere known to include commercial species especially anchovies and sardines, and so some degree of ‘biological interaction’ would seem likely.
(Lissodelphis peronii Southern right whale dolphin
Rice and Sheffer (1968) describe the distribution of this species as in ‘temperate’ waters of the Southern Ocean, but there do not appear to be any clear records of it occurring in area 51, neither is this species recorded by Gambell et al (1975) in their survey of the waters south of Madagascar. Its existence in this area is therefore uncertain and interactions with fisheries improbable).
(Phocoena dioptrica Spectacled porpoise
There is one possible sighting of this species from this area, (Frost and Best 1976). No other information is available on population status, feeding, or interactions with fisheries and the occurrence of the species in this are must remain questionable).
Neophocaena phocaenoides Finless porpoise
Hershkovitz (1966) gives the distribution as from South Africa to Japan, but Leatherwood and Reeves (1983) state that this porpoise occurs only in coastal waters of Pakistan and the Indian subcontinent in this area. Jones (1976) refers to this species as one of the most common in the seas around India, and states that it is often caught in inshore fishing operations. Leatherwood and Reeves (1983) also state that the diet includes prawns and shrimps, cephalopods, and small fish. Recorded interactions with fisheries in this area are confined to a by-catch in Indian inshore waters, which Jones (1976) suggests involves large numbers. The effect on the population is unknown.
Platanista minor Indus susu Jones (1976) states that this species is caught in seines and other multipurpose nets in the Indus river system. The population is critically low, but the extent to which this situation is due to interactions with fisheries is unknown.
Artocephalus tropicalis Subantarctic fur seal
The fur seal breeds on isolated subantarctic islands, occasionally wandering to South Africa. Food is thought mainly to be squid (Rand 1956), and no interaction would seem likely with fisheries at present.
Dugong dugon Dugong
At present rare throughout this area, the dugong is nevertheless still apparently caught incidentally in fishing nets on the Kenyan coast (Martin 1981), and in Ceylon (Bertram and Bertram 1970); this may represent an important source of mortality. Few data are published, but for a coastal species such as this, by-catches probably occur throughout its range in significant numbers.
At least 39 species of marine mammals are known to inhabit the waters of area 51, although information on species distribution is very poor for the Indian Ocean as a whole. The area has been declared a cetacean sanctuary by the IWC (IWC 1980) whereby commercial exploitation of cetaceans is prohibited.
At least 10 of the species occurring in this area are thought to be wholly or partly squid eating. There are also 8 baleen whale species, only one of which is known to feed on fish in this area. It has been suggested that there may be year round population of certain species of baleen whales in the tropical Indian Ocean. If so these may also feed on fish. Of the remaining cetacean species, 7 or 8 are known or thought to eat commercial fish or shrimp species. The remaining species are too poorly known to comment on.
The interactions listed above include at least 9 species which are involved in operational interaction and one, Tursiops, which has been accused of damaging fish stocks. It seems probable that given the lack of information on most of the species and the nature of most of the fisheries in the area, there are many more operational types of interactions than are recorded.
DEMERSAL FISH RESOURCES
The shelf area in the Indian Ocean is comparatively small (Gulland 1983), which means that demersal catches are limited. Furthermore, trawling is not so important a fishing method here as it is elsewhere. The FAO Atlas of Living Marine Resources (FAO 1981) suggests a total potential yield in area 51 of around 2 million tonnes, whereas the demersal catch in 1981 was less than 0.5 million tonnes. According to Gulland (1983) most of the fisheries around India are artisanal, with some trawling for shrimps, which produce by-catches of other species.
Harapadon nehereus Bombay duck Providing the largest demersal catches in this region, in 1980 115 000 tonnes were taken, mostly by Indian fisheries.
Sciaenidae Drums and Croakers The second largest catch record is for miscellaneous Sciaenids, which amounted to 113 000 tonnes in 1980. This family is distributed throughout the region especially in warmer waters, there are no overall estimates of potential, nor is the state of the stocks known.
The catch statistics (FAO 1983) list very few species in the demersal fish catch, most catches being lumped either into families, or else into larger groups. The 3rd largest catch records are of ‘demersal percomorphs not elsewhere included’, which amounted to 55 000 tonnes in 1980.
Other fish caught include the usual assemblage of tropical families, Serranidae, Lutjanidae, Sparidae, Lethrinidae, Pomadasyidae and Leiognathidae. There is very little published on the state of the stocks of these species, but Gulland (1983) notes that some local stocks such as those around Mauritius and on east African reefs are heavily fished, whereas in other areas such as the Gulfs, are still under exploited.
There is little data on marine mammal feeding on demersal fish in this area, but Tursiops, Sousa and possibly Delphinus and Neophocaena are all possible predators of demersal fish, in that they all frequent coastal zones.
PELAGIC FISH RESOURCES
The FAO Atlas of Living Marine Resources (FAO 1981) provides an estimate of total potential pelagic resources of the Indian Ocean as around 4.6 million tonnes, at least 2 million tonnes of which are distributed in the western half. The largest fishery is the Indian oil sardine fishery.
Sardinella longiceps Indian oil sardine Dense concentrations of this species exist on the south and west coasts of India, and were, until recently, fished for almost exclusively by traditional methods, especially beach seines (Gulland 1983). These nets are known to capture a number of small cetaceans, in particular the common dolphin, bottlenose dolphin, spinner dolphin, finless porpoise and Indo-Pacific hump-backed dolphin (Jones 1976). There are no statistics collected for by-catch of small cetacea, but Jones gives one example of 17 finless porpoises being landed in one haul. It may be that this by-catch has a significant effect on the population of at least one species. In 1980 210 000 tonnes of oil sardines were landed, including an increasing proportion of catches taken by small purse seiners. Gulland (1983) suggests that the potential for small pelagic fish catches on the Indian coast is much greater, but that the lack of more modern fishing methods means that much of the resource remains unexploited, offshore. Presumably this provides a number of marine mammals with an adequate food supply.
Tunas
A number of tuna species are taken, and this is one of the few fisheries in the Indian Ocean on which foreign fleets operate. Korean and Japanese boats both take a few tens of thousands of tonnes of tuna from this area, using longlines. At least two species, the killer whale and false killer whale are both known to take fish from tuna longlines, and specific examples are known of Orcinus conflicting with fishermen in this area in this way. There are no obvious records of such a type involving Pseudorca in this area, but Mitchell (1975a) states that they occur worldwide.
Until 1983 there was very little of the large scale tuna seining operations as seen in the Pacific, but several vessels operated in 1983, and perhaps two dozen are expected to operate in 1984 (Gulland, pers. comm.). There is evidence that Stenella schools over tuna in this area, and so there is an obvious risk of mortality to these species which could result from the development of the tuna fishery (Gulland, pers. comm.).
The total catch of tuna species in the area in 1980 was under 100 000 tonnes; the potential for the entire Indian Ocean has been put at 600 000 tonnes. The proportion of this which might be expected in the western half is not stated.
Other important pelagic species include other clupeoids, ‘pelagic percomorphs’, amberjacks and some mackerel species. Bryde's whale has been noted by Leatherwood et al (1983) as a probable predator on shoals of mackerel which yield around 50 000 tonnes throughout the area.
There are also, according to Gulland (1983) other underexploited stocks of sardines in the Gulf regions, which at present are uneconomic to fish.
INVERTEBRATE RESOURCES
CRUSTACEA
Shrimp trawling is known throughout most of the area and is an important fishery economically. Over 250 000 tonnes of Natantian decapods were taken in 1980. Again the most productive areas appear to be around India and Pakistan, where traditional fishing methods are employed alongside trawlers. Gulland (1983) argues that the stocks of shrimp in both the Indian region and in the Gulf are currently overexploited. Only one species of marine mammal, the finless porpoise, is known to feed on shrimps. The effect of the exploitation of shrimp stocks in the area on the population of Neophocaena is unknown.
CEPHALOPODS
The cephalopod fisheries of this area took around 17 000 tonnes in 1980. Voss (1973) has found that there is very little information on cephalopod resources in this area, and cites Gulland (1971) for a rough estimate of several hundred thousand tonnes in coastal waters. Clearly here as in most other areas, cephalopods represent a vastly under-utilised resource. There are at least 10 partly or wholly squid-eating cetacean species in this area, for none of which is there a reliable population estimate. The total predatory biomass on squid must be at least several hundred thousand.
Gulland (1983) provides a brief summary. Most fishing in this area seems to be small scale, although locally based small trawlers and purse seiners operate in several parts, especially off India. Foreign boats are very few and take less than 4% of the total catch. Longliners are and now some purse seiners take tuna, and some trawling occurs in the Arabian Sea.
Local fishing methods include handlining and trapping on reefs, and gill nets almost everywhere. Jones (1976) has included a brief description of some types of Indian fishing, which include 600 m “rampani” and other beach seine nets, small boat seines and fixed gill nets. Many of these are presumed to take coastal marine mammal species as a by-catch.
The major fishing nations of the area are India, with catches of over a million tonnes and Pakistan and Sri Lanka with catches of a few hundred thousand tonnes each. A few other countries also take tens of thousands of tonnes a year, but in general the reported catches are small when compared with other areas.
Operational interactions
These may be split into 2 categories
By-catches of a number of species occur, apparently throughout the region, but are seldom reported. In South Africa Sousa chinensis, Tursiops truncatus and Delphinus delphis are taken in shark nets off Natal. In the waters around India a number of species, notably Neophocaena phocaenoides and Delphinus delphis are taken in a variety of gears particularly shore-based seine nets. There are some other scattered reports of marine mammal capture in gill and seine nets, including Dugong dugon, the population of which may be under pressure from such mortalities.
Other operational interactions include harassment of tuna longliners by killer whales and, possibly, the false killer whale, Pseudorca crassidens. Dolphins of the genus Stenella are known to associate with tuna in the area; although this has led to little if any mortality so far, the development of a purse-seine fishery makes future by-catches more likely.
Biological interactions
Here as elsewhere, biological interactions with fisheries remain obscure. Certain species, notably Balaenoptera edeni, Delphinus delphis and Tursiops truncatus almost certainly prey on commercial fish stocks. Neophocaena phocaenoides feeds largely on shrimps in coastal waters, which may be overexploited. Large amounts of squid are currently consumed by a number of marine mammal species, but at the moment scarcely any cephalopods are fished for in this region. Dolphins of the genus Stenella are known in other areas to feed on small mesopelagic fish. It is interesting at this point therefore to note that Gulland (1983) has suggested that mesopelagic fish form a large part of the fish biomass between Somalia and Pakistan. At present these stocks are unexploited, largely for technical reasons.
Eubalaena glacialis Right whale
Hershkovitz (1966) states that the right whale occurs as far north as 30°S in the western Indian Ocean. Breeding sites exist along the south and western coasts of Australia, but the population is at present severely depleted. There are no population estimates, but in 1981 42 animals were sighted off Australia during aerial surveys (IWC SC/34/Prog Rep Australia 1983). The Report of the Workshop on the Status of Right Whales (IWC SC/35 Rep. 2 1983) notes one individual which was caught in a shark net in South Australia in 1982, but does not state whether the animal died or was released. If death by entanglement in netting does occur, even a few deaths could be significant to such a small population.
Caperea marginata Pygmy right whale
Marcuzzi and Pilleri (1971) note that the maximum density is observed around southern Australia and New Zealand, and Ross et al (1975) state that the most northerly point from which this species is known is 30°S on the west Australian coast. No interactions with fisheries are known, and there are no population estimates either.
Balaenoptera physalus Fin whale
Known to occur throughout the area, although Tomilin (1967) states that it is rare in the tropics. There are no reliable population estimates in this area, and no recorded interactions with fisheries. The diet is not known to include any fish in southern oceans (Nemoto 1959).
Balaenoptera musculus Blue whale
Known from all seas (Tomilin 1967), there are no population estimates in this area, but the population could number in the thousands. No interactions with fisheries are known. The diet does not include commercial species.
Balaenoptera acutorostrata Minke whale
Rice and Scheffer (1968) state that the minke whale is rare in tropical waters but widely distributed in all oceans. The diet in warmer waters is unknown, if indeed there is any feeding at lower latitudes. The population in area IV of the Antarctic, which corresponds roughly with FAO's area 57 in latitude, has been estimated at just under 100 000 (IWC 1983 p 94)
Balaenoptera borealis Sei whale
Found in all oceans (Rice and Sheffer 1968). The sei whale population in area 57 is unknown but may be presumed to be similar to that of Antarctic area IV, between 10 and 20 000. There are no records of this species consuming commercial species in area 57 and interactions with commercial fisheries seem unlikely.
Balaenoptera edeni Bryde's whale
Ivashin (1980) records this species from Western Australia, India and Malacca; presumably it occurs throughout area 57. There do not appear to be any population estimates or published information on the diet of this species in area 57. Commercial fish are consumed elsewhere, and so presumably may be here as well. There are no apparent records of interactions with fisheries here either.
Megaptera novaeangliae Humpback whale
Breeding grounds exist off the western coast of Australia, to which humpbacks migrate from Antarctic waters (Marcuzzi and Pilleri 1971). The population size is unknown but probably numbers in the hundreds. There does not appear to be any evidence of feeding outside the Antarctic in this area, and no obvious interactions with fisheries either.
Berardius arnuxii Arnoux's beaked whale
Mitchell (1975) describes this species from South Australia. Nothing is known of the population size, nor the diet in this area, although this presumably consists of squid.
(Mesoplodon pacificus Longman's beaked whale
One specimen is recorded from Queensland in Australia (Rice and Sheffer 1968) and another from Somalia; if the distribution is continuous this species might be expected to inhabit area 57 also. The diet is presumably squid, and the population size unknown.)
Mesoplodon densirostris Blainville's beaked whale
Rice and Scheffer (1968) state that this species is distributed in tropical and warm temperate waters of all oceans. Leatherwood and Reeves (1983) record it from Tasmania and the Nicobar Islands. No interactions with fisheries seem likely at present.
Mesoplodon layardii Strap-toothed whale
Leatherwood and Reeves (1983) state that this species has been found in southeastern Australia and Tasmania. There is no information on the population size.
Mesoplodon hectori Hector's beaked whale
Recorded from Tasmania (Rice and Scheffer 1968) in area 57, a circumpolar distribution in temperate water is suggested. There is no information on population size.
Mesoplodon grayi Gray's beaked whale
Recorded form South Australia (Leatherwood and Reeves 1983) this appears to be another species with a circumpolar distribution in southerly waters.
Mesoplodon bowdoini Andrew's beaked whale
Rice and Scheffer (1968) state that this species has been recorded from Tasmania and Western Australia. The distribution in the rest of area 57 is therefore conjectural.
(Mesoplodon ginkgodens Ginkgo-toothed beaked whale
Recorded from Japan and Ceylon (Rice and Scheffer 1968), if the population is continuous, then area 57 should also be included in the distribution of this species.)
Ziphius cavirostris Cuvier's beaked whale
Found in all temperate and tropical seas, as with all other beaked whales, there are no population estimates, and the food is presumed to be squid.
Hyperoodon planifrons Southern bottlenose whale
Known from Australia and off Antarctica in the Indian Ocean sector (Rice and Scheffer 1968), Mitchell (1975) describes it as widespread in all southern oceans. No abundance estimates are available. The food is thought to be squid (Mitchell 1975), and there are no apparent conflicts with fisheries.
Physeter macrocephalus Sperm whale
Townsend's (1935) charts show dense catching grounds off Western Australia. The population is currently recovering after the cessation of Australian sperm whaling in the late 1970's, which operated from Albany in Western Australia. The population size is unknown, but could number in the hundreds of thousands for the whole of area 57.
Kogia breviceps Pygmy sperm whale
Leatherwood and Reeves (1983) state that this species has been found in southeast Australia, implying that it does occur in area 57; they suggest that it is found in all temperate warm waters of the world. There is no population estimate, but this does not appear to be a common species. There are no data on feeding in area 57 either, and no apparent interactions with fisheries.
Steno bredanensis Rough-toothed dolphin
Leatherwood and Reeves (1983) state that this oceanic dolphin has been recorded from much of Indo-Australian archipelago. There are no indications of abundance, nor of any interactions with fisheries reported.
Sousa chinensis Indo-Pacific hump-backed dolphin
Leatherwood and Reeves (1983) were told in Penang that this species was found in the waters thereabouts, and Leatherwood and Reeves (1983) reports hump-backed dolphins from India to the middle of the west coast of Australia. There do not appear to be any estimates of population abundance or of feeding in this area, but Jones (1976) states that this species is taken in coastal fisheries in India and Bangladesh.
Orcaella brevirostris Irrawaddy dolphin
Hershkovitz (1966) describes the distribution in coastal and estuarine waters from the Bay of Bengal to northern Australia, and in several river systems. There do not appear to be any indications of abundance, though Watson (1981) states that it is still fairly common everywhere. U Tin Thein (1977) describes how this species helps local river fishermen by herding fish into their nets. Leatherwood et al (1983) were informed by local fishermen on the Irrawaddy river that the dolphin eats catfish.
Peponocephala electra Melon-headed whale
Leatherwood and Reeves (1983) describe this species as having a worldwide distribution in tropical and subtropical seas. There do not appear to be any data relating to abundance, feeding, or interactions with fishermen in this area.
(Feresa attenuata Pygmy killer whale
Rarely recorded worldwide, there do not appear to be any records of this species in area 57, but its presence is inferred by Mitchell (1975) and other authors.)
Psuedorca crassidens False killer whale
Distributed in tropical and warm temperate waters, normally offshore (Mitchell 1975); Harwood et al (1983) provide one of the few records of this species. They state that 1 was recovered from Taiwanese gill nets, fishing for sharks, tuna and mackerel, in northern Australian waters, but it is not clear whether this was in area 57 or 71. This species is also said to damage tuna on longlines worldwide (Mitchell 1975a). There does not appear to be any other information regarding interactions with fisheries, abundance, or feeding habits in this area.
Orcinus orca Killer whale
Found in all seas (Hershkovitz 1966), Leatherwood et al (1983) report the probable sighting of an individual north of the Andaman Islands, and there are numerous accounts of the species off southwestern Australia. Reports of interactions with fisheries include the account of Sivasubramanian (1964) who states that killer whales are often found around tuna longlining boats, where they damage up to 4% of the catch and may scare fish away from, or onto, the hooks. Other accounts of interactions in this area relate to the Australian whaling industry at Twofold Bay, where several killer whales were in the habit of helping whalers, apparently by alterting them to the presence of humpback whales and aiding in their capture. The killer whales were rewarded with whale meat. Killer whales are also known to take up to 30% of hooked fish in a dropline fishery off the east coast of Tasmania (IWC 1981 annexe H). There are few other published records of killer whales in this area, so their abundance and diet are unclear.
Globicephala melaena Long-finned pilot whale
This species is recorded from all temperate southern seas (Leatherwood and Reeves 1983). There do not appear to be any abundance estimates, feeding data or recorded interactions with fisheries.
Globicephala macrorhynchus Short-finned pilot whale
Jones (1976a) provides a summary of information on this species in the tropical and subtropical Indian Ocean, stating that it does not occur in Indian coastal waters. There seem to be no abundance estimates, feeding data or records of interactions with fisheries in this area.
Lagenorhynchus obscurus Dusky dolphin
Rice and Scheffer (1968) describe this as a coastal species, found in southern Australia. There do not appear to be any published accounts of its abundance or feeding habits in this area, nor any accounts of interactions with fisheries.
(Lagenorhynchus cruciger Hourglass dolphin
Brownell (1974) describes the distribution of this species as pelagic and circumpolar in the southern hemisphere, but it does not appear to have yet been recorded in the southern Indian Ocean.)
(Lagenodelphis hosei Fraser's dolphin
Perrin et al (1973a) suggest a continuous distribution in the tropical high seas of the Indian and Pacific Oceans, but there do not appear to be any records from area 57, although its presence is presumed).
Tursiops truncatus Bottlenose dolphin
Leatherwood and Reeves (1983) describe the distribution of the bottlenose dolphin
throughout the Indian Ocean from Australia to South Africa. Jones (1976) describe this as one of the species which is caught accidentally in the coastal waters of India and Bangladesh by artisanal fisheries. Harwood et al (1983) also note that this species is one of the most frequently caught in Taiwanese gill net fisheries off northern Australia; some of these catches are apparently made in area 57. There seem to be no published accounts of diet or abundance for this area. As in other areas, interactions with fisheries are likely throughout the area, even though not reported.
Grampus griseus Risso's dolphin
Recorded from all tropical and temperate seas (Mitchell 1975). Leatherwood et al (1983) provide a record from the Bay of Bengal. There do not appear to be any abundance estimates nor accounts of interactions with fisheries. The diet is presumed to be mostly squid.
Stenella longirostris Spinner dolphin
Mitchell (1975) records this species from Australia, Ceylon and Indonesia. Jones (1976) records it as one of the coastal species caught in local fisheries around the coast of India and Bangladesh, but there are no data on this by-catch, nor on abundance or feeding in the area. This species is known to associate with tuna around the Seychelles, and so may be vulnerable to dolphin associated tuna purse seining in this area also (see area 51). There seem to be few other records of this species in area 57.
Stenella coeruleoalba Striped dolphin
Rice and Scheffer (1968) state that this species is widely distributed in temperate and tropical waters around the world. Leatherwood et al (1983) record it in the western Indian Ocean, but not in area 57. The only other obvious record of this species in the area is that of Watson (1981) who reports seeing large schools “south of Java”. No population estimates, data on feeding or reports of interactions with fisheries are available for this area.
Stenella attenuata Spotted dolphin
Spotted dolphins are apparently distributed throughout the warm waters of the Indian Ocean from the Maldives, south and east to New Zealand (Hershkovitz 1966, Leatherwood and Reeves 1983). Leatherwood et al (1983) report Stenella attenuata from the Bay of Bengal, but there appear to be no reports of interactions with fisheries, nor any published information relating to abundance or feeding for area 57.
Delphinus delphis Common dolphin
Described by Jones (1976) as one of the commonest species in coastal waters around India and Bangladesh. Leatherwood et al (1983) record this species in the Bay of Bengal; Rice and Scheffer (1968) describe this species as widely distributed in all warm temperate and tropical ocean areas. There do not appear to be any abundance estimates or data on feeding for this area. Jones (1976) provides the only report of interactions with fisheries, reporting that many are taken as a by-catch in Indian coastal fisheries. Other interactions would seem likely elsewhere in area 57, but are not reported.
Lissodelphis peronii Southern right whale dolphin
Distributed around the southern hemisphere in cold waters (Brownell 1974) there are no records of interactions with fisheries in this area and none seem likely at present.
Neophocaena phocaenoides Finless porpoise
One of Jones' (1976) two most common species of coastal marine mammal, and one which he states is frequently caught in beach seines and other artisanal fishing gear along the Indian coasts. Mitchell (1975) records this species from throughout southeast Asia.
Interactions between fisheries and this species would seem to be very likely due to its neritic habitat but are not reported. Elsewhere the diet is said to consist largely of shrimps, which are commercially fished for in this area.
Platanista gangetica Ganges susu
The population has been estimated at around 4 – 5 000 (Jones 1982). Mitchell (1975) states that this species occurs with commercial fish species and that fishermen set their nets around dolphins. Small numbers are said to be taken in seine nets. Jones (1982) describes accidental drownings of susu in drag nets and seine nets, which he states are not uncommon. Jones also states that the susu's food is mainly catfish, prawns and other bottom living animals. The by-catch does not seem to be having too dramatic an effect on the population at least below Farakka and in the entire Brahmaputra-Meghna complex of rivers in India and Bangladesh, where Jones (1982) states “there are no signs of depletion in susu population”.
Neophoca cinerea Australian sea lion
Confined to area 57, around the south coast of Australia. Walker and Ling (1981a) suggest that this species was almost wiped out by commercial sealing in the last century, and that its range is less extensive than previously. Warneke (1982) has estimated the population at between 3 – 5 000. Little is known of the diet but this may include fish, squid and penguins. Storr (cited in Walker and Ling 1981a) reports this species feeding on salmon (Aripis trutta) and causing damage to nets whilst doing so. And Warneke (1982) also states that salmon fishermen dislike the sea lion as it attacks their nets to get at fish. Walker and Ling (1981a) report this species taking whiting (Sillaginodes sp.) from the nets of fishermen on Kangaroo Island, and similar occurrences with shark fishermen. They add that the sea lion has been observed to take crayfish and lobsters too. Warneke (1982) suggests that there is no widespread complaint against this species by the fishing industry, probably because it does not occur in large numbers in any one place.
Artocephalus pursillus doriferus Australian fur seal
Warneke (1982) estimates the population size at around 20 000 animals, two thirds of which breed in Bass Strait. The diet is predominantly cephalopod, including Notodarus, Sepioteuthis, Sepia and Octopus, but fish are also eaten(Warneke 1982). Warneke also refers to recoveries of drowned seals from traps and trawl nets, so there is evidently some by-catch of this species in the local fisheries, but this has not been quantified. He continues that fishermen widely maintain that this species damages fish stocks, but that such claims are not substantiated by data on feeding. The Australian fur seal does pose a problem to sedentary mesh net fisheries in Port Philip and Western Port Bays in Victoria, which are near to a large breeding colony. Individual seals can do extensive damage to nets and catch, which Warneke states is only effectively remedied by the prompt destruction of the offending seal.
Arctocephalus forsteri New Zealand fur seal
Crawley and Warneke (1979) have described the distribution of this species in southern Australia; which population Warneke (1982) suggests may not exceed a few thousand individuals. He adds that the diet in Australian waters is unknown. By comparison with the diet in New Zealand, cephalopods and barracouta might be presumed to be important. Warneke (1982) also suggests that this species does not occur in sufficient numbers to be considered a problem by fishermen in Australia, but Crawley and Warneke (1979) suggest there may be some incidental losses through drowning in net and rock lobster fisheries.
Mirounga leonina Southern elephant seal
Marlow (1967) states that in former times this species occurred in large numbers on King Island and Tasmania, but that after the disappearance of these colonies only occasional stragglers appear. The diet is known to include fish and squid, but as the population in this area is apparently so small, there are unlikely to be any significant interactions with fisheries.
Hydrurga leptonyx Leopard seal
During spring some stragglers appear on Australian beaches, normally young animals (Marlow 1967). Feeding is not known to include any commercial fish species and interactions with fisheries in area 57 seem unlikely.
Leptonychotes weddelli Weddell seal
Another Antarctic species, the Weddell seal has been recorded once on an Australian beach (Marlow 1967) but presumably feeds in the southerly waters of area 57. There are no published records of interactions with fisheries but these might be possible if Antarctic fish are to be harvested in any quantity.
Dugong dugon Dugong
Known to occur in area 57 from the Indian subcontinent to North and Western Australia (Bertram and Bertram 1973). Described as rare throughout much of its range (FAO 1978) there are no data on incidental captures, but these are thought to be one of the major reasons for the population decline (FAO 1978).
The amount of published information on marine mammals in area 57 is very small, with the exception of some Australian species, notably the pinnipeds. About 49 species of marine mammal are thought to occur in this area, and for most of these almost nothing is known about their abundance or feeding habits in the area.
There are 8 species of baleen whale, 7 of which feed mostly in Antarctic waters on pelagic crustacea. There have been some suggestions, however, that some species such as the humpback and minke whales may be present all year in the Indian Ocean, and this prompts the question of what they eat. Certainly Bryde's whales feed in tropical and subtropical waters, and it is assumed that commercial species are eaten. It is possible that other baleen whale species also feed on fish in this area.
There are possibly 10 species of beaked whale known to occur in the area all of which might be presumed to feed on squid.
Of the remaining 24 cetacean species, the diets of most are unknown. Susu are known to eat catfish and other bottom dwelling organisms, and catfish are also thought to be in the diet of Irrawaddy dolphins. Finless porpoises eat shrimps, and in view of killer whale harassment of tuna longlines, these may consume some tuna. For the rest, it could be assumed that some species such as the bottlenose and common dolphins eat some commercial species of fish.
The diets of the pinnipeds by comparison, are very well known. Squid is the major food item with a number of commercial fish species also taken to a much smaller extent.
DEMERSAL FISH RESOURCES
The magnitude of the demersal resources in this area is not well known, recent estimates being in the range of 2–3 million tonnes. The statistics for a number of countries are incomplete, and there is little information on species composition. Of the listed groups of fish in the FAO Fisheries Statistics Yearbooks, only 4 have recorded catches of more than 10 000 tonnes. The total catch of demersal species is probably a little over half a million tonnes (FAO 1981a).
These are Leiognathids (33000 tonnes), Sciaenids (20 000), sea catfish (Ariidae: 22000 tonnes) and other percoids (15 500 tonnes).
There are no records of interactions between demersal fisheries and marine mammals, and no indication of any feeding by marine mammals on demersal species apart from the Irrawaddy river dolphin which is thought to feed on catfish (Leatherwood et al 1983). The state of most of the stocks is unknown, although it is believed that the inshore stocks along the densely inhabited coastlines of South and Southeast Asia are heavily exploited.
PELAGIC FISH RESOURCES
The total potential of pelagic fisheries in the eastern half of the Indian Ocean is unknown, but exceeds 800 000 tonnes. The total recorded catch of pelagic species in 1981 was 371 000 tonnes, but again, there were 780 000 tonnes of miscellaneous marine fish also caught, which presumably increases the true pelagic catch. The state of most of the stocks is unknown.
Sardinella longiceps
The Indian oil sardine dominates the list of identified species 75 000 tonnes having been reported in 1981. As with area 51, most of this seems to have been taken by artisanal methods such as beach seines, though purse seines are used in some areas.
Other species
Carangids, anchovies and mackerels are all important stocks in this area, and may all represent food species for a number of cetaceans, notably Bryde's, and possibly other baleen whales.
Tuna
Several species are taken, catches of all species exceeding 40 000 tonnes in 1981 (FAO 1983). Japanese and Korean catches of all species in area 57 totalled 15 000 tonnes in 1981 (FAO 1983), most or all of which was presumably tuna, as Gulland (1983) suggests this is about all that foreign fleets take in the area. Longlines are used extensively for catching tuna, but Harwood et al (1983) indicate that Taiwanese vessels take some tuna off northern Australia by gill nets. This fishery leads to extensive cetacean mortality, and the longlining fishery is known to come into conflict with killer whales (see above).
INVERTEBRATE RESOURCES
CRUSTACEA
Natantian decapods are possibly the most important fishery resource in the area. In Indonesia for example, the value of the banana prawn, udang putih (Penaeus merguiensis) was around Rp 54 000 million, individually identified species, more than twice the value (Rp 21 000 million) of the next most valuable tongkol (Euthynnus spp) (Indonesia Fishery Statistics 1981). Gulland (1983) suggests stocks of shrimps around India may be heavily fished. The interaction between such fisheries and cetaceans such as the finless porpoise, which feeds on shrimp, are unknown.
CEPHALOPODS
The total cephalopod catch in the area was less than 8 000 tonnes in 1981; Voss (1973) cites Gulland (1971) in suggesting that the potential for the whole Indian Ocean may be at least several hundred thousand tonnes.
Gulland (1983) summarises the fisheries of area 57. As with 51, the emphasis is heavily on small scale fisheries. In India these include beach seines, boat seines, gill nets and cast nets; similar gears are used off Sumatran and Javan coasts. Industrial scale fishing is developing, including trawling, especially for shrimp, and purse-seining.
Further south, off Australia, stocks of fin-fish are underexploited (FAO 1981a); the main fishery there appears to be for lobster and shrimp. Harwood et al (1983) describe Taiwanese gill netting operations on the northern coast, which extend into area 57. They estimate that thousands of small cetaceans, mostly Tursiops are killed in this fishery every year (4 500 from June 1981 to February 1983).
The extent of small scale fisheries in this area, coupled with the information that “there is increasing evidence ….… that many stocks are already heavily exploited” (FAO 1981a) in the more northerly regions, should indicate some considerable interaction with some of the 49 or so marine mammal species. Information on the subject, however, is sparse.
Operational interactions
Jones (1976) has stated that 5 species of small cetacean, the common dolphin, bottlenose and spinner dolphins, the Indo-Pacific hump-backed dolphin and the finless porpoise, are all caught in seine nets around the Indian subcontinent. These are all coastal species and are taken in coastal fisheries but there are no data on the numbers caught.
Harwood et al (1983) indicate that bottlenose dolphins, spotted and spinner dolphins, and at least one false killer whale have been taken in gill net fisheries off northern Australia. Their map indicates that some of these catches (4 out of 86) were taken in waters in area 57, the species involved here are not stated however.
Killer whales are known to harass tuna longliners in the Indian Ocean (Sivasubramanian 1964).
There is some conflict between fishermen and pinnipeds in southern Australia. Sea lions are known to damage nets and catch, as do some fur seals in fixed gill nets.
One right whale has been reported in a shark net off South Australia. (IWC SC/35/Rep 2, 1983).
Bannister (1977) states that a few small cetaceans are taken in Australian fisheries, without giving data for area 57. He reports that most kills are due to fishermen shooting dolphins because of their real or assumed interference with fishing operations.
Dugongs are known to be taken in nets throughout the area (FAO 1978). It would seem very likely that the reported cases of gear conflicts in this area represent only a small number of the total. The area is characterised in the northerly part at least, by intensive coastal fishing, and a relatively large number of coastal small cetaceans. The combination of these 2 factors seems likely to produce a great number of incidental captures of small cetaceans, particularly Sousa, Tursiops, Stenella spp, Orcaella, Neophocaena, Delphinus and Platanista.
The susu is taken in small numbers in the Ganges as a by-catch in seine nets (Jones 1982).
The Irrawaddy dolphin is said to help fishermen to catch fish by herding the fish into the nets (Tin Thein 1977).
Biological interactions
Fishermen in southern Australia are reported to claim that fur seals damage fish stocks (Warneke 1982), but such claims, it is suggested, are not borne out by analysis of the seals' diet.
The information being so sparse, there is little that can be surmised even concerning possible biological interactions. Certainly the presence of at least 10 species of squid eating cetaceans should be noted in the event that the greatly underexploited squid resources of this area are to be developed. The possible presence of year round baleen whale populations in tropical waters also poses interesting problems concerning the future expansion of either offshore pelagic fisheries, or of the baleen whale populations.
