139736eo.pdf (20MB) - Japan Oceanographic Data Center

EXPLOITABLE LIVING RESOURCESThe first reported survey of the fish stocks in the Gulf of Aden was given in FAO (1973),based on the work of A. Druzhinin. Surveys were conducted in 1975/76 on the R/V Dr. F. Nansen,as reported in FAO/NORWAY/UNDP (1978), INSTITUTE OF MARINE RESOURCES BERGEN(1975-77), KESTEVEN et al. (1981). A stock assessment of cuttlefish in PDR Yemen waters wasmade by SANDERS (198 l), while stocks of oil sardines on this coast were assessed by SANDERSand BOUHLEL (1984). The results presented here were obtained from the R/V Ibin Magid, and alsoby participation in the 1984 surveys of R/V Dr. F. Nansen.DEMERSAL FISH STOCKSSeasonal ChangesWest of Aden, the dominant families in the October through March period are Leiognathidae(pony fish), Carangidae (jacks), Pomadasyidae (sweet lips), Lethrinidae (emperors) and Nemipteridae(threadfin breams). In the central sector, just east of Mukalla, dominant “fish” are Sepia sp.(cuttlefish), Sparidae (sea breams), Dasyatidae (rays), Pomadasyidae and Synodontidae (lizard fish).In the east, on the main trawl ground west of Ras Fartak, dominant stocks are Sepia sp., Ariidae(catfish), Sparidae, Dasyatidae and Sphyraenidae (barracudas).Generally, the differences between the Aden area and localities east of Mukalla are moremarked than differences between localities on the eastern part of the coast. Trawl catches in the eastare influenced by the large resident stocks of cuttlefish, which do not extend significantly into Omaniwi+.ers (SANDERS, 1981). During upwelling in August 1984, the catches in the west sector weredominated by Centrolophidae (Indian ruffs), Sparidae, Synodontidae, Sepia sp. and Lofigo sp.(squids). The first taxon usually occurred in deeper waters, while the Sparidae consisted of speciesnormally found below 100 m. In the central sector at Mukalla the dominant taxon was Callionymidae(dragonets), with small amounts of Sepia, Triglidae (gurnards) and Sparidae. The first was notencountered in October through March and was presumed to have migrated from greater depths. TheTriglidae also were deeper water fish. In the east sector Callionymidae again dominated, followed byTriglidae, Nemipteridae, Clupeidae (sardines) and Synodontidae.These data indicate that during upwelling the normal fish stocks migrate to shallower depths,to be replaced by deeper water groups. Some typical taxa were found close inshore, while others weretaken in pelagic trawls near the surface. The occurrence of these truly demersal types, particularlyspecies lacking swim bladders, at the surface (e.g. gurnards and cuttlefish) suggest that vertical as wellas inshore migrations had occurred. To the east of Ras Fartak a few large catches of Nemipteridae andcuttlefish were made at 17 m depth, giving the impression that these had migrated from trawl groundson the west side.Generally speaking, trawl catches were highest around Ras Fartak in the non-upwellingperiod, lowest around Mukalla, and intermediate at Aden. During upwelling a large variation in CPUE(catch per unit effort) along the coast was between 0 and 3,058 kg/hour, giving the impression ofpockets of low and high density stocks.Depth ChangesTrawl catch composition and CPUE changed significantly with depth in a seasonal pattern.October through March at Ras Fartak, a large component of Sepia was found at 15 and 30 m, due tomigration of mature adults into shallow water for spawning, Here the Ariidae (catfish) were animportant component of catches, with Sparidae being abundant at 30 m. At 50 m depth,Carcharhinidae (small sharks) dominated, with Carangidae and Pomadasyidae as the other maincommerical fish. Below this, at 70 m, portunid crabs dominated, with Nemipteridae and Carangidaeas the commercial fish. At this time of the year the CPUE was highest around 30 m due to thecuttlefish.266