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Investigation of the abundance and distribution of demersal stocks of prime importance for the Greek fishery in the north Aegean Sea (Greece)

A study of demersal stocks in the north and west Aegean Sea was carried out in 8 commercial trawler with the duration of each haul ranging between 60-120 minutes, depending on the season, the geographical location and the level of catch.

The following points have been examined for each target species: seasonal abundance; geographical, seasonal and vertical distribution; length and age composition; growth, assessed by standard techniques; mortality rate (total, fishing and natural); age and season of recruitment; reproduction, sex ratio, age at maturity stages; feeding habits; location of nursery and spawning grounds; eggs and larvae distribution; eggs, larvae and 0-group distribution of hake; total biomass assessment for each target species, as well as study of the biotic parameters which could affect the distribution of the studied species.

A total of 143 fish species and 29 cephalopods were identified in the study area. The ichthyofauna and teuthofauna of the area consisted mainly of Atlanto-Mediterranean taxa with some boreal and truly tropical elements. Most of the collected fish larvae were pelagic or mesopelagic. More fish eggs were generally caught in the west than in the north Aegean Sea, with reproduction of most species taking place between March and June. The concentration of fish larvae was also higher in the west Aegean Sea than in the north Aegan Sea. No clear seasonal trends in the abundance of hake larvae was established, although there is some evidence that their abundance is higher during the winter months. An analysis of the species of low or no commercial value, but exhibiting high abundance in the catches, was also provided.

The biomass values were higher in the north Aegan Sea when compared with the west Aegean Sea, while biomass values exhibited substantial differences between the various depth zones, a fact corroborating the view that fish stocks undertake seasonal vertical migrations. The seasonal variations of the biomass estimates did not seem to be influenced by the period when trawlers operate, especially in the north Aegean Sea which is the largest fishing ground of the Greek seas. The seasonal and depth biomass variations are most possibly related to the biology and ecology of the fish populations.

Reported by

National Centre for Marine Research
Aghios Kosmas Hellinikon
16604 Athens
Greece
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