Abundance, biomass, and seasonal variation of fish on shallow soft bottoms in the Askö area, northern Baltic proper

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Abstract
The abundance and biomass were estimated using drop-traps. The investigation was carried out from April 1976 to October 1978. Of 185 samples only 8 did not contain fish. Fish of 12 different species and juveniles of one undetermined species were caught. On a yearly basis the mean abundance was 17.64 ind/m2 and the mean biomass was 2.98 g/m2. Four species (the common goby Pomatoschistus microps (Krøyer), the sand goby Pomatoschisius minutus (Pallas), the nine-spined stickleback Pungitius pungitius (L)., and the three-spined stickleback Gasterosteus aculeatus L.) were dominant, constituting over 85% of both abundance and biomass. The two Pomatoschistus species alone constituted over 50 % of both the total abundance and biomass. The common goby was the most abundant species and the sand goby was most important with respect to biomass. There was a strong seasonal variation with the highest values in late summer/autumn (20–30 ind/m2, 2–6 g/m2) and the lowest values in spring/early summer (2–8 ind/m2, 1–2 g/m2). The fish consisted mainly of a single year class per season due to the short life-span of the three commonest species, which is about 1–1.5 years.