Seasonal distribution, abundance and diversity of demersal fishes in the inner Ria de Arosa, Northwest Spain

Abstract

A year of seasonal trawling was initiated in Ria de Arosa, Spain in an area with mussel rafts and an area without mussel rafts, to assess the effect of the presence of the mussels and their associated fauna on the distribution and abundance of the demersal fishes. The demersal fish community exhibited a strong resident component comprising greater than 96% of the total catch and was dominated by gobiid species. The dominance of gobies resulted in a fish community composed of a large number of small fish ( x ̄ = 0.22 individuals/m 2). There were no overwhelming differences in the fish communities or community indices of the raft and non-raft areas, although biomass and diversity were generally higher in the raft area and the abundances of several species were significantly different in the two areas. Seasonal biomass estimates ranged from 1.19 to 2.08 g m −2 ( x ̄ = 1.69 ) in the raft area and were highest in September and lowest in January. Biomass in the non-raft area ranged from 0.93 to 2.18 g m −2 ( x ̄ = 1.45 ) and were highest in April and lowest in July. Diversity ( H) was higher in the raft area (0.94 to 1.39) than in the non-raft area (0.81 to 1.15). Pooled annual Diversity ( H) was 1.41. Similarly, other community indices such as Species Richness ( D) and Evenness ( J) were generally higher in the raft area. The above biomass and diversity values are moderate when compared with values for other estuarine areas. Small decapods, polychaetes and amphipods dominated the gut contents of the specimens analysed, with the crab, Pisidia longicornis the single most important food item.