Diversity of Invertebrate Discards in Small and Medium Scale Aegean Sea Fisheries

Abstract

In the present work, an attempt is made to evaluate and compare the diversity of invertebrate discards from small (gill/trammel nets) and medium (otter trawling) scale fisheries in Thermaikos Gulf (North Aegean Sea), which is a major fishing area of the eastern Mediterranean but still unexplored for its benthic community structure. Sampling was performed under normal fishing activities in 21 otter trawl hauls and 62 set nets operations. One hundred thirty-two invertebrate species were altogether discarded in medium and small scale fishery over the study area, classified in 16 classes and 7 phyla. Small scale fisheries yielded almost 70 % of the total invertebrate diversity, while otter trawling only 50 %. Molluscs were the most diverse group in both fisheries followed by crustaceans and echinoderms. Multivariate analysis revealed a clear differentiation in discard species composition between the two fisheries reflecting different benthic habitats. According to the species composition of the discards certain benthic biocoenoses were identified. The Coastal terrigenous muds biocoenosis prevailed in medium scale fishing areas, accompanied by the Coastal detritic, Muddy detritic, and Bathyal mud biocoenoses. Several plant-dominated communities (mostly those of Infralittoral photophilus algae, Circalittoral sciaphilus algae, and Posidonia meadows), were recognized through small scale fishery discards. The higher diversity of the latter was attributed to the great variety of habitats and established communities in the relevant fishing grounds. These results show that invertebrate discards could contribute background data for monitoring the complex benthic system.