Changes in catch and bycatch composition and in species diversity of a semi-floating shrimp-trap fishery in three eastern Atlantic island ecosystems with different degrees of human alteration

José G Pajuelo,Sandra Correia,Ana R Góis,José A González,Albertino Martins,RaüL Triay-Portella,João Delgado

doi:10.3989/scimar.04782.25a

Abstract

Composition and bycatch of semi-floating shrimp-trap fisheries (SSTF) were compared among areas with different levels of anthropogenic alteration of marine ecosystems. The three areas selected were Madeira, the Canary Islands and Cape Verde. Mean species richness and diversity of the SSTF did not show significant differences among areas. The dominant species in catches of the SSTF for all regions studied was the main target species, Plesionika edwardsii, which accounted for 96.0% of the catch in Cape Verde, 75.8% in Madeira and 59.1% in the Canary Islands. Targeted pandalid shrimps accounted for more than 96.8% of total catches for all areas combined. Numbers of non-target species caught were 18 (Madeira), 14 (Canary Islands) and 16 (Cape Verde), of which 13 (Madeira), 8 (Canary Islands) and 11 (Cape Verde) were always discarded. Bycatch accounted for 0.5% (Madeira), 0.7% (Canary Islands) and 3.1% (Cape Verde) in numbers. Shark species accounted for 0.11% of all individuals caught. A total of 5 species in Madeira, 6 in the Canary Islands and 4 in Cape Verde, accounting for 0.2% to 0.8% of total catches, were not landed due to the small size of individuals or low numbers of individuals caught (self-consumption). The present results suggest that the selectivity of traps for the main target species, P. edwardsii, in SSTF changes due to changes in species dominance, which are probably linked to the degree of human fishing exploitation of the marine ecosystems in each area.

Highlights

The impact of the fishing activity on non-target species or bycatch species, together with overexploitation of target species and impacts on habitats, is considered one of the main problems of marine ecosystems (Dulvy et al 2003, Kappel 2005, Shester and Micheli 2011)
The dominant species in catches of the semi-floating shrimp-trap fisheries (SSTF) for all regions studied was the main target species, Plesionika edwardsii, which accounted for 96.0% of the catch in Cape Verde, 75.8% in Madeira and 59.1% in the Canary Islands
Bycatch accounted for 0.5% (Madeira), 0.7% (Canary Islands) and 3.1% (Cape Verde) in numbers

Summary

Introduction

The impact of the fishing activity on non-target species or bycatch species, together with overexploitation of target species and impacts on habitats, is considered one of the main problems of marine ecosystems (Dulvy et al 2003, Kappel 2005, Shester and Micheli 2011). The bycatch level in small-scale fisheries can cause major ecological impacts and, when scaled to per-unit of total catches, be comparable to that in industrial fisheries (Bellido et al 2011, Shester and Micheli 2011, Zimmerhackel et al 2015). In view of these findings, two priority goals emerge: a) to determine and reduce the impact of fishing activity on bycatch species, and b) to find a selective gear that minimizes the capture of non-target species. These goals are of particular importance when the fishing activity is focused on shrimp species, for which the biomass discarded is higher than the marketable biomass (33.0% of all world fishery discards) (Alverson et al 1994, Stobutzki et al 2001, Bellido et al 2011), and attaining them will help the search for alternatives to bottom trawling

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Discussion

Conclusion