Scientia Marina, Vol 82, No S1 (2018)

Bycatch and discard survival rate in a small-scale bivalve dredge fishery along the Algarve coast (southern Portugal)


https://doi.org/10.3989/scimar.04742.08A

Mariana Anjos
Centro de Ciências do Mar (CCMAR), Universidade do Algarve, Portugal
orcid http://orcid.org/0000-0001-5518-2110

Fábio Pereira
Centro de Ciências do Mar (CCMAR), Universidade do Algarve - Instituto Português do Mar e da Atmosfera (IPMA), Portugal
orcid http://orcid.org/0000-0002-1806-0189

Paulo Vasconcelos
Instituto Português do Mar e da Atmosfera (IPMA) - Centro de Estudos do Ambiente e do Mar (CESAM), Departamento de Biologia, Universidade de Aveiro, Portugal
orcid http://orcid.org/0000-0002-2119-2297

Sandra Joaquim
Instituto Português do Mar e da Atmosfera (IPMA) - Centro Interdisciplinar de Investigação Marinha e Ambiental (CIIMAR), Universidade do Porto, Portugal
orcid http://orcid.org/0000-0002-6324-5908

Domitília Matias
Instituto Português do Mar e da Atmosfera (IPMA) - Centro Interdisciplinar de Investigação Marinha e Ambiental (CIIMAR), Universidade do Porto, Portugal
orcid http://orcid.org/0000-0002-2191-7497

Karim Erzini
Centro de Ciências do Mar (CCMAR), Universidade do Algarve, Portugal
orcid http://orcid.org/0000-0002-1411-0126

Miguel Gaspar
Centro de Ciências do Mar (CCMAR), Universidade do Algarve - Instituto Português do Mar e da Atmosfera (IPMA), Portugal
orcid http://orcid.org/0000-0001-9245-8518

Abstract


Although the bivalve dredge used on the Algarve coast (southern Portugal) is highly selective for the target species, in some periods of the year the bycatch can exceed the catch of the commercial species. The present study aimed to quantify the bycatch and discards, estimate damage and mortality, and propose management measures to minimize discards and mortality. A total of 15 fishing surveys (60 tows) were performed using two types of dredges (“DDredge” targeting Donax trunculus and “SDredge” targeting Spisula solida and Chamelea gallina). Of the 85257 individuals (392.4 kg) of 52 taxa that were caught, 73.4% belonged to the target species, 22.1% to commercially undersized target species and 4.5% to bycatch species. Bycatch rates were lower for SDredge (13.5% in number and 6.3% in weight) than for DDredge (46.0% in number and 32.9% in weight). Damage and mortality rates were also lower using SDredge (1.3% and 1.0% of the total catches, respectively) than using DDredge (4.0% and 2.8% of the total catches). Survival experiments revealed the diverse vulnerability of the taxa and confirmed the influence of the damage score on the mortality rate. The results gathered in the present study encourage the adoption of a bycatch reduction device to reduce both direct and indirect mortality.

Keywords


bivalve dredging; bycatch; discards; damage score; survival rate; metallic grid dredge; fishing gear technical design; bycatch reduction device

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