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

Mariana Anjos; Fábio Pereira; Paulo Vasconcelos; Sandra Joaquim; Domitília Matias; Karim Erzini; Miguel Gaspar

doi:10.3989/scimar.04742.08A

Authors

Mariana Anjos Centro de Ciências do Mar (CCMAR), Universidade do Algarve https://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) https://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 https://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 https://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 https://orcid.org/0000-0002-2191-7497
Karim Erzini Centro de Ciências do Mar (CCMAR), Universidade do Algarve https://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) https://orcid.org/0000-0001-9245-8518

DOI:

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

Keywords:

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

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.

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