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- Bycatch and discard survival rate in a small-scale bivalve dredge fishery along the Algarve coast (southern Portugal)Publication . Anjos, Mariana; Pereira, Fábio; Vasconcelos, Paulo; Joaquim, Sandra; Matias, Domitília; Erzini, Karim; Gaspar, MiguelAlthough 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.
- Fishers, let us talk: validating métiers in a multi-gear coastal fishing fleetPublication . Szynaka, Monika; Fernandes, Mariana; Anjos, Mariana; Erzini, Karim; Gonçalves, Jorge Manuel Santos; Campos, AidaIn the multi-gear coastal fleet in the Algarve (South Portugal), fishers own licenses for various fishing gears. However, they generally do not use all these licenses, and therefore, it is difficult to estimate the impacts this fleet has on the local environment. In this study, two types of questionnaires were used directed to the local fishers from the multi-gear fleet during interviews carried out between November 2019 and July 2021 with the objective to validate the métiers proposed for this fleet in a previous study using multivariate analysis on past landing profiles. A total of 10 out of the 11 proposed métiers were validated, including four métiers with gillnets, three with dredges, two with trammel nets, and one with traps. Additional métiers were identified not found in the previous study. The results obtained with the two types of questionnaires are presented, and their usefulness in validating the gear used and the seasonality of fishing activities are discussed, as well as their contribution to a clearer distinction between target species and commercial by-catch.
- Bycatch in bivalve fisheries of AlgarvePublication . Anjos, Mariana; Erzini, KarimThe present study assessed bycatch in Algarve grid dredge fisheries and estimated fishing gear inflicted damage and mortality, with the purpose of formulating mitigation measures, specifically fishing gear modifications. Bycatch using this dredge has been shown to surpass target species catch and, although it would not be a major problem if the discarded individuals survive, it nonetheless creates an issue of concern for fishers. Fishing surveys were conducted bimonthly onboard commercial fishing vessels in the same coastal areas near Olhão, throughout six months, in order to ascertain seasonal variation. Fishing targeted commercially valuable clam species, either Donax trunculus, using the DDredge, or Spisula solida and Chamelea gallina, using the SDredge. All individuals captured were attributed scores from a damage table ranging from 1 to 4, where 1 or 2 equate organism survival and 3 or 4 mortality. Results showed significant differences between fisheries regarding total catch composition, confirming dredge capacity to maximize target catch, but none for bycatch, demonstrating similar benthic communities in all sampled sites. Bycatch reached a maximum of 57.5% in abundance, and was significantly higher using the DDredge. Damage and mortality, although overall low, varied as a result of the morphological characteristics of the taxa itself, as such Echinodermata was presented as most subject to damage. Higher percentages of bycatch in the DDredge indirectly led to higher mortality rates as well. Seasonality analysis indicated the influence of spring on an increase of bycatch abundance in the DDredge. The implementation of a BRD and net bag in the grid dredge are proposed to reduce bycatch, as well as its damage and mortality, while maintaining fishing yield. Comparative studies are advised as to evaluate BRD effects on catch composition, bycatch amount, mortality, and discard rates. Additionally, the re-evaluation of the damage table through survival experiments is recommended.