Scientia Marina, Vol 67, No 3 (2003)

Quantifying the roles of competing static gears: comparative selectivity of longlines and monofilament gill nets in a multi-species fishery of the Algarve (southern Portugal)


https://doi.org/10.3989/scimar.2003.67n3341

Karim Erzini
CCMAR, Universidade do Algarve, Portugal

Jorge M.S. Gonçalves
CCMAR, Universidade do Algarve, Portugal

Luís Bentes
CCMAR, Universidade do Algarve, Portugal

Pedro G. Lino
CCMAR, Universidade do Algarve, Portugal

Joaquim Ribeiro
CCMAR, Universidade do Algarve, Portugal

Konstantinos I. Stergiou
Department of Ichthyology, Aristotle University of Thessaloniki, Department of Biology, Section of Zoology, Greece

Abstract


Fishing trials with monofilament gill nets and longlines using small hooks were carried out in Algarve waters (southern Portugal) over a one-year period. Four hook sizes of "Mustad" brand, round bent, flatted sea hooks (Quality 2316 DT, numbers 15, 13, 12 and 11) and four mesh sizes of 25, 30, 35 and 40 mm (bar length) monofilament gill nets were used. Commercially valuable sea breams dominated the longline catches while small pelagics were relatively more important in the gill nets. Significant differences in the catch size frequency distributions of the two gears were found for all the most important species caught by both gears (Boops boops, Diplodus bellottii, Diplodus vulgaris, Pagellus acarne, Pagellus erythrinus, Spondyliosoma cantharus, Scomber japonicus and Scorpaena notata), with longlines catching larger fish and a wider size range than nets. Whereas longline catch size frequency distributions for most species for the different hook sizes were generally highly overlapped, suggesting little or no differences in size selectivity, gill net catch size frequency distributions clearly showed size selection. A variety of models were fitted to the gill net and hook data using the SELECT method, while the parameters of the logistic model were estimated by maximum likelihood for the longline data. The bi-normal model gave the best fits for most of the species caught with gill nets, while the logistic model adequately described hook selectivity. The results of this study show that the two static gears compete for many of the same species and have different impacts in terms of catch composition and size selectivity. This information will be useful for the improved management of these small-scale fisheries in which many different gears compete for scarce resources.

Keywords


gill nets; hook; longlines; artisanal; multi-species; selectivity; Portugal; Algarve

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