An application of two techniques for the analysis of short, multivariate non-stationary time-series of Mauritanian trawl survey data

Min/max autocorrelation factor analysis (MAFA) and dynamic factor analysis (DFA) are complementary techniques for analysing short (> 15-25 y), non-stationary, multivariate data sets. We illustrate the two techniques using catch rate (cpue) time-series (1982-2001) for 17 species caught during trawl surveys off Mauritania, with the NAO index, an upwelling index, sea surface temperature, and an index of fishing effort as explanatory variables. Both techniques gave coherent results, the most important common trend being a decrease in cpue during the latter half of the time-series, and the next important being an increase during the first half. A DFA model with SST and UPW as explanatory variables and two common trends gave good fits to most of the cpue time-series. (c) 2004 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.

Cape Verde coastal ecosystem: a study of community structure, trophic interactions and exploitation pattern

Tese de dout., Ciências e Tecnologia das Pescas, Faculdade de Ciências do Mar e do Ambiente, Universidade do Algarve, 2005

Comparing Atlantic and Mediterranean populations of the velvet belly lanternshark, Etmopterus spinax, with comments on the efficiency of density-dependent compensatory mechanisms

Etmopterus spinax is a small-sized deep-water lantern shark that occurs in the Eastern Atlantic and the Mediterranean. Differences in depth distribution, densities, size at maturity and fecundity were compared between a population that has suffered high levels of fishing mortality during the last decades (Southern Portugal in the northeast Atlantic) and a population where low fishing pressure below 500 m occurs at present or has occurred in the last decades (Northern Alboran Sea in the western Mediterranean). The density of this species, as derived by experimental bottom trawl survey, off the coast of Southern Portugal, is substantially lower than in the Northern Alboran Sea throughout the entire depth range. The Atlantic population is maturing at smaller sizes than the Mediterranean population and has a lower mean fecundity. Specifically, sizes at maturity for Southern Portugal and the Northern Alboran Sea were, respectively, 25.39 and 28.31 cm TL for males and 30.86 and 34.18 cm TL for females, while mean fecundities for Southern Portugal and the Northern Alboran Sea were, respectively, 9.94 and 11.06 oocytes per mature female. This work demonstrated the possible presence of density-dependent mechanisms in the Southern Portuguese population of E. spinax that has lowered the size at maturity as a possible result of excessive fishing mortality. However, given that this is an aplacentary viviparous shark, where fecundity is dependent on female size, this compensatory mechanism seems to have a limited efficiency.

Using a modified Nordmore grid for by-catch reduction in the Portuguese crustacean-trawl fishery

By-catch and discards are a common problem to all fisheries. Recent studies of the Portuguese crustacean-trawl fishery show that discards average 70% of the total catch. This situation poses a threat not only to the management of target and commercial fish by-catch species stocks, but also in terms of the ecosystem impact of the discarded species whose survival is generally low. Previous attempts to address this problem by using oblique separator mesh panels associated with square-mesh windows, or square-mesh windows alone, provided encouraging results, but these are unlikely to have commercial applicability at present. Therefore, we tested the efficiency of a modified Nordmore grid in excluding some of the most captured non-commercial by-catch species, such as the blue whiting, Micromesistius poutassou, and the boarfish, Capros aper, evaluating simultaneously the losses of the crustacean target species (rose shrimp, Parapenaeus longirostris, Norway lobster, Nephrops norvegicus and red shrimp, Aristeus antennatus) and commercially valuable fish by-catch. A total of 41 valid hauls were carried out during 2001, and 15 in 2002 on board the R/V "Noruega". Results from both years varied considerably, with higher by-catch exclusion rates, in weight, registered in the second survey (73-74 and 48-63% for blue whiting and boarfish, respectively). The corresponding percentage reduction for target species was 8-15% for the Norway lobster, 4-9% for rose shrimp and 7-10% for red shrimp. The level of exclusion of the non-commercial by-catch is encouraging, although short-term loss of Norway lobster, where the escapees comprised larger individuals, raises some concern with regards to fishers' acceptance of mandatory use of grids. (C) 2004 Elsevier B.V. All rights reserved.