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The apparent disappearance of Loligo forbesi from the south of its range in the 1990s: trends in Loligo spp. abundance in the northeast Atlantic
conference contribution
posted on 2024-03-22, 10:45 authored by C.-S. Chen, G.J. Pierce, J. Wang, J.-P. Robin, J.C. Poulard, J. Pereira, A.F. Zuur, P.R. Boyle, N. Bailey, D.J. Beare, I. Sobrino, L. Orsi ReliniNo abstracts are to be cited without prior reference to the author.
Since the early 1990s, Loligo forbesi has apparently disappeared from much of the southern part of its former range, with catches off the Iberian Peninsula, for example, declining dramatically during the 1990s. The present paper assembles data from fishery and research cruise databases to examine the evidence for a shift in distribution and identify possible environmental correlates. Time-series of abundance of Loligo forbesi and L. vulgaris were assembled using fishery and survey data from Scotland, France, and Portugal. Based on availability of data and timing of the main fishery, data for autumn (October-December) were selected. Nine squid series and two explanatory variables (sea surface temperature and the NAO index) were analysed using dynamic factor analysis (DFA). The optimal DFA model contained two common trends and two explanatory variables. The first common trend shows an increase from 1977-1997, and a slight decrease after 1998 onwards, and is positively related to L. vulgaris survey abundance in Portugal and L. forbesi fishery abundance in Scotland – and negatively related to L. forbesi survey abundance in Portugal. The second trend identifies an increase from 1990-1995, followed by a decrease until 2001, and is positively related to the squid (L. forbesi and L. vulgaris) abundance series from French surveys and fisheries. SST series was significantly related to three squid abundance series: positively with abundance of small L. forbesi in French surveys and negatively with the abundance of small L. forbesi from Scottish surveys and abundance of L. vulgaris in Portuguese surveys. The NAO series showed no significant relationship to the original squid series. The increase in SST after 1993 and subsequent high level may thus be associated with the decrease of Loligo abundance in the south area (France and Portugal) and the increase in Loligo abundance in the north area (Scotland).