The apparent disappearance of Loligo forbesi from the south of its range in the 1990s: Trends in Loligo spp. abundance in the northeast Atlantic and possible environmental influences

Abstract

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, examine the relationship between abundance of this species and that of the partially sympatric Loligo vulgaris, and identify possible environmental correlates. Time-series of abundance of L. 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 (October sea surface temperature and the winter NAO index) were analysed using dynamic factor analysis (DFA). The optimal DFA model contained two common trends and both of the explanatory variables. The first common trend shows an increase from 1987 to 1999, and a slight decrease after 2000 onwards, and is positively related to L. forbesi abundance in the north of its range (Scotland), while negatively related to squid abundance (both species) in the south of their ranges (France and Portugal). The second trend identifies an increase from 1990 to 1995, followed by a decrease until 2002, and is positively related to the squid (L. forbesi and L. vulgaris) abundance series from French surveys and fisheries. The 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 winter NAO series was significantly related to the abundance of small L. forbesi from Scottish surveys. 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).

An analysis of the impacts of climatic variability and hydrology on the coastal fisheries, Engraulis encrasicolus and Sepia officinalis, of Portugal

“…However, in the present study, S. offi cinalis presented a signifi cant positive relationship with NAO-Win index at south coast, while signifi cant negative relation with UPW and River discharge-Spr at southwestern and northwestern coast, respectively. There is no study about the relationship between NAO index and S. offi cinalis, however, the abundance of small L. forbesi, an important squid fi shery resource in the north Atlantic, was signifi cantly related to the NAO-Win index in Scottish waters (Chen et al 2006). The spatial distribution of SST data displayed that in the south coast, yearly and seasonal SST values were always higher than southwestern and northwestern coast of Portugal.…”

“…This limits the scope to explain the trends for individual species and explanatory variables that infl uence particular fi sheries, instead it explains the potential multiple common trends and relationship of a group of species and combined explanatory variables (Zuur et al 2003a(Zuur et al , 2003bZuur, Pierce 2004;Erzini 2005;Erzini et al 2005;Chen et al 2006;Ligas et al 2010;Santos et al 2012;). Understanding the potential role of climatic variables on individual species is very important because it can provide adequate information to fi sheries managers for a particular species of interest, and thus can play signifi cant role in managing fi sheries.…”

Trends in abundance of marine fishery resources in India examined through dynamic factor analysis

“…Dynamic factor analysis (DFA) is a statistical tool used to identify and extract common trends existing in multivariate time series data and it can be used to estimate common trends in short and non-stationary time series (Zuur et al, 2003;Zuur and Pierce, 2004). Globally there were several attempts to model trends in marine fishery resources with the help of DFA (Zuur et al, 2003;Zuur and Pierce, 2004;Chen et al, 2006;Huang et al, 2006). In this study recent historic data were analysed to delineate the common trends for major fishery resources landed along the Indian coast.…”

Wavelet analysis of correlation among Canary Islands octopus captures per unit effort, sea-surface temperatures and the North Atlantic Oscillation

“…In this way, yearly recruitment (Robin and Denis, 1999), and consequently the availability to the fishery (Agnew et al, 2002;Chen et al, 2006), is conditioned by the effects that climatic variability has on their relatively large pelagic paralarvae stages in relation with their longevity (Waluda et al, 1999). Therefore, it is likely that those climatic variables that can be measured at surface level (i.e., SST) may have direct effects on the survival rates of these pelagic stages.…”

“…The influence could be explained either through growth, food availability or natural mortality due to other causes (Forsythe, 1993;Caveriviere et al, 1999;Robin and Denis, 1999;Waluda et al, 1999;Leporati et al, 2007;Pierce et al, 2008). It could therefore be more feasible to differentiate climatic effects from the influence of fishing in these species, because their response to environmental fluctuations should be faster (Hernández-García et al, 2002;Chen et al, 2006;Caballero-Alfonso et al, 2010).…”