The Argentine shortfin squid (Illex argentinus) is a common
neritic species occurring in waters off Brazil, Uruguay, Argentina, and the Falkland/Malvinas Islands in the southwest Atlantic. Illex argentinus is the most important
fished cephalopod species in
the area and plays a significant role in the ecosystem. It is object of
major fisheries using both trawlers (mostly from European countries) and
jigging vessels (mainly from Asian countries) and estimated total annual
average catch for the last 15 years (1988-2003) is about 700 000 tons. The
present paper aims to develop predictive models of squid abundance in
relation to physical and environmental conditions, models that could
ultimately be applied to fishery forecasting. Fishery and biological data
collected by scientific observers aboard commercial trawlers between 1988
and 2003 were analysed in relation to physical and environmental factors to
establish the spatio-temporal pattern of the species' distribution and
quantify the influence of environmental variables (e.g. SST, depth) on local
abundance. The data included 26 168 fishing haul records, of which 11 103 were
positive for Illex. CPUE (Catch Per Unit Effort, kg h−1) was used as
abundance index. The analyses were based on time-series maps created using
Geographical Information Systems (GIS). GIS maps showed that highest CPUE
values were recorded during the first four months of the year (the Austral
summer-autumn), with peak values higher than 5000 kg h−1 mainly located
within 42° S, 46° S and MN (North part of Malvinas/Falkland)
areas. Generalised additive models (GAMs) were used to describe variation in
Illex argentinus abundance in relation to geographical and environmental variables. The
presence/absence (PA) of Illex and its abundance (CPUE) in areas of presence were
modelled separately. Predictors retained in the optimal models included SST,
latitude, longitude, month, average fishing depth and year. Both models
suggest a clear seasonal effect: maximum catchability was found during March
(PA model) and the maximum abundances were found during the first quarter of
the year (CPUE model). GAM models also demonstrated that higher catches and
maturity of squid were related, in general terms, to warmer and deeper
water.