Long Term Changes in the Spiny Dogfish (Squalus acanthias) Trophic Role in the Southwestern Atlantic

BELLEGGIA MAURO; FIGUEROA DANIEL E.; SÁNCHEZ FELISA; BREMEC CLAUDIA

Minneapolis, Minnesota.

Congreso; Joint Meeting of Ichthyologists and Herpetologists; 2011

American Society of Ichthyologist and Herpertologists (ASIH)

This study describes the diet of the spiny dogfish Squalus acanthias in the SouthwesternAtlantic Ocean (35 °S - 55 °S) by examining stomach contents data collected between1984 and 2010. Of the 3638 individuals examined, 2217 (60.77%) had prey, at differentstages of digestion, in their stomachs. Generalized Linear Models were used to evaluatethe support in our data for five independent variables (Sex, Predator?s Total Length,Season, Region and Decade) that may explain the consumption of given prey. Ourresults reveal changes in the trophic level and the diet composition over the time series.The frequency of Fish, M. hubbsi and Benthos in the stomachs decreased over the timeseries, whereas the squid Illex argentinus and Jellyfishes exhibited positive trends. Wepropose that the changes in the trophic relationships, which have been affected duringthe last 30 years, are probably a consequence of the increasing fishing effort. The trophic level of S. acanthias fell from 4.68 in 1980s to 4.1 and 4.2 in 1990s and 2000srespectively, showing evidence of substantial fishing down the food webs phenomenon.The consumption of argentine anchovy (Engraulis anchoita) was best explained byRegion and Season as independent variables; this underexploited species was the uniqueprey not explained by GLMs including Decade. In agreement with the distribution andabundance of E. anchoita, the spiny dogfish preyed more in Northern than in SouthernRegion, and the consumption was also greater in Warm than in Cold Season.