Diet of spring and summer spawning groups of Illex argentinus inhabiting coastal waters in San Matias Gulf (northern Patagonia, Argentina)

Abstract

To study the diet of 2 coastal spawning groups of Illex argentinus, we analyzed the stomach contents of 3645 specimens (10 to 36 cm in mantle length). More than half (58%) of observed stomachs were empty. There were no differences in the prey consumed between specimens of different sex and maturity stages. Additionally, no differences were observed in the diet among individuals belonging to either the summer or spring spawning groups. The most frequent prey item was fishes (0.79 frequency of occurrence), followed by cephalopods (0.18) and lastly by crustaceans (0.09). The seasonal variation of empty stomach frequency and the mean stomach fullness revealed that squids fed more actively in spring and summer and mainly preyed upon small pelagic fishes. KEY WORDS: Illex argentinus · Near-shore waters · Diet · CephalopodsResale or republication not permitted without written consent of the publisher Aquat Biol 14: 99-103, 2011 MATERIALS AND METHODSSamples were obtained with 21 surveys while onboard trawling from vessels which were operating in the San Matias Gulf (42°S, 64.5°W) between June 2005 and October 2007. Tows were conducted during the day with a bottom trawl net (120 mm mesh size) at approx. 4 knots within the deep range, 90 to 150 m. A total of 3645 individuals of both spawning groups (1516 SSG and 2129 SpSG) were collected and were preserved chilled for posterior dissection in the laboratory. During dissection, the stomach of each individual was extracted and supplementary biological information of each specimen was recorded: dorsal mantle length to the nearest cm, sex, and macroscopic maturity condition (Nigmatullin 1989). To analyze the data, maturity stage (I to VII) was grouped into 3 categories as defined by Laptikhovsky & Nigmatullin (1993): immature individuals (stages I and II), physiologically mature individuals (stages III and IV), and functionally mature individuals (stages V, VI and VII).Stomachs were analyzed under 60× magnification, and the hard structures found in the contents were stored and used for prey identification to species level. To determine what the species consumed, identification keys (Clarke 1986, Boschi et al. 1992, Gosztonyi & Kuba 1996, Volpedo & Echeverría 2000 and reference material were used. In the cases of stomachs without hard structures, tissue remains (i.e. muscle, gladius, crystalline, exoskeletons) were used to assign prey into main categories such as fishes, cephalopods or crustaceans. Additionally, for each specimen the stomach fullness (SF) was recorded following the scale proposed by Amaratunga & Durward (1978): 0 = empty, 1 = half full, 2 = full, 3 = distended.A generalized linear model (GLM) was fitted to data (McCullagh & Nelder 1998) to compare the frequency of prey consumed using the maturity condition of individuals, spawning group and sex as covariates. In this model, the dependent variable was the frequency of stomachs corresponding to each category of the covariates and was assumed to follow a Poisson distribution. The function used to lin...

Feeding strategy and cannibalism of the Argentine hake Merluccius hubbsi

“…In SMG, exceptional abundances of I. argentinus were recorded during autumn and winter of 1995, 1997, 2001 and 2003, which favoured their capture by a jigger fleet, but the interannual variation in abundance was evidenced by low catches and landings of trawlers and jiggers during the remaining years (Romero et al , 2007). Crespi Abril (2010) analysed also the diet of squid during 2005–2008 and did not find evidence that M. hubbsi was an important prey. This may indicate that within SMG there are no important and direct trophic relationships between M. hubbsi and squid, at least when squid are in low abundance.…”