Weddell seals, leptonychotes weddelli, as biological samplers of cephalopods in the food webs of the antarctic ecosystem.

NEGRI A; DANERI G.A.; CEIA F; VIEIRA R; CHEREL Y; CORIA N.R; CORBALÁN A.; XAVIER J.

Puerto Madryn

Congreso; 15ª Reunión de Trabajo de Expertos en Mamíferos Acuáticos de América del Sur. 9º Congreso SOLAMAC; 2012

Weddell seals are important apex predators in the food webs of the Antarctic marine ecosystem. The aims of the present study were: 1) To examine in detail the cephalopod portion of their diet by means of scat analysis; 2) To assess the habitat use and trophic level of the different cephalopod prey taxa of weddell seals identified. From mid january to February 2009 a total of 48 faecal droppings were collected at Hope Bay (Lat, 63°24 S; Long. 57°00 W), Antarctic Peninsula, and kept frozen at -20°C. Once in the laboratory these were sieved (mesh size 0.9 mm) through running water and prey remains sorted under a binocular microscope. Cephalopods were mainly represented by a total of 83 beaks (34 upper and 49 lower). All the lower beaks were identified to the lowest possible taxonomical level using reference collections and appropriate guides. Mantle length and mass of the different cephalopod species were estimated from the lower hood length of beaks using previously published regression equations. Furthermore, subsamples of beaks were separated, cleaned and kept in 70% ethanol for further isotopic analysis. Relative abundance of stable isotopes of carbon (13C/12C) and nitrogen (15N/14N) were determined by continuous-flow isotope-ratio mass spectrometry (CFIRMS). The analysis of scats containing prey remains (n=46) indicated that fish were the most frequent prey of seals occurring in 100% of samples followed by cephalopods which were present in 37% of scats. The occurrence of crustacean remains was negligible. Cephalopods were represented uniquely by octopods of the subfamily Eledoninae. The dominant prey species was Pareledone turqueti which occurred in almost 70% of scats containing cephalopod remains and represented over 40% in terms of numerical abundance and 60.5% in mass of cephalopods consumed. This species was followed by the ?Papillated Pareledone? species group and Adelieledone polymorpha. The ä13 C and ä15 N mean (± sd) values in beaks of these three octopodid taxa combined were -18.9 ± 1.1? and 7.1 ± 0.6? respectively. Based on the results obtained in this study it is suggested that during the summer season Weddell seals preyed primarily on benthic prey resources. Furthermore, the relatively similar ä13 C and ä15 N values in beaks of the three octopod prey taxa would indicate that these share the same type of habitat and occupy similar trophic level positions in waters close to the Antarctic Peninsula.13C/12C) and nitrogen (15N/14N) were determined by continuous-flow isotope-ratio mass spectrometry (CFIRMS). The analysis of scats containing prey remains (n=46) indicated that fish were the most frequent prey of seals occurring in 100% of samples followed by cephalopods which were present in 37% of scats. The occurrence of crustacean remains was negligible. Cephalopods were represented uniquely by octopods of the subfamily Eledoninae. The dominant prey species was Pareledone turqueti which occurred in almost 70% of scats containing cephalopod remains and represented over 40% in terms of numerical abundance and 60.5% in mass of cephalopods consumed. This species was followed by the ?Papillated Pareledone? species group and Adelieledone polymorpha. The ä13 C and ä15 N mean (± sd) values in beaks of these three octopodid taxa combined were -18.9 ± 1.1? and 7.1 ± 0.6? respectively. Based on the results obtained in this study it is suggested that during the summer season Weddell seals preyed primarily on benthic prey resources. Furthermore, the relatively similar ä13 C and ä15 N values in beaks of the three octopod prey taxa would indicate that these share the same type of habitat and occupy similar trophic level positions in waters close to the Antarctic Peninsula.