Cephalopoda as prey of juvenile Southern elephant seals at Isla 25 de Mayo/King George, South Shetland Islands

Abstract

ABSTRACT. The aim of the present study was to enhance the knowledge of the feeding habits of the juvenile component of the population of Southern elephant seals [Mirounga leonina (Linnaeus, 1758)] from Isla 25 de Mayo, South Shetland Islands, age class whose diet information is scarce. A total of 60 individuals were stomach lavaged in the spring -summer seasons of three consecutive years (2003, 2004 and 2005) of which 53.3 % (n = 32) presented food remnants. The Antarctic glacial squid Psychroteuthis glacialis Thiele, 1921 was the dominant prey taxon in terms of frequency of occurrence (68.7%), numerical abundance (60.1%) and biomass (51.5%), contributing 84.1% to the total relative importance index. Other squid prey species of importance were Slosarczykovia circumantartica Lipinski, 2001 in terms of occurrence (37.5%) and numerical abundance (14%) and Moroteuthis knipovitchi Filippova, 1972 in terms of biomass (16%). All identified cephalopod prey taxa are distributed south of the Antarctic Polar Front, except for the squid Martialia hyadesi Rochebrune & Mabille, 1889 which has a circumpolar distribution associated to the Polar Frontal Zone. No significant differences in the sizes of P. glacialis preyed upon by elephant seals were found between sexes and years. However, significant interannual differences were found in the taxonomical composition of their diet. This would be associated with temporal changes in food availability at the foraging areas of seals, which in turn may have been influenced by changes in oceanographic conditions as a result of the El Niño Southern Oscillation (ENSO) phenomenon that occurred during part of the study period. Furthermore, a differential response of males and females to this temporal variation was observed, with the former being also associated to a predation on octopods. This would suggest a sexual segregation in foraging habits of this species from the early stages of its life cycle. KEYWORDS. Mirounga, diet, Antarctica.RESUMEN. Cephalopoda como presa de juveniles de elefantes marinos del sur en la Isla 25 de Mayo/King George, Islas Shetland del Sur. El objetivo del presente estudio fue el de incrementar el conocimiento de los hábitos alimentarios del componente juvenil de la población de elefantes marinos del sur [Mirounga leonina (Linnaeus, 1758)] de Isla 25 de Mayo, Islas Shetland del Sur, clase de edad cuya dieta es poco conocida . Un total de 60 ejemplares fueron sometidos a técnicas de lavaje estomacal durante primavera -verano de tres años consecutivos (2003, 2004 y 2005) de los cuales el 53,3 % (n = 32) presentaba restos alimentarios. El calamar antártico Psychroteuthis glacialis Thiele, 1921 fue el taxón presa dominante en términos de frecuencia de ocurrencia (68,7%), abundancia numérica (60,1%) y biomasa (51,5%), contribuyendo en un 84,1% al índice de importancia relativa total. Otros calamares presa de importancia fueron Slosarczykovia circumantartica Lipinski, 2001, en términos de ocurrencia (37,5%) y de abundancia numérica (14%), y Moroteuthis knipovitchi F...

Trophic ecology drives trace element concentrations in the Antarctic octopod community

“…This has been previously shown for other oceanic areas (Bustamante et al, 1998a;Penicaud et al, 2017). Pinnipeds such as the Antarctic fur seal Arctocephalus gazella and the Southern elephant seal Mirounga leonina might be exposed to elevated trace element concentrations due to their octopod-rich diet (Burdman et al, 2015;Casaux et al, 1998). Consistently, elevated Cd concentrations have been measured in liver and kidney tissues of A. gazella, which were associated with hepatotoxicity and nephrotoxicity (De Moreno et al, 1997;Malcolm et al, 1994).…”

“…Benthic octopods have a role as both predator and prey, and are crucial in the transfer of energy and trace elements in the Antarctic food web, linking low trophic level consumers to high-level predators (Allcock,1997;2005;Allcock et al, 2001;Daly, 1996;Piatkowski et al, 1998;Strugnell et al, 2017). A wide variety of predators feed on benthic octopods, for example: elephant seals (Mirounga leonine, Burdman et al, 2015;Daneri et al, 2000;Rodhouse et al, 1992), Weddell seals (Leptonychotes weddellii, Acevedo et al, 2015;Casaux et al, 1997;Lipinski and Woyciechowski, 1981;Negri et al, 2016), Patagonian toothfish (Dissostichus eleginoides, Xavier et al, 2002), and the black-browed albatross (Thalassarche melanophris, Xavier and Croxall, 2007). In turn, benthic octopods prey on crustaceans, polychaetes, bivalves, gastropods (Daly, 1996), and amphipods (Daneri et al, 2000;Piatkowski et al, 2003).…”

Cephalopod diet of juvenile male southern elephant seals Mirounga leonina at Marion Island, South Indian Ocean

“…Cephalopods comprise a large proportion of the diet in some seals, but no seal is a specialist cephalopod feeder, with elephant seals the only seals that are regular squid eaters (Klages 1996). Similar to juvenile SES (n = 32) which were stomach lavaged successfully at King George Island, South Shetland islands (Burdman et al 2015), there was a total absence of fish remains in the stomach contents of the two juvenile seals (this study). However, SES are predominant squid and fish eaters (Laws 1956;de Bruyn et al 2016), and the differential retention of squid beaks and fish otoliths in stomachs (Tollit et al 1997;Harvey and Antonelis 1994), is likely to have biased the actual composition of the SES diet.…”

“…The squid Moroteuthopsis longimana (previously Kondakovia longimana), was previously isolated from the stomach of a SES at Marion Island (Ryan and Bester 2008). Whereas S. circumantarctica is commonly taken by SES from Heard Island (Green and Burton 1993;Slip 1995), Macquarie Island (Green and Burton 1993;van den Hoff 2004;Field et al 2007), South Georgia (Rodhouse et al 1992) and the South Shetland islands (Piatkowski et al 2002;Daneri et al 2015;Burdman et al 2015), it has not as yet been recorded for the South Orkney islands (Clarke and MacLeod 1982) and East Antarctica (van den Hoff et al 2003) (Online Resource 1). On the other hand, B. skolops has only been recorded in very low number in the diet of SES at South Georgia (Rodhouse et al 1992).…”