Toothed whales in the northwestern Mediterranean: Insight into their feeding ecology using chemical tracers

Abstract

a b s t r a c tRisso's dolphins, pilot whales and sperm whales rarely strand in the northwestern Mediterranean. Thus, their feeding ecology, through the analysis of stomach contents, is poorly known. The aim of this study was to gain further insight into the segregation/superposition of the diet and habitat of Risso's dolphins, pilot whales and sperm whales using chemical tracers, namely, stable isotopes (d N values were obtained in Risso's dolphins (11.7 ± 0.7‰), sperm whales (10.8 ± 0.3‰) and pilot whales (9.8 ± 0.3‰), revealing different trophic levels. These differences are presumably due to various proportions of Histioteuthidae cephalopods in each toothed whale's diet. Similar d 13 C contents between species indicated long-term habitat superposition or corroborated important seasonal migrations. Lower congener 180 concentrations (8.20 vs. 21.73 lg.g À1 lw) and higher tDDT/ tPCB ratios (0.93 vs. 0.42) were observed in sperm whales compared with Risso's dolphins and may indicate wider migrations for the former. Therefore, competition between these species seems to depend on different trophic levels and migration patterns.

POPs in free-ranging pilot whales, sperm whales and fin whales from the Mediterranean Sea: Influence of biological and ecological factors

“…Indeed, fin whales mainly forage during summer on a small euphausiacean, Meganyctyphanes norvegica (Bentaleb et al, 2011;Druon et al, 2012), while long-finned pilot whales and sperm whales are teuthophageous, feeding exclusively or preferentially on bathypelagic cephalopods of the Histioteuthidae and Ommastrephidae family (Astruc and Beaubrun, 2005;Praca and Gannier, 2008). Stomach content analysis from stranding events in the French and Italian coasts, showed that sperm whales are true specialists in terms of food selection, as 90% of their diet consists on species of the Histioteuthidae family (Praca and Gannier, 2008;Praca et al, 2011). Long-finned pilot whales are more generalist feeders as 40-50% of their diet consists of Todarodes sagittatus, 10-20 % of H. bonnelii and H. reversa and 10% is made up by several other prey species (Praca and Gannier, 2008;Praca et al, 2011).…”

“…Beside the threat of POPs potential hazard to marine mammal populations, the levels and profile of these contaminants can serve as an intrinsic marker from which population structure can be defined (Praca et al, 2011;Ryan et al, 2013b). Indeed, these compounds reflect the ecosystem conditions under which marine mammals live and feed and therefore can infer their geographical distribution (Aguilar et al, 2002;Borrell et al, 2006;Praca et al, 2011).…”

“…Indeed, these compounds reflect the ecosystem conditions under which marine mammals live and feed and therefore can infer their geographical distribution (Aguilar et al, 2002;Borrell et al, 2006;Praca et al, 2011). In addition, as the chemical analysis requires only a small amount of sample, it can be performed using biopsies; allowing the study of living and healthy animals (Praca et al, 2011).…”

“…Other chemical tracers such as stable isotope ratios of carbon ( 13 C/ 12 C or δ 13 C in delta notation) and nitrogen ( 15 N/ 14 N, δ 15 N in delta notation) demonstrated their usefulness in exploring feeding ecology of cetaceans (Frodello et al, 2000;Capelli et al, 2008;Newsome et al, 2010;Praca et al, 2011;Ryan et al, 2013b). As terrestrial and marine carbon sources differ in their 13 C composition, with terrestrial and coastal areas more enriched than lessproductive offshore regions, δ 13 C permits to discriminate between offshore/nearshore and benthic/pelagic foraging behaviour (Newsome et al, 2010;Praca et al, 2011).…”

“…As terrestrial and marine carbon sources differ in their 13 C composition, with terrestrial and coastal areas more enriched than lessproductive offshore regions, δ 13 C permits to discriminate between offshore/nearshore and benthic/pelagic foraging behaviour (Newsome et al, 2010;Praca et al, 2011). Moreover, the depletion in marine organic matter with increasing latitude can be used for investigating seasonal changes in foraging areas (Bentaleb et al, 2011).…”