Foraging ecology of five toothed whale species in the Northwest Iberian Peninsula, inferred using carbon and nitrogen isotope ratios

Abstract

International audienceThe feeding ecology and habitat use of the most frequently sighted and/or regularly reported stranded or bycaught toothed whale species of the North Western Iberian Peninsula (NWIP) were examined, with a special focus on their trophic position (TP) and relationships with their prey. With this aim, the stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) of common dolphin (Delphinus delphis), bottlenose dolphin (Tursiops truncatus), harbour porpoise (Phocoena phocoena), striped dolphin (Stenella coeruleolba) and long-finned pilot whale (Globicepahala melas) were analyzed in muscle samples taken from stranded and by-caught animals between 2004 and 2008. Stable isotopes were also measured in 17 species of fish and cephalopods previously identified as prey species, based on stomach content analyses, and in plankton. The trophic enrichment factors (TEF) were calculated for all five species and in addition, isotopic mixing models were applied to estimate the proportional contribution of each prey source to the diet of the common dolphin, which was the toothed whale species best sampled in our study. Plankton, fish and cephalopods exhibited an increasing trend in their δ13C values (from−19.6‰to−15.3‰) along the offshore-inshore axis, with a less clear spatial pattern observed for δ15N values. Striped dolphins exhibited the lowest mean δ13C, δ15N and TP values (−17.6‰, 10.8‰ and 4.3, respectively), which confirms the oceanic character of this species and its lower trophic position when compared to the other toothed whales analyzed. The common dolphin exhibited mean δ13C, δ15N and TP values that were at an intermediate level (−17.0‰, 11.7‰ and 4.7, respectively) and results of the mixing model indicated that blue whiting (Micromesistius poutassou) was the main component of the diet. The harbour porpoise, bottlenose dolphin and pilot whale exhibited higher and very similar isotopic compositions and TPs. The mean TEF obtained between predators and their main prey were 1.4‰ for δ15N and 0.8‰ for δ13C. These results provide information on stable isotope incorporation data for toothed whales, which are essential if conclusions are to be drawn in issues concerning trophic structures and habitat use in the NWIP

Small pelagic fish feeding patterns in relation to food resource variability: an isotopic investigation for Sardina pilchardus and Engraulis encrasicolus from the Bay of Biscay (north-east Atlantic)

“…However, the spatial variability of δ 13 C and δ 15 N values from the base of the different food webs in the area (Chouvelon et al 2012), and also shown here with isotope values of mesozooplanktonic species, rather supports the hypothesis of more offshore feeding habits for anchovies than the hypothesis of a lower trophic level. Anchovies would effectively be able to capture larger particles than sardines (Louw et al 1998;Van der Lingen et al 2006), thanks to differences in gill raker morphology between both species and the existence of a larger branchial apparatus in anchovies (James and Findlay 1989).…”

“…In autumn 2011, the spread of isotope values for anchovies was relatively large. Chouvelon et al (2012) ). In autumn, abundances of mesozooplankton may effectively stay at levels that anyway sustain energetic needs of both species and other plankton feeders.…”

Use of carbon and nitrogen stable isotopes to study the feeding ecology of small coastal cetacean populations in southern Brazil

“…13,no. 4 inshore to offshore areas (France 1995, Clementz & Koch 2001, Kurle & Gudmundson 2007, Cherel & Hobson 2007, Newsome et al 2010, Ohizumi & Nobuyuki 2010, Gibbs et al 2011, Méndez-Fernandez et al 2012. Based on these constraints, a future line of investigation could apply molecular tracers to more accurately identify the ecological niches of these animals (Fernández et al 2011).…”

Feeding strategies and ecological roles of three predatory pelagic fish in the western Mediterranean Sea

“…However, in some cases competing marine predators coexist in the same habitat because they segregate in the exploitation of trophic resources (Albo-Puigserver et al, 2015;Linke et al, 2001;Mèndez-Fernandez et al, 2012;Romeo et al, 2009). For this reason, little tunny and Atlantic bonito probably segregate their main trophic resources as a mechanism allowing their coexistence in the pelagic habitat.…”