However, previous studies have found low spatio-temporal variability both δ15N and δ13C values of M. norvegica in the NEA (38º–45ºN, 12º–13ºW) whereby seasonal differences in isotope values were not significantly different (Bentaleb et al. 2011). Protein Tyrosine Kinase inhibitor Mixing model solutions confirmed that fin and humpback whales are both planktivorous and piscivorous in the CS. While krill (M. norvegica and N. couchii) make up a large proportion of

their diets, especially for fin whales, both whale species were also found to have a preference for age 0 sprat and herring respectively. Proportions of both age 0 sprat and age 0 herring were not easily differentiated by the mixing models. It is likely that this is ecologically relevant rather than a model artifact, given the propensity for mixed species shoals of age 0 sprat and herring in the CS, collectively known as “whitebait.” Similarly, sprat and herring fisheries are unlikely to be selective in catching these shoals. The importance of age 0 PLX4032 chemical structure sprat and herring in the diet of both fin and humpback whales should be considered in the management of CS fisheries. The weak negative correlation between age 0 herring an M. norvegica in fin whale diet solutions may also be an ecological effect. Fin whales may

feed either on herring on the shelf or on M. norvegica where they are most abundant at the shelf break, situated ca. 200 km from where the biopsies were collected. It is unlikely that they feed on both species over small temporal scales given 上海皓元 the distances between the core habitats of these prey species. Krill species including both M. norvegica and N. couchii comprised about half of the diet in fin whales. Humpback whales by comparison consumed significantly lower proportions of krill species, indicating a more piscivorous diet. This result is consistent with recent findings based on stable isotope analysis of baleen, which suggest that humpback whales occupy a

higher trophic level than fin whales in the CS (Ryan et al. 2012b). Given that krill comprised one of the smallest dietary components in humpback whales, exploitation of shared resources between fin and humpbacks whales in the CS might only be short-lived. The proportions of each krill species that are being consumed remain to be resolved. M. norvegica and N. couchii occur chiefly in offshore and shelf waters respectively, therefore discerning which of these species comprise the preferred prey for fin and humpback whales should be a research priority. This may shed light on feeding strategies when the whales are foraging offshore, beyond the current reach of researchers. Fatty acid analysis of blubber biopsies may provide more conclusive insights on this issue (Borobia et al. 1995, Grahl-Nielsen 2009).