Differences in the isotopic niche width of two Southeast Pacific humpback whale feeding grounds: Antarctic Peninsula and Strait of Magellan, Chile

HARO DANIELA; RICCIALDELLI LUCIANA; CACERES IRIS; ACEVEDO JORGE; OLAVARRIA CARLOS; AGUAYO-LOBO ANELIO; SABAT, PABLO

Halifax

Congreso; 22nd Biennial Conference on the Biology of Marine Mammals; 2017

The Society for Marine Mammalogy

Different feeding strategies imply that organisms are, to a greater or lesser extent, vulnerable to spatial and/or temporal variations in the availability of prey. Species with generalist feeding strategies consume a wide range of prey items, whereas others with a more specialist diet consume a more limited range. The Southeast Pacific humpback whale population (Stock G), seems to specialize according to available resources found in their different feeding grounds. In this study, we evaluated possible differences in feeding strategies (type of prey consumed and niche width) presented by Stock G individuals in two of their feeding areas, western coast of the Antarctic Peninsula and Magellan Strait, Chile. Stable isotopes of 13C and 15N were analyzed from whale biopsies of both feeding zones for estimating the isotopic niche area (?2) using Bayesian ellipses in SIAR. Carbon and nitrogen mean values were significantly lower in Antarctica (-23.2 + 1.2? in 13C, 8.0 + 0.6? in 15N), with a smaller isotopic niche area (SEAc=1.98), with respect to individuals from Magellan (-16.5 + 1.1? in 13C, 14.4 + 1.3? in 15N, SEAc=5.06). These results indicate that for the Antarctic feeding area, individuals are consuming a smaller prey species spectrum, reflecting a narrower isotopic niche, compared to those in Magellan. Isotopic differences recorded between these two zones respond, on one hand, to isotopic spatial differences existing in the basis of the Antarctic vs. Subantarctic food webs, and, on the other hand, to the consumption of different trophic level prey items. Our results agree with previous records, indicating that in Antarctic humpback whales mainly consume organisms of low trophic level (euphausiids), as opposed to Magellan, where they consume organisms of low (euphausiids, lobster krill), and medium trophic levels (fuegian sprat). This work demonstrates the feeding plasticity of the Stock G to prey on different trophic resources.