Immature euphausiids do not appear to be prey for humpback whales ( Megaptera novaeangliae) during spring and summer in Southeast Alaska

• Published in: Marine Mammal Science
• Main Author: Szabo, Andrew
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2014
• Subjects: Pacific; Stephens Passage; Megaptera novaeangliae; Alaska; Copepods
• Online Access: http://dx.doi.org/10.1111/mms.12183; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fmms.12183; https://onlinelibrary.wiley.com/doi/pdf/10.1111/mms.12183

Abstract Humpbacks whales ( Megaptera novaeangliae ) have shown a remarkable recovery in the North Pacific, raising concerns regarding their impact on marine communities. In Southeast Alaska, humpbacks feed heavily on euphausiids; however, it remains unclear whether they target immature individuals despite evidence that they do so elsewhere. I evaluate the hypothesis that humpbacks target immature euphausiids in late spring‐summer in Southeast Alaska. Plankton samples were collected at random sites ( n = 44) and near whales ( n = 53) between 8 June and 9 September 2008 in Frederick Sound and Stephens Passage. The proportion of samples containing immature euphausiids, and immature euphausiid abundance within those samples, were compared between the two sample types. Similar analyses were conducted for adult euphausiids (prey) and calanoid copepods (nonprey) for comparison. I found no statistical difference between the whale and random samples with respect to the occurrence or numerical density of immature euphausiids, which is consistent with the hypothesis that whales did not target them in 2008. Smaller size, insufficient numerical densities and lower energy density of immature euphausiids are suggested as possible reasons. These findings can assist in resolving regional humpback abundance and distribution patterns, and can contribute to an understanding of the trophic interactions characterizing the local ecosystem.