ABSTRACT
Knowledge of the diet of marine mammals is fundamental to understanding their role in marine ecosystems and response to environmental change. Recently, animal-borne video cameras have revealed the diet of marine mammals that make short foraging trips. However, novel approaches that allocate video time to target prey capture events is required to obtain diet information for species that make long foraging trips over great distances. We combined satellite telemetry and depth recorders with newly developed date-/time-, depth- and acceleration-triggered animal-borne video cameras to examine the diet of female northern elephant seals during their foraging migrations across the eastern North Pacific. We obtained 48.2 h of underwater video, from cameras mounted on the head (n=12) and jaw (n=3) of seals. Fish dominated the diet (78% of 697 prey items recorded) across all foraging locations (range: 37–55°N, 122–152°W), diving depths (range: 238–1167 m) and water temperatures (range: 3.2–7.4°C), while squid comprised only 7% of the diet. Identified prey included fish such as myctophids, Merluccius sp. and Icosteus aenigmaticus, and squid such as Histioteuthis sp., Octopoteuthis sp. and Taningia danae. Our results corroborate fatty acid analysis, which also found that fish are more important in the diet, and are in contrast to stomach content analyses that found cephalopods to be the most important component of the diet. Our work shows that in situ video observation is a useful method for studying the at-sea diet of long-ranging marine predators.
FOOTNOTES
Competing interests
The authors declare no competing or financial interests.
Author contributions
Conceptualization: A.T., D.P.C., Y.N.; Methodology: K.Y., A.T., T.A., Y.N.; Formal analysis: K.Y., A.T.; Investigation: K.Y., A.T., T.A., D.P.C., P.W.R., S.H.P., L.A.H., R.R.H., Y.N.; Writing - original draft: K.Y., A.T.; Writing - review & editing: T.A., D.P.C., P.W.R., S.H.P., L.A.H., R.R.H., Y.N.; Project administration: A.T., D.P.C., P.W.R., Y.N.; Funding acquisition: A.T., D.P.C., Y.N.
Funding
This study was supported by funding from the Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (23255001 and 15K14793), Grant-in-Aid for JSPS Fellows (12 J04316), the Office of Naval Research grants N00014-10-1-0356 and N00014-13-1-0134, and the E&P Sound and Marine Life Joint Industry Project of the International Association of Oil and Gas Producers.
Data availability
Data associated with this article are available at the ADS (Arctic Data archive System) of the National Institute of Polar Research (https://ads.nipr.ac.jp/dataset/A20191218-001).
Supplementary information
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.212936.supplemental
- Received August 27, 2019.
- Accepted January 31, 2020.
- © 2020. Published by The Company of Biologists Ltd
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