Quantitative examination of long-term impact of implant tagging on survival of gray and blue whales

Citation

Calambokidis, J, A Zerbini, K Flynn, A Douglas, S Norman, B Mate, C Hayslip, D Gendron, R Sears, J Jacobsen, and D Goley. 2015. Quantitative examination of long-term impact of implant tagging on survival of gray and blue whales. Abstract (Proceedings) 21st Biennial Conference on the Biology of Marine Mammals, San Francisco, California, December 14-18, 2015.

Abstract

Deployment of tags on whales using approaches that either embed or anchor the tag into the blubber and muscle layer have been commonly used for many decades. Follow up studies on the potential impact of these tags have relied mostly on limited or short term observations of tagged animals. We conducted a quantitative assessment of the long term survival of gray and blue whales in the eastern North Pacific that were tagged by the Marine Mammal Institute of Oregon State University and compare these to a group of control whales present at the tagging location and same time period but not tagged. Eighteen gray whales tagged in 2009 and 39 control whales were all part of the Pacific Coast Feeding Group (PCFG) that feed in the Pacific Northwest through the summer and fall and are frequently resighted as part of a long-term collaborative photo-ID effort. Resightings of the tagged and control animals were similar prior to tagging. Starting in 2011, resightings for the next 3 years were higher for control animals (85-90%) than tagged animals (72% each year) primarily as a result of three tagged whales (17%), two not resighted at all for 2011-2013 and one seen but known to have died in 2011 of undetermined causes. Cormack-Jolly-Seber (CJS) capture recapture models to test the influence of tagging on survival (acute or chronic) showed reduced survival of tagged animals but were nearly equally supported by AICc as models without tag effects. Follow up observations of additional PCFG whales tagged in 2012 and 2013 will strengthen this sample size in the future. For 81 blue whales representing 83 satellite tag deployments from 1993 to 2008, 64 (79%) were seen in at least one later year (up to 17 years post-tagging) compared to 197 of 268 (74%) of control animals. These data to date show a possible small difference in survival from tagging for gray whales but no evidence of a survival effect on blue whales. These results highlight the importance of follow-up observations of tagged whales to allow quantitative assessments of long term impacts including potential small differences in survival.

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