[MARMAM] New publication: Gray whale migration patterns through the Southern California Bight

Regina Guazzo rguazzo at ucsd.edu
Thu Aug 29 13:07:31 PDT 2019

Dear Colleagues,

My co-authors and I are excited to announce the following open-access

Guazzo RA, Schulman-Janiger A, Smith MH, Barlow J, D’Spain GL, Rimington
DB, Hildebrand JA (2019) Gray whale migration patterns through the Southern
California Bight from multi-year visual and acoustic monitoring. Mar Ecol
Prog Ser 625:181-203.

DOI:   https://doi.org/10.3354/meps12989

Abstract: Sightings and acoustic recordings from eastern North Pacific gray
whales in the Southern California Bight were analyzed for interannual
changes and compared with concurrent environmental measurements during 7
migration seasons (2008-2009 to 2014-2015). Acoustic call counts recorded
on an offshore hydrophone were highly variable from year to year. Assuming
an average calling rate of 7.5 calls whale-1 d-1, the estimated number of
whales migrating by this hydrophone would be <10% of the population within
20 km of the offshore hydrophone in most years. In contrast, the estimated
number of gray whales migrating off Santa Barbara and Los Angeles based on
visual surveys grew at a greater rate (11% yr-1 and 26% yr-1, respectively)
than the population size growth rate (5% yr-1). Over the studied migration
seasons it seems an increasing proportion of the population was using the
nearshore migration corridor in the Southern California Bight, especially
near Los Angeles. This trend could increase the negative anthropogenic
impact on this species. Although several large-scale climatic events
occurred between 2008 and 2015, neither water temperature in the Southern
California Bight nor sea ice timing in the gray whale Arctic feeding area
improved generalized additive models of gray whale nearshore sightings or
offshore acoustic presence. Over these times, the gray whale migration
timing appears to be driven more by their biological clock and instinct
than by the extrinsic factors accounted for in the present analysis. Future
work should test if other factors influence the gray whale migration over
longer timescales.

Please email me (rguazzo at ucsd.edu) if you have any questions about this

All my best,


Regina A. Guazzo, PhD
Environmental Readiness Branch
Naval Information Warfare Center Pacific
(c) 908.507.1421
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