[MARMAM] New publication: “Porpicide” in California: Killing of harbor porpoises by coastal bottlenose dolphins

Mark Cotter markpcotter at hotmail.com
Sun May 8 12:42:04 PDT 2011

Dear Colleagues, 

We are pleased to announce the recent online publication of the following


Cotter, M. P., Maldini, D. and Jefferson, T. A. (2011),
“Porpicide” in California: Killing of harbor porpoises (Phocoena phocoena) by coastal
bottlenose dolphins (Tursiops truncatus).
Marine Mammal Science, 27: no. doi: 10.1111/j.1748-7692.2011.00474.x


Between 2007 and 2009, we witnessed three aggressive
interactions between harbor porpoises and bottlenose dolphins in Monterey Bay,
California. This is the first time such aggression has been documented in the
Pacific, and the first time a harbor porpoise was collected immediately after
witnessing its death, inflicted by bottlenose dolphins. Of the bottlenose
dolphins present, 92% were males either confirmed (61%) or putative (31%).
Since 2005, 44 harbor porpoise deaths inflicted by bottlenose dolphins were
documented in California. Aberrant behavior was rejected as a cause of
aggression, based on widespread documentation of similar behaviors in other
populations of free-ranging bottlenose dolphins. The evidence for interspecies
territoriality as a form of competition for prey was weak: there is little
dietary overlap and there are differences in bottlenose dolphin and harbor
porpoise distribution patterns in California. Object-oriented play was
plausible as a form of practice to maintain intraspecific infanticidal skills
or a form of play to maintain fighting skills between male associates.
Contributing factors could be high-testosterone levels, as attacks occurred at
the height of the breeding season, and/or a skewed operational sex ratio.
Ultimately, we need more information about bottlenose dolphin social structure
at the time of the aggression.


Please feel free to contact me directly for a copy of the
pdf. (markpcotter at hotmail.com)


Best regards,


Mark P. Cotter
Field Director
Moss Landing, CA  95039
Phone: 508-944-4664
markpcotter at hotmail.com

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