[MARMAM] New publication on the population status of type C killer whales in McMurdo Sound, Antarctica (Robert Pitman)

Robert Pitman - NOAA Federal robert.pitman at noaa.gov
Tue Feb 6 12:32:33 PST 2018


New paper published in Polar Biology: Pitman, R. L. , H. Fearnbach, and J.
W. Durban. 2018. Abundance and population status of Ross Sea killer
whales (*Orcinus
orca*, type C) in McMurdo Sound, Antarctica: Evidence for impact by
commercial fishing?



Abstract:

For over a century, the Ross Sea killer whale (RSKW; *Orcinus orca*,
Antarctic type C), a fish-eating ecotype, has been commonly reported in
McMurdo Sound (McM), Ross Sea, Antarctica. However, a significant
population decline reported at Ross Island after 2006 has been linked to a
commercial fishery that began in the Ross Sea in 1996–1997 and targets
large Antarctic toothfish (*Dissostichus mawsoni*)—the presumed primary
prey of RSKW. We assessed RSKW population abundance and trends using
photo-identification data collected in McM during seven summers from
2001–2002 to 2014–2015. We identified 352 individual RSKWs and estimated an
average annual population of 470 distinctly marked whales. Using a Bayesian
mark–recapture model, we identified two population clusters: ‘regulars’
showed strong inter- and intra-annual site fidelity and an average annual
abundance of 73 distinctive individuals (95% probability: 57–88);
‘irregulars’ were less frequently encountered but comprised a larger
population with an annual estimate of 397 distinctive individuals
(287–609). The number of seasonally resident regulars appeared to be stable
over the period of purported RSKW decline, with the estimated annual number
of deaths (6; 95% probability: 1–22) offset by the number of recruits (6;
2–19). As an alternative to the decline-due-to-fishery hypothesis, we
suggest that the presence of mega-iceberg B-15 at Ross Island during the
“iceberg years” (2000–2001 to 2005–2006) could have temporarily disrupted
normal RSKW movement patterns, resulting in an *apparent *decline.
Continued population monitoring of toothfish and their predators will be
important for assessing ecosystem impacts of commercial fishing in the Ross
Sea.



Link to full text article at: https://doi.org/10.1007/s00300-017-2239-4 or
PDF available from robert.pitman at noaa.gov


Robert Pitman
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