The following article on killer whale attacks on humpback
whales as discerned through rake mark scars has recently been published:
Steiger,
G.H., J. Calambokidis, J.M. Straley, L.M. Herman, S. Cerchio, D.R. Salden, J.
Urbán-R, J.K. Jacobsen, O. von Ziegesar, K.C. Balcomb, C.M. Gabriele, M.E.
Dahlheim, S. Uchida, J.K.B. Ford, P. Ladron de Guevara-P, M. Yamaguchi and J.
Barlow. 2008. Geographic variation in killer whale attacks on
humpback whales in the North Pacific: implications for predation pressure.
Endangered Species Research 4:247-256.
ABSTRACT: We examined the incidence of rake mark scars
from killer whales Orcinus orca on the flukes of humpback whales Megaptera
novaeangliae throughout the North Pacific to assess geographic variation in
predation pressure. We used 3650 identification photographs from 16 wintering or
feeding areas collected during 1990 to 1993 to determine conservative estimates
in the percentage of whales with rake mark scarring. Dramatic differences were
seen in the incidence of rake marks among regions, with highest rates on
wintering grounds off Mexico (26 vs. 14% at others) and feeding areas off
California (20 vs. 6% at others), 2 areas between which humpback whales migrate.
Although attacks are rarely witnessed, the prevalence of scars demonstrates that
a substantial portion of animals are attacked, particularly those that migrate
between California and Mexico. Our data also suggest that most attacks occur at
or near the wintering grounds in the eastern North Pacific. The prevalence of
attacks indicates that killer whale predation has the potential to be a major
cause of mortality and a driving force in migratory behavior; however, the
location of the attacks is inconsistent with the hypothesis that animals migrate
to tropical waters to avoid predation. Our conclusion is that, at least in
recent decades, attacks are made primarily on calves at the wintering grounds;
this contradicts the hypothesis that killer whales historically preyed heavily
on large whales in high-latitude feeding areas in the North Pacific.
The article can be downloaded for free from the publishers website:
http://www.int-res.com/articles/esr2008/4/n004p247.pdf
or from Cascadia Research web site