[Marmam] Hawaii false killer whales and the long-line fishery

Robin W. Baird rwbaird at cascadiaresearch.org
Sat Aug 27 13:24:37 PDT 2005


The following new publication is available as a pdf from
http://www.cascadiaresearch.org/robin/hawaii.htm

Baird, R.W., and A.M. Gorgone. 2005. False killer whale dorsal fin
disfigurements as a possible indicator of long-line fisherey interactions in
Hawaiian waters. Pacific Science 59:593-601.

Abstract: Scarring resulting from entanglement in fishing gear can be used
to  examine cetacean fishery interactions. False killer whales (Pseudorca
crassidens) are known to interact with the Hawai'i-based tuna and swordfish
long-line fishery in offshore Hawaiian waters. We examine the rate of major
dorsal fin disfigurements of false killer whales from near-shore waters
around the main Hawaiian Islands to assess the likelihood that individuals
around the main islands are part of the same population that interacts with
the fishery. False killer whales were encountered on 11 occasions between
2000-2004, and 80 distinctive individuals were photographically documented.
Three of these (3.75%) had major dorsal fin disfigurements (two with the
fins  completely bent over and one missing the fin). Information from other
research suggests that the rate of such disfigurements for our study
population may be more than four times greater than for other odontocete
populations. We suggest the most likely cause of such disfigurements are
interactions with long-lines, and that false killer whales found in
nearshore  waters around the main Hawaiian Islands are part of the same
population that  interacts with the fishery. Two of the animals documented
with disfigurements  had infants in close attendance and were thought to be
adult females. This  implies that even with such injuries, at least some
females may be able to  produce offspring, despite the importance of the
dorsal fin in reproductive  thermoregulation.

In addition for those interested in false killer whales, there is a report
on  the same site examining inter-island movements and estimating population
size  of false killer whales around the main Hawaiian islands (abstract
below).  This research is on-going, and I would be interested in hearing
from anyone  working with this species in the wild.

Robin Baird

-------------------


Baird, R.W., A.M. Gorgone, D.L. Webster, D.J. McSweeney, J.W. Durban, A.D.
Ligon, D.R. Salden, and M.H. Deakos. 2005. False killer whales around the
main Hawaiian islands: an assessment of inter-island movements and
population  size using individual photo-identification. Report prepared
under Order No.  JJ133F04SE0120 from the Pacific Islands Fisheries Science
Center, National  Marine Fisheries Service.

The current best estimate of population size for false killer whales within
Hawaiian waters is only 268 individuals (Barlow 2003), though the estimate
is  not very precise (CV = 1.08). False killer whales are considered a
"strategic" stock by the National Marine Fisheries Service, as "takes" in
the  Hawai'i-based swordfish and tuna long-line fishery exceed the
"Potential  Biological Removal" (PBR) level. We studied false killer whales
as part of  small-boat based surveys for odontocetes around the main
Hawaiian islands  from 2000 through 2004, and in this report we assess
inter-island movements,  examine "mark" change over time on individual
animals, estimate the  proportion of marked individuals within the
population, and provide a  mark-recapture population estimate. Dedicated
surveys for odontocetes were  undertaken around all the main Hawaiian
islands, and all groups of false  killer whales encountered were approached
and attempts made to  photographically identify all individuals present.
False killer whales were  encountered on 14 occasions in directed surveys
(2.9% of all odontocete  sightings), in eight of the 10 months of the year
surveyed, and in three of  the four island-areas surveyed. Encounters were
in a wide range of water  depths (37 to 3,950 m). Photographs from seven
opportunistic encounters were  also available. Seventy-seven percent of
individuals photographed were  considered to have markings that could be
recognized in the long-term  (between-years). Seventy-six individuals with
such long-term markings were  documented, 47 of which were seen on two or
more occasions. Ten individuals  were documented with mark changes, though
the rate of mark change was low  (approximately one change every six years).
Re-sighting analysis suggest that  there are considerable inter-island
movements of individuals (for example, 19  of 21 individuals identified off
O'ahu have been recorded off the island of  Hawai'i or around the
"4-islands"). A multi-site mark-recapture analysis,  taking into the
proportion of marked individuals in the population, resulted  in an estimate
of 123 individuals in the population (CV = 0.72). This  estimate applies to
a population of false killer whales that used the study  area; however the
geographic range of that population is not known. Also, we  assumed
population closure and homogenous capture probabilities among  individuals.
The degree to which these assumptions may have been violated and  the
resulting estimate biased remain unclear.



============================================
Robin W. Baird, Ph.D.
Research Biologist
Cascadia Research Collective
218 1/2 W. 4th Avenue, Olympia, WA 98501 USA
http://www.cascadiaresearch.org/Robin/robin.htm
Phone 1-360-943-7325
Fax 1-360-943-7026
E-mail rwbaird at cascadiaresearch.org or rwbaird at dal.ca





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