[MARMAM] Hawaii Peponocephala stranding report available

MARMAM Editors marmamed at uvic.ca
Sat Apr 29 16:26:33 PDT 2006


Southall, B.L., R. Braun, F.M.D. Gulland, A.D. Heard, R.W. Baird, S.M.
Wilkin and T.K. Rowles. 2006. Hawaiian melon-headed whale (Peponocephala
electra) mass stranding event of July 3-4, 2004. NOAA Technical Memorandum
NMFS-OPR-31. 73 pp.

Available from http://www.nmfs.gov/pr/health/mmume/event2004jul.htm

Executive Summary

On July 3-4, 2004, between 150-200 melon-headed whales (Peponocephala
electra) occupied the shallow waters of Hanalei Bay, Kaua'i, Hawai'i for
over 28 hours. Attendees of a canoe blessing observed the animals entering
the Bay in a single wave formation at 0700 hrs* (local time) on July 3,
2004. The animals were observed moving back into shore from the mouth of
the Bay at 0900 hrs. The usually pelagic animals milled in the shallow
confined bay and were returned to deeper water with human assistance. The
animals were herded out of the Bay with the help of members of the
community, the Hanalei Canoe Club, local and federal employees, and
volunteers/staff with the Hawaiian Islands Stranding Response Group
beginning at 0930 on July 4, 2004 and were out of visual sight by 1030
hrs.

Only one animal, a calf, was known to have died (on July 5, 2004)
following this event. The animal was noted alive and alone in the Bay on
the afternoon of July 4, 2004 and was found dead in the Bay the morning of
July 5, 2004. On July 7, 2004, a full necropsy, magnetic resonance
imaging, and computerized tomography examination were performed on the
calf to determine the manner and cause of death. The combination of
imaging, necropsy and histological analyses found no evidence of
infectious, internal traumatic, congenital, or toxic factors. Although
cause of death could not be definitively determined, it is likely that
maternal separation, poor nutritional condition, and dehydration
contributed to the final demise of the animal. Although we do not know
when the calf was separated from the female, the movement into the Bay,
the milling and re-grouping may have contributed to the separation or lack
of nursing especially if the maternal bond was weak or this was a
primiparous calf.

Environmental factors, abiotic and biotic, were analyzed for any anomalous
occurrences that would have contributed to the animals entering and
remaining in Hanalei Bay. The bathymetry is similar to many other sites
within the Hawaiian Island chain and dissimilar to that which has been
associated with mass strandings in other parts of the U.S. The weather
conditions appear to be normal for this time of year with no fronts or
other significant features noted. There was no evidence for unusual
distribution or occurrence of predator or prey species, or unusual harmful
algal blooms. Weather patterns and bathymetry that have been associated
with mass strandings elsewhere were not found to occur in this instance.

This event was spatially and temporally correlated with Rim of the Pacific
Exercises (RIMPAC) which is a biennial, sea control/power projection fleet
exercise that has been conducted since 1968 and involves U.S. forces and
forces from various Rim-of-the-Pacific nations. Official sonar training
and tracking exercises in the Pacific Missile Range Facility (PMRF)
warning area did not commence until approximately 0800 hrs (local time) on
July 3 and were thus ruled out as a possible trigger for the initial
movement into the Bay.

However, the six naval surface vessels transiting to the operational area
on July 2 intermittently transmitted active sonar [for ~9 hours total from
1315 to 0030] as they approached from the south. The potential for these
transmissions to have triggered the whales' movement into Hanalei Bay was
investigated. Analyses with the information available indicated that
animals to the south and east of Kaua'i could likely have detected active
sonar transmissions on July 2, and reached Hanalei Bay on or before 0700
on July 3, 2004. However, data limitations regarding the position of the
whales prior to their arrival in the Bay, the magnitude of sonar exposure,
behavioral responses of melon-headed whales to acoustic stimuli, and other
possible relevant factors preclude a conclusive finding regarding the role
of sonar in triggering this event. Propagation modeling suggest that
transmissions from sonar use during the July 3 exercise in the PMRF
warning area may have been detectable at the mouth of the Bay. If the
animals responded negatively to these signals, it may have contributed to
their continued presence in the Bay. The U.S. Navy ceased all active sonar
transmissions during exercises in this range on the afternoon of July 3,
2004. Subsequent to the cessation of sonar use, the animals were herded
out of the Bay.

While causation of this stranding event may never be unequivocally
determined, we consider the active sonar transmissions of July 2-3, 2004,
a plausible, if not likely, contributing factor in what may have been a
confluence of events. This conclusion is based on: (1) the evidently
anomalous nature of the stranding; (2) its close spatiotemporal
correlation with wide-scale, sustained use of sonar systems previously
associated with stranding of deep-diving marine mammals; (3) the directed
movement of two groups of transmitting vessels toward the southeast and
southwest coast of Kaua'i; (4) the results of acoustic propagation
modeling and an analysis of possible animal transit times to the Bay; and
(5) the absence of any other compelling causative explanation. The
initiation and persistence of this event may have resulted from an
interaction of biological and physical factors. The biological factors may
have included the presence of an apparently uncommon, deep-diving cetacean
species (and possibly an offshore, non-resident group), social
interactions among the animals before or after they entered the Bay,
and/or unknown predator or prey conditions. The physical factors may have
included the presence of nearby deep water, multiple vessels transiting in
a directed manner while transmitting active sonar over a sustained period,
the presence of surface sound ducting conditions, and/or intermittent and
random human interactions while the animals were in the Bay.



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