SC/M05/BR6
Relationship between Bryde’s whales to be surveyed and harvested in thewestern North Pacific and those in Southern Hemisphere stock
Luis A. Pastene
Institute of Cetacean Research,
Toyomi 4-5, Chuo-ku,
Tokyo 104-0055, JapanINTRODUCTION
Annotations of the draft agenda for the intersessional workshop for North PacificBryde’s whales encouraged papers on the relationships between the whales to besurveyed and harvested and those in Southern Hemisphere Stock. Discussions on thistopic conducted at the Scientific Committee meetings are summarized.
RELEVANT ISSUES DISCUSSED ATSCIENTIFIC COMMITTEE MEETINGSz A paper was presented in 1995 that summarized relevant information ondistribution of Bryde`s whales based on sighting data collected during 37 cruises
conducted in August and September, 1988-1994 (SC/47/NP9). During thediscussion of that paper it was suggested that the apparent equatorialconcentration of whales during the austral winter may include some whales fromSouthern Hemisphere populations.
Mark-recapture analyses conducted for Western North Pacific Stock of Bryde`swhales strongly indicate an annual north-south migration between northern summergrounds and southern wintering grounds (SC/47/NP10; SC/50/RMP18). Some whales
marked in winter at 1°S were recovered in the summer whaling ground (see details inFor Info 14). An analysis that compared Japanese Bryde`s whale catches and fishingeffort data with the corresponding sightings information (SC/51/RMP14) confirmed aseasonal south to north migration beginning in February and the return southward
beginning in October.
By analogy a similar pattern of movement can be postulated for Bryde`s whales of theWestern South Pacific Stock. Therefore mixing of animals from the two stocks areminimized because of the complementary north-south migrations in the twohemispheres. The winter ranges of northern and southern hemispheres stocks may,
however, extend a few degrees into the other hemisphere, respectively.
To deal with this situation, southern boundary of sub-area 1 in the trial specifications
has been set at 10°N so that harvest and surveys are assumed to occur north of 10°N.
z In 1998 a genetic paper based on mtDNA control region sequences was presented(SC/50/RMP9). While no significant genetic differences were found among two
longitudinal sectors in the western North Pacific, striking differences were found1

between Western North Pacific and Western South Pacific (represented by whales
from the Fiji Islands) Stocks (SC/50/RMP9). In discussion of this paper it wassuggested the possibility of trans-equatorial movement because the two stocks
shared some haplotypes. During the 2004 Committee meeting this possibility wasreiterated and the reason given was that some Bryde`s whales sampled in markets
in Japan shared the same haplotypes with Bryde`s whales found off New Zealand.

DNA analyses based on both mtDNA and microsatellite have shown striking genetic
differences between whales from the Western North Pacific and Western South
Pacific (SC/50/RMP9; SC/54/O17 Appendix 10). These differences should not be sostriking if some degree of mixing occurs. Whales from the two stocks share some few
mtDNA haplotypes. However shared haplotypes is insufficient to form conclusions on
movement between hemispheres. Time of divergence could not be large enough toaccumulate unique genetic characters in these populations.
z Other current restriction on whaling in the North Pacific includes an IWC
restriction on whaling south of 20°N to protect the breeding area (JCRM 2, pp89).
This would restrict harvest south of 20°N, but surveys for assessment should
account for regions from 10°N to the north.
CONCLUSION
Given these biological and technical aspects, it is considered that no furtherspecifications to account for concerns on movement/mixing of whales from the twohemispheres are necessary in the trials.

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