1999 

 OUR LIVING OCEANS 



Humpback whale. Southeast 

 Alaska. 



cal power to detect trends remains low. Indica- 

 tions of a decline were most evident in the south- 

 ern part of central California, between Point Con- 

 ception and Monterey Bay. A real popidation de- 

 cline would be somewhat surprising since fishery 

 mortality has been declinmg during this same time 

 period. Harbor porpoise abundance appears to be 

 correlated with changes in sea surface temperature, 

 and apparent trends could be caused by changing 

 oceanographic conditions. 



Status of Stock 



The estimated PBR of 3.i animals for this stock 

 is calculated as the product of one half of the mini- 

 mum population estimate (3,431), one-half the 

 default maximum net growth rate for cetaceans 

 (4%), and a recovery factor of 0.48 (for a species 

 of unknown status with a mortality rate coeffi- 

 cient of variation equal to 0.44). 



The harbor porpoise in CLilifornia is not listed 

 as rhrcatened or endangered under the ESA nor as 

 depleted under the MMPA. Calculation of har- 

 bor porpoise status relative to historic carrying ca- 

 pacity suggests that the central ("alifornia popula- 

 tion could have been reduced to between 30% and 

 97% of its carrying capacity by incidental fishing 

 mortality. Present information is insufficient to 

 narrow the range of this estimate, and the status 

 of harbor porpoise relative to their OSP levels in 

 central California is unknown. The average mor- 

 tality rate of 14 animals over the past 3 years is 

 less than the calculated PBR (33 animals) for cen- 

 tral California harbor porpoise; thus, the central 

 California harbor porpoise population is not con- 

 sidered a strategic stock under the K4MPA. The 

 Pacific Scientific Review Group (established by the 

 MMPA) recommended, however, that this stock 

 be considered strategic because it appears to be in 

 decline and may be listed as threatened under the 

 Endangered Species Act unless this trend is 

 stopped. Because fishery mortality has been re- 

 duced over the past 10 years and because there is 

 some indication that the decline in animals may 

 be due to natural causes, the NMFS does not be- 

 lieve that a strategic status is justified at this time. 

 Research will continue to monitor this population 

 si/.e and to imestigate the possible causes of its 

 decline. 



HUMPBACK WHALE: CALIFORNIA/ 

 OREGON/WASHINGTOIM-MEXICO STOCK 



Stock Definition and Geographic Range 



Four relatively separate migrator\' populations 

 of humpback whales have been identified in the 

 North I'acific based on sightings of distinctively 

 marked individuals. Ehese are the coastal ("alitor- 

 nia/Oregon/Washington-Mexico stock, the 

 Mexico offshore island stock (feeding destination 

 unknown), the central North Pacific stock (Ha- 

 waii/Alaska), and the western North Pacific stock 

 (Japan/feeding destination probably the Aleutian 

 Islands). The California/Oregon/Washington- 

 Mexico stock ranges from Costa Rica to southern 

 British Columbia hut is most common in coastal 

 waters of C'alifornia (in summer and fall) and 

 Mexico (in winter and spring). 



Significant levels of genetic differences exist 

 between the California and Alaska feeding groups 

 based on analyses of mitochondrial DNA and 

 nuclear DNA. The genetic exchange rate between 

 California and Alaska is estimated to be less than 

 one female per generation. Genetic profiles from 



242 



