Baker et al Population characteristics of Meqaptera novaeanghae in southeastern Alaska 



435 



wise comparisons of years with the largest sample of 

 identified whales, 1984-86 and 1985-86 (see Table 1). 

 Regardless of the exact number of individuals inhab- 

 iting this region, the individual identification surveys 

 and mark-recapture estimates suggest that the south- 

 eastern Alaska herd increased from 1979 to 1986. In 

 Frederick Sound, overall survey effort decreased since 

 1981-82 but, with the exception of 1983 when only a 

 single 4-day survey was conducted, the number of iden- 

 tified whales increased. As confirmed by photographic 

 documentation, a general increase in the number of 

 whales in the Glacier Bay area during the last few years 

 was the result of the continued return of past residents 

 and the recruitment of their offspring (Baker et al. 

 1988). In terms of overall regional abundance, the 

 mark-recapture estimates from pair-wise comparisons 

 of 1986 to previous years suggest an increase from 484 

 to 606 across 1979-86, while estimates from contiguous 

 years suggest an increase from 307 to 606 (Table 1). 

 Requiring an annual rate of increase from 3.4 to 10.4%, 

 these trends in estimated abundance are within the 

 range reported for population growth of other unex- 

 ploited baleen whales based on individual identification 

 data (e.g., Hammond 1990, Best and Underbill 1990, 

 Bannister 1990). More accurate estimates of the cur- 

 rent abundance and the true rate of increase in the 

 southeastern Alaska subpopulation will require further 

 detailed analyses of survival rates and the biases in- 

 troduced by heterogeneity of identification records. 

 Although apparently sufficient to sustain some de- 

 gree of population growth, the observed reproduction 

 rate of humpback whales in southeastern Alaska seemed 

 low in comparison with other studied populations and 

 to the maximum reproductive potential of 0.50, or even 

 1.00 (calves/mature female • year M as observed in 

 some individually identified females (Darling 1983, 

 Glockner-Ferrari and Ferrari 1984 and 1990, Baker et 

 al. 1987, Clapham and Mayo 1987 and 1990, Straley 

 1989). The estimated calving rate of 0.36 (calves/mature 

 female- year- 1) across the 1980-86 study suggests 

 that females from this region give birth to a calf that 

 survives its first migration from the wintering grounds 

 about once every 2.8 years. In the Gulf of Maine, 

 Clapham and Mayo (1990) report an average reproduc- 

 tion rate of 0.41 (calves/mature female • year" ' ) and an 

 average calving interval of 2.35 years for the period 

 1979-87, using individual identification methods sim- 

 ilar to those used here. Pregnancy rates from exploited 

 populations, as summarized by Baker et al. (1987), all 

 exceed the estimated calving rate for southeastern 

 Alaska, although this historical comparison is con- 

 founded by differences in methodology. 



Seasonal trends and foraging strategies 



The number of whales identified in Glacier Bay and Icy 

 Strait was greatest during late June and early July, 

 and declined through August and September. Since 

 survey effort in Glacier Bay was high relative to total 

 number of whales identified, and constant throughout 

 the study period, we believe that trends in the month- 

 ly censuses or counts of individuals reflected changes 

 in seasonal abundance for this subregion. Although 

 surveys of Frederick Sound were not frequent enough 

 to track the seasonal increase in whales during early 

 summer, the greatest numbers of whales were found 

 during late July and August, approximately 1 month 

 after the local peak in Glacier Bay. 



We could not determine if these seasonal trends 

 reflect primarily changes in the timing of migratory 

 arrival on the feeding grounds or the pattern of local 

 movement among subregions of southeastern Alaska. 

 Within the geographic limits of our surveys, seasonal 

 changes in influx were accompanied by some local 

 movement between subregions; the decline in numbers 

 of whales in Glacier Bay was, in part, the result of their 

 relocation to Frederick Sound. Studies in previous 

 years also demonstrated that local movement between 

 these subregions tends to be one-directional, resulting 

 in the whales congregating in Frederick Sound during 

 late summer and fall (Baker 1984, Perry et al. 1985, 

 Krieger and Wing 1986). Large areas of available 

 habitat in southeastern Alaska remain entirely un- 

 surveyed (see Fig. 1), including the outer coast of 

 Baranof Island and the inside passage to the south of 

 Frederick Sound. The increase in percentage of newly- 

 identified whales during the late-fall survey of 1986 

 suggests local movement from these unsurveyed 



areas. 



Local movement may be an attempt to take advan- 

 tage of seasonal changes in prey availability. Hump- 

 back whales in Frederick Sound fed almost entirely on 

 euphausiids while those in Glacier Bay fed almost en- 

 tirely on schooling fish. Movement from Glacier Bay 

 to Frederick Sound was presumably accompanied by 

 a shift in primary prey species. Similar contrasts in the 

 primary prey species of whales in these two subregions 

 have been documented in previous years (Krieger and 

 Wing 1984 and 1986). Some whales, however, showed 

 a strong preference for particular prey species or local 

 habitat throughout the summer. This was indicated by 

 the persistence of certain individual whales feeding on 

 herring in Icy Strait late through the summer, when 

 other whales had moved to feed on euphausiids in 

 Frederick Sound. 



