Calambokidis et al.: Distribution and abundance of marine mammals off the northern Washington coast 



577 



whaling; humpback whales were commonly observed in 

 the inside waters of Washington and British Columbia 

 (Scheffer and Slipp, 1948; Webb, 1988) and have not 

 returned to these areas in any numbers (Calambokidis 

 and Steiger, 1990). 



The distribution of humpback whales within our study 

 area was not uniform and indicated that some specific 

 areas were important feeding habitat for this recovering 

 species. The region between the Juan de Fuca Canyon 

 and the shelf edge (the Prairie) — the mouth of Bark- 

 ley Canyon and Swiftsure Bank — was the area where 

 humpback whales were concentrated. In monthly aerial 

 surveys in 1989-90 by Green et al., 5 there were only a 

 total of 13 sightings of 25 humpback whales along the 

 entire Washington coast between July and September. 

 Over half of those sightings were in the Prairie area. 



Our line-transect estimates revealed that about 100 

 humpback whales inhabit the northern Washington 

 coast waters each summer; substantially more (over 

 500), however, were present in 2002. Although this is a 

 small number compared to estimates of just under 1000 

 humpback whales for California, Oregon, and Wash- 

 ington (Calambokidis and Barlow, 2004), our study 

 area encompasses a relatively small area and reflects a 

 high density of animals. Additionally our line-transect 

 estimates were not corrected for any missed animals; 

 therefore they are probably biased slightly downward. 



Despite the relatively high density of humpback 

 whales in this region, the photographic identification 

 data indicated that a relatively small number of indi- 

 viduals use the area consistently. Both the line-transect 

 and the photographic identification data (increasing 

 capture-recapture estimates, as well as decreased pro- 

 portions of animals sighted multiple years) showed that 

 the number of whales using this region has increased in 

 recent years. The growing number of whales in this re- 

 gion could be either the result of births or immigration 

 into this area. Births alone could not account for this in- 

 crease, especially because the proportion of whales that 

 were mothers with calves seen in this region was not 

 high. There did not appear to be a shift in distribution 

 of animals from areas to the south because interchange 

 with those areas dropped from 1999 to 2002. The most 

 likely explanation for these changes is that there was a 

 shift of animals from feeding areas from the north into 

 this region beginning in the late 1990s. 



This interchange of humpback whales with feeding ar- 

 eas to the south provides new insight into the structure 

 of humpback whale feeding aggregations. In a study 

 that examined interchange rates of humpback whales 



6 Green, G. A., J. J. Brueggeman, R. A. Grotefendt, and C. 

 E. Bowlby. 1992. Cetacean distribution and abundance 

 off Oregon and Washington, 1989-1990. In Oregon and 

 Washington marine mammal and seabird surveys (J. J. 

 Brueggeman, ed. I, 100 p. Final report of OCS Study MMS 

 91-0093 by Ebasco Environmental, Bellevue, Washington, 

 and Ecological Consulting, Inc., Portland, Oregon, for the 

 Minerals Management Service, Pacific OCS Region, U.S. 

 Dept. of Interior, 770 Paseo Camarillo, Camarillo, CA 

 93010. 



along the west coast, Calambokidis et al. (1996) iden- 

 tified northern Washington as a demographic bound- 

 ary between the whales feeding area along California, 

 Oregon, and Washington and those to the north. The 

 larger sample reported here shows the same general 

 pattern of decreasing interchange with distance from 

 a feeding area as that reported previously for whales 

 off California (Calambokidis et al., 1996). The decreas- 

 ing rate of interchange with distance among feeding 

 areas does not allow for a clear demarcation between 

 feeding areas, however, as suggested by Calambokidis 

 et al. (1996). Although humpback whales demonstrate 

 site fidelity to specific feeding locations, their feeding 

 aggregations may not have clear boundaries and may 

 occupy overlapping ranges. 



The commercial whaling data also tended to support 

 the existence of somewhat discrete feeding areas off the 

 west coast of the United States and British Columbia. 

 Commercial whaling resulted in the depletion of hump- 

 back whales off British Columbia by 1917, whereas the 

 numbers taken off Washington and California did not 

 decline until the mid-1920s (Scheffer and Slipp, 1948; 

 Clapham et al., 1997; Gregr et al, 2000). 



The relatively small proportion of mothers with calves 

 identified in our study is consistent with findings off 

 California and Oregon (Steiger and Calambokidis, 

 2000). Steiger and Calambokidis reported reproductive 

 rates along the California, Oregon, and Washington 

 coasts that are lower than those reported for other re- 

 gions in southeastern Alaska and the North Atlantic 

 (Clapham and Mayo, 1987, 1990; Baker et al., 1992; 

 von Ziegesar et al., 1994). In aerial transect surveys, 

 no humpback whale calves were seen among the 68 

 humpbacks observed off the Oregon and Washington 

 coasts in 1989-90 (Green et al. 5 ). If geographic segre- 

 gation is occurring by humpback mothers and calves, 

 as was suggested by Steiger and Calambokidis (2000), 

 this northern region is not the area where mothers and 

 calves are congregated. It is interesting to note, how- 

 ever, that mothers and calves were distributed around 

 the periphery of the main feeding region — a finding that 

 suggests that a more local segregation may be occurring. 

 A bias in sampling would occur if large concentrations of 

 whales are targeted and mother with calves feeding on 

 the perimeter of these groups were underrepresented. 



In contrast to humpback whales, no other large ror- 

 quals (blue, fin, or sei whales) were observed during 

 any of our ship or small boat surveys. Likewise, these 

 species were absent in other recent surveys of Wash- 

 ington waters (Wahl, 1977; Von Saunder and Barlow. 

 1999; Shelden et al., 2000; Green et al. 5 ), although 

 they were seen in surveys farther offshore in surveys in 

 July 1994 (Thomason et al. 6 ). Fin whales were common 



,; Thomason, J., M. Dahlheim, S. E. Moore, J. Braham, K. 

 Stafford, and C. Fox. 1997. Acoustic investigations of 

 large cetaceans off Oregon and Washington: NOAA ship 

 Surveyor (21 July-1 August 1994), 27 p. Final report by 

 the National Marine Mammal Laboratory, 7600 Sand Point 

 Way NE F/AKC3, Seattle. WA 98115. 



