BROWN and MATE: ABUNDANCE, MOVEMENTS OF HARBOR SEALS 



400 



300 



CO 



_i 

 < 



UJ 

 CO 



o 



200 



100 



\-\ / 



/ J 



■.-"- /V ,''\ 



/ /-\ \ 



-"^T ...-t-.rrrrrr -/• / \\ \ 



V. \ 



\x 



v / 



\ / 



V 



x 1978 



• 1979 



+ 1980 



o |98I 



1978 



1979 273 



1980 183 



1981 246 



200 



195 

 307 



M 



304 

 138 

 325 



285 

 260 

 359 



M 



392 

 312 

 330 



444 

 353 

 314 

 456 



262 

 353 

 394 

 390 



375 

 485 

 434 



414 



437 

 289 

 386 



310 



273 

 191 

 316 

 236 



N 



260 

 255 

 250 

 220 



229 

 207 

 198 



FIGURE 3.— Seasonal abundance of harbor seals at Tillamook Bay, Oreg., shown by a plot of monthly mean numbers of seals hauled out in the 

 bay. Listed at bottom of figure are monthly maximum numbers of seals observed on haul-out areas. 



desirable for birth and care of young. Beach et al. 9 

 identified females with neonates in Grays Harbor 

 and Willapa Bay, Wash., and in Tillamook Bay, Oreg., 

 (Jeffries footnote 4) that were tagged as pregnant 

 females in the Columbia River. No pups were ob- 

 served in the Rogue River and very few were seen in 

 the Columbia River. Peaks in seasonal abundances of 

 harbor seals during the winter months have been ob- 

 served in the Rogue (Roffe 1981) and Columbia 

 Rivers (Everitt and Jeffries 10 ), although this pattern 

 has been less commonly reported. 

 Local changes in harbor seal abundance may occur 

 in response to variations in the availability of food 

 (Scheffer and Slipp 1944; Fisher 1952; Graybill 

 1981). Beach et al. (footnote 9) suggested that the 



'Beach, R. J., A. C. Geiger, S. J. Jeffries, and S. D. Treacy. 1982. 

 Marine mammal-fisheries interactions on the Columbia River and 

 adjacent waters, 198 1. Second Annual ReportNovember 1 , 1980 to 

 November 1,1981. Wash. State Dep. Game to Northwest and Alas- 

 ka Fish. Cent, Natl. Mar. Mammal Lab., Natl. Mar. Fish. Serv., 

 NOAA, Seattle, WA 98115. NWAFC Proc. Rep. 82-04, 186 p. 



10 Everitt, R. D., and S. J. Jeffries. 1979. Marine mammal inves- 

 tigations in Washington State. In Abstracts from presentations at 

 the Third Biennial Conference of the Biology of Marine Mammals, 

 October 7-11, 1979, Seattle, Wash., p. 18. 



winter increase in harbor seal abundance in the 

 Columbia River occurred in response to the presence 

 of eulachon, Thaleichthys pacificus, in the river at 

 that time. At Netarts Bay, the late fall return of chum 

 salmon constitutes the only regular occurrence of a 

 salmonid species in the Bay (Lannan footnote 2). The 

 coincidence of peak harbor seal abundance and the 

 chum salmon run suggests that this highly seasonal 

 food source may have influenced harbor seal abun- 

 dance in the bay. 



At Tillamook Bay, seasonal peaks in harbor seal 

 numbers and salmonid abundance did not coincide. 

 The numbers of harbor seals declined to low annual 

 levels from September through December while 

 steelhead, Salmo gairdneri; chinook salmon, On- 

 corhynchus tshawytscha; coho salmon, 0. kisutch; 

 and chum salmon were passing through the estuary 

 (Heckeroth 11 ). High counts of harbor seals during the 

 summer did, however, coincide with peaks in annual 

 abundances of northern anchovy, Engraulis mordax; 



"D. Heckeroth, Oregon Department of Fish and Wildlife, 6617 

 Officers Row, Tillamook, OR 97141, pers. commun. September 

 1978. 



295 



