FISHERY BULLETIN: VOL. 81, NO. 2 



not be identified. Even in the presence of such 

 limitations, feces collection and prey hard part iden- 

 tification can provide useful information on the prey 

 species being used by seals (Pitcher 1980b). 



SUMMARY AND CONCLUSIONS 



The seasonal abundance of harbor seals auling out 

 in Tillamook Bay displayed a general peak during 

 June, July, and August, coincident with the pupping 

 and molting periods. These high counts did not coin- 

 cide with the fall peak in salmonid abundance in the 

 bay. Two other factors may be more important in 

 regulating seal abundance here: 1) High densities of 

 many smaller fish species, known to be seal prey, oc- 

 cur during the summer months, and 2) Tillamook Bay 

 provides the habitat preferred by seals during the 

 pupping season. 



The peak in the seasonal abundance of harbor seals 

 at Netarts Bay coincided with the return of chum 

 salmon to the Whiskey Creek hatchery during the 

 months of October and November. Conditions for 

 successful predation were ideal here: Shallow water, 

 narrow channels, the concentrating effect that occurs 

 as salmon funneled into the creek, and a general lack 

 of disturbance to feeding harbor seals. Compared 

 with the fall, the lower numbers of harbor seals 

 hauled out during the spring months may indicate 

 that Netarts Bay was not a highly preferred 

 pupping area. 



The estimated losses to the Netarts Bay chum 

 salmon returns through harbor seal predation at 

 Whiskey Creek (1.5-7.2% per year) might have been 

 tolerated if numbers of returning chum salmon were 

 great enough to provide ample brood stock for future 

 releases (Lannan 14 ). However, while an attempt was 

 being made to build the stock, any loss of eggs 

 through predation on female spawners was con- 

 sidered serious. 



Recovery and identification of prey hard parts from 

 feces indicated that while feeding in Netarts Bay and 

 in coastal waters, harbor seals appeared to select fish 

 species that were found near the bottom of the water 

 column. The seven top-ranking food items were 

 benthic or epibenthic species, or, as in the case of the 

 Pacific sand lance, spent at least some time closely 

 associated with the bottom (Howe 1980). 



As evidenced by movements of tagged animals, in- 

 terchange of harbor seals between coastal estuaries 

 was common and occurred up to distances of at least 



14 J. E. Lannan, Department of Fisheries and Wildlife, Oregon State 

 University, Marine Science Center, Newport, OR 97365, pers. 

 commun. March 1980. 



550 km. Groups of harbor seals hauling out in dif- 

 ferent estuaries apparently do not represent isolated 

 stocks, but may instead be part of a common popula- 

 tion of animals. The movements of harbor seals were 

 seemingly related to the use of particular areas 

 specifically preferred by harbor seals for feeding, for 

 birth and care of young, or for both. 



ACKNOWLEDGMENTS 



We are indebted to J. Harvey for his invaluable con- 

 tribution of ideas and skills during planning, field, 

 and reporting stages of this project; to J. Lannan and 

 the Department of Fisheries and Wildlife at Oregon 

 State University for use of the Fisheries Research 

 Station at Netarts Bay; to J. Fitch for identification of 

 otoliths and to C. Bond for identification of teeth of 

 seal prey species; and to D. Herzing and the many in- 

 dividuals who donated their time and energy in the 

 field. N. Brown typed drafts and the final manuscript. 

 We are grateful to B. Antonelis, R. DeLong, D. 

 DeMaster, J. Gilbert, M. Johnson, T. Loughlin, K. 

 Pitcher, and Washington Department of Game 

 Marine Mammal Project personnel for critical review 

 of manuscript drafts. This work is a result of research 

 sponsored by the Oregon State University Sea Grant 

 College Program supported by NOAA Office of Sea 

 Grant, U.S. Department of Commerce, under grant 

 no. NA79AA-D-00106. 



LITERATURE CITED 



Bigg, M. A. 



1969. The harbour seal in British Columbia. Fish. Res. 

 Board Can., Bull. 172, 33 p. 

 Bonner, W. N., and S. R. Witthames. 



1974. Dispersal of common seals (Phoca vitulina), tagged 

 in the Wash, East Anglia. J. ZooL (Lond.) 174:528-531. 

 Boulva, J., and I. A. McLaren. 



1979. Biology of the harbor seal, Phoca vitulina, in eastern 

 Canada. Fish. Res. Board Can., Bull 200, 24 p. 

 BOWLBY, C. E. 



1981. Feeding behavior of pinnipeds in the Klamath River, 

 northern California. M.A. Thesis, Humboldt State Univ., 

 Areata, Calif., 74 p. 

 Brown, R. F. 



1981. Abundance, movements and feeding habits of the 

 harbor seal, Phoca vitulina, at Netarts Bay, Oregon. M.S. 

 Thesis, Oregon State Univ., Corvallis, 69 p. 

 Demory, R. L. 



1971. Depth distribution of some small flatfishes off the 

 northern Oregon-southern Washington coast. Res. Rep. 

 Fish. Comm. Oreg. 3:44-48. 

 DlVINYI, C. A. 



1971. Growth and movements of a known-age harbor seaL J. 

 Mammal. 52:824. 

 EVERITT, R. D., C. H. FlSCUS, AND R. L. DELONG. 



1979. Marine mammals of the northern Puget Sound and the 



300 



