626 



Aging fish otoliths recovered from 

 Pacific harbor seal iPhoca vitulina) 

 fecal samples 



Susan D. Riemer (contact author) 



Oregon Department of Fish and Wildlife 



1495 East Gregory Road 



Central Point, Oregon 97502 



Email address: SusanDRiemeriS'stateorus 



Robert Mikus 



Oregon Department of Fisfi and Wildlife 

 4412 Silverton Road NE 

 Salem, Oregon 97305 



Seals and sea lions are opportunis- 

 tic predators that feed on a variety 

 of fish and cephalopods, including 

 some commercially and recreation- 

 ally important species. Concerns over 

 their interactions with commercial 

 and sport fishing operations, and 

 other human activities, has a long his- 

 tory in the Pacific Northwest (Ever- 

 itt and Beach, 1982). The perceived 

 increase in such interactions led, in 

 part, to the U.S. Congress amending 

 the Marine Mammal Protection Act 

 (MMPA) m 1994. Chief among the 

 amendments was a call for research 

 to determine 1) whether California 

 sea lions (Zalophus californianus) and 

 Pacific harbor seals ^Phoca vitulina) 

 were affecting the recovery of listed 

 or depleted salmonids, and 2) what 

 broader impacts they may have on the 

 coastal ecosystems of Oregon, Wash- 

 ington, and California (NMFS, 1997). 

 In this note, we begin to address 

 the latter question. Specifically, we 

 describe a novel application of otolith 

 aging techniques that can be used to 

 increase the understanding of pin- 

 niped foraging ecology and, thus, 

 their potential impact on the fishery 

 resources of coastal ecosystems. 



The Oregon Department of Fish 

 and Wildlife's (ODFW) Marine Mam- 

 mal Research Program has studied 

 harbor seal foraging habits since 

 the mid-1980s, primarily through 

 the collection and analysis of scat 



(fecal) samples (Riemer and Brown, 

 1997; Riemer et al.^; Wright et al.-). 

 Our results, as well as those from 

 other pinniped food habit studies in 

 Oregon (Graybill, 1981; Brown and 

 Mate, 1983; Roffe and Mate, 1984; 

 Orr et al., 2004), indicate that these 

 animals consume a large number 

 of diverse prey species. Concurrent 

 research in Oregon indicates that 

 Pacific harbor seals have increased 

 significantly following protection un- 

 der the MMPA; Brown et al. (2005) 

 estimated that the 2002 statewide 

 population total was 10,087 indi- 

 viduals. As noted above, these types 

 of increases in pinniped abundance 

 have led to more frequent interac- 



1 Riemer, S. D., R. F. Brown, B. E. Wright, 

 and M. Dhruv. 2001. Monitoring 

 pinniped predation on salmonids at 

 Alsea River and Rogue River. Oregon: 

 1997-1999. Unpubl. Contract Rep. to 

 Pacific States Marine Fisheries Com- 

 mission, NCAA Grant No. NA87FX0464. 

 38 p. [Available from OR Dept. Fi.sh. 

 and Wild!., 7118 NE Vandenberg Ave., 

 Corvallis, OR 97330.1 



- Wright, B. E., R. F. Brown, S. D. Riemer, 

 and A. M. Ougzin. 2002. Pinniped pre- 

 dation on adult salmonids in the Alsea 

 Estuary, Oregon. Unpubl. Contract Rep. 

 to Pacific States Marine Fisheries Com- 

 mission, NOAA Grant No. NA17FX1603, 

 35 p. lAvailable from OR Dept. Fish, 

 and Wild]., 7118 NE Vandenberg Ave., 

 Corvallis, OR 97330.] 



tions with coastal fish resources and 

 hence an increased interest in the 

 composition and abundance of prey 

 in their diet. 



Fortunately, new techniques have 

 recently been developed to analyze 

 pinniped diets. For example, rather 

 than using traditional methods that 

 rely strictly on otoliths (fish ear 

 bones) for identifying prey, many 

 researchers now try to identify all 

 skeletal structures recovered from 

 scats, which provide a more complete 

 picture of pinniped diets (Olesiuk 

 et al., 1990; Cottrell et al., 1996; 

 Riemer and Brown, 1997; Browne 

 et al., 2002). In addition, research- 

 ers are beginning to use molecular 

 genetic methods to provide greater 

 resolution in determining diet com- 

 position (Purcell et al., 2004; Deagle 

 et al., 2005; Kvitrude et al, 2005). In 

 this note, we add to this growing list 

 of techniques by describing a novel 

 use of fish otolith aging techniques 

 to further our understanding of pin- 

 niped diets. 



Fisheries scientists have aged fish 

 otoliths to aid in the management of 

 commercial and recreational fisheries 

 (Love et al., 2002). Marine mammal 

 scientists, on the other hand, have re- 

 lied upon the identification of otoliths 

 recovered from scats to identify the 

 prey of pinnipeds (Brown and Mate, 

 1983; Beach et al.^; Harvey, 1989; 

 Pierce and Boyle. 1991). However, the 

 age of prey has rarely been consid- 

 ered when describing seal and sea 

 lion diets. We believe that estimates 



■'Beach, R. J., A. C. Geiger, S. J. 

 Jeffries, S. D. Treacy, and B. L. 

 Troutman. 1985. Marine mammals 

 and their interactions with fisheries of 

 the Columbia River and adjacent waters, 

 1980-1982. NWAFC ( Northwest Alaska 

 Fisheries Science Center) processed rep. 

 85-03, 316 p. NWAFC, National Marine 

 Fisheries Service, Northwest Region, 

 7600 Sand Point Way N.E., Seattle, WA 

 98115-0070. 



Manuscript submitted 1 June 2005 

 to the Scientific Editor's Office. 

 Manuscript approved for publication 

 29 November 2005 by the Scientific Editor 



Fish. Bull. 104:626-630 i2006l. 



