NOTE Riemer and Mikus Aging fish otoliths lecoveied from fecal samples of Phoca vilulina 



629 



to more accurately estimate appropriate fishing levels, 

 particularly for rockfish species (Love et al., 2002). This 

 information can also contribute to assessing the impact 

 of pinnipeds on these species and can improve stock 

 assessment models. Otolith age can provide informa- 

 tion on the size of fish consumed when the age-length 

 composition in the population or subgroup is available 

 (Salthaug, 2003). In addition, age estimates provide 

 information on the reproductive maturity of the prey 

 consumed. Aging will also provide a more accurate esti- 

 mate of the MNI of a particular prey species consumed 

 than an estimate based on the maximum number of left 

 or right otoliths of a similar size, particularly because 

 different age fish can have otoliths of approximately 

 the same size. 



Researchers should note that the digestive process 

 does cause erosion of otoliths and can result in under- 

 estimation of fish ages. We did not attempt to deter- 

 mine how otolith-based age estimates were affected by 

 erosion, but a carefully designed captive feeding study 

 would be able to address this issue in the future. How- 

 ever, because there are few other methods to determine 

 the age distribution of fish taken by pinnipeds, this 

 technique is useful when describing the diet of seals 

 and sea lions. 



Acknowledgments 



Funding for this project was provided by the National 

 Marine Fisheries Service, Northwest Regional Office 

 (with the assistance of the Pacific States Marine Fisher- 

 ies Commission) and the Oregon Department of Fish and 

 Wildlife, Marine Resources Program. We thank Bryan 

 Wright, Robin Brown, and Monique Lance for their sup- 

 port of this project and the editing of an earlier draft of 

 the manuscript. We thank Patty Burke and Mark Sael- 

 ens for their input and support. We extend our thanks to 

 our field staff Aicha Ougzin, Mark Dhruv, and Jonathon 

 Scordino. We also thank Mark Karnowski and William 

 Miller for their help with data and revisions. Finally, 

 we thank the two anonymous reviewers who provided 

 comments on this manuscript. 



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