Tollit et al.: A method to improve size estimates of Theragra chalcogramma and Pleurogrammus monopterygius 



507 



category, rather than on improving regression formulae. 

 For both prey species, QUAD in good condition and 

 OTO in fair condition, in addition to pollock INTE in 

 fair condition and Atka mackerel HYPO in fair condi- 

 tion, provided the most reliable estimates of prey size 

 (Table 2). DENT in fair condition, particularly for Atka 

 mackerel, provided the least reliable estimate of prey 

 size (Table 2). Measurement error was relatively insig- 

 nificant, but attention should be taken when measuring 

 ANGU and HYPO (Tollit et al., 2004, this issue). 



Companion studies by Tollit et al. (2004, this issue) 

 and Zeppelin et al. (2004, this issue) demonstrate the 

 feasibility of applying DCFs to structures other than 

 otoliths and the need to consider the degree of diges- 

 tion to correctly estimate the length of prey eaten by 

 pinnipeds and other piscivores. Applying appropriate 

 digestion correction factors will lead to more refined 

 estimates of consumption (mass of prey) by marine 

 mammals, as well as the extent of potential overlap 

 (length of prey) with the length of fish caught by com- 

 mercial fisheries. 



Acknowledgments 



Funding was provided to the North Pacific Universities 

 Marine Mammal Research Consortium by the National 

 Oceanographic Atmospheric Administration and the 

 North Pacific Marine Science Foundation. We would 

 like to thank the marine mammal trainers and staff of 

 the Vancouver Aquarium Marine Science Centre, the 

 contribution of personnel of the UBC Marine Mammal 

 Research Unit of the UBC EM facility, J. L. Laake for 

 statistical advice, T. J. Orchard, C. J. Gudmundson, S. J. 

 Crockford, M. Wong, E. H. Sinclair, and two anonymous 

 reviewers. We would also like to express gratitude to the 

 organizations and companies that have donated fish to 

 the project. Work was undertaken in accordance with 

 UBC Animal Care Committee guidelines. 



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