FISHERY BULLETIN: VOL. 85, NO. 4 



may be sufficiently allometric for the symphyseal 

 knob to seem exceptionally prominent and the 3d 

 anal-fin spine exceptionally small in some large 

 specimens. 



Most body dimensions average smaller in fe- 

 males than in males, but bellies are larger in 

 females. The same mechanism, opposing rela- 

 tional movements of the pelvic girdle and the 

 anal-fin spines, is responsible for sexual and geo- 

 graphic variation in belly size. Although sexual 

 dimorphism increases with growth, sexual differ- 

 ences are not prominent and have broadly over- 

 lapping distributions. As a result, sexes probably 

 cannot be reliably identified by gross examina- 

 tion of any of the 18 characters. 



Neither geographic nor sexual variation is 

 quantitatively similar between measurements in 

 Pacific ocean perch — characters tend to vary with 

 their absolute size. Overall, geographic variation 

 is most poorly discriminated by the measure- 

 ments of the 3d anal-fin spine, symphyseal knob, 

 and 6th spinous ray in dorsal fin, and best dis- 

 criminated by the belly, hind-trunk ventral, and 

 head. Sexual dimorphism is most poorly discrimi- 

 nated by the measurements of the hind-trunk 

 dorsal, spinous dorsal-fin length, and body-depth 

 pelvic, and best discriminated by the belly, hind- 

 trunk ventral, and pelvic insertion. Measure- 

 ments that have been used for taxonomy of 

 Pacific ocean perch in the past are relatively poor 

 discriminators of geographic variation or possible 

 genetic stocks or subspecies. Although body form 

 changes significantly with geographic region, 

 sex, and growth, differences are too small and 

 unexplained variation too large for differences to 

 be of value for distinguishing single specimens 

 geographically. 



Because of questions concerning validity and 

 importance of published morphological informa- 

 tion supporting supposed subspecies of Pacific 

 ocean perch, it seems prudent that further claims 

 for subspecies based on morphology be postponed 

 until variation is reliably assessed over the entire 

 species' range and definitive characteristics are 

 known to be genetically based. 



ACKNOWLEDGMENTS 



My special thanks to Elizabeth Lu Hall for her 

 exacting work in converting photographic images 

 into data and to Richard E. Haight and Richard 

 H. Carlson, also of the Auke Bay Laboratory, for 



assistance in photographing the specimens. Many 

 of the photographs were taken aboard the Univer- 

 sity of Hokkaido Faculty of Fisheries' RV Oshoru 

 Maru and through the kindness of her captain, T. 

 Fugii. My thanks also to Jergen Westrheim of the 

 Nanaimo Laboratory and Fisheries and Oceans 

 Canada, for permission to photograph specimens 

 aboard the RV G. B. Reed. Evan B. Haynes and 

 Bruce L. Wing of the Auke Bay Laboratory pro- 

 vided helpful reviews of the manuscript. 



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