Cooper et al.: Fecundity of Sebastolobus alascanus and Sebastolobus altivelis 



21 



collected at later ovarian development stages would avoid 

 this potential error (Tuene et al., 2002). 



Because of a nonrandom distribution of vitellogenic 

 and nonvitellogenic oocytes in the ovary, it was neces- 

 sary to average Weibel grid counts over an entire ovary 

 cross section. Larger ovaries that did not fit on a single 

 slide could not be used, so that fecundity of larger fish 

 had to be determined with the gravimetric method. This 

 was a major limitation because few fish greater than 60 

 cm had ovaries small enough to be suitable for the ste- 

 reological method. This limitation, however, might not 

 apply to fish species with vitellogenic oocytes randomly 

 distributed throughout the ovary. 



The number of Weibel grid counts required was larger 

 in our study than in Emerson et al. (1990), and the extra 

 counts increased the amount of time involved with com- 

 putation of fecundity estimates. In addition to the time 

 required to prepare histological sections, the time to 

 obtain stereological estimates took approximately twice 

 as long as those obtained with the gravimetric method. 

 Our estimates of shortspine thornyhead fecundity at 

 length (Fig. 3) appeared lower than the regression pub- 

 lished by Miller (1985), but our longspine thornyhead 

 fecundity estimates were higher than those published by 

 Wakefield (1990) (Fig. 6). Several potential explanations 

 exist for the differences. Temporal or geographic differ- 

 ences in fecundity could exist. Samples from different 

 decades were used in the two studies, and Wakefield 

 (1990) used longspine samples taken from off Point 

 Sur, California, whereas we used samples collected off 

 Oregon and Washington. However, the differences may 

 also be explained by methodological differences between 

 authors, including different criteria to include oocytes 

 in fecundity estimates, and differences in the ovarian 

 development of samples. Relatively small sample sizes 

 from our study and from Wakefield (1990) may add un- 

 certainty to these fecundity estimates. The length range 

 of samples could also affect comparisons for shortspine 

 thornyhead fecundity. The fecundity estimates from 

 Miller (1985) did not include any fish greater than 60 

 cm, whereas we used fish approaching 80 cm. 



Wakefield (1990) grouped fecundity data by date, 

 that is to say before the start of spawning and after 

 the start of spawning. His data indicated a decline in 

 fecundity after spawning begins, which he attributed 

 to batch spawning. Similar temporal groupings in our 

 study did not necessarily show a decrease in fecundity 

 that was indicative of batch spawning in longspine or 

 shortspine thornyhead. An important caveat regarding 

 these comparisons is that the combination of small 

 sample sizes and high variability in fecundity at length 

 would cause only large differences in fecundity to be 

 detected. However, the sample sizes used for compari- 

 son before and during spawning season (shortspine 

 thornyhead n=ll, 41) (longspine thornyhead n = 17,ll) 

 were close to the sample sizes Wakefield (1990) used as 

 evidence for batch spawning (rc=ll,22). Larger sample 

 sizes for both species would help answer the question 

 of whether these are batch-spawning species. Pearson 

 and Gunderson (2003) did not find any hydrated oocytes 



or postovulatory follicles co-occurring with vitellogenic 

 oocytes in histological sections of either species used in 

 our study. They concluded that batch spawning does not 

 occur from off Northern California to Alaska for short- 

 spine thornyhead, and from off Northern California to 

 Washington for longspine thornyhead, and the results 

 of the present study support this conclusion. 



Ovaries are often opportunistically collected dur- 

 ing commercial fishing seasons or scheduled fisheries 

 surveys and may not provide oocyte samples from the 

 optimum time of year for estimating fecundity with 

 gravimetric techniques. Nevertheless, the stereological 

 technique enabled us to make fecundity estimates for a 

 greater number of the available samples. The technique 

 could be used in similar instances where the logistics 

 of sampling require collections to be made earlier than 

 the optimal date for gravimetric estimates. 



Acknowledgments 



Dave Douglas of the Oregon Department of Fish and 

 Wildlife collected many samples, as did numerous NMFS 

 RACE and REFM division scientists and the following 

 NMFS observers: C. Colway, A. Hayward, W. Mitchell, 

 E. White, N. Spang, K. Redslob, M. Waters, and D. Tran. 

 We thank Frank Morado, Lisa Appesland, and Dan 

 Nichol of the NMFS Alaska Fisheries Science Center 

 (AFSC) for use of equipment and equipment instruc- 

 tion. We also thank Marcus Duke of the UW SAFS for 

 creating a Weibel grid. Jim Ianelli and Rebecca Reuter 

 of the NMFS Alaska Fisheries Science Center provided 

 quantitative assistance. Cathy Schwartz of the UW 

 SAFS assisted with the figures and tables. We thank 

 two anonymous reviewers for providing useful comments. 

 This research was supported by the Joint Institute for 

 the Study of the Atmosphere and Ocean (JISAO) under 

 NOAA cooperative agreement no. NA17RJ1232. 



Literature cited 



Best, E. A. 



1964. Spawning of longspine channel rockfish, Sebastolo- 

 bus altivelis Gilbert. Calif. Fish Game 50:265-267. 

 Emerson L. S., M. G. Walker, and P. R. Witthames. 



1990. A stereological method for estimating fish fecundity. 

 J. Fish Biol. 36:721-730. 

 Erickson, D. L., and E. K. Pikitch. 



1993. A histological description of shortspine thornyhead, 

 Sebastolobus alascanus, ovaries: structures associated 

 with the production of gelatinous egg masses. Environ. 

 Biol. Fishes 36:273-282. 

 Gaichas, S., and J. N. Ianelli. 



2003. Assessment of thornyheads iSebastolobus spp.) in 

 the Gulf of Alaska. In Stock assessment and fishery 

 evaluation report for the groundfish resources of the 

 Gulf of Alaska, p. 659-698. North Pacific Fishery 

 Management Council, Anchorage, AK. 

 Hoff, G. R., and L. L. Britt. 



2003. The 2002 eastern Bering Sea upper continental slope 



