Rickey: Maturity, spawning, and seasonal movement of Atheresthes stomias 



137 



differences in size at maturity. However, differences 

 between results for Oregon and the present study 

 could be explained by differences in sampling distri- 

 butions across months, or by different interpretations 

 of maturity codes by different observers; therfore they 

 may not represent a biological change. 



Size-selectivity and areal or bathymetric sampling 

 biases are critical to estimates of L 509l (Welch and 

 Foucher, 1988; Trippel and Harvey, 1991). Predicted 

 length at maturity may be biased if fish are size-seg- 

 regated by area or depth (e.g. if immature fish do 

 not migrate to spawning depths while targeted com- 

 mercial trawl fisheries typically operate where large 

 fish are most likely to be found in quantity, i.e. the 

 spawning grounds). Smaller arrowtooth flounder 

 were not well represented in commercial landings. 

 Size selectivity in commercial fisheries occurs either 

 through net selection (a lesser problem in the trawl 

 survey) or through size-selective targeting and dis- 

 carding. Net avoidance by larger fish may also be a 

 factor. In the extreme case of male arrowtooth floun- 

 der, estimated L 5m was below the size range of fish 

 in market samples though well within the size range 

 of fish in commercial discards and survey catches. 

 Because the trawl survey sampled the widest size 

 range of arrowtooth flounder over a fairly large area 

 and depth range prior to peak spawning in 1992, size- 

 at-maturity estimates from the trawl survey repre- 

 sent the best available. 



Hunter et al. (1992) estimated size at maturity for 

 female Dover sole and found samples taken during 

 the spawning season yielded higher estimates of L 50% 

 than did samples taken before spawning. They at- 

 tributed this to the presence of postspawning females 

 with "highly regressed" ovaries that were histologi- 

 cally indistinguishable from immature females, and 

 they concluded that estimates of length or age at first 

 maturity should always be conducted prior to the 

 onset of spawning, when such females are rare. I 

 found the opposite seasonal pattern in length at 

 maturity for female arrowtooth flounder; lowest L 50% 

 was estimated from commercial samples collected in 

 the fall during spawning, and highest L 509c was esti- 

 mated from months preceding spawning. Market 

 samples collected in summer (before spawning) 

 tended to underrepresent smaller arrowtooth floun- 

 der and yielded extremely high estimates of female 

 length at maturity. In the case where sampling is 

 limited to commercial trawl fisheries, it may be pref- 

 erable to pool year-round sampling data to generate 

 estimates of L 5Q% if fish are moving in and out of 

 range of the trawl fleet, rather than to attempt to 

 narrow the sampling window to just prior to spawn- 

 ing as suggested by Hunter et al. (1992). This in- 

 volves the explicit trade-off of some assumed increase 



in the misclassification of small fish with the signifi- 

 cant bias caused by a seasonal inability to obtain 

 representative samples of the entire size or bathy- 

 metric range of a population. Perhaps coincidentally, 

 female length-at-maturity curves generated from the 

 year-round commercial data and the survey data 

 were strikingly similar (Fig. 4), although statistically 

 the curves were different. 



Acknowledgments 



Thanks go to Marion Larkin and the crew of the FV 

 Larkin for their gracious assistance. Jack Tagart and 

 Han-lin Lai advised on sampling design and statis- 

 tical analyses, and Nancy Tonjes arranged routine 

 sampling. I thank Ken Weinberg, Mark Wilkins, and 

 other participants in the 1992 NMFS surveys for 

 their assistance and cooperation, and the anonymous 

 reviewer whose thoughtful comments vastly im- 

 proved the manuscript. This paper is funded in part 

 by a grant from the National Oceanic and Atmo- 

 spheric Administration. 



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