Hannah et al : Length and age at maturity for Eopsetta joi dcni 



717 



1 25 



1 00 



e 075 



50 



025 



00 



20 23 26 29 32 35 38 41 44 47 50 53 56 59 



Length (cm) 



Figure 4 



Comparison of fitted pctralc sole female maturity cui"ves 

 from September samples (our study) and 1986-91 com- 

 mercial fishery data used in the last two stock assess- 

 ments (Turnock et al.'l. Bars show 1986-91 maturity 

 data used to fit the curve from Turnock et al.' Dashed 

 line shows the maturity curve fitted to the 1986-91 sam- 

 ples by using only data from the fall-winter period. 



in a combined maturity curve. However, errors in deter- 

 mining maturity status, caused by including samples from 

 time periods when maturity status cannot be accurately 

 assessed visually, would have the same effect. This can be 

 seen in a comparison of the maturity data generated in 

 our study from macroscopic and microscopic evaluations. 

 The macroscopic curve (bars and solid line in Figure 7) is 

 flattened in relation to the curve according to microscopic 

 evaluation (dashed line). The curve is also shifted to the 

 right because, in this case, more large fish were incorrectly 

 classified than small fish. At other times of the year, errors 

 could be more common with smaller fish and the cui-ve 

 would shift the other way. In either case, however, the 

 curve should, in theory, be flatter than the true maturity 

 curve. This flattening of the maturity curve is caused by 

 the way the most likely errors change along a maturity 

 ogive. In small or young fish, which are mostly immature, 

 most of the errors encountered will be immature fish mis- 

 takenly considered mature. At larger sizes or older ages, 

 the reverse will be true. Near the inflection point, the two 

 types of errors offset each other and have little impact on 

 the slope because the population is split roughly 50/50 

 with respect to maturity. These effects, in combination, 

 tend to flatten the resulting curve. 



Compared to a length at 50% maturity of 33 cm for the 

 central Oregon coast (our study), the Astoria data from 

 the commercial fishery are consistent with an increase in 

 the length at 50% maturity with latitude, as suggested 

 by Ketchen and Forrester (1966) and Castillo (1995). The 

 methods developed in our study could be applied to petrale 

 sole samples collected over a wider geographic range to shed 

 more light on how length at maturity varies with latitude. 

 Best ( 1961) reported a length at 50% maturity of 35.5 cm for 

 female petrale sole from California waters, and Harry^ re- 

 ported 40.0 cm for the Columbia River area. In comparison 

 with the recent data from Astoria fishery samples (Fig. 5) 



1,25 



1,00 



075 



0.50 



0,25 



000 

 1 00 



075- 



o 0,50 



Q. 

 O 



qI 



0,25 



0,00 

 1 00- 



0,75 



0,50 



0,25 



0,00 



Astona Samples 1986-1991 



Jl 



B 



Astoria Samples l'i'):'-;?0()() 



Charleston Samples 1992-2000 



20 23 26 29 32 35 38 41 44 47 50 53 56 59 62 



Length (cm) 



Figure 5 



Proportion of female petrale sole identified as mature from 

 November-February samples of trawl landings in Astoria 

 and Charleston. Oregon, 1986-1991 and 1992-2000. 



and from the central Oregon coast (Fig. 3), the data from 

 Harry'' suggest a very large decrease in the length at 50% 

 maturity for female petrale sole since the 1960s. If this 

 decrease is a biological reponse to exploitation, it could ex- 

 plain how petrale sole stocks have held up quite well under 

 heavy commercial harvest (Sampson and Lee'). 



The data presented in our study suggest that the collec- 

 tion of maturity data by sampling on spawning aggrega- 

 tions does cause bias in estimates of female age and length 

 at maturity for petrale sole. Use of spring and summer 

 maturity samples in data sets used to estimate age and 

 length at maturity has also caused errors. Our analysis 

 shows that the overall effect on estimates of age and length 



'' Harry, G. Y. 1959. Time of spawning, length at maturity, 

 and fecundity of the English, petrale and Dover soles iPar- 

 ophrys vetulus, Eopsetta jordani, and Microstomus pacificus, 

 respectively). Fish. Comm. Oregon, Research Briefs 7(1):5-13. 



