711 



Abstract— The problem of bias in IV- 

 male petrale sole a^e and lenglh-at- 

 maturity relationships caused by sam- 

 pling; from spawninfj aggregations was 

 investigated. Samples were collected 

 prior to aggregation, and histological 

 methods were used to determine matu- 

 rity status. Mature and immature fish 

 were classified by inspecting oocytes 

 for the presence of yolk in September, 

 when substantial divergence in yolked 

 and unyolked oocyte diameters had 

 been observed. Comparison of macro- 

 scopic and microscopic assessment of 

 maturity showed that maturity status 

 cannot be determined accurately by 

 using macroscopic inspection during 

 the summer. Female petrale sole from 

 the central Oregon coast were 50'^ 

 mature at 33 cm and 5 years of age. 

 Comparison of data fi-om our study with 

 data used in recent petrale sole stock 

 assessments showed that both sampling 

 bias and the use of samples fi-om sea- 

 sons when status cannot be accurately 

 determined have likely caused eiTors in 

 fitted maturity relationships. 



Length and age at maturity of female 



petrale sole (Eopsetta jordani) determined from 



samples collected prior to spawning aggregation 



Robert W. Hannah 

 Steven J. Parker 



Oregon Department of Fish and Wildlife 



Marine Resources Program 



2040 Marine Science Drive 



Newport, Oregon 97365 



Email address (for Robert W Hannah) Bob HannahigJhmsc.orsl.edu 



Erica L. Fruh 



National Marine Fishenes Service 



Northwest Science Center 



Fishenes Research and Monitoring Division 



2030 Manne Science Dnve 



Newport, Oregon, 97365 



Manuscript accepted 21 March 2002. 

 Fish. Bull. 100:711-719 (2002). 



Petrale sole (Eopsetta jordani) have 

 been the target of a valuable com- 

 mercial trawl fishery off the U.S. West 

 Coast since before World War II (Samp- 

 son and Lee' ). Management and assess- 

 ment of petrale sole is complicated by 

 the fact that modern fishing activity 

 targets winter deepwater aggregations 

 of spawning fish (Fig. 1). Because most 

 of the available female maturity data 

 are derived from the winter commer- 

 cial fishery, they are potentially biased 

 with respect to age and length at matu- 

 rity (e.g. small mature fish are more 

 likely to be sampled than small imma- 

 ture fish). Some summer samples are 

 available for analysis, including those 

 from the National Marine Fisheries 

 Service triennial shelf survey (e.g. Zim- 

 mermann et al., 1994). However, in the 

 summer, when mature and immature 

 fish are well mixed, maturity status is 

 not easily determined visually because 

 of the similarity in appearance between 

 ovaries of immature fish and those of 

 fish in the "resting" state (Ketchen and 

 Forrester, 1966). 



The age and length at maturity for 

 female fish is an important param- 

 eter in many stock assessment models. 

 Clark (1991), Lunsford (1999) and Al- 

 Jufaily (1996) have demonstrated that 

 variation in the age at 50% maturity, 

 especially in relation to the median age 

 of recruitment to the fishery, can have 



a major influence on the calculation 

 of a target fishing rate. Target fishing 

 rates are currently used by the Pacific 

 Fishery Management Council (PFMC) 

 to manage most groundfish stocks 

 (Clark, 1991: PFMC'-). An example of 

 a target fishing rate would be F^q'/,' 

 the fishing mortality rate that would 

 reduce spawning stock biomass per 

 recruit to 40% of the unexploited level. 

 The potential influence of errors in es- 

 timating the median age of female ma- 

 turity can perhaps best be illustrated 

 with an example. In Lunsford's (1999) 

 study of maturity of Pacific ocean perch 



' Sampson, D. B., and Y. W. Lee. 1999. An 

 assessment of the stocks of petrale sole 

 off Washington. Oregon and Northern 

 California in 1998. In Pacific Fishery 

 Management Council. 1999. Appendix 

 to the status of the Pacific coast groundfish 

 fishery through 1999 and recommended 

 acceptable catches for 2000: stock assess- 

 ment and fishery evaluation. Pacific 

 Fishery Management Council, 2130 SW 

 Fifth Avenue, Suite 224, Portland, Oregon, 

 97201. 



- Pacific Fishery Management Council. 

 2000. Status of the Pacific Coast ground- 

 fish fishery through 2000 and recom- 

 mended biological catches for 2001: stock 

 assessment and fishery evaluation. (Docu- 

 ment prepared for the council and its 

 advisory entities.) Pacific Fishery Man- 

 agement Council 2130 SW Fifth Avenue, 

 Suite 224, Portland, Oregon 97201. 



