396 



Abstract — This study investigates 

 the temporal stability of length- and 

 age-at-maturity estimates for female 

 Pacific cod (Gadus macrocephalus) 

 in the Gulf of Alaska and eastern 

 Bering Sea. Females reached bO% 

 maturity (A^q) at 4.4 years in the 

 Gulf of Alaska and at 4.9 years in 

 the eastern Bering Sea. Total hody 

 length at 509^ maturity iLT^,,) was 

 significantly smaller (503 mm) in the 

 Gulf of Alaska than in the eastern 

 Bering Sea (580 mm). The estimated 

 length- and age-at-maturity did not 

 differ significantly between winter 

 and spring in either the Gulf of Alaska 

 (1999) or Bering Sea (2003) areas. 

 The results of this study raised the 

 spawning biomass estimate of female 

 Alaskan Pacific cod from 298x10^ t 

 for 2005 to 499x103 t for 2006. The 

 increased spawning biomass estimate 

 resulted in an increased over-fishing 

 limit for Pacific cod. 



Geographic and seasonal variations 

 in maturation and growth of female Pacific cod 

 {Gad us macrocephalus) in the Gulf of Alaska 

 and Bering Sea 



James W. Stark 



Email address: iim.starkminoaa.gov 



Resource Assessment and Conservation Englneenng Division 

 Alaska Fisheries Science Center 

 NOAA/National Marine Fishenes Service 

 7600 Sand Point Way NE 

 Seattle, Washington 98115 



Manuscript submitted 20 September 



2006 to the Scientific Editor's Office. 



Manuscript approved for publication 

 23 March 2007 by the Scientific Editor. 



Fish. Bull. 105:396-407 (2007). 



Pacific cod (Gadiis macrocephalus) was 

 the fourth most important commercial 

 species landed in the United States 

 during 2003 by volume, and catches 

 totaled 27x10'' metric tons (t) and had 

 a value of $160 million. The Pacific 

 cod stocks in Alaska were not consid- 

 ered to be overfished in 2005 (Thomp- 

 son and Dorn, 2005; Thompson et al., 

 2005). Pacific cod range from Califor- 

 nia, around the North Pacific Rim, 

 to the Sea of Japan (Hart, 1973). In 

 Alaska, this species is found along the 

 continental shelf and upper slope, pri- 

 marily at depths <300 m (Matarese et 

 al., 2003). The objectives of this study 

 were to determine the length- and 

 age-at-maturity, as well as growth 

 of female Pacific cod, in order to pro- 

 vide for significantly improved stock 

 management in the Gulf of Alaska, 

 eastern Bering Sea, and Aleutian 

 Islands. Previous estimates of Pacific 

 cod length-at-maturity were based 

 on visual (macroscopic) observations 

 of ovaries taken during the spawn- 

 ing season (Welch and Foucher, 1988; 

 Thompson et al., 2005), or on a gonad- 

 osomatic index (/G) (Teshima, 1985; 

 Hattori et al., 1992). 



The macroscopic observation and 

 IG methods can introduce sampling 

 bias through misclassifications of the 

 stage of oocyte maturity (Hunter et 

 al., 1992). The macroscopic method 

 of maturity classification is contin- 

 gent upon differentiating between ova 

 that contain yolk (mature ova) which 

 can appear transparent to the naked 

 eye, and opaque ova that do not con- 



tain yolk. The change in opacity is 

 the result of yolk sequestering within 

 the ova, resulting in distension and 

 transparency of the chorion (exter- 

 nal covering of the ova). Opacity is 

 more difficult to discern in the small 

 ova that are produced by smaller fish. 

 Therefore, the macroscopic method 

 of classification can result in a bias 

 against smaller fish. 



With macroscopic classification, 

 there is also a bias against specimens 

 in early vitellogenesis, because during 

 this period only a small quantity of 

 yolk has been sequestered within the 

 ova, resulting in an opaque chorion 

 that is not distended. With macro- 

 scopic observation methods, an ovary 

 containing only postovulatory follicles 

 and opaque ova would be classified as 

 immature; postovulatory follicles can 

 be detected only through the use of 

 histological methods. 



Macroscopic observations also have 

 the disadvantage of generally being 

 conducted under less than ideal light- 

 ing and weather conditions. Maturity 

 classifications based on histological 

 examination are not subject to these 

 biases because the maturity classifi- 

 cations are based on a comprehensive 

 microscopic assessment of ova and 

 associated structures, such as post- 

 ovulatory follicles, under controlled 

 laboratory conditions. Histological 

 methods provide a high probability 

 that yolk sequestered within ova will 

 be detected because ova are sectioned 

 and stained with eosin that renders 

 yolk pink. 



