400 



Fishery Bulletin 105(3) 



BS 



r;()\ 



BS 



BS 



(lOA CIOA 



CiOA 



o 



Q. 

 O 



January 

 2003 



January 

 1999 

 2004 



February 

 2003 



Mar^h 

 2003 



April 

 1999 



June 

 1999 



Oclober 

 1998 



ro Perinucleus 



I Cortical alveoli 



P Vitellogenesis 



m Hydraled oocytes 



Rl Post ovulatory follicles 



Figure 3 



Ovary development of Pacific cod (Gadus macrocephalus), based 

 on maturity-stage classification results from specimens that had 

 reached the minimum length at maturity and that had been 

 collected from 1998 through 2004 in the Gulf of Alaska (GOA) 

 and 2003 Bering Sea (BS). Selecting samples from the entire 

 length range of mature females provided for the investigation of 

 the full seasonal progression of ovary development. 



(P<0.001) associated with the time of month and not 

 significantly associated with Lj, (P=0.06), age (P=0.06), 

 or ambient water temperature (P=0.21). However, by 

 April and June in the Gulf of Alaska, Lj. was slightly 

 (P=0.01) associated with the likelihood of spawning. 

 Spawners ranged in Lj, from 420 mm to 1060 mm. The 

 age-at-spawning ranged from 4 year olds up to the old- 

 est females taken, at 10 years of age. Spawning female 

 Pacific cod were found in all areas, including bays and 

 offshore gullies, sampled during April and June 1999 

 in the Gulf of Alaska. Ambient seawater temperatures 

 were similar in 1999 during January and April (2.21°C 

 to 6.10°C), and increased only slightly in June (3.7°C 

 to 7.01°C). 



The estimates of Lj,^^ did not differ significantly be- 

 tween the two histology-based methods used to define 

 mature females, except for a slight difference (P=0.02) 

 with January Gulf of Alaska estimates, which used the 

 combined data from 1999 and 2004. The January Lj. 

 estimates were 503 mm based on a mature classification 

 that did not include cortical alveoli (CA) stage ovaries, 

 and 437 mm when CA-stage ovaries were included as 

 part of the mature category. 



However, there was a significant area difference 

 (P<0.001, Fig. 4, Table 2) between the January 1999, 

 2004 Gulf of Alaska LT^^^ (503 mm) and the February 

 2003 Bering Sea LTg^ (580 mm). In both areas, the es- 

 timates of length-at-maturity did not differ significantly 

 between months, with the exception of a slight differ- 



ence (P=0.03) between January (496 mm) and June 

 (601 mm) 1999. In the present study the expected Lj. 

 range of mature female P. cod was adequately assessed 

 from a sample Lj distribution that extended to 130 mm 

 Lj. in the Gulf of Alaska and 350 mm L^. in the Bering 

 Sea (Table 3) and on the documentation of only a single 

 specimen smaller than 420 mm Lj^ 



The estimated age at which 50% of the females 

 reached maturity (Agg) did not differ significantly be- 

 tween the two histological methods for assigning ma- 

 turity. With either method, the A^q differed slightly 

 (P=0.02) between the Gulf of Alaska (4.4 years) and 

 Bering Sea (4.9 years. Table 4, Fig. 5). However, within 

 each area, the estimated ages at maturity did not differ 

 significantly between months (P>0.16). Similarly, the 

 January 1999 and 2004 Gulf of Alaska female cod ages 

 at maturity did not differ significantly (P=0.19). 



The otoliths taken during the 2003 AFSC bottom 

 trawl surveys of the Gulf of Alaska (/!=711) and east- 

 ern Bering Sea (7i = 1360) provide the largest and most 

 comprehensive collection of age data available for fe- 

 male and male Pacific cod. The otolith specimens were 

 selected by region, sex, and Lj. Pacific cod had wide 

 variations in age at length (Fig. 6, Table 5). Based on 

 these collections, the von Bertalanffy growth function 

 differed significantly (P<0.001) between the Gulf of 

 Alaska and Bering Sea for both males and females 

 (Table 5). Female Pacific cod length at age was smaller 

 in the Gulf of Alaska than in the Bering Sea. The Gulf 



