Stark: Temporal and spatial variations in maturation and growth of female Godus macrocephalus 



401 



2(1(1 4(1(1 000 800 



Figure 4 



The proportion of mature female Pacific cod (Gadiis macro- 

 cephalus) by total length (Lj., mm) in (A) the Gulf of Alaska 

 January 1999 and 2004 collection (n = 157) and in (B) the Bering 

 Sea February 2003 collection (n = 133). The mean length at 509c 

 maturity=502.56 (A) and 579.96 mm (B), and the 95% confidence 

 intervals are represented by parallel dotted lines. 



of Alaska female Pacific cod growth differed signifi- 

 cantly {P<0.001) from the growth of males. The rate 

 of growth declined more with age for males than for 

 females in the Gulf of Alaska (Fig. 6). However, in the 

 Bering Sea, male growth was nearly as rapid (P= 0.015) 

 as that of females. Males were estimated to reach a 

 slightly smaller maximum theoretical L, of 1044 mm in 

 the Gulf of Alaska than in the Bering Sea (1101 mm). 



Discussion 



This study provides the most extensive and representa- 

 tive estimates of female Pacific cod length- and age-at- 

 maturity and growth available. This is the first Pacific 

 cod study to rely on histological methods to assess ovary 

 maturity, and the first to make temporal comparisons 

 of maturity. It is the first northeast Pacific Ocean study 



to assess Pacific cod age-at-maturity. Before this study, 

 managers of the Alaska Pacific cod fishery (Thompson 

 and Dorn, 2005; Thompson et al., 2005) used a female 

 Lj. estimate of 670 mm from macroscopic maturity 

 classifications made by commercial fishery observers 

 on specimens collected after March in 1993 and 1994. 

 However, the macroscopic maturity classification method 

 can introduce sampling bias and misclassifications. In 

 contrast, in this study, it was determined that the most 

 representative method for estimating Lj. relied on 

 making histological maturity assessments of large num- 

 bers of ovary samples from a wide L^, range of specimens 

 collected before the late spawning period. 



The results from this study are similar to the re- 

 sults from studies conducted in other areas. The es- 

 timated female Pacific cod Agp differed only slightly 

 between the Gulf of Alaska and Bering Sea study 

 areas and were similar to the ages estimated for Sea 



