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



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Figure 1 



Locations (+) sampled by survey crews of the National Oceanic and Atmospheric 

 Administration Alaska Fisheries Science Center from October 1998 through Janu- 

 ary 2004 for Pacific cod {Gadus macrocephalus). 



Materials and methods 



Ovaries and otoliths were collected from Pacific cod in 

 two geographic areas, the Gulf of Alaska and eastern 

 Bering Sea (Fig. 1). Seasonal sampling was used to esti- 

 mate the time of spawning, rate of ovary development, 

 and length- and age-at-maturity for female Pacific cod. 

 The first area, located in the central Gulf of Alaska, was 

 sampled during October 1998, January 1999, and April 

 1999 (Table 1) during a cooperative seasonal maturity 

 study conducted by the Alaska Department of Fish and 

 Game (ADFG) and the National Oceanic and Atmo- 

 spheric Administration Alaska Fisheries Science Center 

 (NOAA/AFSC). The area was sampled with bottom trawl 

 gear again in June 1999 during the annual ADFG crab 

 survey and during the commercial fishery in January 

 2004. Seawater temperature, and depth data were col- 

 lected with a calibrated trawl-mounted microbathyther- 

 mograph. The second area, within Unimak Pass and the 

 adjacent southeastern Bering Sea, was sampled during 

 the January, February, and March 2003 AFSC Pacific 

 cod pot study. Growth was determined by using the cod 

 length- and geographic area-stratified otolith collections 

 from the 2003 AFSC area wide surveys in the Gulf 

 of Alaska and eastern Bering Sea (Table 1). Otoliths 

 were aged by using the methods developed during 2002 

 for Pacific cod (Roberson et al., 2005; Thompson and 

 Dorn, 2005) by personnel of the AFSC Age and Growth 

 Program. 



In both the Gulf of Alaska and Bering Sea collec- 

 tions, ovaries were removed and placed in individu- 



ally labeled cloth bags and stored in a solution of 4% 

 buffered formaldehyde. The ovary samples for the Gulf 

 of Alaska consisted of whole ovaries and samples from 

 the Bering Sea area were excised ovarian cross-sec- 

 tions (minimum of two 16.4-mm-diameter samples per 

 individual). For each whole ovary sample, a section was 

 taken from the posterior region of the ovary. From 50 

 of these specimens, two additional sections were taken 

 from the anterior and median regions. 



Oocytes within each ovary were classified into five 

 histological stages based on criteria used by Hunter 

 et al. (1992) and Stark and Somerton (2002). The five 

 stages were perinucleus, cortical alveoli, vitellogenesis, 

 hydrated oocytes, and postovulatory follicles. Individual 

 ovaries were classified according to the most advanced 

 stage of oocytes present in the histological sections. In- 

 dividuals classified as spawners were those with ovaries 

 containing either hydrated oocytes or post-ovulatory 

 follicles. Mature individuals were defined by using two 

 different classification criteria in order to compare re- 

 sults from each method. One method classified mature 

 specimens as those with ovary stages ranging from 

 vitellogenesis through postovulatory follicles. The other 

 method included the additional stage of cortical alveoli 

 ovaries in the mature category. 



Ovarian development was compared across months, 

 by tabulating the proportion of fish classified within 

 each of the five histological stages only for females that 

 had reached the minimum total body length (LT) at ma- 

 turity, as determined by a length-at-maturity analysis. 

 A selection of samples from the entire length range of 



