Stark: Temporal and spatial variations in maturation and growth of female Gadus macrocephalus 403 



Spawning participants sampled during this study, 

 included female Pacific cod as small as 420 mm Ly 

 in the Gulf of Alaska and 460 mm in the Bering Sea 

 area. In comparison, cod (Gadus morhua) from the 

 northwest Atlantic Ocean initiated spawning in 1995 at 

 400 mm — a decline from 500 mm in 1992 (Saborido-Rey 

 and Junquera, 1998). 



Spawning is an annual occurrence for female Pacific 

 cod according to the results of seasonal ovary develop- 

 ment, the Iq cycle, and the wide range in age and body 

 length composition of the spawning population each 

 month. This conclusion was consistent with that from 

 Teshima's (1985) study, which found that the Bering 

 Sea Pacific cod gonadosomatic index increased in No- 

 vember and December because of maturation and that 

 spawning was not expected to occur until the following 

 year. Similarly, Atlantic cod individuals have an annual 

 reproductive cycle (Norberg et al., 2004) and spawn 

 despite being raised in captivity under conditions of 

 starvation (Kjesbu et al., 1991). 



Based on results from this study, the spawning 

 activity for female Pacific cod is believed to begin 

 during late winter and peak during the spring. This 

 estimated period of peak spawning, based on results 

 summarizing ovarian maturities by month of collec- 

 tion, is validated by larval abundance estimates from 

 the Gulf of Alaska and Bering Sea ichthyoplankton 

 surveys conducted since 1980 by the AFSC (Matarese 

 et al., 2003). Similarly, the Sea of Okhotsk population 

 is estimated to have a peak spawning period that in- 

 cludes the months of March and May, based on a 1995 

 study (Rovnina et al., 1997). Spawning probably ends 

 in early summer in the Gulf of Alaska, as indicated by 



the lack of any specimens in June with vitellogenesis- 

 stage ovaries. 



The likelihood of female Pacific cod spawning was 

 strongly associated (P<0.001) with the time of month, 

 and later in the spawning season, spawning was as- 

 sociated (P=0.01) with LT. There were no associations 

 with spawning and age, or ambient water temperature; 

 consequently these factors probably do not regulate the 

 timing of spawning for Pacific cod. Similarly, seawater 

 temperature was not the most important environmental 

 cue regulating the maturation and spawning of Atlantic 

 cod and other commercially cultured Atlantic Ocean 

 fish species, including rainbow trout (Oncorhynchus 

 mykiss), Atlantic halibut {Hippoglossus hippoglossus) 

 and sole (Solea solea) (Norberg et al., 2004). For these 

 cultured Atlantic species, photoperiod is the most im- 

 portant regulator of the reproductive cycle. Pacific cod 

 maturation and spawning was significantly associated 

 with time of month, as determined by this study, which 

 would indicate that photoperiod may regulate the re- 

 productive cycle in this species. Photoperiod should 

 be similar for both the Gulf of Alaska and Bering Sea 

 study areas sampled by this survey, given their similar 

 latitudes (Fig. 1), and could account for the similarity in 

 the timing of spawning within the Gulf of Alaska and 

 Bering Sea waters found during this study and during 

 the ichthyoplankton surveys. 



Regardless of where spawning occurs, the reproduc- 

 tive effort by the fish represents a substantial invest- 

 ment, based on ovary weight that represents up to 30% 

 of the total female Pacific cod body weight and Atlantic 

 cod body weight (Lambert and Dutil, 2000). Pacific 

 cod have among the highest fecundities of any tele- 



