Goldman and Musick; Growth and maturity of Lamna ditiopis 



287 



5 years of age and 140 cm PCL (Tanaka, 1980; Naga- 

 sawa, 1998). From our small sample size, the logistic 

 method provided an estimate that male salmon sharks 

 in the ENP mature between the ages of 3 and 5, and 

 MPCL = 124.0 cm PCL (Fig. 6). Clasper lengths did not 

 enhance the ability to determine male length at sexu- 

 al maturity because specimens around the calculated 

 MPCL were not sampled. Although the MPCL for males 

 indicates a smaller length at maturity, our confidence in 

 the accuracy of the male MPCL estimate (due to sample 

 size) is low (Fig. 6). 



The lack of spermatozoa in any of the oviducal gland 

 samples analyzed is not surprising considering no 1am- 

 niform shark examined to date has shown evidence of 

 sperm storage (Pratt, 1993). However, specimens we 

 examined were specifically chosen from the time pe- 

 riod of late July through late August when mating was 

 likely to have been taking place (Goldman and Human, 

 2005; Goldman and Musick, in press). A larger sample 

 size taken through that time period and extending 

 through September may resolve the question better 

 regarding the suspected residence time of sperm in 

 the oviducal gland of lamniform sharks — a residence 

 time that is probably only a few days timed with ac- 

 tual mating activity (Pratt, 1993). The large number 

 of eggs produced to feed oophagous young (Wourms, 

 1977; Gilmore et al., 1983; Gilmore. 1993) could have 

 "flushed" any stored sperm out of the oviducal gland 

 (Pratt, 1993). 



In the WNP, salmon sharks are born in the spring 

 of the year and pups range in length from 60 to 70 cm 

 PCL (Tanaka, 1980; JAMARC, 1980; Nagasawa, 1998). 

 Litter size in the WNP is up to 5 pups, and the ratio 

 of male to female is 2.2:1 (Tanaka, 1980). Our data 

 support a similar timing for pupping and for length at 

 birth in the ENP, but no pregnant females were taken 

 during the course of our research and therefore infor- 

 mation on litter size and pup sex ratio is not available 

 for the ENP. 



Nagasawa (1998) characterized salmon shark growth 

 through age ten as follows; after birth, "they grow to 

 between 90 and 105 cm PCL by the next spring ... 

 subsequent annual growth is 10-15 cm per year up to 

 age-4 fish." He stated, in addition, that females and 

 males attain an average length of 173 cm PCL and 163 

 cm PCL, respectively, by age 10. Our data indicated that 

 the average growth rate (cm per year) for salmon sharks 

 in the ENP is very similar to the rate in the WNP 

 through age 4. By age 5, ENP females are growing at 

 a considerably faster rate than WNP females, reaching 

 an average of 185.4 cm PCL by age 10 (Table 4). Male 

 salmon sharks in the ENP appear to begin outgrowing 

 their WNP counterparts by age 4 (Table 4). Salmon 

 shark longevity appears to be similar in the ENP and 

 WNP. Maximum observed age for females in our study 

 was 20, whereas it was 17 in the WNP (Tanaka, 1980); 

 however, maximum observed age for males was only 

 17, whereas it was 25 for the WNP. We were unable to 

 obtain samples of male salmon sharks at or near maxi- 

 mum age because of our small sample size. 



Salmon sharks in the ENP and WNP attain the same 

 maximum length (about 215 cm PCL for females and 

 about 190 cm PCL for males). However, WNP salmon 

 sharks take longer to reach a given length than those 

 in the ENP (Table 4). Additionally, the weights for the 

 same length females and males are considerably dif- 

 ferent except at male maximum length, which appears 

 to be equivalent to females of similar length. Our data 

 indicate that the weight-at-length differences between 

 ENP and WNP salmon sharks begin at approximately 

 110 cm PCL for females, and at 140 cm PCL for males 

 (Fig. 7, A and B). Although a greater sample size could 

 enhanced precision and may alter the equations pre- 

 sented in the present study to some degree, the data 

 show that weight-at-length is particularly greater for 

 adult salmon sharks in the ENP than in the WNP. As 

 with the von Bertalanffy growth models, it is possible 

 that the discrepancy between female and male sample 

 sizes may have influenced the outcome of the likelihood 

 ratio test. However, the sample-size discrepancy was not 

 as large as with the growth curve data and standard 

 errors were small for both sexes; therefore it is unlikely 

 that an increased male sample size would have altered 

 the test result. 



Although season and size at birth appear to be simi- 

 lar for salmon sharks in the ENP and WNP, the loca- 

 tions where females pup are different. A salmon shark 

 pupping and nursery ground exists along the transi- 

 tional boundary of the subarctic and central Pacific 

 currents (Nakano and Nagasawa, 1996). Our data indi- 

 cate that a second pupping and nursery ground exists, 

 ranging from southeast Alaska to the northern end of 

 Baja California, Mexico (central California being the 

 most common area for ages zero and one [see Table 3] ). 

 Ages zero through 5 were caught only between southern 

 California and southeast Alaska, and ages 5 and above 

 were caught only in Alaska waters. The latitudinal size 

 segregation observed in the ENP indicates that preg- 

 nant females may move south along the California coast 

 to give birth in the spring. 



The high degree of sexual segregation across the 

 Pacific Basin (Nagasawa, 1998; Goldman and Musick, 

 in press), along with the age- and length-dependent 

 latitudinal distribution are important factors in pur- 

 suing responsible management and conservation of the 

 salmon shark. Although latitudinal migrations and 

 movements are documented in this species (lino, 1939; 

 Kosugi and Tsuchisaki, 1950; Tanaka, 1980; Balga- 

 derov, 1994; Nakano and Nagasawa, 1994; Weng et 

 al., 2005), they are still poorly understood. Similarly, 

 although trans-Pacific movements have been inferred 

 from fisheries bycatch data (Goldman and Musick, in 

 press), there has yet to be documentation of individuals 

 moving across the North Pacific. However, the degree 

 of the sexual segregation by itself (in regard to finding 

 a mate) would seem to indicate that movements across 

 the Pacific are likely. 



Another critical element for successful management 

 of salmon sharks is stock structure, which is not well 

 understood at this time; however a study of population 



