Goldman and Musick Growth and maturity of Lamna ditropis 



279 



southern catches generally occur in deeper waters (Na- 

 gasawa, 1998; Goldman and Musick'). 



Shark catches in Alaska waters have been reported 

 to be as high as those from Washington, Oregon and 

 California combined (Camhi, 1999), and there is con- 

 cern over the amount of shark bycatch being taken 

 (Gaichas^). In 1997, state managers closed commercial 

 shark fishing in Alaska state waters and imposed con- 

 servative sport-fishing limits (1 shark per person per 

 day, 2 per year) that legally encompass federal waters 

 too. Federal managers are currently addressing elasmo- 

 branch management issues (Goldman, 2001). 



Because of the ever-increasing importance of provid- 

 ing accurate and timely life history parameters to foster 

 responsible management efforts, we had two main ob- 

 jectives in our study. The first was to estimate growth 

 parameters and the age and length at sexual matu- 

 rity of salmon sharks in the ENP. The second was to 

 compare our results to those previously published on 

 salmon sharks from the WNP to elucidate any exist- 

 ing variability in the life history parameters of this 

 highly sexually segregated population. Lastly, because 

 of the small number of samples for female juvenile age 

 classes, a small overall sample size for males, and the 

 fact that samples (for both sexes) were not obtained for 

 each month, we applied several back-calculation meth- 

 ods to our data (see Cailliet and Goldman, 2004 and 

 Goldman, 2004) and provide a demonstration and brief 

 discussion on the importance of choosing an appropriate 

 back-calculation method. 



Materials and methods 



Salmon shark vertebrae were obtained from numer- 

 ous sources and locations ranging geographically from 

 southern California to Kodiak Island (»=182) between 

 1997 and 2002. The majority of samples came from 

 research cruises in the Gulf of Alaska (GOA) and Prince 

 William Sound (PWS), by accompanying sport-fishing 

 vessels on salmon shark trips in the GOA and PWS, and 

 from Alaska Department of Fish and Game (ADF&G) 

 port samplers. Vertebral samples collected from British 

 Columbia to southern California came from incidental 

 catches and recently beached animals. 



Precaudal, fork, and total length (PCL, FL, and TL) 

 were measured on a straight line and recorded along 

 with date, location, and sex (and clasper length in males). 

 Samples provided by additional sources included at least 

 one of the necessary straight-line measurements, date 

 and location of capture or wash-up, and sex. Weights 

 were obtained from 20 females ranging from 67.1 to 

 213.4 cm PCL, and 7 males ranging from 69.5 to 187 cm 



PCL. The power function, W = aL'\ was fitted to the data 

 (in SigmaPlot, vers. 6.0, SPSS Inc., Chicago, IL), where 

 W = weight (kg) and L = length (cm PCL). Specimens 

 weighed had been collected from southern California to 

 Alaska. A likelihood ratio test was used to determine 

 whether differences between female and male weight- 

 length parameters were significant or if a single set of 

 parameters described the data better (Kimura, 1980; 

 Quinn and Deriso, 1999; Haddon, 2001) (SAS, vers. 8.0, 

 SAS, Cary, NO. A 20- to 25-cm section of vertebrae 

 was removed from directly in front of the first dorsal fin 

 (above the gills) and stored frozen. We used PCL mea- 

 surements to make direct comparisons with previously 

 published salmon shark age and growth data from the 

 WNP. Linear regression equations, based on our samples, 

 were developed for converting PCL to FL and TL. 



Vertebral samples were thawed, cleaned of excess 

 tissue, separated into individual centra and stored in 

 70% ethyl alcohol for at least 24 h. Centra were sagit- 

 tally sectioned immediately adjacent to the center of 

 the focus and then cut again approximately 1.5 mm off- 

 center by using an Isomet rotary diamond saw (Buehler, 

 Lake Bluff, IL). The sections were pressed between two 

 pieces of Plexiglas (to prevent warping), air-dried for 24 

 h under a ventilation hood, and then mounted onto mi- 

 croscope slides with a mounting medium. After drying, 

 sections were polished with wet fine grit (320-, 400-, 

 and 600-grit) sand paper to approximately 0.5 mm and 

 air-dried. Sections were viewed by using a binocular 

 dissecting microscope with transmitted light. 



Centrum radius (CR) and distance to the outer mar- 

 gin of each ring were measured to the nearest 0.001 

 mm along a straight line from the central focus to the 

 center of the outer margin of the corpus calcareum 

 (Fig. lA) using a compound video microscope with the 

 Optimus image analysis system (Media Cybernetics, 

 vers. 6.5., Silver Spring, MD). PCL was plotted against 

 CR to determine the proportional relationship between 

 somatic and vertebral growth. 



A banding pattern was readily distinguishable in 

 sectioned centra; wide bands were separated by distinct 

 narrow opaque bands. This pattern occurred on both 

 arms of the corpus calcareum and extended across the 

 intermedialia. Each pair of wide-narrow bands was 

 considered a growth cycle; the narrow opaque bands, 

 hereafter referred to as "rings," were counted (Fig. 

 lA). An angle change in the intermedialia and a ring 

 on the corpus calcareum were present approximately 5 

 to 6 mm from the focus of each centrum and were con- 

 sidered to represent a birthmark. The "prebirth ring" 

 reported by Nagasawa (1998) was present in most speci- 

 mens just prior to the birthmark but was not counted 

 nor measured (Fig. lA).-^ A distinct notch was usually 



' Goldman, K. J., and J. A. Musick. 2002. Unpubl. 

 data. Alaska Department of Fish and Game, 3298 Doug- 

 las PI., Homer, AK 99603, and Virginia Institute of Marine 

 Science. 1208 Greate Rd. Gloucester Ft.. VA 23062. 



- Gaichas, S. 2002. Personal commun. NMFS Ala.ska Fish- 

 eries Science Center, 7600 Sand Point Way NE, Building 4, 

 Seattle WA 98115. 



■^ Our aging protocol was independently developed by the senior 

 author and a co-reader, and later found to be identical to 

 that used for salmon sharks in the western North Pacific i H. 

 Nakano, pers. commun.) Vertebral images were exchanged 

 and aged by the senior author and H. Nakano (and read 

 randomly and blindly). The results validated that aging 

 was conducted in an identical manner between studies. 



