266 



Abstract— Growth parameters were 

 estimated for porbeagle shark tLamna 

 iiasus) in the northwest Atlantic Ocean 

 on the basis of vertebral annuli. A total 

 of 578 vertebrae was analyzed. Annuli 

 were validated up to an age of 1 1 years 

 by using vertebrae from recaptured oxy- 

 tetracycline-injected and known-age 

 sharks. Males and females grew at sim- 

 ilar rates until the size of male sexual 

 maturity, after which the relative growth 

 of the males declined. The gi-owth rate of 

 the females declined in a similar manner 

 at the onset of maturity. Growth cui-ves 

 were consistent with those derived from 

 tag-recapture analyses iGROTAG) of 

 76 recaptured fish and those based on 

 length-frequency methods with mea- 

 surements from 13,589 individuals. Von 

 Bertalanffy growth curve parameters 

 (combined sexes) were L., = 289.4 cm fork 

 length. A' = 0.07 and /„ = -6.06. Maxi- 

 mum age, based on vertebral band pair 

 counts, was 25 and 24 years for males 

 and females, respectively. Longevity cal- 

 culations, however, indicated a maxi- 

 mum age of 45 to 46 years in an unfished 

 population. 



Validated age and growth of the porbeagle shark 

 {Lamna nosus) in the western North Atlantic Ocean 



Lisa J. Natanson 



Joseph J. Mello 



National Marine Fisheries Service 



28 Tarzwell Dr 



Narragansett, Rhode Island 02882 



E-mail address (for L J Naianson) Lisa Natansonia'noaa gov 



Steven E. Campana 



Marine Fish Division 



Bedford Institute of Oceanography 



PO Box 1006 



Dartmouth, Nova Scotia 



Canada B2Y 4A2 



Manuscript accepted 22 August 2001. 

 Fish. Bull. 100:266-278 (2002). 



The porbeagle iLamna nasiis) is a 

 large pelagic shark in the family Lam- 

 nidae that occurs in the coW, temper- 

 ate waters of the North Atlantic, South 

 Atlantic, and South Pacific oceans. The 

 species extends from Newfoundland to 

 New Jersey in the western North Atlan- 

 tic (Castro, 1983), and from Iceland and 

 the western Barents Sea to Morocco and 

 the Mediterranean in the eastern North 

 Atlantic (Compagno, 1984). Directed 

 commercial fisheries for porbeagle have 

 existed in the western North Atlantic 

 in both U.S. and Canadian waters since 

 the early 1960s (Campana et al.M, The 

 fishery collapsed in 1967, apparently 

 from overfishing. Canadian fishermen 

 maintained low and apparently sus- 

 tainable catches in the 1970s and 1980s, 

 which allowed the stock to rebuild. A 

 renewed fishery for porbeagle began in 

 both the United States and Canada in 

 the 1990s (Campana et al.M. 



Accurate age determinations are nec- 

 essary for both the assessment and 

 management of the porbeagle shark be- 

 cause they form the basis for calcula- 

 tions of growth and mortality rates, age 

 at maturity, age at recruitment, and 

 estimates of longevity. Aasen (1963), 

 in an early study of porbeagle growth, 

 generated a growth curve for the west- 

 ern North Atlantic population based on 

 analyses of length frequencies from a 

 single year and on vertebral readings 

 of one fish. However, he did not pro- 



vide any independent confirmation of 

 the accuracy of his age estimates. Fran- 

 cis and Stevens (2000) used length-fre- 

 quency analysis to estimate the growth 

 of juvenile porbeagles in the South Pa- 

 cific. Both of these studies indicated 

 that porbeagle grow relatively rapidly 

 through the first year of life, but only 

 minimal information has been avail- 

 able for older fish. 



In view of the history of the porbea- 

 gle fishery and the need for accurate 

 biological information for management 

 of this species, an intensive U.S. -Cana- 

 dian cooperative research program was 

 initiated in 1999 to obtain detailed 

 life-history and population data. This 

 study reports on one portion of this pro- 

 gram, specifically, the use of vertebrae 

 to determine age and growth. The ver- 

 tebral growth readings were validated 

 as annuli on the basis of recaptures 

 of tetracycline-injected and known-age 

 sharks and verified by comparison with 

 growth curves based on tag-recapture 

 and length-frequency analyses. 



' Campana, S., W. Joyce, L. Marks. P. Hurley, 

 L. J. Natanson, N. E. Kohler, C. F. Jensen, 

 J. J. Mello, and H. L. Pratt Jr 2000. 

 The rise and fall (again) of the porbeagle 

 shark population in the Northwest Atlan- 

 tic. Unpubl. manuscr. Marine Fish Divi- 

 sion, Bedford Institute of Oceanogi'aphy, 

 P.O. Box 1006, Dartmouth, Nova Scotia, 

 Canada B2Y 4A2. 



