Conraih et a\ Age and growth of Mustelus canis 



679 



mately 20-cm size difference in both maximum length 

 and length at maturity for males and females. Female 

 growth parameters (Fig. 6) were L = 123.57 cm, K = 

 0.2919/yr, and tg = -1.9432 years (Table 3). The largest 

 female was 132 cm TL, and 50% of females were found 

 to mature at 102 cm TL and at four to five years of age 

 (Conrath and Musick, 2002). The oldest estimated age for 

 a female smooth dogfish in the study was 16 years and 

 age of the largest female was estimated at nine years old. 

 Male growth parameters (Fig. 6) were L,, = 105.17 cm, K = 

 0.4399/yr, and t^ = -1.5235 years (Table 3). The largest 

 male in the study was 112 cm TL, and 50% of males were 

 found to mature at 85 cm TL and two to three years of age 

 (Conrath and Musick, 2002). The oldest estimated age for 

 a male smooth dogfish in the study was 10 years, and age 

 of the largest male was estimated at six years old. 



The plot of seasonal growth of age-0 and age-1 smooth 

 dogfish indicated a plateau in growth between the months 

 of October and February or March, suggesting slow growth 

 during this period (Fig. 7). There was also a plateau in 

 growth between October and February for both the 1997 

 and the 1998 cohorts. The mean TL of the 1997 cohort in 

 September 1997 was 51.62 cm {n=31, SE=0.552) and the 

 mean TL of the 1998 cohort in September 1998 was 53.39 

 cm ln=23. SE=0.579), whereas the mean TL of the 1997 

 cohort in February 1998 was 57.89 cm (n = 18, SE=0.836) 

 and the mean TL of the 1998 cohort in February 1999 was 

 57.29 cm (/! = 14, SE=1.605). Assuming a birth length of 40 

 cm, age-0 animals grew approximately 12-14 cm between 

 May and September and only 4-7 cm between September 

 and February. 



Discussion 



Precision estimates, marginal increment analysis, and 

 seasonal growth patterns justify the use of vertebrae as 

 an aging tool for the North Atlantic population of smooth 

 dogfish. The agreement within one year between two read- 

 ers was high for all size groups (>90%) with the excep- 

 tion of the largest size class (123-132 cm). At this length 

 it becomes very difficult to interpret the margin of the 

 vertebrae and to distinguish between real growth bands 

 and growth checks. Therefore, the maximum age may be 



