Sulikowski et al : Age and growth estimates of Leucora/a ocellata 



409 



Discussion 



The relationship between TL and centrum diameter was 

 linear and significant, indicating that the centra grew pro- 

 portionally to skate length for all size classes, and thus this 

 structure was useful for age analyses (Kusher et al., 1992). 

 The 5.8% lAPE index suggests that our aging method rep- 

 resents a precise approach to the age assessment of L. ocel- 

 lata. Minimal width of the marginal increment for winter 

 skates captured in May supports the hypothesis of annual 

 band formation in this species. Moreover, these results 

 compare favorably to growth cycles in marginal incre- 

 ments for other skates found in temperate waters whose 

 vertebral bands are formed annually (Holden and Vince, 

 1973; Waring, 1984; Natanson, 1993). 



Von Bertalanffy parameters, as determined by our study, 

 suggest that females attain a slightly larger asymptotic TL^ 

 (1374 mm) than males (1218 mm) and grow more slowly 

 (/f=0.059 and 0.074, respectively). This trend follows a com- 

 mon pattern in batiods. Holden ( 1977), Waring ( 1984), Ry- 

 land and Ajayi ( 1984), Brander ( 1981 ), and Walmsley-Hart 

 et al. (1999) found similar tendencies in several species of 

 skates, and Martin and Cailliet (1988) found comparable 

 results in the bat ray (Myliohatis californica). 



Our estimates of L„ exceeded those of the largest speci- 

 mens in our field collections (940 mm for females and 932 

 mm for males). Nevertheless, data from extensive trawl 

 surveys in the western Gulf of Maine and the Mid-Atlantic 

 offshore region spring and autumn bottom trawl surveys 

 from 1967 to 2000 (Northeast Fisheries Science Center-) 

 indicated that mean TL did not exceed 1000 mm. Thus, 

 we suspect that our von Bertalanffy equation produces an 

 accurate estimation of L,^ for winter skate. Walmsley-Hart 



et al. (1999) overestimated L^ fori?. puUopunctata and sug- 

 gested that small sample size and rareness of large indi- 

 viduals were most likely responsible. Because fishing gear 

 was not biased towards a specific marketable skate size 

 and because all size classes of L. ocellata were represented, 

 it is quite possible that the rareness of large individuals led 

 to the augmented L.^ in combined and individual sexes in 

 our study. Possibly, a larger sample size of winter skates 

 would produce significant and divergent results with re- 

 gard to von Bertalanffy parameters. However, the close fit 

 of the data to the VBGC for L. ocellata indicates the VBGC 

 is an appropriate model for this species. 



Preliminary estimates of age and growth parameters are 

 available for winter skate in Canadian waters ( eastern Sco- 

 tian Shelf) from Simon and Frank ( 1996), who reported the 

 results of a study conducted at St. Mary's University by R. 

 Nearing. Combined sexes of winter skates (/2=242) with TL 



