Age and growth estimates of the winter skate

Age and growth estimates of the winter skate (Leucoraja ocellata) in the western Gulf of Maine 西緬因灣眼斑鰩年齡與成長評估 James A. Sulikowski Michael D. Morin Seung H. Suk W. Huntting Howell Fishery Bulletin. 101: 405– 413 (2003). 指導教授 莊守正老師 學生 陳婧綺 學號M 95310001

Winter Skate l l l Morphology Distribution Biology © George Burgess

Morphology l l l Disk rounded. With many small dark spots on upper surface, usually 1 -4 ocelli. Young have long middorsal row of large spines on disk and tail. www. osl. gc. ca/. . . /poiss/sp/images/l-ocellata. jpg © James Sulikowski

Distribution l Western Atlantic: Newfoundland Banks and southern Gulf of St. Lawrence in Canada to North Carolina, USA. http: //fishbase. fishinfo. cn/Summary/Species. Summary. php? id=2562

Biology l l l Prefer sandy and gravelly bottoms in shoal water in the north range. Mostly inactive during daylight hours, but active under dark conditions. Distinct pairing with embrace. Young may tend to follow large objects, such as their mother. http: //www. osc. mun. ca/oscpictures/container/Harbour%20 Main%20 April%2018, %202005/target 11. html

Introduction Little is known about the biology of many elasmobranchs’ life history. l Difficulty in obtaining samples. l Recent assessment studies suggest that the biomass of the winter skate maybe below threshold-levels, mandated by the Sustainable Fisheries Act. l

l To add insight into the life history of the species and the status of the stock, we estimated age and growth rates of L. ocellata by interpreting annular counts and marginal increments on vertebral centra from specimens collected in the western Gulf of Maine.

Materials and Methods Sampling l l l Sampling period: November 1999 and May 2001. Sampling amount: 304. Sampling site: New Hampshire’ coast. Approximate depth: 9 -107 m. Captured by otter trawl Total length, disc width, and total wet weight were measured and recorded.

Preparation of vertebral samples l Vertebral samples, taken from above the abdominal cavity, were removed from 230 winter skates (132 females and 98 males) labeled, and stored frozen.

Counts of annuli

IAPE(平均百分誤差指數) l l N= the number of skate aged R= the number of readings Xij= the ith age determination of the jth fish Xj= the average calculated for the jth fish

Marginal increment analyses D: 椎徑 Dn: 脊椎骨最外輪之輪 Dn-1: 脊椎骨次外輪之輪徑 l Kruskal-Wallis one-way analysis of variance on ranks was used to test for differences in marginal increment by month. l

Growth estimates A von Bertalanffy growth function (VBGF) was fitted to the data with the following equation (von Bertalanffy, 1938): where Lt = total length at time t (age in years) L∞= theoretical asymptotic length k = Brody growth constant t 0 = theoretical age at zero length (minus)

Results

Morphology measurements （ｍｍ） （ｍｍ）

Vertebral analyses

Age and growth estimates Males: L∞ = 1218 mm (TL). Females: L∞ = 1374 mm (TL). IAPE=5. 8%

The oldest age estimates obtained for the winter skate were 19 and 18 years for males and females

Discussion The important of IAPE l The relationship between TL and centrum diameter was linear and significant, indicating that the centra grew proportionally to skate length for all size classes, and thus this structure was useful for age analyses. l Holden(1977), Warning(1984), Ryland Ajayi(1984), Brander (1981)and Walmsley-Hart et al. (1999) found similar temdencies in several species of skates and Martin and Cailliet(1988) found comparable results in the bat ray(Myliobatis californica). l

Conclusion

Our study provides some basic age and growth parameters for the winter skate and it supports the hypothesis that L. ocellata, like other elasmbranchs, require conservative management because they grow slowly and are susceptible to overexploitation.

Thanks for your attention

IAPE

Kruskal-Wallis one way analysis

y=a+bx

Raja ocellata 之分類系統表　 脊椎動物亞門　Subphylum Vertebrata 軟骨魚綱　Chondrichthyes 板鰓亞綱　Elasmobranchii 鯆魮目　Rajiformes 鯆魮科　Rajidae 鰩屬　Raja 眼斑鰩　Raja ocellata 本魚種非台灣魚種