. 2005. Age determination, growth and reproduction in the lesserspotted dogfish, Scyliorhinus canicula (L.). J. Northw. Atl. Fish. Sci., 35: 89-106. doi: 10.2960/J.v35. m504 Abstract Successful fisheries management is based on the knowledge of species-specific life history data, comprising age and general morphometric information. This study presents such information for the lesser-spotted dogfish (Scyliorhinus canicula).Four samples of S. canicula, totalling 745 individuals (310 males and 435 females), were collected by fisheries scientists from research and commercial vessels in ICES areas VIIa and VIIg, over the period November 1999-November 2000. A further 10 hatchling specimens (5 males and 5 females), from a commercial aquarium, were also collected. The total body length range for males was from 10.4 cm to 71.0 cm and for females was 10.3 cm to 70.0 cm.A total of 706 specimens (301 male and 405 female) were aged using crystal violet stained sagittal sections of vertebral centra. Centrum length grew in proportion to total body length for males and females. Age estimates ranged from 0 years (hatchlings) to 11 years for males and 0 years to 12 years for females. Annual periodicity of growth increment deposition was suggested following analysis of the centrum edge characteristics of a subsample of specimens by all three readers. The von Bertalanffy growth parameters L ∞ , K and t 0 were estimated for males (L ∞ = 87.42 cm, K = 0.118, t 0 = -1.09) and females (L ∞ = 75.14 cm, K = 0.15, t 0 = -0.96) separately. The length at 50% maturity for males was 53.5 cm and for females was 57.0 cm. These findings increase the life history data available for S. canicula and form a valuable contribution to the implementation of basic management measures to ensure the sustainability of catches of this by-catch species.

The age, growth and maturity of 1 554 individuals (268 Raja brachyura, 258 R. clavata, 468 R. montagui and 560 Leucoraja naevus) of the main commercial ray species from the Irish Sea were determined from samples taken from commercial and research trawls between 1997 and 1998. Sagittal sections of vertebral centra stained using crystal violet enhanced the underlying band patterns of each species, allowing the derivation of age and von Bertalanffy growth parameters. Age estimates were relatively low for each species, with a maximum age of 7 yr recorded for R. montagui and 8 yr for each other species. Growth rate parameters ranged between K = 0.093 (L ∞ = 139.500 and t 0 = -1.841) for female R. clavata and K = 0.304 (L ∞ = 72.400 and t 0 = -0.924) for male R. montagui, and were notably higher for both the smaller growing R. montagui and R. naevus. Morphological assessment of maturity, revealed that; male R. montagui matured at the smallest size (53.651cm) and earliest age (3.410 yrs), male and female R. clavata matured at the greatest age (6.130 yrs) and female R. brachyura matured at the largest size (83.560 cm). In each species, an abrupt increase in clasper size in males and nidamental gland width in females was closely associated with the onset of maturity. Age, growth and maturity are discussed for each species with respect to previous studies and observed trends in the fishery.

The holocephalan, Chimaera monstrosa, constitutes 13-15% of the discards in deepwater trawlers operating off the West Coast of Ireland. Given the increased interest in the production of dietary supplements for human consumption derived from the liver oil of this species, a directed fishery has the potential to develop in areas of occurrence. In common with the majority of shelf slope and deepwater species, there is a paucity of biological and life history information available on this species. No information is available on the growth and maturation rates, with the closest comparative material being from commercially retained Callorhinchus species from New Zealand. A total of 62 specimens (10 male, 52 female) were collected non-randomly, by at-sea observers in the Rockall Trough and Faroe-Shetland Channel (ICES areas; 27 IVa, VIIb and VIIc) in August and October 2001 from the hauls of commercial fishing vessels. Specimens ranged in size from 26 cm to 74 cm pre-supra caudal fin length. The range of maturity was from juvenile to mature for both sexes. Dorsal fin spines were removed and serial cross-sections were used to establish the optimum position of section. Growth increments were counted in ground and polished transverse sections, and four readers conducted 3 independent readings of each section. The estimated ages ranged from 3 to 30 years and 4 to 26 years, for males and females, respectively. The von Bertalanffy growth parameters of Chimaera monstrosa were: L ∞ = 78.87 (cm), K = 0.0673 per year and t 0 =-2.513 (yr). These parameters, together with the estimated ages, indicate that Chimaera monstrosa is a long lived, late maturing species. A significant relationship between the corrected total spine length and the estimated age was determined. As the removal of the dorsal fin spine is a simple technique, which does not decrease the commercial value of the fish, this method could provide a useful tool for the interim determination of age prior to confirmation by more detailed techniques.

Caudal thorns from bathyrajids (family Rajidae), for which surface band patterns have previously been correlated with an annual cycle of vertebral band deposition, were examined to ascertain the underlying growth band structure with a view to understanding their growth processes. Caudal thorn samples from Bathyraja brachyurops, a commercial ray species from the Falkland Islands were sectioned transversely using both resin embedding and decalcification/wax embedding procedures. Sectioning revealed that internal bands formed as a series of cones underlying each other, and that broad surface bands formed annually during periods of rapid somatic growth. Surface ridges representing a near stasis in somatic growth formed at the periphery of each cone. This proposed growth process was further verified by the incorporation of tetracycline at the periphery of caudal thorns from a tagrecaptured bathyrajid. The benefits of using sectioning to enhance band resolution of larger specimens of slower growing species, particularly in the case of worn and tightly spaced surface band patterns are also discussed.

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