Preliminary Age and Growth Estimates of the Rabbitfish,Chimaera monstrosa, with Implications for Future Resource Management

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 t0 = -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.