Age determination and growth of the beaked skate, Dipturus chilensis, in Northern Patagonia

ILEANA AVERSA, MARINA; SILVANA DANS; ENRIQUE CRESPO

St., Louis, Missouri, EEUU

Congreso; Joint Meeting Of Ichthyologists And Herpetologists.; 2007

Age and growth of the beaked skate were estimated from bands in the vertebral centra of 405 individuals obtained from incidental catches of the Argentine hake (Merluccius hubbsi) fishery. Age estimates were not validated and was assumed that the relationship between a hyaline plus an opaque ring corresponds to one year age.  All skates collected were sexed, sized and weighted and a section of the vertebral column including the first 20 elements was removed. The histological technique used to enhance the growth bands on the vertebral centra was found to be satisfactory used for ageing marine mammals and some elasmobranches species. Stained sections provided repeatable and consistent bands counts though marginal crowding in the centra of older skates may leaded to underestimate the number of rings. The oldest male was 16 yr old and 101 cm of total length; the oldest female was 24 yr old and 133 cm of total length. Gompertz and von Bertalanffy growth models were fitted to the age and length data (L) and to age and disc width data (DW). Both growth models fit the data well. Maximum likelihood tests indicated that models constructed for males and females separately described growth data of the beaked skate better than one with both sexes combined.  The von Bertalanffy growth curves derived from this technique indicate that female beaked skates reach greater size (L¥=138 cm; DW¥= 102 cm) and have a lower growth rate (K=0.08) than males (L¥=110 cm; DW¥= 81 cm; K= 0.117). Beaked skates in northern Patagonia had lower estimates of  L¥ than their conspecifics in the Pacific Ocean.