Age and Growth

Chondrichthyan vertebra

Age and growth studies of sharks and rays have been initiated to fill gaps that are discovered during the compilation of the life history data matrix. Estimates of growth rates and longevity in sharks and rays are typically obtained by microscopic examination of the banding pattern deposited within the vertebrae. Skates are one focus of PSRC age and growth studies. In recent years, skate landings have greatly increased in all Pacific states. In addition, they form a large part of fisheries’ bycatch and discard in the region. The susceptibility of skates to commercial fishing pressure has been well documented in the North Atlantic, however very little is known of the biology of skates throughout the eastern North Pacific (ENP). Age and growth estimates are necessary to gain insight into the population structure and dynamics of a species. Appropriate techniques, using vertebrae, will be determined for clarifying growth zones in selected ENP skates, including the sandpaper (Bathyraja kincaidii), the roughtail (Bathyraja trachura), and California (Raja inornata) skates. Suitability of caudal thorns as an ageing structure will also be investigated, possibly providing another non-lethal ageing technique for this group. Age-at-size estimates based upon microscopic examination of vertebrae and other calcified structures will be fit to appropriate growth models to describe population and individual growth characteristics. These studies will provide estimates of age-at-maturity, longevity, and growth rates that are fundamental to stock assessment and sustainable fisheries management.