Bomb dating and age determination of skates (family Rajidae) off the eastern coast of Canada

Abstract

Abstract McPhie, R. P., and Campana, S. E. 2009. Bomb dating and age determination of skates (family Rajidae) off the eastern coast of Canada. – ICES Journal of Marine Science, 66: 546–560. Recent declines in abundance of skates off the eastern coast of Canada have heightened the need for validated age and growth estimates in the region. In all, 502 winter (Leucoraja ocellata), little (Leucoraja erinacea), thorny (Amblyraja radiata), and smooth (Malacoraja senta) skate vertebral centra collected seasonally between 1999 and 2004 were sectioned using a mass processing method, then used to reconstruct growth in each species. Bomb radiocarbon (Δ14C) analysis was used to provide evidence of annual band-pair deposition in thorny skates. Estimates of L∞ from traditional von Bertalanffy growth models (VBGM) ranged from 60.6 cm (little skate) to 89.7 cm (thorny skate), and K estimates from 0.07 (thorny skate) to 0.19 (little skate). A modified two-parameter VBGM (Lmax = 94.1 cm) fitted to winter skate length-at-age data yielded a value of K of 0.15. Maximum observed ages ranged from 12 (little skate) to 19 years in both winter and thorny skates. The year-specific incorporation of Δ14C milled from thorny and winter skate vertebral sections closely resembled shark-derived reference chronology values from the Northwest Atlantic. Pre-bomb Δ14C in a thorny skate collected in 1988 and aged at 23 years appeared to validate age interpretations and suggested that thorny skate reach an absolute age of at least 28 years, the oldest validated age reported for any species of batoid.