Catch, discarding, age estimation, growth and maturity of the squalid shark Deania calceus west and north of Ireland

摘要

Deania calceus (Lowe, 1839), the bird-beak dogfish, is a dominant species in trawl and longline catches in the Rockall Trough and the slopes of the Porcupine Bank, west and north of Ireland. It is discarded because the carcass is currently of no commercial value. The distribution and biology of this species was investigated from trawl and longline surveys (1996-1999) of the continental slope off Ireland from 49degreesN to 58degreesN. The highest catch rates were in the depth range 500-900 m on the southern slopes of the Rockall Trough and western slopes of the Porcupine Bank. Males outnumbered females in all but the greatest depths. The length range was 56-117 cm for females and 55-109 cm for males. First and second dorsal spines were used for age estimation and each produced similar results. Age estimates, whilst not validated, ranged from I I to 35 years for females and from 13 to 29 years for males. Comparisons with a published study in Portuguese waters show that smaller and younger specimens not present in the study area were present off Portugal. The results of this study and from the Portuguese study were used to construct von Bertalanffy growth curves for males and females. Mean ripe oocyte number was 13 (range: 6-14). Very few gravid females were recorded and most females were immature. Length at 50% maturity was 85 cm for males and 106 cm for females.