Sibling Species Amblyraja hyperborea and A. jenseni in Slope Waters of Eastern Canada: An Ecomorphological Description

Abstract

Deepwater survey data and specimens collected from the Grand Banks to Baffin Bay in the Northwest Atlantic were used to examine the distribution, morphometrics, meristics and maturity of two siblings, Amblyraja hyperborea and A. jenseni. Our study confirmed that the two species occupy different locations, their distributions separated by Davis Strait, a biogeographic break separating Atlantic from Arctic waters. A. hyperborea with a smaller maximum size and size at maturity inhabited colder Arctic slope waters in Baffin Bay while larger A. jenseni were located in warmer Atlantic slope waters. Despite their distributional separation and thus reproductive isolation, spine counts and body morphology were almost indistinguishable between species. Only upper jaw teeth row count and difference in the size of spines on the mid-rear wings differentiated the two species. Also, for both species, the proportion of dorsal fins joined, disc shape and relative tail length changed with total length. Secondary reproductive anatomy, clasper length and vas deferens weight, shell gland and uterus weight underwent initial acceleration in growth when the gonads transitioned to stage 2 (adolescent, maturing). Also, YOY A. hyperborea were found to distribute at shallower depths than larger stages, constituting a nursery, which was not observed for A. jenseni.