Reproductive biology of two commercially exploited skates, Raja binoculata and R. rhina, in the western Gulf of Alaska

Abstract

This study provides the first detailed information on the reproductive biology of two large and abundant eastern North Pacific Ocean skate species: big skate ( Raja binoculata) and longnose skate ( Raja rhina). Skates were collected in the western Gulf of Alaska during 2005 and 2006 after a targeted fishery for these two species developed around Kodiak Island, Alaska; both species are also taken as by-catch to other fisheries. A total of 307 females (20.1–183.3 cm TL) and 138 males (19.5–143.7 cm TL) R. binoculata, and 354 females (18.1–145.0 cm TL) and 318 males (21.1–135.8 cm TL) R. rhina were collected. Female R. binoculata were found to attain first (e.g., smallest individual) maturity at 125.8 cm TL and 50% at 148.6 cm TL. Males were found to attain first and 50% maturity at 124.0 and 119.2 cm TL, respectively. No gravid female R. binoculata, with egg cases in utero, were encountered during the study. Female R. rhina were found to attain first and 50% maturity at 102.2 and 113.1 cm TL, respectively. Gravid female R. rhina, with egg cases in utero, were recorded throughout the sampling period. Males attained first maturity at 101.0 cm TL and 50% maturity at 102.9 cm TL. Histological analysis did not reveal significant changes in spermatocyst production for either species during the sampling period. Both species appear to be reproductively active year-round as no seasonal cycle was evident. This study provides new and essential information on the reproductive biology of these two commercially targeted skate species.