Reproductive Characteristics and Mortality of Female Giant Grenadiers in the Northern Pacific Ocean

Abstract

Giant grenadiers Albatrossia pectoralis are caught as bycatch in deep‐sea commercial fisheries in relatively large numbers. The population appears to be stable, although there is no directed fishery, catch limits, or reporting requirements. The purpose of our study was to describe and quantify the reproductive life history characteristics and natural mortality of female giant grenadiers. During the summers of 2004 and 2006, a total of 338 specimens were collected from the Gulf of Alaska. Every phase of reproductive development was found, suggesting a protracted annual spawning season. An ovarian wall thickness technique was used to successfully place 31% (n = 24) of the fish with an unknown maturity status into a known category. Female age at 50% maturity was 22.9 years, and preanal fin length at 50% maturity was 26 cm. Total fecundity ranged from 35,000 to 231,000 oocytes (mean = 106,761), with a mean mature oocyte diameter of 1.26 mm. We developed a new technique for preparing otoliths for age determination by grinding off the distal surface to elucidate the growth zones; age ranged from 14 to 58 years. Estimates of natural female mortality ranged from 0.052 to 0.079 and estimates of total female mortality from 0.061 to 0.149. This life history information will be essential for future management of giant grenadier populations in the North Pacific Ocean.