Different maturity scales affect estimations of fecundity, TEP and spawning stock size of Greenland halibut, Reinhardtius hippoglossoides (Walbaum, 1792)

Abstract

Based on 138 samples from female Northeast Arctic Greenland halibut (Reinhardtius hippoglossoides) taken in November–December 2011 at spawning grounds on the continental slope of the Barents Sea, the relationships between fecundity and fish size were established and found to be in the same range as those of estimates from 1996, 1997 and 1998. Ovarian maturity stages were determined by using a scale proposed by Kennedy et al. in 2011 based on microscopic oocyte diameter measurements. These data were compared to the maturity stages determined at sea in a routine manner, based on a standard macroscopic scale and a macroscopic scale previously developed for Greenland halibut. Maturity ogives were derived based on the three different maturity scales and an overestimation of both spawning stock size and total egg production (TEP) of approximately 20% was found when the macroscopic scales were used in the conventional way to determine maturity ogives. Most accurate ogives are assumed to be derived based on the microscopic scale, but this method can be impractical at sea on routine surveys. Thus, it is proposed to use the special macroscopic scale for Greenland halibut females, but consider both truly immature (stage 1) and early maturing (stage 2) females as non-spawning. This adjustment gives maturity ogives that do not deviate significantly from those based on the microscopic scale, and results in estimates of spawning stock size and TEP that we consider appropriate for stock assessment purposes.