Estimates of reproductive potential of Greenland halibut (Reinhardtius hippoglossoides) in East Greenland based on an update of maturity status

When estimating reproductive potential (RP), correct interpretation of the maturity status is essential. It has now become apparent the presence of vitellogenic oocytes within the ovary of Greenland halibut (Reinhardtius hippoglossoides) does not necessarily indicate they will spawn within the next twelve months.

This has led to a revision of the interpretation of the maturity scale where fish which contain only a developing cohort (DC) of oocytes are considered immature. Comparisons were made of estimates of L50 of female Greenland halibut in East Greenland using the previous interpretation of maturity status where the leading cohort (LC) and DC oocytes are not differentiated with the new interpretation where they are.

Differentiation led to an increase from 63.8 to 80.2cm and from 61.2 to 74.1cm for the northern (between 63°40′N and 67°00′N) and southern area (between 61°45′N and 62°40′N), respectively. Combining the maturity data with abundance data of Greenland halibut in East Greenland, spawning stock biomass (SSB) and total egg production (TEP) was estimated in four quadrants between 1998 and 2012 using both the previous and current interpretation of the maturity scale.

Using the new interpretation of the scale led to a decrease in SSB estimates of 28–92% in specific areas and years, with an average of 56%. Estimates of TEP were directly proportional to SSB so this approach did not offer any advantages over SSB as a measure of reproductive potential. Length composition of Greenland halibut caught by Norwegian fishing vessels fishing in East Greenland indicate that 85 and 57% of the females caught by the trawl and longline fleet respectively in the northern area and 46% caught by the longline fleet in the southern area were immature.