A major nursery area around the Svalbard archipelago provides recruits for the stocks in both Greenland halibut management areas in the Northeast Atlantic

Abstract

Abstract Greenland halibut in the Northeast Atlantic currently have two separate management units: the Northeast Arctic (NEA) stock and the West Nordic (WN) stock. The biological basis for this separation is weak, and while the NEA stock has a well-described nursery area in the waters around the Svalbard archipelago, no such major nursery area is known for the WN stock. To examine the linkages between these two stocks, a tagging experiment was conducted in the Svalbard nursery area, which is the only known large nursery area for Greenland halibut in the Northeast Atlantic. A total of 25 149 juvenile Greenland halibut were tagged and released in the period 2005–2008, and as of January 2014, there were 155 recaptures: 92% were caught more than 170 km from the tagging site, while 59% had travelled more than 1500 km. During the first 2 years after tagging, recaptures were reported only from the fishing grounds in the NEA management area. Subsequently, the number of recaptures decreased in the NEA management area, while recaptures were beginning to be reported from the WN management area, which by 2014 accounted for 61% of the total number of reported recaptures. It was concluded that the stocks in the two management areas for Greenland halibut in the Northeast Atlantic have a common nursery ground, and that a recruitment index based on data from the nursery around Svalbard would reflect possible recruitment to the stocks of both management units. The lack of recaptures on the Southeast Greenland shelf suggests a stock boundary west of Iceland. It is suggested to further explore the stock delineation in these areas and that future stock assessments should explore the potential advantage of using a combined assessment model for the two current management units.