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

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.

Genetic population structure in Greenland halibut (Reinhardtius hippoglossoides) and its relevance to fishery management

“…Our results are consistent with previous studies (Fairbairn 1981;Riget et al 1992;Knutsen et al 2007;Albert and Vollen 2015), but most of these studies do not cover the wide geographic range of the species. Both Knutsen et al (2007) and Roy et al (2014) found significant genetic differences between samples across the barrier we detected.…”

“…Evidence of isolation by distance was found across the Atlantic, both calculated along the major currents and shortest marine distance. This subdivision of the Greenland halibut across the Atlantic has been suggested in earlier studies (Fairbairn 1981;Riget et al 1992;Knutsen et al 2007;Albert and Vollen 2015) and is corroborated by a recent morphometric comparison of otoliths from South Greenland and Norway, respectively (Harbitz and Albert 2015). No evidence for subdivision of Greenland halibut was found either within the western Atlantic (south and west of Iceland) or within the eastern Atlantic (north and east of Iceland).…”

“…A combination of our results with earlier studies (Knutsen et al 2007;Roy et al 2014;Albert and Vollen 2015) suggests that subdividing Greenland halibut into at least two genetic components in the North Atlantic may be appropriate. We acknowledge the scarcity of data both from lack of samples southeast of Iceland, towards the Faroe Islands, and from unavailability of spawning fish and scarcity of genetic data, reducing the power to detect more detailed structure.…”

“…The geographic population structure of Greenland halibut has been described using several approaches, including morphometrics, tag recovery, and genetics (see Introduction of Roy et al 2014). Albert and Vollen (2015) suggested that the two stocks in the Northeast Atlantic (West Nordic and Northeast Arctic) share a common nursery ground in the waters off Svalbard, because a substantial proportion of juveniles tagged around Svalbard were recaptured in the West Nordic area. Almost all recaptures in the West Nordic area were reported from north and east of Iceland, a few recaptures were from the southwest of Iceland, and no tagged fish were recaptured from the fishing grounds on the southeastern Greenlandic shelf.…”

Fisheries Bycatch of Chondrichthyes

“…However, given that black scabbardfish and deep-water sharks apparently spatially overlap, other management measures should be introduced [109]. In contrast, many ray and skate species are usually taken as target species and bycatch in demersal fisheries for flatfish with thornback ray (Raja clavata) and thorny skate (Amblyraja radiata) accounting for 90-95% of the total skate bycatch in the North Sea and in the Barents Sea ecoregions, respectively [113,114]. In the North West Atlantic, sharks and their relatives are generally taken in direct fisheries and also incidentally captured, mainly in USA, Canada and Mexico (Atlantic side), and with less extent in Caribbean waters [16,115,116].…”