Atlantic bluefin tuna (Thunnus thynnus) in Greenland — mixed-stock origin, diet, hydrographic conditions, and repeated catches in this new fringe area

Abstract

Based on collaboration with the Greenlandic fishing fleet, we document the presence of Atlantic bluefin tuna (Thunnus thynnus) in most years from 2012 to 2018 in the waters east of Greenland (northern Irminger Sea). In total, 84 individuals have been registered as bycatch in the commercial fisheries in Greenland waters, which indicates that the first catch of 3 individuals in 2012 was not a single extreme observation, but that East Greenland waters have become a new outer limit of an expanded tuna habitat. Genetic analyses indicate that specimens from this region are mostly of Mediterranean origin with a small proportion originating from the Gulf of Mexico stock. Stomach content analysis suggests that the main prey is Atlantic mackerel (Scomber scombrus). The tunas ranged in size from 140 - 270 cm corresponding to an estimated age range of 5-16 years; most were probably mature. The wide size-age range suggests that many year-classes are participating in the migration to this region. Sea temperatures during summer have been above the long-term average in recent years of interest. Summer residence of bluefin tuna in the region could be due to a combination of increasing temperatures and higher overall abundances of both bluefin tuna and a key prey species (Atlantic mackerel)

New historical data for long-term swordfish ecological studies in the Mediterranean Sea

“…For example, swordfish also spawn in the eastern Mediterranean (Tserpes et al, 2008), and the presence of multi-ple spawning sites could be associated with different subpopulations within the Mediterranean Sea, especially if individuals possess migration fidelity to specific spawning sites (Romeo et al, 2009b). However, the locations of feeding areas and overwintering sites used by potentially distinct spawning groups and the possibility that individuals from multiple spawning sites use common feeding areas (as is the case in other pelagic species such as bluefin tuna and Atlantic herring (Dickey-Collas et al, 2010;Jansen et al, 2021;Rodríguez-Ezpeleta et al, 2019; are unknown and remain to be described for Mediterranean swordfish. New analyses of multiple sources of catch data having broader spatial-temporal coverage, supplemented with new tagging studies, could be used to investigate reproductive and migratory processes such as these.…”

Skilful decadal-scale prediction of fish habitat and distribution shifts

“…Entirely independently, mechanistic bioenergetics modelling of the oxygen requirements and aerobic capacity of the species also reached a similar result (Muhling et al , 2017). Like others (MacKenzie et al , 2014; Jansen et al , 2020), we therefore employ the 11°C isotherm for the August mean (the warmest month in the region) to define the maximum limit of thermally-suitable feeding habitat for this species in the northern North Atlantic.…”

“…The Northeast Atlantic stock of mackerel supports one of the most valuable fisheries in Europe and recent distribution shifts into Icelandic and Greenlandic waters (Jansen et al , 2016) have driven the aforementioned conflict over fishing rights. Atlantic bluefin tuna ( Thunnus thynnus ) is a large commercially valuable and endangered top-predator: in recent years the species has shifted into the Irminger Sea and Denmark Strait (MacKenzie et al , 2014), opening up new fishing opportunities for Iceland and Greenland (Jansen et al , 2020). Blue whiting ( Micromesistius poutassou ) has at times been one of the world’s largest fisheries and its spawning distribution shifts regularly between the waters of the UK, Ireland, Faroe Islands and areas beyond national jurisdiction (Miesner and Payne, 2018), a potential problem in light of the UK’s departure from the EU.…”

Are transboundary fisheries management arrangements in the Northwest Atlantic and North Pacific seaworthy in a changing ocean?

“…Migration is believed to be linked to the rising ocean temperature off eastern Greenland and the migrations of key prey, especially mackerel, into the region (MacKenzie et al , Jansen et al 2016Jansen 2019, personal communication). A reported 84 bluefin tunas have been taken as bycatch since 2012 (Jansen et al 2020). Greenlandic catches raise substantial governance challenges.…”