Jesper Boje

A cascade of warming impacts brings bluefin tuna to Greenland waters

Rising ocean temperatures are causing marine fish species to shift spatial distributions and ranges, and are altering predator-prey dynamics in food webs. Most documented cases of species shifts so far involve relatively small species at lower trophic levels, and consider individual species in ecological isolation from others. Here, we show that a large highly migratory top predator fish species has entered a high latitude subpolar area beyond its usual range. Bluefin tuna, Thunnus thynnus Linnaeus 1758, were captured in waters east of Greenland (65°N) in August 2012 during exploratory fishing for Atlantic mackerel, Scomber scombrus Linnaeus 1758. The bluefin tuna were captured in a single net-haul in 9-11 °C water together with 6 tonnes of mackerel, which is a preferred prey species and itself a new immigrant to the area. Regional temperatures in August 2012 were historically high and contributed to a warming trend since 1985, when temperatures began to rise. The presence of bluefin tuna in this region is likely due to a combination of warm temperatures that are physiologically more tolerable and immigration of an important prey species to the region. We conclude that a cascade of climate change impacts is restructuring the food web in east Greenland waters.

Oceanic Boundary Conditions for Jakobshavn Glacier. Part I: Variability and Renewal of Ilulissat Icefjord Waters, 2001–14*

JakobshavnGlacier, west Greenland, has respondedtotemperaturechangesinIlulissatIcefjord,intowhich it terminates.ThisstudycollectedhydrographicobservationsinsideIlulissatIcefjordandfromadjacentDiskoBay between2001and2014.ThewarmestdeepDiskoBaywaterswereblockedbytheentrancesillanddidnotreach Jakobshavn Glacier. In the fjord basin, the summer mean temperature was 2.88C from 2009 to 2013, excluding 2010, whenitwas 18C cooler. Despitethisvariability,summerpotential densities in the basinwereinthe narrow range of 27.20 # su # 27.31kgm 23 , and basin water properties matched those of Disko Bay in this layer each summer. This relation has likely held since at least 1980. Basin waters from 2009 and 2011‐13 were therefore similar tothosein1998/99, whenJakobshavn Glacier began toretreat, whilebasin watersin2010wereascoolas in the 1980s. The 2010 basin temperature anomaly was advected into Disko Bay, not produced by local atmospheric variability. This anomaly also shows that Ilulissat Icefjord basin waters were renewed annually or faster. Time series fragments inside the fjord did not capture the 2010 anomaly but show that the basin temperatures varied little subannually, outside of summer. Fjord velocity profiles from summer 2013 implied a basin renewal time scale of about 1 month. In model simulations of the fjord circulation, subglacial discharge from Jakobshavn Glacier could drive renewal of the fjord basin over a single summer, while baroclinic forcing from outside the fjord could not, because of the sill at the mouth.

Sexual maturity cycle and spawning of Greenland halibut Reinhardtius hippoglossoides in the Davis Strait

Female sexual maturation cycle and the main spawning time of Greenland halibut Reinhardtius hippoglossoides in the Davis Strait were studied through regularly collected samples during 1 year starting in spring 2003. Samples were collected from the southern slope of the Davis Strait Ridge between Canada and Greenland in the depth range 1000-1500 m. Female sexual maturation was described using different approaches: gonado-somatic index, visual macroscopic maturity stage index, histological microscopic maturity index and oocyte diameter measurements. A significant increase in the gonado-somatic index was seen from September onwards until February with a maximum estimated value of 18%. The proportion of mature fish increased from December until March. At the same time, the proportion of females with a low gonado-somatic index also increased from February, indicating that spawning had occurred and females were recovering. Oocyte diameter distribution revealed a leading cohort development during autumn through to December to February. A coupling between sexual maturity and fish condition was seen for females in maturing condition indicating a steady build up of stored energy in the liver from June to November.

Geographic extent of introgression in Sebastes mentella and its effect on genetic population structure

Genetic population structure is often used to identify management units in exploited species, but the extent of genetic differentiation may be inflated by geographic variation in the level of hybridization between species. We identify the genetic population structure of Sebastes mentella and investigate possible introgression within the genus by analyzing 13 microsatellites in 2,562 redfish specimens sampled throughout the North Atlantic. The data support an historical divergence between the “shallow” and “deep” groups, beyond the Irminger Sea where they were described previously. A third group, “slope,” has an extended distribution on the East Greenland Shelf, in addition to earlier findings on the Icelandic slope. Furthermore, S. mentella from the Northeast Arctic and Northwest Atlantic waters are genetically different populations. In both areas, interspecific introgression may influence allele frequency differences among populations. Evidence of introgression was found for almost all the identified Sebastes gene pools, but to a much lower extent than suggested earlier. Greenland waters appear to be a sympatric zone for many of the genetically independent Sebastes groups. This study illustrates that the identified groups maintain their genetic integrity in this region despite introgression.

Cryptic Sebastes norvegicus species in Greenland waters revealed by microsatellites

Cryptic Sebastes norvegicus species in Greenland waters revealed by microsatellites Atal Saha*, Lorenz Hauser, Rasmus Hedeholm, Benjamin Planque, Svein-Erik Fevolden, Jesper Boje, and Torild Johansen Institute of Marine Research, Tromsø Department, PO Box 6404, Tromsø 9294, Norway School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98195-5020, USA Greenland Institute of Natural Resources, Kivioq 2, PO Box 570, Nuuk 3900, Greenland Hjort Centre for Marine Ecosystem Dynamics, Bergen 5817, Norway Department of Arctic and Marine Biology, UiT The Arctic University of Norway, Tromsø 9037, Norway DTU Aqua – National Institute of Aquatic Resources, Charlottenlund DK 2920, Denmark *Corresponding author: tel: þ47 97959302; fax: þ47 55238531; e-mail: atal.saha@imr.no

Evaluating Biological Robustness of Innovative Management Alternatives

The influence of innovative management alternatives (participatory governance, effort management, decision rules) on biological robustness (BR) in various fisheries relevant to the EU (Baltic, Western Shelf, Faroe Islands, North Sea), was investigated with a numerical simulation model developed in the EU projects EFIMAS (2004–2008) and COMMIT (2004–2007). The index for BR was set as the percentage of years in which standard biological reference points (Bpa, Fpa) were met. The results suggest that new information obtained through participatory governance may affect BR by reducing bias rather than increasing precision, implying that participatory governance should rather focus on potential sources of bias than on (perceived) low sampling efforts. Further analyses suggest that effort-based regimes combined with catch quota restrictions improve BR. However, the relative effect of catch quotas versus effort management on BR varies with circumstances, implying that careful and case-specific analyses are needed to weigh one against the other. This requires more detailed data than generally available at present, including electronic surveillance, detailed catch data, environmental/productivity data, recruitment and misreporting. Finally we analysed a decision rule consisting of a two-step management system, which allows TAC adjustment according to the state of the stock monitored during the fisheries season. Such measures may improve the BR.