Ecosystem Variability in West Greenland Waters

Arctic puzzle: Pioneering a northern shrimp (Pandalus borealis) habitat model in Disko Bay, West Greenland

Recent advancements in spatial modelling leverage remote sensing data and statistical species-environment relationships to forecast the distribution of a specific species. Our study focuses on Disko Bay in West Greenland, recognized as a significant marine biodiversity hotspot in the region. We conducted comprehensive analyses using multiple datasets spanning from 2010 to 2019, incorporating shrimp and fish surveys, commercial shrimp fishery catches, high-resolution (25 × 25 m) multibeam bathymetry and backscatter data along with a medium-resolution (200 × 200 m) bathymetric model, measured and modelled oceanographic data, and satellite chlorophyll data. Through multivariate regression analysis, we tested the significance of various physical factors (seafloor depth, sediment class, bottom water temperature, bottom water salinity, bottom current velocity, space, and time), biological factors (chlorophyll a, Greenland halibut (Reinhardtius hippoglossoides)), and anthropogenic impact (shrimp fishery; standardized catch per unit effort) on the density of northern shrimp in the area. Our results indicate a significant association between northern shrimp density, seafloor depth, and sediment class, explaining 36 % of the variation in shrimp density. Subsequently, we developed a high-resolution (optimized) spatial linear mixed-effect model to map the distribution of northern shrimp across Disko Bay, representing the first model of its kind developed for an Arctic area. The optimal habitat for northern shrimp is characterized by medium-deep waters (approximately 150-350 m), turbulent conditions, and mixed sediments, predominantly located in the northern and southern regions of Disko Bay. Notably, the northern region hosts a relatively diverse benthic community, with northern shrimp and sponges as the primary contributors of epibenthic biomass. This novel high-resolution model significantly enhances our understanding of the physical drivers and detailed spatial patterns influencing the distribution of northern shrimp in the Arctic.

Impact of Holocene environmental change on the evolutionary ecology of an Arctic top predator

The Arctic is among the most climatically sensitive environments on Earth, and the disappearance of multiyear sea ice in the Arctic Ocean is predicted within decades. As apex predators, polar bears are sentinel species for addressing the impact of environmental variability on Arctic marine ecosystems. By integrating genomics, isotopic analysis, morphometrics, and ecological modeling, we investigate how Holocene environmental changes affected polar bears around Greenland. We uncover reductions in effective population size coinciding with increases in annual mean sea surface temperature, reduction in sea ice cover, declines in suitable habitat, and shifts in suitable habitat northward. Furthermore, we show that west and east Greenlandic polar bears are morphologically, and ecologically distinct, putatively driven by regional biotic and genetic differences. Together, we provide insights into the vulnerability of polar bears to environmental change and how the Arctic marine ecosystem plays a vital role in shaping the evolutionary and ecological trajectories of its inhabitants.

Concentration of mercury and other metals in an Arctic planktonic food web under a climate warming scenario

Arctic marine ecosystems act as a global sink of mercury (Hg) and other metals, and high concentrations of these have been measured in higher trophic-level organisms. Nevertheless, the concentrations of metals at the basis of the marine food web in the Arctic is less known despite the likelihood of biomagnification from dietary sources. We investigated the concentrations of mercury (Hg) and other metals in different size fractions of plankton in West Greenland. All size fractions contained detectable levels of Hg (ranging from 4.8 to 241.3 ng g dw-1) at all stations, although with high geographic variability, likely reflecting the sources of mercury (e.g., meltwater). In many cases, the concentrations in the larger-size fractions were lower than in the smaller-size fractions, suggesting depuration through the metabolic activity of mesozooplankton. Concentrations of Cd, Pb, V, Ni, and Cr were higher than previously reported elsewhere in the Arctic.

Historical DNA documents long-distance natal homing in marine fish

The occurrence of natal homing in marine fish remains a fundamental question in fish ecology as its unequivocal demonstration requires tracking of individuals from fertilization to reproduction. Here, we provide evidence of long-distance natal homing (>1000 km) over more than 60 years in Atlantic cod (Gadus morhua), through genetic analysis of archived samples from marked and recaptured individuals. Using a high differentiation single-nucleotide polymorphism assay, we demonstrate that the vast majority of cod tagged in West Greenland and recaptured on Icelandic spawning grounds belonged to the Iceland offshore population, strongly supporting a hypothesis of homing. The high degree of natal fidelity observed provides the evolutionary settings for development of locally adapted populations in marine fish and emphasize the need to consider portfolio effects in marine fisheries management strategies.

The ups and downs of trophic control in continental shelf ecosystems

Traditionally, marine ecosystem structure was thought to be determined by phytoplankton dynamics. However, an integrated view on the relative roles of top-down (consumer-driven) and bottom-up (resource-driven) forcing in large-scale, exploited marine ecosystems is emerging. Long time series of scientific survey data, underpinning the management of commercially exploited species such as cod, are being used to diagnose mechanisms that could affect the composition and relative abundance of species in marine food webs. By assembling published data from studies in exploited North Atlantic ecosystems, we found pronounced geographical variation in top-down and bottom-up trophic forcing. The data suggest that ecosystem susceptibility to top-down control and their resiliency to exploitation are related to species richness and oceanic temperature conditions. Such knowledge could be used to produce ecosystem guidelines to regulate and manage fisheries in a sustainable fashion.

The northern shrimp (Pandalus borealis) offshore fishery in the Northeast Atlantic

This chapter describes the development and current situation of the offshore shrimp fisheries in Iceland, Greenland, Svalbard, Jan Mayen and the Norwegian Barents Sea area, with information on the biology of Pandalus borealis and its relation to the environment. Some additional information about the inshore shrimp fisheries of Iceland and Greenland of relevance to this study is also included. The Icelandic offshore shrimp fishery started in 1975 and has formed between 68% and 94% of the annual catch of shrimp since 1984. Landings peaked at 66,000 tons in 1997. The offshore fleet increased threefold from 1983 to 1987, and catch per unit of effort doubled. The first signs of overfishing were detected in 1987, when the first total allowable catch (TAC) was set, and catches decreased during the next few years despite the discovery of new fishing grounds. Good recruitment allowed catches to rise steadily from 1990 to 1996. However, catches and stock index have decreased markedly since then, with a minimum catch for the period 1998-2003 of 21,500 tons in 2000. It has been suggested that predation by cod is an important factor affecting shrimp stock size, but mortality from predation is slightly lower than fishing mortality, so that the impact of fishing cannot be disregarded. The Greenland offshore shrimp fishery is one of the largest in the North Atlantic and it generates 90% of the export value of the country. The fishery started in 1970 in West Greenland with landings of 1200 tons, but since 1974 it has formed between 59% and 89% of the annual shrimp catch. In 2004, landings reached 113,000 tons and the fishable stock was estimated at 300,000 tons. The significant spatial expansion of the fishery from the original fishing grounds off the Disko Island area to all of the West coast south of 75 degrees N and the fleet improvement over the past three decades have made possible this spectacular growth. Other fishing grounds off the East coast have been fished since 1978, mostly by foreign vessels. Catches in this area oscillated between 5000 and 15,000 tons during the period 1980-2004. The main problem of the shrimp fishery in Greenland is its overlapping with nursery areas of redfish, Greenland halibut, cod and other groundfish species, some of which show declining trends of biomass and abundance. This led to the implementation in 2000 of sorting grids and laws that forbid fishing when the bycatch exceeds legal limits. However, it is likely that ecological processes only partially understood, such as the trophic web and hydrography of the area, greatly influence the stock abundance of the demersal community. The offshore Norwegian fishery started in 1973. The main fishing grounds are off Svalbard and in the Barents Sea. Catches at Jan Mayen have never exceeded 5% of the total annual catch of northern shrimp. Large fluctuations in catches and stock size are the main characteristic of this fishery. Stock size seems to be largely dependent on the annual hydrographic variability in the area and trends in abundance of predator species, especially cod. However, shrimp mortality due to predation has been estimated to be the same as fishing mortality, and therefore fishing probably accounts for part of the observed variability in stock size. Large populations of juvenile cod, haddock, redfish and Greenland halibut are often found on the shrimp fishing grounds. The implementation of sorting grids in 1991 and a bio-economical model in 1993 to estimate allowable maximum catches of the commercial bycatch species have not solved the bycatch problem. All the commercial fish species present on the shrimp grounds are currently below safe biological limits. This is the only fishery within the studied area that is not regulated by means of a TAC system.