Diet and feeding strategy of Northeast Atlantic mackerel (Scombrus scomber) in Icelandic waters

Publisher's versionPredator-prey relations, as well as the trophic ecology of highly migratory marine species, is important to understand their impact on the ecosystem. Conventional methods were used to study the diet composition and feeding strategy of the Northeast Atlantic mackerel (Scombrus scomber), during their summer feeding migration to Icelandic waters in 2009–2014. In addition, generalised additive modelling (GAM) was used to determine which biological and environmental factors contribute to the variation of their stomach weight in the years 2011–2014. From the dietary analysis, we found that calanoid copepods (especially Calanus finmarchicus) were the most important contributor to the overall diet of mackerel in the years studied. Although in some years and areas, they also preyed heavily on larger prey items such as euphausiids, amphipods and megalopa larvae of crab and shrimp. The GAM showed that temperature and the time the day of sampling were significant explanatory variables for the stomach weight, while zooplankton biomass did not seem to have much influence. The Northeast Atlantic mackerel are ferocious feeders upon copepods, as well as exhibiting an overall opportunistic feeding strategy. During their feeding migration in Icelandic waters, they were found to feed on the most dominant species available to them.This research was funded by the Icelandic Centre for Research (grant number: 163371-051), the Marine and Freshwater Institute of Iceland and Matis as a part of a PhD project on the ecosystem impact of mackerel in Icelandic waters.Peer Reviewe

Mechanisms and consequences of life cycle diversity of beaked redfish, Sebastes mentella

Recent genetic research, supported by life history information, indicates that there are three biological stocks of S. mentella in the Irminger Sea and adjacent waters: a ‘Deep Pelagic’ stock (>500m), a ‘Shallow Pelagic’ stock (<500m), and an ‘Icelandic Slope’ stock. Throughout their range, Sebastes species are adapted to a diversity of ecological niches, with overlapping spatial distributions of different species that have little or no morphological differences. Divergence of behavioral groups into depth-defined adult habitats has led to reproductive isolation, adaptive radiation and speciation of several Sebastes species. Congruent differences in fatty acid composition and parasites suggests that the three genetically distinct populations of S. mentella are adapted to disparate trophic habitats in pelagic waters (shallower and deeper than the deep-scattering layer), and in demersal habitats on the continental slope. Patterns of morphology are also consistent with adaptation to different habitats, because pelagic forms are more streamlined. Although genetic differences and evidence for reproductive isolation are clear, these populations appear to share common nursery habitats on the Greenlandic Shelf. Spatial overlap at early life stages and depth-defined adult populations present challenges for stock identification and fishery management. Effective resource monitoring, conservation and fishery management requires that the spatial definition of management units reflects biological stock structure. We describe a proposal for a redefinition of practical management units that are based on geographic proxies for biological stocks which minimizes mixed-stock catches according to spatial patterns of the recent fishery

Evidence of unidirectional hybridization and second‐generation adult hybrid between the two largest animals on Earth, the fin and blue whales

Biodiversity in the oceans has dramatically declined since the beginning of the industrial era, with accelerated loss of marine biodiversity impairing the ocean's capacity to maintain vital ecosystem services. A few organisms epitomize the damaging and long‐lasting effects of anthropogenic exploitation: some whale species, for instance, were brought to the brink of extinction, with their population sizes reduced to such low levels that may have cause a significant disruption to their reproductive dynamics and facilitated hybridization events. The incidence of hybridization is nevertheless believed to be rare and very little information exist on its directionality. Here, using genetic markers, we show that all but one whale hybrid sample collected in Icelandic waters originated from the successful mating of male fin whale and female blue whale, thus suggesting unidirectional hybridization. We also demonstrate for the first time the existence of a second‐generation adult (male) hybrid resulting from a backcross between a female hybrid and a pure male fin whale. The incidence of hybridization events between fin and blue whales is likely underestimated and the observed unidirectional hybridization (for F1 and F2 hybrids) is likely to induce a reproductive loss in blue whale, which may represent an additional challenge to its recovery in the Atlantic Ocean compared to other rorquals

Implementing the Ecosystem Approach to Fisheries Management

Formal principles underlying the utilization of marine resources have been under scrutiny and development for several decades. After centuries of largely uncontrolled fishing, methods for ascertaining population dynamics were developed and implemented through stock assessments. The principal international legal instrument of the 1982 United Nations Convention on the Law of the Sea provided guidance. In addition, international organizations were set up to provide consistent advice on the utilization of fish stocks and shellfish (Marashi, 1996). For many nations, the development of national rules and regulations also increased. Initially, the development mostly pertained to the sustainable harvesting of individual fish stocks, but later also increasingly around general rules for responsible behavior with regard to resource utilization. For example, discarding of unwanted catch was an obvious issue that needed addressing, as well as damage to the benthic ecosystem caused by certain fishing techniques.The research leadSing to these results received funding from the European Union’s Seventh Framework Programme Project Mareframe: Co-creating Ecosystem-based Fisheries Management Solutions under Grant Agreement no. 613571

The genetic composition of feeding aggregations of the Atlantic mackerel (Scomber scombrus) in the central North Atlantic: A microsatellite loci approach. ICESJMS-2019-497.R1

Microsatellite data for Atlantic Mackere