Arve Lynghammar

Molecular markers reveal spatially segregated cryptic species in a critically endangered fish, the common skate (Dipturus batis).

Many sharks and skates are particularly vulnerable to overfishing because of their large size, slow growth, late maturity and low fecundity. In Europe dramatic population declines have taken place in common skate (Dipturus batis L.), one of the largest demersal fish in regional shelf seas, leading to extirpations from substantial parts of its former range. Here we report the discovery of cryptic species in common skate collected from the northeast Atlantic continental shelf. Data from nuclear microsatellite markers indicated two clearly distinct clades and phylogenetic analysis of mitochondrial DNA sequences demonstrated monophyly of each one of them. Capture locations showed evidence of strong spatial segregation, with one taxon occurring mainly in waters off the southern British Isles and around Rockall, while the other was restricted to more northerly shelf waters. These apparently cryptic species showed overlapping substrate and depth preferences, but distributional limits were closely related to temperature gradients, potentially indicating thermal limits to their distributions. This discovery of hidden diversity within a large, critically endangered marine vertebrate demonstrates how marine biodiversity can be underestimated, even in such a relatively well-studied and heavily exploited region.

Species richness and distribution of chondrichthyan fishes in the Arctic Ocean and adjacent seas

The sea ice cover decreases and human activity increases in Arctic waters. Fisheries and bycatch issues, shipping and petroleum exploitation (pollution issues) make it imperative to establish biological baselines for the marine fishes inhabiting the Arctic Ocean and adjacent seas (AOAS). Species richness, zoogeographic affiliations and Red List statuses among chondrichthyan fishes (Chondrichthyes) were examined across 16 AOAS regions as a first step towards credible conservation actions. Published literature and museum vouchers were consulted for presence/absence data. Although many regions are poorly sampled, 49 chondrichthyan species have been reported from the AOAS. Skates and rays are the most species-rich taxon, represented by 27 species in family Rajidae and one species in family Dasyatidae. The sharks comprise 20 species in 13 families and the chimaeras one species in family Chimaeridae. The Norwegian Sea (28), Barents Sea (19) and Bering Sea (18) are particularly species-rich, and despite similar species numbers the two latter seas have no species in common. The remaining AOAS regions are inhabited by six species or less. Large-scale commercial fisheries for chondrichthyans are yet to be developed in the AOAS, but the precautionary principle should be implemented as abundances, basic taxonomy and biology are still largely unknown.

DNA barcoding of the northern Northeast Atlantic skates (Chondrichthyes, Rajiformes), with remarks on the widely distributed starry ray

The skate fauna in the northern Northeast (NE) Atlantic is poorly investigated, and misidentifications are common. Here, ‘DNA barcoding’ was used to analyse 105 specimens of 15 species previously reported from the area to investigate the occurrence of species. Of these 15 species, three were new to the region and confirmed with voucher specimens. Three previously reported taxa were not obtained from the study area, providing a total number of 12 skate species for the northern NE Atlantic. Only one specimen of the critically endangered Dipturus batis complex was found. It occurs frequently in the literature and commercial fisheries catch records, and we argue that the vast majority of these are misidentifications. Due to striking differences in Amblyraja radiata life history parameters across the North Atlantic, cryptic species diversity has previously been suspected. A total of 80 A. radiata cytochrome c oxidase subunit I sequences from across the North Atlantic were sampled, and the highest fixation index (FST) was found when maximising geographical distance (FST = 0.133). A lower index was found when grouped according to life history (FST = 0.067). These results are not strongly supportive for the occurrence of cryptic species.

The first confirmed cases of full albinism in rajid species.

Three albino skate specimens (Rajidae) were captured from the North Sea and English Channel between 2008 and 2011. Using DNA barcoding (COI gene) and morphometric analyses, species were identified as a spotted ray Raja montagui, a blonde ray Raja brachyura and a thornback ray Raja clavata. This finding represents the first record of full albinism (a lack of skin and retinal pigmentation) in rajid species.

Dispersal routes of marine range expansions into the Arctic

As a result of ocean warming, the species composition of the Arctic seas has begun to shift in a boreal direction. One ecosystem prone to fauna shifts is the Northeast Greenland shelf. The dispersal route taken by boreal fauna to this area is, however, not known. This knowledge is essential to predict to what extent boreal biota will colonise Arctic habitats. Using population genetics, we show that Atlantic cod ( Gadus morhua ), beaked redfish ( Sebastes mentella ), and deep-sea shrimp ( Pandalus borealis ) specimens recently found on the Northeast Greenland shelf originate from the Barents Sea, and suggest that pelagic offspring were dispersed via advection across the Fram Strait. Our results indicate that boreal invasions of Arctic habitats can be driven by advection, and that the fauna of the Barents Sea can project into adjacent habitats with the potential to colonise putatively isolated Arctic ecosystems such as Northeast Greenland.As a result of ocean warming, the species composition of Arctic habitats has begun to shift in an Atlantic direction. One ecosystem exposed to such a change is the Arctic Northeast Greenland shelf. However, the dispersal route taken by boreal fauna to this area is unknown. This knowledge is essential to predict to what extent boreal biota will dominate and alter Arctic ecosystems. We show that Atlantic cod (Gadus morhua), beaked redfish (Sebastes mentella), and deep-sea shrimp (Pandalus borealis) specimens recently found on the Northeast Greenland shelf originate from the Barents Sea, and suggest that a likely dispersal route is via advection across the Fram Strait. Our results indicate that boreal invasions of Arctic habitats can be driven by the dispersal of pelagic offspring, and that the fauna of the Barents Sea can project into adjacent habitats with unknown consequences to the structure and function of putatively isolated Arctic communities.

First record of juvenile northern wolffish Anarhichas denticulatus Krøyer, 1845, on the continental slope of Northeast Greenland

The first record of the juvenile northern wolffish Anarhichas denticulatus was reported 570 km away from the nearest border of the species natural habitat near the island of Jan Mayen, on the continental slope of Northeast Greenland. Also original and published data on the occurrence of juvenile northern wolffish in the European Arctic and North Atlantic are presented.

Arctic skate Amblyraja hyperborea preys on remarkably large glacial eelpouts Lycodes frigidus

During scientific surveys on the continental slopes north-west of Spitsbergen and off north-east Greenland (c. 600 and 1000 m depths), two female Arctic skates Amblyraja hyperborea were caught while swallowing extraordinary large individuals of glacial eelpout Lycodes frigidus. The total length (LT) of the prey constituted 50 and 80% of the LT of the skates, which reveal that A. hyperborea are capable predators of fishes of surprisingly large relative size.