Franz Josef Land: extreme northern outpost for Arctic fishes

The remote Franz Josef Land (FJL) Archipelago is the most northerly land in Eurasia and its fish fauna, particularly in nearshore habitats, has been poorly studied. An interdisciplinary expedition to FJL in summer 2013 used scuba, seines, and plankton nets to comprehensively study the nearshore fish fauna of the archipelago. We present some of the first underwater images for many of these species in their natural habitats. In addition, deep water drop cameras were deployed between 32 and 392 m to document the fish fauna and their associated habitats at deeper depths. Due to its high latitude (79°–82°N), extensive ice cover, and low water temperatures (<0 °C much of the year), the fish diversity at FJL is low compared to other areas of the Barents Sea. Sixteen species of fishes from seven families were documented on the expedition, including two species previously unknown to the region. One Greenland shark, Somniosus microcephalus (Somniosidae), ca. 2 m in length, was recorded by drop camera near Hayes Island at 211 m, and Esipov’s pout, Gymnelus esipovi (Zoarcidae), was collected at Wilton Island at 15 m in a kelp forest. Including the tape-body pout, Gymnelus taeniatus, described earlier from the sub-littoral zone of Kuhn Island, 17 fish species are now known from FJL’s nearshore waters. Species endemic to the Arctic accounted for 75% of the nearshore species observed, followed by species with wider ranges. A total of 43 species from 15 families are known from FJL with the majority of the records from offshore trawl surveys between 110 and 620 m. Resident species have mainly high Arctic distributions, while transient species visit the archipelago to feed (e.g., Greenland shark), and others are brought by currents as larvae and later migrate to spawn grounds in the south (e.g., Atlantic cod Gadus morhua, Capelin Mallotus villosus, Beaked redfish Sebastes mentella). Another species group includes warmer-water fishes that are rare waifs (e.g., Glacier lanternfish Benthosema glaciale, White barracudina Arctozenus rissoi). The rapid warming of the Arctic will likely result in significant changes to the entire ecosystem and this study therefore serves as an important baseline for the nearshore fish assemblages in this unique and fragile region.


INTRODUCTION
Owing to its unique biogeographic and climatic histories, the Arctic Ocean has produced a distinctive fish fauna dominated by phylogenetically young families (e.g., Zoarcidae, Stichaeidae) (Andriashev, 1939;Dunbar, 1968;Mecklenburg, Møller & Steinke, 2010). Older groups eliminated during the rapid cooling of the Middle Miocene were followed by younger families invading the Arctic mainly from the Pacific via the opening of the Bering Strait 3-3.5 million years ago (Andriashev, 1939;Savin, 1977;Mecklenburg, Møller & Steinke, 2010), while a few families have also invaded the region from the Atlantic (e.g., Gadidae, Anarhichadidae) (Svetovidov, 1948;Mecklenburg, Møller & Steinke, 2010). Of the 504 species currently comprising the Arctic ichthyofauna, those with Atlantic-Arctic ranges comprise 58% of the total richness, followed by species with Pacific-Arctic ranges (20%), while those endemic to the Arctic region account for an additional 14% (Chernova, 2011).
The Franz Josef Land (FJL) Archipelago is located within the Barents Sea Large Marine Ecosystem, which is a transition zone where relatively warm, more saline water from the Atlantic mixes with Arctic and Polar waters (Johannesen et al., 2012a). These oceanographic conditions result in high productivity (Cochrane et al., 2009) that supports major fisheries, including the largest remaining stock of Atlantic cod (Gadus morhua) (Johannesen et al., 2012b). Currently >200 fish species from 66 families are found in the Barents Sea (Stiansen & Filin, 2008;Dolgov, 2011). The dominant families are: eelpouts (Zoarcidae), sculpins (Cottidae), codfishes (Gadidae), snailfishes (Liparidae), flatfishes (Pleuronectidae), which collectively account for nearly 80% of the species regularly occurring in the Barents Sea.
FJL is a zakaznik (protected area, equivalent to IUCN category IV), currently managed by the Russian Arctic National Park. Its remoteness and harsh physical environment makes it one of the least known places on earth. The archipelago is situated in the NE Barents Sea (79 • -82 • N, 43 • -67 • E) and consists of 192 islands, covering 16,134 km 2 (Barr, 1994) Although FJL lies at the same latitude as Svalbard, Norway, the fish assemblages are very different (Fossheim, Nilssen & Aschan, 2006;Stiansen et al., 2009). The warm Atlantic currents that run along the northern continental slope of the Barents Sea, are greatly diminished by the time they reach FJL (Schauer et al., 2002), resulting in a biota consisting mainly of cold-water organisms (Wassmann et al., 2006). Because of remoteness and severe ice conditions most of the year, the FJL fish fauna has not been well studied.

Previous fish survey of FJL
The first records of fishes from FJL come from the Austro-Hungarian expedition of 1872-74, which noted blackbelly snailfish (as Liparis gelatinosus) and polar cod (as Gadus morue) (Payer, 1878). During the Norwegian Polar Expedition of 1893-1896, polar cod (Boreogadus saida) were observed in the stomachs of several sea bird species (Collett & Nansen, 1899). The 1894-97 British Expedition to FJL spent a winter at Cape Flora on Northbrook Island and collected a few polar cod (Jackson, 1899). The same species was collected by the Italian expedition led by Duke of the Abruzzi, Luigi Amedeo, who wintered on Rudolf Island in 1899-1900 (Camerano, 1903).
The expedition of the Zoological Institute of the Russian Academy of Sciences (ZIN) to FJL in 1981-82 used scuba to collect nearshore fishes. In 1991 and 1992, the expedition of the Murmansk Marine Biological Institute (MMBI) conducted additional scuba sampling at FJL, resulting in new information on three species of snailfishes (Chernova, 1993;Chernova, 2007). In addition, a new zoarcid fish, the tape-body pout Gymnelus taeniatus was described from one specimen found in the sub-littoral zone off Kuhn Island (Chernova, 1999a).
Surveys of the Barents Sea were conducted from 2004 to 2009 under the Russian-Norwegian Cooperation Program, and resulted in an atlas of Barents-Sea fishes (Wienerroither et al., 2011). More than 30 species were listed from FJL, including the White barracudina, Arctozenus risso, and Esmark's eelpout, Lycodes esmarkii. PINRO produced a key to the identification of Barents Sea fishes that listed 11 species for FJL including the thorny ray, Amblyraja radiata, which was collected near Alexandra Land and Prince George Land (Dolgov, 2011).
Currently, a total of 43 fish species from 15 families and 9 orders are known from FJL, with most species collected by trawling southwest of the archipelago at depths from 100 to 600 m (Table S1). In the summer of 2013, an interdisciplinary research expedition to FJL, led by the National Geographic Society and the Russian Arctic National Park, conducted an assessment of the biodiversity of the ichthyofauna using a suite of sampling methods with the objectives of describing the taxonomy and ecology of the nearshore ichthyofauna, while also exploring the deep sea environment around the archipelago.

Sample design
Nearshore fishes were collected using (1) scuba and snorkeling, (2) beach seines, (3) plankton net, and (4) samples regurgitated from seabirds. Observations and in situ photography were also used to conduct species identification. Approval to conduct research on vertebrate animals was granted by the Russian Federation Ministry of Education and Science Approval Ref. No. 14-368 of 06.05.2013. Approval to conduct field studies was granted by the Russian Federation Ministry of Education and Science Approval Ref. No. 14-368 of 06.05.2013 permission to the Russian Arctic National Park.

Diving methods
Three groups of divers conducted 68 dives at 19 localities at depths ranging from 0 to 34 m around the archipelago (Fig. 1). While diving, fish samples were collected using hand aquarium nets, nets and clove oil, or by hand. In addition, photographs were taken in situ to document underwater coloration and associated habitat.

Beach seines
Beach seines were used at four locations: Tikhaya Bay at Hooker Island (40 hauls), Cape Tegetthoff at Hall Island (6 hauls), Nilsen Bay at Bell Island (4 hauls) and Phoka Bay at Northbrook Island (6 hauls). The seine was 10 m long by 2 m high with 10 mm stretch mesh.

Plankton net
Larval and young-of-year fishes were collected by plankton net. Plankton sampling was conducted at 20 locations, primarily in the straits between islands at depths between 200 and 340 m, using vertical hauls from the bottom to surface. Plankton nets were of standard construction, with a mesh of 0.2 mm or 0.074 mm.

Deepwater drop camera
To explore the deep sea environments, deep drop-camera surveys were conducted. National Geographic's Remote Imaging Team developed Deep Ocean Drop-cams, which are high definition cameras (Sony Handycam HDR-XR520V 12 megapixel) encased in a borosilicate glass sphere and rated to a 10,000 m depth. Viewing area per frame was between 2 and 6 m 2 , depending on the steepness of the slope where the Drop-cam landed. Cameras were baited with 1 kg of frozen herring (Clupeidae) placed in a burlap bag and deployed for ca. four hours. The number of individuals of each taxa per drop-cam deployment was estimated from the maximum number of individuals observed per frame (N max ).

Field processing of fish samples
Collected fishes were measured and weighed on board and preserved in 4% buffer formaldehyde solution. Samples were send to the Zoological Institute, St. Petersburg, Russia (entry number ZIN No 6-013) and examined by the senior author. Vertebra and fin ray number were counted on radiograms.

RESULTS
Our expedition identified sixteen species of fishes from seven families and three orders in the waters around FJL (Table 1). Of these, Scorpaeniformes was the most specious order, accounting for 81% of all species observed (Table 2). Species endemic to the Arctic accounted for 75% of the nearshore species observed (three-fourths of which had circumpolar distribution), followed by species with wider ranges, including the N. Atlantic and N. Pacific. Species with benthic or meso-benthic habitat preferences accounted for 75% of the observed nearshore assemblage, followed by bentho-pelagic species (18.8%), and one cryopelagic and benthopelagic species, Boreogadus saida. FJL nearshore waters are at the upper limit of vertical distribution for fishes of all species. The vast majority   of the fishes observed around FJL were invertebrate feeders, while three were facultative piscivores (e.g., Greenland shark, Atlantic cod, Parr's snailfish), with one-the cryopelagic polar cod-feeding primarily on zooplankton under the ice.

Drop-cams
A total of 24 camera drops were conducted during the expedition, at depths from 32 to 292 m. Although numerous benthic organisms were observed (e.g., amphipods, soft corals, brittle stars, bryozoans) fishes were not common. Five fish taxa were observed during drop-cam surveys, with Polar cod the most common, occurring in 37.5% of the camera

Species accounts
Family Somniosidae-Sleeper Sharks

Somniosus microcephalus (Bloch et Schneider, 1801)-Greenland shark (Fig. 2)
One 2 m specimen was recorded on drop camera off Hayes Island in 211 m (80 • 38.4N, 58 • 08.4E). This species was previously not known to occur around FJL (Dolgov, 2011;Wienerroither et al., 2011). This sighting therefore represents the first record of a Greenland shark from FJL and is the most north-eastern record for this species. Polar cod were mentioned in FJL by numerous researchers dating back to the earliest expeditions (Payer, 1878;Jackson, 1899;Nansen, Johansen & Nordahl, 1900;Collett & Nansen, 1899;Knipowitch, 1901). Workers at the Tikhaya Bay Hydro-Meteorological station on Hooker Island (80.3 • N, 52.8 • E) in 1931-32 regularly observed polar cod, most often during ice-hummock formation (Burmakin, 1957). Explosives were used to collect these fishes at 10-15 m, resulting in >100 fish per blast event. In the summer of 1975 and 1979, the staff of the Hydro-Meteorological station at Hayes Island observed schools of polar cod "so large that they were scooped up by hand net" (Borkin, 1983). PINRO expeditions found polar cod were common south-east of the archipelago at depths of 170-460 m (Borkin, 1993). Other sources state that polar cod occur north towards the North Pole among the ice pack (Andriashev, Mukhomediyarov & Pavshtiks, 1980;Mel'nikov & Chernova, 2013a;Mel'nikov & Chernova, 2013b (Borkin, 1993). Adult cod were found south-west of FJL during the Russian-Norwegian Cooperation Program from 2004(Wienerroither et al., 2011.

Family Cottidae-Sculpins
Icelus bicornis (Reinhardt, 1840)-Twohorn sculpin (Fig. 4) Individuals were recorded at 8 islands between 7 and 21 m. The Hamecon was a common inshore species and appeared to be highly site attached among rocks and boulders. A variegated color pattern was observed in mixed sand and rocky habitat. Hamecon were found in habitats ranging from the shallow red algae zone at Bliss Island to deeper (8-20 m) Laminaria spp. beds off Prince Rudolf Island (SD Grebelniy, pers. comm., 2014).

Triglops nybelini-Bigeye sculpin
One fish was identified by a photograph taken 20.08.2013 by MV Gavrilo at Torup I. (Fig. 6). The fish, ca. 15 cm TL, was in the mouth of a Black guillemot Cepphus grylle (family Alcidae). It was identified as a Bigeye sculpin, Triglops nybelini, based on its elongated body, wide pectoral fins, cottoid-like shape, and a line of black spots above the anal-fin base. Bigeye sculpin are frequently caught in trawls around FJL, primarily over silty sand in 100-500 m (Knipowitch, 1901;Andriashev, 1964b). Hundreds of young-of-year (age 0+, 60-112 mm) were caught by pelagic trawl west of FJL (Borkin, 1993). The presence of two other Triglops species around FJL (T. murrayi and T. pingelii) (Wienerroither et al., 2011) need to be verified.
Cyclopteropsis mcalpini-McAlpin's smooth lumpfish (Fig. 9) An adult Cyclopteropsis mcalpini ca. 40 mm TL was observed sitting on the empty shell of the Gastropod Neptunea sp., with its egg mass inside the shell. This shell was collected between Torup and Howen islands at 81 • 31N, 58 • 31.7E, 20.08.2013, st 29, dp 18-31 m, habitat-rock, stones, sand, shells; coll. OV Savinkin. Forehead is wide and flattened, mouth is up turned; a row of 4 small spiny plates present on body sides; color is pale with dark brown irregular net-like spots. The eggs, ca. 6 mm in diameter, had well developed larvae that were nearly ready to hatch. Andriashev (1964a) noted parental care in Cyclopteropsis when a male was found on an empty gastropod shell protecting juveniles.

Family Liparidae-Snailfishes
Liparis bathyarcticus Parr, 1931-Parr's snailfish (Fig. 10 Parr's snailfish (ZIN 6-013/3) were found at 8 m, in rocky habitat with gravel and clay. A pair was observed sitting in a hole between rocks among small brown and green algae, at 1.5-6 m. Larval L. bathyarcticus were observed 17.08.2013 in large numbers at 10-15 m at Pioneer Island. Densities were as high as 10 s m −2 . Similar densities were observed on nearby Kuhn Island between 6 and 10 m on 16.08.2013 (A Friedlander). Mean length of larvae was 13 mm (n = 12) and were without pigment. Early stage juveniles (TL 15-16 mm; egg sack still present; sucking disk entirely developed) were present in our samples. The gill slit is as in adults, large and reaching down to mid-base of pectoral fin upper lobe (in other arctic snailfishes it only extends from the 1st to 6th pectoral fin ray). The name L. bathyarcticus was revalidated (Chernova, 2008). Adults feed partly on fishes.
Liparis tunucatus Reinhardt, 1837-Kelp snailfish (Fig. 11) We recorded twelve specimens (TL 46-166 mm) at four islands between 6 and 30 m.    (Chernova, 1989;Chernova, 1991;Chernova, 1993). Fish were dark red and usually attached to lower surface of kelp thalli, or under rock using their sucking disks. Spawning is known to occur in March, and previous underwater observations found blackish-green egg clutches on kelp thalli at 6 to 25 m during this time.
Liparis cf. fabricii Krøyer, 1847-Blackbelly snailfish (Fig. 12) Specimens were found by divers at 6 islands between 10 and 25 m; fry SL 31-83 mm were collected by plankton net between 142 and 400 m.  The blackbelly snailfish Liparis fabricii is a species complex which differs from other Arctic snailfishes in that it has a black peritoneum (i.e., wall of body cavity) (Chernova, 2008).
The form from FJL collected by our expedition had a rounded head (head width is equal to head depth) and a tapered snout with a prominent point. The posterior nostril is half the size of the anterior nostril, without flap-like projections. The mouth is horizontal with small anterior teeth, jaws are trilobate, posterior teeth have small lateral shoulders. Snout folds are undeveloped, opercular flaps are rounded. Gill slits reach to 5-8th pectoral rays. Some anterior dorsal fin rays are shorter than posterior rays. The upper pectoral fin lobes reach slightly behind the anal fin origin. The disk is well developed and the skin of adult males is covered by cone-like prickles. Vertebrae 50-53 (11 + 39 − 42); D 44-49, A 37-41; P 36 (28 + 8). Caudal fin includes 9-10 principal rays, 2 upper and 2 lower secondary rays. Color is blackish with small black spots; between 3 and 5 wide oblique bands present at dorsal and anal fins. Peritoneum black, after preservation without silvery pigmentation. Pelagic young have a dark band along the dorsal fin base; dorsal and anal fins are semi-transparent, with 5 and 3 transversal blackish spots, respectively; the peritoneum is black and distinctly visible through body wall, masked from the outside by silvery guanine pigmentation that quickly disappears after preservation in formaldehyde.
Underwater observation shows adults close to the bottom, among thalli of kelp, at a depth 10-25 m; ground-silty sand with stones, overgrown by algae (mainly Sacharina latissima and Alaria esculenta).
One specimen was found on the deck of the ship partially digested and likely deposited by a seabird (caudal portion missing). The specimen has infraorbital pores absent; the origin of the dorsal fin was near vertical of the anal-fin origin; pre-dorsal distance (from tip of snout to dorsal fin origin) is 205% of head length (lc). Radiogram counts: abdominal vertebrae 21. The first ray of D-fin located between vertebrae 14 and 15; 11 interneuralia bear no corresponding dorsal fin ray, the first is between vertebrae 4 and 5. Head depressed. Pectoral fin length 57.5% lc. Pectoral-fin rays 10.
Anderson's pout differs from G. viridis by the posterior position of dorsal fin origin, with the pre-dorsal distance 2x longer than the head length. Gymnelus andersoni differs from G. retrodorsalis (with similar position of dorsal fin origin) by having reduced sensory pores in the infraorbital canal (pores below eye are closed or entirely absent)   (Chernova, 1998a;Chernova, 1998b Gymnelus esipovi differs from G. andersoni in its anterior dorsal fin position (pre-dorsal distance <1.3 larger than head); infraorbital pores are well developed. This species was previously known only from Spitsbergen, the northern Barents Sea near Novaya Zemlya (75 • 53-76 • 30N, 51 • 55-57E), and the northern Kara Sea (Chernova, 1999a). This is the first record of Gymnelus esipovi from FJL.

FJL fish fauna diversity
Our expedition identified 16 species of fishes from 7 families mainly in nearshore FJL (<34 m). We added two species previously unknown for FJL; the Greenland shark (Hayes Island, 211 m) and Esipov's pout (Wilton Island,15 m). For many other species, our expedition increased the numbers of localities within the archipelago where these species are known, as well as identifying new upper depth limits for many species. The only nearshore fish species previously recorded from the archipelago but not found during our expedition was the tape-body pout Gymnelus taeniatus, which is likely locally endemic to Franz Josef Land (Chernova, 1999a).
Most of the trophic diversity is comprised of invertebrate feeders while three species (Greenland shark, Atlantic cod, and Parr's snailfish) are facultative piscivorous. However the vast majority of the fish biomass for the region is likely polar cod which can feed on zooplankton under the ice. The low observed abundance of this species may be explained by the lack of sea ice near FJL during our expedition.
Species endemic to the Arctic accounted for three quarters of the nearshore species, the majority of which are common at high latitudes and circumpolar in the Arctic (Chernova, 2011). The distribution of some species (e.g., Arctic eelpout, Anderson's pout, Esipov's pout, and McAlpin's smooth lumpfish) is currently not fully known. The presence of larvae and young-of-year of many of the nearshore fishes suggests as least some local spawning and self-recruitment. The nearshore waters around FJL are important as nursery habitat for a number of fishes found in deeper water.
Compared with much of the Barents Sea, the fish fauna of FJL is depauperate. The waters around FJL are at or below freezing year round and the littoral zone is covered by ice during much of the year. As a result, nearshore fishes are restricted to a zone between 6 and 25 m, in areas dominated mainly by macrophytes.
Several species may only spend a portion of their lives in FJL. The Greenland shark S. microcephalus is nomadic. FJL is not recognized as a nursery or feeding area for young Atlantic cod and capelin, but favorable currents and oceanographic conditions may allow these species to survive until they migrate to spawning areas towards the south and west. The Arctic cod, Arctogadus glacialis, is a cryopelagic (sympagic) species that occurs south of FJL, as well as northward to the North Pole (Andriashev & Chernova, 1994;Chernova, 2011). The lack of pack ice around FJL during our expedition may account for the absence of this species from our list. Some mesopelagic fishes are also non-residents. Glacier Lanternfish Benthosema glaciale (Borkin, 1986) and White Barracudina Arctozenus risso occur south and west of the archipelago, but the extreme environment conditions of FJL likely prevent these species from reproducing in these waters. Many of the other species that are known from FJL occur in >34 m and therefore not encountered on our surveys.
Trawl catches around FJL in depths 100-600 m have recorded 43 fish species from 15 families. Most are primarily demersal, non-migrating species with the exception of the commercially important black halibut, which spawns on the western continental slope of the Barents Sea. Nursery and feeding areas for black halibut occur west of FJL in the Franz Victoria Trough, as well as in the Voronin and St. Anna troughs to the east. With the exception of black halibut, there are currently no fish species in commercially-exploitable abundance around FJL.

Abundance of FJL fishes
Notes published from the Jackson-Harmsworth Expedition of 1894-97 state: "Though angling with line and hook was tried, it proved unsuccessful; and in order to obtain specimens of fish, it became necessary to stand on the shore and wait for the birds that came flying in from the distant open water with fish in their mouths. These birds were promptly shot, and came tumbling down with the fish still in their grip. This is an instance, I fear, of highway robbery with violence to the person, but science condones much". Later in the text they state: "Fishing with line met with no success, but many specimens were taken from birds, and are preserved and brought back" (Brice & Fisher, 1896).
Our results confirm that fishes in FJL are not abundant. The density of fishes observed during dives was very low. On average, only a few individuals were observed on any dive (N = 68). These low densities likely reflect very low standing stock of benthic fishes, but also related to the fact that many of the individuals were extremely cryptic, occurring on the underside of kelp fronds or hiding within rocks and/or kelp holdfasts. Underwater visual surveys of fishes off West Greenland yielded densities of 0.03 fishes m −2 (Gremillet et al., 2004) and are typical for other Arctic rocky shores (Hoff, 2000;Born & Böcher, 2001). Results of our beach seine efforts confirm fish scarcity. In 56 hauls at 4 locations no fishes were collected and no fishes were observed in this habitat. There was continuous daylight during the entire expedition so it is unclear if the abundance patterns we observed are similar during other times of the year. However due to sea ice conditions during the winter months, abundances are likely highest during the summer period when our sampling was conducted.
The blood serum of most fishes freezes at <−0.07 • C (Holmes & Donaldson, 1969) and therefore the shallow water or extremely cold, ice-laden deep waters surrounding FJL are inhospitable for most species. Fish that live in the polar oceans survive at low temperatures by virtue of 'antifreeze' plasma proteins in the blood that bind to ice crystals and prevent these crystals from growing (Fletcher, Hew & Davies, 2001;Marshall, Fletcher & Davies, 2004). The blood of the cryopelagic fishes, such as Notothenioids Pagothenia borchgrevinki and Dissostichus mawsoni (Perciformes) in Antarctic and cod species B. saida and A. glacialis in the Arctic, contains glycoproteins that serve as antifreeze agents.
No commercial fishing occurs in FJL due to extensive ice cover for most of the year and the absence of commercially abundant fishes. The Atlantic cod, haddock, capelin, red-fishes, wolf fishes, and flat fishes either are absent from FJL or occur at densities too low for commercial exploitation. Polar cod are common in FJL waters, with enormous shoals sometimes observed, but the low value of this species has precluded commercial exploitation. Polar cod are important ecologically in high-Arctic areas. They are an essential link in the cryopelagic food web by grazing on under-ice zooplankton and in turn are a major food component of many seabirds and marine mammals (Bradstreet et al., 1986;Finley, Bradstreet & Miller, 1990;Welch, Crawford & Hop, 1993). Many questions on the biology and ecology of arctic fish still remain unanswered.

Trends assuming climate change scenarios
The climate projections for the eastern Arctic show a warming that will cause a shift from sea-ice algae-benthos-dominated to zooplankton-dominated communities (Bates & Mathis, 2009). Such a fundamental shift may have negative consequences on large marine carnivores (e.g., seabirds and marine mammals), but have a positive influence on the abundance of smaller carnivores (e.g., fishes), because the average body size of prey will decrease substantially (Karnovsky et al., 2003).
Until recently, the north-eastern Barents Sea has had permanent ice-cover, but during the last decade the entire shelf sea has been ice-free during the summer months (Johannesen et al., 2012a). A retreat and thinning of the ice cover in the Barents Sea likely will result in the northern portion becoming more Atlantic in character, with a higher productivity at the sea floor (Cochrane et al., 2009). The northern fish fauna currently has low biomass, but a shift towards more productive Atlantic water will likely result in an overall increase in benthic biomass to the north.
A northern shift in the penetration of Atlantic water will likely make the area more similar in faunal structure and ecosystem function to the southern parts of the Barents Sea. The Barents Sea today supports large commercial fisheries, and a potential climate-driven increase in their harvestable areas is of high social and economic interest. Under warming conditions, trophic interactions in the ecosystem could weaken as a result of increased diversity at each trophic level caused by range expansion of species found in warmer areas. Cod larvae are spread by currents from spawning grounds throughout the Barents Sea. As the waters around FJL warm, Atlantic cod and other boreal and sub-Arctic species will likely become more abundant. The impact of fisheries on the Arctic, which can be expected to increase, as industrial fisheries move into a warming Arctic following the invasion of boreal species. The lack of basic knowledge regarding fish biology and habitat interactions in the north, complicated by scaling issues and uncertainty in future climate projections limits our preparedness to meet the challenges of climate change in the Arctic with respect to fish and fisheries (Reist et al., 2006).