FISHES (Chapter 6)

Authors:  Jørgen S. Christiansen and James D. Reist  

Contributing Authors: Randy J. Brown, Vladimir A. Brykov, Guttorm Christensen, Kirsten Christoffersen, Pete Cott, Penelope Crane, J. Brian Dempson, Margaret Docker, Karen Dunmall, Anders Finstad, Vincent F. Gallucci, Johan Hammar, Les N. Harris, Jani Heino, Evgenii Ivanov, Oleg V. Karamushko, Alexander Kirillov, Alexandr Kucheryavyy, Hannu Lehtonen, Arve Lynghammar, Catherine W. Mecklenburg, Peter D.R. Møller, Tero Mustonen, Alla G. Oleinik, Michael Power, Yuri S. Reshetnikov, Vladimir I. Romanov, Odd-Terje Sandlund, Chantelle D. Sawatzky, Martin Svenning, Heidi K. Swanson and Frederick J. Wrona

SUMMARY

Having occupied Earth’s waters for about five hundred million years, fishes are the oldest group of living vertebrates. Fishes have radiated to occupy most aquatic habitats on the planet, and estimates of total biodiversity range from 28,000 up to about 35,000 species. Fishes are associated with both marine and freshwater habitats, and some migrate between these biomes. Globally, about 16,000 species occupy marine waters, 12,300 are found in fresh waters, and 225 use both habitats during their lives. It is within this global diversity context that the diversity of Arctic fishes must be assessed.

Freshwater fishes are those confined to low salinity aquatic habitats; diadromous fishes are those which regularly migrate between fresh and marine waters. The latter occur as two major groups – anadromous fishes spend much of their lives in marine waters migrating to fresh water to reproduce, and catadromous fishes do the converse. Anadromous fishes constitute the majority of diadromous fishes in the Arctic. Between 17 and 19 families (3-4% of 515 worldwide) of freshwater and diadromous fishes occur in Arctic waters with about 123-127 recognized species (1% of 12,547 extant freshwater and diadromous species globally). Many of these taxa are unresolved species complexes, consist of multiple types that have differentiated in separate glacial refugia and/or exist as multiple life history and/or ecophenotypic forms. All these forms tend to function as, and may be the equivalent of, taxonomic species. Accordingly, an estimate of simple parameters such as species richness and taxonomic and phylogenetic diversity is fraught with problems and generally under-estimates the true diversity present. To facilitate this, we will use the upper estimate (127 species) herein.

Local indigenous fishermen from Pokhodsk and Nutendli report that muksun Coregonus muksun (a freshwater fish) amounts have decreased. Fyodor Innokentyevich Sokorikov, former head of the fishing sovhoz in Pokhodsk reports that muksun was caught in the amounts of 1,500 tonnes annually in the 1980s but says that in late 1980s and early 1990s there was overfishing of muksun and that is why it has collapsed now. Mustonen 2007.

Five families (salmonids – 50+ species of chars, whitefishes (sensu Coregonus), salmons; cyprinids – 25 minnows; cottids – nine sculpins; percids – eight perches; and petromyzontids – six lampreys) account for most of the freshwater taxonomic diversity present. Ecotones, areas where distinct habitats or physiographic realms meet, exhibit high local diversity, particularly in lake and river deltas and the estuaries of the large Arctic river basins. Similarly, large water bodies with complex habitats (e.g. deep lakes, large rivers) exhibit high diversity that may be manifested at sub-specific levels. Geologically young landscapes experiencing active disturbance, taxonomically labile fishes, generalist biological strategies and inherent capacity for rapid change in many key groups result in the Arctic being an area where rapid evolution of these fishes appears to occur. This underscores their significance in a global context.

Spatially, freshwater fish diversity decreases with latitude (e.g. in North America species richness is 40 at 60° N, 31 at 70° N along the mainland margin, three at 74° N and one farther north to the maximum extent of fresh waters on land at about 84° N). Longitudinally, the greatest diversity is present in areas that were unglaciated during the last ice age (i.e. much of Siberia and Beringia; see Fig. 2.2 in Payer et al., Chapter 2), declining to low levels in the eastern Canadian Arctic and Greenland that were deglaciated last and still retain large ice sheets. Time lines are too short and monitored sites too few to document temporal trends in species diversity in the Arctic. However, recent evidence suggests northward colonizations by freshwater fishes along river corridors and diadromous species into marine environments where climatic constraints have recently decreased. At present, no documented local extirpations or extinctions of taxa are known in the Arctic, although local population declines have occurred. Anthropogenic stressors are increasing in importance as risk factors both locally and throughout the Arctic. Local ‘hotspots’ of diversity and several globally significant water bodies are present.

 Arctic freshwater and diadromous fishes are of particular importance to humans both inside the Arctic and elsewhere. Food fisheries by indigenous peoples (i.e. subsistence fisheries) are extensive throughout the Arctic and historically always have been. 

Pervasive stressors such as climate change result in significant and rapid habitat alterations (indirect effects) as well as direct effects (e.g. thermal stresses) which challenge these fishes. Productivity shifts associated with climate change may create new opportunities (i.e. increased population sizes, growth potential) for freshwater and diadromous fishes.

Localized stressors (e.g. fisheries, hydrocarbon development, industrial activities, mining, water withdrawals, hydroelectric dams) affect populations either directly (fisheries) or through habitat impacts.

Marine fishes reproduce and spawn in seawater although juveniles and adults may occur also in the low salinity waters of fjords, coastal areas and river deltas. Here, we review the marine fishes across the Arctic Ocean and adjacent Arctic seas (AOAS). Altogether 16 regions and seas are examined for species richness, including the main entrances i.e. ‘Arctic gateways’ that connect the Atlantic and Pacific Oceans with the Arctic Ocean and Arctic shelves. While nearly 250 marine fish species are known from Arctic waters sensu stricto, the AOAS encompass pro tem 633 known fish species in 106 families. Cartilaginous fishes such as sharks and skates are well represented with about 8% of the species, whereas 92% are bony fishes. From a zoogeographic point of view, only 10.6% of the bony fishes are considered genuinely Arctic and 72.2% are boreal.

The fish faunas of the Arctic gateways are relatively well known compared with the Arctic seas as they support some of the largest commercial fisheries in the world. They are undeniably also the most species-rich regions of the AOAS and include 385 species in the Bering Sea, 204 species in the Norwegian Sea and 153 species in the Barents Sea. This is in stark contrast to the Arctic Ocean and Arctic shelves where only 13-87 species are recorded to date.

Fishes of the AOAS may display extraordinary phenotypic variation, and the taxonomic status is still unsettled and controversial for several fish species, particularly within the most species-rich families: snailfishes (Liparidae), eelpouts (Zoarcidae) and sculpins (Cottidae). Moreover, new fish species are described regularly, mainly due to recent efforts in Arctic marine research, whereas others are synonymized and lose their taxonomic rank following molecular and genetic studies.

Species richness increases with sea-surface area for the relatively well studied Arctic gateways, which is to be expected. By contrast, there is no species-area relationship for the understudied Arctic seas, and they display disproportionately low numbers of species. The paucity of credible data and lack of time-series for fishes in the Arctic Central Basin and Arctic shelves clearly preclude trend analyses and elaborate studies on biodiversity.

Ocean warming in the marine Arctic has become increasingly critical for the fish fauna native to Arctic waters. The marked shifts in distribution patterns for many targeted fishes, from sub-Arctic to high latitude seas, will inevitably attract modern fishing fleets into hitherto pristine areas, and may conflict with extant subsistence livelihoods among indigenous peoples along the Arctic coasts. Fishes native to Arctic marine waters are mainly associated with the seabed, and they are particularly vulnerable to conventional bottom trawling as they end up as unwanted and unprecedented bycatch. Although of no commercial value, bycatch fishes include species that are indispensable to structuring and functioning of Arctic marine ecosystems.

Credible assessments are the scientific link to legitimate conservation actions. Scientific uncertainty is at present a hallmark for the conservation of Arctic marine fishes, and precautionary management policies are urgently needed for future Arctic fisheries.

Significant gaps exist in the knowledge base for diversity of Arctic fishes. Practical measures to document trends and conserve diversity are thus compromised.

INTRODUCTION

This chapter provides an up-to-date overview of the fish species for which occurrence is scientifically confirmed within the borders of the Arctic mainland and the Arctic Ocean and adjacent seas. We use ‘fishes’ in the wide sense of the word and include four fish and fishlike vertebrate classes: the hagfishes (Myxini), the lampreys (Petromyzontida), the cartilaginous fishes (Chondrichthyes) and the bony fishes (Actinopterygii) (Nelson 2006). In the Arctic, the four classes show some notable differences in habitat choice: the lampreys are confined to freshwaters for reproduction, the hagfishes and the cartilaginous fishes are exclusively marine, whereas the bony fishes inhabit all aquatic environments.

The genuine freshwater fishes and most diadromous fishes require freshwater for reproduction. Diadromous fishes are those species that undertake regular migrations between freshwater and marine habitats, either for refuge, feeding or reproduction (McDowall 1992). Among these are the well-known fish families: lampreys (Petromyzontidae), and whitefishes and salmonids (Salmonidae) as well as some lesser-known groups.

The marine fish fauna, on the other hand, encompasses species that spawn at sea: in the littoral zone along the coastlines, in estuaries and fjords, on the shelves and seaward. Several habitats are oligohaline (salinity < 5 practical salinity units (psu)), such as estuaries, but they are still considered within the geographic realm of the marine Arctic.

In the Arctic, the freshwater and diadromous fishes are significantly molded by glaciation, deglaciation and geological events during the late Pleistocene and Holocene epochs (i.e. ~ 126,000 and 12,000 years ago, respectively). The evolutionary history of the marine fish fauna, on the other hand, dates back to the Neogene period as the modern circulation in the Arctic Ocean began to form some 14-17 million years ago (Krylov et al. 2008, Polyak et al. 2010). For reasons of clarity and because of the marked differences in habitat choice and evolutionary history, this overview of Arctic fishes is organized into two separate subchapters: (1) freshwater and diadromous fishes of the Arctic and sub-Arctic (J.D. Reist), and (2) marine fishes in the Arctic Ocean and adjacent seas (J.S. Christiansen).

CONCLUSIONS AND RECOMMENDATIONS- FRESHWATER AND DIADROMOUS 

Conclusions

• The documentation, delineation, synonymization, uniqueness and nature of taxonomic, functional and biological types of diversity are poorly known throughout much of the Arctic and sub-Arctic for freshwater and diadromous fishes. Remote and geographically large diverse areas are particularly poorly studied. Basic information such as specific occurrences and distributional limits is generally lacking for most areas. Taxonomic confusion and unresolved complexities of diversity are apparent in many groups of these fishes and across all levels from local population structuring to that of the species.
• Similarly, both natural and anthropogenic factors that maintain (or promote), truncate or differentially affect diversity within and among these levels  are poorly known. Generally, anthropogenic factors appear to affect diversity directly (e.g. specific taxa or forms exploited in fisheries) and indirectly by altering processes by which diversity is maintained (e.g. climate change affecting productivities of water bodies). Effects of cumulative interactions are particularly problematic. 
• Association of various types and levels of diversity with particular ecosystem types, specific ‘hotspots’ and/or geographic scales is somewhat better understood, but large gaps remain. Additionally, although some distinctive types of diversity have been documented and/or locations with unique diversity are known, it is likely that many undocumented situations exist. 
• Rates of anthropogenically driven change (e.g. resource extraction, climate variability) in the Arctic suggest that much diversity will likely be lost before it is adequately understood or documented.
• Understanding of roles and relative importance of both the types of diversity and the various levels within those types is generally required. 
• Documentation of the nature and consequences of anthropogenic effects on diversity is required.
• Documentation of ecosystem roles (e.g. stability/ resiliency) and services that accrue from these fishes and their varying levels of diversity are required in terms of those directly accrued by humans (especially indigenous peoples locally) and for other valuable ecosystem components (e.g. as key prey items for marine biota). 
• Better documentation of cultural and traditional uses and relevance of fishes to indigenous peoples is required. These, and levels of use for food (7 above) and selectivity for particular forms, require better documentation. 
• Better documentation is required of local commercial and sport fisheries, both of which are often underreported.
• Development of protected areas for aquatic biota, particularly for areas where unique or highly diverse groups are present, is in its infancy (in comparison with that for terrestrial biota). Most efforts at conservation are directed towards taxonomic diversity, rather than to functional diversity or dynamic habitats, which might change over time, or to key processes which maintain diversity. Adapting existing models to a dynamic, more vaRiable and changing world is required. 
• Development and implementation of relevant and rapidly assessed indicators of effects of change on fish biodiversity are required. 
• A multitude of definitions of species coupled with highly variable taxonomic philosophies result in wide inter-regional disparity of practical definitions at the species level. This undermines spatial and temporal assessments of diversity, changes therein and linkages to causation. 
• Although many species of Arctic endemic or Arcticcentric fish species can be considered iconic, this diversity is unknown and/or under-appreciated by most. 

Recommendations

Based upon the above conclusions, the following five recommendations are made regarding research and management of Arctic freshwater and diadromous fishes:

• Concerted and coordinated effort to document and understand the roles of diversity of Arctic freshwater and diadromous fishes is rapidly required throughout much of the Arctic, at a wide range of geographic scales using a range of techniques. This includes active research to resolve taxonomic complexes and relationships among levels of diversity, issues which are especially prevalent in these fishes.
• Development and implementation of comprehensive circumpolar monitoring of freshwater and key diadromous fish populations and their supporting ecosystems (e.g. through a dispersed observatory network) is required across the range of ecosystem and diversity types present. This needs to include parallel monitoring of key locally originating and pervasive anthropogenic stressors. 
• Ecosystem-level research programs are required across the Arctic, and these must include all aspects of human interaction with the fishes and their ecosystems. Programs should be explicitly linked with stressors impinging upon biodiversity, key ecosystems and processes which maintain biodiversity, endemism or areas of high diversity. Research linking ecosystem processes to diversification of forms is a priority given the overall relevance of such understanding to global issues. 
• Alternative approaches are required which realistically reflect conservation of diversity, habitats currently used (and those possibly used in the future as change is effected) and processes relevant to maintaining and/or promoting diversity.
• Development of clear, workable circumpolar definitions of taxonomic diversity at various levels for these fishes and their relevance to human activities is required. Communication and outreach both among taxonomic experts and between these experts, users of their information and the public (both within and outside the Arctic) is required to enhance awareness, importance and conservation actions for this group of fishes.

CONCLUSIONS AND RECOMMENDATIONS- MARINE

Key knowledge gaps

Once patterns of biodiversity emerge, it is essential to identify the underlying processes to counteract negative trends. Still, patterns remain fragmentary for the majority of fishes in the Arctic Ocean and adjacent seas (AOAS). The following issues are suggested to increase present knowledge to a point where sensible hypotheses may be proposed and tested, credible forecasts made and legitimate actions executed (Christiansen et al. 2013):

• Long-term time series of real-world and diagnostic data are essential for forecasting biological and environmental trends. Therefore, key sites and baseline transects for long-term studies of functional biodiversity should be identified in the AOAS (cf. CBMP online).
• Natural history collections (NHC) hold essential information for studies of biodiversity (Harrison et al. 2011, Lister et al. 2011), and information from fishery logbooks has proven valuable in historical analysis of population trends (Alexander et al. 2009). Therefore, NHCs should be continuously upgraded and archival data critically examined and employed to reconstruct long-term time series for specific AOAS regions.
• Taxonomy and conservation are two sides of the same coin. Classic taxonomy is a critically endangered science and a craft that cannot be substituted by DNA profiles and gigabytes (Bacher 2012, Deans et al. 2012, Scotland & Wood 2012). Therefore, training programs in taxonomy sensu lato and biogeography for young researchers should be encouraged.
• Habitats of particular significance for conservation, such as breeding grounds and biodiversity hotspots, should be identified in time and space and protected accordingly, cf. the debate on Marine Protected Areas (MPAs) (Henriksen 2010, Barry & Price 2012, Rice et al. 2012). 
• Fishing gear technology designed for sustainable fisheries in Arctic waters is poorly developed. Multidecadal datasets from the North Sea unequivocally demonstrate that conventional bottom trawl fisheries for groundfishes are extremely efficient but also highly damaging to the environment, as they impoverish, perturb and change the functional composition of benthic communities (Tillin et al. 2006, Thurstan et al. 2010). Arctic fish species are largely bottomliving and territorial (Karamushko 2012), and since Arctic groundfish fisheries are expected to increase in coming years, less harmful fishing technologies should be developed and used to minimize bycatch and seabed destruction.
• Abrupt shifts in abundance trends are warning signals for conservation. Therefore, accurate bycatch statistics in upcoming Arctic fisheries are crucial and call for adaptive monitoring plans and policies to meet conservation aims (Lindenmayer et al. 2012). A range of management policies for marine fisheries are in operation worldwide (Pitcher & Lam 2010), and fisheries founded on balanced rather than selective harvesting are currently debated (Garcia et al. 2012, Borrell 2013). No single harvesting practice is foolproof. But any management policy would be desireable if it relies on the principle of full accountability– that is a procedural change from the present-day selective fishing and fixed landing quotas of targeted species to catch quotas that embrace the entire biomass extracted from the sea, i.e. targeted and non-targeted species alike. For example, catch quota management (CQM) seems a promising policy that has been tentatively implemented in the North Sea fisheries (Kindt-Larsen et al. 2011, Schou 2011). Combined with taxonomic expertise on non-targeted Arctic species, CQM may well be the immediate and first step toward obtaining credible and urgently needed bycatch data as a precautionary measure for upcoming Arctic fisheries.
• Traditional ecological knowledge (TEK) and citizen science (Hochachka et al. 2012) would generate valuable and complementary information that should be critically scrutinized to increase the legitimacy of biodiversity assessments across the marine Arctic. This would require a completely new setting, and a designated forum of TEK-informants and scientists is called for, to ensure that trust-building and respectful and equal sharing of information and methods are also put into practice.
• An ambitious interdisciplinary science plan should be outlined and implemented as a precautionary and fundamental measure to meet large-scale human intervention in understudied Arctic waters (cf. PEG 2012)