Increased importance of cool-water fish at high latitudes emerges from individual-level responses to warming.

High latitude ecosystems are experiencing the most rapid warming on earth, expected to trigger a diverse array of ecological responses. Climate warming affects the ecophysiology of fish, and fish close to the cold end of their thermal distribution are expected to increase somatic growth from increased temperatures and a prolonged growth season, which in turn affects maturation schedules, reproduction, and survival, boosting population growth. Accordingly, fish species living in ecosystems close to their northern range edge should increase in relative abundance and importance, and possibly displace cold-water adapted species. We aim to document whether and how population-level effects of warming are mediated by individual-level responses to increased temperatures, shift community structure, and composition in high latitude ecosystems. We studied 11 cool-water adapted perch populations in communities dominated by cold-water adapted species (whitefish, burbot, and charr) to investigate changes in the relative importance of the cool-water perch during the last 30 years of rapid warming in high latitude lakes. In addition, we studied the individual-level responses to warming to clarify the potential mechanisms underlying the population effects. Our long-term series (1991-2020) reveal a marked increase in numerical importance of the cool-water fish species, perch, in ten out of eleven populations, and in most fish communities perch is now dominant. Moreover, we show that climate warming affects population-level processes via direct and indirect temperature effects on individuals. Specifically, the increase in abundance arises from increased recruitment, faster juvenile growth, and ensuing earlier maturation, all boosted by climate warming. The speed and magnitude of the response to warming in these high latitude fish communities strongly suggest that cold-water fish will be displaced by fish adapted to warmer water. Consequently, management should focus on climate adaptation limiting future introductions and invasions of cool-water fish and mitigating harvesting pressure on cold-water fish.

Occurrence of fish species in the inland water of Murmansk Region (Russia): research in 1972-2021.

BACKGROUND: Knowledge about the distribution of organisms on Earth is important backbone of biological sciences and especially for deeper understanding of biogeography. However, much of the existing distributional data are scattered throughout a multitude of sources (including in different languages), such as taxonomic publications, checklists and natural history collections and often, bringing them together is difficult. Development of the digital storage facilities may prevent loss of important data (Ruchin et al. 2020). Project GBIF is a good example of a successful data storage facility, which allows investigators to publish biodiversity data in one safe place in one uniform format. Our dataset describes the degree of the investigation of the fish fauna of the inland water of the Murmansk Region. Murmansk Region is a Euro-Arctic Region with a heterogeneous landscape, which determines diversity of the habitats for the fish occurrence. Our dataset contains valid information about distribution of the fish species. This dataset was built upon information obtained by the members of a Laboratory of the aquatic ecosystems of the Institute of North Industrial Ecology Problems of Kola Science Center of the Russian Academy of Science (INEP KSC RAS). The dataset includes 18,509 records about 16 fish species from 14 genera (eight families) collected from 1972 to 2021. A total of 67 water bodies from 15 different basins (rivers from basins of the White and Barents Seas) was screened in order to characterise ichthyocenoses. The main purpose of publishing a database is to make our data available in the global biodiversity system to a wide range of users. The data can be used by researchers, as well as helping the authorities to manage their territory more efficiently. NEW INFORMATION: All occurrences are published in GBIF for the first time. We would like to make this data available to everyone by adding it in the global biodiversity database (GBIF).

Improved Environmental Status: 50 Years of Declining Fish Mercury Levels in Boreal and Subarctic Fennoscandia.

Temporally (1965-2015) and spatially (55°-70°N) extensive records of total mercury (Hg) in freshwater fish showed consistent declines in boreal and subarctic Fennoscandia. The database contains 54 560 fish entries ( n: pike > perch ≫ brown trout > roach ≈ Arctic charr) from 3132 lakes across Sweden, Finland, Norway, and Russian Murmansk area. 74% of the lakes did not meet the 0.5 ppm limit to protect human health. However, after 2000 only 25% of the lakes exceeded this level, indicating improved environmental status. In lakes where local pollution sources were identified, pike and perch Hg concentrations were significantly higher between 1965 and 1990 compared to values after 1995, likely an effect of implemented reduction measures. In lakes where Hg originated from long-range transboundary air pollution (LRTAP), consistent Hg declines (3-7‰ per year) were found for perch and pike in both boreal and subarctic Fennoscandia, suggesting common environmental controls. Hg in perch and pike in LRTAP lakes showed minimal declines with latitude, suggesting that drivers affected by temperature, such as growth dilution, counteracted Hg loading and food web exposure. We recommend that future fish Hg monitoring sampling design should include repeated sampling and collection of pollution history, water chemistry, fish age, and stable isotopes to enable evaluation of emission reduction policies.