The Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis>) populations of Windermere,UK: population trends associated with eutrophication,climate change and increased abundance of roach (<Emphasis Type="Italic">Rutilus rutilus</Emphasis>)

The north and south basins of Windermere in the English Lake District, UK, support autumn- and spring-spawning populations of Arctic charr, Salvelinus alpinus, which have been studied since the 1930s. Continuous investigations of the population dynamics of Arctic charr at this lake have involved gill netting since 1939, collection of fishery catch-per-unit-effort data since 1966, and hydroacoustic surveys since 1990. Analysis of these and associated long-term data on the abiotic environment and other components of the fish communities revealed recently contrasting fortunes of the Arctic charr populations of the north and south basins, the latter of which has been significantly impacted by eutrophication while both basins have shown elevated water temperatures and increasing roach, Rutilus rutilus, populations. Despite the introduction of phosphate stripping in 1992 and some subsequent initial improvement, the hypolimnion of the south basin still remains significantly eutrophicated and the fishery catch-per-unit-effort in this basin is now at record low levels. In addition, the spatial distribution of roach has expanded to form significant components of the fish communities of inshore and offshore surface habitats, where this cyprinid may compete with Arctic charr for zooplanktonic prey. It is concluded that the Arctic charr populations of Windermere, particularly those of the south basin, currently face a number of significant environmental pressures and continued management action is required to ensure their survival.     

Lake enrichment and the status of Windermere charr, Salvelinus alpinus (L.)

All English populations of Arctic charr, Salvelinus alpinus (L.), are found in the Lake District (northwest England). There are at least four races of charr in Windermere, the largest lake in England; the North and South basins of the lake each contain two distinct races that spawn in autumn and spring respectively. The spring spawners in both basins probably represent less than 15% of the total population in the lake.
Changes in the population density of charr in the lake are described briefly and examined in relation to the trophic status of the lake. Other factors that could possibly affect the charr population are reviewed, especially the influence of climate change.     

Arctic charr in Lake Myvatn: The centennial catch record in the light of recent stock estimates

In Lake Myvatn, Arctic charr (Salvelinus alpinus) is economically the most important fish species. It is fast growing fish and its size at maturity is 35–50 cm at the age of 4 to 5 years. Catch statistics that are available for the whole 20th century show considerable long-term variation with the highest catch in the 1920s. The catches after 1970 are about 40% lower than the average from 1930–1969 and the annual catches for the last decade are the lowest. Stock size during the winter fishing season fluctuated considerably between years, with average annual fishing mortality of 83.9%. The Arctic charr population has been monitored annually since 1986, using standard series of gill nets of different mesh sizes. In 1988 one to three-year-old fish were heavily reduced in numbers during the summer months. There are indications of a similar event in 1997. In both years the charr changed its main diet from Cladocera and chironomid midges to three-spined sticklebacks Gasterosteus aculeatus and snails. At the same time its condition deteriorated. The catch in the monitoring fishery in Lake Myvatn correlates with the stock size in the beginning of the following winter fishing season deduced from Leslie's method and can give prospects for the fishery in the successive fishing season. An index of abundance of young charr also correlates with the number of chironomids and cladocerans and also with ducklings that feed on the same food as the charr. Large fluctuations in the Arctic charr population in Lake Myvatn seem to be related to changes in the main food species. The catch records available from Lake Myvatn can to a large extent be used as a measure of changes of the Arctic charr population in the lake for the past century.     

The present state of an Arctic charr (Salvelinus alpinus L.) population in Lake Imandra subjected to over-fishing

The influence of fishery on the state of Arctic charr (Salvelinus alpinus L.) population in Lake Imandra. The largest freshwater water body of the Kola Peninsula, is considered. Retrospective analysis of the catches during the period 1930–2010 revealed that the consequences of uncontrolled fishing are comparable with those of technogenic pollution. As a result of intensive and long-term antropogenic influence on the lake the number of age-groups decreased; the weight and length indices changed; the structure of fish population was simplified. Even after improving of environmental conditions, the numbers of fish continued to decrease due to uncontrolled angling and poaching which led to almost complete extinction of charr in the lake.     

The food of Charr,*Salvelinus willughbii (Günther), in Windermere

The stomach contents of 1015 charr, (Salvelinus willughbii Günther)] from Windermere, of which 658 were feeding fish, were examined. The fish were caught over a period of several years and in every month of the year. The data were analysed by two methods, by a points system, which takes into account the abundance and volume of the food organisms, and by the frequency of occurrence of each organism. Charr of all sizes had fed mainly on planktonic Crustacea (particularly Cladocera); larval and pupal chironomids and Chaoborus were also important. From November to April most stomachs of charr netted on the spawning grounds contained charr eggs. The diet of charr is compared with that of seven other fish species in Windermere. There was almost no overlap between the food of charr, which was obtained in the pelagic region, and that of the seven other species, which was mostly bottom fauna, obtained from the littoral region. Thus by occupation of these two different niches the charr and the seven other fish in no way compete for food in Windermere. Some limited data from six other lakes in the English Lake District are presented, in these planktonic Crustacea are also found to be the main food.     

Does global warming threaten the dynamics of Arctic charr in Lake Geneva?

In France, the Arctic charr (Salvelinus alpinus) is native in only two lakes (Lakes Bourget and Geneva), in the most southerly part of its distribution area. It is a profundal morph living at depths of between 30 and 100 m in Lake Geneva. Following considerable stocking of Lake Geneva with juvenile Arctic charr and some good results during the 1980s, catches are currently declining. Several hypotheses have been proposed to explain this decrease, but the potential influence of warming of the lake in the 1990s has not been considered. This article studies the relationship between the strength of the cohorts and the temperature in Lake Geneva from 1992 to 2002, and discusses the various potential causes of the population collapse observed. The findings reveal close correlation between water temperature and the strength of the cohorts. It is concluded that the recent warming of Lake Geneva may have a significant direct or indirect impact on the Arctic charr population.     

Habitat use and life history of brown trout (Salmo trutta) and Arctic charr (Salvelinus alpinus) in some low acidity lakes in central Norway

Habitat utilization and the life history of browntrout Salmo trutta and Arctic charr Salvelinus alpinus were investigated in fivesympatric populations and five allopatric brown troutpopulations in Høylandet catchment, a atmosphaericlow deposition area in Mid Norway. There was asignificant inverse correlation in abundance ofepibenthic Arctic charr and brown trout in theselakes, indicating that the latter species is dominant.The largest numbers of sympatric brown trout andArctic charr were caught in epibenthic habitat. In twolakes, brown trout to some extent also occurredpelagically, while pelagic individuals of Arctic charrwere found in all five lakes. The main food items forboth epibenthic and pelagic brown trout wereterrestrial surface insects and chironomid pupae.Zooplankton was the primary food item for Arctic charrin both habitats. Although the age distribution wasvery different in the populations, neither speciesseem to suffer from recruitment failure. There was nosignificant difference in survival rates betweensympatric populations of brown trout and Arctic charr.We found a significant inverse correlation betweenepibenthic catches of brown trout and the mean weightof 4+ fish, the most abundant age group. However, ifusing weight data for three-year-old fish, no suchrelationship was found for Arctic charr. Brown troutand Arctic charr reached asymptotic lengths of197–364 mm and 259–321 mm, respectively. Both speciestypically reached sexual maturity at age 2–3, and nomaturation-induced mortality was evident. We concludethat fish populations in Høylandet lakes areregulated throughout their lifes by inter- andintraspecific competition.     

Takvatn Through 20 Years: Long-term Effects of an Experimental Mass Removal of Arctic Charr, Salvelinus Alpinus, From a Subarctic Lake

Between 1984 and 1989, the experimental removal of 31 tons (666000 fish) of stunted Arctic charr, Salvelinus alpinus, from Takvatn in northern Norway, had strong effects on the populations of Arctic charr, brown trout, Salmo trutta, and three-spined sticklebacks, Gasterosteus aculeatus. The littoral catch per unit effort (CPUE) of charr had decreased by 90% in 1990 and then increased to about 50% of the initial level by 1994 while the pelagic CPUE had decreased to zero. Growth in both charr and trout greatly improved when the charr density had decreased, and large fish of both species appeared in the catches. These large fish became predators on small charr in the littoral zone. The incidence of trout increased from below 1% to 15% from 1988 to 1999 after a brief peak at 30% in 1992 and 1993. The charr population attained a bimodal size distribution and did not return to the stunted state during the 10 years following the intensive fishing period. The mass removal experiment showed that it is possible to change the structure of a charr population by intensive fishing. Predation on small charr from cannibals and large trout was probably essential for maintaining the new population structure. An increase in the growth of young charr from 1995 to 1997 was related to a high consumption of Daphnia and Eurycercus. Rapid changes in the growth of charr followed the density fluctuations in sticklebacks, which show large annual variations in this system; the rapid changes in charr growth were probably caused by variations in the competition intensity for cladoceran prey between young charr and sticklebacks. Twenty years of data has provided important information, but even more time is needed to follow the long-term trends in northern lakes such as Takvatn.     

The upper critical thermal limits for alevins of Arctic charr from a Norwegian lake north of the Arctic circle

Mean values ±95% CL of the upper incipient (T_IL) and ultimate (T_UL) lethal temperatures, determined at five acclimation temperatures ( T_A ), increased for T_IL from 19.2 ± 0.4° C ( T_A 0.5° C) to 21.0 ± 0.4° C ( T_A 20° C), and for T_UL from 22.6 ± 0.1° C ( T_A 0.5° C) to 26.6 ± 0.4° C ( T_A 20° C). Mean values were close to those obtained for Arctic charr alevins from Windermere (north-west England). These comparative data for alevins, and previous data for 0+ year parr, indicate negligible geographical variation in the thermal limits of Arctic charr.     

An electrophoretic and biometric study of Arctic charr, Salvelinm alpinus (L.), from ten British lakes

Samples of Arctic charr, Salvelinus alpinus (L.), were collected from the eight Cumbrian lakes containing all the known English populations. Comparative material was obtained from North Wales and southern Scotland. Comparisons were performed using otolith ages, meristic and morphological characters and by assessing allele frequencies for serum esterase and for skeletal muscle malate dehydrogenase. The results confirm that both basins of Windermere contain spring and autumn spawning races of charr. As well as differing genetically and exhibiting differing growth rates, the two races have different mean gill raker numbers and mean gill raker lengths. The latter two variables were used to derive a discriminant function which enables individual charr to be ascribed to the correct race with 94-96% accuracy. Within both principal races there were further significant differences between charr from the north and south basins of the lake and possibly also between different spawning grounds within each basin. Variation between six of the remaining seven Cumbrian populations is significant but generally no greater than that between the Windermere spring and autumn spawners. The exception is the Ennerdale charr which stands out on morphological, meristic and genetic characters, has a rapid growth rate despite its oligotrophic environment, and is a river rather than a lake spawner. The charr from North Wales and southern Scotland were clearly distinct, both from each other and from the English populations.     

Data limited assessment of selected North American anadromous charr stocks

Charr populations are particularly susceptible to change, either from the application of harvest or environmental conditions such as climate variation. As an alternative to conventional fishery analysis, we analyze the sustainability and viability of selected North American charr stocks using a number of approaches. We compare several methods for data limited situations to determine the allowable harvest of the Ekalluk River, Paliryauk River, Halovik River, Jayco Lake and Lauchlan River Arctic Charr including Cadima’s Maximum Sustainable Production Method, Hierarchical Bayesian Surplus Production Models, a Status Quo Total Allowable Harvest method, Long-term Average Catch methods and the Depletion-Corrected Average Catch method. Each method provided a similar outcome in terms of the relative importance of stocks to the fishery. The predicted sustainable harvest of larger stocks such as the Ekalluk and Jayco varied more according to the method applied than the other stocks studied. While not a replacement for more comprehensive fishery models these methods can be useful in data poor situations.     

Trying to collapse a population for conservation: commercial trade of a marine invasive species by artisanal fishers

Implementing new and effective control strategies to reduce populations of invasive species is needed to offset their negative impacts worldwide. The spread of Indo-Pacific lionfish (Pterois sp.) through much of the western Atlantic has been one of the most publicized marine invasions globally, and is considered a major biodiversity threat whose longer-term impacts are still uncertain. Marine managers have explored several strategies to control lionfish, such as fishing tournaments (derbies) and commercial fisheries. Commercial fisheries for invasive species are controversial because they could create perverse incentives to maintain these populations, and they have never been demonstrated to successfully control target populations. We analyzed the development and impacts of an opportunistic fishing operation aimed at commercializing invasive lionfish in the Mexican Caribbean. We examined official lionfish landings and compared them to catches from lionfish derbies and lionfish densities from locations in the state of Quintana Roo, Mexico. We found that commercial fishers, particularly from one fishing cooperative on Cozumel Island, were effective at catching lionfish, with landings peaking at 20,000 individuals in 2014. This number is comparable to the number of lionfish caught in derbies across the entire Caribbean in the same year. Ecological survey data suggest a?~?60% reduction in lionfish density on Cozumel reefs over two years (2013–2015), matching the peak landings in the lionfish fishing operation. However, the fishery’s apparent success as a control tool during the time window analyzed seemed to trigger its own demise: a decline in landings was followed by evaporating market interest and loss of economic viability. If fisheries are to be established and used as management strategies to control future invasions, managers must develop strategic collaboration plans with commercial fishing partners.

     

On the Origin of the Lacustrine Charr <Emphasis Type="Italic">Salvelinus alpinus</Emphasis> Complex from the Kolyma and Sea of Okhotsk Basins

Morphological and genetic characteristics are used for the analysis of the origin of charrs from the lakes of the Kolyma basin (Chuk, Gek, Gulyaevskoe-4, Gulyaevskoe-6, and Lenkovoe) and the Sea of Okhotsk basin (Lake Chistoe). In addition to these samples, the fragments of the control region of mitochondrial DNA (CR mtDNA, 550-bp) and exon 2 of recombination activating gene 1 (RAG1, 899-bp) are sequenced in the charrs from lakes Dzhul’etta and Cherechen’ (Kolyma basin) and lakes Elikchanskie, Bol’shoi Mak-Mak, Ueginskoe (Sea of Okhotsk basin), Ulakhan-Silyan-Kyuel’ (Yana River basin) as well as in northern Dolly Varden from the Kamchatka River. The charr from Lake Chistoe is represented by northern Dolly Varden. In the charrs from lakes Chuk, Gek, Gulyaevskoe-4, Gulyaevskoe-6, Lenkovoe, Cherechen’, Elikchanskie, Bol’shoi Mak-Mak, and Ueginskoe, the haplotypes of mtDNA of the Bering group (a haplogroup of northern Dolly Varden) are revealed. Based on the morphological and RAG1 data, populations of charrs from these lakes belong to the Salvelinus alpinus complex. A transfer of mtDNA of northern Dolly Varden to the charrs from the Kolyma and Sea of Okhotsk basins occurred during the last postglacial expansion and subsequent hybridization. Based on the results of morphological and genetic analysis, the charrs from the Kolyma and Sea of Okhotsk basins cannot be unambiguously referred to the phylogenetic groups of Eurasian Arctic charr or Taranets charr. The presence of mtDNA haplotypes of the Arctic group (a haplogroup of Taranets charr) in the populations of lakes Dzhul’etta, Maksi, and Ueginskoe shows a possibility of their belonging to the group of Taranets charr.     

Diet of Arctic charr (Salvelinus alpinus (L.)) and brown trout (Salmo trutta L.) in sympatry in two high altitude alpine lakes

Lake Pisses and Lake Labarre are two oligotrophic high altitude alpine lakes that have sympatric populations of Arctic charr and brown trout. These two lakes have similar morphometric, physical and chemical characteristics. The zooplanktonic and benthic fauna show little diversity. But the density of benthos (Chironomidae) and zooplankton is higher in Lake Pisses. The fish fauna of Lake Pisses is slightly more abundant than that of Lake Labarre, althought in both lakes fish density is low. A study of the diet of the two species revealed differences. In Lake Pisses, where the food supply is better, Arctic charr takes exclusively pelagic and benthic prey, whereas in Lake Labarre it also takes exogenous prey and thus comes into competition with trout. Length and body weight growth rates for Arctic charr are higher in Lake Pisses than in Lake Labarre. For trout, maximum length recorded was in Lake Pisses. The results show that the abundance of Chironomidae favours coexistence of the two species in Lake Pisses and confirm that, in the face of shortage of food, Arctic charr is better adapted than trout. This revised version was published online in July 2006 with corrections to the Cover Date.     

Assessment of long-term changes in habitat availability for Arctic charr (Salvelinus alpinus) in a temperate lake using oxygen profiles and hydroacoustic surveys

1. Hydroacoustics (2002–04) and long‐term oxygen data (1969–2004) have been used in conjunction to examine the habitat of Arctic charr in the north and south basins of Windermere, U.K., a temperate lake subjected to cultural eutrophication and subsequent nutrient management. 2. Since 1969 there has been a gradual decline in the oxygen concentration in the bottom waters of both basins of 0.03–0.04 mg L^?1year^?1, resulting in up to 43% of the volume of the south basin having an oxygen concentration <5 mg L^?1 in the early autumn. 3. Hydroacoustic data indicate that most Arctic charr routinely avoid the upper 10 m of the water column irrespective of temperature, with the implication that an observed gradual warming of the lake has not yet directly impacted upon their habitat. 4. In recent years there has been a behavioural response of the Arctic charr population to migrate vertically to avoid oxygen concentrations <2.3–3.1 mg L^?1. Further, the depth of the lower bound of the Arctic charr population is shown to be highly correlated with the deep water oxygen concentration throughout the year prior to autumnal overturn.     

European smelt Osmerus eperlanus in the eastern Gulf of Finland,Baltic Sea: Stock status and fishery

In the eastern Gulf of Finland, European smelt Osmerus eperlanus occurs as an anadromous ecological form that spawns in coastal, low-salinity zones and in several rivers entering the gulf, most importantly in the River Neva. Osmerus eperlanus is a key commercial fish species for the population of St. Petersburg, and the city's fish symbol. However, the state of the smelt stock has considerably deteriorated over the past few decades. Monitoring shows that annual catches during 1965–1992 averaged 2274 t, compared to 292 t in 2002–2017, although some improvement is inidicated by a gradual increase in catches in recent years (e.g., to 595 t in 2017). This paper addresses long-term and recent changes in the fisheries for smelt in the eastern Gulf of Finland, including both commercial and recreational fisheries, and the range of fishing gears used. The commercial smelt fishery is mainly conducted during the spawning period (April–May) on migrating fish, using trap nets of various designs and beach seines. There has been an increase in recreational fisheries for smelt; in years when ice cover on the gulf during winter (December–April) is steady, recreational fishers from St. Petersburg, using hook and line, may catch quantities that are comparable to those of commercial catches. Several factors may account for the stock dynamics and associated changes in catches of smelt: these include a decrease in prey availability in the gulf; loss and degradation of spawning and nursery habitats, partly associated with large-scale hydroengineering operations in Neva Bay; and illegal, unreported and unregulated (IUU) fishing which became widespread in post-Soviet decades. In spite of a gradual increase in smelt abundance in the most recent 15 years, a failure to accurately monitor and manage the extent of IUU and recreational fishing for smelt, to assess the status of the stock, or to forecast catches, increases the risk of overfishing of the spawning stock.     

The Relevance of Individual Size to Management of Arctic Charr, Salvelinus Alpinus, Populations

Arctic charr, Salvelinus alpinus, tend to form stunted populations presumably due to competition for limited resources. In this context a long-term intensive fishery programme aiming at reducing charr density, and thereby increasing growth and harvestable sizes, was initiated in the early 1980s in a Norwegian alpine lake. Here we present long-term data on catch statistics and changes in mean weights of charr caught with gill nets on spawning grounds, as well as changes in mean weight of juvenile charr caught with funnel traps during the 1990s. Furthermore, we present results from shorter-term studies on growth, size- and age-distribution, and size-related habitat and resource utilisation of Arctic charr and brown trout, Salmo trutta, in this lake. Mean weight (± SD) of charr caught on the spawning grounds increased significantly from 129.8g (±11.9) in the years 1982–1990 to 213.1g (±37.8) in the years 1996–1999, whereas catch per unit of effort decreased significantly. Mean weight of juveniles caught in funnel traps increased significantly from 21.2g (±6.9) in 1993 to 41.9g (±14.8) in 1999. Apparently the increase in weight of spawning charr coincided with the onset of trap fishing for juvenile charr. Compared to generally shallow dwelling trout, charr grew rapidly and were generally found in deeper areas of the lake. Charr went through a distinct size-related niche shift from mainly consuming small zooplankton in the pelagic to consuming large benthic prey in shallower waters. Resource and habitat utilisation in different size-groups of charr and trout are discussed with respect to possible competitive and predatory intra- and interspecific interactions, and with regard to management of charr populations.     

Combining Telephone Surveys and Fishing Catches Self-Report: The French Sea Bass Recreational Fishery Assessment

Fisheries statistics are known to be underestimated, since they are mainly based on information about commercial fisheries. However, various types of fishing activities exist and evaluating them is necessary for implementing effective management plans. This paper assesses the characteristics and catches of the French European sea bass recreational fishery along the Atlantic coasts, through the combination of large-scale telephone surveys and fishing diaries study. Our results demonstrated that half of the total catches (mainly small fish) were released at sea and that the mean length of a kept sea bass was 46.6 cm. We highlighted different patterns of fishing methods and type of gear used. Catches from boats were greater than from the shore, both in abundance and biomass, considering mean values per fishing trip as well as CPUE. Spearfishers caught the highest biomass of sea bass per fishing trip, but the fishing rod with lure was the most effective type of gear in terms of CPUE. Longlines had the highest CPUE value in abundance but not in biomass: they caught numerous but small sea bass. Handlines were less effective, catching few sea bass in both abundance and biomass. We estimated that the annual total recreational sea bass catches was 3,173 tonnes of which 2,345 tonnes were kept. Since the annual commercial catches landings were evaluated at 5,160 tonnes, recreational landings represent 30% of the total fishing catches on the Atlantic coasts of France. Using fishers'' self-reports was a valuable way to obtain new information on data-poor fisheries. Our results underline the importance of evaluating recreational fishing as a part of the total amount of fisheries catches. More studies are critically needed to assess overall fish resources caught in order to develop effective fishery management tools.     

A preliminary assessment of the biomass of the pelagic sardine Limnothrissa miodon in Lake Kariba

The sardine Limnothrissa miodon was very patchily distributed in Lake Kariba in 1981–1983 and its mean biomass was 59 23 kg ha⁻¹, declining from 90–91 kg ha⁻¹ in 1981 to 38–66 kg ha⁻¹ in 1983. In addition, the mean size of the fish fell from 55–2 mm in 1981 to 49–9 mm in 1983. These changes are attributed to the effects of drought and reduced river flows as well as to the high level of commercial fishing for this species. There was a correlation between commercial catches and biomass estimates which allowed estimation of biomass in previous years from fishing statistics. Fishing effort appeared to be a major influence on sardine abundance: total biomass in 1985 was about 10% of what it was in 1974 when the fishery began. When expressed in terms of unit area, as is usual for African lakes, the pelagic biomass appeared to be greater in Lake Tanganyika, where Limnothrissa is endemic, than in Lake Kariba, although there is little difference in their primary productivity, but consideration in terms of volume rather than area shows that this was not the     

Resilience and stability of north Labrador Arctic charr, <Emphasis Type="Italic">Salvelinus alpinus</Emphasis>, subject to exploitation and environmental variability

There are relatively few studies that have examined in detail the effects of long term exploitation on population characteristics of Arctic charr, Salvelinus alpinus, coincident with natural changes in environmental conditions. This is particularly the case for anadromous charr despite their widespread use and importance in areas such as northern Canada. Here, the response of north Labrador charr to major reductions in commercial exploitation following long periods of intense fishing is described for three stock complexes with emphasis on changes in size, growth, and age configurations. Changes in age and size distribution, specifically long-term declines in weight, are linked with periods of intensive exploitation and possibly with variability in the climate of the northwest Atlantic that resulted in identifiable diet shifts during the early 1990s. Despite observed changes in some metrics, populations have maintained relatively stable length compositions with variations in weight showing resilience to return to earlier configurations as exploitation was reduced and environmental conditions ameliorated. Results of the long-term investigations challenge traditional beliefs associated with the inability of all anadromous charr to withstand periods of intense exploitation.