Anadromous Whitefish Research Articles

Characteristics of the spawning migration of anadromous broad whitefish (Coregonus nasus) in the lower Mackenzie River

Characteristics of the spawning migration of anadromous broad whitefish (Coregonus nasus) in the lower Mackenzie River

Changes in age and maturity of anadromous whitefish (Coregonus lavaretus) in the northern Baltic Sea from 1998 to 2014

The maturation of anadromous whitefish (Coregonus lavaretus) was analysed from samples taken from commercial coastal fishing in 1998–2014 in the Gulf of Bothnia. Whitefish matured at a younger age from year to year. The proportion of older (5–12 sea years) mature males decreased from 79% to 39% in the northern Gulf of Bothnia (66°N–64°N) and from 76% to 14% in southern (64°N–60°30'N) during the study period. At the same time, the proportion of young males (2–4 sea years) increased. Whitefish matured younger: the proportion of mature fish at age four increased in both the north and south among females (13% → 98%; 6% → 85%) and males (68% → 99%; 29% → 89%). The catch length of four-year-old fish increased during the study period in both sexes. In contrast, the length of six-year-old females decreased from year to year. Sea surface temperatures increased during the study period, and were possibly associated with a decrease in the age of maturation and faster growth.

Investigating fish migration, mortality, and physiology to improve conservation planning of anadromous salmonids: a case study on the endangered North Sea houting (Coregonus oxyrinchus)

Understanding migratory behavior, mortality, and physiology is essential for conservation of many species, particularly anadromous fish. In this study, freshwater and marine migrations of the endangered salmonid North Sea houting (Coregonus oxyrinchus (Linnaeus, 1758)) were investigated using telemetry. Furthermore, physiological samples were collected from North Sea houting and from resident and anadromous populations of the closely related European whitefish (Coregonus lavaretus (Linnaeus, 1758)) to compare hypo-osmotic tolerances. On average, North Sea houting spent 193 days at sea where the mortality was 36%. Most fish returned from sea in the autumn, and river entry correlated inversely with river temperature and positively with discharge. Fish spent an average of 49 days in the estuarine area. Artificial lakes negatively affected migration speeds. Migration speeds did not differ consistently between individuals (i.e., not a repeatable trait) but correlated positively with water temperature. Fish arrived at spawning areas in November. In the post-spawning state, Na+/K+-ATPase activities were elevated in North Sea houting and anadromous whitefish compared with resident whitefish, while osmolality was elevated only in North Sea houting. Our study provides important information for conservation planning related to the Habitat Directive of the European Union that lists the North Sea houting as critically endangered.

Different growth trends of whitefish ( Coregonus lavaretus ) forms in the northern Baltic Sea

The sea growth of two whitefish forms, anadromous (Coregonus lavaretus lavaretus) and sea‐spawning (Coregonus lavaretus widegreni), was analysed using samples collected from the commercial sea catch in the Gulf of Bothnia (GoB) in the northern Baltic Sea during 1998–2014. In the GoB area, these two forms are possible to identify because the gill‐raker number and size at maturity vary between forms. The growth rate of the forms is linked to their feeding area. Sea‐spawning whitefish, which has a feeding migration near its home site, was shorter in the northern GoB (66°N–64°N) at the ages of 3–11 than those in the southern GoB (64°N–60°30′N). In the data, most whitefish were caught with gill nets in the GoB. The mesh sizes of gill nets capturing the anadromous form were mostly 35–45 mm, while those capturing the sea‐spawning form were <35 mm in the northern GoB. It is likely that the different growth trends for small and large whitefish were connected with differences in their recruitment for fishing. The length of anadromous females at the age of four sea years increased significantly, but the length of six‐year‐old anadromous female whitefish decreased over the catch years from 1998–2014. In contrast, the length of slow‐growing sea‐spawning whitefish of six years or older increased significantly in relation to the catch year in the gill‐net catch. The increase in the growth of young age groups in both forms was probably associated with the increasing temperature and the low fishing pressure on small fish. The decreasing age at capture for both forms and the depression of the mean size of old anadromous whitefish are signs of high fishing pressure with a high gill‐net effort that selectively removes the largest and oldest individuals of both forms.

Testing the devil\u2019s impact on southern Baltic and North Sea basins whitefish (Coregonus spp.) diversity

BackgroundThe diversity and phylogeny of whitefish of the genus Coregonus is complex, and includes many endemic species of high conservation concern. However, because of commercial importance of whitefish fisheries, stockings and translocations have occurred repeatedly, which challenges the identification of local populations as conservation units. This study analyses the phylogenetic relationships of 15 contemporary and two historical populations of lake-resident and anadromous whitefish (Coregonus spp.) from the southern Baltic and North Sea basins. We elucidated the complex history of Lake Schaal (northern Germany) whitefish, for which a local tale suggests that the devil threw whitefish from the Central European Lake Constance into this lake. Studies from the early twentieth century indeed suggested numerous stocking events for Lake Schaal from Lake Constance, from Estonian/Russian Lake Peipsi and from the anadromous whitefish of the Baltic Sea.ResultsAnalyses of 13 microsatellite markers showed that Lake Constance whitefish are unrelated to any northern Germany whitefish population, including the contemporary whitefish population from Lake Schaal. Comparison with four historical specimens further showed that the native Lake Schaal whitefish (C. holsatus) vanished from the lake, but has survived as a non-native population in the north German Lake Drewitz. The whitefish currently occurring in Lake Schaal and three adjacent lakes are identified as C. maraenoides, introduced from Lake Peipsi. The contemporary anadromous whitefish populations from the Baltic (German and Finnish coast) and the German River Treene (North Sea basin, stocked from Danish River Vida) grouped together, but showed significant genetic differentiation. The 14 historical specimens of C. oxyrinchus from Rivers Rhine and Schelde were assigned to several contemporary whitefish populations, but among them only one specimen was assigned to the contemporary River Treene population. Therefore, we do not support the view that the whitefish from River Vida/Treene are identical with the historical C. oxyrinchus.ConclusionsOur study demonstrates that lake and anadromous whitefish in the Baltic and North Sea basins reflect a complex phylogeography, which is further blurred by the effects of repeated stocking and translocations. To identify conservation units, the genetic identity of each population has to be scrutinized.

Short feeding migration associated with a lower mean size of whitefish in the River Tornionjoki, northern Baltic Sea

AbstractThe size of anadromous whitefish caught with dip nets in the River Tornionjoki in the northern part of the Gulf of Bothnia has decreased during recent decades. To find an explanation for this trend, ascending whitefish were sampled in the lower part of the river in August 2016, and they were divided into two groups according to fish length. The length of the SMALL group was ≤ 32 cm (n = 32) and that of the LARGE group ≥ 33 cm (n = 65). The elemental analysis of otoliths revealed that the barium concentration was clearly higher in otoliths from the SMALL group compared to the LARGE group. This indicates that the fish in the LARGE group had migrated to feed further south in the Gulf of Bothnia, with a higher salinity, than the fish in the SMALL group. Because of this migration difference, and a decline in the gillnet effort, especially in the feeding areas near the river mouth, it is assumed that proportionally more fish in the SMALL group are able to ascend the river to spawn than previously, thus decreasing the mean size. At the same time, the heavy gillnet fishery in the south removes fish from the LARGE group.

Whole otolith elemental analysis reveals feeding migration patterns causing growth rate differences in anadromous whitefish from the Baltic Sea

AbstractImpact of feeding migration pattern on growth rate of whitefish (Coregonus lavaretus L.) from River Kemijoki was investigated. River Kemijoki is located in the northernmost Gulf of Bothnia (Baltic Sea). Whitefish ascending the river to spawn show major growth rate variations. To study whether these variations are related to different feeding areas (migratory connectivity), whole otoliths from fast‐growing (FASTG) whitefish (n = 9, age 4 years, average weight 790 g) and slowly growing (SLOWLYG) whitefish (n = 9, age 8 years, average weight 600 g) were analysed for elemental (Ba, Sr, Mg, Zn, Mn, Ca) concentrations by inductively coupled plasma‐optical emission spectrometry. Results showed that the FASTG whitefish had much lower otolith Ba concentration (~45%, p ≤ .01) than SLOWLYG whitefish, revealing that FASTG whitefish have spent more time in water of higher salinity/lower latitude, that is at feeding grounds in the southern Gulf of Bothnia. Otoliths of the FASTG whitefish had also higher Mg (~25%, p ≤ .001) and Zn (~20%, p ≤ .05) concentrations, but lower Ca (~5%, p ≤ .01) concentrations, than the otoliths from SLOWLYG whitefish. These results further reveal that FASTG and SLOWLYG whitefish have been spatially separated. In conclusion, bulk otolith elemental analysis revealed spatial separation and migration differences in river‐spawning whitefish subpopulations in the Gulf of Bothnia, which apparently lead to differences in fish growth rate. Our results increase the understanding of river‐spawning whitefish biology and its population structure and dynamics and may contribute to a sustainable management of river‐spawning whitefish stocks.

Running Silver: Restoring Atlantic Rivers and their Great Fish Migrations

49 Anadromous salmon in the Pacific and Atlantic oceans are iconic species that have been the subjects of numerous natural science texts that narratively describe their common plight. Among my favorites is Bruce Brown’s Mountain in the Clouds: A Search for Wild Salmon. Reading this book is one reason that I became passionate about wild salmon conservation. However, there has been a gap in this narrative for the eastern United States, where Atlantic Salmon Salmo salar is only part of a mosaic of ocean-going species. Running Silver is an intriguing read that fills this void. The book weaves the story of the plight of Northwest Atlantic diadromous fish with source material as varied as Thoreau and Atlantic States Marine Fisheries Commission management actions. Despite the diverse sources, this narrative achieves the author’s goal of explaining the demise of this complex of species while trying to restore biological and cultural awareness of what has been lost ... and could be restored. John Waldman’s passion and dedication to the sea run fish community (both the fish and the people) is apparent in each of the book’s 20 relatively short 10-20 page chapters. Although they are woven together into a compelling story, most of the chapters are largely independent, allowing easy reading in small doses. The text transitions between number heavy text needed to explain harsh facts of lost abundance and hectares of concrete that block Atlantic Ocean rivers to very personal narrative observations of fish and river systems. I particularly appreciated the frequent conversational text where Waldman related discussions and observations of river keepers, managers, and scientists. The reader feels as if they are at the table or the river’s edge. The first four chapters set the stage and describe the fish species and river systems of the Atlantic realm. Chapter 3, The Seasonal Parade, was a favorite. Waldman uses the annual sequence of migration to introduce the reader to both the primary diadromous species and some that may be better characterized as euryhaline wanderers. This chapter was concise yet nuanced in its description of diversity within and among diadromous fish in their ecology and habitat use. And who knew there were anadromous whitefish! Running Silver: Restoring Atlantic Rivers and their Great Fish Migrations BOOK REVIEW

PIXE analyses of polished otoliths for identification of anadromous whitefish in the Baltic Sea

In this work we describe an application of particle-induced X-ray emission (PIXE) to the elemental analysis of polished otoliths of whitefish. Two spots on polished otoliths were irradiated; one spot in the core region of the otolith and another one close to the edge. The irradiations were performed in air with a collimated 0.5mm proton beam. The ratio of the strontium concentrations in the two spots was used to distinguish between different ecotypes (river, sea, lake) of whitefish. Criteria on the ratios were suggested for identification of the whitefish forms. The results were compared to results of μ-beam PIXE scans as well as multi-point scans with the 0.5mm proton beam. The measuring set-up and the results are discussed.

The large‐scale stocking of young anadromous whitefish (Coregonus lavaretus) and corresponding catches of returning spawners in the River Tornionjoki, northern Baltic Sea

AbstractStocking and fishing effort are two important potentially conflicting factors in fish stock management that require appropriate assessment to ensure a sustainable fishery. In the River Tornionjoki, which discharges into the northern Baltic Sea, a summer‐ascending whitefish, Coregonus lavaretus L., stock has long been a target by traditional dipnet fishing. Enhancement stocking of young whitefish started in the River Tornionjoki in the 1970s after a collapse in catches, with millions of age‐0 whitefish stocked annually in the river, but after about three decades, the stocking rates were considerably reduced. As a result, dipnet catches of whitefish in the Kukkolankoski Rapids rose simultaneously, peaking in the 1980s and 1990s, and then subsequently decreased. There was a significant positive correlation between stocking intensity and catch, both in weight and in numbers, revealing a strong relationship between whitefish releases and dipnet catch. Changes in gillnet fishing effort in the sea affected dipnet catches in weight as well as in mean size of captured whitefish. When the combined effect of stocking and gillnet effort was evaluated, only stocking significantly affected dipnet catches.

Characteristics of anadromous whitefish (Coregonus lavaretus (L.)) rivers in the Gulf of Bothnia

In order to study anadromous whitefish spawning river requirements, we sampled 41 rivers in the Gulf of Bothnia for newly hatched whitefish larvae for one to three consecutive years. Chemical and m ...

Decline of the North Sea houting: and protective measures for an endangered anadromous fish

Once an abundant fish species in the rivers of the Wadden Sea in northwest Europe, the North Sea houting Coregonus oxyrinchus (NSH) was at the brink of extinction 25 yr ago. The very last stronghold for this species was in the small Danish River Vidaa. In an attempt to preserve this anadromous whitefish species, juveniles were hatchery-reared and stocked in 6 Danish rivers flowing into the Wadden Sea. These stocking efforts were fairly successful, and the houting estab- lished populations in at least 2 of the rivers, but the underlying problem of habitat degradation and migration obstacles was not solved. Since a national management plan was issued in Denmark in 2003, large-scale river restoration measures have been undertaken, including the removal of 13 large obstacles in 3 NSH rivers and reestablishment of meanders in the lower river reaches. These measures were all intended to increase the spawning area for NSH and reduce juvenile mortality of NSH. The generic effect of these recent and ongoing changes is, however, not yet known. The NSH population has been irregularly monitored under various programs. Results from 15 yr of field investigation using passive integrated transponder (PIT)-tagging showed that the NSH pop- ulation in the River Vidaa remains stable, but in the other 2 rivers populations are decreasing. However, due to the recent physical improvements in river habitat and connectivity, we expect a substantial improvement in the population status of the NSH in the near future. Once they reach sexual maturity, NSH grow relatively slowly (mean: 2.55 cm yr �1 , ranging from 0 to 13.8 cm yr �1 ) and can reach an age of 10 to 12 yr. The number of repeated recaptures year after year indicates low mortality for adult fish. Six individuals were recaptured in rivers other than the one in which they were initially PIT-tagged, indicating some exchange/straying between adjacent rivers. Over- all there is a good chance that this unique species was saved in the 11th hour by intervention from managers and the EU.

Karyotype of the anadromous whitefish Coregonus lavaretus pidschian (Gmelin, 1788) from the Northern Dvina River (White Sea Basin)

The karyotype of anadromous whitefish from the Northern Dvina River was examined. The chromosomal complement consists of 9 pairs of biarmed chromosomes (8 pairs of meta- and 1 pair of submetacentrics) and 31 pairs of uniarmed (subtelo- and acrocentric) chromosomes, 2n=80, NF=98. The variability in the length of metacentrics of the first pair and the number of B-chromosomes was found.

Elevated water temperature impairs fertilization and embryonic development of whitefish Coregonus lavaretus

The adverse effects of high temperatures on the early life stages of anadromous whitefish Coregonus lavaretus were experimentally examined by assessing fertilization success, the percentage of developmental abnormalities, cumulative mortality and the rate of embryogenesis across a range of temperatures. Temperatures >or= 7 degrees C increased the proportion of unfertilized and abnormally dividing eggs, deformed embryos and consequent mortality. The higher the temperature, the more severe were the effects. When eggs were fertilized and constantly incubated at various temperatures, the effective level for 50% of the eggs and embryos (EL50) of temperature was 7.6 degrees C at the developmental stage when eye pigmentation was visible. Fewer developmental abnormalities and a lower cumulative mortality rate were observed when embryos were exposed to high temperatures from the later, gastrula stage, than from fertilization or the four-cell stage. Irrespective of retarded development in terms of day-degrees (i.e. the sum of daily mean temperatures), a high incubation temperature reduced the development time of C. lavaretus, leading to earlier hatching, and hatched fry were shorter than at the reference temperature of 4-5 degrees C. Global warming will particularly pose risks for stenothermic species such as C. lavaretus, with early life stages being especially susceptible. Thus, relatively small increases and fluctuations in river water temperatures during the spawning season of this anadromous species may have substantial negative impacts on its recruitment and population persistence.

Genetic differentiation among European whitefish ecotypes based on microsatellite data

The amount of genetic differentiation at DNA microsatellite loci in European whitefish (Coregonus lavaretus) was assessed among ecotypes, populations and run-timing types. The magnitude of genetic changes potentially caused by hatchery broodstock rearing were also compared with those observed in corresponding natural populations. A total of 35 populations were studied, including 33 Coregonus lavaretus populations and two samples of Coregonus peled. Five of the six whitefish ecotypes in Finland were represented within C. lavaretus populations. Genetic diversity among C. lavaretus populations proved to be high compared to two C. peled populations. The genetic D(A) distance between these two species was as high as 0.86. The genetic differentiation among ecotypes was generally low and thus gives support for the hypothesis of one native European whitefish species in Scandinavia. Among the ecotypes the northern, large sparsely-rakered, bottom-dwelling whitefish was most unique. Thus, observed genetic differences in quantitative traits have either developed independently of phylogenetic lineages, or have mixed and later changed according to environments and selection pressures. Overall genetic distances between the anadromous whitefish populations along the Finnish coast, especially in the Bothnian Bay area, were small. Populations of this area have been heavily influenced by human activities, and they also have the highest probability of mixing by natural means. In two cases, the Rivers Iijoki and Tornionjoki, statistically significant genetic differences could be observed between summer- and autumn-run spawning-time types. Wild populations had slightly higher allelic diversity than hatchery-reared populations of corresponding rivers. Although some reduction in genetic diversity during hatchery rearing is possible, it is an important aid in maintaining endangered populations.

Fertilization and embryonic development of whitefish ( Coregonus lavaretus lavaretus) in acidic low-ionic-strength water with aluminum

The fertilization rate and extent of the cortical reaction of anadromous whitefish decreased with increasing acidity (0.034 mmol Ca 2+ L −1); at pH 4.5 the fertilization rate was 46% of that at pH 6.5. Aluminum (250 μg L −1) decreased the percentage fertilization independently of pH and reduced the cortical reaction magnitude at all pH levels. In eggs at pH 5.0, especially at pH 4.5, and in solutions with Al, the growth of embryos was impaired by a perivitelline space that was too narrow. The proportion of embryos with a curved tail tip and those with blood circulation failure increased with decreasing pH. No fry hatched at pH 4.5 and those few that hatched at pH 5.0 did not survive. No fry survived Al-containing water at pH 5.5 and survival was decreased at pH 6.5 with Al. It is concluded that for successful recruitment of anadromous whitefish, pH should preferably remain >5.5 in dilute soft water when toxic concentrations of Al are present.

The effect of stocking size on the first winter survival of whitefish, Coregonus lavaretus (L.), in the Gulf of Bothnia, Baltic Sea

The anadromous whitefish, Coregonus lavaretus (L.), is the most numerous fish species stocked in the Gulf of Bothnia, Baltic Sea. One‐summer‐old‐whitefish fingerlings are mostly 8–10 cm long when released annually in September–October, whereas the wild whitefish are 10–12 cm at that time. About 6 million, one‐summer‐old, spray‐marked, whitefish were released in the northern and central parts of the Gulf in 1995–1998. To study the effect of the stocking length on the survival of the marked fish, the length of the recaptured whitefish as 1‐year‐olds was back‐calculated. Altogether 1106 whitefish recaptured in the Gulf of Bothnia were analysed. The back‐calculated length was slightly greater than the stocking length but not as large as the length of the wild fish. In the central part of the Gulf of Bothnia, where the mean stocking length was more than 10 cm, the back‐calculated length was 10.5–11.1 cm. In the northern part of the Gulf the mean stocking length varied between 8.8 and 10.0 cm annually, and the corresponding back‐calculated mean lengths were 9.3–9.7 cm. It also seemed that bigger fingerlings started their feeding migration earlier or they migrated faster than the smaller ones to the southern parts of the Gulf of Bothnia.

Attitudes and opinions of commercial fishermen on whitefish management in the Gulf of Bothnia, Finland

Abstract Catches of anadromous whitefish in the Gulf of Bothnia have declined since the early 1990s. It is generally assumed that the cause is overfishing. The professional fishermen interviewed in the present study were united in the opinion that it is necessary to set limits on the fishing of whitefish, but had differing views about the means of achieving this. These different arguments involved separate whitefish stocks, various types of gear and different motives for fishing. Most of the professional fishermen accepted a minimum mesh size for gill nets. Other means proposed included setting limits on non‐professional fishing and sales of catches. There were conflicting attitudes about seasonal restrictions because their experiences with fishing restrictions for salmon had been negative. On the whole, decision‐making requires more regional information on whitefish stocks and fishing, but also on the social and economic flexibility of fishermen.

Ion Regulation in Whitefish (Coregonus lavaretusL.) Yolk-Sac Fry Exposed to Low pH and Aluminum at Low and Moderate Ionic Strength

Anadromous whitefish [Coregonus lavaretus(L.)] were exposed during the yolk-sac phase to combinations of pH values of 6.0, 5.5, 5.0, 4.5, and 4.0 and nominal Al concentrations of 0, 100, 200, and 400 μg liter−1for 4 days. The test waters were: (1) lake water diluted 1:1 with ion exchanged water (DLW) and (2) artificial water (AW). The major differences were: [Ca2+] 0.069 mmol liter−1in DLW versus 0.034 mmol liter−1in AW, [Na+] 1.5 and [Cl−] 1.8 times higher in DLW, with no dissolved organic material in AW. The fry were sampled daily for the analysis of exchangeable body Na+and Cl−contents, and the swimming activity and mortality were registered. Aluminum initially protected yolk-sac fry against acidic water at pH 4.0 both in DLW and in AW. Generally, however, an increase in [Al] and a decrease in pH increased the adverse effects, seen as decreased exchangeable body Na+and Cl−content, decreased swimming activity, and increased mortality. The effects of Al were more pronounced in AW compared with DLW. In AW, the Na+and Cl−content of the fry already decreased after 1 day of exposure to a level that predicts mortalities. There was a time trend in DLW toward decreasing exchangeable body Na+and Cl−concentrations as a function of increasing acidity and [Al]. In DLW, mortalities occurred primarily at pH 4.0; at that pH value in AW, the mortality rate was even higher, and mortalities also occurred after 2 to 4 days at all other pH values. There was a threshold limit in exchangeable body Na+and Cl−concentrations at which yolk-sac fry became passive; it was at approximately 0.3 μmol per fry in DLW and was slightly higher in AW. In the DLW control with moderate ionic strength, the Na+/Cl−ratio was above 1 from the second exposure day on but remained closer to 1 in soft AW control. The Na+/Cl−ratio was predominantly >1 in AW when the fry were exposed to moderate acidities but approached 1 at pH values <5.0. The Na+/Cl−ratio was mostly ≤1 in DLW, irrespective of the exposure, indicating cation selectivity of ion leakage pathways in slightly harder water.

Radioactive strontium (85Sr) in marking whitefish [Coregonus lavaretus (L.)] larvae and the dispersal of larvae from river to sea

Anadromous whitefish [Coregonus lavaretus (L.)] yolk‐sac larvae were marked with a radioactive strontium isotope, 85Sr. Before marking the method was tested in accumulation‐elimination tests using various strontium concentrations. The first‐phase effective half‐life of 85Sr in yolk‐sac larvae was 4 days. The mean 85Sr radioactivity was 81 Bq per larva at the day of release and the half‐life of the slow component was 51 days, so the strontium label was easily detected up to 60 days after marking. The larvae were released into the River Simojoki about 12 km upstream from the river mouth and recaptured from early May to the end of July. Marked larvae were found at the river mouth 12–13 days after release, while the last marked fish in the river were found at 16 days. It is likely that all leave the river within 2 to 3 weeks post‐hatching. Two months after marking some larvae had attained a distance of 10 km from the river mouth.