Baltic Main Basin Research Articles

Multi-level assessment of the origin, feeding area and organohalogen contamination on salmon from the Baltic Sea

The Atlantic salmon (Salmo salar) population in the Baltic Sea consists of wild and hatchery-reared fish that have been released into the sea to support salmon stocks. During feeding migration, salmon migrate to different parts of the Baltic Sea and are exposed to various biotic and abiotic stressors, such as organohalogen compounds (OHCs). The effects of salmon origin (wild or hatchery-reared), feeding area (Baltic Main Basin, Bothnian Sea, and Gulf of Finland), and OHC concentration on the differences in hepatic proteome of salmon were investigated. Multi-level analysis of the OHC concentration, transcriptome, proteome, and oxidative stress biomarkers measured from the same salmon individuals were performed to find the key variables (origin, feeding area, OHC concentrations, and oxidative stress) that best account for the differences in the transcriptome and proteome between the salmon groups. When comparing wild and hatchery-reared salmon, differences were found in xenobiotic and amino acid metabolism-related pathways. When comparing salmon from different feeding areas, the amino acid and carbohydrate metabolic pathways were notably different. Several proteins found in these pathways are correlated with the concentrations of polychlorinated biphenyls (PCBs). The multi-level analysis also revealed amino acid metabolic pathways in connection with PCBs and oxidative stress variables related to glutathione metabolism. Other pathways found in the multi-level analysis included genetic information processes related to ribosomes, signaling and cellular processes related to the cytoskeleton, and the immune system, which were connected mainly to the concentrations of Polychlorinated biphenyls and Dichlorodiphenyltrichloroethane and their metabolites. These results suggest that the hepatic proteome of salmon in the Baltic Sea, together with the transcriptome, is more affected by the OHC concentrations and oxidative stress of the feeding area than the origin of the salmon.

Effects on the Liver Transcriptome in Baltic Salmon: Contributions of Contamination with Organohalogen Compounds and Origin of Salmon.

Hatchery-reared Atlantic salmon (Salmo salar) has been released to support the wild salmon stocks in the Baltic Sea for decades. During their feeding migration, salmon are exposed to organohalogen compounds (OHCs). Here, we investigated the OHC levels and transcriptome profiles in the liver of wild and hatchery-reared salmon collected from the Baltic main basin (BMB), the Bothnian Sea (BS), and the Gulf of Finland (GoF) and examined whether salmon origin and OHC levels contributed to the hepatic transcriptome profiles. There were no differences in the OHC concentrations between wild and reared fish but larger differences between areas. Several transcript levels were associated with non-dioxin-like polychlorinated biphenyls, polybrominated diphenylethers, chlordanes, and dichlorodiphenyltrichloroethane in a concentration-dependent manner. Between wild and reared salmon, lipid metabolism and related signaling pathways were enriched within the BMB and BS, while amino acid metabolism was altered within the GoF. When comparing the different areas, lipid metabolism, environmental stress and cell growth, and death-related pathways were enriched. Class coinertia analysis showed that the covariation in the OHC levels and the transcriptome were significantly similar. These results suggest that the hepatic transcriptomes in wild and hatchery-reared salmon are more affected by the OHC levels rather than the origin of salmon.

Increasing temperature associated with increasing grilse proportion and smaller grilse size of Atlantic salmon

Effects of temperature on Atlantic salmon (Salmo salar) were analysed using Carlin tag recovery data (1985–2014), and mixed‐stock catch data (smolt years from 2001 to 2012) in northern parts of the Baltic Sea. During warmer summers, the mean smolt length of the recaptured salmon tended to be smaller, and salmon were recaptured more frequently in feeding grounds closer to the home rivers in the Gulf of Bothnia, while colder summers were associated with more recaptures further south, in the Baltic Main Basin. Moreover, a warmer spring in the smolt year was associated with decreased weight of male grilses in mixed stock data. Further, warmer spring temperatures during the smolt year were associated with a higher proportion of one‐sea‐winter (1SW) males during the return migration in mixed stock data. These results suggest that the increasing global temperature may affect Atlantic salmon life history demographics.

Spatial variation in transcript and protein abundance of Atlantic salmon during feeding migration in the Baltic Sea.

The fitness and reproductive output of fishes can be affected by environmental disturbances. In this study, transcriptomics and label-free proteomics were combined to investigate Atlantic salmon (Salmo salar) sampled from three different field locations within the Baltic Sea (Baltic Main Basin (BMB), Gulf of Finland (GoF), and Bothnian Sea (BS)) during marine migration. The expression of several stress related mRNAs and proteins of xenobiotic metabolism, oxidative stress, DNA damage, and cell death were increased in salmon from GoF compared to salmon from BMB or BS. Respiratory electron chain and ATP synthesis related gene ontology-categories were upregulated in GoF salmon, whereas those associated with RNA processing and synthesis, translation, and protein folding decreased. Differences were seen also in metabolism and immune function related gene expression. Comparisons of the transcriptomic and proteomic profiles between salmon from GoF and salmon from BMB or BS suggest environmental stressors, especially exposure to contaminants, as a main explanation for differences. Salmon feeding in GoF are thus “disturbed by hazardous substances”. The results may also be applied in evaluating the conditions of pelagic ecosystems in the different parts of Baltic Sea.

Genetic differentiation of southeast Baltic populations of sea trout inferred from single nucleotide polymorphisms

Sea trout (Salmo trutta m. trutta) is a migratory form of brown trout common in the Baltic Sea. Nine populations from the southeast Baltic (Poland; Lithuania; Denmark, Bornholm; Estonia and Russia) were genotyped using iPLEX Gold technology (Sequenom) with 62 informative SNPs. A diagnostic panel of 23 SNPs was applied to estimate genetic differentiation and assess the population structure of Baltic sea trout. The highest level of pairwise FST differences was observed between the Russian (East Gulf of Finland) and Polish (Baltic main basin) populations. The lowest differences were between the two Polish and the Polish and Lithuanian populations. A genetic similarity was noted between the Estonian Riguldi River and Danish Bornholm populations, and this finding was supported by a Bayesian and factorial correspondence analysis. Diversity within populations was highest for populations from Estonia and lowest for the Lithuanian population. Genetic structure analysis indicated that individuals from the nine populations were clustered into four groups.

Cost–benefit analysis of Atlantic salmon smolt releases in relation to life-history variation

Cost–benefit analysis was applied to estimate the net present value (NPV) of Atlantic salmon (Salmo salar, Carl Linnaeus) hatchery smolt releases and the spatial distribution of the present value of benefit [PV(B)] in the Baltic Sea. The benefit was assessed for the commercial fishery and separately from hatchery-reared and wild smolts. Data on Carlin tagging and on the proportions of individual salmon stocks in the commercial catches were used. The NPV of hatchery smolt releases appeared to be negative with current rearing costs and the range of applied discount rates (2–4%), and especially with the currently low overall survival of salmon smolts in the sea (<2%). A 5% recapture rate had been needed for a positive outcome. The PV(B) of wild salmon smolts was higher than that of reared salmon smolts due to their larger catch size and higher recapture rate. Both wild and reared salmon mostly benefited the fishermen operating in the Baltic Main Basin, while few fish and minor revenues were left for the coastal and river fisheries in the Bothnian Bay. Six salmon stocks, three wild and three reared, originating from the Bothnian Bay accounted for 60% of the total Atlantic salmon catch in the Baltic Sea. The current economical benefits from hatchery smolt releases to professional fishermen barely overcome the costs they cause to rearing and releasing counterparties.

Post-smolt migration of Atlantic salmon,Salmo salarL., from the Simojoki river to the Baltic Sea

Summary The migration pattern of Atlantic salmon (Salmo salar L.) post-smolts in the Baltic Sea was investigated based on tag recoveries of Carlin-tagged wild and hatchery-reared smolts released in the Simojoki river in 1972–2005. Exact date of sea entry was known only for the wild smolts. Tag recoveries of wild salmon in the estuary within 10 km from the river mouth were received on average 3.5 days (±2.0 SD) after release. Time required for emigration from the estuary was dependent on the sea surface temperature (SST) off the river (R2 = 0.625, P = 0.004), being shorter in years with warmer than colder sea temperatures. Outside the estuary, the wild and hatchery-reared post-smolts migrated southwards along the eastern coast of the northern Gulf of Bothnia, the tag recoveries coinciding with the warm thermal zone in the SST occurring along the coastal area. After arriving in the southern Gulf of Bothnia in late summer the post-smolts mostly migrated near the western coast, reaching the Baltic main basin in late autumn. The relationships between the marine conditions and migration patterns are discussed.

Annual changes in the proportions of wild and hatchery Atlantic salmon (Salmo salar) caught in the Baltic Sea

Abstract DNA-level information from an eight-loci microsatellite baseline database of 32 Atlantic salmon (Salmo salar) stocks was used with a Bayesian estimation method to assess the stock and stock group proportions of Finnish salmon catches in the Baltic Sea area. The proportions of seven stock groups, important to fisheries management, were assessed in catch samples taken between 2000 and 2005. In the Gulf of Bothnia area, the proportion of wild fish in catches showed an increasing trend in all areas until 2003, mainly because of the decrease in total catches caused by the relatively greater mortality of hatchery-reared fish compared with wild fish. In 2004, the total number of wild fish caught had also increased, indicating an increase in the abundance of wild stocks. In catches from the Åland Sea, the proportion of wild fish increased from 44% in 2000 to 70% in 2004, while the catch during the same period increased from 4628 to 7329 fish. In the Gulf of Finland, the local Neva salmon stock, which is released by Estonia, Finland, and Russia, made the largest contribution. In the western part of the Gulf of Finland, fish originating in the Baltic Main Basin also made a substantial contribution to catches. The threatened eastern Estonian and Russian wild stocks were recorded only in the western part of the Gulf of Finland, where the proportion of wild fish increased from 9% in 2003 to 19% in 2004.

Classical individual assignments versus mixture modeling to estimate stock proportions in Atlantic salmon (Salmo salar) catches from DNA microsatellite data

Mixture modeling is shown to outperform classical individual assignments for both estimating stock composition and identifying individuals' sources in a case study of an eight-locus DNA microsatellite database from 26 Atlantic salmon (Salmo salar) stocks of the Baltic Sea. Performance of the estimation methods was compared using self-assignment tests applied to each of the baseline samples and using independent repeat samples from two of the baseline stocks. The different theoretical underpinnings, hypothesis testing versus decision theory, of the methods explain their estimation capacities. In addition, actual catch samples from three northern Baltic Sea sites in 2000 were analysed by mixture modeling, and estimated compositions were consistent with previous knowledge. Baltic main basin and Gulf of Finland stocks were each minor components (&lt;1% at any site), and three groups of Gulf of Bothnia stocks, wild (36%–43% among sites), Finnish hatchery (15%–49%), and Swedish hatchery (11%–41%), were each important with the two hatchery contributions trending geographically.

Population genetic structure and postglacial colonization of Atlantic salmon (Salmo salar) in the Baltic Sea area based on microsatellite DNA variation

The genetic structure and phylogeography of Atlantic salmon (Salmo salar) across the Baltic Sea basin and neighbouring areas (eastern Atlantic Ocean, North Sea, Barents Sea, White Sea, and two Russian lakes, Onega and Ladoga) were studied to resolve the partly contradictory hypotheses of the species' postglacial colonization history. Thirty-eight populations (total of 2180 individuals) were studied for nine DNA microsatellite loci. Within the Baltic Sea, the anadromous populations formed three clear groups, corresponding to the northern (Gulf of Bothnia), eastern (Gulf of Finland and eastern Baltic Main Basin), and southern regions (western Baltic Main Basin). The genetic differences among these three groups were clearly greater (GGB5.6%; GGBbeing the proportion of diversity components between regions within basins) than were those among population groups in the eastern Atlantic Ocean (GGB2.2%) from Ireland to the White Sea. The isolation-by-distance model explained part of the differentiation within, but not between, the regions. The results strongly indicate colonization of the Baltic Sea by at least three glacial lineages. Potential refugium areas for each lineage are proposed.

Differences in sea migration between wild and reared Atlantic salmon ( Salmo salar L.) in the Baltic Sea

The effect of origin, smolt size and year of release on the sea migration pattern of Atlantic salmon ( Salmo salar L.) in the Baltic Sea was examined by tagging experiments conducted in 1991–1993 on wild and reared smolts of the Simojoki river salmon stock. The tag recovery data analysed by log-linear models revealed significant differences in both spatial and temporal sea migrations between the wild and reared salmon; the variation was attributed to the year of release and to the origin of the fish. Grilse accounted for the majority of reared returners (76%) but for a smaller proportion (46%) of the wild fish. The effect of smolt size could be studied only in the smolt groups tagged in 1991. Wild fish were more frequently (71%) caught in the Baltic Main Basin than were reared fish (51%) during their second sea year, and the size variation between wild and reared smolts did not explain the recovery site. No such differences in spatial distribution were found during the third sea year. The tagging place (hatchery/trap) of the reared fish did not affect their later sea migration. The differences in sea migration patterns suggest that the wild salmon are more vulnerable to the intensive salmon fishery in the Baltic Main Basin than are reared fish.

The effect of sexual maturation on the spatial distribution of Baltic salmon

This study examines the migratory habits of tagged mature and immature Atlantic salmon parr Salmo salar released from the Norrfors hatchery on the River Umeälven, Sweden from 1975 to 1977 and 1988 to 1990. Tags were recaptured in the Baltic Main Basin, the Gulf of Bothnia, and in the Umeälven. Ninety‐three per cent of previously mature males were recovered in the Umeälven compared with 23% of the previously immature smolts during the calendar year of release. In the second year after release (grilse year), the proportion of early maturing males recovered in the Umeälven was significantly greater than the proportion of previously immature smolts recovered in the Umeälven. Likewise, the proportion of previously mature males recovered in the Main Basin was significantly less than the proportion of previously immature smolts recovered in the Main Basin in the second calendar year after release. Previously mature males rematured after fewer years at sea, on average, than the previously immature smolts. Following the second calendar year after release, the proportions of previously mature males and previously immature smolts were not significantly different throughout the Baltic Sea.

The effect of sexual maturation on the spatial distribution of Baltic salmon

This study examines the migratory habits of tagged mature and immature Atlantic salmon parr Salmo salar released from the Norrfors hatchery on the River Umeälven, Sweden from 1975 to 1977 and 1988 to 1990. Tags were recaptured in the Baltic Main Basin, the Gulf of Bothnia, and in the Umeälven. Ninety-three per cent of previously mature males were recovered in the Umeälven compared with 23% of the previously immature smolts during the calendar year of release. In the second year after release (grilse year), the proportion of early maturing males recovered in the Umeälven was significantly greater than the proportion of previously immature smolts recovered in the Umeälven. Likewise, the proportion of previously mature males recovered in the Main Basin was significantly less than the proportion of previously immature smolts recovered in the Main Basin in the second calendar year after release. Previously mature males rematured after fewer years at sea, on average, than the previously immature smolts. Following the second calendar year after release, the proportions of previously mature males and previously immature smolts were not significantly different throughout the Baltic Sea.

Distinguishing between resident and migrating Atlantic salmon (Salmo salar) stocks by genetic stock composition analysis

The possibility of using the genetic stock identification (GSI) method to distinguish between individual Atlantic salmon (Salmo salar) stocks and stock groups in Finnish catches was studied. In the Baltic Sea, the Atlantic salmon is a target of a mixed-stock fishery, and information about stock composition would be valuable for the management of the species. The salmon catches on the Finnish west coast consist of two seasonally variable components: a group of northern stocks migrating through the area to the Baltic main basin and the resident Neva salmon. The migratory component includes two endangered wild stocks (Tornionjoki and Simojoki). The allele frequency differences at four polymorphic loci among the stocks allowed reliable catch composition estimates to be made of the migratory and resident components; one stock (Oulujoki) from the northern group could also be identified with reasonable accuracy. Northern migrating stocks accounted for over half the catches at the time of this study. The estimate of natural (nonhatchery) stocks was very low (3% in total).