Sub-challenge: For each river bordering the sea basin, a time series of annual inputs to sea of salmon (both inwards and outwards).

Salmon in the Arctic is not common, on the Pacific side Chum, Pink, Sockeye, Coho and Chinook salmon have been encountered and Atlantic salmon on the Atlantic side (Irvine et al. 2009; Verspoor et al. 2007). Data on the in- and outflow of salmon in the main Arctic rivers is sparse and very much scattered spatially as well as temporally. The same goes for general abundance datasets. No major overview exists of in- and output for all major rivers in the Arctic system. The bulk of the (online) available English data stems from the Alaskan and Canadian rivers or coastal areas, which is site-specific and local.

However, to get a first impression on the in- and output of Salmon, we chose to focus on the Chinook salmon (Oncorhynchus tshawytscha) in the Alaskan area, where data are available. The native range of the Chinook salmon is in the Northern Pacific coastal areas, as can be seen on Figure 4.

native range Chinook salmon
Figure 4: Native range of Chinook salmon. Source: Fishbase.org.

Chinook salmon only reproduces once in their life, after which they die. The adult fish swimming upriver will not return to the sea, however the hatchlings will. On the website for the Alaskan department for Fish and Game, fish counts can be retrieved for multiple species and rivers. Figure 5 shows the Alaskan areas where salmon fisheries are present, including the dominant species and principal river systems.

salmon fisheries Alaska
Figure 5: Salmon fisheries in Alaska. Source: http://www.adfg.alaska.gov/index.cfm?adfg=CommercialByFisherySalmon.salmonmaps_management

According to the Alaska department of Fish and Game, the Northern coasts of Alaska are occasionally home to small numbers of chum, pink, and Chinook salmon, however no count data is available. There is no data available from Chinook salmon on rivers opening into the Chukchi Sea. The only Chinook salmon count data available close to the study area of the Sea Basin Checkpoint project is from several rivers opening in the Norton Sound (Figure 6), we will show several as examples.

rivers entering Norton sound
Figure 6: Rivers entering into the Norton Sound, which in turns opens into the Bering Sea. Source: http://www.adfg.alaska.gov/static/fishing/PDFs/commercial/nortonsound_salmon_statmap.pdf

On the Eldorado River, Chinook salmon counts have been monitored since 1995 from a counting tower (for more information on counting techniques, please go to http://www.adfg.alaska.gov/index.cfm?adfg=sonar.nonsonartools). The cumulative daily fish counts of Chinook salmon on the Eldorado River from 2005 to 2015 are shown in Figure 7. The cumulative daily fish counts of Chinook salmon on the Kwiniuk River from 2005 to 2015 are shown in Figure 8. The daily and cumulative counts are also available (http://www.adfg.alaska.gov/index.cfm?adfg=commercialbyareanortonsound.salmon_escapement).

fish count Chinook salmon Eldorado
Figure 7: Cumulative daily fish count of Chinook salmon on the Eldorado River in Alaska, from 2005 to 2015. Source: Alaskan department of Fish and Game.

fish count Chinook salmon Kwiniuk
Figure 8: Cumulative daily fish count of Chinook salmon on the Kwiniuk River in Alaska, from 2005 to 2015. Source: Alaskan department of Fish and Game.

Further to the South is the Yukon River Delta, opening into the Bering Sea (Figure 9). In this area, Chinook salmon are more common as can be seen in the daily and cumulative counts (Figure 10). The daily counts are available as well (http://www.adfg.alaska.gov/index.cfm?adfg=commercialbyareayukon.salmon_escapement).

location Yukon river
Figure 9: Location of Yukon River and the Pilot Station.

fish count Chinook salmon Yukon
Figure 10: Cumulative daily fish count of Chinook salmon on the Yukon River in Alaska (Pilot Station, sonar monitoring), from 2005 to 2015. Source: Alaskan department of Fish and Game.

In the Northern Bering Sea the Yukon River Chinook salmon are the predominate stock group, as can be seen on Figure 11, from Murphy et al. (2009). Murphy et al. also describe this stock group reaches up North into the Chukchi Sea, especially during warmer winters with lesser amounts of sea-ice.

mixtures juvenile Chinook salmon
Figure 11: Genetic stock mixtures of juvenile Chinook salmon (Coastal Western Alaska, Middle Yukon, Upper Yukon, and ‘other’ stock groups) captured during U.S. BASIS surface trawl surveys on the eastern Bering Sea shelf (mid-August to early October), 2002–2006. Mixtures are overlaid on a map of juvenile Chinook salmon distribution and black bars identify the spatial extent of samples used for each mixture. Genetic mixtures are overlaid on the CPUE prediction surface from a Kriging spatial model. Contours are shaded at geometric intervals of the prediction surface. Source: Murphy et al. 2009.

In the “Yukon river salmon 2016 season summary and 2017 season outlook” (JTC, 2017) a figure is shown of the estimated amount of juvenile chinook salmon from the Yukon River (Figure 12), based on the stock-specific abundance estimates in the Northern Bering Sea. As the Chinook salmon spend three to four years in the ocean, predictions can be made to the returns after this period of time. With the known data and the estimated numbers, a recruitment curve can be drawn (Figure 13).

estimates Canadian origin Chinook salmon
Figure 12: Juvenile abundance estimates of Canadian-origin Chinook salmon from the Yukon River based on pelagic trawl research surveys in the northern Bering Sea (2003–2016). Source: YRJTC 2016.

Chinook salmon recruits vs spawners
Figure 13: Yukon River Canadian-origin Chinook salmon recruits versus spawners, Ricker curve, and 1:1 replacement line. Brood years 1982-2010 are included. Source: YRJTC, 2016.

In Norway, Atlantic salmon is monitored yearly. Norway has approximately 400 watercourses in which Atlantic salmon is present, as indicated in Figure 14.

Norway atlantic salmon watercourses
Figure 14: Norway with Atlantic salmon watercourses. The dots are the river outlets, the river areas avaulbe to salmon are the orange lines. In addition there are 31 other watercourses with Atlantic salmon, but the available nursery area in these are likely too small to support viable populations in isolation. The major regions of Norway and the large Tana watercourse are also indicated. Source: Forseth et al. 2017.

During the last 10 years the numbers of Atlantic salmon returning to Norway has been relatively low, as can be seen in Figure 15. Because Atlantic salmon is an important commercial species in Norway, total abundance and river populations are carefully monitored. Exploitation is managed on both the total population as well as per river basin.

numbers wild salmon returning
Figure 15: Estimated number of wild salmon returning from the ocean towards Norwegian rivers (pre-fishery abundance, black line), number of wild salmon entering the rivers (red line, i.e., the number left after catches in sea fisheries), and the number of wild salmon left for the spawning populations (green line, i.e., the number left after catches in sea and river fisheries) during the period 1983-2016. Source: Source: Vitenskapelig Råd for lakseforvaltning, 2017.

The Norwegian wild salmon population is threatened by several different factors, as summed up by the Vitenskapelig Råd for lakseforvaltning (2017):

  • Escaped farmed salmon;
  • Salmon lice;
  • The introduced parasite Gyrodactylus salaris;
  • Freshwater acidification;
  • Infections related to fish farming;
  • Hydropower regulation;
  • Other habitat alterations.

The graph in Figure 16 shows these threats on a scale, indicating the severity of the effects. The background color gives an indication of the severity of the impacts, with dark as more severe (Vitenskapelig Råd for lakseforvaltning, 2017). To ensure a healthy salmon population the Norwegian government issued a quality norm which all salmon populations should attain sanctioned by the Nature Diversity Act.

threats Norwegian Atlantic salmon
Figure 16: Threats to the wild Norwegian Atlantic salmon population. Green squares = Extensive knowledge and small uncertainty, yellow circles = moderate knowledge and moderate uncertainty, and red triangles = poor knowledge and high uncertainty. Source: Vitenskapelig Råd for lakseforvaltning, 2017.

Conclusion and recommendations
As an important commercial species in many countries, salmon stocks are usually quite well monitored. Depending on the catchment area, monitoring can be done on rivers or at sea. However, when looking from a river’s perspective, finding the data can be hard. Depending on the questions asked, data can either be readily available or very hard to come by.

We recommend to focus research on areas relevant for commercial salmon fisheries, creating op open database with stock information for the entire Arctic area or even global. The focus should not be on a single river or river basin, but instead on the species populations or stocks, looking at the entire geographical area the species uses.