Salmon on the lam: Drivers of escaped farmed fish abundance in rivers
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Abstract The production of Atlantic salmon in aquaculture has grown substantially over the last 40 years. The unintentional release of domesticated salmon poses a significant risk to the long‐term persistence of wild Atlantic salmon populations through ecological interactions and genetic introgression. Our ability to link aquaculture production to farmed escaped salmon in rivers is still limited and hinders identifying the appropriate production capacity of salmon aquaculture to reduce unwanted interactions between wild and escaped Atlantic salmon. Here we use a 14‐year dataset of farmed escapee abundance in rivers to model how the a priori selected covariables of wild salmon abundance, aquaculture intensity, river discharge, hydropower and fjord placement of the river affects escapee abundance across 54 rivers in western Norway. Then, we evaluate the predictive strength of the model to provide context for its use to minimize escapees. We found that the abundance of escaped farmed Atlantic salmon in rivers is correlated to aquaculture intensity. Furthermore, the abundance of wild Atlantic salmon, mean yearly discharge, and the interaction between fjord placement and wild salmon abundance were important predictors of escapee abundance in rivers. The model was 40% accurate when predicting the abundance of farmed escaped salmon in rivers. However, the accuracy improved to 75% when using risk categories derived from modelled intrusion rates that induced long‐term genetic changes to the wild population (low < 4%, medium 4%–10%, and high > 10% escaped farmed salmon). Synthesis and applications . This study links aquaculture production, at relevant spatiotemporal scales (75 km from rivers), to the abundance of escaped farmed Atlantic salmon in rivers, and provides governmental agencies with a tool to help regulate domesticated salmon production based on the carrying capacity of the system to buffer against introgression between conspecifics. Furthermore, understanding this relationship will be beneficial when establishing new aquaculture sites in pristine ecosystems where they would overlap with wild Atlantic salmon. Finally, future mitigation efforts should continue to focus on new technologies (e.g. triploid females) that can eliminate the risk of introgression without limiting aquaculture production.The report describes the travel time of marked yearling and sub-yearling chinook salmon (Oncorhynchus tshawytscha), sockeye salmon (O. nerka), and steelhead trout (Salmo gairdneri) between points within the system, and reports the arrival timing and duration of the migrations for these species as well as coho salmon (O. kisutch). A final listing of 1984 hatchery releases is also included. 8 refs., 26 figs., 20 tabs.
Chinook wind
Hatchery
Listing (finance)
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Escaped salmonids are considered among the most serious threats to the aquatic environment. One hundred and nine escape incidents were reported in Chile from 2004-2021, representing some 8.53 million escaped salmonids. Of this total, 5.73 million were Atlantic salmon Salmo salar (67.2%), 0.83 million coho salmon Oncorhynchus kisutch (9.8%), and 1.96 million were rainbow trout O. mykiss (23.0%). It is estimated that 70.1% of the escaped salmonids were recorded in the Los Lagos Region, 23% in the Aysén Region, and 4.6% in the Magallanes Region. In total, 80.5% of the escapes were recorded from seawater facilities, while freshwater units accounted for 19.5%. The highest percentage of escaped salmon recorded in seawater over 2004-2021 was 1.71% of harvested salmonids in 2013. Some 39.5% of the escapes in 2015-2021 were attributed to rupturing of net cages, mainly due to adverse climatic conditions. The additional regulations introduced in 2020 by the Chilean authority, has helped to minimize the escape of farmed salmonids. As a consequence, just one escape event was reported in 2021, corresponding to 3.85% of the total number of escapees recorded from 2004-2021.
Escapement
Smoltification
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Partial abstract: Past spawning areas (those removed from use before 1969) and present ones (those in use in 1969) are described for steelhead trout, Salmo gairdneri; coho salmon, Oncorhynchus kisutch; sockeye salmon, O. nerka; and chum salmon, O. keta (p. 1).
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The culture production of Salmonid species was increasing steadily with annual production above 2.4 million tons,which was 1989 tons during 2000-2009.Species with total ten-year production of 100,000 tons included Atlantic salmon(Salmo salar),rainbow trout(Oncorhynchus mykiss),coho salmon(O.kisutch),chinook salmon(O.tshawytscha),and sea trout(Salmo trutta),whose production can be calculated separately included 13 Species in 5 genera.The culture production of Atlantic salmon,rainbow trout,coho salmon accounted for 97% of total production.The top three countries in aquaculture production are Norway,Chile,and the United Kingdom.Salmonid culture was carried out in 67 countries and 2 regions(Taiwan and le de la Re union),including 33 countries in Europe,13 countries in America,11 countries and 1 region in Asia,6 countries and 1 region in Africa,and 4 countries in Oceania.Rainbow trout is of the predominant species being farmed in 64 countries and 2 regions in 5 continents.
Brown trout
Chinook wind
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Saprolegnia
Brown trout
Myxozoa
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Chinook salmon, Oncorhynchus tshawytscha, and steelhead, Salmo gairdneri, were captured at Little Goose Dam in the Snake River during their seaward migration and transported 400 km downstream to the lower Columbia River below Bonneville Dam. Their survival was increased from 1.1 to 15 times as compared with control fish which passed by seven mainstem low-level dams and reservoirs. Variations in survival were mainly dependent on species and environmental conditions in the river during the period fish were transported. The homing ability ofthe adult fish was not significantly diminished; less than 0.2% of strays occurred among adult returns from groups transported. Transportation did not affect ocean age or size of returning adult steelhead, but ocean age of returning adult chinook salmon may have been affected. Steelhead returned to Little Goose Dam at a substantially higher rate (1.4-2.7%) than chinook salmon (0.1-0.8%) from groups transported. The timing of adult returns of both species to Little Goose Dam was not related to the time of capture and downstream release of smolts. Salmonid populations of the Snake River and its Idaho tributaries have declined rapidly in recent years to the point that the very survival of some stocks is threatened. The total run (i.e., catch plus escapement) of chinook salmon, Oncorhynchus tshawytscha, attributable to the Snake River dropped from 120,000 adults in 1972 to 50,000 in 1974 (Raymond 1979). Similarly, the total run of steelhead, Salmo gairdneri, an anadromous form of rainbow trout, declined from 100,000 adults in 1972 to below 20,000 in 1974. The downward trend ofthe anadromous salmonid popUlations has been ascribed to losses ofjuvenile migrants at the series ofeight dams (Figure 1) and associated reservoirs in the Snake and Columbia Rivers through which the smolts must pass on their way to the sea (Raymond 1979). With the goal of protecting the migrants from the hazards of dams, a system for transporting smolts around the dams was investigated by the National Marine Fisheries Service. The juvenile migrants were collected from the Snake River at Little Goose Dam (the uppermost dam-Figure 1), transported around the entire series of dams, and released below Bonneville Dam (the lower
Chinook wind
Escapement
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The finfish aquaculture industry of Maine is in a relative state of infancy, with production primarily of rainbow trout (Salmo gairdneri) and brook trout (Salvelinus fontinalis). Coho salmon (Oncorhynchus kisutch) were reared in floating pens in the early 1970's, but operations ceased. Today, there is a pilot program in the ocean ranching of Pacific salmon, and interest in pen-rearing of Atlantic salmon (Salmo salar), pen-fattening of bluefin tuna (Thynnus thynnus), and culture of American eels (Anguilla rostrata), rainbow smelt, and flatfishes. To increase finfish production by the aquaculture industry in Maine, several economic, social, and legislative problems must be overcome. But the result could be a significant increase in the state's economy, currently one of the poorest in the nation.
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