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Oil spill pathway shows likely route of 700 million hatchery pink salmon early migration from Prince William Sound

Spring migration route of some 700 million hatchery pink salmon releases in Prince William Sound likely follows EV oil spill pathway

 

Each spring, upwards of 700 million hatchery pink salmon are released in Prince William Sound and start their early migration along the Gulf of Alaska nearshore coastal waters. These hatchery pink salmon start their migration weighing about 1 gram. Those that survive to return as adults the following year will grow on average to 1,500 grams, or 3.3 pounds. Pink salmon have the fastest rate of growth of the five Pacific salmon species, and also have the earliest timing for out-migration, getting a head start in marine growth over other salmon species.

The pathway of the Exxon Valdez oil spill took during the spring of 1989 shows the likely migration pattern of these PWS hatchery pink salmon each spring.

 

Figure 1. Map of the 1989 Exxon Valdez Oil Spill, courtesy of Avalon Travel.

The oil spill started in eastern PWS and flowed westward along the Gulf of Alaska coastal waters, to include the North Gulf Coast, Lower Cook Inlet, Kodiak, and the Alaska Peninsula past Chignik Bay. Each spring, upwards of 700 million PWS hatchery pink salmon begin their marine migration along the same pathway, and encounter other out-migrating wild and hatchery salmon along the nearshore coastal waters of the western Gulf of Alaska.

Figure 2. Map of the Exxon Valdez Oil Spill, with timeline of westward movement.

While the exact timing of the oil spill and 700 million out-migrating hatchery pink salmon may or may not be comparable, one can get a sense of the westward flow with time. As young salmon move westward, adult salmon return to PWS and the Cooper River, Cook Inlet, Kodiak and Chignik to spawn during the summer months.

2015 witnessed the largest harvest of PWS pink salmon – close to 100 million, the majority of which were hatchery pinks (see figure below). 2015 was the second highest harvest of wild and hatchery salmon (~250 million) in the history of Alaska, with one-third being hatchery fish.

Figure 3. Graph courtesy of ADFG.

 

While 2015 was a banner year for commercial harvest of adult salmon, it does not appear that it was very successful for out-migrating young salmon in the Gulf of Alaska. 2016 produced a dismal return for adult pink salmon, meaning few out-migrating pinks in the Gulf survived from the 2015 cohort. 2018 saw equally dismal returns for sockeye and king salmon along the Gulf of Alaska. Copper River, Cook Inlet, Kodiak and Chignik faced restrictions and or closures of salmon fisheries. Some initial data indicates a significant part of the downturn might be related to the 3-year ocean class of salmon, also from the 2015 out-migrating salmon cohort into the Gulf of Alaska.

The ADFG 2018 Upper Cook Inlet commercial salmon fishery season summary notes that the UCI total sockeye run was about one-third below the forecast. It states that the largest deviations from the 2018 forecast occurred with 3-year ocean sockeye salmon (age 1.3 and 2.3), which returned at 10 percent and 50 percent of forecast levels, respectively. This decline in 3-year ocean sockeye salmon in Cook Inlet will be interesting to compare with the Copper River, Kodiak and Chignik sockeye returns, as well as king returns across the Gulf of Alaska.