searun
Well-Known Member
Found this interesting research paper published in June 2017, which suggests steelhead smolts experience highest mortality in near estuary areas. Those who a concerned about the collapse of steelhead populations, should start looking more closely at the role that pinnipeds play. Its been long noted that ocean survival was the main factor in declining steelhead, but little research had been completed to help narrow where, when and how steelhead were experiencing post out-migration mortality. New leading research suggests that takes place within a close spatial area nearby natal estuaries.
The report goes onto point out that pinniped predation appears to be a strong likely contributor to the spatial mortality pattern (close to home river estuaries). Pinnipeds, particularly harbour seals, appear to play a more significant role in declining steelhead survival. Appears steelhead out-migrant smolts are similarly targeted by harbour seals as their Chinook & Coho counterparts, but that they experience higher degrees of predation - little wonder because both are fairly large meals when they first leave their natal streams, but steelhead are considerable larger out-migrants making them a desired prey source for harbour seals.
The mounting body of scientific research is pointing to the significant role that pinnipeds are playing in declining salmon and steelhead abundance. We can no longer keep sticking our heads in the sand on this issue. Finding the right approach to controlling the predation is another challenge however. The research indicates that not all individual harbour seals in estuary areas (seals are highly territorial) target out-migrant smolts. Any measures aimed at controlling or shifting predation need to be surgical efforts, aimed at shifting the predation behaviours of specific individual animals.
Interesting quote from the article:
Recent research in inland seas, including Puget Sound and Georgia Basin, suggests that pinnipeds such as harbor seals (Phoca vitulina) contribute to the mortality of migrating smolts, including steelhead (Berejikian et al. 2016) and other salmon (Thomas 2015). Puget Sound steelhead experience high levels of mortality in the Sound during their migration to the ocean despite relatively short migration distances, mortality rates that could not be sustained and have any adults return to spawn (Moore et al. 2010b, 2015). Friedland et al. (2014b) also suggested that punctuated, sized-mediated predation controls marine survival of Keogh River steelhead smolts. This mortality may have contributed to the different smolt survival patterns we observed for Puget Sound and Keogh River steelhead smolts compared with other regions. Also, it is interesting that Puget Sound populations grouped with the Keogh River population for two reasons: (i) they are located farther apart (430–490 km) than other populations we assessed (e.g., coastal populations are generally ≤200 km apart); and (ii) this was contrary to a similar smolt survival analysis of coho salmon, which found that the Keogh River coho smolt survival time series grouped with those of coastal populations rather than those of Puget Sound populations (Zimmerman et al. 2015). This suggests that factors influencing steelhead from both the Puget Sound and Keogh River early in their marine residence may differ from those faced by coho salmon.
Here's the full article:
http://www.nrcresearchpress.com/doi/full/10.1139/cjfas-2016-0486#.W7D_yNhKhsM
The report goes onto point out that pinniped predation appears to be a strong likely contributor to the spatial mortality pattern (close to home river estuaries). Pinnipeds, particularly harbour seals, appear to play a more significant role in declining steelhead survival. Appears steelhead out-migrant smolts are similarly targeted by harbour seals as their Chinook & Coho counterparts, but that they experience higher degrees of predation - little wonder because both are fairly large meals when they first leave their natal streams, but steelhead are considerable larger out-migrants making them a desired prey source for harbour seals.
The mounting body of scientific research is pointing to the significant role that pinnipeds are playing in declining salmon and steelhead abundance. We can no longer keep sticking our heads in the sand on this issue. Finding the right approach to controlling the predation is another challenge however. The research indicates that not all individual harbour seals in estuary areas (seals are highly territorial) target out-migrant smolts. Any measures aimed at controlling or shifting predation need to be surgical efforts, aimed at shifting the predation behaviours of specific individual animals.
Interesting quote from the article:
Recent research in inland seas, including Puget Sound and Georgia Basin, suggests that pinnipeds such as harbor seals (Phoca vitulina) contribute to the mortality of migrating smolts, including steelhead (Berejikian et al. 2016) and other salmon (Thomas 2015). Puget Sound steelhead experience high levels of mortality in the Sound during their migration to the ocean despite relatively short migration distances, mortality rates that could not be sustained and have any adults return to spawn (Moore et al. 2010b, 2015). Friedland et al. (2014b) also suggested that punctuated, sized-mediated predation controls marine survival of Keogh River steelhead smolts. This mortality may have contributed to the different smolt survival patterns we observed for Puget Sound and Keogh River steelhead smolts compared with other regions. Also, it is interesting that Puget Sound populations grouped with the Keogh River population for two reasons: (i) they are located farther apart (430–490 km) than other populations we assessed (e.g., coastal populations are generally ≤200 km apart); and (ii) this was contrary to a similar smolt survival analysis of coho salmon, which found that the Keogh River coho smolt survival time series grouped with those of coastal populations rather than those of Puget Sound populations (Zimmerman et al. 2015). This suggests that factors influencing steelhead from both the Puget Sound and Keogh River early in their marine residence may differ from those faced by coho salmon.
Here's the full article:
http://www.nrcresearchpress.com/doi/full/10.1139/cjfas-2016-0486#.W7D_yNhKhsM
