Abstract
AbstractThe abundance of anadromous salmon is partially determined by size‐selective mortality during the early marine life phase. Consequently, identifying the growth patterns of juvenile salmon during this life phase is important in understanding the dynamics of salmon populations. We examined patterns of early marine growth in juvenile pink salmon Oncorhynchus gorbuscha released by four hatcheries in Prince William Sound (PWS), Alaska, and explored how these patterns related to marine survival. Since larger individuals are thought to experience reduced mortality, we partitioned the data into weight‐based quartiles and compared growth rates (% body weight/d) of all fish, the largest fish (top 25%), and the smallest fish (bottom 25%). Sampling occurred during summer 1997–2004 in PWS, the inshore Gulf of Alaska (GOA), and the offshore GOA. Growth rates varied significantly among years and sampling locations; however, the growth rate patterns were markedly similar among size‐groups and hatcheries. Growth rates tended to be high in 1997, 2002, and 2004 and lower in 1998, 2001, and 2003. Fish sampled in the offshore GOA typically had faster growth rates than those sampled elsewhere, although this was less pronounced for the largest fish. For all size‐groups, the relationship between survival and growth rate was strongest for fish captured in the offshore GOA and weakest for those captured in PWS, indicating that the likelihood of survival is greater for juveniles that migrate offshore earlier. The strength of the growth rate–survival relationship for pink salmon captured in the offshore GOA was similar among all size‐groups, suggesting that once fish migrate offshore they are less vulnerable to size‐selective predation.
Highlights
The abundance of anadromous salmon is partially determined by size-selective mortality during the early marine life phase
For all hatchery groups and size-groups, growth rates were generally higher in fish captured offshore, this was less pronounced for the largest fish and for fish released from Armin F. Koernig Hatchery (AFK)
The AFK fish had lower variation in growth rates among sampling locations than fish from the other hatcheries and did not display the same midsummer growth rate pattern observed in fish from the other hatcheries (i.e., Prince William Sound (PWS) < inshore Gulf of Alaska (GOA) < offshore GOA; Figure 2)
Summary
The abundance of anadromous salmon is partially determined by size-selective mortality during the early marine life phase. We examined patterns of early marine growth in juvenile pink salmon Oncorhynchus gorbuscha released by four hatcheries in Prince William Sound (PWS), Alaska, and explored how these patterns related to marine survival. The strength of the growth rate–survival relationship for pink salmon captured in the offshore GOA was similar among all size-groups, suggesting that once fish migrate offshore they are less vulnerable to size-selective predation. Physical conditions, such as increased water temperatures, have been associated with faster growth rates and higher marine survival of juvenile salmon (Mortensen et al 2000). We investigated the variation in early marine growth rates of different-sized juvenile pink salmon and how this variation related to marine survival
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