Long-term Changes in Length at Maturity of Pacific Salmon in Auke Creek Alaska
Although decreasing length at maturity has been observed in some Alaska salmon populations, the generality of this trend is poorly understood. This study was undertaken to determine whether this pattern holds for multiple species of salmon from a small watershed in Southeast Alaska (Auke Creek), and, if so, what abiotic and biotic factors are contributing to this phenomenon. We analyzed up to 32 years of data (early 1980s - 2012) for coho salmon (Oncorhynchus kisutch), sockeye salmon (O. nerka), and pink salmon (O. gorbuscha). We observed statistically significant decreases in mean length at maturity for coho salmon adults, as well as increases in mean length of saltwater age-2 sockeye salmon. Non-significant trends in mean length were observed in coho salmon jacks, pink salmon, and saltwater age-3 sockeye salmon. Abiotic and biotic variables that explained interannual variation in length include a combination of climate and resource availability effects. These observed changes should be considered in future management decisions to ensure sustainable harvest for Southeast Alaska’s sport, commercial, and subsistence fisheries.
A temporal trend toward decreasing body length at maturity in some Pacific salmon populations was identified over 30 years ago (Ricker 1981). Since that time, this subject has become a growing source of concern and a focus of research due to its implications for commercial, sport, and subsistence fisheries. Understanding how salmon length has responded to past fishing pressures and environmental variation is important for predicting future salmon responses to harvest and climate variability.