Growth Of Western Alaska And Asian Chum Salmon (Oncorhynchus Keta) In Relationship To Climatic Factors And Inter- And Intraspecific Competition

Abstract

Ocean climate shifts and interspecific interactions with Russian pink salmon and Asian chum salmon are all believed to influence the growth of chum salmon in the North Pacific Ocean. Stepwise generalized least squares regression and Mantel's tests were used to examine factors influencing mean annual growth from adult scales collected during 1962-2008. First-year scale growth was affected by warmer regional temperatures, the North Pacific Index (NH), and reduced ice cover. Significant negative effects of Asian chum salmon abundance were found on third-year growth of five of six age 0.3 populations and three of four age 0.4 populations examined, indicating intraspecific competition. I found a negative correlation with third-year growth, North Pacific annual sea surface temperature (SST), and NM. Effects of interspecific interactions on third-year growth due to Russian pink salmon abundance were smaller than effects of Asian chum salmon abundance and SST. Warmer large-scale SSTs associated with reduced third-year growth contradicted the original hypothesis and suggested that the abundance of Asian chum salmon created a masking effect overwhelming other factors promoting growth. Strong correlations among third-year growth suggested that chum salmon experienced similar environmental conditions in the North Pacific and had overlapping distributions. More synchronous growth was observed among populations from close rivers than distant ones, indicating the importance of regional scale versus oceanwide studies. In the first year, intercircular distance declined then rapidly increased at circuli 5-9, Intercircular distance was similar by gender until the third year when male growth exceeded female growth for all populations except Japan. Back-calculated lengths indicated that fish reach ~494 mm fork length by the third year before returning as age 0.3 adults. Smolts entering the ocean during odd years had greater distances between adjacent circuli the next year, indicating reduced growth in the first year and compensatory growth during the second and third years. Overall, these results suggested possible effects on chum salmon growth due to abundance of Asian chum salmon, and this effect led to a reduction in length of approximately 42 mm, potentially affecting fecundity by 3%. These results contribute to growing evidence of competition among conspecific salmon.