A tool to identify pink salmon ( Oncorhynchus gorbuscha) × Chinook salmon ( O. tshawytscha) hybrids in the St. Marys River, Michigan–Ontario

Abstract

The first putative hybrid between pink salmon ( Oncorhynchus gorbuscha) and Chinook salmon ( O. tshawytscha) in the Laurentian Great Lakes was reported in 1992. Since that time, many St. Marys River anglers have reported catching hybrid ‘pinook’ salmon, but their true identity was often undetermined. Although Great Lakes populations of pink and Chinook salmon exhibit similar life history strategies to their Pacific coast counterparts, temporal and spatial overlap of spawning activities in the St. Marys River has made hybridization between these species common. We examined meristic and morphometric data from pink, Chinook and hybrid salmon captured in the St. Marys River during spawning migrations from 1999 to 2002. In addition, we determined spawning migration timing, size structure, age-at-maturity, and sex ratios for pink salmon, Chinook salmon and their hybrids. Spawning migrations of hybrid salmon were composed primarily (93%) of male fish. Peak migration for hybrids (20–30 September) was intermediate to peak migrations for the parent species (pink salmon: 10–19 September, Chinook salmon: 01–10 October). Hybrid salmon were intermediate for most meristic and morphometric characters examined. Using meristic and morphometric data, multivariate models were built and tested to determine the utility of using these data to aid in the identification of hybrids and the parent species. The result was an easy-to-use identification tool that requires counts of only four characters (lateral line scales, gill rakers, branchiostegal rays, and mandibular teeth) to identify pink salmon, Chinook salmon, and their hybrids.