California roach (Hesperoleucus symmetricus) in the Eel River of northwestern California: native or introduced?

Abstract

To explore the history of California roach (Hesperoleucus symmetricus) in the Eel River, we compiled mitochondrial DNA data for the putatively introduced Eel River population and comparative collections from throughout the native range. Consistent with an introduction scenario, we found that: 1) one haplotype occurred at high frequency in the Eel River, Russian River and Clear Lake populations, making the Russian River and Clear Lake likely source areas, and 2) the introduced population exhibited reduced haplotype diversity in comparison to populations from the native range. However, we also detected four private haplotypes in the putatively introduced population, despite examining 269 individuals from the likely source areas. Extrapolation of the haplotype richness of the likely source population suggested that even with the large sample size, many haplotypes in the source population remained uncollected. The most parsimonious conclusion of our results is a recent introduction of a small number of California roach to the Eel River of California from a nearby drainage. This result aligns with findings for two other California cyprinids introduced into the Eel River from adjacent drainages, Sacramento pikeminnow (Ptychocheilus grandis) and speckled dace (Rhinichthys osculus).