Biology and Management of Inland Striped Bass and Hybrid Striped Bass

Releasing Hybrid Morone in Natural Waters with Congeneric Species: Implications and Ethics

Reginal M. Harrell


Abstract.—Since the 1950s, sympatric, congeneric species of the Morone complex have been transplanted outside their native range. Also, since the late 1960s, conspecific, artificially produced Morone hybrids have been introduced in systems with native congeneric “pure” stocks. Following previous documentation of F1 and F2 hybrid Morone being artificially produced under hatchery conditions and introduced into natural and artificial systems (i.e., impoundments), these “introductions” have resulted in reports of introgression (outcrossing of conspecifics) or natural hybridization within the Morone complex. Even though natural hybridization has been documented, based on the number of years transplanted hybrids and pure Morone have coexisted in the same bodies of water, such events appear to be rare or at least undocumented. Unfortunately, because of lack of consistent empirical evidence to make definitive statements, the seriousness of the issue is unclear and points to a need for more intensive sampling effort for verification. A survey of the literature and various state agencies responsible for managing inland and coastal systems that contain sympatric populations of Morone and artificially produced hybrids indicate that such hybridization appears to be the exception and therefore, unless otherwise documented, appears to be of minor concern. However, given that artificially produced backcrosses (a hybrid crossed back to a pure parent) are difficult to visually (phenotypically) distinguish from the “pure” parents, it may be possible that management agencies are unaware of outcrossing or backcrossing occurring. Because the impact of gene introgression is difficult to track, introgressive hybridization could affect behavior, recruitment, and even predator–prey interactions. Thus, if one is concerned about the potential consequences of hybridization or outcrossing of Morone with its conspecifics or its congeneric hybrids either genetically, ecologically, or even ethically, then it may be prudent to follow the precautionary principle until verification that such stocking does not present sufficient risk.