Bigheaded Carps: A Biological Synopsis and Environmental Risk Assessment

Chapter 10: Potential Range of Bigheaded Carps Hypophthalmichthys nobilis in the United States


Predicting the potential distribution of an introduced species is far from an exact science. Nevertheless, knowledge of several environmental and ecological factors can greatly enhance one’s ability to more accurately predict the potential range of an introduced organism. Climate and temperature extremes within the native range of the species or in areas where the species has been introduced successfully are among those factors. This information is often available in scientific literature. For fishes, however, an understanding of habitat preferences, migrations, spawning requirements, behavior, fecundity, longevity, food preferences, and feeding habits is also critical to make such predictions. For many fish species, these data are often missing or lacking in detail in the literature. Fortunately, this was not the case for bighead Hypophthalmichthys nobilis and silver H. molitrix carps, although much of the literature was in foreign languages. Relevant data on the largescale silver carp H. harmandi, however, was extremely limited. The scarcity of information for this species was due, in part, to its relatively limited native range.

Knowledge of the biology of a species within its native or introduced ranges does not always answer the important question of how an organism will adapt to other ecosystems. Many introduced species originate from a relatively small geographic area within their native ranges, and introductions often consist of a few individuals. In such cases, the introduced species have only a small fraction of the genetic diversity of that species found within its native range of distribution. This phenomenon is referred to as a “genetic bottleneck” (Cox 2004). This genetic limitation may preclude an introduced species from successful establishment, restrict it to a narrow range following establishment, or result in its eventual extinction from its novel habitat.

After a nonnative species becomes established, its genetic makeup is subject to alteration through natural selection. Events resulting in selection of one trait over another cannot be predicted. Additional introductions of the same species, especially (but not necessarily) from other parts of its naturalized distribution, increase the genetic variability of the introduced species, thereby increasing its potential invasive capabilities (Kolbe et al. 2004). It has been noted that “Because introduced species may not express an invasive nature beyond localized areas or negative impacts to native biota and/or habitat until years or decades following initial releases or ingress, every introduction must be viewed as a potential biological ‘time bomb’ waiting to explode” (Courtenay 1993).