Bigheaded Carps: A Biological Synopsis and Environmental Risk Assessment

Chapter 13: Environmental Risk Assessment Process for Bigheaded Carps in the United States


Bighead Hypophthalmichthys nobilis and silver H. molitrix carps were brought into the United States in the early 1970s, primarily to control phytoplankton in culture ponds and in wastewater treatment lagoons. In addition, because bighead carp is a popular food fish in China, a market developed for sale of the species in Asian live seafood markets in the United States and Canada. Silver carp is not presently being cultured commercially in the United States, but two live, wild-caught silver carp were observed in an Asian live seafood market in Toronto, Ontario, on October 7, 2004 by Courtenay and Chapman. Bighead carp is cultured in the United States and appears to be accepted in the market by Asian immigrants. To our knowledge, the largescale silver carp H. harmandi has not been imported into the United States.

This assessment of the organism risk potential of each of the three species of Hypophthalmichthys to the United States uses the Generic Nonindigenous Aquatic Organisms Risk Analysis Review Process (Risk Assessment and Management Committee 1996) and draws on information presented earlier. Citations for all statements in this section that are presented as fact are provided in the biological synopsis portion of this document. Those statements that are conjecture based on the best available information are clearly indicated. The Generic Nonindigenous Aquatic Organisms Risk Analysis Review Process involves the rating of seven elements of risk (four assessing the probability of establishment and three assessing the consequences of establishment) to determine the overall organism risk potential. Each element is assigned an estimated level of risk, rated as high, medium, or low. The degree of certainty associated with risk-level assignment is also expressed for each of the seven risk elements. Categories for certainty include Very Certain, as certain as we are going to get; Reasonably Certain, certain within reason; Moderately Certain, more certain than not; Reasonably Uncertain, uncertain within reason; and Very Uncertain, a guess. Below, risk assignments and the associated degree of certainty are provided for each of the seven elements of risk required to assess the organism risk potential for each of the bigheaded carp species. See Risk Assessment and Management Committee (1996) for detailed methods on using this risk-analysis process.

In many respects, the biology and natural history of the three bigheaded carp species are so similar that we dealt with them together in text. We considered the species separately for the characteristics and circumstances in which they differ. Species-specific organism risk potential models for bighead, silver, and largescale silver carps follow the discussion of the rating elements of the risk.