Answered
What is the population of bighead carp?
I am assuming that the question refers to the rivers of the central USA, where bighead carp and its close relative the silver carp have reached extremely high abundances in th…e last ten years, and where these fish are considered a nuisance. This question has no good answer, because there has never been a reliable population estimate of any fish of any species in any really large river system. It is not possible with traditional fisheries science methods to get arrive at an estimate of the actual number of fish. Capture-recapture methods that are used on more finite systems that are less variable over time and space just don't work on large rivers, for a variety of complex statistical reasons. In large rivers, fisheries biologists use "catch per unit effort" (CPUE) to determine how populations change over time. Using similar methods year after year, if the catch increases (and other conditions are reasonably similar) you can reliably conclude that the population has increased. In the case of bighead and silver carp, CPUE in the Mississippi and Illinois river increased dramatically -by orders of magnitude- in the 1990s and early 2000s. But anyone that tells you an actual number of fish just does not know what he is talking about. (MORE)
