Fish, Populations

The fish of inland waters are diverse, long-lived, large-growing, and an important source of food for humans and other vertebrates, features which have combined to attract the attention of humans for millennia. Such historical interest, stemming principally from fisheries, has acted as a major global driver for studies of fish populations in terms of changes in population abundance and individual growth rates. Despite a long history of inland fisheries, the scientific quantitative sampling of fish from such habitats using passive, active, and remote techniques remains a significant challenge. The population dynamics of inland fish are reviewed with the approach that their future abundance is a function of present abundance plus immigration, minus emigration, plus reproduction, and minus mortality. The considerable locomotory powers of fish mean that migratory movements into and out of the local habitat are frequent and can have significant implications for local population dynamics, while reproduction is characterized by high fecundities and complex behaviors. Mortality is correspondingly high and is particularly severe in early life stages, leading to complex and highly dynamic age distributions for the population as a whole. As a result, fish populations of inland waters typically show great variations in abundance on both short- and long-term timescales and these are discussed.