River flow and fish life histories

Posted on September 23, 2013

Because patterns of water flow play a key role in structuring aquatic environments and habitats, it’s been proposed that the life history strategies adopted by freshwater species should reflect hydrological conditions.  To date, most studies in this area have related life history features only to single aspects of the flow regime, such as the variability, the predictability or the seasonality of discharge.   And few studies of the relationships between environmental factors and fish species occurrence have been carried out from a life history perspective.  These deficiencies have been addressed in a wide-ranging investigation based on data from 109 fish survey sites and nearby gauging stations across the continental United States.  Life history information for the sampled species, obtained from multiple sources, included data on body size at maturation, fecundity, egg size and parental investment.  Regression analysis supported the idea that the prevalence of fish species with the same type of life history is related to a particular type of flow regime.  Specifically, the proportion of opportunistic species (those that suffer high juvenile mortality and mature early) was positively related to  flow variability, and negatively related to flow predictability.  The results suggested that a minimum level of flow disturbance – presumably enough to reconnect isolated habitats after drought – was needed for opportunistic species to persist.  In contrast, the proportion of “periodic” species that mature late, produce lots of eggs and grow to a large size , was highest where flows were strongly seasonal and predictable and where flow variability was low.  Finally, the proportion of “equilibrium” species, that typically produce few eggs, show parental care and enjoy high  juvenile survival, was highest under conditions where flows were predictable and varied little.  Studies such as this, that link species traits to hydrological conditions, can help to develop environmental standards for flow-regulated rivers. 

Reference:   Mims, M.C. & Olden, J.D.  2012.  Life history theory predicts fish assemblage response to hydrologic regimes Ecology 93(1), 35–45.