Two analytical approaches for quantifying physical habitat as a limit to aquatic ecosystems

Abstract

An early activity in any environmental flow study is the identification of factors limiting both human and environmental benefits derived from the aquatic ecosystem. Limiting factors include (1) physical habitat, (2) water quality, especially water temperature, (3) energy inputs from the watershed, (4) biotic interaction between species, and (5) characteristics of the streamflow regime. Physical habitat is a necessary, but not sufficient, condition for aquatic animals. We present two analytic approaches potentially useful in quantifying limiting factors: quantile regression analysis and dynamic models. Both of these tools are helpful in understanding limits on the aquatic ecosystem caused by characteristics of the physical habitat and other factors. The quantile regression analysis case study presented is for twenty Atlantic salmon streams in Newfoundland Canada, and shows that physical habitat may be limiting along with organic anions and nitrates. The population model example shows that multiple factors may limit fish production, and the importance of a factor can vary between years. The population model calculates mortality as a function of the time series of water temperatures (in turn affecting in vivo egg, fry, and parr lifestages) and dynamic streamflow (affecting the probability of redd superimposition, as well as egg incubation and fry habitat quantity). In any given year, it is the combination of one or more of these factors that tend to control salmon production in the modeled river. Both techniques can help elucidate the relative contribution of the array of potential limiting factors.

Keywords:

• Physical habitat
• habitat limits
• SALMOD
• fish production modeling
• limiting factor