Elicited estimates of intensity of predation on delta smelt (Hypomesus transpacificus), 1980–2016

Predation is hypothesized to be among the many factors affecting the status of delta smelt delta smelt (Hypomesus transpacificus), but there is little field data on predation. We examined whether delta smelt and six of their potential predators [striped bass (Morone saxatilis), white catfish (Ameiurus catus), channel catfish (Ictalurus punctatus), largemouth bass (Micropterus salmoides), white sturgeon (Acipenser transmontanus), and Sacramento pikeminnow (Ptychocheilus grandis)] are likely to have similar responses to some types of environmental change, including those that might result from management. For example, if a manipulation of salinity that is intended to benefit delta smelt benefits its predators to an equal or greater extent, then the net result might be a further decline in the viability of delta smelt. We based estimates of predation intensity on an analysis of information from a formal expert elicitation. The elicitation also yielded weights of the relative proportion of predation by each of the six species. Therefore, the process first estimated the probability that each species would prey on delta smelt given values of selected environmental variables, and then used the weights to estimate an index of predation intensity for each region, month, and year.