Predicting the Effectiveness of Wedge-Wire Screens at Reducing Entrainment of Larval Fishes Using Head Capsule Morphology

The effectiveness of wedge-wire screens of various slot dimensions at reducing entrainment of larval fishes was modeled using head capsule morphology for several taxonomic categories of larval fishes collected in greatest abundance from entrainment studies in California over the past two decades. The first step in the analysis was to develop allometric regression models of the relationship between notochord length and head capsule width and depth for these taxa. Using the parameters from the regressions, Monte Carlo techniques were then used to determine the probability of entrainment for each mm notochord length increment. These probabilities were then used to estimate losses to the population that is no longer subject to entrainment. This approach provides estimates similar to extrapolating using an adult-equivalent model but does not require stage-specific mortality estimates, which may not be available for the species being evaluated. The estimates can be refined using site-specific data on the length frequency of the larvae subject to entrainment as is shown using data from the Diablo Canyon Power Plant in California.