Fish passage structures can be improved for the benefit of multiple species, if they are designed to account for differences in behavior, physical ability and size, according to a new literature review.
Historically, most fish passages have been designed to help native salmon return to their upstream habitat and spawning grounds, with little consideration for other migrating species such as sturgeon and lampreys. “There is an assumption that if you just build a fish passage structure, fish will go thorough it, but that is not always the case,” says Department of Water Resources fisheries biologist Zoltan Matica, who conducted the review
. “The challenge is to understand that this isn’t only a physical barrier, it can be also a mental barrier.” For example, some species that engage in schooling behavior, such as shad, may refuse to even enter a structure if it limits them to passing one at a time. According to the review, which appears in the September issue of San Francisco Estuary and Watershed Science, other factors that may affect fish passage access include water depth, velocity and turbulence. The key, says Matica, is to take the needs of different species into account from the outset. “You can build a structure that is multi-species friendly in many circumstances,” says Matica.