Electrofishing in the Delta, courtesy Ryan McKenzie
Electrofishing is a powerful but underutilized tool for monitoring Delta fish, particularly species favoring “structured” habitats that are difficult to sample using more common methods like trawls and seines.
By analyzing fish catch data from past surveys, researchers Ryan McKenzie, of the US Fish and Wildlife Service, and Brian Mahardja, of the US Bureau of Reclamation, determined that electrofishing resulted in better detection rates for many native and non-native species than net-based surveys. Although electrofishing is currently restricted to freshwater areas of the Estuary and is more selective of larger fish and those with swim bladders, McKenzie and Mahardja recommend that resource managers employ the technique more widely to support long-term conservation planning. Electrofishing, or e-fishing as it’s sometimes known, uses a generator aboard a small boat to pass electricity through the water beneath and in front of the boat. “When the electricity moves through the water, it can immobilize the fish within the zone of being shocked,” says McKenzie. “It’s a really cool method. You’re looking down at the water, and then all of a sudden fish pop out of the water.” Briefly incapacitated, fish are collected via dip net and placed into a holding tank, where they come to their senses within a minute or so and can be identified, measured, and otherwise studied before being returned to the water. Electrofishing has been used intermittently by various agencies for fish monitoring in the Delta since the early 1980s, but received criticism in the 2000s due to concerns over high injury rates to some species, particularly salmonids. “Since that time, there’s been newer research conducted using more standardized methods for e-fishing, and those are the methods we currently use, which have lower injury rates for those species,” McKenzie says. “That’s why going forward, I think e-fishing is a viable option.” The study appears
in the March 2021 issue of San Francisco Estuary and Watershed Science