New Study: Gulls Taking a Bite Out of Salmon Population

A young steelhead salmon has about a 30 percent chance of being eaten by Western gulls during its transit to sea through creek mouths in San Mateo and Santa Cruz counties, according to a new study by California Sea Grant-funded researchers.

Gauntlets of gulls lining narrow streams may consume anywhere from 7-83 percent of young steelhead in the Waddell, Scott and Gazos watershed mouths, according to the study found here. 

“We have thought of the ocean as this big dangerous place,” said Sean Hayes, a co-investigator on the Sea Grant project and a salmon ecologist at NOAA Southwest Fisheries Science Center. “But, it may be that the last 200 or 300 meters of a river and estuary are the most dangerous. These fish are literally being scooped out right before they enter the ocean.”

Ironically, the gulls may truly only be snacking on salmon, and feasting on trash. Tagging and tracking studies show the birds make frequent trips to the Santa Cruz landfill. This virtually endless supply of easily accessible human-waste food may be artificially increasing both gull populations and, by extension, opportunistic predation on young steelhead and salmon.

“We see thousands of gulls at the landfill,” said Ann-Marie Osterback, the California Sea Grant graduate student trainee on the project and the lead author of the 2013 study.