When the sockeye salmon are running in British Columbia, bull trout are feeding and the amount they can eat is stunning.
According to new research reported in the Journal of Animal Ecology, bull trout feeding on sockeye salmon in Lake Chilko, British Columbia are capable of ‘binge-feeding’ to the point of having some 30-60 salmon smolts in their stomachs at one time.
Nathan Furey, a Ph.D. candidate at the University of British Columbia said, “These are conservative numbers because some fish are partially digested. It is likely that some bull trout had 100 individual fish in their stomach. In some stomachs, the smolts were almost all in really fresh condition, so they ate a lot in a really short period of time.”
With one of the largest populations of sockeye salmon in BC, the Lake Chilko run can consist of 10 to 40 million juvenile sockeyes leaving the lake for one month each year. When the smolts begin to congregate in the river, the bull trout are there waiting.
Matt Miller, writing for Nature.org reported that “an adult bull trout in the Chilko could eat 5 to 12 percent of its body weight in a given day,” which is like “a 180-pound person eating 18 to 60 pounds. In a day.”
“Just because you eat something doesn’t mean you have to digest it that day,” said Furey. In other words, the trout have the ability to store food in their gut while slowly digesting it. This means that the marauding trout can, well, binge eat to their heart’s desire.
The fact remains that migrating salmon have a resounding effect on nature, especially predators. When large masses of the protein rich fish gather, feeding animals will gather with them.
Furry said, “Binge feeding is an important part of these interactions between bull trout and (migrating) salmon migration. It impacts both predator and prey.” How much they eat is stunning, but eat they will.