Trout Eat More Mammals Than You’d Think

Study reveals the curious dietary habits of fish.

From the Fishing the World 2015 issue of  Sporting Classics, on newsstands April 1. 

 

University of Washington researchers recently published a study in Ecology of Freshwater Fish that concludes grayling and trout consume more mammals, namely shrews, than previously assumed. The findings address questions about the fishes’ feeding habits, which have long fueled intrigue among anglers and scientists. 

Of the 1,568 grayling and 2,424 trout examined over the 13-year study in Alaska’s Bristol Bay watershed, researchers found 75 shrews and one vole in the fishes’ stomachs. More interestingly, scientists discovered shrews in 25 percent of the fish larger than 12 inches in length. In addition, the number of shrews found in the fish fluctuated during the course of the study, with eight years producing no shrews. Researchers surmise this variability may stem from changes in shrew’s abundance, not the fishes’ appetites.  

What remains unclear is how or why shrews enter the water in the first place. Peter Lisi, who helped write the report, believes shrews likely fall into the water when seeking insects along river shores. Shrews are poor swimmers, and once in a river or stream, they’re easy meals for grayling and trout. 

The study concludes that shrews are episodically important to trout and grayling; likely, the fish eat the mammals for dietary value and to keep smaller fish from feeding and becoming greater competitors for food. For fish, these warm-blooded vertebrates are not meals of necessity but feasts of opportunity. —The Editors

 

Cover image: Curtis Fry/Flickr