{"id":4387,"date":"2024-10-07T08:11:46","date_gmt":"2024-10-07T12:11:46","guid":{"rendered":"https:\/\/ncseagrant.ncsu.edu\/hooklinescience\/?p=4387"},"modified":"2024-10-07T08:13:54","modified_gmt":"2024-10-07T12:13:54","slug":"are-anglers-competing-with-river-otters-for-the-same-fish","status":"publish","type":"post","link":"https:\/\/ncseagrant.ncsu.edu\/hooklinescience\/are-anglers-competing-with-river-otters-for-the-same-fish\/","title":{"rendered":"Are anglers competing with river otters for the same fish?\u00a0"},"content":{"rendered":"\n\n\n\n\n

A new study of river otter carcasses from fur traders sheds light on a longstanding question.<\/em><\/strong><\/p>\n\n\n\n

Research Need<\/strong><\/p>\n\n\n\n

North American river otters are common across North Carolina, from the mountains to the sea, and are comfortable in water and on land. Considered a key predator in our aquatic environments, river otters are \u201coptimal foragers\u201d in that they will select large and slow prey if presented the opportunity. In short, they eat to survive. <\/p>\n\n\n\n

While they are known to consume reptiles, amphibians, fish, shellfish, and even birds, their preferred prey depends on what is available in their local environment, which makes it different to broadly classify what river otters eat. <\/p>\n\n\n\n

So, what happens if river otters occupy the same places as anglers? Does that mean that river otters like to eat the same fish that anglers like to catch?<\/p>\n\n\n\n

North American mountain trout anglers think they compete with river otters for fish, for instance. However, previous studies have shown that except for specific lake environments outside our state, trout make up a small fraction of the river otter diet. <\/p>\n\n\n\n

But a North Carolina angler might ask how do we know what river otters eat in our state?<\/em><\/p>\n\n\n\n

What did they study?<\/strong><\/p>\n\n\n\n

A team of researchers collected the stomachs from 522 river otter carcasses obtained from licensed trappers and fur dealers from 2009 to 2016. Sample collection occurred only during the trapping season (November through February) across North Carolina \u2014 including fourteen river basins with habitat such as bogs, black and brown water systems, freshwater tidal wetlands, pocosins, natural lakes, reservoirs, impoundments, and saltwater estuaries. <\/p>\n\n\n\n

The team counted and identified items from river otter stomachs using two different methods: \u201cby hand\u201d (using field guides and a dissecting microscope), and through a newer approach called DNA metabarcoding analysis. The researchers also hoped to learn if one method was superior to the other.<\/p>\n\n\n\n

What did they find?<\/strong><\/p>\n\n\n\n

Scientists confirmed that river otters in North Carolina consume a wide variety of prey, mostly vertebrates, with fish the most common item. Perches and sunfish made up 62% of the fish consumed, with carps and minnows present in about 14% of the otters\u2019 stomachs. <\/p>\n\n\n\n

Other vertebrates, such as snakes and lizards, were present in 7% of stomachs. Crayfish, crabs, and shrimp were popular invertebrates that otters consumed.<\/p>\n\n\n\n

Other prey for otters included suckers, catfishes, largemouth bass, bluegill, and redear sunfish.<\/p>\n\n\n\n

The research team identified brook trout by DNA analysis in only two river otter stomachs, both from the North Carolina mountain region. <\/p>\n\n\n\n

Anything Else?<\/strong><\/p>\n\n\n\n

It turns out that both the manual and DNA methods of prey identification had shortcomings. For example, the manual method was only able to classify fish at the family or order level, in part, because often only hard parts, such vertebrate and scales, remained. The DNA method was able to identify fish species but had difficulty with invertebrate identification.  <\/p>\n\n\n\n

In addition, the DNA analysis revealed something interesting about male and female otters.  Across the state, males otters ate significantly more fish than female otters. Other than fish, male and female river otters in the same locations ate roughly the same prey.<\/p>\n\n\n\n

So What?<\/strong><\/p>\n\n\n\n

River otters in the North Carolina mountain region do not seem to rely on freshwater trout. The authors acknowledge that future diet studies should expand sampling to include March through October, as diets may shift seasonally. In addition, advanced DNA analyses, coupled with scat surveys, could paint a broader picture of river otter diet throughout the year.<\/p>\n\n\n\n

Reading<\/strong><\/p>\n\n\n\n

Sanders II, C. W., S. F. Spear, K. Black, C. Olfenbuttel, and C. S. DePerno. 2023. Diet of the North American river otter (Lontra canadensis) in North Carolina using 2 methods. Wildlife Society Bulletin<\/em> 47: e1502. https:\/\/doi.org\/10.1002\/wsb.1502<\/em>.<\/p>\n\n\n\n

The NC Wildlife Resource Commission, the Federal Aid to Wildlife Restoration Program, the Wilds at the Columbus Zoo and Aquarium, and the Fisheries, Wildlife, and Conservation Biology program at North Carolina State University funded this research. <\/em><\/p>\n\n\n\n

lead photo credit: NPS.<\/em><\/p>\n\n\n\n

BY SCOTT BAKER<\/strong><\/p>\n\n\n\n

The text from Hook, Line & Science<\/em> is available to reprint and republish at no cost, but only in its entirety and with this attribution: Hook, Line & Science<\/em>, courtesy of Scott Baker and Sara Mirabilio, North Carolina Sea Grant. <\/p>\n\n\n\n

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