The Swift River is one of the most unique and popular trout fishing destinations in Massachusetts. In addition to the wild brook trout found in the Swift, MassWildlife also stocks rainbow and brown trout from its McLaughlin Hatchery. Many anglers travel for miles to fish the cold, clear waters of the Swift in the hopes of landing a big trout. But what exactly happens to the hatchery trout once they are released into the river? This spring, MassWildlife launched a study to get a better understanding of the survival and movement of stocked trout from month to month and from year to year.
The Swift is bounded by the Quabbin Reservoir’s Winsor Dam to the north and by the Bondsville Dam about 5 ½ miles downstream. So, while some fish enter the reach from Quabbin or from the adjacent McLaughlin Hatchery and some escape over the Bondsville Dam, the study area is a mostly closed system. This means that biologists can estimate population size and learn about fish survival by conducting a series of mark-recapture surveys. MassWildlife biologists will mark every fish stocked into the Swift and then periodically sample the stream and record information on the fish they catch. This type of survey allows biologists to estimate fish populations throughout the year in an area where it is impractical or impossible to count each individual fish.
The fish will be marked in two ways. Biologists will use Visible Implant Elastomer (VIE)—a dye injected just below the skin—to tag trout and indicate the month in which they were stocked. For 2021, all VIE tags will be placed just behind the left eye and different colors will indicate the month the fish was stocked. Additionally, the adipose fins of fish stocked upstream of Route 9 will be clipped; fish stocked elsewhere will not be clipped. The adipose fin is a small fatty fin on the dorsal surface (back) of the fish. MassWildlife staff will use electrofishing equipment to sample the river about once a month for most of the year. This method briefly stuns fish so they can be easily netted, inspected, and then quickly released. By looking at the combination of markings, biologists can learn when and where a trout was stocked in the river compared to when and where it was re-captured.
Anglers will also be able to use the marking to learn about the fish they catch. A website has been launched with details about this ongoing project. Anglers and interested individuals can visit mass.gov/swift-trout to get a list of VIE tag and fin clip combinations that shows release dates and release location. A schedule of electrofishing sampling dates will also be available on the website.
In time, study results will also be posted to mass.gov/swift-trout. Results from this study will provide valuable details about the short- and long-term survival of stocked brown and rainbow trout. As always, the goals of MassWildlife’s fisheries staff are to gain a better understanding of fish and fish ecology, share the information learned with the public, and provide exceptional opportunities for fishing and other outdoor recreation. It’s important to note that while some hatchery trout can survive year-round in deep ponds with cold water and some coldwater streams like the Swift River, MassWildlife’s stocking program is primarily designed as a put-and-take resource for anglers to enjoy catching trout in the hundreds of lakes, ponds, rivers, and streams stocked statewide.