The U.S. Fish and Wildlife Service (USFWS) annually stocks more than a million brook trout of different life stages across the country. In the Midwest region, Iron River National Fish Hatchery maintains a captive line of Isle Royale strain coaster brook trout for stocking in Lake Superior waters in support of the Brook Trout Rehabilitation Plan for Lake Superior., Coaster brook trout exhibit a unique life history trait in their use of shoreline waters of Lake Superior. Historically, coasters were widespread throughout shoreline waters of Lake Superior. To maintain genetic diversity within the brood stock, new brood lines are periodically developed. Every three to five years biologists from the USFWS Ashland Fish and Wildlife Conservation Office, Iron River National Fish Hatchery, and Genoa National Fish Hatchery travel to Isle Royale National Park to collect gametes from the self-sustaining coaster brook trout population in Tobin Harbor.

A USFWS staff holding up a breeding male coaster Brook Trout. Photo credit: USFWS.

Isle Royale National Park is situated in northwest Lake Superior closer to Minnesota and Ontario than to mainland Michigan. The crew used the U. S. Geological Survey vessel, R/V Mayfly, to make the 60-mile trek from Grand Portage, Minnesota to a Park Service cabin in Rock Harbor and set up gear in Tobin Harbor. Tourist season was over, so power and plumbing had been shut down to the cabin. We would be on our own in the wilderness with a Honda generator, camp stove and some portable Buddy heaters to provide some comfort, communication and cooking source. Our drinking water would be from the lake itself, after a good boiling of course.
Brook trout spawning occurs in October at Isle Royale National Park. In Tobin Harbor, fish spawn along the shoreline in a mixture of sand, gravel, and cobble substrate. Fish are collected throughout Tobin Harbor using fyke nets placed along the shoreline. Nets are monitored daily, and length, weight, sex and reproductive condition data are collected from all brook trout captured. If the fish are releasing gametes, they are transferred to a temporary holding pen for spawning.
Spawning commences once we collect enough ripe adults to meet our target number of families or when we reach the deadline for the work boat to be loaded onto the Park Service vessel, Ranger III, for transport off the island. Approximately 400 eggs are collected from each female, roughly one quarter of the total produced. After milt and egg collection the fish are released back to the wild. Eggs collected from each female are evenly divided into up to five batches and each batch is fertilized with milt from one male creating up to five families per female.
The fertilized eggs are then transported from Isle Royale National Park to an isolation rearing facility at USFWS Iron River Fish Hatchery. There they are incubated, and the newly hatched fish raised to breeding age during which time they undergo several fish health inspections by staff at the USFWS La Crosse Fish Health Laboratory in Onalaska, Wisconsin. If the brood class passes three fish health inspections and are confirmed healthy, they are ready to be incorporated into the coaster brook trout brood program to produce offspring for restoration stocking by USFWS and partner fishery agencies in Lake Superior.
By: Nick Bloomfield, Henry Quinlan, Joe Amundson, and Josh Hartin