Acoustic Tracking of Stocked Lake Sturgeon in Lake Superior
BY SHARON RAYFORD, ASHLAND FWCO
In 2013, the USFWS, in partnership with Michigan DNR, Ottawa National Forest, Upper Peninsula Power Company, Keweenaw Bay Indian Community, Michigan Technological University, with funding from the Great Lakes Restoration Initiative, began operating a Lake Sturgeon streamside rearing trailer on the Ontonagon River, a tributary to Lake Superior located in Michigan's Upper Peninsula. The purpose of the rearing trailer is to restore a lake sturgeon population to the Ontonagon River while increasing the likelihood of stocked fish imprinting on the Ontonagon River.
This past fall 25 of the largest lake sturgeon (average length 8.8 inches) reared in the trailer were tagged with small acoustic transmitters. Over 500 lake sturgeon, including the 25 with transmitters, were released at two locations within the Ontonagon River (20 and 24 miles from Lake Superior). The objective was to examine the survival, movement, and distribution of lake sturgeon reared in the Ontonagon River trailer. Acoustic receivers were deployed at ten locations throughout the river to detect the “ping” from tagged lake sturgeon if they swam past.
In addition to stationary receivers, biologists used active manual tracking by canoe on eight occasions to locate tagged fish residing between the receivers. Manual tracking allowed us to acquire an idea of how quickly fish were moving downstream without having to retrieve, download and redeploy receivers, to determine general habitat usage, and to detect shed tags/deceased fish. We were also able to range test each receiver, which revealed that receivers’ detection range fully covered the width of the river.
Credit: Sharon Rayford, USFWS
All 25 tagged fish have been detected through a combination of stationary receivers and active tracking. Nine fish were detected at the river’s mouth within a week (as early as two days post-stocking) and five more between 14 and 43 days post-stocking. Seven fish remained upriver for the duration of this study, displaying longer river residency. Only one fish moved upstream but it receded back downstream after two days, eventually entering Lake Superior nine days post-stocking. Active tracking demonstrated that tagged fish did not congregate at specific areas or habitats. Habitat variables collected at time of nearest detection indicated that fish were in water two feet deep and greater, with dominant substrate types being gravel and cobble. Few fish were detected over sandy substrate, and no fish were detected over bedrock. A majority of the fish detections occurred in run or pool habitats, though the lack of detection in riffles could have been caused by the turbulent riffle environment. Four transmitters have not moved since initial detection and we presume the tags have been shed or the fish have died.
We were able to observe movement and distribution of stocked young-of-year sturgeon in the Ontonagon River. More than half the fish swam downstream, exiting the river into Lake Superior within 30 days of stocking, while about 30 percent of the stocked fish remained in the river for at least a month. Assuming that tagged fish survived at an equal or lesser rate than other stocked fish, survival is assessed to be at a minimum 84 percent. Armed with knowledge that we can successfully tag and track young-of-the-year lake sturgeon, future tagging and tracking efforts are anticipated.