Conserving this Nation’s fish and other aquatic resources cannot be successful without the partnership of Tribes; they manage or influence some of the most important aquatic habitats both on and off reservations. In addition, the Federal government and the Service have distinct and unique obligations toward Tribes based on trust responsibility, treaty provisions, and statutory mandates.
Hydroacoustic Assessment of Spawning Lake Sturgeon ~ Bad River Band of Lake Superior Chippewa
The Ashland Fish and Wildlife Conservation Office in cooperation with the Bad River Band of Lake Superior Chippewa installed a hydroacoustic unit in the Bad River of Wisconsin to assess spawning lake sturgeon abundance.
Hydroacoustic equipment used for fishery assessments functions similarly to fish finders used by recreational anglers, except they are much more precise and implement sophisticated acoustic technologies. A stationary hydroacoustic transducer was placed in the water where it emitted pulses of acoustic energy across the entire river channel. As the pulse of energy traveling through the water encounters an object, such as a fish, a portion of the energy pulse is reflected back to the transducer, which is called an echo.
The unit in the Bad River uses a technology referred to as split-beam hydroacoustics which uses four quadrants that each emit and receive an acoustic pulse which enables users to determine the exact location, size, and swimming direction of individual fish. This type of application is especially valuable for fixed location sampling where fish swim past a transducer, such as lake sturgeon migrating upriver to spawn. Then the number of fish (i.e., echos) moving upstream and the number moving downstream are counted to get a population estimate – all without handling a single lake sturgeon!
This hydroacoustic technique was previously used with success on lake sturgeon in the Sturgeon River of Michigan and therefore recommended for use as a rapid assessment tool for Great Lakes tributaries where the status of lake sturgeon was uncertain, presumably due to low abundance. On the Bad River this year, the hydroacoustic sampling was implemented in conjunction with a mark-recapture assessment to help validate abundance estimates by using both techniques. While hydroacoustics cannot decipher the exact species of fish, it works well for spawning lake sturgeon because their large size produces greater target strengths than most other fishes in Great Lakes tributaries. To validate the expected target strength of spawning lake sturgeon, we released spent fish captured during our netting efforts in front of the hydroacoustic transducer. This allowed us to distinguish a spawning lake sturgeon echo from those of other fish species.
Currently fishery biologists, Joshua Schloesser and Mike Seider, are working on post-processing the hydroacoustic data collected almost continuously for 24 hours a day from April 4 to May 11. In the future we hope to move the hydroacoustic unit to other historic lake sturgeon spawning tributaries within the Lake Superior basin and perform additional spawning assessments. Funding through the Great Lakes Restoration Initiative supported this hydroacoustic lake sturgeon spawning assessment.
For more information contact Joshua_Schloesser@fws.gov
