Sonar technology takes scientists under Ozette Lake's water, revealing new picture for threatened sockeye's recovery

Fall 2013

Sonar has long played a role in underwater exploration, from mapping the seabed to archeological surveying. Now sonar technology is being used to census adult fish in one of Washington State’s most pristine bodies of water—Ozette Lake.

Surveyors are using imaging sonar at the lake’s outlet and along its shoreline to quantify the number of sockeye returning to the lake. The lake’s threatened sockeye population is protected under the Endangered Species Act and scientists do not have an adequate understanding of how many fish return annually. Though the number of fish spawning in the lake’s tributaries is well documented, less is known about a second group of spawners—beach spawners. By providing sound pulses and converting the returning echoes into digital images, the technology is providing scientists and recovery planners with a clearer picture of the sockeye population’s size and reproductive behavior.

For decades, surveyors counted adult fish returns at a weir placed in the Ozette River at the outlet of the lake. But it was not possible to use the weir during high spring flows, when some adults return to Ozette Lake. This limited the ability to count all returning fish. In addition, fish were forced to congregate below the weir prior to reaching the lake. This contributed to high rates of predation on the already threatened population.

Historical methods for counting beach spawners—using everything from shoreline surveyors to scuba divers—were also inconsistent and variable at best. Low visibility due to naturally occurring tannins in the lake water coupled with high waves during the spawning period limited researchers’ ability to census beach spawners effectively. As a result of these challenges and the subsequent lack of data, scientists do not have a complete understanding of the population’s abundance.

Imaging sonar allows us to fill in the missing pieces, so to speak. By providing a visual image of the fish, the sonar is helping surveyors collect accurate data on total run size and beach spawning sockeye abundance. It’s allowing researchers to overcome the challenges associated with historical methods because it works well in high flows at the lake’s outlet and in the murky waters of the spawning beaches. The technology is also unearthing valuable information about sockeye behavior. The visualization allows us to see just how deep sockeye spawn in the water column, whether they spawn in areas not previously documented, and how they interact with predators, among other behaviors.

The technology was first tested in Lake Ozette in 2011, and by the 2012-2013 spawning season it was used to conduct three different surveys. During these surveys, the sonar captured images of nearly 950 live sockeye in very high densities at critical locations—core spawning areas on Olsen’s Beach and at Allen Beach. The sonar will also be used to survey habitats that sockeye may use, but where spawning fish have not been identified previously. This detailed information will improve managers’ ability to guide conservation efforts for this threatened population.

Exploring the use of imaging sonar in Lake Ozette’s sockeye recovery efforts was made possible because of partnerships among NOAA Fisheries West Coast Region, the Northwest Fisheries Science Center, the Makah Tribe, and the Washington State Salmon Recovery Funding Board (SRFB). Partners tested the technology and applied different surveying techniques to examine the effectiveness of this tool. In addition to NOAA Fisheries’ own testing and surveying, a nearly $105,000 grant from NOAA Fisheries’ Pacific Coastal Salmon Recovery Fund (administered through the SRFB), together with funding from the Makah Tribe and additional support from the SRFB, enabled the Makah Tribe to census returning adults using similar sonar technology.

“This tool allows us to advance and adapt monitoring methods,” said Stephanie Martin with the Makah Fisheries Management Program. “The sonar imagery ensures we collect quality data and it complements other research, monitoring, and restoration efforts underway to recover the sockeye population.”

Imaging sonar technology is revealing the unknown secrets of Lake Ozette sockeye. We now are able to “see,” with near video quality, below the lake’s waters—gaining vital information about the fish and how they use beach habitats to reproduce. These new discoveries will contribute to a restored Lake Ozette sockeye population that can be removed from the Endangered Species list once and for all.  

For More Information on Lake Ozette Sockeye Recovery…

Recovery Planning: http://www.westcoast.fisheries.noaa.gov/protected_species/salmon_steelhead/recovery_planning_and_implementation/lake_ozette/lake_ozette_salmon_recovery_sub_domain.html

Lake Ozette Sockeye Recovery Plan: http://www.westcoast.fisheries.noaa.gov/protected_species/salmon_steelhead/recovery_planning_and_implementation/lake_ozette/lake_ozette_sockeye_salmon_recovery_plan.html

NOAA Fisheries’ Five-Year Status Review: http://www.westcoast.fisheries.noaa.gov/publications/status_reviews/salmon_steelhead/sockeye/5-yr-ozt.pdf