Tagging Green Sturgeon with Acoustic Transmitters for Evaluation of Habitat Use Along the Washington Coast

The Southern distinct population segment (sDPS) of green sturgeon Acipenser medirostris is federally listed as a threatened species under the United States (U.S.) Endangered Species Act (ESA). Large aggregations of both the Northern distinct population segment (nDPS) and sDPS of green sturgeon can be found congregating in Washington’s coastal estuaries mid-summer. This provides a unique opportunity to capture and study this elusive species. Existing telemetric data indicates that these fish make long migrations along the Pacific Coast with a possible year-round presence in near-shore marine waters along Washington and Oregon’s coastline. The U.S. Navy is interested in the occurrence of the threatened sDPS of green sturgeon in the Northwest Training and Testing (NWTT) study area, which is offshore of Washington, Oregon, and northern California.

Through a multi-agency collaborative effort, multiple acoustic receiver arrays were placed along the Pacific Northwest coast and estuaries to analyze the migratory patterns of green sturgeon and other migratory species, including an offshore acoustic receiver array along the coast of Washington and Oregon (funded by the U.S. Navy and operated by the National Oceanic and Atmospheric Administration, National Marine Fisheries Service [NOAA-NMFS]), a freshwater array within and at the mouth of Grays Harbor, Washington (funded by the U.S. Navy and NOAA-NMFS, operated by Washington Department of Fish and Wildlife [WDFW]), a freshwater array within and at the mouth of Willapa Bay, Washington (funded by the U.S. Navy and NOAA-NMFS, operated by WDFW and NOAA-NMFS), and a freshwater array within the Columbia River estuary, Washington (funded by NOAA-NMFS, operated by WDFW). All acoustic telemetry data was collected on VEMCO 69-kHz VR2W, VR2Tx, or VR2AR acoustic receivers.

WDFW’s operations to capture and sample green sturgeon in Grays Harbor and Willapa Bay in 2020 and 2021 was also a multi-agency collaborative effort. The U.S. Navy funded the costs associated with implanting 50 fish with acoustic transmitters out of the 110 total fish implanted with acoustic transmitters described in this study. Additionally, The U.S. Navy funded the genetic analysis of 188 fish, including 109 of the fish implanted with acoustic transmitters (an error in the field resulted in the missed collection of the genetic sample from one tagged fish). The U.S. Army Corps of Engineers provided 10 acoustic transmitters that were implanted in fish captured in Grays Harbor in 2020. NOAA-NMFS contributed funding for the 2021 tagging operations, except WDFW provided the 50 acoustic transmitters implanted in fish captured during 2021.

In total, 230 green sturgeon were handled in Grays Harbor and Willapa Bay, Washington in 2020 and 2021. In that time, 110 green sturgeon were implanted with VEMCO 69-kHz V16 acoustic transmitters, 108 of which were also newly tagged with Biomark 12mm Passive Integrated Transponder (PIT) tags. Two of the fish receiving acoustic transmitters already had a PIT tag upon capture. An additional 77 green sturgeon were newly tagged with PIT tags and another two fish already had a PIT tag upon capture, totaling to 185 fish receiving new PIT tags and four fish previously PIT tagged upon capture out of the 230 fish handled. If a fish was in poor condition upon capture or too many fish were captured at the same time, fish were counted and released immediately to ensure survival – this resulted in 41 green sturgeon releases without any tags applied or detected from previous sampling events across both years. No green sturgeon mortalities were detected as a result of this study.

To evaluate detections unique to each distinct population segment (DPS), a small fin clip was collected for genetic assignment to DPS from 188 fish sampled, including 109 of the fish implanted with acoustic transmitters. Using a genetics technique involving single nucleotide polymorphism (SNP) assay data, fish were assigned to either the nDPS (n=134 fish; 71%) or sDPS (n=54 fish; 29%). Of just the fish implanted with acoustic transmitters, 71 fish (65%) were assigned to the nDPS, 38 fish (35%) were assigned to the sDPS.

Acoustic data indicates that some green sturgeon can be detected on the offshore acoustic receiver array year-round, with peak detections occurring around May. A majority of individual fish were detected on the offshore acoustic receiver array moving back and forth between the Columbia River estuary, Willapa Bay, and Grays Harbor during this period, though some individuals displayed long migrations up the coast and were detected off the coast of British Columbia. Within the NWTT, there were no significant differences in residence time between distinct population segments (DPSs) in 2019–2022; however inconsistent and limited array coverage within the NWTT limit further analysis within this area. Within the coastal estuaries, there were no significant differences in residence time between DPSs in any estuary in 2019–2022, with the exception of 2019 and 2020 in which the nDPS spent significantly more time than the sDPS fish within Grays Harbor. Finally, with additional data provided from collaborators operating acoustic receivers within the San Francisco Estuary and into the Sacramento River, we were able to evaluate the time at large for fish migrating between California and the Pacific Northwest. On average, fish migrating South were at large for approximately 5 months, while fish migrating North averaged 8 months at large. If funding allows, we intend to continue collecting telemetry data for another year to further evaluate the differences in the spatial and temporal use of the offshore array between the nDPS and sDPS of green sturgeon.