Supporting evaluation components of the Lake Huron Technical Committee’s Cisco reintroduction study for FY23

Jose Bonilla-Gomez (USFWS, jose_bonillagomez@fws.gov), Amanda Ackiss (USGS), Cory Brant (USGS), Dave Fielder (MIDNR), Darryl Hondorp (USGS), Jason Smith (Bay Mills Indian Community), Timothy O’Brien (USGS), Kevin McDonnell (USFWS), Todd Hayden (USGS), Andrew Honsey (USGS)

The U.S. Fish and Wildlife service conducted larval coregonine surveys in 2023 aimed at documenting the current distribution, composition, and density of the larval coregonid community in Saginaw Bay. Sampling of the ichthyoplankton community was limited to pelagic neuston net tows and beach seining. Pelagic ichthyoplankton surveys were conducted weekly at 40, randomly selected, spatially balanced, depth stratified sites throughout Saginaw Bay from March 15th – May 15th, 2023 (Fig. 1). During each ichthyoplankton sample larvae were sampled within 1m of the surface using a 500-µm, 2 x 1m neuston net. Larval coregonine were present in each depth bin >3m throughout the entire Bay in six weeks of sampling. Observed Larval coregonid densities of individual neuston tows ranged between 0 and 0.12 individuals/m3 with sampled coregonid larvae ranging between 4.67 and 20.77 mm in total length. Observed larval coregonid densities pooled across sampling weeks and depth bins indicated that densities were low during the sampling period and appeared to be a poor year for coregonid production in general (Fig. 2). We relied on genetics to identify larval samples. Approximately 570 larval coregonine from Saginaw Bay were made available for genetic sequencing, where no Cisco was detected, and all were Lake Whitefish confirmed. Following larval sampling, age-0 coregonines were sampled using onshore beach seines. Beach seining was done at 6 sites on both sides of Saginaw Bay (Tawas, Bessinger Rd End, AuGres, Sleeper State Park, Oak Beach, and Jenks Park). Beach seines (50 m in length, 3.175 mm mesh) were conducted between June 7th – June 28th, 2023, at each site. A total of 17 young of year Lake Whitefish (mean total length 39.70 mm) were sampled during the sampling in Saginaw Bay. Unfortunately, no other coregonine were observed during any of the other beach seines. In August 2023 Lake Huron acoustic survey (hydroacoustic transects and midwater trawls) was made by Michigan DNR to assess post-stocking survival of Cisco, but no Cisco was captured. Additionally, in the fall of 2023 we implemented a spawning gill net survey to sample spawning adults in Saginaw Bay. In fall of 2023 was the second year that the first-year class of stocked Cisco may have reached maturity (age 4), assuming the 2018-year class survived and successfully spawned in Saginaw Bay. We were able to sample for 29 sites between December 5th and December 20th (Fig. 3). Overnight gill nets were set on sites adjacent to the stocking locations, and in other sites along the bay (Fig. 4). To confirm their hatchery origin and release season of all Cisco caught in Saginaw Bay during the fall spawning survey, we used a methodology of detection with florescence microscopy, where all specimens were evaluated for the presence of oxytetracycline hydrochloride (OTC) marks in the vertebras of the caudal peduncle (Fig. 5). Each vertebra was exposed under a stereoscope (8-40X magnification) with an ultraviolet light (~365 nm) between 3 and 6 minutes in the centrum area in a cross-section position. Each vertebra was then examined for a circle fluorescent OTC mark. Circle mark quantity was graded 0 (no mark, presumed wild), 1 (spring release), and 2 (fall release). Otoliths were used to age all specimens collected. From the 6 adult spawners Cisco caught (383 mm mean total length) in sites outside of the AuGres River mouth (Fig. 2), 5 were of hatchery origin and 1 were considered wild. For the fish without OTC marks, genetic test results (over 70% match of genetic strain structure) confirmed that was wild from Bruce/Saugeen Peninsula strain. This work has documented adult stocked cisco surviving to maturity and returning to historical spawning locations based on OTC presence and genetics. For now, these initial results suggest hatchery Cisco stocked can survive and spawn in Saginaw Bay, however it is yet to be determined if they can produce viable recruits.