Deep-water cisco captive broodstock developed from wild-caught juveniles: proof of concept with Lake Michigan bloater

Dale Hanson (USFWS, dale_hanson@fws.gov), Nicole Watson (USGS), Dan Yule (USGS), Kevin Keeler (USGS), Owen Gorman (USGS), Yana Grueneis (USGS), Orey Eckes (USFWS), Brandon Keesler (USFWS), Josh Hug (USFWS), Jason Smith (Bay Mills Indian Community), Gary Michaud (Little Traverse Bay Band of Odawa Indians), Dimitry Gorski (USFWS), Ted Treska (USFWS), Charles Bronte (USFWS), Roger Gordon (USFWS), Doug Aloisi (USFWS), Carey Edwards (USFWS), John Coll (USFWS), Amanda Ackiss (USGS), Dave Warner (USGS), Ben Turschak (MIDNR), Matthew Herbert (TNC), Kevin Donner (Little Traverse Bay Band of Odawa Indians), Mike Sneider (USFWS), Ken Phillips (USFWS)

This project evaluated wild juvenile capture in lakes Michigan and Superior as a novel method to source coregonine broodstock for restoration in the Great Lakes. We used a ‘Mamou’ trawl to fish the upper 2 m of surface waters and an ‘Aluette’ trawl to fish within the epilimnion (2 m – 20 m); each of these trawls were fished at night when we anticipated coregonines to exhibit diel vertical migrations (DVM). Both trawls were fished over a short duration (e.g. 10 - 15 minutes) and equipped with an aquarium style cod-end to mitigate injuries and exhaustion during capture. In Lake Michigan, we dedicated four nights of trawling in late September 2024 near Ludington, MI, but did not capture age-0 bloater (Coregonus hoyi) with either trawl style. This result was unexpected since we previously confirmed age-0 bloater presence at this location in the epilimnion during mid-August (USGS pelagic prey fish survey; Dave Warner, personal communication), and in the mid-September USGS bottom trawl survey conducted in daylight hours (Ralph Tingley, personal communication). We conclude that age-0 bloater had likely transitioned to hypolimnetic waters by our late-summer survey dates and were inaccessible to our trawls. In Lake Superior, we directed four nights of Aluette trawling in late June 2024 near the Apostle Islands. In total, we completed 28 trawls (Figure 1) and captured 754 juvenile cisco (Coregonus artedi) and 9 juvenile kiyi (Coregonus kiyi). Captured fish were held in onboard tanks, transported to shore, and most (n = 723) were trucked five hours to the Genoa National Fish Hatchery (NFH) for rearing; the exception involved 25 juveniles from the last capture date that were kept locally (USGS Ashland) as a spontaneous ‘transportation control’. Mortality immediately after capture was low; we removed a total of 15 (2.0%) moribund fish at the dock to ensure only live, visually healthy fish were transported to Genoa NFH. However, following transport to the Genoa NFH we observed a mean mortality of 33.6% on the day of arrival (within 24 hours of capture) and 93.2% of all transported fish died within 72 hours post-capture. In total, 13 fish (1.8%) survived beyond 21 days. Among fish reared locally (‘transportation control’ group), no mortality occurred within 72 hours of capture although 84% of fish experienced delayed mortality at 4 – 12 days post-capture; 4 fish (16%) survived beyond 21 days (Figure 2). Post-mortem examinations of the transportation control group revealed up to 50% scale loss but also signs consistent with barotraumatic injury including hemorrhaging (petechiae and hematomas externally and internally), bloody fluid in pericardium, yellowing of body wall tissue (early necrotic progression), darkened hearts, livers, gonads, intestine, and kidney, as well as perforations of organ linings and formation of bubbles in organs (Figure 3). We did not anticipate barotrauma injuries given that coregonines were captured within the epilimnion (mean headrope depth of 4.0 m and mean footrope depth of 10.8 m); we hypothesize these coregonines likely inhabited deeper water in diurnal hours and at the time of capture still retained elevated levels of dissolved nitrogen in their tissues that diffused into their blood and formed emboli when brought to the surface and held at 0 atm. Key lessons emerged from this pilot study. We confirmed use of specialized trawls, with aquarium style cod-ends, enabled capture of juvenile coregonines that may display excellent near-term survival, however most fish die within the first week with symptoms consistent with barotrauma; stress associated with transport accelerates this mortality. Therefore, our results suggest coregonine broodstock wild capture methods may succeed when targeting the larval epilimnetic life-stage. Alternatively, barotrauma mitigation strategies, such as recompression in a hyperbaric chamber, may succeed with later stage juvenile collections. Minimizing scale loss may also increase overall survival with a likely reduction of infection or other superficial related injury. Addressing these key stressors will likely increase the survival of live-captured, wild coregonines with potential to rear as broodstock in captivity.