Coregonine Captive Broodstock Developed from Wild-Caught Juveniles: Strategies to Increase Survival of Captured Juvenile Coregonines and Exploration of Long-Term Holding and Spawning

Nicole Watson (USGS, nwatson@usgs.gov), Dale Hanson (USFWS), Tyler Firkus (UWSP), Kevin Keeler (USGS), Amanda Ackiss (USGS), Ben Breaker (USFWS), Steve Davis (USFWS)

Coregonine restoration has largely relied on established hatchery broodstocks, human-facilitated spawning of ripe fish in the field, or leveraging commercial fisheries for gamete collection. These methods can induce unintended consequences such as hybridizations and changes in allelic frequencies. This research builds upon previous years of study that have provided key lessons towards establishing a coregonine captive broodstock from wild-caught juveniles. In prior years, we have explored different gear options, an Aluette trawl and a floating Mamou trawl, both equipped with an aquarium style cod-end. These specialized trawls have proven successful at capturing juvenile coregonines with minimal initial mortality. In 2024 and 2025, this work was expanded with exploration of the effects of transportation stress (2024) and barotrauma treatment (2025), with a primary focus on Cisco (Coregonus artedi). A manuscript is in progress summarizing the results of the FY2023 funding and has been summarized in the FY2025 proposal. A completion report is currently in progress for the previous year’s funding. Key lessons were learned from each of these prior years. Briefly, transportation was found to be a critical stressor, resulting in high mortality associated with long-distance initial transport (FY2024). Fish were found to have evidence of barotrauma, leading to FY2025 research focused on minimizing both transportation stress and the effects of barotrauma. Preliminary results from FY2025 research shows minimal difference in overall survival between the control and barotrauma treatment groups (Figure 1). Barotrauma treatment was immediately performed in a hyperbaric chamber for fish (HAfF) upon capture aboard the R/V Kiyi, with maximum pressure corresponding to the depth fish were believed to be inhabiting prior to capture during daylight hours. At the end of each sampling night, fish were transported the short distance from Bayfield, WI to the Lake Superior Biological Station in Ashland, WI. 25% of the control treatment fish (no barotrauma treatment) and 27% of the fish treated for barotrauma survived to 40-days post capture. There was no significant difference in survival between the two treatment groups (p = 0.67, Pearson’s Chi-square test for homogeneity). While the Station can act as a temporary holding facility, complications were encountered: 1) the recirculating system is not equipped with round tanks; 2) it does not have the ability to create a circulating current conducive to holding coregonines and facilitating “normal” swimming behavior; and 3) it did not have the volume required to hold the number of fish needed for the study due to the size of the fish at capture. These complications were likely contributors to mortality. To increase survival and further explore the potential for establishing a wild, live-captured broodstock, this current proposal seeks to capture coregonines using the Aluette trawl with aquarium cod-end, during the night once fish have migrated into the upper water column. We will seek to capture Kiyi (C. kiyi), Bloater (C. hoyi), and Cisco, with a primary focus on Kiyi and Bloater. Fish will then be transferred to a nearby aquaculture facility with experience in rearing coregonines for an initial holding of 60 days, with an option to continue holding the population as an early exploration into long-term retention and broodstock development. This research further expands on prior years’ experience, further explores the feasibility of the development of a wild-captured broodstock from juvenile coregonines and assesses spawning potential of captive held fish.