Lake Superior Bloater Reproductive Biology

Mark Vinson (USGS, mvinson@usgs.gov), Ian Harding (Red Cliff Band of Lake Superior Chippewa), Jamie Dobosenski (TNC), Dray Carl (Wisconsin DNR), Amanda Ackiss (USGS)

Bloater (Coregonus hoyi) have been the dominant Laurentian Great Lakes chub since the decline of Shortjaw Cisco (C. zenithicus) in the 1950s (Dryer and Beil 1968). Most of what we know about Bloater life history in general and reproductive biology in particular comes from historical work describing spawning timing. Surprisingly, Koelz had nothing to say about Lake Superior (Koelz 1929:469) and Lake Huron (Koelz 1929:465) Bloater breeding habits but he noted that Lake Michigan Bloater spawned in February-March. Pritchard (1931) wrote that Lake Ontario Bloater spawn from November to January. Dryer and Beil (1968) conducted the most complete study of Lake Superior Bloater from 1958-65. They reported on spawning timing, February and March, as well as sex ratios, age and size of maturity, and fecundity. Contemporary data for comparison exists for Lake Michigan Bloater (Bunnell et al. 2009; Bunnell et al. 2012), but not Lake Superior. Contemporary Lake Michigan Bloater fecundity was less than observed in the late 1960s, perhaps due to the decline of Diporeia, a primary prey (Bunnell et al. 2009). Our rationale for wanting to repeat the work of Dryer and Beil (1968) is that Lake Superior is warmer, and the composition of chubs have changed on Lake Superior since Dryer and Beil’s (1968) work. To this point, Vinson et al. (2023) found that contemporary Lake Superior Kiyi (C. kiyi) spawning timing was about a month later than historically observed perhaps due to recent climate warming (Van Cleave et al. 2014). Also, beyond a few anecdotal captures in 2018 (Lucke et al. 2020), no information has been reported on larval Bloater temporal or spatial dynamics in Lake Superior.