Large‐Scale Changes in Bloater Growth and Condition in Lake Huron

Abstract

Native Bloaters Coregonus hoyi have exhibited multiple strong year‐classes since 2005 and now are the most abundant benthopelagic offshore prey fish in Lake Huron, following the crash of nonnative Alewives Alosa pseudoharengus and substantial declines in nonnative Rainbow Smelt Osmerus mordax. Despite recent recoveries in Bloater abundance, marketable‐size (>229 mm) Bloaters remain scarce. We used annual survey data to assess temporal and spatial dynamics of Bloater body condition and lengths at age in the main basin of Lake Huron from 1973 to 2014. Basinwide lengths at age were modeled by cohort for the 1973–2003 year‐classes using a von Bertalanffy growth model with time‐varying Brody growth coefficient (k) and asymptotic length (Lnormal∞) parameters. Median Bloater weights at selected lengths were estimated to assess changes in condition by modeling weight–length relations with an allometric growth model that allowed growth parameters to vary spatially and temporally. Estimated Bloater lengths at age declined 14–24% among ages 4–8 for all year‐classes between 1973 and 2004. Estimates of Lnormal∞ declined from a peak of 394 mm (1973 year‐class) to a minimum of 238 mm (1998 year‐class). Observed mean lengths at age in 2014 were at all‐time lows, suggesting that year‐classes comprising the current Bloater population would have to follow growth trajectories unlike those characterizing the 1973–2003 year‐classes to attain marketable size. Furthermore, estimated weights of 250‐mm Bloaters (i.e., a large, commercially valuable size‐class) declined 17% among all regions from 1976 to 2007. Decreases in body condition of large Bloaters are associated with lower lipid content and may be linked to marked declines in abundance of the amphipods Diporeia spp. in Lake Huron. We hypothesize that since at least 1976, large Bloaters have become more negatively buoyant and may have incurred an increasingly greater metabolic cost performing diel vertical migrations to prey upon the opossum shrimp Mysis diluviana and zooplankton. Received March 4, 2016; accepted July 12, 2016 Published online October 7, 2016

A Multitracer Approach to Quantifying Resource Utilization Strategies in Lake Trout Populations in Lake Huron

“…However, there was not a significant difference in the relationship between energy derived from zooplankton as the ultimate energy source of an age cohort for North Channel or Georgian Bay lake trout. The declines in rainbow smelt biomass (Riley et al 2008;He et al 2015He et al , 2016 and the size of bloaters (Prichard et al 2016) indicate that resource limitation is leading to increased competition among species in the upper pelagic zone. This conclusion is supported by data for the Main Basin, where declines in zooplankton biomass and shifts in community composition have occurred (Barbiero et al 2009(Barbiero et al , 2012.…”

Niche Partitioning among Native Ciscoes and Nonnative Rainbow Smelt in Lake Superior

“…The fish were separated into small (juvenile) and large (adult) groups for each species. The total length cutoffs for the two size-groups were a compromise between observing natural breaks in the length-frequency distributions of our data in order to maintain adequate sample sizes for analyses (Appendix Figure A.1) and the estimated length at transition from immature juveniles to sexually mature adult fish from published (Bailey 1964;Dryer and Beil 1964;Prichard et al 2016;Lepak et al 2017) and unpublished age-length data that were collected by the U.S. Geological Survey Lake Superior Biological Station. The length cutoffs between size-groups were 180 mm for Bloater, 250 mm for Cisco, 160 mm for Kiyi, and FIGURE 1.…”

Comparison of traditional and geometric morphometrics using Lake Huron ciscoes of the Coregonus artedi complex

“…Hybrida is a vertically migrating form that Eshenroder et al (2016) hypothesized comprised a hybrid swarm (Seehausen 2004). In addition to addressing the effects of bloating, hybrida, having undergone severe declining growth (Prichard et al 2016), are small bodied and provide size contrast.…”