Response of Bloater Population Demographics to Changes in the Lake Huron Foodweb

In Lake Huron, Bloater Coregonus hoyi are the sole extant species of a diverse clade of deepwater ciscoes that historically supported commercial fisheries and native piscivore diets before populations collapsed in the late 1960s. Following declines of Rainbow Smelt Osmerus mordax and Alewife Alosa pseudoharengus during 2002-03, Bloater have become the primary offshore constituent of the forage fish community. Using annual (1973-2014) bottom trawl survey data, we explored how Bloater abundance, body condition, and age structure have changed in response to a changing foodweb. Bloater showed periods of near-zero recruitment from 1975-80 and 1990-2004, while moderate (1982-83) and strong (1988-89) year classes supported high age-1+ Bloater biomass 1987-97 (19.9 kg/ha annual mean). Bloater recruitment showed evidence of density dependence and poor recruitment was correlated with female-biased adult sex ratios. Age-1+ biomass consistently increased from 2009-12 and is currently at a moderate level, albeit higher than low estimates in 2001-06. Among all ages, four of the five highest lakewide Bloater densities were observed 2011-14; 2012-13 marked peak densities in the series (1019 and 876 n/ha, respectively). Despite recent recoveries in abundance and biomass, mass-length relations and length-at-age significantly decreased throughout the time series, likely owing to changes in the lower foodweb.