Larval lake whitefish distribution in the open waters of Green Bay, Lake Michigan

Abstract

Most lake whitefish populations within Lake Michigan are experiencing widespread population declines due to low levels of recruitment. However, the stock within Green Bay is flourishing, and various assessment tools suggest consistent recruitment to the juvenile stage each year. The distribution of offshore and drifting lake whitefish larvae were last described in the 1970s, prior to the resurgence of the southern Green Bay stock and prior to increasing knowledge of adult spawning behavior. We conducted a Green Bay wide survey of lake whitefish larvae over three years to provide an update of larval abundance and distribution and to discern influential biotic and abiotic factors that correlate to larval densities. In contrast with historical studies, our sampling illustrated high densities of larvae in both offshore and nearshore environments. Offshore expansion may be a factor in the population increase, but long term survival effects are still unknown. This study also provides the first documentation of larvae within the southern end of the bay below Chambers Island, WI and near re-colonized rivers. Average overall densities were relatively consistent each year, ranging between 29.5 and 49.6 per 1000 m3. Lake whitefish larvae were patchy in distribution and were associated with warmer and more productive waters at small spatial scales. Larval lake whitefish appear to be distributed widely throughout the entirety of Green Bay during the drift life stage, and we discuss our results in light of re-established river spawning and the overall increase in abundance.