Temperature-Driven Decline of a Cisco Population in Mille Lacs Lake, Minnesota

Abstract

Mille Lacs Lake, Minnesota, has experienced a decline in the population of Cisco Coregonus artedi since the 1980s. Cisco is a coldwater stenotherm, and the population decline is often attributed to a general increase in the lake temperature. However, there also has been a fishery for this species during the last 20 years. To investigate the influence of temperature on this decline, three versions of a surplus production model (SPM) were formulated: (1) SPM with observation error only, (2) SPM with observation error and a maximum temperature anomaly, and (3) state-space SPM with a maximum temperature anomaly and random effects process error. Data on CPUE of sampling gill nets from 1985 to 2007 were used as an index of fish abundance for the lake population. The model parameters were estimated by fitting the predicted CPUE to the observed CPUE. The analysis indicated that temperature explained 36% (model 2) and 40% (model 3) of the change in Cisco abundance. Temperature-influenced, time-varying carrying capacity and maximum sustainable yield (MSY) were also estimated. We concluded that the causes of Cisco decline were a combination of temperature and fishing pressure.

Received April 26, 2012; accepted March 12, 2013

ACKNOWLEDGMENTS

We thank Minnesota Department of Natural Resources for providing data and funding for the research. We especially thank staff at the Fisheries Section, MDNR, in Aitkin for their consistent cooperation.