THE BAD RECRUITMENT PARADIGM: A NEW LENS ON CISCO POPULATION DYNAMICS AMIDST WEATHER EXTREMES

Cisco (coregonus artedi) were once abundant in the Great Lakes, but populations have declined due to overfishing, invasive species, and climate change. Cisco were extirpated in many of the Great Lakes, but populations in Lake Superior are gradually on the rise. However, Lake Superior’s population and commercial harvest are supported by a handful of successful year classes, and recruitment patterns are erratic and not well understood. Using the “Bad Recruitment Paradigm” we evaluate if weather extremes can lead to cisco recruitment failures. We used the catch per unit effort of age-1 Cisco from USGS bottom trawl surveys from 1978-2023 as an index of recruitment. During this time period “boom” years were defined as those with recruitment over 33 fish per ha swept, with remaining years characterized as “bad”. From publicly available sources, we collected data on wind speed, air temperature, and ice cover and in critical development periods to evaluate the correlation between weather extremes and poor recruitment years. Findings reveal that warmer air temperatures in May, June, November, and December, and cooler temperatures in August and September, typically lead to poor cisco recruitment. By linking recruitment to weather extremes, this paradigm could make it possible to anticipate years with poor recruitment, offering valuable insights for Great Lakes Cisco populations and enhancing resilience against climate change. 

Primary Presenter: Olivia Nyffeler, University of Minnesota Twin Cities (nyffe008@umn.edu)

Authors:

Lynn Waterhouse, Minnesota Cooperative Fish and Wildlife Research Unit (UMN)  (lwater@umn.edu)

Gretchen Hansen, University of Minnesota Twin Cities  (ghansen@umn.edu)

Daniel Yule, USGS Great Lakes Science Center, Ashland, WI  (dyule@usgs.gov)