Modelling invasion potential of Bighead Carp under climate change: effects of seasonal temperatures on a recruitment bottleneck

Because young-of-year (YOY; age-0) are vulnerable to overwinter mortality, fishes invading higher latitudes could encounter colder conditions that impose population bottlenecks, but warming under climate change could reduce such restrictions. To examine how populations might respond to anticipated warming and whether they could establish, we developed a life-history model, integrating four published empirical relationships (daily YOY growth, length-energy relationships, length- and temperature-dependent energy loss, and length-dependent energy thresholds for mortality), to estimate YOY performance of invasive Bighead Carp (Hypophthalmichthys nobilis) in tributaries of the Laurentian Great Lakes under baseline, mid-century, and end-of-century climatic conditions. Based on daily temperatures, the model projected dates when spawning could occur, fish length and energy reserves acquired by the start of winter, and the amount of energy required to overwinter successfully. We determined that warming will increase YOY performance, overwinter survival, and the difficulty of managing a potential invasion due to increased growth, shorter periods of overwinter starvation, and longer periods of potential spawning activity. Advanced onset of spawn (e.g. up to 54 and 74 days earlier in the Nipigon River, by mid- and late-century) was the primary determinant of increased winter survival as early spawned fish had more opportunity to grow and acquire the energy necessary to endure overwinter starvation. As larger portions of each year become suitable for spawning, timelines for management will become less concentrated and control could be required for periods up to 2.5 times longer than baseline by end of century (from 67 to 164 harvest-days in the Genesee River). To optimize preventative measures against potential Bighead Carp invasions, we recommend focusing efforts on mitigating spawning in earlier months when YOY are most expected to survive winter, and to prioritize locations projected to have earlier spawning activity.