Assessing natal spawning site fidelity of northern pike using otolith microchemistry

Background/Question/Methods

            Breeding migrations are a common component of fish life histories, and are a critical concern for conservation and management as well as ecological understanding.  Northern pike (Esox lucius) are a ubiquitous, migratory species of great ecological and recreational value across the northern hemisphere. They serve as the top predator species in many systems and are a regular target for sport fishing. Drastic changes in land use over the last century threaten northern pike populations by reducing suitable spawning habitat and stifling connectivity among systems. Understanding pike migrations is essential for the effective management of this important species. Our study examines the feasibility of using otolith micro-chemistry to track northern pike spawning migrations from Lake Michigan into the tributary network in Green Bay, Wisconsin. To determine whether we could track the spawning movements of individual northern pike, we first sought to characterize the environmental chemistry of six tributaries that flow into Green Bay using laser ablation inductively coupled plasma mass spectrometry. We used otoliths of young-of-year (YOY) northern pike to characterize the environmental chemistry of tributaries used by adults for spawning. 

Results/Conclusions

Discriminant function analysis of our YOY otolith micro-chemistry data revealed that the six tributaries were chemically distinct and often distinguishable from one another. YOY pike were assigned to their natal stream with 50% to 80% reclassification success. These patterns serve as a point of reference for testing whether adult northern pike show natal spawning site fidelity. After comparing the origin of adult otoliths with YOY otolith chemistry, we will definitively know whether or not adult pike return to the same spawning reaches during their annual migration. Our work demonstrates the potential for otolith microchemistry methods to elucidate the migratory strategy of potamodromous fishes.  Our results have significant implications for designing restoration and stocking programs that account for natal site fidelity in northern pike.