Growth and recruitment dynamics of young‐of‐year northern pike: Implications for habitat conservation and management

Abstract

AbstractMaximising growth during the months after hatching is critical for fishes to surpass predator gape limits, make ontogenetic shifts in diet and increase overwinter survival. Constraints on growth during early life stages can have population and community‐level implications, yet are rarely addressed by habitat restoration or fishery management efforts. To assess environmental controls on larval growth rates, we sampled adult and young‐of‐year (YOY) northern pike (Esox lucius) emigrating from spawning grounds in six tributaries of Lake Michigan. We found that YOY growth rates differed significantly among natal streams, in parallel with variation in hatch date and water temperatures. Within each stream, individual growth rates were positively associated with trophic position, as measured by nitrogen isotope enrichment and gut contents. Earlier hatching individuals also grew faster, but the strength of this relationship varied with warming water temperatures (i.e., 21–27°C). Ageing of adult spawners indicated no differences among streams in average growth rates later in life. Our findings suggest that restoration efforts should replicate ecological conditions found in habitats producing large numbers of fast‐growing YOY. Key habitat attributes include adequate water level throughout the spring spawning season, and stable, warm water temperature conditions. Providing these environments during early life history could enhance the robustness of northern pike populations by boosting fitness from hatching to emigration to adult habitats.