Meta-analysis of growth rates for a circumpolar fish, the northern pike ( Esox lucius), with emphasis on effects of continent, climate and latitude

For circumpolar species, little is known on how somatic growth rates can vary at large, transcontinental spatial scales. In this study, a meta-analysis of growth rates was conducted for northern pike ( Esox lucius) across North America and Eurasia. Growth rates of northern pike did not differ between North American and coastal Eurasian pike (e.g., UK, Ireland, Sweden), while growth rates for both of these groups were significantly higher compared to inland Eurasian pike (mainly in Russia). There was no difference in growth between lentic and lotic habitats on either continent. In North America, pike growth was positively correlated with temperature, but in Eurasia, pike growth correlated poorly with most climatic variables. Similarly, maximum longevity in pike populations was significantly predicted by latitude in North America, but not in Eurasia. After standardising annual pike growth by the thermal opportunity for growth, a highly significant countergradient growth relationship was found for North American pike, while a significant, but considerably less predictive countergradient growth relationship was found for Eurasian pike. This study provides novel insights into the ecology of a circumpolar species and how populations function at extraordinarily large spatial scales. First, pike appear to be cosmopolitan across hydrologic habitats having fast or slow growth in either lentic or lotic environments. Secondly, continental-scale differences in pike growth rates are suggestive of major genetic and life-history differences. Finally, variable climategrowth relationships and countergradient growth patterns indicate that global climate change is likely to affect circumpolar fishes like pike in complex, nonlinear ways.