Spatially explicit model predicting the spawning habitat and early stage mortality of Northern pike (Esox lucius) in a large system: the St. Lawrence River between 1960 and 2000

Abstract

Discharge fluctuations in the St. Lawrence River (Canada) affect reproduction habitat for Northern pike (Esox lucius Linnaeus). We developed a spatially explicit model for that large-scale river system to predict spawning habitat surfaces available for egg deposition and the potential mortality by dewatering occurring during the embryonic-larval stages. The spatial model used simulated current velocity, wetland type and water temperature at a high spatial resolution over the entire fluvial St. Lawrence River, Canada. Those three variables were integrated into a habitat suitability index (HSI) and weighted according to the literature. A new thermal preferendum curve, based on a field experiment, was included in the HSI, reflecting that the probability of observing pike spawners in a given area increased with temperature. The reproduction chronology was predicted every year with an original model based on air temperature in order to reconstitute the historic habitat surfaces for the period 1960–2000. The results revealed that discharge had a substantial effect on both suitable habitat for egg deposition and potential mortality following dewatering. The best and the largest spawning habitats were identified, as well as the most limiting regions in the river. The present findings have already been used to prepare a new discharge regulation plan for the Lake Ontario–St. Lawrence River system.