Estimating Connectivity Between Spawning and Nursery Habitats of Northern Pike to Identify the Most Rewarding Habitat to Protect (St.Lawrence River, Canada)

Managing fish habitats by focusing on only one apparent habitat type, such as spawning sites, may wrongly leads us believing that, once protected, sites exhibiting high potential for egg deposition will eventually favour recruitment. Some supposedly high potential spawning sites may in fact exhibit low potential for recruitment when considering their isolation to surrounding nurseries habitats. Maximising recruitment, after hatching fish larvae needs to access nurseries rapidly . Therefore, it is crucial to estimate precisely the connectivity between such key habitats. We quantified the probability of reaching nursery habitats for young larvae of Northern pike (Esox Lucius), a species using heterogeneous shallow habitats exposed to large water-level variations. The spatially explicit model developed for >130 km of the St.Lawrence R. allowed us to map the potential spawning and nursery habitats at high resolution. Using two softwares dedicated for the analysis of connectivity (Anaqualand, Chloe) we quantified spatial metrics, such as the number of sites, the surface of habitats, the proximity index, the hydrographic distance. Preliminary results revealed a higher fragmentation within narrow sections of the river and changed for several presumed high potential spawning sites their overall value once considering their connectivity to neighboring nurseries.