Otolith elemental fingerprints reveal source-sink dynamics between two Greenland halibut nurseries in the St. Lawrence Estuary and Gulf

Abstract

In fisheries science, it is important to understand the population dynamics of commercial species and also their movements from the nursery to the population, especially for juvenile individuals, to avoid overfishing. To determine their migration patterns among nurseries, we collected juvenile Greenland halibut Reinhardtius hippoglossoides from 2 nurseries inside our study area, the Estuary and Gulf of St. Lawrence, in the summer of 2016. We measured the concentrations of chemical elements in their otoliths along a margin-core transect and used the margin elemental fingerprints of Mg, Mn, Sr, and Ba to infer migratory behaviour between 2 sample sites, the Estuary and North Anticosti nurseries. Using a random-forest analysis, we achieved an overall reclassification success of margin elemental fingerprints to their capture site of 77%. Most fish sampled from both sample sites originated from the estuary (82.5%), suggesting an important asymmetry in the source-sink dynamics between these nurseries. Juvenile Greenland halibut migrate towards the North Anticosti nursery at a smaller-than-expected size (approximately 26 cm) corresponding to 2.5-3 yr old fish. Despite sexual dimorphism in growth, sex does not affect migratory behaviour or timing of migration before sexual maturation. Our study highlights the recruitment dynamics of Greenland halibut and confirms the estuary as the main nursery in the St. Lawrence system.