Research Document 2016/111

Describing krill distribution in the western North Atlantic using statistical habitat models

By Plourde, S., Lehoux, C., McQuinn, I.H., and Lesage, V.

Abstract

The objective of this study was to describe the spatial distribution of krill in eastern Canadian waters using a statistical modelling approach in support of the identification of important habitat for the western North Atlantic (WNA) blue whale (Balaenoptera musculus). Generalized Additive Models (GAMs) were constructed from krill biomass data obtained during multifrequency acoustic surveys conducted in the Gulf of St. Lawrence (GSL) and a set of static (bathymetry and slope steepness) and satellite-derived dynamic (sea surface temperature, chlorophyll a biomass, sea level height anomalies) environmental correlates. GAMs were built for the spring and summer seasons for different krill taxa/categories. GAM results showed that environmental conditions promoting high krill biomass are species-specific and varied with season. Static and dynamic environmental variables were selected in all GAMs, indicating that dynamic oceanographic processes were important in controlling krill aggregations and distribution. GAMs predicted spatial patterns of krill biomass generally similar to those obtained with independent plankton net and acoustic data. GAMs were then used to predict ‘Significant Aggregations of Krill’ (SAK), i.e., areas where dense krill aggregations would have a greater probability of occurring. SAK cover less than 2% of the entire spatial domain and their location varied among krill categories and seasons. SAK were generally predicted in the lower St. Lawrence Estuary, along the Gaspé Peninsula and in the Shediac Valley, along the coast of southern and northeast Newfoundland, as well as along the slope of the deep channels in the GSL, off the Nova Scotian and Newfoundland continental shelfs, and in the outer Bay of Fundy. These SAK are interpreted as areas where environmental conditions promote krill aggregation on a regular basis and therefore are potentially important for WNA blue whale foraging in eastern Canadian waters.

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