C-Scape Update. First trajectories simulated of humpback whales migrating from their breeding ground in the North Atlantic Ocean

Release date: 9 June 2016

Authors: Jean-Marc Guarini, Ian O'Connor (GMIT), Jennifer Coston-Guarini
Contact: Jean-Marc Guarini, jm.guarini@entangled-bank-lab.org

Preliminary model results showing the predicted humpback whale migration trajectories between their breeding and feeding grounds in the North Atlantic Ocean. J-M Guarini. 9 June 2016.

In the North Atlantic Ocean, humpback whales (Megaptera novaeangliae) reproduce in the warm waters of the Sargassum Sea and Cape Verde, which are two of the fifteen distinct population segments (DPS) identified by NOAA (Bettridge et al. NOAA-Technical Memorandum 540, 2015). But where do they go after this? They are observed in the cold waters of the Artic and in different coastal sites, but they have only very rarely been observed during their migration.

An individual-based model was designed to test if a global migration pattern of the whale population can emerge from the representation of local individual behaviours. The local individual behaviour is defined with horizontal displacements and vertical diving for foraging, and varies according to the current local position of the organisms, implying that their perception of the environment is very limited compare to the travel distances that they cover. In addition, it was assumed that their perception of the environment is flat, and that they are unaware of the Earth’s rotundity. Consequently, if they follow (in average) a constant direction, the route taken by whales should be loxodromic and not orthodromic. Hence from a constant heading (different from 90° or 270°), individuals always end-up in polar regions.

Small cumulative errors in the headings followed were added that can modify very slightly trajectories. In the accompanying image, we show the calculated migrations of 100 whales (50 in Sargassum Sea, blue, and 50 in Cape Verde, red), following a North route at the optimal average speed of 2.1 knots (Braithwaite et al. Conservation Physiology. 3, 2015) for 30 months were simulated. Preliminary results suggest that there is a strong dispersion and a large connectivity between the two DPS. Further modelling refinements will include a fuller description of the physical and biological environment perceived by the individual whales.

Photograph: Simon Berrow, GMIT.