Ocean processes underpinning whales behaviour

Understanding ocean physics is vital to understanding marine ecosystems because ocean currents move water and heat around the globe and determine its chemical composition. Ocean currents are a major component of the climate system, and together with the wind circulation determine where it is more likely for whales to find the proper conditions for their life cycle, from the sea ice margin in Antarctica to the continental shelves, where upwelling of deeper water brings nutrient-rich waters close to the surface and promote plankton growth. Coastal currents may also favour the persistence of smaller areas of warm waters at the mid-latitudes, which contributes to breeding and reproduction of many marine species.

Ocean currents thus influence food availability and habitat conditions, affecting the distribution of species from primary producers to the largest organisms such as whales and top predators.
Due to the central role circulation plays in sustaining marine life, the Whale and Climate project has a strong focus on understanding and describing the physical processes driving ocean circulation and ocean conditions. Our research is focused on the Southern Hemisphere, specifically the regions utilised by humpback Whales (Megaptera novaeangliae) during feeding (Southern Ocean/Antarctic Waters) migration and breeding (coastal waters of Australia, the African continent, and the South American continent). In addition to global datasets provided by satellite observations, and drogue programs, additional data are being obtained during Southern Ocean research cruises, and from moored monitoring stations. These data are used in combination with numerical ocean models to capture past and present ocean circulation features and ocean conditions.

Figure 1: Schematic illustration of major currents in the Antarctic feeding grounds of humpback whales.

Figure 2: Sea Surface Temperature in Antarctica in early November 2018 showing unusual high water temperatures.

Humpback whale super-groups and regional simulation in the Southern Benguela

The humpback whales in the southern hemisphere generally migrate from summer feeding grounds in the southern ocean to winter breeding and nursery grounds in subtropical and tropical coastal waters. However, big tightly-spaced groups (20 to 200 individuals) of humpback whales were evident showing feeding behavior and stayed at least one month in October/November of 2001, 2014, and 2015 across 220 nautical mile region of the southern Benguela. These groups are called humpback whale “super-groups”, which were never seen before 2011. Employing a high-resolution regional ocean model, Coastal and Regional Ocean Community model (CROCO), we are simulating the ocean state and analyzing the physical driver for the super-groups. The animation shows the evolution of simulated surface current and sea surface temperature during October and November in 2011 and the locations (the black dots) of the super-groups sighted by October/November 2011 research cruise.

Apart from the physical parameters, there could be the biological drivers also impacting the humpback whales. Our research will combine systematic observations and simulations of CROCO coupled with a biogeochemical component for better understanding of the underlying mechanisms.

Figure 3: Sea surface temperature (coloured shading) and surface currents (vectors)
simulated by CROCO. The black dots on 12-14 November represent the location of the humpback whale super-groups.

Main Aims and Objectives

Our main objectives are to utilize verified ocean models to understand what drives whale distributions and to run scenarios of future conditions, in order to understand how circulation processes may alter the current habitat conditions.

The study of ocean physics will allow us to answer the following questions:

  • Will future ocean circulation continue to pump nutrients to the surface in Antarctic feeding grounds or will upwelling and downwelling be moderated as ocean waters warm and atmospheric conditions alter?
  • Will the migration and breeding ground ranges of humpback whales change in response to changes in ocean conditions, including water temperature?
  • What caused the phenomenon of humpback whale super-groups, recently observed along the eastern African coast and are we likely to see an increase in the future?

We will do so through the following activities:

1. Simulation of the physical and biogeochemical processes in the Australian waters and Southern Benguela using a wide array of regional models.

2. Analysis of past, current, and future whale feeding habitat in the Atlantic Southern Ocean and marginal sea ice zone.

3. Simulation of physical and biological processes in the Atlantic Southern Ocean in connection with whale feeding behaviour.

the research runs under 4 major themes