There are four researchers studying whales on this cruise. Koen Van Waerebeek and Russell Leaper are visually searching for whales for the International Whaling Commission (IWC) and Ana Širović (Scripps Institution for Oceanography) and Debbie Salmon (British Antarctic Survey) are monitoring for sounds made by the whales. Little is known about the foraging behaviour and movements of whales in relation to their environment. Whales are at the top of the food chain but there may be many factors that affect their distribution. We know that krill provides the most important food source for many species of baleen whales but we do not know how whales find krill, how much krill they eat, nor how much time they spend feeding.
The Southern Ocean is an important feeding area for a large proportion of the world’s whales and includes many populations that were severely depleted by the whaling industry. It is estimated that the biomass (total weight) of whales is now only around 10% of what it was before whaling began. In 1994, the International Whaling Commission voted to adopt the majority of the Southern Ocean south of 40oS as a sanctuary in which all commercial whaling is prohibited. There is now a need to monitor whale populations and to understand the role that different species play in the Southern Ocean ecosystem.
The objective of our visual observations is to allow us to relate patterns of whale distribution to the other biological and oceanographic information, and in particular to the distribution of krill (the main prey item for most baleen whales in the Antarctic), that is being collected from the research ship James Clark Ross. As well as whales, we also note down any seals that we see because seals are also important predators.
Counting whales is not easy because they spend much of their lives out of sight under water and even when they come to the surface they are sometimes difficult to see especially in rough seas. For some species we see a tall blow (or spout) whereas with others all we see is a small part of the animal’s back. The method used to work out how many whales there are is a statistical technique called line-transect sampling. While the ship travels along a pre-determined route of survey ‘transects’ we count how many whales of each species that we have seen and also work out the area of the ocean that we have surveyed. The distance at which we can see whales varies according to the sea and weather conditions and this needs to be taken into account in the analysis. We search the sea with binoculars from the highest deck on the ship (called the ‘monkey island’) and directly record information about the whales that we see on a computer.
Since sailing on the 7 January the weather has been good enough to allow us about 35 hours of visual observations along about 300 nautical miles of survey transects. So far we have observed seven different species of whale and two species of dolphin. These include baleen whales such as fin, sei, humpback, and minke whales which were all targets of the 20th century commercial whalers. We have also seen toothed whales, including southern bottlenose whales, an unidentified ‘mesoplodont’ (a small type of beaked whales), killer whales, Peale’s and Commerson’s dolphins. Sometimes we are not able to identify the species of whales that we see, particularly for beaked whales that show little body when surfacing, resemble each other, and are amongst the least studied of the whales.
As well as the
whales that have been seen on our survey transects, we have also had some
exciting encounters when the ship has been stopped. While preparing to sail from
Commerson’s dolphin in
We saw our first
humpback whales close to
A humpback whale lifting its tail flukes as it dived beside the ship
The tall, powerful blow of a fin whale can be seen several miles away
The acoustics team aboard JR82 has two primary goals. One is the deployment of one Acoustic Recording Package (ARP), a passive, continuous acoustic recorder. The other is opportunistic deployment of sonobuoys, expendable underwater listening devices, while underway. Both of these data sets will get analysed for whale calls.
The ARP is moored at the ocean bottom for a period of about a year, collecting low-frequency (up to 500 Hz) acoustic data. It is best suited for recording various baleen whales species: blues, fins, minkes, humpbacks, and southern right whales, which are known to make loud, low-frequency calls. The ARP consists of a data logging system, 2 hard disks for data storage, acoustic release system, batteries, hydrophone suspended 10 m off the bottom, and flotation. Several such instruments have already been deployed at various locations around the Antarctic, as well as other places in the world, and have yielded exciting data. We deployed the ARP on January 13 at 60ºS, 51º 54′W. The ARP is set to record for 500 days, by the end of which period it will get recovered and data will be downloaded for analysis.
Most of our time on this cruise, however, will be spent listening, real-time, to sounds recorded by sonobuoys deployed off the steaming ship. Sonobuoys consist of a hydrophone, a radio transmitter, a float, and a salt-water battery. They transmit a radio signal of the acoustic noise back to the ship up to 8 hours after deployment. This signal gets picked up by an antenna mounted on the ship’s mast and can be listened to in real-time. It also gets recorded on digital audio tapes for subsequent analysis. We will be deploying 2 kinds of sonobuoys during this voyage: directional fixing and ranging (Difar) and omnidirectional sonobuoys. Difars have an omnidirectional hydrophone which is complemented with two pairs of sensors and an internal compass that enable us to determine the bearing to the sound source. Their acoustic range, however, is limited to 3.5 kHz (from 10 Hz). Omnidirectional sonobuoys can record sounds up to 20 kHz (and also as low as 10 Hz) but do not have bearing-determining capabilities. They are well suited, however, for recording of toothed whales and dolphins. Sonobuoy data is mostly used to complement ARP data and in conjunction with visual observations can be used to determine the types of calls that are made by different whale species.
Debbie preparing to deploy a sonobuoy