A Whale of a Time
Vol.5. 16th June 2017
Guest post by Guiherme Bortolotto, University of St Andrews, UK
Guilherme Bortolotto is a researcher at the Sea Mammal Research Unit at the University of St Andrews. He is on board the RRS Discovery as part of the Cetacean team led by Claire Lacey.
If you’re curious about whales and dolphins, and are lucky enough to have the opportunity to be out on the high seas looking for them, one question that you’re bound to ask is “how many of them are there?” That’s the question that this group of researchers from the Sea Mammal Research Unit (SMRU, University of St Andrews, UK), in collaboration with Gísli Víkingsson (Marine and Freshwater Research Institute, Reykjavik, Iceland), are trying to answer on this trip.
Blue Whales © Marguerite Tarzia
Out for the count – The ‘Distance Sampling’ Method
Because we cannot count all the animals in the entire area that we are interested in (it is impossible to go everywhere!), we need to do an estimate. This means that we count the animals in the places that we go and use this information to make a good guess on the total number for that larger area. However, there are some issues when we’re trying to count animals that spend most of their time underwater where they cannot be seen from the ship. Also, animals that are closer to the ship may be more easily seen than those far away. Sometimes the weather conditions may influence how easy or difficult is to see them (it’s hard to spot a small dolphin in a foggy day, unless it’s very close!). To deal with that, we use a statistical method called Distance Sampling, which helps us to correct our counts for the animals that we don’t see for various reasons.
Whale team on watch © Marguerite Tarzia
There she blows!
The way we get the information needed for estimating the number of whales and dolphins using this method is by searching and detecting them while the ship travels along straight lines. On detecting one animal or a group (if they are grouped), we then take note of several things, such as the species observed, the group size and, very importantly, the distance from the animals to the line being travelled. It may be the case that animals usually form large groups, like many dolphins species do. Groups can also be formed by very few individuals (sometimes by only 1). Large groups are not rarely seen for many large species, such as fin, sei or blue whales.
In the first ten days of our trip, we have seen some common dolphins, a bottlenose dolphin, pilot whales, humpback whales, sperm whales and fin whales. Because the sea has been rough on some days, and on other days the animals spotted were not showing much more than a blow (when expelling the air during breathing at the surface), we could not identify all the large whales we saw down to the exact species.
The RRS Discovery's position © Marguerite Tarzia
One of the most interesting moments so far, was when a group of around 50 pilot whales with some small calves, came very close to the ship, providing an excellent opportunity to see them. These whales were one of the most regularly spotted species in the first week of our survey. There are actually two species of pilot whale – the long finned pilot whale and the short finned pilot whale. They are very difficult to distinguish at sea, and both could be in the area in which we are working. Although, going on the location, the ones we are observing are more likely to be long-finned.
Pilot Whales © Marguerite Tarzia
Both species of pilot whales are around 6-7m long, with males being slightly larger than females. They can live at least 60 years and are very social animals, usually seen in large groups. Though the group we saw yesterday from the vessel numbered around 50 animals, up to 100 is not unusual, and groups of over 1,000 have been reported. The groups we have been seeing have included young individuals. Calves can be born at any time of year, and are just under 2m in length at birth, although the youngsters we’ve observed are not new-borns. Pilot whales are relatively deep divers. They do most of their feeding between 200m-500m below the surface, and eat primarily squid with the addition of some fish species as well. Being social animals, they are very vocal and produce a great variety of different vocalisations – they are great to listen too on the hydrophone.
Regardless of the species, the size of the group or weather conditions, every sighting of a whale or dolphin is an exciting moment that brings us the feeling that our efforts to better understand these animals are worthwhile.
To read more about these amazing sea-mammals, read Claire Lacey’s post on how the team are using acoustics to monitor the ocean for whales and dolphins.
Follow the RSS Discovery's position on the National Oceanography Centre's 'Vessel Tracker'.