Number of animals
When observing groups of cetaceans we record the number of animals present during the sighting. To do this you should record the maximum number of animals that you see at the surface at one time – this number is a physical count of the number of animals surfacing simultaneously and will always be the same between observers.
A group of 5 Risso’s dolphins surfacing; 2 of which are calves.
For example, if you originally see 3 fins at the same time as the group surfaces, then 5, then 8, do not add them together. Instead record 8 as the maximum number of fins seen at the same time in the observation period. This is also known as a ‘minimum count’ as it reflects the number of animals that you are absolutely confident are present but does not include your ‘feeling’ that it was actually a group of 10 even though you only saw 8 animals. Record the ‘minimum count’ in the group size column on your data sheet.
Note: when filling in group size and calves on the data sheet you are recording the total number (minimum count) of animals in present, including any calves, in the group size column and then stating how many of this total ‘group size’ are calves. i.e. In the data sheet above the group size is 4 and no. of calves is 1; in other words a total of 4 animals are present 1 of which is a calf NOT 4 adults and 1 calf making a total of 5 animals present.
Identifying and counting calves
Next you should determine if any of the animals in the group are calves? Look at the size, colour and position of the animals. Calves will be smaller in size and positioned very close to an adult, often touching, and slightly behind the adult so the young animal can swim in the slip stream created by the mother as it moves though the water. In some species calves will be a different colour to the adults. Bottlenose dolphin calves are lighter; appearing pale grey, light brown or even a little yellowish depending on the light. Risso’s dolphin calves are born darker and get lighter with age, so young animals will be darker than the adults. Young calves will also display foetal folds which form vertical creases down the flanks. These creases are formed when the animal was folded inside the mother before birth. Record the number of calves in the group in the no. calves present column on your data sheet.
Calf positioned next to and slightly behind the adult.
Two day old bottlenose dolphin calf with obvious foetal folds.
Slightly older bottlenose dolphin calf with faded foetal folds.