The bottlenose dolphins (Tursiops truncatus) of Cardigan Bay, Wales: safe from harm?

Heather Payton, BSc (Hons) Coastal Zone and Marine Environment Studies, University of Glamorgan

Social animals like bottlenose dolphins live their lives in complex communities in which communication, collaboration and competition are the norm. They benefit from the ability to recognise, pass on information and learn from others, and they take on different roles within the group. It is important therefore for the future wellbeing of the network that its social structure and cohesiveness are maintained.
More than 300 well marked animals from the Cardigan Bay population have been photographed and positively identified and it’s thought they may be the biggest resident or semi resident population in United Kingdom waters. At present they face no major identified threat though others of their species elsewhere in the world do. Attacks from the usual predators, killer whales and sharks, are unknown in Cardigan Bay - making them unusual in global terms. But that’s not to say that potential threats, mostly from human influences, don’t abound. And disease has all but wiped out dolphin populations elsewhere in the recent past.
This study uses network analysis techniques, developed for the study of human populations, to identify animals with large numbers of affiliations or which play the role of ‘brokers’ in their society, acting as links between sub communities. The study then simulates attacks on the population as might be caused by disease or habitat degradation, removing animals first at random and then by targeting the attacks on the ‘brokers’ and the animals with large numbers of associates. In fact the network maintains its cohesiveness relatively well even when thirty percent of the individuals are removed at random, simulating a truly catastrophic attack. But it’s a different story when the attacks are targeted against the individuals who play important roles. The networks fragment rapidly, which in real life would deprive the animals of the advantages that enable them to live in a challenging environment.
The results would therefore suggest that targeted attacks on individuals in dolphin networks can have a disproportionately large effect on the community as a whole, and that an attack capable of removing any animals should be taken seriously.

Download the full dissertation here.