Species behaviours

Why is understanding behaviour critical for river dolphin conservation?

Documenting a species’ distribution and range is the first step in understanding which parts of a river need to be studied and protected to conserve the species. Next, it is essential to identify and describe the specific habitats that dolphins use. Once we know where the dolphins are, it is important to understand what they are doing in those areas. It is vital that conservation strategies are designed to enable dolphins to carry out essential life cycle functions, such as feeding, resting, mating, giving birth, or nursing young. Identifying where and when dolphins are engaged in these critical behaviours is necessary to determine when and where certain activities that might interrupt or prevent these behaviours need to be controlled. For example, if dolphins are regularly observed feeding in a particular portion of a river, it will be important to ensure that they are not at risk of being entangled in fishing nets that are targeting the same fish resources, or that the echolocation clicks they use to find fish prey will not be masked by the sound of passing vessels or construction activities. Similarly, we must think about the sources of contamination that may introduce water-borne pollutants into the food chain in those areas, thus compromising river dolphins’ health.

How do we study and document dolphin behaviour?

There are several ways to study and document dolphin behaviour in order to provide information on how human activities might affect individuals and populations:

1. Direct observation during vessel-based or shore-based surveys: Data on behaviour can often be collected by observing dolphins carefully during surveys that are designed to document distribution or habitat use, but can be difficult to combine with line transect surveys to document abundance (time taken to stop and observe dolphin behaviour may violate the assumptions or protocols for line transect surveys). A first insight into dolphin behaviour can be derived from the composition of the dolphin group. How many animals are there? Are there calves present? This provides insight into social groupings and reproductive behaviour. The next step is to classify the dolphins’ behaviours, if possible using standardised categories utilised by researchers around the globe. These include categories such as feeding, traveling, socialising, resting, etc. Direct observations have been used to describe a range of behaviours in the Amazon and Orinoco river basins¹¹² as well as in the Mahakam river¹³¹⁶. In some cases, where river dolphins have been kept under human care, behaviours observed in captivity can inform our understanding of how animals may behave in the wild ^{17, 18}.
2. Photo identification can be used to enhance our understanding of how individual dolphins behave in relation to others – for example, mothers with calves. It can also be used to document the movements or site fidelity of individual dolphins over time. Photo-identification has been a key element in studying Irrawaddy dolphin behaviour over time in the Mahakam River, Indonesia¹⁴¹⁶. However, this technique is only possible with species that have dorsal fins and/or lasting marks that are visible above the water surface and can be reliably photographed over time.
3. Acoustic monitoring is also an effective way of learning about dolphin behaviour and responses to human activities. River dolphins rely heavily on sound to communicate and find food in the often turbid and murky waters in which they live. As such, they are frequently vocalising and echolocating. Acoustic behaviour can be monitored with passive acoustic devices that are anchored in areas of core habitat where dolphins (or porpoises) are likely to be passing and vocalising. This method is an ideal way to collect data on dolphin presence and behaviour in conditions (e.g. night time) that make it impossible for researchers to make direct observations. Acoustic behaviour can also be studied with towed arrays, or portable hydrophones, which are deployed from a vessel during boat-based surveys. Acoustic monitoring has been used to study communication between river dolphins in the Amazon¹⁹²⁰, Ganges river dolphins and Irrawaddy dolphins in the Sundarbans²¹, and to study the potential impact of vessel traffic and other underwater noise on Yangtze finless porpoises²²²⁵. Passive acoustic monitoring is also currently being used to study the potential impact of acoustic deterrent devices (‘pingers’) on Irrawaddy dolphins in the Mahakam River.
4. Satellite tagging can provide insights into the movement of individual animals as well as the differences between the ways in which various age groups and/or males and females move and use habitat. An extensive satellite tagging project in South America revealed that Amazon river dolphins tend to move together in family groups, but that males may range further than females²⁶.  See this infographic for more information.