The soundscapes of our oceans have undergone substantial changes as a result of human anthropogenic activities. This, in turn, threatens the existence of ocean mammals such as the Bryde’s whale, as they use sound to navigate, communicate, avoid predators, recognise prey for survival and function properly within their ecosystem. Anthropogenic activities include shipping, offshore exploration, geophysical seismic surveys, and naval sonar operations. These activities have been detrimental to marine fauna and caused, amongst others, physical injury, physiological dysfunction, and behavioural modification. Overall, it caused a decrease in reproduction rate. Nevertheless, very little information regarding the population dynamics and taxonomic status of Bryde’s whales exists. Recent research strongly suggests that the two ecotypes, namely the resident inshore Bryde’s whale and the seasonal offshore Bryde’s whale, can be split at a species level. This can have far-reaching implications, putting the inshore Bryde’s whale species at a real and substantial risk of extinction.
1. Overview of the project
Considering the above, Prof Jaco Versfeld and his team set out to use passive acoustic monitoring together with machine learning to recognise and distinguish between individual inshore Bryde’s whales. This will allow for an improved estimate of population size and the ability to conduct studies such as movement tracking. According to Prof Versfeld, “once we can distinguish between individuals, we can make more accurate estimations on the population size of the inshore Bryde’s whales resident to False bay. Also, with the ability to distinguish between individuals, we can track the movements of these mammals, gaining invaluable information. The movement data can be used to see whether these whales enter busy shipping lanes, a very high-risk area for both the whales and ships.” This movement data coupled with fish stock data can assist biologists to gain an improved understanding of the whales’ dietary habits. The ability to recognise individual whales can also facilitate population estimation techniques such as mark and recapture.
2. Passive acoustic monitoring techniques
This project sets out to mainly use passive acoustic monitoring techniques in the final stages of the project. There are several advantages attached to using passive acoustic monitoring (PAM). The major advantage of PAM is that these systems record day and night, and during all types of weather, while other types of studies are weather dependent. The PAM recorders record autonomously and are not based on human observations. Finally, because these recorders are passive, they have minimal disturbance on the environment. “The ability to identify individual inshore Bryde’s whales, as well as the ability to track their movements will enable us to more accurately estimate the population size of the inshore Bryde’s whales resident in False Bay” according to Prof Versfeld. “This will also allow us to assess anthropogenic threats to these whales in False Bay, which can lead to proposed mitigation strategies, such as the recent temporary ban on octopus traps in False Bay”, he explains.
Spectrogram – representing the pulse call.
3. The potential impact of the project
The methods and techniques that are developed in this project are transferable to other areas where other populations of inshore Bryde’s whales are present. The methods and techniques could also be adapted and applied to other species, for instance studying offshore Bryde’s whales. Furthermore, during sea trials and data collection, an easily recognisable call of the inshore Bryde’s whale was discovered. Using these calls together with other vocalisations, the team aims to use techniques similar to speaker recognition for human speech, to distinguish between individual inshore Bryde’s whales. The ability to discern individual Bryde’s whales based on their vocalisations will be an extremely powerful tool that can be used in population estimation, tracking and movement studies, and many other studies. Studies using passive acoustic monitoring of Bryde’s whales have been done overseas, but no formal studies have been done locally in South Africa. No studies, both locally and internationally, have attempted to identify individual inshore Bryde’s whales using calls only.
The goal of this project is to develop methods and techniques that can be used by other conservationists and researchers to assess the abundance and population density of Bryde’s whales and possibly other types of cetaceans in many other areas. The techniques and methods can be used in remote areas of South Africa, such as the West Coast, where little information about Bryde’s whales exist. This project can furthermore catalyse effective research into Bryde’s whale populations both in and around South Africa, and internationally.
Read the full research here: https://ieeexplore.ieee.org/document/9110497