Abstract
Photo-identification is one of the best practices to estimate the abundance of cetaceans and, as such, it can help to obtain the biological information necessary to decision-making and actions to preserve the marine environment and its biodiversity. The Risso's dolphin is one of the least-known cetacean species on a global scale, and the distinctive scars on its dorsal fin proved to be extremely useful to photo-identify single individuals. The main novelty of this paper is the development of a new method based on deep learning, called Neural Network Pool (NNPool), and specifically devoted to the photo-identification of Risso's dolphins. This new method also includes the unique function of recognizing unknown vs known dolphins in large datasets with no interaction by the user. Moreover, the new version of DolFin catalogue, collecting Risso's dolphins data and photos acquired between 2013-2018 in the Northern Ionian Sea (Central-eastern Mediterranean Sea), is presented and used here to carry out the experiments. Results have been validated using a further data set, containing new images of Risso's dolphins from the Northern Ionian Sea and the Azores, acquired in 2019. The performance of the NNPool appears satisfying and increases proportionally to the number of images available, thus highlighting the importance of building large-scale data set for the application at hand.
Highlights
Top predators such as marine mammals help maintain functionality and resilience of the ecosystem, while actions that contribute to their conservation can generally be beneficial to marine biodiversity [1]
We found 93 different Risso’s dolphins, photo-identified using the algorithm SPIR [4], [5] and their photographs are freely accessible using the new release of DolFin platform
The accuracies, specificities and sensitivities of RUSBoost classification over the 23 dolphins are shown in Table 3, where PIQE median value and Median absolute deviation (Mad) of images are reported in the last two columns.The classifier of ERARDR is built on the highest number of images, having fair qualities, as shown by PIQE median and Mad, the specificity is good, as it corresponds to 82%
Summary
Top predators such as marine mammals help maintain functionality and resilience of the ecosystem, while actions that contribute to their conservation can generally be beneficial to marine biodiversity [1]. The Risso’s dolphin Grampus griseus (Cuvier, 1812) is one of the least-known cetacean species on a global scale, with Mediterranean subpopulation ranked as Data Deficient by the IUCN Red List [2]. The associate editor coordinating the review of this manuscript and approving it for publication was Zahid Akhtar. This species, a key component is obtained through photoID studies. It is, their appearance, that makes the Risso’s dolphins suitable for this kind of research. Adult Risso’s dolphins display extensive white scarring on their bodies, solid grey at birth (see Figure 1)
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