"Allo Cétacés" Program
Presentation
Long-billed dolphins (Stenella longirostris) regularly find residence in many bays and passes on high islands and atolls. These sedentary cetaceans come to rest, socialize and reproduce in the bays, most often all morning, before returning to fish at sea. These are therefore important moments in the life cycle of a dolphin.
Their regular visits attract the attention of dolphin enthusiasts for leisure or commercial activities. We are seeing an increase in boat, jet ski or swim tours from year to year, mainly in Punaauia Bay, located in Tahiti, just 10 minutes by boat from Taapuna Pass. In this context of growing activity, an acoustics study was carried out for the Environment Department of Polynesia, recording variations in acoustic signals emitted by dolphins during stressful or non-stressful situations in order to assess the situations disturbing the animals.
Some results
Extracts from the BENET.A report. 2017. Acoustic and ethological impact study on populations of spinner dolphins (Stenella longirostris) in Punaauia Bay (Tahiti): Assessment of the impact of activities of anthropogenic origin. PROGEM. Directorate of the Environment of French Polynesia. Final report. 53 p.
The entire study is at DIREN, of which here are some extracts. The whole thing can be consulted at the DIREN in Papeete.
Long-billed dolphins in Punaauia Bay, like their snowdrifts in other regions of the world, frequent the bay in the morning mainly to rest (79%). Rest in cetaceans is the equivalent of sleep in humans.
63% of motorboats and 80% of jet skis frequenting this area do not respect the rules for approaching cetaceans and cause a change in dolphin behavior (escape, change in respiratory rate, etc.)
The pressure most observed on dolphins relates to hunting which is carried out by both motorboats and jet skis.
While the regulated speed is less than 3 knots within a 300 meter radius of cetaceans, 14% (motor boats) and 19% (jet skis) exceed 10 knots.
Resilience time (time it takes for the dolphin to return to its behavior before disturbance) is approximately 20 minutes.
When dolphins are at rest and regularly disturbed, their rest can be interrupted by more than ’1 hour by disturbances + resilience time.
If the disturbances continue all morning, the dolphins' rest time becomes non-existent.
Human-induced disturbances lead to changes in dolphin communication, which we recorded using a hydrophone.
Influence of anthropogenic pressure on dolphin whistles during the resting phase.
Conclusion
All of these results demonstrate that long-billed dolphins in Punaauia Bay may show signs of modification of their inter-individual communication. Indeed, animals are forced to modify their communication (frequency, shape and number of whistles) due to a general increase in ambient noise, which indicates that they are leaving their comfort zone; it is therefore a response to discomfort caused.
By associating the acoustic results with those of the behavior of motorboats on this site, namely, more than 63% of boats and 80% of jet skis frequenting the area which do not respect the approach rules with different induced anthropogenic pressures (see figures above), the disturbances caused warn of repetitive and regular disturbance in this area.