Following two years of research in Bunbury and almost 200 hours on the water, Murdoch University PhD student Valeria Senigaglia and colleagues from the University of Hawaii and Aarhus University in Denmark have revealed the downside of feeding wild dolphins.
The peer-reviewed study, involving more than 10 years of systematic data collection, found feeding dolphins decreases their reproductive success and hinders calf survival, even under State-issued permits.
While feeding wild dolphins is illegal, permits are issued to allow routine feeding in certain locations including Bunbury.
The study of Bunbury's population of bottlenose dolphins showed from 63 dolphins including eight who were provided with food - only one out of three calves from provisioned mothers survived to weaning age (three years old) compared to 74 per cent survival rate of calves from non-provisioned females.
The results add to previous studies, which showed the local population is in decline and facing additional pressures of port expansion and increased boat traffic.
Ms Senigaglia said the findings showed the seemingly harmless action of giving a fish to a dolphin could have detrimental consequences.
"Dolphins are long lived animals so it is very hard to collect enough data to quantify long-term consequences of tourism which makes my study even more important," she said.
"Previous study conducted in the late 90s on the feeding in Monkey Mia showed similar results and some anecdotal evidences collected by my colleagues suggested that feeding dolphins could have a negative effect on the reproductive success of dolphins in Bunbury. "
Ms Senigaglia said on analysing the data she collected there were behavioural differences between dolphins who were hand fed compared to those who were not.
"In Monkey Mia, provisioned females provide less maternal care than non-provisioned individuals - loosely speaking, they are worse mothers because they spend too much time at the beach where calves cannot lactate," she said.
"Food rewards condition dolphins and teach them to associate humans with food, this leads to begging behaviour and put dolphins at greater risk of collisions and propeller injuries."
Due to the findings of her research, Ms Senigaglia said she believed any impact on dolphins from humans needed to be minimised and the welfare of the dolphin population should be prioritised.
"We should find a sustainable way forward to protect and conserve the welfare of this dolphin population," she said.
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