Ocean tours promoting swimming “encounters” with wild dolphins can significantly disrupt a pod’s feeding behaviour, including co-operative herding of fish, according to New Zealand research.
Scientists found that common dolphins (Delphinus delphis and Delphinus carpensis) spent less time hunting for prey, and took much longer to return to feeding once disrupted by commercial tour boats.
The study, led by Anna Meissner from Massey University in Auckland, is the first to investigate the impacts of commercial tourism and recreational boats on NZ dolphins in open ocean habitat in the Bay of Plenty.
The results are published in PLOS ONE , and raise concerns about the long-term impact of disruptions to dolphin feeding behaviour.
“Dolphin foraging behaviour was significantly altered by boat interactions,” the research paper says.
“Dolphins spent less time foraging during interactions and took significantly longer to return to foraging once interrupted by vessel presence.”
It says that in an ocean environment like the Bay of Plenty, where prey such as fish, squid and crustaceans are widespread and unpredictable in distribution, these disruptions could deplete the energy needed by dolphins to forage over a large area.
The majority of dolphin tourism in NZ occurs during summer, during the peak calving season, and this could affect survival and reproduction.
“Although the consequences of reduced feeding for nursing groups remain unclear, it is likely to have bigger effect on pregnant and lactating females,” the study says.
“Disrupting the foraging behaviour of females and immature dolphins is likely to add extra physiological constraints to these individuals and could potentially reduce their reproductive success and negatively affect population dynamics on a long-term basis.”
Commercial tourism also exposes dolphins to noise pollution and exhaust emissions which could lead to chronic auditory damage and other health problems, the study says.
“Close encounters with wild cetaceans at sea have also become more and more intrusive,” the paper says.
“However, despite numerous concerns raised by the scientific community, the cetacean-watching industry is still experiencing a fast world-wide expansion, as the economic benefits of marine mammal based-activities represent a significant part of the ecotourism industry.”
In New Zealand, the industry is worth more than US$80 million a year, and permits to watch or swim with wild dolphins have increased from 90 in 2005 to 112 in 201.