A team of Scottish dolphin experts from the University of Aberdeen say tens of thousands of marine tourists are affecting dolphins' feeding behaviour to the point where the females haven't the energy to feed their calves.
The teams' studied the impact of tour boats on the foraging efficiency of an endangered population of Bottlenose Dolphins off the coast of New Zealand. Their findings suggest these boats are hindering the dolphins' ability to feed.
Dr David Lusseau explains: "Bottlenose dolphins in Doubtful Sound, Fiordland, New Zealand, hunt in deep waters. They have to make prolonged dives to reach the fish they try to capture, so they have to spend some time at the surface to catch their breath after each of these dives."
Building on previous studies
Marine scientists have shown in the past that tour boats disrupt the activities of dolphins when tourists try interact with them. It is these interactions that's cutting the amount of time the dolphins can spend on other things. Most seriously female dolphins haven't the energy to feed their young properly and they are starting to die.
"At that time we thought that the negative impacts were caused by dolphins having to expend more energy to deal with tour boats because they were spending more time travelling and less time resting. We thought that because the dolphins were foraging at depth, their actual hunt would not be hindered by the presence of boats. Indeed, when we looked at the typical duration of a hunt, it was not affected by the presence of tour boats", says Dr David Lusseau.
In 2010 the International Union for Conservation of Nature (IUCN) listed the Doubtful Sound dolphin population as critically endangered.
New research at the University of Aberdeen
MSc. student John Symons has developed a model to describe the mechanism of a dive for these unique dolphins. This model aimed to integrate the effect of the presence of a risk at the surface (such as a boat) on the amount of time a dolphin could spend hunting at depth and how much time it would have to catch its breath at the surface.
John Symons' study shows that, depending on the way a dolphin perceives this risk, a boat will affect its dive cycle. It can either spend less time at the surface catching its breath, so reducing the time it can spend underwater during each dive to seek food, or the diving dolphin will try to spend more time underwater to stay away from the risk. In that case the dolphin will be able to do fewer dives over the whole hunt because it will not have enough breath left. In both cases, dolphins have less time to spend at depth hunting for food.
The model provides helps identify tell-tale clues in the dive patterns of dolphins so that we can calculate whether dolphins reacted to the presence of boats as a risk. The study also suggests some interesting differences between the behaviour of male and female dolphins.
"Looking at dolphin diving patterns in Doubtful Sound, we indeed found that their dive cycle was disrupted by the presence of boats. They perceived them as a risk - but males and females did so in different ways. Males hung around more underwater and so performed fewer dives during a hunt. Females did the reverse and tried to spend little time at the surface, leading them to be able to spend less time underwater at each dive, explains Dr Lusseau.
The University of Aberdeen study shows that dolphin's hunting behaviour was changed by the tour boats and they lost opportunities to feed.
"These lost opportunities are very hard to compensate, and the tactics they use to deal with the presence of the boats means that they eat less when boats are around. Lost eating opportunities are going to quickly affect the energy balance of individuals, and this could explain why we saw rapid changes in the survival of calves and juveniles in the population as the number of tour boats operating in Doubtful Sound increased.
"This work points to new management actions needed to protect this critically endangered species. We need to make sure that tour boats spend little time around them when they are hunting, to protect the foraging success of these exceptional animals and ensure that they can flourish as a healthy sustainable population," Dr David Lusseau said"
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