Human influences on the Moray Firth Dolphins

Human influences on the Moray Firth Dolphins
Professor Paul Thompson is Director of Aberdeen University’s Cromarty Lighthouse Field Station. He described the potential influences of human activities on the firth’s famous dolphins.

A recent global assessment of human impacts on marine ecosystems highlighted that the waters of the Northeast of Scotland were amongst the most heavily impacted areas in the world. But how might all these different human activities affect the bottlenose dolphins in the Moray Firth and, more importantly, how might we mitigate against these effects to ensure the dolphins continue to use this area.

The greatest impacts come from those threats which may directly kill animals, whether this is entanglement in fish nets, collisions with boats, or the impact of underwater explosions. More subtly, the animals may be impacted by changes in the availability of their food; possibly through competition with commercial fisheries but also as a result of wider scale global change as seen with many seabirds around Scotland.

Another subtle effect can be disturbance by noise. This can be from shipping, or occasionally from much louder piling noise, for example when constructing wind turbines or coastal defences. High levels of noise can potentially cause direct damage to animals, whereas lower levels may lead to animals moving out of their favourite areas or disturbing their feeding and social behaviour.

Another concern comes from reductions in water quality, such as industrial pollution directly affecting reproduction or disease patterns, or indirect effects of these pollutants upon the dolphin’s prey. On the whole, much has been done to improve water quality around the North Sea over recent decades, but some problems remain and we still find a range of novel chemical contaminants in marine organisms.

The Moray Firth Special Area of Conservation has been set up to try and mitigate these effects, and also to promote positive management, for example, through schemes such as Operation Fishnet which aims to reduce the use of illegal salmon nets that might endanger both salmon and dolphin populations. Importantly, the Special Area of Conservation also aims to ensure that new developments undergo more rigorous assessments to ensure that they won’t have a significant adverse impact on the conservation status of dolphins in the Moray Firth.

A key problem here is that it is not easy to assess the effects of these new developments. If, for example, we see a boat approaching a group of dolphins, or jet skis harassing these animals, how can we really tell whether the dolphins have responded to that disturbance? They are not easy to track underwater, and we can’t ask them in for a blood test after they swim through polluted coastal waters. Even when we do see unusual diseases on the animals, as we have seen with certain skin diseases in recent years, we can’t easily determine what has caused these diseases. Similarly, if we find a dead animal on the beach, it’s often impossible to determine the cause of death. Some of this scientific uncertainty is due to limited resources and a lack of relevant research. But even with unlimited funds, it is often impossible to come up with suitable scientific methods for addressing some of these questions.

A second problem is that we often lack baseline information. Over the last 15-20 years, the Moray Firth dolphins have become one of the best studied populations in the world. However, we know next to nothing about how this population fared before the late 1980’s. For example, we have no idea about the distribution or abundance of dolphins in the Moray Firth prior to the start of oil exploration both here and in the rest of the North Sea. What we have seen over the last 10-20 years is some evidence of movement out of the Moray Firth, and an increase in sightings of bottlenose dolphins in areas further south along the Scottish east coast. However, the reasons for these changes are uncertain. Is it because conditions have worsened in the Moray Firth, or improved somewhere else? Given our difficulty in understanding historic patterns, it is even more difficult to predict what might happen in the future.

Ecologists are not alone here, and economists in the Highlands would have similar problems predicting the relative success of different business sectors in 10 or 20 years time. As scientists, we therefore have to accept this uncertainty and be open about this when we advise how best to manage existing and new developments in the marine environment. We must use the best available data to predict various likely scenarios, and in some cases we may be able to predict the most likely scenario. But, in particular, we must not be over confident about an apparent absence of adverse effects.

We can often see dolphins leaping off the point at Chanonry, but this doesn’t necessarily mean that dolphin numbers across the whole of the Moray Firth have remained stable. It’s especially important to remember that we’re dealing with a very small and vulnerable population here. We are extremely lucky in the Inner Moray Firth. We have the animals here on our doorstep, and are able to reap the economic and cultural benefits they bring. Whilst 130 dolphins on our doorstep may seem a lot, we must remember that this represents just about all the bottlenose dolphins that can be found across the whole of the North Sea.

We must also remember that it is the population’s ability to maintain itself into the future that is important here. These are long lived animals that don’t start reproducing until they are 8, 9 or 10 years old. And once they have started reproducing, they may produce a calf only every 2-5 years. When thinking about all those 130 dolphins, one also needs to remember that around half of them are males (who really don’t count very much when it comes to population dynamics). And of the females, around 60% of them are not yet old enough to breed. Bearing in mind that the adult females that remain only have a calf every 2-5 years, the number of calves produced in a year is extremely low.

That population of bottlenose dolphins in the whole of the North Sea, therefore, is barely bigger than the population of humans living on some small islands like Gigha. So, as we explore how best to balance the costs and benefits of developing the Moray Firth, we should remember that, like those fragile Scottish communities, this dolphin population is small and vulnerable and requires special measures to remain viable.