Industry Insight

Tidal’s environmental impact: does it get the seal’s approval?

25 January 2012

Recent studies finding that MCT's Seagen turbine has had little if any impact on sea and sea bird life has given the tidal industry a great boost. Other findings in the US have found that seals, while inquisitive by nature, have to date had little interest or concern over turbines. But some environmental researchers say that more turbines in differing water conditions are required to get an accurate picture of the overall environemtal impact.

By Elisabeth Jeffries

A single seal from Strangford Lough swam across the Irish Sea to England. The rest of the colony stayed at home, and none has been disturbed by Seagen, Marine Current Turbines’ (MCT) device in Northern Ireland. These are some of the findings to have emerged from environmental studies of the turbine in this conservation zone due to be published in 2012. 

More significant questions, such as how seals react when right up close to the turbine and whether they avoid or try to swim through it, remain unanswered due to licensing rules obliging MCT to switch off the turbine when seals go within 30 metres of the device.  Joe Kidd, site development manager at MCT, confirms that Seagen has been switched off several times as a result of seals coming fairly near it.

“The whole programme showed we’re not having any impact on a wider scale.  But our hands are tied because of this mitigation rule and we can’t make assumptions about near field behaviour...we’re just showing how likely it [a seal] is to come within the vicinity of turbine,” he says, commenting on the findings of the research.

Half the research at Strangford Lough aimed to study the behaviour of local seals because of potential threats to the species, known as the harbour seal, which is fairly inquisitive by nature.  The rest of the research focused on seabirds, marine life in the seabed and other issues. 

Seal observations

“The emphasis on seal observation was of major concern in Strangford Lough because the harbour seal is on the EU endangered red list,” explains Dr Graham Savidge, a researcher at Queens University Belfast, who was engaged in the five year project.   Harbour seal numbers have declined significantly in Northern Britain in recent years according to the Sea Mammal Research Unit at St Andrews University, Scotland.  Savidge comments: “We saw no change in the population of seals around the coast of Northern Ireland...it’s very encouraging.”

In other locations with different licensing restrictions, tests around turbines indicate mammals have not been swimming close up to them.  Professor Gayle Zydlewski of Maine University, US, who monitored fish in 2010 around a 12 metre ORPC turbine in Cobscook Bay, Maine, reports: “we didn’t see any other marine life around it” – although seals and porpoises swim in the region. 

Dr Brian Polagye, an expert from the University of Washington, who collated research on this issue from various countries, confirms: “Data to date suggests that pilot projects will not pose a significant risk to marine mammals in terms of direct interaction.”  

Nonetheless, scientists assert that the data on the issue are incomplete due to the few turbines in the water.  A range of other variables need to be tested, such as the effect of different turbines in different locations.  Species also vary in each location and may react differently to the devices.

Seabirds

At the European Marine Energy Centre (EMEC) in the Orkney Islands, for example, seals are lower on the research priority list, according to Dr Savidge:   “There is very little concern about the possible effects of tidal devices on the seal population, and more about the effects on seabirds because at the EMEC site there are higher populations of seals anyway,” he states. 

This is because the dominant seabird population in the Orkneys has been declining. Meanwhile in the Bay of Fundy, Nova Scotia, there are yet other considerations.  “In Fundy the concern is the migration routes of local whale populations,” explains Dr Savidge. 

Last but not least the ecological effects of a tidal array have yet to be tested.  If tidal stream energy becomes fully commercialised, these could be as numerous as turbines in offshore wind farms in coming decades. 

“It is still difficult to know, with certainty, how marine mammals would respond to a much larger installation.  Avoidance behaviour, on a large enough scale, has biological consequences,” states Dr Polagye.

The migratory patterns of fish, mammals and other sea life are among the concerns of scientists considering tidal arrays.  Comparing tidal turbine arrays with dams built for hydropower, Professor Zydlewski points out: “Migrating paths may be changed; there are different levels of impact. If you injure one animal, are you going to harm the population?” These are some of the as yet unanswered questions in relation to future arrays.

Different conditions, common conclusions

Despite the somewhat different conditions at each pilot site location, some common conclusions can be drawn from these early studies, according to Dr Graham Savidge. “To say we would be starting from scratch at a new location would be way too negative.  The information already built up from Seagen could have potential relevance to other deployment,” he states. 

Observation techniques used by scientists include the use of laser binoculars from the shore to detect activity on the water’s surface and the more powerful sonar technique, which tracks marine life in water columns well under the surface.