Muc Mhara Ireland's Smallest Whale - Marine Institute Open Access ...

piles, jackets, gravity structures, conventional anchors, chains and mooring ropes. All devices will
be large and have a significant presence in the marine environment. Many, particularly tidal-stream
and wave devices will have moving parts in contact with the marine environment and all require
boat attendance for servicing / harvesting and particularly their construction.
With these renewable energy technologies poised to enter the marine environment, are there any
implications for harbour porpoises? From other marine industries, particularly oil and gas, shipping,
fishing, aquaculture and aggregate extraction we know that conflicts with cetaceans do often arise
and that these typically distil down to the following issues: entanglement; habitat alteration; noise;
chemical pollution and collisions.
Entanglement of cetaceans in fishing nets is well known, but it is becoming increasingly apparent
that entrapment in lines as simple as risers for crab/lobster pots does occur particularly for larger
whales. This appears to be less common for small cetaceans particularly porpoises, but studies of
habitat use by dusky and bottlenose dolphins suggest that aquaculture using suspended ropes may
exclude animals from the immediate vicinity. This habitat alteration may be because of intrinsic
avoidance of these structures or because such structures alter the otherwise featureless open water
habitat in which these animals forage. Thus alterations in the predator prey dynamic may produce
this area avoidance rather than direct entanglement concerns. The behaviour of “neophobic”
harbour porpoises around such structures is unknown.
Underwater noise pollution has been a significant concern for the developing offshore wind
industry. Operating turbine noise itself appears to be relatively unobtrusive and any effects are
likely to be local but construction noise, on the other hand, is much more pervasive. Wind turbines
are held in place by piles driven into the sea bed. The percussive noise generated by pile driving has
sufficient intensity to produce auditory injury in marine mammals and their prey. Behavioural
impacts at greater distances are also likely.
Unlike the oil and gas industry, renewable energy devices are unlikely to be significant sources of
chemical pollution. Many devices will however, require anti-fouling and contain lubricants for
machinery though these are unlikely to directly impact porpoises.
Of more direct concern are physical collisions between marine mammals and devices, particularly
those with moving parts in already moving water – notably tidal-stream devices. Contrary to
popular belief, collisions between marine mammals and ships are relatively frequent events and
include the bow as well as propellers. Tidal-stream devices, particularly tidal turbines are different
to ship’s propellers as they are being passively turned by the water and taking energy from it rather
than turning the water and adding energy. However, the parallel between turbine blades and the
bows of ships is much stronger. Turbines are likely to be large at 12-20 meters in diameter and tip
speeds are likely to range up to 12 ms -1 .
To investigate the magnitude of a collision threat, a model was constructed of the potential
frequency of encounters between a hypothetical commercial-scale coastal development (100
turbines) and the harbour porpoise population off western Scotland (Wilson et al. 2007). Because
cetacean responses to turbines are unknown it was assumed that they were neither attracted to nor
avoided these devices. The model predicted that in a year of operation up to 1300 individuals (3 to
10% of the population) would share the same space and time as a rotating blade and thus have the
potential to make physical contact. The model highlights body size as a critical factor and so
collision rates for larger species may be greater still than for the porpoises. Nevertheless, were these
interactions to result in mortality for porpoises it would lead to unsustainable population impacts.
Thus the behavioural response of porpoises to tidal turbines is critical to whether or not collisions
are going to be a significant conservation issue. At present little is known about how porpoises will
respond (avoid or be attracted) to these devices.
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Proceedings of the 2 nd IWDG International Whale Conference: Muc Mhara - Ireland’s smallest whale
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