As WDCS fieldwork in Gairloch, in the North-west of Scotland comes to an end, we hear from Ian French, owner-operator of Gairloch Marine Wildlife Centre & Cruises (formed in 1989 as Sail Gairloch), where marine survey data has been collected over the last two decades. A marine biologist (specialising in sublittoral biology particularly spirobis tubeworms), since taking over the business, Ian has expanded the data collection to include noise pollution and disturbance. Harbour porpoises are a focal species for Ian.
Loch Gairloch has proved to be a small but perfect study area for cetaceans with many species being recorded over the last twenty-one years. Being the smallest of the UK cetaceans, harbour porpoise are fairly hard to study, spending fractions of a second at the surface. Due to the poor mass / surface area ratio and possessing only a thin 12mm layer of blubber they have to continuously swim to maintain the core body temperature. They will eat any kind of fish and crustacean but have a tendency for bottom dwelling fish. Ian has helped in several necropsy's on harbour porpoise and gathered a considerable amount of important data on stomach contents, age and bio accumulated chemicals within the blood and tissues.
Porpoise tend to be seasonally migrational with the onset of winter the porpoise tend to leave the Loch and head out into the deeper water where they have been recorded feeding down to depths of 300 metres. With the return of spring, coinciding with plankton blooms and sand eels returning from semi hibernation the porpoise return to the coastal feeding grounds, with the pod numbers steadily increasing through the year. As marine surveys begin in the spring the porpoise have little interest in any interaction, primarly feeding and foraging. By mid summer calves are born and interaction with the survey boat increases. The behaviour exhibited is almost as if the mothers are 'showing' the newborns a boat.
A slow quiet approach near to where the porpoise are feeding, stopping and sometimes shutting down the engine is often rewarded with good interaction with breathing clearly heard. Reinforcing the name 'puffing pig' or 'pig fish'. Young calves are often seen to be logging, panting at the surface as if catching thier breath. A lot of interaction at this time of the season is probably due to the ease of feeding and often play behaviour and mock fights and lunges are regularly witnessed.
Gairloch porpoises do not seem to behave as others and many dolphin researchers have spent time aboard the research vessel Starquest and dispute what they are seeing until clearly recognising the cetacean as a harbour porpoise and not a dolphin. Approaching slowly and stopping off at distance it allows the porpoise control and confidence with the situation resulting in good interaction with the passengers and boat.
The harbour porpoise have a life span of around thirteen years, this is reinforced by tooth data collected by Ian, and as many are seen to be born in Loch Gairloch the porpoises here seem to become habitualised with the research vessel, quite simply unique behaviour. Non-invasive survey techniques are used, including digital photo survey and video and acoustic data collection via a purpose built hydrophone.
Pollution with chemicals into the seas is a problem for everything but manifests itself in the porpoise in the form of skin legions and ulcers. Again necropsys aided by ian have shown high levels of PCBs (polycholrinated Biphenyls) acumulated in the blood and skin layer of the harbour porpoise. Possibly the biggest problem the harbour porpoise have to contend with is noise and data collected has shown noise pollution to be a major factor in the population abundance of the harbour porpoise.
Feeding by sonar, porpoises simply cannot find food if the sea is full of boat traffic, particularly speed boats with such speed and power they produce a vacuum cavitation underwater creating an enormous sound level. With sound travelling five times faster in water and many times further porpoises are moving away from busy areas and indeed have become forced out of certain areas around the UK with the direct increase in pleasure craft taking to holiday hot-spots. Thankfully Loch Gairloch has not become too noisy although sightings data has shown a declining population which gives cause for future concern.
NATO disturbance in the area is another cause for concern, indeed Gairloch Marine Wildlife Centre was part of a pressure group that successfully persuaded NATO and the MOD to change the timing of their large scale manouvers which used to take place during June / July right in the porpoise and dolphin calving season. In the past this resulted in many dead porpoises and aborted feotusus but thankfully March and October are now when the joint operations take place although data suggests again that cetaceans leave the area during these live firing operations.