Habitat loss and degradation HW&DT

HABITAT LOSS AND DEGRADATION

Abstract courtesy Hebridean Whale and Dolphin Trust

Prey depletion

The West of Scotland holds many important fishing grounds, however, a large proportion of fishermen operating in this area are not from West Scotland, but originate from other Scottish regions (e.g. Aberdeen) or Europe (e.g. Spain). As mentioned previously, many local fishermen have turned to exploiting shellfisheries, partly because reduced fish stocks have made it commercially unviable for small-scale, local operators in West Scotland. Many commercially important fish species caught in the region, such as herring and mackerel, are also important prey species for cetaceans.

There is currently a fisheries quota system in operation in Scotland, brought in to relieve the problem of over-fishing. However, the quotas are based upon the amount of fish landed at recognised ports. The quotas do not take into account fish which are discarded at sea, a common practice when fish which are too small or are from non-target species. This discard may account for a weight as much as a third of the total reported catch (Hughes, 1997). In addition, the illegal landing of fish is also a serious problem and is common practice in many areas. It has been estimated that 40-60% of landed fish are done so illegally and are, therefore, not officially entered into catch statistics (Hughes, 1997). Due to a combination of these two factors, fisheries quotas are being greatly exceeded, dramatically reducing the stocks of fish upon which whales and dolphins are dependant.

Fisheries

Another impact of Scottish fisheries upon the marine ecosystem is the obliteration of swathes of seabed by beam trawling. As fisheries effort increases in West Scotland, in the pursuit of fewer fish, so does the amount of damage to marine life on the seabed. One of the problems with trawl fisheries, particularly in coastal areas, is that the seabed is not left to recover before being trawed again. If coastal waters were managed by local fishing organisations, which allowed seabed recovery before re-trawling, it would not only increase the yields of fishermen, but also help protect the habitat and prey of whales and dolphins. However, this is currently not possible as trawlers frequently come in to coastal waters from outside areas, with no knowledge of whether the seabed has been recently trawled or not.

Scallop dredging is another fisheries type which adds to the degradation of cetacean habitats. Not only does the dredging process destroy seabed habitats so thoroughly that it may be several years before there is any recovery, but also the noise produced by the dredging process can carry for dozens of miles. This noise pollution could pose a serious problem to whales and dolphins as they depend so much upon using sound to navigate, communicate and find prey.

Oil exploration

In addition to the potential risk from oil-related pollution as mentioned above, the oil industry also poses a threat to cetaceans with respect to the degradation of their habitats. Several oil companies are currently conducting a series of seismic surveys off the coast of the Outer Hebrides in a search for new oil fields. The area in which these seismic surveys are being conducted is known to be inhabited by several species of cetacean, in particular beaked, bottlenosed, sperm, fin, sei and pilot whales and Atlantic white-sided dolphins (Northridge et al., 1995; Hughes et al., 1998; Lewis et al., 1998). Several scientists have highlighted the potential impacts of seismic surveys upon cetacean populations and have expressed concern about the resulting degradation of cetacean habitat (e.g. Evans and Nice, 1996; Gordon and Moscrop, 1996; Swift, 1997). In a recent study off the Outer Hebrides, Swift (1997) monitored the acoustic behaviour of dolphins and sperm whales before, during and after seismic surveys and noted significant changes in their behaviour. The UK Government has recently issued the oil industry with a code of practice to attempt to reduce the impacts of seismic surveys upon cetaceans. This code of practice should prevent some effects of seismic testing (e.g. hearing damage) but the issue of habitat degradation and disturbance of cetaceans within breeding and resting grounds as the result of oil exploration still remains.

Fish farms

The fish farm industry has already been highlighted above as a major source of pollution and degradation within cetacean habitats. Another area in which fish farms cause an impact on coastal cetaceans is the use of acoustic harassment devices to scare seals away from fish farm cages ("seal scrammers"). These devices not only repel seals from fish farm sites, but could also exclude whales, dolphins and porpoises from breeding, feeding or resting sites.

Shipping

The West of Scotland has a substantial amount of shipping activity. Shipping can impact upon whale and dolphin populations in two ways. Firstly, collisions with shipping may injure or kill cetaceans. So far, this has not been reported in West Scotland. Secondly, the noise produced by shipping may cause disturbance, stress and degrade the habitats of cetaceans. Several scientists have reported changes in behaviour and distress reactions resulting from shipping-produced noise (Evans et al., 1992; Richardson, 1995; Gordon and Moscrop, 1996).

However, to date, there has been only one study into the impacts of shipping upon cetaceans in the waters of West Scotland. Simmonds (1999) reported an incident on the Isle of Skye where a pair of Northern bottlenose whales displayed reactions to boat movements. Simmonds (1999) also noted concern that an increase in boat activity resulting from the presence of the whales, may have been detrimental to the animals. However, since this event, a code of conduct for marine-users when in the vicinity of cetaceans has been drafted and distributed in West Scotland (Hebridean Whale and Dolphin Trust, 1999- copies may be ordered by email). This code of conduct will hopefully help reduce some of the disturbance caused by marine shipping.

Military Activities

Vonk and Martin (1989), Simmonds and Lopez-Jurado (1991), and Frantzis and Cebrian (1999) have suggested that military activities, notably the testing of low fequency sonar, may have caused a mass stranding of Cuvier’s beaked whales in the Canary Islands and the Ionian Sea. The West of Scotland is the site of many military exercises. In particular, submarine exercise areas occupy most waters in the region. The extensive use of sonar and a high density of submarine activity could disturb a variety of cetacean species in their feeding, breeding and resting grounds.

In addition, the Ministry of Defence’s British Underwater Test and Evaluation Centre is situated near the Kyles of Lochalsh. The adjacent area is used as a torpedo testing range. Some 130 squares miles of the Sound of Raasay are considered to be a danger area to shipping because of the use of explosives in this region. This area is also an important habitat for cetaceans, notably the Northern bottlenose whale and harbour porpoise.
A missile firing range is situated on the island of South Uist. A large number of cetacean strandings are reported from this region, suggesting a diverse whale and dolphin population in the waters next to the missile range (Bones and Mclennan, 1994a,b; Sheldrick, 1989). In particular, there have been a large number of sperm whale strandings in this area (Evans, 1997).

Every year, a joint forces training exercise is conducted in West Scotland. Concern has been voiced from wildlife tour operators that this exercise coincides with a period when cetacean sightings decrease substantially in the area (B. Fairbairns and I. Birks, pers. comm.).

The amount of military activity in Northwest Scotland is considerable. However, getting detailed information about military activities is difficult within the UK. Therefore, the extent of the impacts of military activities upon cetaceans is likely to remain unknown.