Please note that many of these articles were originally written for the old GB Wildlife site in between 2008 – 2010 and organisations may have changed since then.
Wildlife Blogs – Wildlife Trusts’ Basking Shark Survey
This report into basking sharks around the coast of Britain is courtesy of the Wildlife Trusts and illustrates the excellent research work they do in conjunction with many other wildlife, nature and conservation charities and organisations. Above all it shows how important the contribution of volunteers’ time and expertise is in contributing to reports which will hopefully lead to greater conservation measures for our wildlife.
The basking shark is the ultimate gentle giant – a seven-tonne shark that cruises the oceans in search of its microscopic prey. At 11 metres long, this plankton-eater is the world’s second biggest fish. Looming out of the blue, mouth agape, the basking shark is surely one of the most awe-inspiring sights in the entire animal kingdom.
More than 80,000 basking sharks were slaughtered in the north-east Atlantic in the 20th century, and numbers are thought to have declined by 95% or more from historic levels. Rare, elusive and difficult to study, it is only in recent years that this giant has begun to give up its secrets.
Between 1999 and 2007, The Wildlife Trusts’ basking shark survey counted, observed and photographed sharks off the western coasts of the UK. The largest boat-based study of its kind, the survey revealed basking shark hotspots off the South West of England, where sharks gather for feeding and courtship. They may also visit these sites to give birth to their young. Further hotspots were revealed in Northern Ireland and Scotland.
The study highlighted a remarkable change in shark distribution over the study period, with a marked decline in sightings in the South West of England, and an increase off Scotland.
This summary focuses primarily on the English hotspots, as well as considering shark ecology and the conservation issues relevant to basking sharks throughout UK seas. A more detailed report of the English survey results is available at www.naturalengland.org.uk. A report on the Scottish hotspots is due in 2009.
Identifying hotspots helps us understand basking shark ecology, and may be critical to protecting the species. Congregating at the surface in these sites, basking sharks may be especially vulnerable to collisions with boats, entanglement in fishing gear and other threats. As such, protection of hotspots might make a significant contribution to conserving basking sharks in UK waters.
Basking shark ecology
During early spring and summer, warm water from the Atlantic pushes into coastal waters on the western coasts of the UK. Where this warm water meets cooler seas inshore, upward currents lift nutrients from the depths to the surface. Here, microscopic plants (known as phytoplankton) are fertilised by the increase in nutrients, causing a population explosion – a ‘plankton bloom’. In some years, the bloom is so immense that it turns the seas into a milky slick, visible from space. The bloom, in turn, feeds an explosion of tiny animals (known as zooplankton), which prey on the phytoplankton. Amongst the most numerous animals are a group of shrimp-like crustaceans called copepods – and these are the basking shark’s favourite food.
Using its highly developed senses, the shark forages over enormous distances, seeking out the densest patches of plankton, such as at tidal fronts that develop close to headlands. These fronts can be caused by abrupt differences in temperature, strong tidal flows and sudden variations in seabed depth. The high productivity of these frontal areas is an important element of the coastal food chain, supporting fish, seabirds and marine mammals, as well as basking sharks.
Under most conditions, zooplankton remain in deeper water in the daytime, rising to the surface by night. Foraging sharks follow this behaviour, making them very hard to observe. However, where fronts occur, zooplankton reverse their daily migration, occurring at the surface in daylight – and so do the sharks.
Recent research has revealed that basking sharks are 60 times more likely to be seen at the surface in a frontal area than in a non-frontal area. This may have implications for their conservation, as sharks at the surface may be much more vulnerable to certain threats.
Basking sharks in peril
Before the 19th century, basking sharks were abundant along the western coasts of the UK in spring and summer. They were also found in the North Sea. Valued for their liver oil (used in lamps and as a lubricant), sharks were hunted with harpoons during the 18th, 19th and early 20th centuries, and perhaps earlier, taking a few hundred sharks per year. In the second half of the 20th century, hunting pressure increased. Norwegian, Irish and UK vessels killed thousands of animals each year. Records show that more than 80,000 basking sharks were killed in the north-east Atlantic during this period.
Basking sharks are slow-growing, late to reach sexual maturity (at 12-20 years) and produce few young (bearing five or six pups for a gestation of one to three years). This makes them extremely vulnerable to over-exploitation. Even when threats are removed, numbers take a very long time to recover. The basking shark population in the northeast Atlantic is estimated to have declined by more than 95% from historic levels.
No more than a few hundred sharks remain to visit UK waters each summer, and sightings are mainly restricted to the South West of England (especially Cornwall), the Isle of Man and the west coast of Scotland. The last UK basking shark fishery closed in 1995, and the species has been legally protected in the UK since 1999. However, many sharks are thought to die as a result of injuries inflicted, while feeding at the surface, from collisions with boats. Others become entangled in fishing nets and ropes. To date, it has been difficult to identify practical measures to address these threats and ensure the survival and recovery of basking sharks in UK seas.
The Wildlife Trusts’ basking shark survey
The Wildlife Trusts’ basking shark survey ran from 1999 to 2007, aboard the yacht “Forever Changes”, skippered by survey leader and basking shark expert Colin Speedie.
The survey was conducted in two phases, surveying the western English Channel for:
– one week per month in May, June, July and August from 1999-2001
– eight weeks during May and June from 2002-2004.
In July, between 2002 and 2004, Forever Changes travelled up through the Irish Sea, conducting the first ever ‘line transect’ survey work along the coastline of Northern Ireland. In August and September, from 2002-2005, the team continued north to survey the Clyde Sea and the Sea of the Hebrides. The survey vessel spent the whole of the 2006 season in the waters of west Scotland, working on hotspots in that area as well as photoidentification studies. In 2007, the survey returned south to work in the English Channel but, due to difficult weather conditions, very few sharks were recorded.
Using standardised survey methods, the crew watched for sharks whilst sailing in straight lines – transects – across the survey area. Transects were surveyed in a range of inshore and offshore locations, to determine the presence of key sites – hotspots – for the basking shark within the larger area. Records were made of shark numbers, size and behaviour, along with a photographic record to identify individual sharks.
Volunteer crews were recruited from The Wildlife Trusts and Earthwatch Institute (Europe) membership to help with the surveys. All volunteers received full training in all aspects of appropriate survey technique, from observation procedures to data gathering and recording.
Results: English hotspots
In order to establish the distribution of basking sharks across the survey region, it was split into eight separate areas. To avoid bias, the frequency of shark sightings was divided by the amount of survey effort. This provides a ‘Sharks Per Unit Effort’ value (SPUE), which allows the areas with highest SPUE values – hotspots – to be identified.
A total of 141 sharks were sighted on transect over 206 hours of observation. A high average SPUE value was established over the three years, largely due to a high peak in 1999.
BASKING SHARK SIGHTINGS 1999-2001
Sharks were only recorded in three of the eight survey areas on transect, with a distinct bias towards the areas west of Lizard Point.
Spatial distribution of shark sightings 1999-2001
A total of 56 sharks were recorded by the second survey. During this period, there was a large-scale shift in the distribution of surface-sighted sharks. In the latter years, far fewer sharks were observed in English waters, and many more sharks were observed in Scottish waters, especially in the Sea of the Hebrides.
Although the overall number of shark sightings declined during this period, the western sections of the English Channel survey area continued to be important.
During the 2006 season, the project recorded 303 sharks, the most ever recorded in a season. In 2007, there was difficult weather in Cornwall in the early part of the season, and it was a poor year for surfacesighted sharks in the region.
Throughout the survey period, one area stood out clearly as a shark hotspot: Area 5, from Lizard Point to the Runnelstone Buoy. From 1999-2001, 78% of all sightings were made in this area, and from 2002-2004 it generated a SPUE value of 0.481 sharks per hour.
Area 4, from St Anthony’s Lighthouse to Lizard Point, was not a strong site in the first three years, but in the latter period was the next most consistent area, with 0.165 sharks per hour. Fronts are known to develop in both Areas 4 and 5, owing to their strong tidal streams and uneven bottom topography. Area 6, West of the Runnelstone including Scilly, also generated a good sightings record. In 1999-2001, 21% of sightings were recorded there, and from 2002-4 it produced a SPUE value of 0.103 sharks per hour. Each of these three areas might be considered a basking shark hotspot. Although Area 7, north of the Runnelstone and north Cornwall, produced the highest SPUE value from 2002-2004, all the sightings were recorded on a single survey day in 2002. As such, there is insufficient data to confirm it as a hotspot.
Shift in distribution
The observed shift in the distribution of sightings is difficult to interpret at this time. In the later years, there were more sightings off Scotland and fewer off the South West of England. Shark sightings around the UK seem to vary in a cyclical manner, related to changes in large-scale climatic events which affect the distribution of plankton.
However, rising sea temperatures may also be having an effect on the timing and distribution of plankton, as cold water species move further north and warmer water species move in from the South. Basking sharks are efficient foragers, though, and will travel over large distances to find their prey. As such, they may be able to adapt to the changing regime.
Basking shark behaviour
The most commonly recorded behaviour was feeding. Sharks were observed swimming at the surface with their mouth agape, filtering plankton from the water.
The survey was also able to observe basking sharks displaying courtship behaviour. This involves two or more sharks swimming parallel to each other, following close behind one another, and occasionally making contact. This behaviour was recorded on four occasions across the survey region, including three times to the east of The Lizard.
Basking sharks breach on occasion, sometimes leaping entirely clear of the water before turning in mid-air, inverting and landing on their back with a loud, percussive splash. Sharks were observed breaching on 15 occasions. Breaching has been suggested to be an aspect of social behaviour that may be linked to courtship or reproduction, and appears to be a group activity. During the survey, sharks were only observed breaching when groups of sharks were present, and only sharks of mature size (over 7 metres) were recorded breaching.
The basking shark is believed to give birth to a litter of five or six live pups, each around 1.6 – 1.8 metres in length. As a result, sharks under 2 metres in length have been generally accepted as being young of the year, born in the season of their sighting. During the survey, 10 sharks under 2 metres were recorded, principally in Areas 4 and 5, to the east and west of The Lizard. This suggests that births may occur within, or near, these areas.
Collision with vessels
The waters off Cornwall are a playground for leisure boat users, attracting tourists from Europe and beyond. The area around the eastern side of The Lizard peninsula sees considerable amounts of waterborne traffic, lying as it does along the typical route to and from the busy port of Falmouth, and the popular yachting centres of the Fal, St Mawes and the Helford River. The majority of sharks recorded were sighted along the route usually taken by small craft travelling around Lizard Point to Black Head and to the East of the Manacles buoy. In recent years an increasing frequency of collision with sharks at, or just below, the surface has been reported in the yachting press, particularly from the region around The Lizard. Collision with a shark at the surface may not only result in serious injury or mortality to the animal, but may also pose a considerable risk to a small craft and its occupants. While many collisions are with boats travelling at speed, small craft manoeuvring close to sharks, in order to observe them, may also a present a risk of disturbance and accidental collision. Shark movements can be surprisingly fast and erratic.
Entanglement in fishing gear
Basking sharks are vulnerable to entanglement in a range of fishing gear, including pot ropes, trawls and bottom-set gill nets. These threats apply throughout the basking shark’s range, but are probably most severe in frontal areas. As well as being vital for sharks, the productive nature of these areas makes them highly important zones for inshore fisheries.
Where sharks and fisheries meet, there is a risk of shark entanglement. During the course of this survey, Cornwall Wildlife Trust recorded a number of basking sharks entangled in ropes attached to fixed fishing gear. There is currently no regulatory requirement to record such events or inform agencies if such an incident occurs. As it is now illegal to land and sell a basking shark, it is likely that most entangled sharks are simply dumped at sea; thus it is very difficult to evaluate the significance of this threat and develop ways to minimise it. There is an urgent need for practical approaches to minimise this risk, especially in the hotspots identified by this study.
Disturbance from marine ecotourism
One of the UK’s fastest growing tourism activities in recent years has been marine ecotourism, in particular commercial pleasure craft taking paying passengers to view marine wildlife. Around the South West, one species that is often highlighted on operators’ promotional material is the basking shark. Basking sharks do not appear to be highly vulnerable to disturbance from responsibly handled craft. However, repeated approaches may cause problems, and there is an elevated risk of collision where craft are not handled with due regard to sensible speed. The risk of disturbance or injury is particularly serious in those areas where groups have been observed and courtship behaviour recorded, as disruption of breeding behaviour could have a disastrous impact on the UK basking shark population.
Conclusions and recommendations
Few countries can boast of the number of basking shark sightings recorded in the UK each year. The results presented here form an integral component of a larger survey. A report for the Northern Ireland Environment Agency on the Northern Ireland study area was published in 2004. A report covering the surveys carried out in the Clyde Sea and the Sea of the Hebrides for Scottish Natural Heritage is in preparation and due for publication in 2009. A more detailed report of the English survey results is available at http://www.naturalengland.org.uk. Basking shark hotspots have been established in all of the areas surveyed, and a range of current and potential threats have been identified.
Over six years of study, the survey of the western English Channel has identified three areas – east and west of The Lizard peninsula and west of Land’s End – that have demonstrated consistently elevated levels of basking shark sightings during both high and low periods of general abundance. These sites are also areas in which above-average levels of human activity take place, involving both commercial and leisure activities, and where courtship behaviour has consistently been recorded. It should be noted that the areas identified here, locations at which fronts form, represent typical habitat for surface-sighted sharks. The threats that exist in these areas are by no means unique, but also exist to a greater or lesser degree at other key sites. The mitigation measures presented here could be considered equally for other such sites around the UK.
We believe that the following protective measures should be considered at basking shark hotspots:
1. Educational measures targeted at Masters of commercial and leisure craft navigating through these areas, informing them that aggregations of basking sharks may be encountered at the surface on a seasonal basis. This might take the form of information supplied via the UK Hydrographic Office, such as Notices to Mariners, electronic or paper charts, pilot books, nautical almanacs or harbour guides, and should aim to reduce the levels of surface collision, safeguarding both vulnerable sharks and small craft and their occupants.
2. A joint evaluation with local inshore fishermen to establish annual levels of shark entanglement within the sites, and to determine whether there are particular areas or types of gear that are implicated. Agreement might then be sought on voluntary avoidance of setting such gear within those localities on a seasonal basis, or when numbers of sharks are known to be present, to reduce incidental entanglement. A benefit for fishermen would be a reduction in the amount of nets/gear lost or damaged by basking sharks.
3. Further emphasis on the reduction of potential impacts of commercial marine ecotourism activities, such as an agreed speed limit in the critical areas on a seasonal basis. This might most effectively be carried out through the WiSe Training and Accreditation Scheme (http://www.wisescheme.org) and could become a mandatory part of any ecotourism operational licence.
4. Promotion of the Basking Shark Code of Conduct and The Wildlife Trusts’ public sightings recording scheme (see http:// wildlifetrusts.org for both), and greater awareness of the presence of basking sharks within these important sites.
5. Consideration of the potential application of site-based protection measures for the key sites. The forthcoming Marine Bill is due to introduce Marine Conservation Zones, a new type of marine protected area offering various degrees of protection. The potential for Marine Conservation Zones to contribute to basking shark conservation should be explored as a matter of urgency.
The project enjoyed the support of many organisations, both financially and in spirit. These include Natural England, Northern Ireland Environment Agency, WWF-UK, Earthwatch Institute (Europe), Born Free Foundation, Shark Foundation (Hai Stiftung), Shark Trust, Marine Conservation Society, Heritage Lottery Fund, National Express Group, Save Our Seas Foundation, Volvo Ocean Adventure, Esmee Fairbairn Foundation, and Canon (UK). Their support has been invaluable.
The backbone of this project were the 600 volunteers who helped to collect the data. Whilst they are far too numerous to acknowledge individually, every one of the volunteers who took part in the surveys played their role in the production of this report, and we thank them for their company and willingness to contribute to the project.