Marine Conservation Society Basking Shark Watch Overview of data from 2009 to 2013 Jean Luc Solandt and Estelle Chassin Edited by David Jay Highlights The location and persistence of hotspots is reaffirmed for the Isle of Man, West Scotland and southwest England. Peak sightings continue to be made in June for Southwest England and the Isle of Man, and August for Western Scotland. Continuing increase in average size of sharks observed, potentially indicating population recovery. One sighting of 918 individuals in 2012 off Tiree, western Scotland, in August 2012. Offshore wind farm project abandoned due to basking shark presence on site. Introduction The Marine Conservation Society Basking Shark Project was started in 1987 to raise awareness of the species and its major threats, to record and publicise hotspots of basking shark sightings in UK waters, and to provide conservation recommendations to national and international authorities. Since then MCS has succeeded in raising awareness of the species through the media, digital channels and through public talks. MCS is joint lead partner of the Biodiversity Action Plan for the basking shark and was instrumental in securing its listing on the Wildlife and Countryside Act and the Convention on Migratory Species. Recently, MCS has compiled its basking shark data together with that of the Wildlife Trust and Shark Trust, and worked with scientists at the University of Exeter to publish an analysis of over 20 years of basking shark data (1987-2008) in UK waters (Witt et al. 2012). Their analysis revealed: There are three main surface-feeding basking shark summer hotspot areas around the UK that remained consistent between years. These are in Southwest England (Cornwall, Devon and the Isles of Scilly), the Isle of Man, and Western Scotland, particularly the Sea of the Hebrides. The length of the summer basking shark season for surface sightings is strongly affected by the North Atlantic Oscillation (the annual change in air pressure difference between the Azores and the Arctic). A more extreme pressure difference leads to more settled, hotter summers when the highest number of shark sightings is recorded. This is partly because of more reliable presence of plankton at the surface, and partly because weather conditions provide better visibility and encourage more people to spend time on the water. There appears to be an increase in the average size of sharks over the period which may indicate a recovery of the shark population in UK waters, as more sharks are left to mature and grow in the absence of hunting. The purpose of the latest report (of which this is a summary) is to analyse and present data from 2009-2013 (following the first study) sourced from Basking Shark Watch and shark recording schemes, and add to the earlier findings.
1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 Number of Sightings Number of sharks BASKING SHARK WATCH REPORTS Number of reports 3000 9000 2500 7000 2000 5000 1500 1000 3000 Number of Sightings Number of Sharks 500 1000 0-1000 Number of reports, and total number of sharks, per year 1987-2013 in the UK. The highest annual number of Basking Shark Watch sightings received since 1987 was over 2000 reports submitted in 2006, the year which saw sightings schemes developed by the Wildlife Trusts, the launch of the Manx Basking Shark Watch project and the recruitment of a Basking Shark Watch officer at MCS. Following this there was an average of 1060 basking shark reports per year between 2007 and 2013, with the lowest number of reports being 637 in 2011 (dominated by Isle of Man sightings), and the highest 1621 reports in 2009. Sharks Per Sighting The number of sharks per sighting has remained reasonably consistent, at just under 3, throughout the whole period 1987-2013. Often, however, the years in which the lowest numbers of separate shark sightings were reported also saw highest number of sharks reported in each sighting. 1
GEOGRAPHIC DISTRIBUTION OF SIGHTINGS Basking shark hotspots Distribution of 2013 sightings Distribution of 1987-2013 sightings The geographic distribution of basking shark sightings from 2009-2013 was very consistent with observation from the 1987-2008 analysis. This shows clear hotspots in Southwest England, the Isle of Man and Western Scotland (shown in these maps from the latest year and the whole 28 year period). It has been shown that these areas all provide high concentrations of plankton (microscopic marine animals, the basking shark s primary food) at surface level, due to the nature of the prevailing water currents at the site. Periodically there is a surge in reports from other areas (such as the southern Moray Firth in 2013) where an unusual abundance of sharks is reported. Historically there have been similar spikes in sightings from the Hurd Deep in the English Channel and the west of Pembrokeshire. Typically these areas are already known to be hotspots for other species such as commercial fish stocks or sightings of whales and dolphins. 2
Hotspot Sightings West Scotland, 25.6 Isle of Man, 26.9 Southwest England, 41.1 Southwest England Isle of Man West Scotland East Scotland Wales Northern Ireland Ireland SE England NE England France Regional distribution of 1987-2013 sightings. Of the three hotspot areas the largest number of reports over the period came from Southwest England, with Western Scotland and the Isle of Man providing slightly fewer, but comparable numbers to each other. It is worth bearing in mind that the number of reports is dependent not just on the number of sharks but also on the level of human activity at the coast and visibility conditions - more reports are likely to come from more populous areas, or those frequented by tourists, with clearer weather. Hotspot Characteristics Sightings in Cornwall show some distinct patterns, including high levels around the Lands End peninsula and to the west of The Lizard. There is also a cluster of sightings offshore to the north of Lands End which coincides with the Cape Bank reef complex. Since 1987 the number of sightings in Cornwall has risen steadily while the number from Devon (which was lower initially) has dropped further this may in some part be due to publicity efforts intensifying in Cornwall over the period whilst not being pursued in Devon. Hotspot sightings to the west of Scotland are concentrated in the Clyde Sea (Northeast of Ayr and around the Isle of Arran), to the north and west of Mull (and around Tiree and Coll), and around the small Isles of the Inner Hebrides and Hyskeir lighthouse. Many sightings have been recorded in areas currently being evaluated for designations as Marine Protected Areas, especially the site around Rum and Canna. A survey in 2012 to the southwest of the Island of Tiree recorded 918 basking sharks in a single survey the largest single sighting in the whole database. Shark sightings around the Isle of Man are much more abundant to the west of the island due to the prevailing onshore winds. The density of sightings per kilometre of coast for this region is the greatest for the entire UK over the period 1987-2013. However the number of sightings in this hotspot fell each year from 847 in 2009 to 129 in 2012, although it rose again slightly to 160 in 2013. 3
Number of sightings SEASONALITY OF SIGHTINGS Seasonal Overview 200 150 100 50 Isle of Man West Scotland Southwest England Other Regions 0 Average number of sightings reports per month, 2009-2013. The timing of the basking shark season was similar in both Southwest England and the Isle of Man. This typically started in April (in Southwest England) or May (in the Isle of Man) and rose sharply to a peak in June, with sightings then gradually tailing off and usually ending in October or November. There was, however, a second smaller peak in shark sightings in Southwest England waters in August. Overall the season for the Isle of Man was shorter, running from May to September rather than April to October or November. Sightings in Scotland showed a distinctly different pattern, starting in May and rising more gradually to peak in August, then falling off rapidly to end in October or November. SHOAL SIZE Relative occurrence of difference shoal sizes, 1987-2013. Shoal size Range Number of sightings % 1 9728 58,01 1 to 5 5110 30,47 6 to 10 1009 6,02 11 to 20 578 3,45 21 to 50 264 1,57 51 to 100 64 0,38 101 to 200 11 0,07 201 to 500 4 0,02 >501 1 0,01 4
Proportion of total sharks Although recorded shoal sizes ranged from 1 to over 900, almost 90% of sightings were of five animals or fewer. Congregations of between 100 and 300 individuals were reported in all the key hotspot locations, as well as southern Ireland and north Wales, but the only sightings of shoals of 300-499 were in Southwest England. Just one sighting of over 500 animals was recorded, with 918 individual sharks counted in the waters to the southwest of Tiree in August 2012. The sighting was reported during Environmental Impact Assessment boat surveys (carried out on behalf of Scottish Natural Heritage) relating to the proposed construction of an offshore wind farm at the site. The proposal was subsequently dropped, with the shark observations being cited as part of the reason for the decision. SHARK SIZE There has been a small but significant change in the relative sizes of observed sharks since 1987. Sightings of larger sharks (longer than 6 metres) have been on the increase since 2005 whilst there has been a decrease in the proportion of smaller sharks (less than 4 metres) over the whole 28 year period. Witt et al (2012) suggest that this is may be an indication of population recovery from historical over-exploitation. The reduced numbers brought about by continuous hunting will initially increase with the birth and survival of more young sharks, which over time will mature and grow (without being hunted and killed) leading to more larger animals being observed. 0.50 0.40 0.30 0.20 0.10 1987-2013 2006 2013 0.00 <2m 2-4m 4-6m 6-8m >8m Basking shark size distribution in 2006, 2013 vs. 1987-2013. OTHER OBSERVATIONS Between 2001 and 2011 there were 24 sightings specifically mentioning courting or mating behaviour. This is variously described as parallel swimming (nose to tail), sharks circling each other with evidence of copulation, and vigorous subsurface twisting and circling. Sharks of 2m or under were rarely observed, but when seen they were often with other sharks in loose groups, and frequently swimming very close to adults. From 1992-2013 there were 63 reports of sharks suffering ship strike or entanglement in fishing gear. Entanglement in static fishing gear, such as pot lines and gill nets, are most frequently recorded, but there were reports of one shark caught at a depth of 150 metres in the Shetland Islands and another at nearly 250 metres in the seas to the West of Ireland. Basking sharks are more 5
likely to survive such incidents than most other fish, with 6 reports of sharks surviving being caught and then released. There were also several reports of free swimming sharks with obvious marks from nets or rope on their bodies. Conservation Implications The study confirms the importance of Cornish sites for the UK basking shark population. In particular there are high levels of sightings in and around the European Marine Sites (EMS) of Lands End, Cape Bank, Lizard and Fal and Helford. These EMS are not currently designated for the protection of sharks or any other any mobile species, however the report suggests that seasonal protection measures could be considered in these areas, including: (1) Restrictions on boat speed by recreational and commercial vessels. (2) Agreement with fishers to restrict by-catch by limiting set nets in surface waters. (3) Reporting by-catch of sharks to local authorities. (4) Developing Codes of Conduct to assist the implementation of these recommendations. These new findings also confirm the importance of the inner south eastern Minch around Coll and Tiree for basking sharks. This area is already designated as a Marine Protected Area (MPA), but sharks are not currently listed among the key species. Given its status, however, seasonal management measures such as those listed above would seem to be appropriate. Taking the extra step of amending the listing to include basking sharks could also enhance the tourism potential for the area by making it the UK s first basking shark MPA. Enhanced understanding of basking shark presence has recently contributed to a potentially damaging offshore wind farm project being abandoned. The planned Argyll Array, to the West of Tiree, could have led to serious environmental disruption on and around the site. An Environmental Impact Assessment boat survey recorded a sighting of 918 sharks in August 2012. In December 2013 Scottish Power announced that they would be dropping the project, citing the presence of basking sharks as one of the reasons, along with logistic difficulties at the site. Acknowledgments Original report prepared by Dr Jean-Luc Solandt and Estelle Chassin of the Marine Conservation Society. Thanks go to all the collaborators, especially: RSPB Tiree, Manx Basking Shark Watch, Seawatch Foundation, Hebridean Whale and Dolphin Trust, the Wildlife Trust, Seawatch SouthWest, the Shark Trust, Cornwall Wildlife Trust, Biscay Dolphin Watch, Colin Speedie, Dr Matthew Witt (University of Exeter Cornwall Campus),Stephen Frampton and David Jay. Reference Witt MJ, Hardy T, Johnson L, McClellan CM, Pikesley SK, Ranger S, Richardson PB, Solandt JL, Speedie C, Williams R, Godley BJ (2012). Basking sharks in the northeast Atlantic: spatio-temporal trends from sightings in UK waters. Marine Ecology Progress Series 459:121-134 accessible here http://www.seaturtle.org/mtrg/pubs/ 6