The Marine Conservation Society Basking Shark Watch annual report

Transcription

1 The Marine Conservation Society Basking Shark Watch 2009 annual report Jean-Luc Solandt (MCS Biodiversity Policy Officer) Natalie Ricks (MCS volunteer) photo: Lucy Verma 2004 Marine Conservation Society Overross House, Ross Park, Ross-on-Wye, Herefordshire, HR9 7US 1

2 2009 Results Number of Reports 2009 has seen a slight increase in the number of sightings (n=1150) from 2008 numbers (891), and is approximately half the number of the record high of 2006 (n=2,273, Figure 1), when promotion of the project was at its height, with a dedicated Project Officer in place. The total number of sharks sighted in 2009 was Figure 1. Number of reports and total number of sharks, per year

3 s harks per s ig hting This year s shark to sighting ratio (2.44) is lower than the average from the previous 22 years (3.50), indicating slightly smaller shoal sizes reported (Figure 2) Year Figure 2. Annual mean sharks per sighting,

4 Spatial Distribution Figure 3.1 Distribution of 2006 sightings Figure 3.2 Distribution of 2007 sightings Figure sightings Figure sightings 4

5 Sighting hotspots this year have remained mostly in trend with previous years (Fig ). The biggest reduction in spatial distribution of reports is from the Inner Hebrides between Mull and Cape Wrath in By contrast, Southwest England sightings appear more widely dispersed than in 2008, with more records coming from south Devon in the area of coast between Plymouth and Start Point. The 2009 sightings were once again dominated by reports from the Isle of Man (74%, n=863), with other hotspot regions much lower in number of sightings: Southwest England (18%, n=213) and Scotland (6%, n=67) with the other sightings (1%, n=7) coming from the Channel Islands (1), Northern Ireland (4), and Ireland (2). There has been an increasing trend since 2006 of reports from the Manx Basking Shark Watch project dominating UK records ( This is because there has been success at promotion of the project from a single organization for a relatively small community. MCS have been informed by the project staff that there are likely to be a number of repeat sightings a problem they are attempting to remedy by employing constant effort-based watches, in tandem with their public sightings scheme. The Marine Conservation Society has, by contrast, not widey promoted the project in the media and in wildlife-interest publications since 2007, when a dedicated project officer was last in post. Another contributing factor is that there are a number of other basking shark sightings reporting schemes around the UK, which although willing to share data, are likely to have caused some confusion for marine wildlife watchers. The Marine Conservation Society works with the Wildlife Trusts and Shark Trusts as joint Lead Partners on the Biodiversity Action Plan for the basking shark, and regularly share data. Southwest England 19% other areas 1% Scotland 6% Isle of Man Scotland Southwest England other areas Isle of Man 74% Figure 4. Regional distribution of 2008 sightings as percentage of total

6 Scotland Figure Scotland sightings Figure Scotland sightings Considerable densities of basking sharks were recorded from Arran and The Firth of Clyde in both 2008 and 2009 (figures 5.1 and 5.2). Shark sightings from the waters of the Inner Hebrides between Mull and Cape Wrath have dropped in was one of the windiest, wettest summers on record in this region, which causes sharks to feed slightly below the surface of the sea, and impedes visibility at the coast. Colin Speedie of the Shark Trust has been recording basking sharks for a number of years in Scottish waters. He compiled an important report for Scottish Natural Heritage in 2009 detailing the locations of persistent basking shark hotspots, and recommending local protection measures to be implemented in these locations (Fig. 6). 6

7 Figure 6. Basking shark reports for western Scotland collected by Colin Speedie during Wildlife Trust surveys between 2002 and There is consistently a major number of sharks in the area surrounding the Hyskier lighthouse to Canna, and in the narrows between Coll and Tiree. There is one further hotspot to the east of Barra in the outer Hebrides. 1 Speedie CD, Johnson LA and MJ Witt (2009). Basking shark hotspots on the west coast of Scotland: Key sites, threats and implications for conservation of the species. SNH commissioned report #339. 7

8 Southwest England Figure Southwest sightings = Figure Southwest sightings The majority of Southwest England sightings were reported in Cornwall (Figures 7.1 and 7.2). These were concentrated in the area off Gwennap Head and the Runnel stone reef where the Seawatch Southwest project records all shark sightings from July October in 2007, 2008 and This project is planning on recording all marine megafauna in July - October daylight hours up until 2011 using constant effort methodology ( Figure 8. Effort-based recording involves discipline, and often hours spent observing little or nothing. However, zero counts are as important as counts of animals, as it represents genuine periods when animals aren t at surface waters. This then puts the species records into temporal perspective. This is a picture of John Galpin who observes sharks from his house on the west coast of the Isle of Man. 8

9 Seawatch-Southwest 2 results Included in our numerical analysis of results (and mapped in the 2009 charts above) are the records from the headland at Gwennap Head taken by permanent daytime observers between July 15 and October 15 (93 days), totaling almost 1,000 hours of observation (Figure 9a & 9b). 299 sightings of basking sharks were reported from this headland in 2008, with the maximum school size of 26 individuals recorded on September 19 th (Fig 9a). In 2009, only 92 sharks were reported in the three-month observation period, with a maximum school size of 13 recorded on the 25 th September (Fig 9b). Figure 9a. Basking shark frequency occurrence off Gwennap Head between July and October 2008 (source: Seawatch SW) Figure 9b. Basking shark frequency occurrence off Gwennap Head between July and October 2009 (source: Seawatch SW) 2 Data obtained from Seawatch Southwest (2009). National Oceanography Centre, Southampton 9

10 Isle of Man Figure 10a. Isle Of Man 2008 sightings Figure 10b. Isle of Man 2009 sightings British Crown and SeaZone Solutions Ltd. All rights reserved. License This product has been derived in part from material gained from the UK Hydrographic Office with the permission of the Controller of Her Majesty's Stationary Office. Not to be used for Navigation Red points on fig. 10b indicate sightings from The Marine Conservation Society Basking Shark Watch, and yellow from the Manx Basking Shark Watch. Sightings in the Isle of Man dominate the 2009 records (even more so than in 2008 up 11 from 63% of the entire sightings database, to 74% (Fig 10b)). As is usual, most sightings were from the south and southwest side of the island, where the frontal system normally lies (Fig 11&12). However, more than any previous years, there have been a large number of reports northeast of Castletown, around the Langness peninsula, and on into Douglas Bay. Figure 11. Basking shark between Port Erin and Peel on the SW coast of the Isle of Man (Pauline Oliver, 2004) 10

11 Figure 12. Frontal areas of UK seas, where water bodies of different temperatures and densities meet (left), and concentration of basking shark occurrence from archived tagged. These areas are often rich in plankton, as frontal systems often result in considerable mixing of nutrients into the water column, causing increased localized production of phyto- and zooplankton, hence attracting large shoals of planktivorous fish such as mackerel, herring, and basking sharks. (Source of figure Sims et al ). 3 Sims DW, Southall, EJ, Metcalfe JD and M Pawson (2005). Basking shark population assessment. Final report for Global Wildlife Division of Defra. 11

12 Sightings per region over time Figure 13. Numbers of sighting reports in regional sighting hotspots in recent years 4. Sightings from Scotland are very low, down again from 2008 by almost a third, and since 2007 from 345 to 67 an 81% decrease in two years (Figure 13). Southwest sightings reported to the MCS Basking Shark Watch online recording form, Seawatch SW and The Cornwall and Devon Wildlife Trusts (213) decreased this year by just under 54% - that is two falls of over 50% in two years (Figure 13). A similar decrease in shark numbers was also recorded at Gwennap Head between 2007 (656) and 2008 (299) and 2009 (92) of 86%. 4 Data for 2009 includes both the Gwennap Head surveys by Seawatch Southwest, and the Manx Basking Shark Watch data. All data for the entire Southwest England records includes records from Devon and Cornwall Wildlife Trust, and direct reports sent to MCS Basking Shark Watch. 12

13 Seasonal Distribution Figure 14. Total number of sighting reports, per month, in three hotspot regions throughout The poor weather over the months of June, July and August in southern Britain probably led to considerable mixing of the upper water layers, so surface deeper water stratification didn t fully develop until later on in the year (Fig. 14). A consequence of this would be that the copepod blooms, often seen in huge densities at the surface in early spring and summer particularly in southwest England waters, simply weren t as concentrated in surface waters. Shark therefore wouldn t have been feeding at the upper surface where the general public would have recorded them. Two further reasons may be valid for low shark numbers during periods of wet and windy weather: (1) poor visibility at sea - it is simply harder for individuals to see sharks at the surface, and (2), there are likely to be fewer people actually walking and enjoying the coast in times of poor weather, so one could say that the effort to record sharks is likely to be lessened during poor weather conditions. 13

14 Frequency Shark Size Distribution Of the 2,806 individual sharks, size estimates were reported for 1867 (67%) of the sharks. The modal and average shark size is between 4-6 metres as illustrated in figure 15 and through analysis of the median of each size range category. The estimated mean size of each individual sighting (frequency multiplied by the group median) is 5.40 metres Size category (metres) Figure 15. Basking shark overall size distribution,

15 Total frequency of estimated size Southwest England Isle of Man Scotland other regions Size category (m) Figure 16. Regional variation in basking shark size in 2009 Figure 17. Basking shark in amongst schooling fish, Cornwall (Rachel Hoskin). 15

16 Shoal Size The number of sharks reported in shoal sizes above 5 has decreased as a proportion of overall shoal sizes in The results are similar to previous years for sharks in shoals of between 2 and 4 individuals. There were no large shoals above 50 individuals reported to our project website in One shoal of 40 individuals was reported from the Isle of Man, the other of 40 individuals was reported from Sennon Cove (Land s End). Table 1. Occurrence of different shoal sizes in 2007, 2008 and 2009, and overall Shoal 2009 % 2008 % 2007 % % size n/a n/a n/a Figure 18. Basking shark shoaling behaviour, Gulf of Maine, USA (copyright, Wilson 2004). 16

17 Breaching and mating Figure 19. Occurrences of breaching reported to MCS Basking Shark Watch and other surveys. 21 breaching events were reported throughout 2009 (Fig. 19). 15 of these were reported from the south and west of the Isle of Man, four from the southwest of England, and one in Scottish waters. There was also one compelling account of mating behaviour from Carn Gloose which is at Land s End (very near to St. Just). Here, the report said that five sharks were 50 to 100 metres offshore, one of which was a 10 metre shark and 2 were very close touching each other and rolling beneath each other, perhaps mating. Two others were out in the tide. At least five separate reports of potential mating / courtship events were reported from the Isle of Man. Mating behaviour, and strong evidence of courtship has also been observed on the Isle of Man by John Galpin, who has been witnessing basking sharks out of his Niarbyl Bay bedroom window for 15 years. The success of the MCS and Manx Basking Shark Watch projects has definitely led to increased interest in witnessing the interaction and behaviour of this species. Please report your basking shark sightings online to we need all the sightings you provide in order to understand the long-term trends of shark movements. 17

18 Basking shark conference 2009 The first international conference on basking sharks was convened on the Isle of Man from 2-6 August to bring together some of the emerging scientific findings of the ecology, genetics and behaviour of this enigmatic species. It was organized by the Isle of Man government Wildlife Division, the Manx Wildlife Trust and the Save Our Seas Foundation. A short slide film can be seen about the conference - presented by Dr Rupert Ormond, Chief Scientist of the Save Our Seas Foundation. The meeting was set up in order to promote the following: 1. Promote international collaboration to establish the status of basking sharks globally. 2. Develop research to assess the extent of individual movement between regions. 3. Develop strategies to improve conservation, and 4. Refine approaches to management. The meeting was followed up by a meeting of the Biodiversity Action Plan for the species, which essentially supported the recommendations of the conference, for: 1. Increased scientific collaboration across international boundaries (over which the shark migrates). 2. Further research into hotspots. 3. Identification of local threats to basking sharks, and defining harassment of the species. 18