Seawatch SW: Annual Report 2008

Executive summary

SeaWatch SW is a volunteer-based project that started in 2007 and is scheduled to run until 2011 at least. The main aim is to understand better the distribution and behaviour of migratory marine megafauna, for both scientific and conservation purposes. The priority is the Critically Endangered Balearic Shearwater, but other migratory seabirds as well as Basking Sharks, Ocean Sunfish and cetaceans are the focus of intensive monitoring off southwest England.

Balearic Shearwater, Scilly pelagic, Isles of Scilly (Photo: Gary Thoburn)

Part 1: Balearic Shearwater monitoring in UK and Irish waters

A total of exactly 1000 Balearic Shearwater records were submitted to SeaWatch SW and/or BirdGuides from the UK and Ireland in 2008, relating to a maximum of 5391 birds. These figures are comparable to those in 2007, when 834 records referring to a maximum of 5153 birds were received. It should be noted that these maximum totals will include significant duplication, as some birds may remain in one area for several days or are recorded passing multiple watchpoints.

The distribution of Balearic Shearwater sightings in 2008 was also comparable to 2007. After a small influx into southwest England in January, relatively few were seen until birds returned to southwest coasts in June. Numbers built up to a peak in August, at which time birds began to penetrate north into the North and Irish Seas. A rapid retreat to the southwest occurred during October, and very few remained in November and December. Overall, the pattern of Balearic Shearwater sightings in 2007 and 2008 appears to have been remarkably similar.

As with 2007, about two-thirds of Balearic Shearwater records in 2008 came from southwest England, with less than 2% of records coming from Scotland. A significant mid-winter count of about 50 birds off Portland Bill (Dorset) on 13 Jan coincided with unprecedented winter numbers off northern Brittany, and was associated with an influx of 20,000 Razorbills and other seabirds. Likewise, the peak 2008 count of 116 birds off the SeaWatch SW watchpoint at Gwennap Head (Cornwall) on 6th Oct also coincided with unusually large numbers of birds off northwest France.

Part 2: Land-based monitoring from Gwennap Head (Cornwall)

Effort-based monitoring of Balearic Shearwaters, and other target species, was undertaken at Gwennap Head (Cornwall) between 15th July and 15th October 2008. About 40 volunteer observers helped man the watchpoint for 93 consecutive days, with 'dawn-to-dusk' observations totaling almost 1000 hours.

Balearic Shearwaters were seen on 90 out of 93 survey dates, with a maximum total of 1029 birds recorded. This is a slight decrease on 2007, when birds were seen every day and a total of 1361 birds were recorded. However, the pattern of movement was very similar to 2007, with most birds (95.5%) seen flying west, and 60% seen during morning sessions prior to 12:00. The most interesting record was of two birds flying west on 6th October that were attacked over the sea by an escaped falcon; luckily they both evaded capture by plunge-diving into the water!

Totals of other shearwater species seen during the Gwennap Head survey included 26,132 Manx Shearwaters, 561 Sooty Shearwaters, 499 Cory's Shearwaters and 42 Great Shearwaters. The total for Sooty Shearwater is comparable to 2007, but the other three species saw big increases on the 2007 totals. In particular, an impressive influx of Cory's Shearwaters peaked at 377 on 29th–30th July, coincident with a period of rapidly increasing sea surface temperature and a low-pressure system moving north from west Iberia.

Numbers of Arctic Skuas, Great Skuas and Kittiwakes off Gwennap Head all peaked during mid-September, which is about two weeks earlier than in 2007. Arctic Skuas and Kittiwakes in particular appear to migrate together, with the skuas relying on the Kittiwakes for food through klepto-parasitism. All three species were seen in similar numbers to 2007, but there was no repeat of the pre- and post-roost movements off Gwennap Head noted in October 2007.

Small numbers of Guillemots and Razorbills were seen in late July, before most birds departed for offshore waters. Both species then returned in numbers in early October, although Razorbills were much commoner than Guillemots. A total of 129 Puffins were recorded, mostly during July. This is a slight increase on the 104 seen in 2007, and many sightings again referred to birds feeding over Runnelstone Reef.

Fulmars, Gannets and Shags were not systematically recorded due to excessively high numbers and/or local breeding populations. A sample count of Fulmars and Gannets on 24th–25th August produced 211 and 4101 birds, respectively, and counts of Shags feeding or day-roosting off Gwennap Head peaked at 45 on 24th July (compared to a peak of 50 in 2007). There were several records of three-figure feeding flocks of Gannets, often in association with Common Dolphins. Two migrating flocks of about 20 Cormorants were seen moving east during the autumn.

Gannet off Gwennap Head (Photo: Marcus Ward)

Records of rare and scarce seabirds included a Fea's Petrel on 25th August, two Long-tailed Skuas on 7th October and a Roseate Tern on 18th July. Also of note were a Red-necked Grebe, 516 European Storm-petrels, two Leach's Storm-petrels, 41 Pomarine Skuas, three Sabine's Gulls, five Little Gulls, 59 Mediterranean Gulls and up to 24 Black Terns. An influx of Grey Phalaropes in September and October included up to 65 lingering offshore, with many seen associating with feeding Basking Sharks.

Other migrant waterbirds recorded off Gwennap Head included four Barnacle Geese on 5th October, and totals of 25 Little Egrets, 50 Grey Herons and 71 Whimbrel. Particularly unusual records included a Black-tailed Godwit flying west in the company of five Manx Shearwaters on 13th August and a Purple Sandpiper on 21st July. Probably the most bizarre sightings were of a flying cow rescued from the base of the cliff by a Royal Navy helicopter, and a trio of well-meaning mourners who unknowingly scattered the ashes of a loved one over the project co-ordinator while he was sitting below them at the watchpoint!

A first for SeaWatch SW a cow 'flying' north over the watchpoint! (Photo: Russell Wynn)

Migrant land birds seen by SeaWatch SW observers around Gwennap Head and nearby Porthgwarra Valley included Corncrake, Dotterel, Pectoral Sandpiper, Short-eared Owl, Wryneck, Melodious Warbler, Yellow-browed Warbler, Firecrest, Pied Flycatcher and Common Crossbill. At least six different colour-ringed Choughs were seen, including two in October that were also seen in October 2007, and two adults and two juveniles on 1st August.

A notable passage of falcons took place in the autumn, peaking in late September and early October. Two juvenile Hobbies were seen on 26th September and there were several records of migrant Kestrels and Merlins heading out to sea between 9th and 14th October. Hunting was noted on several occasions, with a Kestrel seen catching grasshoppers, Merlins seen chasing butterflies and Meadow Pipits over the sea, and Peregrines seen attempting to take Feral Pigeons, Kittiwakes and even a Chough!

Five species of cetacean were recorded off Gwennap Head during the survey period. Minke Whales were seen on 15 dates, with 33 individual sightings (compared to 44 sightings on 19 dates in 2007). It was a poor year for Risso's and Common Dolphins, with records of Risso's Dolphins on just three dates in September (compared to 15 dates in 2007). A maximum total of 384 Common Dolphins was a marked decrease on the 1600 seen in 2007, and the peak day count was just 50 on 15th September. Common Dolphins were seen bow-riding with local fishing boats on several occasions.

Bottlenose Dolphins were seen in similar numbers to 2007, with regular sightings of one to three animals and a pod of seven or eight animals that included one or two calves. A large pod of 34 animals on 12th October was seen to contain at least four mother-calf pairs.

Harbour Porpoise was the most regularly encountered cetacean, being seen on over 50% of dates. The cumulative total of all sightings was 407 animals, similar to the 2007 total of 443. It was notable that Harbour Porpoises disappeared when large numbers of Bottlenose Dolphins were in the area, presumably due to the latter species bullying its smaller relative.

The Grey Seal haulout located just to the west of Gwennap Head hosted a peak of 18 animals on 16th September, similar to the peak of 21 on 2007. A maximum total of 57 Ocean Sunfish were seen; this is an increase on the 2007 total of 35, largely due to a marked influx of 26 between 26th and 28th July. This influx was at the end of a period of rapidly increasing sea surface temperature, and included several records of breaching animals.

Bull Grey Seal off Gwennap Head (Photo: Russell Wynn)

It was a relatively poor year for Basking Shark sightings in southwest waters, and this was reflected in the data collected from Gwennap Head. The total number of surface sightings was 299, less than half the 2007 total of 656 sightings. Very few sharks were recorded in July or August, and numbers peaked during a two-week period in mid-September with a few lingering into October. The highest count seen in a single scan was of 26 on 19th September. Breaching was noted on three occasions, and apparent courtship behaviour, including 'nose-to-tail following' and 'ring-circling', was sporadically recorded.

For the second year running, the low numbers of sharks seen in mid-summer, combined with the late peak in September, can likely be attributed to seasonal weather patterns. Unsettled weather in mid-summer in both years has hindered development of plankton blooms, and the sharks' zooplankton prey has been widely scattered due to intense mixing of surface waters. In September, the weather has become more settled, with satellite images revealing concentrations of plankton along thermal fronts off Gwennap Head, coincident with increases in shark sightings. Interestingly, peak counts of sharks often coincide with peak numbers of cetaceans, indicating that the plankton blooms are also attracting small shoaling fish, which are a favoured prey of whales, dolphins and porpoises.

Disturbance by boats, kayaks and even a helicopter was seen to affect the short-term behaviour of certain species. Grey Seals at the haulout west of Gwennap Head were frequently flushed into the water by kayaks and leisure boats approaching too closely, while, on a couple of occasions, Basking Sharks were nearly struck by fast-moving boats moving through the area. Leisure boats were also frequently seen approaching Basking Sharks to within a few metres, causing them to submerge. Encouragingly, the small fleet of local fishing boats that operate around Runnelstone Reef were not seen to have any significant impact on marine megafauna during the three-month survey period.

Part 3: Land-based observations from sister sites in southwest UK

Intensive observations were also carried out at three sister sites in southwest UK during the SeaWatch SW survey period between 15th July and 15th October. The sister sites are Berry Head (Devon), Trevose Head (Cornwall) and Strumble Head (Pembrokeshire), and they contributed almost 900 hours of additional observational data during the survey period. These observations help to provide a regional context for Gwennap Head data.

A table showing the rates of birds per hour passing the four SeaWatch SW watchpoints between 15th July and 15th October 2008 is shown below, although note that only those species passing at rates >0.2 birds per hour are listed:

Species	Gwennap	Berry	Trevose	Strumble
Total hours	966	190	165	526.5
Balearic Shearwater	1.07	2.61	2.37	0.34
Common Scoter	0.60	1.23	1.85	6.90
Cory's Shearwater	0.52	0.54	0	0
Sooty Shearwater	0.58	0.45	0.68	0.19
Manx Shearwater	27.05	11.34	621.52	-
European Storm-petrel	0.53	1.21	1.01	0.16
Pomarine Skua	0.04	0.31	0.08	0.06
Arctic Skua	0.69	2.75	0.76	0.96
Great Skua	0.36	1.03	0.74	0.41
Kittiwake	9.68	-	16.53	-
Sandwich Tern	0.36	2.11	3.04	2.15
Common/Arctic Tern	1.07	11.52	2.27	2.36
Guillemot/Razorbill	3.12	-	53.92	-
Puffin	0.13	0.05	0.10	-

The above table reveals some interesting patterns, although variable effort between sites means direct comparisons should be treated with caution. Balearic Shearwaters were seen passing the three sites in southwest England at rates >1.0 birds per hour, but fewer were seen off Strumble Head. In addition, the influx of Cory's Shearwaters in late July was picked up at Berry and Gwennap Head on the southwest coast of the UK, but none of these birds were seen off Trevose or Strumble Head to the north. Common Scoters are three times more abundant off Strumble Head than the other sites; these birds are passing south through the Irish Sea to wintering grounds off south Wales, and don't make it as far as southwest England. Common/Arctic Terns and skuas are most abundant off Berry Head; these birds will have moved west through the English Channel from the North Sea, but evidently detach from the coast before reaching Gwennap Head.

A summary table showing the total number of seabirds and total number of cetacean/fish sightings seen from the four SeaWatch SW watchpoints between 15th July and 15th October is shown below:

Species	Gwennap	Berry	Trevose	Strumble
Total hours	966	190	165	526.5
Balearic Shearwater	1029	496	391	181
Red-throated Diver	7	0	1	37
Black-throated Diver	1	0	1	0
Great Northern Diver	2	2	4	4
Cory's Shearwater	499	103	0	0
Great Shearwater	42	7	3	1
Sooty Shearwater	561	86	113	99
Manx Shearwater	26132	2155	102550	-
European Storm-petrel	516	230	166	83
Leach's Storm-petrel	2	0	2	0
Grey Phalarope	160	3	6	4
Pomarine Skua	41	58	14	34
Arctic Skua	663	522	126	507
Long-tailed Skua	2	10	3	8
Great Skua	347	195	122	216
Meditteranean Gull	59	10	14	59
Little Gull	5	0	4	27
Sabine's Gull	4	13	7	17
Yellow-legged Gull	0	4	2	0
Kittiwake	9348	-	2728	-
Sandwich Tern	352	401	501	1130
Roseate Tern	1	1	1	3
Common/Arctic Tern	1029	2188	374	1240
Little Tern	1	1	5	0
Black Tern	25	18	5	87
Guillemot/Razorbill	3014	-	8896	-
Puffin	129	9	17	-
Minke Whale	33	0	0	1
Risso's Dolphin	7	2	0	0
Bottlenose Dolphin	106	18	0	2
Common Dolphin	384	0	22	120
Basking Shark	299	1	1	4
Ocean Sunfish	57	1	1	26

Harbour Porpoises are regular at all four sites, but other cetaceans are most commonly encountered off Gwennap Head. In addition, very few Basking Sharks were seen away from Gwennap Head, although Ocean Sunfish were recorded in reasonable numbers off both Gwennap and Strumble Head. Other interesting sightings included a Thresher Shark off Berry Head on 25th July, and an unidentified turtle off Strumble Head on 27th September.

One of the most intriguing events of 2008 was a series of sightings of Yelkouan-type shearwaters off southwest England during the late summer and autumn. Yelkouan Shearwater is the eastern Mediterranean counterpart of Balearic Shearwater, and has different structure and plumage to that species. There are currently no accepted records for the UK. However, the taxonomic situation and identification of Puffinus shearwaters from the Mediterranean region is highly complex: for example, small numbers of birds present on Menorca apparently show characteristics intermediate between Balearic and Yelkouan Shearwaters.

The first sighting of a Yelkouan-type shearwater was of a lingering bird seen well and photographed off Berry Head alongside a Balearic Shearwater on 29th July, allowing structural and plumage difference to be documented. A series of reports of this, or other pale Yelkouan-type shearwaters, then came from southwest Cornwall during August. The final sighting of one of these birds was off the SeaWatch SW watchpoint at Gwennap Head on 6th October, although this latter record was possibly just a pale Balearic Shearwater. The photos below show the Berry Head and Gwennap Head birds; they are both captioned as Yelkouan-type shearwaters as precise identification is yet to be determined, and may not even be possible given current knowledge. A short article on these birds is currently in preparation and will be uploaded on to the SeaWatch SW website in due course.

Top Yelkouan-type shearwater, passing Berry Head on 29th July (Photo: Mark Darlaston)
Bottom Yelkouan-type shearwater (left), passing Gwennap Head with a Balearic Shearwater (right) on 6th October (Photo: Russell Wynn)

Part 4: Small boat surveys in the western English Channel

Marinelife again worked closely with SeaWatch SW during 2008, and carried out small boat surveys of marine wildlife offshore of southwest England for the second year in succession. Despite the unsettled summer weather, 43 surveys were undertaken between March and November, covering 2002 line-km.

Relatively few Balearic Shearwaters were recorded in 2008, with just odd ones and twos in offshore areas, and regular sightings of up to eight birds in July in the coastal waters around Portland Bill (Dorset). Over 200 European Storm-petrels and 70 Great Skuas were also seen, often in association with fishing boats. Other notable seabirds included 14 Black Terns, a Roseate Tern, and small numbers of Sooty Shearwater, Puffin, Pomarine Skua and Grey Phalarope. However, the avian highlight was probably a male Montagu's Harrier seen heading north about 50 km south of Portland Bill on 31st May.

White-beaked Dolphin in Lyme Bay (Photo: Adrian Shephard/marine-life.org.uk)

The small boat surveys again encountered White-beaked Dolphins in Lyme Bay, with up to seven animals recorded sporadically throughout the year. The presence of a calf in March confirms local breeding at what is the most southerly known site for this cold-water species in Europe. Two sightings of Long-finned Pilot Whale and a single Humpback Whale on the southern margin of Lyme Bay were also particularly notable. Other cetaceans recorded included regular Harbour Porpoises and occasional Minke Whale, Risso's Dolphin, Bottlenose Dolphin and Common Dolphin, especially in the western half of Lyme Bay.

Part 5: SeaWatch SW project news

SeaWatch SW and SAHFOS co-ordinated the second South West Marine Ecosystems (SWME) meeting, held in Plymouth on 12th December 2008. About 40 invited representatives of various science and conservation organisations were in attendance, and had the opportunity to present and discuss results of marine wildlife monitoring during the year. The main themes were new arrivals of southern invertebrate and fish species, the effects of unsettled summer weather on breeding seabirds and sightings of Basking Sharks, and the continued incidence of cetacean strandings in southwest England.

SeaWatch SW and Marinelife data continue to contribute to various conservation initiatives, particularly relating to monitoring of the Critically Endangered Balearic Shearwater in UK and Irish waters. The importance of the Runnelstone Reef (off Gwennap Head) and Lyme Bay (off Dorset) as 'hotspot' areas for marine megafauna is becoming increasingly apparent, and data collected by our dedicated volunteer observers will guide future protection of these areas.

The SeaWatch SW website again had over 10,000 individual hits in 2008, while news items on Basking Sharks and Kittiwakes appeared in national and regional media. A total of five Masters and one undergraduate student have successfully used SeaWatch SW in their projects during 2007 and 2008, and a new NERC-funded PhD student is working full-time on project data from 2009 to 2011. This latter project will be investigating the spatio-temporal controls on distribution of migratory marine megafauna off southwest UK.

SeaWatch SW will be continuing in 2009, with public sightings and effort-based data on Balearic Shearwaters again being collected at a regional and national level. Effort-based surveys of marine wildlife will be carried out at Gwennap Head between 15th July and 15th October, with supporting observations made at sister sites in Cornwall, Devon and Pembrokeshire. Small boat surveys in the western English Channel will again provide an important offshore perspective.

Sunrise over Gwennap Head (Photo: Russell Wynn)