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Shetland Biological Records Centre

 

 

Frogs in Shetland:  a century of colonisation

Roger Riddington

This report presents the results of ‘Frogwatch’, a Shetland Biological Records Centre survey of Shetland’s Frog population in 1999.  The survey was designed and organised by Roger Riddington and Mick Clifton (Shetland Amenity Trust).  An information pack was distributed to all schools (with the help of the Education Department of Shetland Islands Council) and youth groups in March/April 1999, to all members of Shetland Bird Club, and to as many interested individuals as possible following a publicity campaign in the local media.  The survey pack aimed to provide information and awareness about Shetland’s amphibians, and also produce new records to assess the current distribution of Frogs in Shetland.

Frogs are not native to Shetland, but have been brought in by humans, initially during the late 19th century we believe, spreading throughout Mainland and as far north as Unst by the middle of the 20th century.  As well as being the initial source, humans continue to be a key factor in their distribution within Shetland (though natural movement doubtless occurs too).  Since children have had (and continue to have) a key role in the spread of Frogs in Shetland, it is entirely appropriate that this survey was targetted towards younger age-groups.

An appendix to this report describes the Frog distribution throughout Shetland in more detail, treating the main islands individually, and dividing Mainland into four.  Wherever possible, comparison is made with a similar survey in 1982, by M. G. Richardson on behalf of the Nature Conservancy Council (now Scottish Natural Heritage).

In summary, 198 records were received from 64 participants in response to the present survey.  The map on page 2 shows the distribution of Frogs throughout Shetland.  It is clear that, over the course of the 20th century (which has encompassed the majority of introductions to Shetland), Frogs have spread across all parts of Shetland, and for the most part live happily in this northern landscape.  Skerries remains the only major inhabited island or group of islands where Frogs have not established a sustainable population.  Frogs are most abundant in the wetter and richer agricultural areas of Central and West Mainland.  Distribution on some of the larger uninhabited islands, such as some of the Scalloway islands, is unclear, and perhaps depends on repeated human introduction.  High densities of nesting seabirds, particularly skuas and gulls, may restrict the population here (and this may be an important factor on Skerries too).

As might be expected, Frogs breed somewhat later in Shetland than elsewhere in the British Isles.  Typically, spawn first appears in mid- March, over a month later than might be expected in SW England.  The development of spawn into tadpoles and then Frogs also takes longer than in southern Britain, with most tadpoles appearing after the middle of April.  In 1999, the first spawn reported was on 7th March in Unst, and the first tadpoles on 29th March at Mossbank.

Frog distribution on Shetland

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Note:  Black symbols indicate records since 1990, grey symbols indicate older records.

In contrast to Frogs, there were no confirmed reports of Toads in Shetland during 1999, and it seems that these may have died out following introductions during the first half of the 20th century.  Whether this is due to different ecological requirements of Toads, who may find Shetland a less welcoming environment than Frogs, or whether the initial introductions were simply on too small a scale to establish a viable population, is not known.


Acknowledgements

This survey could not have taken place without the interest and enthusiasm of all those who participated, and sincere thanks is due to all those who sent in records.  Participants are listed in Appendix II.  Records of Frogs, and indeed any other elements of Shetland’s wildlife, are always welcomed by the Shetland Biological Records Centre, and these help to improve knowledge and understanding of the natural environment.  Please send any records to:

Shetland Biological Records Centre, Shetland Amenity Trust, 22-24 North Road, Lerwick, Shetland, ZE1 0NQ. Tel (01595) 694688. sbrc@zetnet.co.uk


Appendix I  Details of Frog distribution throughout Shetland  

Unst

Breeding was noted in three different areas during 1999:  at Uyeasound (the disused quarry and marshy area near the school), at Baltasound (Trolla Water, the small loch adjacent to the school) and in the mires at Haroldswick (predominantly along the Feall road).  At the latter site, spawn was first recorded on 7th March, an exceptionally early date for Unst.  At Baltasound, the main spawning period was mid-March.  Observations at Trolla Water revealed 90 ‘spawn masses’ on 11th March, rising to 160 by the 16th and a maximum 180 on the 24th.

Baltasound and Haroldswick would appear to be the main centres of the Frog population on Unst.  Apart from Uyeasound, breeding has also occurred at Loch of Bordastubble (Richardson, 1982).  The Unst population has received regular injections of frogspawn since the original introduction of Frogs (and Toads) by Saxby in 1931, mostly to Baltasound and Haroldswick, from Mainland Shetland.  Anecdotal evidence suggests that Hazel Laurenson, a teacher at Baltasound school in the early 1970’s, brought in spawn on a regular basis from Sandy Loch in Lerwick.  Frogs were so unusual in Unst at this time that one elderly woman, working on her croft, chased and killed one unfortunate Frog because she was so alarmed by its appearance!

Yell

The only breeding records received for Yell in 1999 were at Burravoe (where spawn was reported in March), and at Basta, where spawn appeared as usual in March/April.  Adult Frogs were reported regularly from Cullivoe between March and May, from Mid Yell in March, Aywick in April and near the Loch of Neapaback (north of Burravoe) in the summer months.

Older records suggest that spawning grounds have been known in the south of Yell (including Coppister, Ulsta and West Sandwick) since the early 1960’s at least (Richardson, 1982 and this survey).  It is believed that spawn was first brought to Basta (see above) in 1963, from stocks at West Sandwick, possibly from the Loch of Scattlands.  Records from North Yell and the crofting areas of East Yell were more frequent in 1999 than reported in the previous survey.  It seems reasonable to assume that Frogs are widely but thinly distributed across Yell.

Fetlar

The sole record from Fetlar in 1999 was a single adult in the Mires of Houbie in July. 

The only known breeding area for Frogs on Fetlar is around the croft at Velzie, north of Papil Water.  The record from Houbie perhaps indicates that Frogs are slowly colonizing the wetter areas of Fetlar.

Whalsay & Skerries

No records were received from Skerries, where there have apparently been no successful introduction attempts.

There were no sightings from Whalsay in 1999, but the survey revealed previous records of adult Frogs at both the Loch of Livister and the Loch of Huxter in the late 1990’s.

A fascinating historical account was provided by Robert Sandison, via his uncle, of a lady in Whalsay named Joan Robertson, born in 1861.  Joan Robertson would recount how, as a young girl, she and her family frequently heard the croaking of Frogs whilst working hay in the meadow of Hamister, behind North Voe beach.  This places the record in the late 1860’s or early 1870’s; well before the previous earliest record of Frogs in Shetland (Brough Lodge, Fetlar, 1895).  There seems no real reason to doubt this record.  Perhaps the only possible confusion might have been the ‘crexing’ of Corncrakes; however, these would have been familiar birds to the crofting community at this time, and anyway they would presumably have been largely silent by hay-making time.  Robert Sandison remarks also that at the end of the 19th century, Hamister meadow was a very wet place with no drainage or ditching.

North Mainland

Breeding was reported from only four locations in 1999:  by the Hillswick/Ollaberry road junction, Assater (north of Urafirth), Ollaberry (the school), and at Nissetter, by Gluss.  The earliest report of spawn in this part of Shetland came from the Hillswick/Ollaberry junction on March 22nd.  However, reports of adult Frogs were much more widespread.  In particular, there were a number of reports from the Eshaness area, whilst records from the more remote parts of north mainland Shetland (such as Tingon, the Beorgs of Skelberry and the North Roe plateau) suggest that Frogs are have now spread throughout the more inhospitable parts of Mainland Shetland.

Richardson (1982) gives a more comprehensive list of areas where breeding was reported, though he too cites Hillswick and Eshaness as areas from which records were more abundant.

Muckle Roe

Adult frogs have been seen occasionally in the Muckle Roe meadows, just south of the bridge, for the past 20 years or so, with the latest sighting being a large adult in the autumn of 1998.  These are the first documented sightings of Frogs in Muckle Roe; whilst no evidence of breeding was reported, it seems very likely that they do breed successfully on the island.

East Mainland

The children of Mossbank primary school sent in comprehensive details about their Frog sightings in the Mossbank area, proving beyond all doubt that Mossbank has a healthy population!  Date of first spawn recorded was not until March 27th (this may have been due to distribution of survey forms at about this time); the first tadpoles were recorded on March 29th, the earliest in Shetland this year.

Elsewhere, breeding was reported from Brae, Voe, Eswick and Stromfirth.  Adults were seen at Billister, North Nesting, and young frogs by Sand Water in August, at peat-cutting time.  This was a very typical sighting, and many folk encounter Frogs in the Shetland landscape when working at the peat banks during the summer.

In 1982, Richardson reported only two records from the northern parts of central Mainland (Voe, and Setter Voe), and suggested that the moorland area of the Kames might act as a natural barrier to amphibians (given the vibrant population centres in southern central and west mainland).  The batch of records this year from Mossbank, and the widely dispersed sightings elsewhere from this region, suggest that whilst the Kames might act as a barrier to natural dispersal, human-assisted movements are clearly not affected!

West Mainland

As in the previous survey of 1982, more records were received from the West Mainland than anywhere else in Shetland.  Whilst the majority of records in 1999 came from Walls and its environs (including Mid-Walls, Brough, Burrastow, Brunatwatt etc.), the grandfather of one young recorder remarked that it would be no surprise to find Frogs in any area of suitable habitat throughout the West Mainland.  Besides Walls, breeding was reported from Aith, West Houlland, West Burrafirth, Clousta, Tresta, Selivoe and Gruting.  The appearance of spawn was remarkably synchronous throughout the region. Clousta narrowly scraped into first place with spawn at Flawton on March 15th, closely followed by Brunatwatt on the 16th, then West Houlland and Troni Shun on the 18th.  Almost all the main breeding areas first reported spawn between the 15th and the 25th.  The first tadpoles were at West Burrafirth and Selivoe on April 23rd.

In addition to breeding records, adults were reported from Bridge of Walls, Bruntskerry, Sandsound and Effirth.  An interesting record from the early times of Frogs in Shetland came from Harold Bowie, now living in the West Midlands, who remembers releasing 24 young frogs at Upperskule, Twatt, in July 1937.  The young froglets were carefully brought north from Scotstown Moor, Aberdeen, and existing records suggest these would have been some of the earliest introductions to the West Mainland.

The results of the 1982 enquiry were broadly similar to the current one, though it is perhaps surprising that no records were received this year from Sandness.
 

Central & South Mainland

After the West Mainland, it is Central and South Mainland (including Lerwick and Scalloway) that scores best for Frogs in Shetland.  In fact, the widespread distribution throughout South Mainland was illustrated well by this year’s survey.  Breeding reports were received from South Whiteness, Califf and Hamars (Gott), Gremista, Staney Hill, Lerwick town centre (various localities), Lerwick Observatory and the hill area to the south, Gulberwick, Wester Quarff, Easter Quarff, Fladdabister, Cunningsburgh, Sandwick, Hoswick and Dunrossness.  Additional sightings of adults came from Scalloway, the Tingwall Valley, Clumlie, Exnaboe and Quendale.  In some areas, Frogs are clearly very abundant, such as Gulberwick, where a small garden pond at Shurton Brae was almost jammed solid with adult Frogs and spawn at the end of March, whilst another householder commented that he was feared to mow his lawn because of the inevitable carnage!  At Gulberwick, the first adult was recorded back at a well-watched pond on February 14th 1999, whilst the first records of spawn were March 14th at Gremista and March 15th in Lerwick (i.e. similar to the West Mainland).

Again, the overall results of the present survey are quite similar to the previous one in 1982, though with perhaps more records from the southernmost part of South Mainland.

Bressay

In contrast to the 1982 survey (when no records were received from Bressay), a number of records were received from the island in 1999, confirming that the suitable habitat here does indeed support Frogs.  Spawn was recorded in 1999 at Voehead, and on both sides of the track up to the Ward of Bressay (on the north-west side).  At the latter site, at least some of the spawn is known to have been introduced to the area from Gulberwick, approximately 10-15 years ago.  In addition, adult animals were reported from Cruetoun (perhaps originating from spawn collected in past years from pools on the Hill of Setter), and to the north of Grindiscol.

Burra, Trondra and surrounding islands

Breeding was reported from West Burra, at Hamnavoe school and the ‘Boggy Loch’, near Hamnavoe (where spawn was present by March 18th).  An adult was seen on Trondra in the summer.  No records were received from any of the uninhabited Scalloway islands (in 1982, there were reports from Hildasay, Oxna and Papa), though of course this may reflect observer bias rather than a real demise of the population.

Foula

The previous survey found Frogs to be relatively common on Foula, an assessment confirmed by this year’s survey.  Spawn was reported from three sites in the Hametoun area on March 10th, with 200 adults in one pool on this date!  Spawn was also recorded along the road north of the school.

Fair Isle

Spawn was reported from two adjacent crofts in the centre of the island, Field and Pund.  Adults were reported at two further sites not far from here, at Setter and at the school.  Frogs now seem well-established on Fair Isle (they were not recorded as present here in the 1982 survey).


Appendix II  List of participants in the 1999 survey.

Morag Adam Jody Johnson
Graham Ball Geoff Leask
Mr Barclay John McKee
Bruce Benson Jimmy Moncrieff
Betty Black Maurice Mullay
Jill Slee Blackadder Natasha
Harold Bowie Mark Newell
Mr & Mrs S. Brown Holly Ann Nicolson
Rebecca Browne Jim Nicolson
Alan Bull Dawn O'Donnell
Fiona Chaff Dave Okill
Nykaela Christie Mike Pennington
Robert Christie-Walterson Michael Peterson
Hannah Clifton George Petrie
Vaila Cumming Terry Rogers
Nicholas Davidson Vivian Ross-Smith
Wendy Dickson Robert Sandison
Clare Dore Sean
Paul Fisher Brian Skinner
Lesley Fitchett Alan Smith
Julie Fletcher Patrick Steer
Grant Fullerton Vic Thomas
James Garrick Ian Tinkler
Barbara Gear Stella Tuckey
Anne Halford-Macleod Val Turner
Paul Harvey Hannah & Kirsty Uttley
Ros Henderson Mrs M.J. Williamson
Jenny Heubeck Susan & Gordon Wilson
Terry Holmes  
Magnus Isbister  
Jim Irvine  
Margaret Jacobson  
Alice & Jack Jamieson  
Chelsea Jamieson  

 

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