Scottish Sanitary Survey Project
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Scottish Sanitary Survey Project Sanitary Survey Report East Burra Firth (SI 055) Aith Voe: Sletta (SI 326) February 2010 Cefas SSS F0903 V1.0 120510 Report Distribution – East Burra Firth Date Name Agency* Linda Galbraith Scottish Government Paul Shave Scottish Government Ewan Gillespie SEPA Douglas Sinclair SEPA Karen Smith Scottish Water Alex Adrian Crown Estate Dawn Manson Shetland Council Sean Williamson Shetland Council Blueshell Mussels Harvester Richard Tait Harvester * Distribution of both draft and final reports to relevant agency personnel is undertaken by FSAS. ** Distribution of draft and final reports to harvesters in undertaken by the relevant local authority. i Cefas SSS F0903 V1.0 120510 Table of Contents 1. General Description ..................................................................................1 2. Fishery......................................................................................................2 3. Human Population ....................................................................................4 4. Sewage Discharges..................................................................................6 5. Geology and Soils...................................................................................10 6. Land Cover .............................................................................................11 7. Farm Animals..........................................................................................13 8. Wildlife ....................................................................................................15 9. Meteorological data ................................................................................19 9.1 Rainfall.............................................................................................19 9.2 Wind ................................................................................................20 10. Current and historical classification status ..........................................23 11. Historical E. coli data...........................................................................24 11.1 Validation of historical data..............................................................24 11.2 Summary of microbiological results .................................................24 11.3 Overall geographical pattern of results ............................................26 11.4 Overall temporal pattern of results...................................................27 11.5 Seasonal pattern of results..............................................................30 11.6 Analysis of results against environmental factors ............................34 11.6.1 Analysis of results by recent rainfall .........................................34 11.6.2 Analysis of results by tidal height and state..............................38 11.6.3 Analysis of results by water temperature..................................44 11.6.4 Analysis of results by wind direction.........................................45 11.6.5 Analysis of results by salinity....................................................45 11.7 Evaluation of peak results................................................................48 11.8 Summary and conclusions...............................................................48 11.9 Sampling frequency.........................................................................49 12. Designated Shellfish Growing Waters Data ........................................50 13. Rivers and streams .............................................................................51 14. Bathymetry and Hydrodynamics .........................................................54 14.1 Tidal Curve and Description ............................................................55 14.2 Currents...........................................................................................56 14.3 Conclusions .....................................................................................60 15. Shoreline Survey Overview.................................................................61 16. Overall Assessment ............................................................................64 17. Recommendations ..............................................................................71 18. References..........................................................................................73 19. List of Tables and Figures...................................................................74 Appendices 1. Sampling Plan 2. Comparative Table of Boundaries and RMPs 3. Geology and Soils Information 4. General Information on Wildlife Impacts 5. Tables of Typical Faecal Bacteria Concentrations ii Cefas SSS F0903 V1.0 120510 6. Statistical Data 7. Hydrographic Methods 8. Shoreline Survey Report © Crown Copyright 2010. Food Standards Agency Scotland and Cefas. All rights reserved. iii Cefas SSS F0903 V1.0 120510 1. General Description Aith Voe and East Burra Firth are located east of St. Magnus Bay on the western coast of mainland Shetland. East Burra Firth is roughly 0.2 km in width and 0.6 km in length, and forms a sidearm of Aith Voe, which is 3.4km long by 1.3 km at its widest point. East Burra Firth is shallow, with a large intertidal area at its head, while Aith Voe has depth of up to 49 m. The nearest settlement is the village Aith, at the head of Aith Voe. This sanitary survey was undertaken in response to an application for classification for common mussels at a site within East Burra Firth. Figure 1.1 Location of Aith Voe and East Burra Firth 1 Cefas SSS F0903 V1.0 120510 2. Fishery There are three active longline mussel farms within Aith Voe and East Burra Firth, as listed in Table 2.1 below. Table 2.1 East Burra Firth and Aith Voe shellfish sites Production Area Site SIN Species East Burra Firth Aith Voe SI 055 863 08 Common mussels (East Burra Firth) (SI 055 421 08) Aith Voe: Sletta Point of Sletta SI 326 393 08 Common mussels Aith Voe: Sletta Slyde SI 326 733 08 Common mussels There are two sites within the Aith Voe: Sletta production area which is currently classified for the harvest of mussels. East Burra Firth was previously classified as SI 055 421 08 but was declassified in 2007. Although the sanitary survey was triggered by an application to harvest mussels at the site within East Burra Firth, the Aith Voe: Sletta production area is included in this sanitary survey as it is immediately adjacent to East Burra Firth. Another former mussel production area (Aith Voe: Ayres, SI 325) lies to the south of Aith Voe Sletta, and to the west of East Burra Firth. This area was declassified in 2009, and although there is a Crown Estates lease within this area, there is currently no tackle on the site. Therefore, this area will only be considered in terms of contamination sources of relevance to the active sites and its historical E. coli classification monitoring results. The Aith Voe Sletta production area is an area bounded by lines drawn between HU 3558 5927 and HU 3377 5990 and HU 3377 5990 to HU 3500 5965 and HU 3522 5800 to HU 3385 5800. The nominal RMP for this production area is located at HU 348 586. A sample location at HU 342 588 , which lies on the Point of Sletta spat line, is now noted as dormant. The boundary of the former East Burra Firth production area is an area inshore of a line drawn between HU 352 580 and HU 351 574. Figure 2.1 shows the relative positions of the mussel farms and the seabed lease areas in East Burra Firth and Aith Voe. East Burra Firth (Aith Voe) This site consisted of three mussel longlines with 6-8m droppers situated just inside the mouth of East Burra Firth. At the time of survey there was little harvestable stock present on this site. The name of the site has been changed from East Burra Firth to Aith Voe due to the application for reclassification being in the new name, although these two names and their associated SINs both represent the same site. Aith Voe: Sletta (Slyde) This site consisted of four mussel longlines with 6-8 m droppers, and was being harvested at the time of shoreline survey. 2 Cefas SSS F0903 V1.0 120510 Aith Voe Sletta (Point of Sletta) This site consists of a single longline that is used for the purpose of collecting spat only. Figure 2.1 East Burra Firth and Aith Voe fisheries 3 Cefas SSS F0903 V1.0 120510 3. Human Population Figure 3.1 shows information obtained from the General Register Office for Scotland on the population within the census output areas in the vicinity of East Burra Firth and Aith Voe. The last census was undertaken in 2001. Figure 3.1 Human Population surrounding East Burra Firth and Aith Voe 4 Cefas SSS F0903 V1.0 120510 The population immediately surrounding East Burra Firth is relatively small,, with a population of 182 for the entire census area. Population is centred around the settlement of Aith, at the head of Aith Voe, although there are dwellings spread around the shores of Aith Voe and East Burra Firth. Some dwellings in the area are believed to be holiday homes, and wildlife tours operate from the marina at Aith suggesting population may increase during the summer months. Therefore, inputs from human sewage are likely to be mainly found at Aith, and may be slightly higher during the summer months. 5 Cefas SSS F0903 V1.0 120510 4. Sewage Discharges One community septic tank was identified by Scottish Water for the area., This tank is consented to serve 300 people and discharges to Aith Voe about 300 m north of Aith and about 125 m off from the east shore of the voe, at a depth of just