SAC Monitoring: Afon Tywi Shad Egg Survey (2013 and 2014)
The Afon Tywi is designated as a Special Area of Conservation (SAC) for a number of qualifying features, including twaite shad (Alosa fallax) and allis shad (Alosa alosa). Shad are migratory members of the Clupeidae (herring) family that ascend rivers to spawn in late spring. In Britain, significant spawning populations occur in the Rivers Severn, Usk, Wye, and Tywi. Populations of both species are threatened throughout Europe, primarily as a result of barriers to migration and declining water quality.
The aim of this study was to contribute to the assessment of the condition of the shad population within the Afon Tywi SAC using egg survey data collected in 2013 and 2014.
The objectives of the study were to:
Conduct shad egg surveys on the Afon Tywi in 2013 and 2014.
Analyse and present the results relating to the spawning distribution population attribute.
Use data obtained from the genetic analysis of shad egg tissue to provide additional context for the assessment.
2013 survey
Shad eggs were recorded at seven of the 13 survey sites (54%). Each of the 13 sites was visited once. Egg sample sizes ranged from 1 to more than 100 eggs per site. The downstream limit of spawning was identified at the tidal limit (Site 16), while the upstream limit was recorded at Manordeilo (Site 11). A total of more than 177 eggs were recorded. The identification of shad eggs was confirmed through genetic analysis at two of the three selected sample sites.
2014 survey
Shad eggs were recorded at eight of the 14 survey sites (57%). Seven sites were visited twice (50%), and four sites were visited three times (29%). The 14 sites were surveyed over six days between 16 May and 11 June 2014 by a team of 13 surveyors.
This dataset provides information on the distribution and spawning activity of shad within the Afon Tywi SAC and contributes to condition assessments undertaken under the Habitats Directive.
- Identification
- Extent
- Distribution
- Quality
- Keywords
- Spatial Reference System
- Content
- Constraints
- Maintenance
- Metadata
Identification
- Identifier
- NRW_DS115889
- Metadata Language
- English
- Lineage
-
The Hillman method is a quantitative survey technique that involves counting shad eggs from 25 kick samples at each survey site.
In 2013, the methodology was modified so that a minimum of 10 kick samples were collected at each site, with the number of eggs recorded for each sample. If 20 or more shad eggs were recorded after the first 10 kick samples, the survey at that site was terminated. However, if fewer than 20 eggs were recorded, sampling continued until either 20 eggs had been found or a maximum of 25 kick samples had been completed.
A standard macroinvertebrate hand net (250 µm mesh) was used to collect material dislodged by kicking (or shuffling) the riverbed upstream of the net for approximately 15 seconds. The net was inspected after each kick sample for the presence of shad eggs, and any detritus or substrate was removed before sampling resumed. The number of shad eggs recorded in each kick sample was counted and entered onto a field recording sheet.
Sampling commenced at the downstream end of each potential spawning site to minimise the risk of re-recording eggs dislodged during previous kick samples.
Where possible, sites at which no eggs were found were revisited later in the spawning season. However, this depended on weather conditions and the availability of survey staff.
The JNCC Common Standards Monitoring Guidance for Freshwater Fauna provides generic guidance on the attributes and targets used to assess freshwater fish populations. These include mandatory and discretionary targets relating to shad populations, flow, water quality, and river morphology.
Assessments are undertaken on a six-year cycle. At the time of this survey, NRW was undertaking the third monitoring cycle (2013-2018). Both allis shad and twaite shad were assessed as being in unfavourable condition during the first (2001-2006) and second (2007-2012) reporting cycles.
- Additional Information
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Afon Tywi SAC shad egg surveys 2013 & 2014. Garrett HM, Thomas Rh, & Hatton-Ellis TW. Report No. NRW Evidence Report No. 48.
- Dataset Reference Date (Publication)
- 2015-02-01
Temporal Extent
- Begin date
- 2013-06-11
- End date
- 2014-05-28
- Topic category
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- Biota
Extent
Extent
- Geographic Extent
- SIR GAERFYRDDIN - CARMARTHENSHIRE
))
Distribution
Distribution
- Format Type and Description
-
-
Binary
(
Unknown
)
- Specification
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A set of spreadsheets containing raw and processed data in XLS format (CCW Document Archive references NRW-13-054339 and NRW-13-054417).
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Database
(
Unknown
)
- Specification
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Data to be entered into Recorder 6.
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Documents
(
Unknown
)
- Specification
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Field notes in paper format, held at the Llandeilo office (file reference unknown). Copies are also held by the Evidence and Analysis Team at Maes y Ffynnon, Bangor; A report in Microsoft Word and Adobe PDF formats (see CCW Document Archive, Ffynnon reference NRW-13-071629).
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Geographic Information System
(
Unknown
)
- Specification
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A series of GIS layers in MapInfo TAB format on which the maps are based.
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Binary
(
Unknown
)
Quality
Data quality
- Quality Scope
- Dataset
- Conformity
- Commission Regulation (EU) No 1089/2010 of 23 November 2010 implementing Directive 2007/2/EC of the European Parliament and of the Council as regards interoperability of spatial data sets and services
- Explanation
-
This dataset has not been assessed for conformance to the referenced INSPIRE regulation.
- Degree
- false
- Lineage
-
The Hillman method is a quantitative survey technique that involves counting shad eggs from 25 kick samples at each survey site.
In 2013, the methodology was modified so that a minimum of 10 kick samples were collected at each site, with the number of eggs recorded for each sample. If 20 or more shad eggs were recorded after the first 10 kick samples, the survey at that site was terminated. However, if fewer than 20 eggs were recorded, sampling continued until either 20 eggs had been found or a maximum of 25 kick samples had been completed.
A standard macroinvertebrate hand net (250 µm mesh) was used to collect material dislodged by kicking (or shuffling) the riverbed upstream of the net for approximately 15 seconds. The net was inspected after each kick sample for the presence of shad eggs, and any detritus or substrate was removed before sampling resumed. The number of shad eggs recorded in each kick sample was counted and entered onto a field recording sheet.
Sampling commenced at the downstream end of each potential spawning site to minimise the risk of re-recording eggs dislodged during previous kick samples.
Where possible, sites at which no eggs were found were revisited later in the spawning season. However, this depended on weather conditions and the availability of survey staff.
The JNCC Common Standards Monitoring Guidance for Freshwater Fauna provides generic guidance on the attributes and targets used to assess freshwater fish populations. These include mandatory and discretionary targets relating to shad populations, flow, water quality, and river morphology.
Assessments are undertaken on a six-year cycle. At the time of this survey, NRW was undertaking the third monitoring cycle (2013-2018). Both allis shad and twaite shad were assessed as being in unfavourable condition during the first (2001-2006) and second (2007-2012) reporting cycles.
Keywords
Keywords
- Type
- Theme
Citation
- Date (Publication)
- 2008-06-01
Keywords
-
NRW Thesaurus
-
- allis shad
- alosa alosa
- Special Areas of Conservation (SAC) - SAC monitoring
- alosa fallax
- Special Area of Conservation Monitoring
- river Tywi (afon Tywi)
- twaite shad
- Type
- Theme
Citation
- Date (Publication)
- 2026-08-27
Spatial Reference System
Content
Content Information
NRW Profile
Custom Elements
- NRW Related Title
-
Afon Tywi SAC shad egg survey 2012
Constraints
Constraints
Limitations on Public Access and Use
- Restriction type
- Other restrictions
Access Constraints Directive
- Limitations
- no limitations
Access Constraints Text
- Other constraints
-
There are no access restrictions to this data. NRW may release, publish or disseminate it freely.
Use Constraints
- Use constraints type
- Other restrictions
- Other constraints
-
© CNC/NRW, 2015. There are no use restrictions on this data. Recipients may re-use, reproduce, disseminate this data free of charge in any format or medium, provided they do so accurately, acknowledging both the source and NRW's copyright, and do not use it in a misleading context. It is the recipient's responsibility to ensure the data is fit for the intended purpose, that dissemination or publishing does not result in duplication, and that it is fairly interpreted. Advice on interpretation should be sought where required. To avoid re-using old data, users should periodically obtain the latest version from the original source.
Attribution Statement
- Other constraints
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Contains Natural Resources Wales information © Natural Resources Wales and Database Right. All rights Reserved.
Licence
- Other constraints
- Open Government Licence
Metadata
Metadata
- File Identifier
- 4f4c4942-4343-5764-6473-313135383839 XML
- Metadata Language
- English
- Parent Identifier
-
SAC Monitoring: Afon Tywi Shad Egg Survey (2012)
NRW_DS115312
- Resource type
- Dataset
- Metadata Date
- 2026-10-01T14:38:23.525Z
- Metadata Standard Name
- NRW
- Metadata Standard Version
-
1.0