© OpenStreetMap contributors
As hydraulic dredging is emerging as a preferred technique in Scottish waters for the fishing of razor clams (Enis spp.), an investigation evaluating the environmental impacts of hydraulic dredging as a fishing technique was carried out. The study investigated the impact of dredging on co-existing fauna and predators as well as the effects on sediment composition and characteristics. Populations of Enis arcuatus and Enis siliqua were studied in the Clyde Sea area and the Hebrides and Orkney Islands. These study sites are commercially sensitive and therefore their exact geographic locations have not been included in the report. Additional sites were also identified within the Clyde Sea area. Hydraulic dredging was found to have a high diversity of by-catch within the Clyde Sea area. Production estimates and recruitment levels of razor clams are discussed within the study.
Data Archive for Seabed Species and Habitats (DASSH)
Dassh Terms and Conditions Apply (https://www.dassh.ac.uk/terms-and-conditions)
| Other details | ||
| Internal code | Internally assigned metadata identifier | 3804 |
| Title | The title is used to provide a brief and precise description of the dataset such as 'Date', 'Originating organisation/programme', 'Location' and 'Type of survey'. All acronyms and abbreviations should be reproduced in full. | 2000-2002 University Marine Biological Station Millport (UMBSM) Clyde Sea Area Hydraulic Dredging Assessment Survey |
| Alternative title | The purpose of alternative title is to record any additional names by which the dataset may be known. | 2000-2002 University Marine Biological Station Millport (UMBSM) Study Contract Clyde Sea Area Hydraulic Dredging Assessment Survey, EC Study Contract 99/078 |
| File Identifier | The File Identifier is a code, preferably a GUID, that is globally unique and remains with the same metadata record even if the record is edited or transferred between portals or tools. | 72a8b5349ec8339f7438ddaf8469090c |
| Resource Identifier | This is the code assigned by the data owner. | DASSH-112 |
| Resource type | The resource type will likely be a dataset but could also be a series (collection of datasets with a common specification) or a service. | dataset |
| Start date | This describes the date the resource starts. This may only be the year if month and day are not known | 2000-09-01 |
| End date | This describes the date the resource ends. This may only be the year if month and day are not known | 2002-09-01 |
| Spatial resolution | This describes the spatial resolution of the dataset or the spatial limitations of the service. | inapplicable |
| Frequency of updates | This describes the frequency with which the resource is modified or updated i.e. a monitoring programme that samples once per year has a frequency that is described as 'annually'. | notPlanned |
| Abstract | The abstract provides a clear and brief statement of the content of the resource. | As hydraulic dredging is emerging as a preferred technique in Scottish waters for the fishing of razor clams (Enis spp.), an investigation evaluating the environmental impacts of hydraulic dredging as a fishing technique was carried out. The study investigated the impact of dredging on co-existing fauna and predators as well as the effects on sediment composition and characteristics. Populations of Enis arcuatus and Enis siliqua were studied in the Clyde Sea area and the Hebrides and Orkney Islands. These study sites are commercially sensitive and therefore their exact geographic locations have not been included in the report. Additional sites were also identified within the Clyde Sea area. Hydraulic dredging was found to have a high diversity of by-catch within the Clyde Sea area. Production estimates and recruitment levels of razor clams are discussed within the study. |
| Lineage | Lineage includes the background information, history of the sources of data, data quality statements and methods. | The study was carried out by researchers at the University Marine Biological Station Millport (UMBSM), the Instituto di Ricerche sulla Pesca Marittima (IRPEM) and the Fisheries Research Services, Marine Laboratory Aberdeen (MLA) and financial assistance was supplied by the European Commission. The report does not necessarily reflect the views of the European Commission. The study project is in support of the Common Fisheries Policy. The MLA studied Enis populations at sites on the east (Brora, Golspie, Cromarty, Black) and west (Longa, Arisaig, Kentra) mainland coast, the Clyde Sea area (Bute, Hunterston) and the Hebrides (Lewis) and Orkney islands (Orkney). These sites are commercially sensitive and therefore their exact locations are not provided. The geographic location of the sites investigated can be provided by contacting T.R.W Howell at the Marine Laboratory, Aberdeen (MLA). The UMBSM study sites (8) are situated on the Isle of Cumbrae, Isle of Bute and surrounding areas. The IRPEM investigated sites in the eastern Mediterranean Sea. At MLA study sites, a "box" or "Irish" Hydraulic dredge was used. The blade of the dredge was 41cm deep and 91cm wide. At UMBSM study sites, a blade dredge was used which had a box-section tooth 39cm wide. This was able to penetrate the sea bed to a depth of 34cm. The blade was tapered to produce a 10mm gap which delivered water into the sand. The face of the blade was drilled with a grid of 54 holes. This allowed water to be propelled forward. Extra holes were situated on the top of the blade which directed water to wash the catch into the collecting cage (185 x 80 x 55cm). 4 x 1.5cm diamond pattern mesh extended behind the dredge mouth. The cage was also fitted with a hinge door. A deck mounted 24.2hp (17.8 kW) Godwin ET 150/TS2 pump (3200 litres per minute) delivered seawater to the dredge at a pressure of approximately 2 bar. This was achieved via 30m of 10cm diameter layflat hose. Water flow was split between the blade and the collecting cage. The water from the blade (forward facing) was used to fluidise the sand ahead of the dredge. The UMBSM vessel RV Aora (15m, 300 hp) was used during towing, however MFV Solway Provider (12m, 150hp) was used between January and March 2001 due to RV Aora undergoing maintenance. The dredge was deployed at depths of between 4 and 10m. The speed over ground of the dredge was approximately 10m per minute. A second blade dredge (Henderson dredge) was used hereafter and fished from MFV Jolanda (10m, 150hp) for comparative purposes. This blade did not have holes on the blade face. The Henderson dredge was able to penetrate the sea bed to a depth of 34cm. The cage (200 x 150 x 100cm) exhibited a 7 x 1.5cm rectangular wire mesh. Water was delivered by the same means via 30m of 15cm diameter layflat hose or by using a submersible hydraulic pump which was fitted to the dredge. The measurement of effective fishing width was determined during the study. The width of dredge track was established by performing six dives in Irvine Bay. RV Aora was involved during each dive. The dredge was lowered onto the sea bed with the water pump switched off. Artificial "razor clams" were hammered into the sea bed at 5cm intervals and at a distance of 1-2m from the front of the dredge by two divers until level with the sea floor. Artificial "clams" were made from 20 x 2.5 x 1cm hardwood blocks and weighted with lead strips. Each "clam" was labelled with its distance (cm) from the dredge centre. Divers then positioned themselves behind the dredge and towing commenced. Both divers followed and any remaining "clams" were collected and their orientation and position was recorded. The hauled dredge was emptied on deck and numbered "clams" were retrieved. Razor clam densities were investigated during the study. Alternative methods of assessment were initially tested during a series of dives. A salting technique was initially tested. This method was abandoned as it was deemed unreliable. An alternative approach of using a diving knife blade was also abandoned. A diver-operated suction airlift was tested. This was in turn abandoned. Another approach consisting of a water jet was tested. A water jet was used to fluidise sediment within a 0.25 meter squared quadrat. A diver on the sea bed was supplied with an 80m long flexible hose by which water flow was supplied via the deck wash pump on board RV Aora. 4-5 replicate quadrats were excavated per hour and clams could be hand collected. Dredge efficiency was determined by populations of clams identified in three of the eight study sites, by a series of towed (5 minutes) replicates. Divers followed the track and recorded the overall length. Divers then applied the 0.25 meter squared quadrat to quantify clam population adjacent to the dredge track. Four quadrats were sampled per tow, within the dredge track. The towed dredges were emptied and enumerated. Damage assessment of organisms was investigated. In the Clyde Sea area, two dredge hauls were fished per month from February 2001 to December 2001 at two study sites. The UMBSM dredge was used. Divers followed the dredge and collected (semi-quantitative) species which were dislodged at the sediment surface of the track. The track was then measured by divers using a tape meter. Catch was processed at UMBSM. Individuals were enumerated and sorted into damage category. Total whole wet weight (g) was recoded of each category. Reburial capacity of organisms was investigated at site UMBSM site. Reburial capacity was assessed on "pristine" and a dredged area for comparison. Animals were gathered from trawls which lasted 7-10 minutes in duration. At the study site, a frame covered in 0.25mm squared plastic Netlon was placed on the sea floor (RV Aora). Divers placed intact trawled species into the frame. Activity was recorded using a Kongsberg Simrad Osprey OE 1362 low-light sensitive colour camera which was fixed to the frame. Video output was recorded via a Panasonic AG 5700 VHS video recorder. Activity was recorded for three hours. Reburial capacity experiments were also conducted within the laboratory. Two tanks were set up to compare the effects of sediment type (dredged and pristine) on reburial. Aquaria were filmed using a Panasonic WV 1460/B CCTV camera mounted on a Dexion frame. Video output was recorded via a Panasonic AG-6730 S-VHS Time Lapse Recorder. Impact and recovery rates of fishing grounds were assessed throughout the study. By-catch and discards of hydraulic dredging was assessed. Three damage classes (intact, light damage and severe damage) were assessed from trawled catch from February 2001 to November 2001 based on criteria. Representative examples of species were preserved in 70 percent industrial methylated spirit. Comparative studies between UMBSM dredge and MFV Jolanda dredge were conducted in August 2001. Qualitative observations of predation on benthos in the dredge path was investigated by divers. A had-held Sony CCD-V800E Hi8 video camera in an Ikelite housing unit was sometimes used. Quantitative observations were conducted in conjunction with reburial field experiments. A record of scavenging activity was collected. Population characteristics, recruitment and production estimates and detailed assessments of lethal (dredging impact) and sub-lethal (metabolic stress) damage of target species were assessed during the course of this study. |
| Related keywords | ||
| Keyword | General subject area(s) associated with the resource, uses multiple controlled vocabularies | Marine Environmental Data and Information Network |
| General subject area(s) associated with the resource, uses multiple controlled vocabularies | Geology | |
| General subject area(s) associated with the resource, uses multiple controlled vocabularies | Sea regions | |
| General subject area(s) associated with the resource, uses multiple controlled vocabularies | Species distribution | |
| General subject area(s) associated with the resource, uses multiple controlled vocabularies | Sedimentary structure | |
| General subject area(s) associated with the resource, uses multiple controlled vocabularies | Shellfish reproduction | |
| General subject area(s) associated with the resource, uses multiple controlled vocabularies | Fishery characterisation | |
| General subject area(s) associated with the resource, uses multiple controlled vocabularies | Shellfish morphology, age and physiology | |
| General subject area(s) associated with the resource, uses multiple controlled vocabularies | Fishing by-catch | |
| Geographical coverage | ||
| North | The northern-most limit of the data resource in decimal degrees | 55.79 |
| East | The eastern-most limit of the data resource in decimal degrees | -4.73 |
| South | The southern-most limit of the data resource in decimal degrees | 55.5 |
| West | The western-most limit of the data resource in decimal degrees | -5.1 |
| Regional sea | Irish Sea | |
| Minches & Western Scotland | ||
| benthic boundary layer | ||
| Responsible organisations | ||
| Role | The point of contact is person or organisation with responsibility for the creation and maintenance of the metadata for the resource. | pointOfContact |
| Organisation name | University Marine Biological Station (UMBS), Millport | |
| Individual name | Carly Cassidy | |
| Postal code | KA28 0EG | |
| City | Millport | |
| Role | The distributor is the person or organisation that distributes the resource. | distributor |
| Organisation name | Data Archive for Seabed Species and Habitats (DASSH) | |
| Position name | Data Manager | |
| Phone | 01752 633102 | |
| Fax | 01752 633291 | |
| Delivery point | Marine Biological Association of the UK, The Laboratory, Citadel Hill | |
| Postal code | PL1 2PB | |
| City | Plymouth | |
| Role | The originator is the person or organisation who created, collected or produced the resource. | originator |
| Organisation name | University Marine Biological Station (UMBS), Millport | |
| Individual name | P.G. Moore | |
| Postal code | KA28 0EG | |
| City | Millport | |
| Role | The custodian is the person or organisation that accepts responsibility for the resource and ensures appropriate care and maintenance. If a dataset has been lodged with a Data Archive Centre for maintenance then this organisation is be entered here. | custodian |
| Organisation name | Data Archive for Seabed Species and Habitats (DASSH) | |
| Position name | Data Manager | |
| Phone | 01752 633102 | |
| Fax | 01752 633291 | |
| Delivery point | Marine Biological Association of the UK, The Laboratory, Citadel Hill | |
| Postal code | PL1 2PB | |
| City | Plymouth | |
| Resource locators | ||
| Locator URL | Web address (URL) that links to the resource | http://dassh.ac.uk/datasets/DASSH-112 |
| Locator name | Name of the web resource | DASSH View and Download |
| Locator URL | Web address (URL) that links to the resource | http://www.dassh.ac.uk |
| Locator name | Name of the web resource | dassh website |
| Dataset constraints | ||
| 20 Limitations on Public Access - Access constraints | ISO restriction code chosen from ISO 19115-1 Codelist | otherRestrictions |
| 20 Limitations on Public Access – Other constraints | Any restriction on the use of the resource such as the need to agree to certain licence conditions. | Dassh Terms and Conditions Apply (https://www.dassh.ac.uk/terms-and-conditions) |
| 21 Conditions for Access and Use - Use limitation | Any restrictions imposed on accessing the resource such as the need to agree to certain licence conditions. | The contents of the study may not be reproduced unless the source of the material is indicated. Dassh Terms and Conditions Apply (https://www.dassh.ac.uk/terms-and-conditions) |
| Available data formats | ||
| Data format | Format in which digital data can be provided for transfer | Delimited |
| Version info | ||
| Date of publication | The publication date of the resource or if previously unpublished the date that the resource was made publicly available via the MEDIN network. | 2002-09-01 |
| Metadata date | The date when the content of this metadata record was last updated. | 2020-02-04 |
| Metadata standard name | The name of the metadata standard used to create this metadata | MEDIN Discovery metadata standard |
| Metadata standard version | The version of the MEDIN Discovery Metadata Standard used to create the metadata record | 2.3.8 |
© OpenStreetMap contributors