Scottish Marine and Freshwater Science Volume 3 Number 9: Data Mining of the Nephrops Survey Database to Support the Scottish MPA Project

Discussion

The data layers based on MSS' Nephrops UWTV survey have been used by JNCC and SNH to augment other sources of information on burrowed mud habitat and, at the time of writing, are contributing to the MPA site selection process. Sediment sampling and particle size analyses have in some cases confirmed putative mud distribution (ground truthing) and in other cases have provided new information on location of mud, particularly in inshore sea areas, sea lochs and on the shelf edge, areas which are not mapped by BGS or other surveys. Nephrops burrow density data from UWTV stations have been provided and ancillary data collected during the surveys were 'mined' to provide information on the occurrence and relative abundance of sea pens, including the tall sea pen F. quadrangularis, which are considered to be of particular relevance in a Scottish context.

It should be borne in mind that the MSS UWTV survey is designed to estimate densities of Nephrops burrows, which are widely distributed over relatively large sediment areas. There are, therefore, some limitations when using other data collected during the survey to map the distribution or estimate the abundance of other biota. The survey design would not be considered particularly suitable for mapping the distribution of more sparsely distributed species or locating fragmented populations.

In addition, the review and analysis of the UWTV footage collected during the survey is conducted primarily to derive accurate counts of Nephrops burrows. The presence or absence of others features is noted and since 2005 MSS has applied its ROCA scale to assess relative abundance of sea pens, but these procedures have not been subject to the rigorous QA and checking that is applied to burrow counts. It is possible that there will be instances when impressions may be misleading, particularly if tow speed is variable or visibility is reduced, or that the scale is not consistently applied by different observers. Clearly, counts could provide more accurate density data for sea pens (providing viewed area is accurately known), than those based on the reviewers' overall impression based on observation of the footage. However, the counting process is labour intensive and time available to review footage was limited. We were, however, reassured by those reviews carried out that the procedures in place in most cases are able to identify stations where sea pens were present, and that relative abundance as assessed on the ROCA scale was reasonably indicative of higher and lower densities and could be used to inform the MPA project.

In general, P. phosphorea and V. mirabilis were more frequently observed in UWTV footage from stations on the east coast of Scotland whilst F. quadrangularis was more frequently observed on the west coast of Scotland. F. quadrangularis was only observed once in the Firth of Forth and once in the Fladen. This is consistent with findings of Greathead et al. (2011) for reviewed footage from 50 survey stations in the Fladen in 2004, finding no F. quadrangularis. The brittle nature of the species and its inability to retract into the sediment are believed to make it extremely sensitive to physical disturbance and it has been suggested that increased fishing pressure may result in a decreased abundance. However, the west coast of Scotland is also heavily fished but F. quadrangularis has been frequently observed.

Evidence of fishing activity was recorded in all areas surveyed and included trawl marks, door marks, evidence of creel fishing, and boats in the vicinity.

The Folk classification system separates sediment type based on grain size distribution. However, our observations suggest that 'mud' biotopes vary regionally and on small spatial scales. Thus 'sandy mud' in the Fladen is not identical to 'sandy mud' in the Clyde. The presence of other burrows and variations in the depth and hydrography can significantly change the appearance of the sediment.

In the event of MPAs being established, displacement effects of fishing effort should be considered and its impact monitored. Data from Nephrops UWTV surveys date back to the early 1990's and continue to be collected on an annual basis. This information could potentially be used as baseline data for monitoring site condition.