Rockall Bank (2005-2009)

 

These surveys were conducted in collaboration with the Fisheries Research Services and the University of Plymouth. The aims of these surveys were to identify and map the range of seabed habitats present on the Rockall Bank seamount, identify areas of Annex I reef and to futher develop the deep water sections of the EUNIS habitat classification system.

 

Using multibeam data collected during the Strategic Environmental Assessment (SEA) 7 surveys, sites for groundtruthing by video and stills were selected for the surveys conducted in September 2005. Further targeted stills and video samples were taken in September 2006 and September 2007. All video drops were carried out at night during a time when FRS could not conduct fishing trawls as part of their annual haddock stock assessment monitoring.

 

The western and north-western summit regions (271-342m water depth) sampled on Rockall Bank were similar in terms of habitats and species. These areas consisted of fine sand seabed scarred by distinct iceberg ploughmarks composed of parallel lines of cobble and occasionally boulder drop stones with an in-filled furrow between. Within this region clump formations of Lophelia pertusa reef were present with characteristic rubble fringe areas. Analysis of the high resolution sidescan sonar suggests these coral clumps are associated with iceberg ploughmark features. Evidence of bottom trawling was apparent in the north-western region with distinct furrows produced by trawl doors visible in the sand associated with large areas of coral rubble.

 

The central summit area sampled on Rockall Bank (141-190m water depth) is different in character to both eastern and western regions sampled with large areas of exposed bedrock and rock outcrop fringed by areas of boulders, cobbles, pebbles and sand. There are signs of increased current activity with distinct megaripples visible at many of the stations sampled.

 

The eastern summit region sampled (210-280m water depth) was similar in character to the western summit region with areas of fine sand seabed scarred by iceberg ploughmarks. However, delineation of each defined habitat was not as clear in the west, in that the bands of cobbles and boulders crossed by the camera, associated with the edges of ploughmarks, were not as distinct as in the west with areas of mixed cobble and pebbly sand present. Unlike the western region, no Lophelia pertusa clumps were encountered although semi-buried coral fragments were observed. Analysis of the high resolution sidescan sonar data suggests there may be reef clumps present.

 

The eastern flank of Rockall Bank (390-1600m water depth) is more complex in terms of habitat than any of hte summit areas sampled. Analysis of multibeam data suggests the area sampled comprises steep slopes between 400m-750m depth. Mixed substrates of boulders, cobbles and pebbles with areas of exposed bedrock and bedrock outcrop were observed between 391-674m depth with no one habitat described as dominant. Clumps of Lophelia pertusa reef were also observed within this region with associated coral rubble fringes. The more southerly stations on the upper eastern flank (551-736m water depth) were less complex with no bedrock or rock outcrop observed. However, these stations lay within an area of the flank identified as a sediment drift from the multibeam analysis. The deeper stations in this region (>1000m water depth) exhibited very little habitat diversity with sandy mud giving way to mud as the dominant habitat type. Near the 1000m isobath, areas of cobbles and pebbles were still encountered, however with increasing depth the only hard substrate was provided by the occasional boulder.

 

The south-eastern region of Rockall Bank sampled (428-585m water depth) lay in an area of more gradual transition from summit to flank. This area was different in character again to the other regions of the bank sampled, consisting almost entirely of muddy sand habitat. At the shallowest and most northerly station a small patch of cobbles and pebbles were observed, however all other observations were of uniform muddy sand environment.

 

Data from these surveys has contributed to North-West Rockall Bank being formally advised to Defra. In summer 2009, survey will be undertaken to gather additional data for the East Rockall Bank Area of Search.