JNCC Offshore Natura Survey : Anton Dohrn Seamount and East Rockall Bank areas of search : 2009/03-JNCC Cruise Report

This cruise report summarises operations and initial observations onboard the M/V Franklin during cruise 2009/03-JNCC on behalf of the Joint Nature Conservation Committee (JNCC). The cruise took place between the 1st and 29th of July 2009 and surveyed two Areas of Search (AoS) for offshore Special Areas of Conservation (SACs): Anton Dohrn Seamount located 155km west of the St Kilda archipelago, and East Rockall Bank located 260km west of the St Kilda archipelago (Figure 1). The main aims of the survey were to acquire acoustic and photographic “ground-truthing” data to enable geological, geomorphological and biological characterisation of the Anton Dohrn Seamount and East Rockall Bank AoS. Specifically, the data acquired will lead to the production of broadscale habitat maps, the identification and description of Annex I reef habitats with particular attention to the occurrence of bedrock, stony and biogenic reef, to identify and record any anthropogenic impacts in the areas of search and finally to evaluate data acquisition methods, techniques and equipment. The work programme was highly successful with 215 line kilometres of multibeam echosounder and 10 photographic “ground-truthing” sites acquired in the Anton Dohrn Seamount AoS, and 692 line kilometres of multibeam echosounder and 168 line kilometres of sidescan sonar data and 17 photographic “ground-truthing” sites acquired in the East Rockall Bank AoS. No physical sea-bed samples were acquired during this cruise. The data revealed the flanks and area immediately adjacent to Anton Dohrn Seamount to comprise predominantly gravel-rich sediment with bedrock outcropping on the steeper sections of the Seamount flanks. East Rockall Bank comprised predominantly gravelly muddy sand on the eastern flank of the Bank with gravel- and sand-rich sediments dominating the crest of the Bank. Interestingly, the parasitic cones surveyed within the Anton Dohrn area of search comprised predominantly corals, including large gorgonian species, small bamboo coral, the soft coral Anthomastus sp. and the antipatharian Leiopathes sp. Significant bedrock reef was encountered during the course of this cruise along an escarpment located on the eastern flank of Rockall Bank roughly coincident with the 500m bathymetric contour. This laterally extensive feature primarily comprises volcanic bedrock with possible sedimentary bedrock cropping out at sea bed colonised by large stylsaterid hydrocorals and sponges. Preliminary observations and interpretation of the data acquired during the course of this cruise suggest that several sites may fit the definition of Annex I reef under the EC Habitats Directive. If they fulfil the criteria for Annex I reef, they will be assessed against site selection criteria as possible areas for consideration as SACs.