Methodology

Manned submersibles.

Remote recording

Diving

 

CFT biotopes are on hard substrata, and these substrata are generally steep and irregular and close inshore. They are mostly in depths exceeding 20 m, and often in areas of considerable wave action and strong currents. These factors severely constrain the methods which can be used in monitoring programmes. A general review of potential methods is given by Worsfold & Dyer (1997).

Surface operated remote sampling methods are inappropriate. Quantitative methods such as grabs and corers, suitable for soft substrata, will not work. Semi-quantitative methods such as rock dredges or rock-hopper trawls are unacceptably damaging, and provide very poor quality data. In the context of SAC management monitoring procedures should, where possible, be non-destructive in any case. Fortunately most of the larger CFT species are clearly visible on the rock surface and can be identified and enumerated in situ, and visual census methods are both practicable, and desirable. These visual methods unavoidably miss the smaller cryptic CFT species, but hopefully if the status of the larger species is preserved, than the habitat and well-being of the cryptofauna will be protected.

Visual monitoring can be carried out using several methods.

Manned submersibles.

These have been used very successfully in deep sea work, but their deployment and operation in the more dynamic inshore environment is untested. In any case their limited availability and very high capital and operating costs rule them out as an instrument in routine SAC monitoring, though they could be valuable in the surveying of deeper sites.

Remote recording.

Towed sledge-mounted camera systems are used successfully on soft bottoms, but cannot be used on irregular hard substrata. The only suitable method for working on CFT biotopes is to use a remote operated vehicle (ROV), which can be controlled and manoeuvred via an umbilical cable from the surface and equipped with still and video cameras. ROVs are used routinely for inspection work on offshore structures and pipelines, but so far only on a trial basis for monitoring work in the circalittoral (Donnan, 1997, 1998). Although they can be positioned with considerable accuracy (c 0.5 m) it would, for instance, still be impossible to position a ROV accurately enough to re-photograph fixed quadrats with the same precision that a diver can achieve. However the technology is available (see Auster, 1993), the cost of the cheaper systems is of the order of 30K, and this may be the only practicable method for monitoring the deeper CFT areas below the depths where divers can operate effectively (see below), and for certain purposes may be as cost effective as diving in shallower conditions. There are considerable areas within candidate/possible SACs which are beyond the range of conventional diving methods, but are of substantial scientific and conservation interest.

 

Diving

Almost all of the previous and ongoing monitoring of CFT communities has been carried out by SCUBA diving, and it is assumed that this will be the predominant technique used in SAC monitoring of CFTs for the immediate future. Diving must be carried out within the framework of the Health and Safety Commission Divers at Work Regulations, and SAC monitoring would normally be conducted under the Approved Code of Practice for Scientific and Archaeological Diving. Whilst this newly established code offers greater flexibility than the preceding legislation, it imposes various limits in the interests of safety. Of major relevance, the limit of safe diving is considered 50 metres. However, without on-site recompression facilities (which are unlikely to be available) the practical limit under the regulations would be 40 metres (to give 30 minutes bottom time and <20 minutes in-water decompression), and in many situations 30 metres would be a more realistic lower limit. In some of the more remote SACs the length of travelling time to recompression facilities may make any diving within the regulations difficult. The increasing use of nitrox gas mixtures and rebreathing systems by scientific divers will improve bottom time capability, but will have limited impact on depth limits. Within the proposed limits of the cSACs most of the CFT biotopes should be within diving range (but not necessarily easily diveable), but significant areas will not. Furthermore, a case may exist for designating SACs in the future to include more of the deeper circalittoral rock biotopes which will be well below diving depths. The design of a monitoring programme must consider the logistics of the diving operations from the earliest stages, and a risk assessment made for each procedure at each location. Realistically diving must be the technique of choice at the current time for most monitoring of CFTs, but alternatives must be developed (see below, and comments above on the use of ROVs).

Various techniques can be used by divers to collect information during monitoring. Direct recording of observations can be made using tick lists, writing pads, voice recorders or waterproof data-loggers. Alternatively records can be made using still or video photography. The second approach has advantages in that it maximises the use of bottom time, much of the recording work may not need scientific skills, and the analysis can be done subsequently at lower cost in the laboratory. Additionally a permanent record is available. However, the recording methods may be constrained by the monitoring format - see below.

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