Echinus esculentus, normally the subject of a small scale commercial fishery in the Isles of Scilly during the winter months, was not collected during the winter of 1985/86. This report presents the results of the third survey of selected Echinus esculentus populations in the Isles of Scilly, which took place during September 1986. These are compared with data from the same sites obtained during September 1984 and 1985. Seven areas were sampled, four of which are classified as unfished and three as fished sites. Within each of the seven areas, sampling sites were located as closely as possible to those studied in the 1985 survey. The mean density of urchins ranges from 0.05/m2 to 0.49/m2. Within the precision of the methodology, these figures compare exactly to the range measured in 1985 (0.05/m2 to 0.40/m2). There is no significant difference in the density of urchins between fished and unfished sites. The mean diameter of E. esculentus ranged from 95 mm to 122 mm with an overall site mean of 105+2 mm (n = 12). This compares with a slightly lower and smaller range of 92 mm to 112 mm during 1985, but a similar overall site mean of 104+2 mm (n = 10). The mean diameter of urchins at unfished sites was smaller than that of fished sites (98+1, n = 4 and 107.6+2, n = 8 respectively), which was also true in both 1984 and 1985. No major physical changes have affected the sites since 1984, and the dominant fauna and flora appear to be unchanged. There is still no evidence of juvenile or young adult individuals (size <5 cm diameter) at the monitoring sites, although it is believed that juveniles are present at deeper sites which cannot be dived or remotely sampled within the remit of the present contract.
