4 Michael Graham 



side; so, on the average, the ground would be swept about 5-6 times. It was possible 

 to be more precise about the examination of the benthos bed before and after the 

 trawling, by choosing the same phase of the tide. The animal tested was Echinocardium 

 cordatum, the Heart Urchin, which was the most vulnerable animal we encountered — 

 certainly not a plaice food at the size (from memory, about an inch and one-half in 

 diameter), but no better animal was found. It had the further disadvantage that 

 dredge catches would fall from 39 in a 10 minute haul to 3 when the tide slackened. 

 This leads to an investigation of where exactly the dredge hauls lay (Table I). 



The dredging ground (52° 44|' N., 4° 16' E.) was some 13 miles southerly of the 

 Haaks Light Vessel, and because many of the hauls were made while the George Bligh 

 was driving with wind and tide it is possible to plot the approximate tidal pattern 

 (Sta. 16, Hauls 1-13, but discarding No. 6, for which the record is suspect). Assuming 

 as a first approximation that the Dhan buoy did not swing during a 10 minute dredge 

 haul, the course of the haul can be plotted out from the bearing and distance at the 

 beginning and end of the haul, taking an arbitrary position for the buoy. Then, as a 

 second approximation, the buoy is assumed to be on that bearing and at a distance 

 of 180 yards (90 fms of wire in 13 fms of depth) from its anchor. The position of 

 dredge haul is then replotted from the assumed true position of the buoy. Most 

 positions of the buoy were found to lie near a N.E. and S.W. zone (magnetic), not 

 very different from that derived from tidal information on admiralty chart 2 182 A 

 for a position 52° 36' N., 4° 10' E. 



The information given in Table I has been plotted on Fig, 1, from which it is seen 

 that there is reasonable overlap of Sta. 16, Hauls 7-13 with Sta. 20, Hauls 2-8. 

 Neither set lay perfectly in the trawlable area; but both lay partly within it. Sta. 16, 

 Hauls 7-13, and Sta. 20, Hauls 1-8, may be said to do so. 



Some benthos material was preserved from these investigations ; but none is to be 

 found 17 years later. It is thought that the jars were buried for safety of staff in 1940, 

 and discarded as not in good order in 1945. Data are therefore in the form of incom- 

 plete identifications written in the log-books at the time. They are so given here= 



During the attempt to break Echinocardium it was found possible to distinguish 

 whole, broken or even fragmentary specimens, as " dead ", meaning " long dead " 

 (having no spines), " recently dead " (having lost some spines), and " broken " 

 (having all the proper spines). By counting fragments containing apical pores, it was 

 possible to estimate the number of whole urchins. 



RESULTS 

 The sanctuaries from trawling showed no marked difference in benthos from 

 outside, so there seems no reason to burden this paper with details of the results. 

 The only point of interest was a bed of Echinocardium within three-quarters of a mile 

 of the Haaks Light Vessel, but because this did not extend around the Light Vessel, 

 we can hardly attribute significance to it, especially because later on we found a 

 localized bed 13 miles away in the fishing area. The fauna also included " flat stars " 

 (Astropecten), Asterias rubens, Portunus depurator, Eupagurus, and a few Mactra, 

 Venus, and razor-shells. These showed no marked differences three-quarters of a 

 mile and 5 miles from the Haaks Light Vessel, and the species and quantities three- 

 quarters of a mile from the Terschelling Light Vessel seemed similar to those close to 

 the Haaks. 



