OCEANOGRAPHIC INVESTIGATIONS 357 



squid has been considered to be primarily a smoke-screen defensive mechanism. From this 

 observation, it thus appears that the discharge also serves as a taste deterrent. 



Over the short time interval the writers occupied Sealab, there was a noticeable change in 

 the types and density of fish present. Sculpin, Scorpaena guttata, were always present, and 

 several counts were made of their density on the bottom. In the area immediately adjacent to 

 Sealab an average of 2 per 0.1 sq m (sq. ft) was observed. These fish decreased in numbers 

 somewhat at a distance from Sealab. At approximately 15 m (50 ft) away an average of only 1 

 per 0.1 sq m (sq ft) was observed. Through conversations with CDR Carpenter, the writers 

 learned that these fish were not present during the early part of Team I's occupancy, but had 

 moved in during the latter part of the first week. The white croakers were always present, 

 but were most numerous during the first week of Team 2's occupancy. About the time the sea 

 lions appeared on the scene, the number of croakers decreased sharply and it is possible that 

 the desirability of croakers as food may have been in part responsible for this decrease. The 

 sea lions were first observed on the night of Sept. 22. This first night they appeared to be 

 somewhat cautious and were seen swimming only at a distance. By the next night, however, 

 the sea lions had apparently decided that Sealab offered no threat and on several occasions they 

 were seen hanging on the diving lights and looking in the ports. All of the fish in the immedi- 

 ate vicinity could somehow sense the approach of a sea lion, and some 10 sec prior to the ap- 

 pearance of a sea lion the fish would rapidly depart from the field of view. Only the sculpin, 

 Scorpaena guttata, seemed to be unaffected by the sea lion's approach, and even though these 

 fish made no attempt to escape, they were never taken by the sea lion. On the night of Sept. 

 23 a marked change in water color was noted, the water changing from a predominantly green, 

 typical of coastal waters, to an oceanic blue. Accompanying this change in water mass was 

 the appearance of the northern anchovy, Engraulis mordax, which occurred in great numbers, 

 becoming the predominant fish present. These fish were strongly attracted by the outside div- 

 ing lights, and the protective screen of these lights often became completely filled with ancho- 

 vies that had gilled themselves. These lights thus became a favorite feeding post for the sea 

 lions, and on several occasions sea lions were seen feeding on the anchovies that had become 

 gilled. By the night of the 25th of September, the water color had changed back to the typical 

 green and most of the anchovies had departed. From conversations with CDR Carpenter, the 

 writers learned that the anchovies had made a similar appearance during Team I's occupancy 

 of Sealab; this appearance also coincided with the occurrence of oceanic blue water. A check 

 of the predicted tides indicates that in both instances this change in water mass occurred dur- 

 ing a period of maximum tide range. 



Underwater Surveying and Mapping 



A problem of major importance to both the Sealab oceanographic program and to other 

 facets of the Sealab work was that of underwater surveying and mapping. Although, as de- 

 scribed in what follows, useful partial solutions have been provided, the problem of accurately 

 positioning, surveying, and mapping the location of underwater objects near Sealab remains as 

 a significant problem yet to be fully solved. The prime reasons for this situation are, of course, 

 that members of an underwater survey team are not only deprived of both aural and visual 

 communication but also of many of the commonly used instruments, such as, e.g., transits. 

 There is a pressing need to provide an vmderwater survey technique that is accurate, yet in- 

 dependent of visual and audio links, and reasonably simple for use by divers. An approach 

 toward solution of this problem as described below, devised primarily for oceanographic ap- 

 plications, turned out to have usefulness in other areas. For example, it became apparent 

 after Team 2 had entered Sealab that the magnetic heading of Sealab was not known with cer- 

 tainty to within less than about ±20 degrees; we were able to reduce this uncertainty to about 

 ±5 degrees. To do this, two simple devices were used: a 61-cm (two-foot) diameter compass 

 rose mounted on the bottom, and a 30.5-m (100 ft) steel-reinforced surveyor's tape in a reel 

 specially designed for underwater use. The compass rose, which was made of plastic, was 

 marked in one-degree increments and mounted on a heavy platform stake so that once set it 

 did not rotate. In use, it was aligned by having a swimmer go out on a known preselected 

 bearing by compass (to a distance such that his compass was not affected by Sealab or other 

 metal objects) with a string attached to the center of the compass rose; after this the compass 

 rose was adjusted so that the preselected bearing was under the string. In this manner the 

 rose was aligned with respect to magnetic north to an accuracy matching that of the compass 



