another major subgroup. They were very com- 

 mon south of Martha's Vineyard but less 

 plertiful at the more easterly stations. 



Representatives of several other phyla were 

 quantitatively important. Mollusks were mod- 

 erately common at the Georges Bank stations. 

 Gastropods, the most abundant molluscan 

 group, were represented chiefly by Buccinum , 

 Neptunea , and Colus. Pelecypods were the only 

 other molluscan group; the principal species 

 were the ocean quahog and the sea scallop. 

 Nearly all crustaceans in the samples were 

 decapods, mainly rock crabs ( Cancer ) and 

 hermit crabs. Coelenterates were rather 

 sparse and were represented by Hydrozoa 

 and Anthozoa. Porifera were very sparse in 

 the dredge samples (maximum density 0.005 

 per square meter) and were not detected in 

 the photographs. 



Fauna revealed by photographs was generally 

 the same throughout the entire strip sampled 

 at each station. Local variation, inferred from 

 changes from one frame to another, was more 

 pronounced for some species than others. 

 Starfishes, for example, were rather uniformly 

 distributed, whereas sand dollars and hermit 

 crabs tended to occur in groups. Large num- 

 bers of sand dollars at stations on Georges 

 Bank were frequently concentrated in patches 

 10 to 20 m. in diameter spaced at intervals of 

 50 to 75 m. Mollusk shells, both the intact 

 shells and shell fragments, also were dis- 

 tributed in groups. At station 42, Arctica 

 shells were clustered in groups about 200 m. 

 apart, but shell fragments were rather evenly 

 distributed. At station 44, where water currents 

 appeared to be strong, both the large intact 

 shells and shell fragments occurred separately 

 in groups. Smaller pieces were commonly 

 found in troughs of sediment ripples. 



For all taxonomic groups combined, the 

 number of individual animals per unit area 

 calculated from photographs was substantially 

 higher at all four stations than estimates 

 made from the dredge hauls. Dredge data 

 yielded estimates of faunal density of 0.02, 

 0.16, 0.3, and 3.3 per square meter at stations 

 5, 42, 44, and 45, respectively, whereas the 

 photographic analyses for these stations 

 yielded estimates of 0.7, 1.7, 1.8, and 8.6 

 per square meter. Intrastation disparity 

 (dredge versus photographs) in density esti- 

 mates ranged from as much as 1:30 at station 

 5 to as little as 1:2.6 at station 45. 



The interstation density of species, genera, 

 and higher taxonomic groups varied in much 

 the same manner described above for all 

 groups combined. Substantial interstation 

 density differences were expected, but the 

 pronounced differences in density estimates 

 from the two sampling methods were unex- 

 pected. 



Quantitative results from the photographic 

 method are judged to be substantially more 



accurate than those from dredge-collection 

 data in this situation. Greater accuracy in 

 measuring the density of large epibenthic 

 invertebrates by analysing sea-bottom photo- 

 graphs, as opposed to dredging, is in keeping 

 with known inadequacies in the latter method. 

 Some of the principal deficiencies in dredging 

 are: (1) insufficient accuracy in measuring 

 the bottom area sampled; (2) inefficiency in 

 capturing specimens that lie in pockets, plus 

 the loss of animals that come in contact with 

 the dredge ground-chain and are pushed aside 

 or below (outside) the dredge bag; and (3) noise 

 or shock waves that may alert motile animals 

 and permit them to avoid capture. Only the 

 last of these is believed to have a detrimental 

 effect on the photographic method; apparently 

 the effect is not excessive. 



Fish 



Although the scallop dredge and photographic 

 system were not designed for capturing fish 

 or measuring fish abundance, a brief summary 

 of results concerning this subject may be of 

 interest. The number of fish caught in the 

 scallop dredge averaged 30 specimens per 

 10,000 square meters per station; all were 

 bottom-dwelling species. In contrast to this 

 apparent low abundance, the estimated density 

 based on photographic analyses were 690 

 specimens per 10,000 square meters per 

 station. The more common species represented 

 in these samples and photographs were: goose- 

 fish, Lophius americanus ; red hake; yellowtail 

 flounder, Limanda ferruginea ; and several spe- 

 cies of skates, Raja. Although the evidence 

 is meager, these results suggest the su- 

 periority of photographic methods over the 

 scallop dredge for judging the abundance of 

 bottom-dwelling fishes. 



Accuracy of quantitative information, plus 

 the capability of sampling large areas quickly 

 and relatively inexpensively, are features of 

 the photographic method that are particularly 

 desirable for certain types of survey and 

 inventory. 



ACKNOWLEDGMENTS 



Frank A. Bailey, Evan B. Haynes, Thomas E. 

 Quigley, and Patrick J. Twohig of the Bureau 

 of Commercial Fisheries Biological Labora- 

 tory, Woods Hole, Mass.; John Schlee, U.S. 

 Geological Survey; and Thomas Schopf, Marine 

 Biological Laboratory, Woods Hole, assisted 

 us aboard the R. V. Albatross IV . Bruce R. 

 Burns, Gilbert L. Chase, and Hariett Murray, 

 Bureau of Commercial Fisheries Biological 

 Laboratory, Woods Hole, processed samples 

 and photographic data in the laboratory ashore. 

 Officers and crew of Albatross IV cooperated 

 in operations at sea. 



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