pelagic fish distribution and abundance. Most 

 obvious of these is the track of the Gulf 

 Stream through the area (fig. 1), with associated 

 thermal gradients and related structures along 

 its frontal zone (von Arx, Bumpus, and Richard- 

 son, 1 955) . Surface and subsurface temperature 

 observations, 2ind more recently ( Delaware 

 cruises 64-10, 65- 1 , 65-3) synoptically charted 

 surface temperature data received by vessel 

 radiofacsimile equipment, have been funda- 

 mental criteria in determining where to set 

 longlines. Other environnnental information 

 collected and used on some of these cruises 

 has included determinations of current (drift), 

 transparency, salinity, and abundance of 

 trophic organisms. 



EFFORT 



The total effort expended is shown by the 

 number of longline sets and hooks fished within 

 each 1° latitude and longitude square (fig. 2) 

 and indicates the relative amount of coverage 

 in the various sections of the area surveyed. 

 The monthly effort, based on the number of 

 longline sets and hooks fished within each 1° 

 square, is given in fig. 3-14. 



In almost all instances the effort reflects 

 exploratory fishing methods, in which sam- 

 pling type gear was used from a single ves- 

 sel. Owing to the vessel's research commit- 

 ments, cruise schedules could not be altered 

 to make up for time lost because of bad 

 weather. To obtain geographic coverage, sta- 

 tions were generally spaced at considerable 

 distances fronn one another; seldom was more 

 than a single day's effort spent at one location. 

 Commercial fishing efforts would likely in- 

 clude more than one vessel, concentrate on 

 most productive areas, adjusttrips to weather, 

 and use gear and methods designed to catch 

 one or a few species at a time. 



CATCH RATES 



Catch rates are based on the number of 

 fish caught per 100 hooks fished. The total 

 and monthly average and maximum catch rates 

 of all longline sets for bluefin, yellowfin, 

 albacore, and bigeye tunas, and swordfish are 

 broken down into 1° latitude and longitude 

 squares (fig. 15-66 and 69-81). The monthly 

 catch rates of skipjack and blackfin tunas are 

 given in fig. 67 and 68. All catch rates have 

 been rounded to one decimal place; rates less 

 than 0.05 are noted by asterisk. 



Where average and maximum rates are 

 the same, generally only one longline set is 

 indicated; however, because of exceptions 

 the number of longline sets in each 1° square 



should be obtained by referring to the corre- 

 sponding effort chart (fig. 2-14) in relating 

 rate and effort. 



All longline sets were used to calculate 

 tuna and swordfish catch rates. Although 

 catches of swordfish were alnnost entirely 

 from longline sets fished during the night, 

 some night sets fished into daylight and caught 

 tuna, and some day sets also caught swordfish. 

 Areas showing no catches of swordfish (fig. 

 69-81), therefore, do not necessarily indicate 

 that there were no swordfish present, but 

 more likely reflect "no catch" because of day- 

 light fishing. To permit a more detailed 

 analysis of day versus night sets, the fishing 

 time for each longline set is included in the 

 fishing log data (tables 2-13). 



ACKNOWLEDGMENTS 



The authors gratefully acknowledge the sup- 

 port of the National Science Foundation 

 (Grants G6172, G19601, G8339, G681), Bureau 

 of Commercial Fisheries (14-17-0007-272), 

 the Lou Marron Science Fund, and the National 

 Geographic Society. 



LITERATURE CITED 



ANONYMOUS. 



1960. Report on exploration of tuna fishing 

 ground of Caribbean Sea, western part 

 of North Atlantic Ocean and southern 

 waters of Australia, on fishing industry 

 of various countries of call and on tuna 

 fishing bases, 1959. #2 Deep Sea Fish- 

 ing Section, Production Department, 

 Japanese Fishery Agency, May 1960. 

 BUREAU OF COMMERCIAL FISHERIES. 



1956. Bluefin tuna commercial distribution 

 in Northwest Atlantic surveyed by M/V 

 Delaware (cruise 27). Com. Fish. Rev, 

 18 (12): 42-44. 



1957a. Excellent catch of tuna nnade south 

 of Nantucket (M/V Delaware cruise 

 57-3). Com. Fish. Rev. 19 (5): 28-29. 



1957b. Experimental long-line tuna trip 

 successful (M/V Delaware cruise 57-5). 

 Com. Fish. Rev. 19 (8): 27-29. 



1958a. Exploratory tuna fishing with long - 

 lines in western North Atlantic (M/V 

 Delaware cruise 57-8). Com. Fish. Rev. 

 20 (1): 38-39. 



1958b. Tuna fishing explorations in western 

 North Atlantic continued (M/V Delaware 

 cruise 58-2). Com. Fish. Rev. 20 (7): 

 35-36. 



1958c, Tuna fishing explorations continued 

 in western North Atlantic (M/V Dela- 

 ware cruises 58-3 amd 58-4). Com. 

 Fish, Rev. 20 (9): 47-48, 



