36 



COMMERCIAL FISHERIES REVIEW 



Vol. 28, No. 7 



eating tuna and swordfish concentrations 

 based on analysis of the thermal environment 

 structure, and (2) survey the distribution and 

 abundance of tuna and swordfish in the North- 

 western Atlantic during late winter. 



Fig. 2 - Station pattern of M/V Delaware Cruise 66-2 (March 8- 

 April 6, 1966.) 



GEAR USED: Fishing gear consisted of 

 165-fathom units of long line with ten branch- 

 lines attached at 15 -fathom intervals. Each 

 10 -hook unit was buoyed from the surface 

 with a 5- or 20 -fathom line. Squid and her- 

 ring baits were alternately used on every 

 other unit. Adjunct equipment included a ma- 

 rine radiofac simile recorder, bathythermo- 

 graphs (BT's), bathykymographs (BKG's), 

 and a recording thermograph. 



METHODS OF OPERATION: The approxi- 

 mate geographic position of each fishing sta- 

 tion was selected using data from general sea 

 surface temperature isotherm charts and 

 sonic layer depth charts received daily from 

 the U. S. Naval Oceanographic Office by the 

 radiofac simile recorder on the vessel. The 

 validity of the data was checked and the ex- 

 act position of each station was determined 

 from analysis of actual observations on sea 

 surface temperature variation by recording 

 thermograph, and BT's along the vessel track 

 into the area. With the exception of two day 

 sets of long-line gear, 60 units of long-line 

 gear (600 hooks) were set after midnight at 

 each station and hauled after sunrise to per- 

 mit the gear to fish during the dark and light 

 hours of the day. The effect of current on 

 the gear was measured by plots of Loran 

 bearings on the ends of the long-line set at 

 time of setout and haulback. BT recordings 

 of the subsurface -temperature profile were 

 taken at the time and position of each Loran 

 bearing. The depth of the gear, and the time 



and depth of fish hooked, were recorded by 

 BKG instruments placed at the centers (be- 

 tween hooks 5 and 6) of several units on each 

 set. An exact time record was kept on each 

 unit of gear retrieved to relate the fish catch 

 to surface temperature variations on the ther- 

 mograph. 



RESULTS: An abundance of large bluefin 

 tuna ( Thunnus thvnnus ) was found in the west- 

 ern portion of ihe area surveyed. At one sta- 

 tion approximately 9 tons were taken on 600 

 hooks, a catch rate of 12.3 fish per 100 hooks. 

 A second sampling at another station in the 

 same area 2 weeks later yielded 3.5 tons on 

 600 hooks with a catch rate of 4.2 fish per 100 

 hooks, and suggests concentrations of more 

 than random occurrence. Bluefin tuna ranged 

 in size from 215 to 340 pounds (round) and 

 averaged 277 pounds. Catches totaling 17 tons 

 at 8 stations covered the entire 750-mile area 

 investigated and indicated a distribution of 

 that bluefin size group along the Gulf Stream 

 area from Cape Hatteras to the Grand Banks. 



Catches of swordfish (Xiphias gladius ) at six 

 stations covering the entire area of investiga- 

 tion indicated a thin distribution of the species 

 alongthe Gulf Stream area at that time of year. 

 Although the catches were small (17 total) it is 

 noteworthy that thesizeof fishinthe western 

 portion of the area (18-110 pounds, 13 fish) was 

 much smaller than fish in the eastern portion 

 (155-350pounds, 4fish). Average size of 

 swordfish on the cruise was 107 pounds. 



Yellowfin tuna ( Thunnus albacares) were 

 found at 4 of the 5 stations having surface 

 temperature of 69° F. or greater. Average 

 weight of 18 fish caught was 35 pounds. Alba- 

 core ( Thunnus alalunga) were taken in small 

 numbers at all but the 3 westernmost stations, 

 providing new distributional information on 

 the species at that time of year. Size of alba- 

 core averaged 34 pounds, with a range of 10 

 to 59 pounds. Big-eyed tuna ( Thunnus obesus ) 

 were taken at 4 stations, with a good catch 

 rate (2.5 fish per 100 hooks) at one of the sta- 

 tions. Size of big-eyed tuna averaged 102 

 pounds, with a range of 31 to 138 pounds. 



Large catches of blue shark ( Prionace 

 glauca) were made throughout the area. A 

 total catch of 359 blue shark from the 12 sta- 

 tions fished weighed an estimated 16 tons. 

 Shark damage to fish was not significant, al- 

 though considerable time was lost due to fre- 

 quent snarls and parting of the gear. 



