DISTRIBUTION OF TUNAS IN NORTHWESTERN ATLANTIC 



339 



of the evidence available, the fish are assumed to 

 migrate from the general oceanic area south of the 

 Gulf Stieam. Yellowfin are seldom reported from 

 inshore areas along the east coast, and confirmed 

 records are nonexistent for the New England in- 

 shore area. However, I received an unconfirmed 

 report of two yellowfin being taken with longline 

 gear on Middle T?ank, south of Gloucester, Mass., 

 during the summer of 10.59. Captures of the 

 species in winter and spring have all been made 

 in the southern areas. The yellowfin captured 

 north of the Bahamas by the Theodore N. Gill in 

 February 1953 (Anderson, Gehringer and Cohen, 

 1956) and the catch rate of 14.1 yellowfin per 100 

 hooks in the Gulf Stream east of Cape Hatteras 

 in May provide evidence to support the assump- 

 tion of migration from oceanic areas in the south- 

 ern portion of the region. 



Temperatures recorded at the fishing depth of 

 the longline gear at stations in the northwestern 

 Atlantic where yellowfin were caught compare 

 favorably with surface water temperatures at sta- 

 tions in the eastern Pacific where surface-dwell- 

 ing yellowfin were caught. Surface temperatures 

 were recorded during extensive tuna-tagging op- 

 erations conducted from 1952-59 by the California 

 Department of Fish and Game, and temperature 

 data were made available by Blunt and Messer- 

 smith (1960) for localities at which tuna were 

 tagged tliat were later rex-overed. Using these 

 data, a weighted average temperature of 71.4° F. 

 was calculated for surface-caught yellowfin in the 

 eastern Pacific. This is closely comparable to the 

 weighted average of 72.1° F., calculated for water 

 depths at which the subsurface yellowfin of the 

 northwestern Atlantic were caught. 



OTHER INHABITANTS OF THE OCEANIC 

 REGION 



In addition to tunas, fishes belonging to several 

 other species were taken by the longline gear 

 ( table 2) . Many of these were little-known species 

 in the oceanic northwestern Atlantic prior to Del- 

 aioare explorations. 



Sharks were taken at a high percentage of long- 

 line stations, and their presence is important in 

 evaluating the commercial potential of oceanic 

 longlining in an area, because longline-caught 

 tuna may be damaged to varying degrees by 

 sharks. Shark damage to individual tuna may 



Table 2.— Species taken on longline gear in the oceanic 

 northirestcni Atlantic (luring Prlairarr cxiiloraliMm 



Family 



Lamnldae 



Carcharhinldae 



Sphymidae 



Alcpisauridae,- 



Sclentlflc name 



Lamprididac-- - 

 Coryphaenidae. 



Tiniinidae - 



Scombridae 



Istiophoridae.. 

 Xlphildae 



hUTUS oxyrinckua Rafinesque 



Lamna na«u« (Bonnatcrrc)-- 



Carcharhinus lloridanut Blcelow.. 

 Carcbarhinus /o/iflimanuj (Poey) 

 Carctiaraliinua obtcurut (LeSueur) 

 CaTcharhimu falciformu (MuUer 

 and Henle). 



Prionace glauca (LUinaeus) 



Sphi/rna sp 



Alepisaurns fero Lowe — 



Alepisauriis bremrostris Glbbs 



Lampris regiun (Bormatene) 



Coryphaena hippurus Linnaeus.. . 



Taractts lonijipiiini! (Lowe) 



AcaiMocyliium solnnderi (Cuvler) 

 Eutbynnn.1 pelamia (Linnaeus) .- 

 Thunnus alalunga (Bonnaterrc). 

 Thunnus alhacarea (Bonnaterrc). 



Thunnus atlantkus (Lesson) 



Thunnus obesus (Lowe) 



Thunnus thynnus (Linnaeus) 



Makaira aUnda (Poey) 



Makaira nigricans LacfpMe 



Xiphias gladius Linnaeus - . 



Common name 



Mako. 

 Porbeaple. 

 Silky shark. 

 Whiietip shark. 

 Dusky shark. 

 Sickle shark. 



Blue shark. 

 Hammerhead shark. 

 Longnose lancetfish. 

 Lance tflsh. 

 Opah. 

 Dolphin. 

 BiKscale pomfret. 

 Wahoo. 

 Skipjack tuna. 

 .Mbacore. 

 Yellowfin tuna. 

 Blackfin tuna. 

 Bigeye tuna. 

 Bluclln tuna. 

 White marlln. 

 Blue marlln. 

 Sword fish. 



vary from minor superficial damage to complete 

 loss. Tunas having minor damage are in most 

 cases acceptable to the canning industry. Per- 

 cents given in the following paragraphs represent 

 only the occurrence of shark damage, not the se- 

 verity of the attack. During explorations in the 

 northwestern Atlantic, 4.2 percent of the tuna 

 caught were reported damaged by sharks. In ex- 

 plorations in the Gulf of Mexico, 13.6 percent of 

 the yellowfin tuna that were caught were damaged 

 to varying degrees (Wathne, 1959), and the Pa- 

 cific Oceanic Fisheiy Investigations recorded 20- 

 percent damage for yellowfin in the Line Islands 

 area (Iversen and Yoshida, 1956). 



In the oceanic areas near the Gulf Stream 

 where bluefin tuna were taken in relatively large 

 quantities, veiy little shark damage occurred. 

 Damage ranged from zero to a high of 12.5 per- 

 cent at stations yielding large quantities of blue- 

 fin. There was no shark damage at stations 

 fished during cruise 59-7, even though approxi- 

 mately 35 tons of bluefin were caught. More yel- 

 lowfin have been damaged by sharks in the Gulf 

 Stream area, however, than bluefin, and the per- 

 centage of damaged yellowfin appears to be com- 

 parable to that of other oceanic areas. Damage 

 ranged from zero to 20.6 percent of the fish caught. 

 All the species of sharks responsible for tuna 

 damage are not known. Sharks observed as they 

 attacked tuna being hauled to a point near the 

 surface were usually whitetips, Carcharhinus 

 longimanm (Poey). A^liitetip sharks are also 

 suspected of damaging tuna in the Gulf of Mexico 



