that a group of white marlin winters off Venezuela 

 and summers in the Gulf of Mexico (Mather et al., 

 I 1972). The distribution of the group which summers 

 off the middle Atlantic coast of the United States co- 

 incides in winter (off northern South America) with 

 that of white marlin which summer off Venezuela and 

 in the Gulf of Mexico, and in spring (in the Straits of 

 Florida) with other fish which summer in the Gulf of 

 Mexico. Thus interchanges between these groups, 

 such as have been indicated by a few tag returns, are 

 probable. 



The fact that not one of the white marlin tagged in 

 the western North Atlantic has been recaptured in 

 other areas, and the low longline catch rates in the 

 equatorial area (Ueyanagi et al., 1970; Hayasi et al., 

 1970; Mather et al., 1972), as well as the widely 

 separated spawning areas (see 3.16), indicate that the 

 marlin stocks of the North and South Atlantic are dis- 

 tinct. The lack of tag returns showing migrations from 

 the western to the eastern North Atlantic is less con- 

 clusive as an indication of stock separation, since the 

 longline and sport fishing efforts in the latter area are 

 slight. 



Robins (1974) cites Ueyanagi et al. (1970, appendix, 

 Figs. 2j, k, 1) as an indication that the white marlin 

 which concentrate off Gibraltar in late summer may 

 move progressively south along the coast of Africa in 

 the fall to about lat. 5°N. 



The monthly distribution of longline catches in the 

 South Atlantic (Fig. 5) shows a heavy concentration of 

 white marlin off Brazil in September-February and a 

 lesser one off western Africa in June-July, with con- 

 siderable areas of high catch rate in various mid- 

 ocean areas in July and October-February (Hayasi et 

 al., 1970; Mather et al., 1972), but it is not certain 

 that these occurrences represent the migrations of a 

 single group of fish. 



Most fish migrations relate to spawning or feeding. 

 The summer concentrations of white marlin in the 

 North Atlantic (Venezuela, Gulf of Mexico, Cape 

 Hatteras-Cape Cod area, and off Gibraltar) are for 

 feeding (see 2.3), and occur in areas which are highly 

 productive, at least in comparison with the surround- 

 ing waters. The spring concentration in the vicinity of 

 the Greater Antilles, the Bahamas, and Florida is for 

 spawning (see 2.3 and 3.16). Tagging has shown that 

 one group of white marlin migrates from a summer 

 feeding area (Cape Hatteras-Cape Cod) eastward and 

 southward to a wintering area (off northern South 

 America) whose attractive properties are not known, 

 then northward to a spring spawning area (Greater 

 Antilles-Bahamas) and thence further north to the 

 summering area. Tagging also indicates that another 

 group of white marlin may migrate from a summer 

 feeding ground in the Gulf of Mexico to winter among 

 the northwestern Bahamas, spawn in spring in the 

 Bahamas-Cuba area, and return to summer in the 

 Gulf. The group, which, on the basis of longline catch 

 distribution (Mather et al., 1972), appears to summer 



in the Gulf and winter in the southeastern Caribbean, 

 may also spawn in spring near the Greater Antilles. 

 In the South Atlantic, the summer concentration 

 off southern Brazil is for spawning (see 2.3 and 3.16). 

 It appears that the marlins move to this area from off 

 northeastern Brazil in October-November and dis- 

 perse northward in March-May (Hayasi et al., 1970). 

 These authors also note a feeding concentration of 

 large females off Africa around lat. 10° S from June 

 through August. 



3.52 Schooling 



Generally not considered a schooling fish, white 

 marlin are most often seen as individuals or in pairs 

 "tailing" with only the dorsal lobe of their caudal fins 

 showing. Small schools (5-12 fish), however, are oc- 

 casionally seen feeding on schools of bait, or tailing, 

 but loose aggregations of numerous fish scattered over 

 fairly large areas are more typical. 



At some point in their life cycle the white marlin 

 may come together in schools. De Sylva and Davis 

 (1963) proposed that they may school according to 

 size or sex at various seasons of the year. Little con- 

 crete evidence is available, however, for determining 

 the extent of time a school may remain together or the 

 size such schools may attain. 



3.53 Responses to stimuli 



As discussed previously, temperature seems to play 

 a crucial part in the response of white marlin. Their 

 disappearance from the Ocean City fishery during a 

 temperature drop of a few degrees and return in 

 numbers similar to catches before the drop as soon as 

 the temperature returned to normal (Earle, 1940) is 

 one example. Similarly the white marlin arrive along 

 the east coast of the United States during the warm 

 summer season and move offshore and to the 

 southward as fall and cold water approach (Mather et 

 al., 1972). Gibbs (1957) noted the relationships 

 between the distribution of white marlin in the Gulf of 

 Mexico and the 75°F (23.9°C) isotherm (see 2.3). 



Hayasi et al. (1970) note that the two separate areas 

 of high hooking rates for white marlin in the North 

 and South Atlantic both shift northward during May- 

 October and southward during November- April. In 

 other words, they both move to higher latitudes as the 

 water warms and to lower latitudes as it cools. 



De Sylva and Davis (1963) performed a most ex- 

 haustive environmental study of white marlin 

 grounds from Atlantic City, N.J. to Ocean City, Md. 

 They found that temperature, salinity, oxygen con- 

 tent, and plankton volumes all played a role in the 

 presence of the white marlin as explained in 2.3. 



If marlin seek certain optimum environmental con- 

 ditions at one time or another, they may swim in 

 deeper layers when surface conditions are not 

 favorable. In such a case types of fishing gear used will 



77 



