4.33 Recruitment 



No information on rates, seasonal patterns, or an- 

 nual variations of recruitment was found in the 

 literature, nor was any information on the relation of 

 recruitment to stock size and reproductive rates. 



The overlapping migratory patterns found for 

 different groups of white marlin (Mather et al., 1972) 

 suggest that some groups may recruit adult fish from 

 others, in addition to their recruitment from spawn- 

 ing. 



The length (from orbit to fork of tail) of white 

 marlin at first capture in the Japanese longline fishery 

 varies with season and area (Fig. 11), but is usually in 

 the 90- to 120-cm range. The length (from tip of lower 

 jaw to fork of tail) at first capture in the sport fishery 

 off the middle Atlantic coast of the United States is 

 about 140 cm for males and 155 cm for females (de 

 Sylva and Davis, 1963). Erdman (1956) reported that 

 the smallest white marlin that he had observed at 

 Puerto Rico was 22 pounds (10 kg). Among the white 

 marlin examined by Krumholz (1958) at Bimini, 

 Bahamas, the smallest male was 20 pounds (9 kg) and 

 the smallest female 45 pounds (20 kg). Nakamura and 

 Rivas (1972) reported that the smallest white marlin 

 taken in each of three areas off northwestern Florida 

 in 1971 weighed 31-42 pounds (14-19 kg), and that the 

 smallest taken off South Pass, La., in each year from 

 1966 weighed 29-39 pounds (13-18 kg). 



4.4 Mortality and Morbidity 



4.41 Mortality rates 

 See 3.32. 



4.42 Factors causing or affecting mortality 



Little is known about the effect of natural factors 

 such as predators, food abundance, and environmen- 

 tal conditions (see 3) on the mortality of the white 

 marlin. The changes in its apparent relative abun- 

 dance (see 4.22) which have occurred since the 

 development of extensive oceanic longline fisheries, 

 however, indicate that fishing is an important cause of 

 mortality. 



4.43 Factors affecting morbidity 

 See 3.35. 



4.44 Relation of morbidity to mortality rates 

 No information appears in the literature. 



4.5 Dynamics of Population (as a Whole) 



De Sylva and Davis (1963) studied the dynamics of 

 the Ocean City-Atlantic City sport fishery up until 

 1960. Assuming similar effort over the years and 

 similar median weights for all fish caught whether 



boated or released, they found no apparent regular 

 decrease in median weight as the number of marlin 

 caught increased over the years observed. Thus, they 

 concluded there was no reason to believe that angling 

 had affected the stocks. 



The present indications that the apparent abun- 

 dance of the stocks and the average size of the fish 

 taken are decreasing, however, show that studies of 

 the dynamics of the population should be undertaken. 



4.6 The Population in the Community and 

 the Ecosystem 



As the white marlin is an oceanic species, no 

 specific study has dealt with the ecology of its wide 

 range of distribution. De Sylva and Davis (1963) dis- 

 cuss the relationship of the white marlin with the 

 round herring. On the basis of frequency of round 

 herring in the marlin stomachs, they determined that 

 areas of subsurface plankton concentration may be an 

 important factor of the white marlin community. 

 Squid, too, are a big item in the marlin's diet. 



Certain physical features of the oceanic environ- 

 ment are also pointed out by these authors. Salinity, 

 temperature, and oxygen patterns seem to play a role 

 in the location of marlin grounds. Submarine ridges 

 also seem to identify marlin feeding areas. This may 

 be due to an upwelling of plankton attracting the fish 

 and squid on which the marlin feed. 



Being members of the holoepipelagic community 

 (Parin, 1968) they perfer the isothermic surface layer 

 of the North subtropical, tropical, and South sub- 

 tropical regions of the Atlantic and adjacent seas. 

 They reside above the main thermocline but during 

 feeding excursions may pass into its upper horizons. 



In the epipelagic environment the white marlin is 

 located on the sixth of seven trophic levels (Fig. 14) 

 beneath only the most powerful and swiftest sharks, 

 Carcharodon and makos (Parin, 1968). 



Fluctuations in populations occur in a cyclical 

 manner according to the seasonal migration and dis- 

 tribution discussed in 2. 



5 EXPLOITATION 



5.1 Fishing Equipment 

 5.11 Gears 



The types of fishing gears used for the white marlin 

 vary somewhat from one area to another but all 

 employ the basic hook and line technique. The major 

 classifications are rod and reel, handline, and 

 longline. 



In the early days of sport fishing for white marlin 

 the equipment (depending on the experience of the 

 angler) consisted of linen line, varying between 9 and 

 18 thread (27- to 54-pound [12- to 25-kg] test), a rod 

 with a 6- to 12-ounce (170- to 340-g) split bamboo tip, 



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