rate over the range of the species is doubtful. Thus, 

 factors affecting recruitment such as growth, preda- 

 tion, and migration act differentially in various stocks 

 of sailfish throughout the world's oceans. 



No estimates of recruitment have been found in the 

 literature. Yet in the light of the high growth rate and 

 high natural mortality suggested by de Sylva, it 

 follows that the reproductive rate and recruitment 

 rate should be higher than in slower growing, longer 

 lived species of similar population size. 



4.4 Mortality and Morbidity 



4.41 Mortality rates 



There have been no studies on the mortality of sail- 

 fish, although de Sylva (1957) stated that it seemed 

 evident that natural mortality is high off southern 

 Florida based on the fact that only two year classes 

 support the sport fishery. 



4.42 Factors causing or affecting mortality 

 See 3.34. 



4.43 Factors affecting morbidity 

 See 3.35. 



4.44 Relation of morbidity to mortality rates 

 Nothing found in the literature. 



4.5 Dynamics of Population (as a Whole) 

 Nothing found in the literature. 



4.6 The Population in the Community and the 

 Ecosystem 



There has been no detailed study of the ecology of I. 

 platypterus over the whole range of its distribution. 

 However, the direct relation between this species and 

 some of the physical features of the biotope in certain 

 localities have been discussed by Voss (1953), 

 Gehringer (1956), Cadenat (1961), Ovchinnikov (1966, 

 1970), Williams (1967, 1970), Kume and Joseph 

 (1969a), and Yurov and Gonzales (1971). On a 

 broader basis these features are discussed fully by 

 Parin (1968). The vertical zone of the community in 

 which the sailfish lives is characterized by good il- 

 lumination and is likely to be delimited below by 

 temperature at the main thermocline (from 10-20 m to 

 200-250 m, depending on area). Temperature is ap- 

 parently important also in the latitudinal distribution 

 of the species and some authors, Ovchinnikov (1966, 

 1970) and Kume and Joseph (1969a), suggested that 

 the 28°C isotherm is optional for the species, while 

 Cadenat (1961) indicated that the increased abun- 

 dance of sailfish in the inshore waters off the Ivory 

 Coast coincided with approximately this 



temperature. The association of larval /. platypterus 

 with the warm waters of the Gulf Stream was in- 

 dicated by Gehringer (1956) and of larvae and adults 

 with the Kuroshio Current by Yabe (1953), Ueyanagi 

 (1959), and Howard and Ueyanagi (1965). It is likely 

 that the greatest effect salinity produces on the 

 ecosystem in which sailfish live occurs at the bound- 

 aries of surface water masses and other regions in 

 which a rise in salinity occurs simultaneously with a 

 rise in temperature, which produces conditions con- 

 ducive to high productivity. Aggregations of sailfish in 

 such areas have been shown off West Africa and off 

 the east coast of Brazil by Ovchinnikov (1966, 1970) 

 and by Ueyanagi et al. (1970). 



5 EXPLOITATION 



5.1 Fishing Equipment 

 5.11 Gear 



The primary commercial fishing gear for sailfish is 

 the tuna longline. Basically, the tuna longline is a 

 drifting horizontal line of considerable length (up to 

 120 km), from which single-hooked branch lines hang 

 down at regular intervals. The gear and fishing 

 methods are well known and have been described by 

 Yoshida (1966). 



Trolling is the primary method used by sport 

 fishermen for catching sailfish and in principal con- 

 sists of towing a baited hook or lure through the water 

 to simulate a swimming fish. The bait is trolled astern 

 of a motor launch, and the line is loosely connected on 

 its passage inboard to a clip attached at the tip of a 

 laterally directed trolling pole (locally called 

 "tangon" or "outrigger"). When a sailfish strikes the 

 bait, the line snaps free from the clip. This momen- 

 tarily stops the bait's progress through the water and 

 is supposed to resemble the effect of the preliminary 

 strike on a live fish after which the sailfish turns and 

 swallows the bait. 



5.12 Boats 



The types of fishing vassels used in tuna longlining 

 have been described, again by Yoshida (1966). No 

 special boat is required by sport fishermen. All that is 

 necessary is one which has an open stern where the 

 angler may stand, a trolling pole on one or both sides, 

 and the power to troll at up to 6 knots. Nevertheless, 

 the design of many modern, sport fishing boats is 

 highly sophisticated, incorporating additional 

 facilities for the fisherman. 



5.2 Fishing Areas 



5.21 General geographic distribution 

 See 5.22. 



116 



