catches in February. It is possible that more inten- 

 sive sampling from July to September would show 

 this time to be equally productive, since Tuning 

 (1955) obtained several larvae during these months 

 despite low fishing effort. 



Temperature and Salinity Relationships 



On the basis of larval catches, it is believed that 

 swordfish do not spawn in waters less than about 

 23°C. At one station where swordfish larvae were 

 found, the surface temperature was 22.4°C, but at 

 all other stations it exceeded 23.4°C. Other authors 

 report similar findings (Arata. 1954; Taning, 1955: 

 Kondritskaya, 1970). Spawning also apparently oc- 

 curs only within a narrow range of salinities. Arata 

 (1954) found larvae only in areas with salinities of 

 35.75"/i)(i or more. FRB sampled a wider range of 

 salinities than did Arata, and also found larvae at 

 lower salinities. One station had a salinity of 

 35.40"/iHi. At all other larval stations, the salinity 

 was 35.46"/ijij or more. 



Thus, while the lower salinity limit remains indef- 

 inite, it must be around 35.5"/(i(i. No estimate can 

 be made of the upper salinity limit since both the 

 FRB and Arata (1954) investigations found larvae 

 at the highest salinities sampled. 



It should be noted that while temperatures and 

 salinities may play an important role in the location 

 of spawning grounds, these cannot be the sole de- 

 termining factors, since very many stations with 

 "ideal'" temperature and salinity conditions pro- 

 duced no larvae. 



Vertical Distribution of Larvae 

 and Time of Capture 



Swordfish larvae appear to frequent surface wa- 

 ters. All but three of our specimens were caught in 

 surface nets. Arata (1954) reported that 70-m 

 oblique tows at each station captured only one lar- 

 va. However, when the same equipment was used 

 for one 30-min surface tow. it netted three small 

 specimens. Most other larval captures were made 

 using dipnets (Arata, 1954; Arnold, 1955; Gor- 

 bunova, 1969) or a variety of nets towed horizon- 

 tally at the surface. Taning ( 1955) used a P/2 to 2-m 

 ring net towed in the upper 30 m. Rivers (1966) 

 reports 1 13 larvae caught in a single cruise with a 

 1-m nekton ring net. Gorbunova (1969) caught most 

 of her specimens using a pleuston net in the upper 

 30 cm. 



Gorbunova ( 1969) and Parin (1967) consider feed- 

 ing behavior in explaining the predominances of 

 larvae at the surface. They found that larvae were 

 most abundant in the catches in the morning and 

 evening and postulated that these twilight hours 

 coincide with the periods of most intensive feeding. 

 Presumably, at these hours the swordfish rise into 

 the more productive surface layers to feed. At mid- 

 day and at night, they disperse away from the sur- 

 face. In contrast, Arata (1954) obtained his best 

 catches by day (only three specimens were caught 

 at night). Arnold (1955) caught most of his speci- 

 mens at night though he may have attracted the 

 larvae by nightlighting. 



Our data do not suggest such periodicity of oc- 

 currence at the surface. Catch rates are similar for 

 both the day (0600-1800) and night (1800-0800) 

 hours. Nor is there any apparent increase in catch 

 rate during the twilight hours. 



Not all surface tows take larvae. Taning (1955) 

 noted that, while larger nets were successful, a Vi-m 

 ring net was easily avoided by even small larvae. In 

 general, larvae more than 70-80 mm in length are 

 seldom taken even in large nets towed at high 

 speeds. 



SUMMARY 



From 1965 to 1972, eight cruises were made to 

 the Caribbean and adjacent seas and to the Gulf 

 Stream. Plankton nets were towed and oceano- 

 graphic observations were made at 280 stations. 



Altogether 1 19 swordfish larvae from 6.5 to 1 10.6 

 mm were found in the following areas: Gulf Stream 

 system from Florida to Cape Hatteras, northeast- 

 ern Gulf of Mexico, northwestern Caribbean, west 

 of Lesser Antilles, southwest of Barbados, and 

 Virgin Islands. 



There appears to be an extensive spawning area 

 in the northwestern Caribbean. Gulf of Mexico, 

 and in the Gulf Stream system north to Cape Hat- 

 teras. Two other spawning areas are proposed: one 

 southeast of Barbados, and one in the Southern 

 Sargasso Sea-Virgin Islands area. 



Swordfish larvae are seldom found in tempera- 

 tures below 23.5°C. They were found only in waters 

 with a salinity of 35.4"/oi) or more. 



The larvae were caught almost exclusively in sur- 

 face nets. Although other authors have suggested 

 daily periodicity in larval abundance at the surface, 

 catch rates for our collections were comparable for 

 all periods of the day. 



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