On the breeding areas of the Swordfish {Xiphias) 447 



35 hauls, 2 in 7 hauls,- and 5 in 1 haul, fished at approximately 30 metres. It was 

 exceptional therefore for more than one specimen to be taken in a haul. This indicates 

 that the fry are scattered, and that they often may be captured when the net is bcmg 

 drawn in. From Table II, it appears that the postlarval stages are to be found chiefly 

 in the upper 30 metres. Furthermore, the smallest specimens of 5-6 mm in length 

 were taken in nets which fished for one or more hours at depths down to more than 

 230 metres. Hence, it is hkely that the great majority, perhaps all, of the smaller 

 specimens taken in the nets which were towed rather deep below the surface were 

 actually caught when the nets were being drawn in. 



The specimens taken in nets towed in the upper 30 metres were on the average the 

 smallest. This may mean, as it does for the postlarval stages of many other oceanic 

 species, that larger specimens are found deeper than the smaller ones. The latter, we 

 must assume, remain chiefly at the surface where the pelagic eggs presumably float. 

 The small size of our nets and the fact that these were not closing nets makes it im- 

 possible, however, to reach any final conclusion on this point. Lutken's and Arata's 

 findings show, however, that the fry do not avoid strong sunlight in the uppermost 

 layers of the sea. They found postlarval stages of 10 mm and up to 5-8 cm at the 

 surface both during the day and at night. Thus, Lutken has. as already mentioned, 

 records from the Atlantic and Indian Ocean (Fig. 2) taken with a drag-net at the sur- 

 face. Arata's series of postlarval specimens and of the adolescent stages of 6-3-80-9 

 mm from the Gulf of Mexico and Straits of Florida were for the most part taken at 

 the surface in dip-nets. For the time being, it is not possible to determine whether 

 most of the postlarval stages live just below the surface or whether they live somewhat 

 deeper, perhaps within the upper 30 metres. 



The few Danish specimens of Xiphias from the Indo-Pacific show a vertical dis- 

 tribution similar to that in the Atlantic. Two specimens were taken with 50 metres 

 of wire out, one with 100 metres of wire out, three with 200 metres of wire out and 

 one with 350 metres of wire out. This means that they were from depths of 15-100 

 metres, unless they were captured when the gear was being hauled in. The size 

 of the specimens ranged from 4-9 to 17-1 mm in length. 



ENVIRONMENTAL FACTORS AND THE DISTRIBUTION OF THE FRY 

 Temperature. The influence of temperature on the distribution of the fry was des- 

 cribed above. It is clear that, in the breeding season, Xiphias seeks tropical or sub- 

 tropical areas with high surface temperatures. Although the species migrates far 

 north or south in northern or southern summers respectively, to feed where the 

 water masses have temperatures as low as 12°-13°C or a little lower," during the 

 breeding season it must migrate to areas where the temperatures are not lower than 

 23-5° C, more especially in water with temperatures between 25' and about 29 C. 

 as shown by the fact that most fry have been taken at localities where the tempera- 

 tures were within these hmits. Presumably Xiphias remains close to the surface 

 during spawning, but there is no definite information on this point. Since the tem- 

 perature at depths of 75-125 m is less than 23^ C at all localities where small 



=:< In one of these hauls from roughly 30 metres depth, one specimen was taken together with the 

 33 mm-specimen mentioned above. The latter is not included m the table. 



t Since Xiphias remains in the Mediterranean throughout the year, it must be able to surMvc m 

 water of 13° C, for the whole water mass falls as low as this m wmter. 



