Papers in Marine Biology and Oceanography, Suppl. to vol. 3 of Deep- Sea Research, pp. 438-450. 



On the breeding areas of the Swordfish {Xiphias)* 



By A. Vedel Taning 

 Marine Biological Laboratory, Charlottenlund Slot, Denmark 



Summary — The Danish oceanographic expeditions with the Research Steamer Dana and other ships 

 have obtained about 60 postlarval stages of Xiphias (between 5 and 46 mm in length) from all 

 oceans. Most of these, however, were taken in the western North Atlantic. 



The distribution of the smallest stages (i.e. smaller than 20 mm in length) indicates that an impor- 

 tant breeding area lies north and northeast of the Lesser Antilles in the southern part of the Sargasso 

 Sea. Breeding areas are also indicated by records of small postlarvae west of Sumatra, in the South 

 China Sea, in the Celebes and Banda Seas and off the Marquesas. 



Some spawning occurs during all seasons, but maximal spawning seems to take place during 

 February-April in the North Atlantic. Spawning probably takes place at the same season in the 

 western Pacific, but it occurs later in the year in the Mediterranean owing to the special temperature 

 conditions there. The fry are usually found in water of about 24° C. or higher. They are generally 

 captured between the surface and a depth of about 30 metres. The material at hand seems to show 

 a growth rate of about 8 cms during the first year, but sufficient material is not yet available for 

 an accurate determination of the growth rate. The fry preferably feed on fish larvae up to nearly the 

 same size as the small voracious Xiphias larva itself (Fig. 1). Figures are given of three develop- 

 mental stages and outline charts show where fry have been taken. Fishing for swordfish may be 

 possible (by floating lines) in the main spawning area in the western North Atlantic. 



Recently the importance of large oceanic fish has increased commercially as well 

 as in sports fishing. It has therefore become not only desirable, but also possible, 

 to broaden our knowledge of the fish fauna on the high seas. Among these large 

 fish, the swordfish (Xiphias) is the most appreciated by epicures and sportsmen 

 alike. Although landings of this fish have increased greatly in the last generation, our 

 knowledge of this species still leaves much to be desired. Recently, however, Arata 

 (1954) has made a valuable contribution to its biology, including a description of its 

 earliest development. Therefore, detailed description of the various developmental 

 stages is omitted here, but we have included a few figures of them (Fig. 1). 



While many pelagic fish are represented by enormous numbers of fry in the material 

 collected by the Dana and other Danish vessels, this is not the case for several of the 

 large species, e.g. the tunny and bill-fish. Thus far, only 500 specimens of the latter 

 have been found in more than 3000 pelagic samples. Some 400 of these belong to 

 the Istiophoridae, and only about 60 to the Xiphiidae. 



The reasons that so few specimens are taken in the youngest stages (about 5-45 mm 

 in length) is undoubtedly chiefly due to the fact that the fry of these large predators 

 of the sea are relatively scarce in comparison with the abundance of the fry of smaller 

 species, and to the fact that they very quickly attain a size which enables them to 

 escape the gear (2 or 1^ metre ring net of stramin or coarse silk) generally used by 

 the Dana in catching fish fry. By the time Xiphias fry reach a length of about 12-13 

 mm, they attain sufficient swimming speed to escape the nets (generally towed at a 

 speed of about 1 metre per second). Thus, only about 20% of the fry caught are over 



* Papers from the Dana Oceanographical Collections No. 45. 



438 



