Biology of Swordfish, Xiphias gladius L., 

 in the Northwest Atlantic Ocean 



JAMES S. BECKETT" 



ABSTRACT 



The present knowledge of the biology of swordfish in the northwest Atlantic ocean is summarized. 

 Distribution of swordfish is bounded by 13°C surface isotherms with smaller (under 160 cm) fish in water 

 above 18°C. Males are smaller (under 200 cm) than females and are more frequent in warmer, southern 

 areas. Large fish make feeding excursions to the bottom, to depths of 500 m or more and temperatures 

 5-10°C. Females attain sizes of 550 kg and males 120 kg, but average size was 54 kg in 1970 commercial 

 landings. Growth is thought to be rapid with weights of 4, 15, 40, 70, and 110 kg attained at annual 

 intervals. Spawning is confined to warmer (over 24'C) southern waters. Tagging data (13 recoveries) 

 suggest fish spend the summer in one locality and return there in subsequent years. High recoveries (18.3%) 

 have been made of fish tagged while swimming free. 



The biology and distribution of swordfish has been 

 investigated by the staff of the Fisheries Research 

 Board of Canada's Biological Station at St. An- 

 drews, N. B. since 1958. This report summarizes the 

 information obtained during this period from a large 

 number of research cruises, from extensive shore 

 sampling of the commercial catch, and from the 

 available literature. 



DISTRIBUTION 



The geographical distribution of swordfish, 

 Xiphias gladius L., m the northwest Atlantic Ocean 

 varies considerably due to the marked seasonal vari- 

 ation in environmental conditions. In winter, the 

 species is confined to the waters associated with the 

 Gulf Stream (Fig. 1), where the surface tempera- 

 ture exceeds 18°C. However, in summer, as the edge 

 of the Gulf Stream moves north and the temperature 

 of the surface waters over the continental shelf in- 

 creases, the fish are found over a much wider area. 

 The summer range extends along the edge of the 

 continental shelf from Cape Cod to the Grand 

 Banks, with fish moving over the shelf in the western 

 part, and, near the mouth of the Gulf of St. Law- 

 rence, along the Cape Breton shore. Occasionally 

 fish are found in the Gulf of St. Lawrence as far 



north as the Miramichi River, while the most north- 

 erly record on the west coast of Newfoundland ap- 

 pears to be Bonne Bay (Wulff, 1943). 



The summer distribution is generally limited by 

 the 13°C isotherm, with few fish encountered below 

 15°C. Distribution by size shows that there is a size 

 differential in that larger fish are found in cooler 

 water, with few fish under90 kg round weight seen in 

 water of less than 18°C. 



Sex ratios also differ with temperature, as few 

 males are found in the colder (under 18°C) water. In 

 warmer water, males comprise some 25-30% of the 

 catch. This difference in sex ratios may be partially 

 explained by the smaller size of males since few 



Canada 



' Fisheries Research Board of Canada, St. Andrews, 

 Brunswick. Canada. 



New 



Figure 1. — Canadian commercial swordfish fishing areas. 



103 



