SCIENTIFIC COMMITTEE THIRD REGULAR SESSION 13-24 August 2007 Honolulu, United States of America EVALUATION OF PARASITE MARKERS TO ACCESS SWORDFISH STOCK STRUCTURE

Executive Summary A preliminary trial was undertaken to determine if there are appropriate parasites in broadbill swordfish (Xiphias gladius) for testing residency hypotheses and stock relationships. The gills and guts of 34 swordfish, eight from New Caledonia, 10 from Australia (Queensland), and 16 from New Zealand, were examined for parasites. Three species of monogenean were found on the gills (Tristoma adintegrum, Tristoma adcoccineum and an unidentified capsalid); three species of nematode in the stomach (Maricostula sp., Hysterothylacium sp. A, and Hysterothylacium sp. B); two cestodes in the stomach and encysted in the mesenteries (Pseudeubothrium sp. and Hepatoxylon sp.); and one digenean in the stomach (Hirudinella sp.). Swordfish from New Caledonia were also examined for ectoparasites. The parasite fauna of swordfish from the three areas was dominated by adult nematodes. The largest of the nematodes, Maricostula sp., showed differences in abundance among the three areas. The other two nematodes, species of Hysterothylacium, also showed significant differences between areas, but these adult worms may have limited application as a biological tag, reflecting short-term feeding patterns of the host. Three parasites were identified that are potential markers of movement of swordfish between tropical and temperate waters. 1) The digenean Hirudinella is likely to be a short lived parasite acquired in tropical areas. 2) Larval cestodes of Hepatoxylon sp. are thought to be acquired in temperate areas. 3) A pennellid copepod recorded in swordfish from New Caledonia, is likely to be acquired in tropical areas. This large ectoparasite is readily observed on whole swordfish, and presence/absence could be recorded by fishery observers, without the need for returning samples to the laboratory.