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Juveniles are common only in tropical and sub-tropical waters and migrate to higher latitudes as they mature (Ref. 7176). In southeastern Australian waters, sharp temperature and salinity gradients across oceanic fronts provide favourable conditions for concentrations of broadbill swordfish (Ref. 6390). Little is known of large scale movements by adult broadbill swordfish. Mature fish make only limited local movements (Ref. 9742). Tracking of fish using acoustic tags has shown that broadbill swordfish typically move to surface waters at night and inhabit deeper waters during the day, reaching depths up to 600 m (Ref. 30447). These vertical movements may be rapid and involve changes in waters temperature as great as 19°C (Ref. 6390). Some tagged fish spend daylight hours near the sea bed close to the continental shelf break or submerged banks and move offshore at night (Ref. 6390). In the eastern Pacific broadbill swordfish are commonly seen basking at the sea surface for short periods during the day, a behaviour that may allow the fish to recover from stress associated with low temperature and dissolved oxygen levels in deep water (Ref. 30447). Broadbill swordfish are normally solitary, but pairs of fish are regularly observed at the surface off the Californian coast (Ref. 30447).
Larvae are most common within a few m of the surface during the day but may move to depths of 30 m at night (Ref. 30448). Swordfish larvae longer than 10 mm feed almost exclusively on larvae of other fish species (Ref. 6390). Young swordfish is preyed upon by blue shark, tuna and marlins. Parasites of the species include a cestode, Fistulicola plicatus; trematode, Tristoma spp.; monogenean, Tristoma coccineumand T. integrum; nematode, Thynnascaris incurva and a copepod, Pennella filosa (Ref. 5951). |
