Spawning aggregation of the lanternfish Diaphus danae (family Myctophidae) in the north-western Coral Sea and associations with tuna aggregations

Abstract

A spawning aggregation of the lanternfish Diaphus danae in the Coral Sea, that is fed on by spawning aggregations of yellowfin and bigeye tuna, has been sampled by mid-water trawling for the first time. Males and females in the aggregation occurred at a ratio of 23 to 1 and occupied two non-overlapping size classes (males 71.2–95.1-mm standard length (SL), females 99.0–121.4-mm SL). Hydrated oocytes with single oil droplets, which indicated imminent spawning, were in higher proportion in the first trawl (2134 hours to 2234 hours) than in the final trawl (0324 hours to 0424 hours) through the aggregation. Maximum estimated female D. danae fecundity (25 803) and gonadosomatic index (34.01) were higher than for any other lanternfish species recorded. Bigeye tuna (Thunnus obesus) individuals collected from aggregations were estimated to have 81–319 D. danae specimens in their stomachs. The annual Coral Sea D. danae aggregation is the only confirmed lanternfish spawning aggregation in Australian waters. The D. danae spawning aggregation provides a rich, transient foraging resource for spawning bigeye and yellowfin tuna in the Coral Sea, these being the only known tuna spawning aggregations in the Eastern Tuna and Billfish Fishery.