A Very Large Spawning Aggregation of a Deep-Sea Eel: Magnitude and Status

Abstract

Multiple lines of evidence substantiate the existence of a very large aggregation of the basketwork eel, Diastobranchus capensis, on the small (3 km2) Patience Seamount off southeast Australia. The aggregation appears to be present year-round, but largest in the austral autumn when composed of spawning eels. Twenty eels caught in April 2015 (14 female, 6 male) were all in advanced stages of spawning condition. The eel’s abundance in the aggregation was very high as measured at seamount, local and regional scales. Hydroacoustic measurement of the spawning aggregation’s dimensions (~100 × 1000 m) and conservative counts of 100 s of eels along camera transects of ~1000–2000 m length indicate 10,000 s individual eels may have been present. The absence of other known spawning locations indicates the Patience Seamount is a regional-scale spatial anchor for spawning. The aggregation was protected in a marine park in 2007 following a decades-long impact from bottom trawling, indicating that the population can be expected to stabilise and recover. Monitoring the aggregation’s status, and validating seasonal spawning, provide important opportunities to examine conservation-led recovery in the deep sea as part of Australia’s new national strategy of Monitoring, Evaluation, Reporting and Improvement (MERI) for conservation values within marine parks.

Occurrence and behavioral rhythms of the endangered Acadian redfish (Sebastes fasciatus) in the Sambro Bank (Scotian Shelf)

“…Summer was excluded from this analysis as it was underrepresented (16 days) compared to the other seasons. Demersal fish can aggregate over wide areas (Williams et al, 2021) to discard potential spatial constraints intrinsic to the lander field view, gregarious data was also assessed in six photo-transects recorded with the ROV Ropos, equipped with a Pacific-Zeux HD Camera with a 96-pixel resolution, that covered several hundreds of meters.…”