The Australian Longline vessel Antarctic Discovery


Latest bioacoustic tracks from FV Antarctic Discovery provide unique data to IMOS

Since July 2010, the IMOS Bio-Acoustic Ships of Opportunity (BASOOP) sub-facility has been delivering calibrated (now multi-frequency) water column acoustic data to characterize ocean basin scale distribution and seasonal behaviour of mid-trophic level organisms.

At present, 17 vessels are participating in the BASOOP program. Between 2010 and 2017 300,786 km of data were collected and processed (Fig. 1). The resulting acoustic snapshots of mid-trophic (macro-zooplankton and micronekton) communities are combined with established ocean observing systems to fill the dark hole in our understanding of marine ecosystems and support their sustainable management.

As a part of the existing industry collaboration, the Australian Longline Pty Ltd fishing vessel Antarctic Discovery successfully recorded 38 kHz acoustic data during its delivery voyage. The hull-mounted echosounder has been calibrated recently that enabled us to publish this vast data set across the oceanic basins (Fig. 1) including Atlantic (7077 km), Pacific (11798 km), and Southern Ocean (6307 km). The processed acoustic backscatter maps reveal large-scale spatio-temporal patterns in pelagic sound scattering layers and diel vertical migration. The diel vertical migration (referred to as the largest daily migration of animals on earth) contribute substantially to the biological pump and regulate the primary production involved in the marine biogeochemical cycles.

The mesopelagic fish communities living in the twilight zone of the ocean (200–1000 m depth) have been identified as one of the least investigated components of the open ocean ecosystem. The mesopelagic fish communities are readily detectable using echosounders and in the ocean the transmitted acoustic signals uncover a principal deep scattering layer (DSL), evidencing its interrelationship with the open ocean fish biomass and primary production (Fig. 1, note net primary production is derived from satellite ocean colour and averaged for the year 2015). With a current stock estimate of ~1,000 million tons, mesopelagic fish likely dominate the total biomass of fish in the ocean. However, the actual biomass is still unquantified and researchers have indicated that the real abundance could be at least 10 times higher than previously assumed. To bridge the gap, IMOS BASOOP program offers the prospect of acquiring new data, novel insights and delving into new research challenges for the sustainable management of our oceans.   

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Figure 1. The lower mesopelagic (400–800 m depth) area backscatter strength variation (magenta circles) along the Antarctic Discovery voyage transect, superimposed on a satellite-derived map of net primary productivity (averaged for the year 2015) and the Longhurst oceanic biogeographical provinces (white lines). The bottom panels display the echogram along the vessel transit covering the Pacific Ocean from Panama to New Zealand, revealing broad transitions between the Longhurst provinces. The center part of the south Pacific (25degS 220degE) highlight oligotrophic regions with low predicted productivity (blue), which is observed in general by the low mesopelagic (400–800 m depth) backscatter strength (small magenta circles). Click to expand.