2021 State of the Environment Report Marine Chapter – Expert Assessment – State and Trend – Mesopelagic fish species

The Marine chapter of the 2021 State of the Environment (SoE) report incorporates multiple expert templates developed from streams of marine data. This metadata record describes the Expert Assessment "State and Trend of mesopelagic fish species". 
<strong><em>A PDF of the full Expert Assessment, including figures and tables (where provided) is downloadable in the "On-line Resources" section of this record as "EXPERT ASSESSMENT 2021 - Mesopelagic fish species"</em></strong>



DESCRIPTION OF HABITAT/COMMUNITY/PROCESS FOR EXPERT ASSESSMENT
Mesopelagic fish species (200 to 1000 m depth) occur throughout the Australian Exclusive Economic Zone (EEZ) region where the seabed depth exceeds 200 m (Flynn and Kloser, 2012; Flynn et al., 2018; Sutton et al., 2018). Mesopelagic fishes reside at depth during the day and a portion migrate to shallower waters to feed at night, revealing diel vertical migration in the sound scattering layer (Figure 1a; Brierley 2014). Ecosystem and carbon models associated with observational studies of mesopelagic fishes highlight their importance to ecosystem services and carbon sequestration role (Fulton et al., 2005; Lehodey et al., 2010; Boyd et al., 2019).  This is particularly important for Australia’s continental slope commercial species and other top predators for ecosystem-based management (Smith et al., 2011). The importance of mesopelagic fishes to ecosystem services is recognized yet their biomass and trophic efficiency are uncertain with net and acoustic estimates differing by 2 orders of magnitude in Tasman Sea Australian waters (Kloser et al., 2009; Irigoien et al., 2014). This difference is due to different sampling gear and methods used to interpret the data.

DATA STREAM(S) USED IN EXPERT ASSESSMENT
The primary data used are the georeferenced, calibrated, and processed single-beam water column volume backscattering coefficient values, representing the linear sum of backscatter from acoustically detectable individual organisms within the sampling volume. The spatial coverage of data used for assessing the state of mesopelagic biogeography is 75oS-45oN and 20oW-330oW with a temporal coverage 2004-2018. The spatial coverage of data used for assessing trends in selected regions is 35oS-50oS and 180oW-220oW with a temporal coverage 2004-2018.



2021 SOE ASSESSMENT SUMMARY [see attached Expert Assessment for full details]

• 2021 •
Assessment grade: Very good
Assessment trend: Improving
Confidence grade: Limited
Confidence trend: Somewhat adequate
Comparability: Grade and trend are comparable to the 2016 assessment
• 2016 •
Assessment grade: Very good
Assessment trend: Stable
Confidence grade: Limited evidence or limited consensus
Confidence trend: Limited evidence or limited consensus
Comparability: Grade and trend are comparable to the 2011 assessment
• 2011 •
Assessment grade: Very good
Assessment trend: Stable
Confidence grade: Limited evidence or limited consensus
Confidence trend: Limited evidence or limited consensus



CHANGES SINCE 2016 SOE ASSESSMENT
The extent of processed bioacoustic data archived under IMOS Bioacoustics sub-Facility is expanding with an improved spatial and temporal coverage, facilitating future state and trend analyses.

Tags: community structure, expert assessment, mesopelagic fish
Organization: Australian Ocean Data Network