Fine and broad (ocean basin) scale acoustic observations of mid-trophic fishes, potential and challenges

Transcription

1 Fine and broad (ocean basin) scale acoustic observations of mid-trophic fishes, potential and challenges Rudy Kloser Tim Ryan Jock Young Mark Lewis Acknowledgements Graham Patchell and Les Scott Petuna Sealords

2 Link to ETBF study 45 gm m-2 Micronektonic fishes Kloser et al basin scale acoustics

3 Background Monitoring of large ecosystems for fisheries, marine planning and climate change. Predict shifts in communities distribution of commercial species (e.g. Tuna), SPC climate change book in prep Tasman Sea is predicted to have the largest change in temperature in the Southern Ocean Need biological baseline and monitoring indicators Need for actual estimates of forage biomass for models that examine changes in ocean ecosystems, particularly fishing and climate change

4 Nets and acoustics selectivity and catchability Nets Selectivity - mesh sizes, towing speed Catchability avoidance/attraction, sampling volume, time of day, variable behaviour. Acoustics Selectivity - frequency and size selective Catchability avoidance, representative Echo integration Segmenting the echo into different trophic groups, what proportions target strength of groups variability with depth and time, seasons. Echo counting Low densities of organisms, resolve individual fish and attribute mean weight

5 Potentially acoustics can segment functional groups vertically and horizontally for input into ecosystem models e.g. Lehodey 2004 Epipelagic Highly-migrant bathypelagic Migrant mesopelagic Mesopelagic Migrant bathypelagic Bathypelagic day night

6 Net and acoustic sampling gear Mid-water opening and closing net (MIDOC) Codend device 5 codends that have preset drop times. Attached to end of a modified IYGPT net Net opening between wingtips ~189 m^2

7 X X X AUSTRALIA Study area TAS Fishing Vessel transects in austral winter 2005,2006, ,2005,2006,2007 New Zealand

8 Vertical structure and net biomass of micronekton Net 5 Net 6 Mean Filtered Biomass (g.10-5 m -3, +SE) Net 1 Net 4 6 / 50 Net 3 Average S A values per 100 metre integration layer Net 2 Net 2 Net 3 Net 4 Net 5 Net 6 Net / Dep th (m ) 5 / / / / 450 Inshore Seamount_1 Offshore Seamount_2 SS0904 two weeks, 20 x 6 trawls, to characterize 3 areas

9 Net 5 sampling from 200 to 100 m Crustacea Squid Myctophidae Gelatinous Dominant Myctophid Ceratoscopelus warmingii with a prominent gas bladder

10 Comparison between actual and acoustic biomass Biomass (+ 1 SD, gm) NASC value depth (m) Acoustic scatter NASC value y = x R 2 = Biomass (g) d e p t h ( m )

11 Dual frequency TS probe for vertical profiling to 600 m for target strength and echo counting measurements

12 Acoustic estimates of myctophids by echo integration and echo counting from lowered TS probe to 600 m depth Echo integration Mean acoustic scatter (Sv) for depth layer from vessel echo sounder Medium density (TS probe depth 150 m) In situ TS for range <30 m within depth layer and < 3 o off axis TS of other acoustic groups estimated from historic values Echo counting Counts of detected targets to 15 m range and < 3 o off axis per ping within depth layer Single targets TS range for myctophids estimated from tracked single fish. Weight of acoustic group estimated by trawl. Calibration sphere

13 Comparison of net, echo integration and echo counting biomass Wet weight (ww) biomass comparison of small fish with gas bladders (dominant myctophids) for a depth stratified net tow at 5 depth zones using net volume filtered, echo integration and echo counting. Myctophidae Biomass Depth MVBS TS Number Length WW Net Integration Counting m db re 1m -1 db re m 2 mm g g m -2 g m -2 g m Reality check 29 g m -2 equates to ~7 fish in a 1 m 2 water volume from 0 to 600 m Total Factor difference

14 Basin scale estimation of micronekton biomass Fishing Vessels for collecting acoustic data is now common practice Weather effects -- transducer location/hull shape. Interference from other instruments/electrical systems. Acoustic systems need to be calibrated and operated on standard settings.

15 Fishing Vessel transects in austral winter AUSTRALIA TAS 2005,2006, ,2005,2006,2007 New Zealand

16 SST imagery for winter 2004,2005,2006 and 2007 with transects overlaid

17 Transect 2005,2006 and Aus-NZ start lat end lat large eddy Aus-NZ start lat end lat Temp. o C Depth m Aus-NZ start lat end lat Vessel noise Mean transect Sv m db Mean transect Sv m db Aus-NZ start lat end lat Mean transect Sv m db Sv db only 25% variation between years Sv db Sv db

18 Transect 2004 and db Sv difference NZ-Aus start lat end lat Temp. o C Aus-NZ start lat end lat Sv db Aus-NZ start lat end lat Mean transect Sv m db Temp. o C NZ-Aust start lat end lat Sv db Need good calibration to infer changes -80 Mean transect Sv m db

19 Transect 2008

20 Estimates of myctophid biomass for Tasman Sea basin scale 4.1 M km 2 vary by factor of 5 to 58. Ecosystem Models 0.5 to 3 g m -2 Lehodey (2004), Fulton (2005) 2.1 to 8.2 M tonnes Nets 1.6 to 2.6 g m Koslow et al to 10.7 M tonnes Acoustics 16 to 29 g m to M tonnes this is in agreement with recent ecopath modeling of the eastern Australian pelagic ecosystem

21 Summary new developments Acoustics from fishing vessels provides a cost effective way to monitor at basin scale but needs refinement Multi-frequencies to improve species id Depth stratified net sampling for species, biodiversity, length weight and life history parameters Visually verified targets using optical devices A solution: Combine net, acoustic and optic sampling on commercial and research vessels trials already completed for orange roughy (Ryan et al. 2008)