Voyage Summary FV Rehua Trans-Tasman Voyage.

Transcription

1 Voyage Summary FV Rehua Trans-Tasman Voyage. Voyage dates: Depart Nelson, New Zealand Wednesday, 17 th 18:15 hrs. Arrived Devonport, Australia Monday, 22 th 14:00 hrs. Voyage name: REH CSIRO Personnel: Tim Ryan Voyage leader, acoustics Mark Lewis Gear and Biologist Jeff Cordell Electronics Technician Overview: In June 2009 scientific sampling of the Tasman Sea micronekton was carried out from a 65 metre factory freezer vessel, the FV Rehua, during its transit from New Zealand to Tasmania. During the five day transit the vessel was under charter from Petuna Sealord to CSIRO Marine and Atmospheric Research for a total of 24 hrs. The charter time was approximately divided into eight three-hour deep-water deployments that formed three sets of day/night experiments. Three main sampling instruments were used: (i) Sampling of micronekton (primarily biota < 20 cm) was made from 1000 m depth to the surface in 5 sets of equally spaced (200 metre) strata using a fine-mesh multiple opening closing net system (MIDOC). This system was fitted to either the vessel s midwater or demersal commercial net (Figure 1). (ii) The digitised return signal from the vessel s 38 khz Simrad ES60 echosounder was logged for the duration of the voyage. This will allow us to map the along-transect acoustic reflectivity at 38 khz of the Tasman Sea basin from the surface down to 1500 metres (Figure 2). (iii) An Acoustic-Optically System (AOS) was attached to the headline of the demersal net to measure the acoustic reflectivity of individual biota at two frequencies (38 and 120 khz) and record concurrent optical images using digital SLR still cameras and PAL video system (Figure 1). The AOS was deployed vertically down to 1000 metres depths on two occasions. On four occasions it was attached to the headline of the demersal net that had been fitted with the MIDOC cod-end. Full details of equipment used along with metadata for key settings are given in Appendix 1. Embedding a charter period within the vessel s transit proved to be an optimal way to obtain valuable acoustic, optical and biological data in waters that are rarely sampled. The companies Petuna Sealord and Sealord NZ are thanked for supporting this 1

2 endeavour. MFish (NZ) and AFMA (Australia) are thanked for facilitating the scientific permits that allowed the sampling program to proceed. We would also like to thank the officers and crew of the FV Rehua for their excellent assistance in making this voyage the success that it was. Figure 1. FV Rehua demersal net fitted with a multiple opening-closing fine mesh net system (MIDOC) at the cod-end and an Acoustic-Optical System (AOS) attached to the net s headline. MIDOC Demersal net AOS 2

3 Results Deployment details are given in Table 1. Table 1. Summary of deployments Op No. Start Date/Time (local) Start Position 1 18/06 21: S E 2 19/06 01: S E 3 19/06 11: S E 4 19/06 19: S E 5 20/06 11: S E 6 20/06 19: S E 7 21/06 12: S E 8 21/06 19: S E End Position S E S E S E S E S E S E S E S E UTC offset Activity Comments +12 MIDOC using Night Midwater net +12 Vertical AOS Night +12 MIDOC using Day Midwater net +12 Vertical AOS Night +11 MIDOC-AOS- Demersal +11 MIDOC-AOS- Demersal +10 MIDOC-AOS- Demersal +10 MIDOC-AOS- Demersal Day Night Day Night Vessel Acoustics The digitised signal from the FV Rehua s 38 khz Simrad ES60 hull-mounted acoustic system was recorded at full sample resolution from the surface down to 1500 metres for the duration of the voyage. Three gigabytes of acoustic data were collected during the Tasman Sea transit. GPS position data were recorded directly to the ES60 acoustic data files (Figure 2). 3

4 Figure 2. Image of resampled echogram from FV Rehua s ES60 38 khz vessel mounted echosounder obtained during the 5 day transit across the Tasman Sea from New Zealand to Australia. The pink lines indicate the economic zones including the 200 Nmile EEZ. MIDOC depth profiles are shown. These are colour coded according to the recorded temperature. MIDOC depth profiles 4

5 AOS Deployments The AOS was deployed on six occasions during the voyage. For the first two deployments the AOS was lowered vertically down to 950 meters in a series of steps, pausing for 5 minutes at 50 meters then again at 100 metre intervals down to 950 metres. The AOS system was also paused on the way to the surface at each 200 metre interval. A tungsten carbide calibration sphere of known reflectivity 38 khz) was suspended by thin Kevlar line 20 metres below the system for these vertical deployments. The next four AOS deployments were made by attaching the system to the headline of the demersal net that also had the MIDOC attached at its cod-end. The acoustic system was set at a short range (0-50 metres) to enable a fast ping rate of ~10 Hz. Many thousands of acoustic target strength (TS) measures at 38 and 120 khz frequencies were made during the six AOS deployments (Figure 3). These highly detailed acoustic measures obtained at close range by the AOS will provide a basis for obtaining quantitative measures of biota density from the basin-scale acoustics collected by the FV Rehua s hull mounted echosounder. Figure 3. Acoustic single targets obtained from the AOS at 120 khz (LHS) and 38 khz (RHS) Single target detections that were within a user defined range (2 to 6 or 7 metres) and threshold (various settings from -65 to -58 db) were used to trigger a stereo pair of Canon 400D digital SLR cameras to try and obtain optical images concurrent with the acoustic measurements. Approximately 6000 images were obtained throughout the voyage. The majority of these contained objects that were barely visible due to the combination of their small size, distance from the camera, resolution of the cameras and amount of available light provided by the strobe units. The fact that objects were too small to be identified yet were able to exceed an acoustic threshold is still an important piece of information. On a number of fortunate occasions good quality images were obtained for a variety of animals including squid, salps and jellies (Figure 4). 5

6 Figure 4. Image of Salp (LHS) and Pyrosoma (RHS) captured by Canon 400D digital SLR camera that was triggered when these objects were detected by the 38 khz AOS echosounder. MIDOC deployments The MIDOC was deployed on six occasions during the voyage giving three sets of day/night pairs. The MIDOC was trawled down to 1000 metres (net 1 fishing) and returned to the surface with the net opening/closing intervals set at 20 minutes (i.e. nets 2 to 6 fishing separately the five 200 metre strata from 1000 metres to the surface). Due to unresolved permit issues, the first two MIDOC deployments were made using the vessel s midwater net system. The permit issues were resolved and the final four deployments were made with the MIDOC attached to the demersal net, which also had the AOS system attached to its headline. Figure 5 is a photograph of a typical catch from one of the MIDOC net cod-ends. The catch was sorted to species level where possible or if not, grouped according to their expected acoustic reflectance based on their morphology. During six three-hour MIDOC tows at total of individuals were recorded for a total weight of kgs. salps made up 80% of this total by weight (Figure 6). The catch by number was dominated by small myctophidae (36%), euphasids (36%) and salps (12%) (Figure 7). Apart from 167 kg of discarded salps, the catch was frozen and taken to the CSIRO Marine and Atmospheric Research laboratories in Hobart for further analysis. 6

7 Figure 5. Typical catch from MIDOC net cod-end. MIDOC 3, net 2 fishing from 1000 to 800 metres. Figure 6. Weight of species caught for top ten species Weight (kg), top ten species 350 Weight (kg) Salps Tubbia tasmanica Brama brama Squid Small Myctophidae Chauliodus sloani Large Fish No Bladder Persparsia kapua Holtbyrnia laticauda 7

8 Figure 7. Number of species caught for top ten species Numbers (kg), top ten species Numbers Small Myctophidae Euphausiidae Salps Jellies / Bracts Prawn Crustaceans Med Myctophidae Chauliodus sloani Squid Myctophidae spp Additional data Wildlife computers MK9 depth-temperature loggers were attached to the MIDOC net and the headline of the trawl net for each of the deployments. A higher accuracy and precision Seabird Electronics SBE 39 depth-temperature logger was also attached to the MIDOC frame. 8

9 Voyage narrative Wednesday 17 th June (Local) The FV Rehua departed Nelson at 18:15 the Wednesday 17 th of June bound for Devonport. ES60 logging was started as the vessel left port. Preliminary setup work for AOS and MIDOC. Thursday 18 th June (Local) Set up of AOS and MIDOC with equipment attached to the demersal trawl net. Key equipment settings All clocks synchronised to UTC. Nelson local time was UTC MIDOC Net timings: 50, 20, 20, 20, 20, 20 minutes. Temperature loggers Seabird SBE39 temperature depth logger was attached to the MIDOC box.. Wildlife computers MK9 logger number 7 was attached to the midwater net headline. Wildlife computers MK9 logger number 6 was attached to the demersal net headline. Oversight in scientific permit meant that we were only allowed to fish with the midwater net until the wording could be clarified with MFish. OP1. Night time. MIDOC shot 1 using midwater net. Start time 09:34 UTC, 21:34 local. No AOS. Friday 19 th June (Local) OP2. Day time.18/06 13:41 UTC, 01:41 local. AOS vertical deployment metres. Stations at 50 metres, then 100 meter intervals down to 950 meters, then back to surface in 200 metre intervals. EK60 s stopped working on the way back up at about 500 meters. Battery cell had failed in Lion battery pack. OP3. Day time.18/06 23:17 (UTC); 19/06 11:17 (Local). MIDOC shot 2. Still awaiting permit issue to be resolved.. OP4. Night time. 19/06 07:32 (UTC); 19/06 21:17 (Local). AOS vertical deployment metres. Camera setup: 2 strobes set to 24 mm zoom, 1/8 th power. Changed F-stop from 4.5 to 3.2. Saturday 20 th June (Local) OP5. Day time. 20/06 00:38 (UTC); 20/06 11:38 (Local). Demersal-MIDOC-AOS deployment. Port camera failed. Video turned on at 50 meters, as expected, but did 9

10 not turn off at 900 metres. Video did not work as lead was disconnected. Lights were probably on for the duration. MIDOC and 38, 120 khz acoustics worked fine. OP6. Night time. 20/06 08:44 (UTC); 20/06 19:44 (Local). 38 khz failed prior to deployment. Ran acoustics with 120 khz only. Attempted change camera trigger source from 38 to 120 khz channel, but this didn t work. Video did not work. No digital photos as no trigger received from 38 khz. MIDOC and 120 khz acoustics worked fine. Sunday 21 st June (Local) OP7. Day time. 21/06 00:38 (UTC); 21/06 11:38 (Local). Demersal-MIDOC-AOS deployment. 38 and 120 khz worked fine this time. Video did not record. DSLR cameras were set to single shots. For starboard camera there were many shots without any illumination. OP8. Night time. 21/06 00:38 (UTC); 21/06 11:38 (Local). Demersal-MIDOC-AOS deployment. 10

11 Appendix 1.Equipment and deployment metadata details Time zones The clocks for all instruments were set to UTC. The ship s local time was UTC+12 hrs when departing Nelson and changed back to UTC+11 and UTC+10 on the 20 th and 21 st of June respectively. Acoustic-Optical System (AOS) Acoustic components - Simrad EK60 38 and 120 khz split-beam GPT s - Simrad ES38DD 38 khz split-beam 7º transducer - Simrad ES120-7D 120 khz split-beam 7º transducer - Simrad ER60 software V2.X logging data at full sample resolution Key Settings: - 38 khz power: 2000W; pulse length: µs (all deployments) khz power: 500W; pulse length: µs (all deployments) - Range 0-50 metres; ping rate ~ 10 Hz Optical components - 2 Canon 400D Digital SLR stereo pair still cameras with strobe units; 35 mm fixed focal length lens - Hitachi HV-D30P 3CCD video camera feeding Outrider video capture card Key settings: Deployment Fstop ISO Shutter speed TS trigger threshold Trigger range (m) Strobes / /8 power /8, 24 deg angle / /8, 24 deg angle / /8, 24 deg angle / ¼, 24 deg angle No Strobes No Burst Shots Stereo DSLR Calibration The DSLR cameras were calibrated prior to the voyage. This calibration will be applicable for deployments 2 and 4. The DSLR cameras had to be removed after deployment 4 but the mounted cameras were not disturbed and the mounting plates were tightly dowelled. Therefore we expect the pre-voyage calibration to still be valid for deployment 5. One of the cameras failed during deployment 5 and hence had to be changed over. A post-voyage calibration was carried out and these results should be used for images taken during deployments 7 and 8. 11

12 Vessel Echosounder: Simrad 38 khz ES60 Key settings: Power 2000 W, pulse length ms. Range set metres. The system was last calibrated for these settings in 2008 by NIWA. When in open water the ES60 can lock onto false bottoms in the water column with the consequence that the full 1500 metre range is not logged. To avoid this, the system was forced to log the entire water column by setting the start of the bottom detection range to 1500 metres and the end to 1501 metres. ES60 full sample resolution raw files were logged from port to port. MIDOC net system The MIDOC is a sampling device box that attaches to the distant end of a trawl replacing the cod end. It was attached to either the vessel s midwater net (MIDOCS 1 and 2) or its demersal net (MIDOCS 3 to 6). The MIDOC contains 6 independent nets that allow depth stratified sampling of 5 layers, with one net sampling the entire water column to the target depth (1000 m), the next 5 nets fish the target layers that were from m, m, m, m and 200 m to the surface. The systems works with a pre-set timer releasing the cod ends at set time intervals. For this voyage the timer was set to give 50 minutes to get to 1000 m, then 20 minutes to fish each depth strata. The electronics package records the unit depth, water temperature, light levels, any attempt to close the nets and how long it took to do so. For this voyage the depth and temperature logging was faulty. Seabird electronics and wildlife computers MK9 loggers attached to the MIDOC frame will provide an alternative depth and temperature log. Net position in the water column was achieved using the vessel s usual trawl monitoring systems. 12