Sperm whales will be exposed by the frigate (OSVE) using the CAPTAS system and pilot/killer whales will be exposed by HUS using the SOCRATES system.
Sperm whale exposures with CAPTAS on OSVE
The full experimental phase will consist of a sequence of four CEE approaches (see table 7) of the focal whale of 40 min each, with a minimum of 1h 20min of post/pre-exposure time in between them. The non-focal tagged whale is not tracked by HUS, but has a Mixed-DTAG which records the track using the on-board GPS-sensor. The approaches of the source ship will be aimed at the focal whale, and thus the position of the second tagged animal relative to the source will not be controlled.
Table 5. During the CEE approaches, one of five different sonar signals will be transmitted, depending on species and source vessel; No-sonar, Continuous active sonar (CAS), Moderate source level pulsed active sonar (MPAS), high source level pulsed active sonar (HPAS) or extra high source level pulsed active sonar (XHPAS)
SIGNAL No Sonar CAS MPAS HPAS XHPAS
SOURCE VESSEL HUS/OSVE HUS HUS HUS/OSVE OSVE
Start and end source level dB re 1μPa∙m
No-signal 141-201 141-201 154-214 HUS 165-214 OSVE
Signal shape No-signal HFM
Upsweep
HFM Upsweep
HFM Upsweep HFM Upsweep Pulse Shading/Signal rise
time
No-signal Cosine envelope with duration of 0.05 sec at start and end of pulse.
Figure 11. The source vessel will approach the whale at a distance of 4nmi or 8nmi from the estimated
tagged whale’s position at the start of exposure, at +/- 45 degrees to the side of the whale’s direction of travel. Approach course will be fixed towards the estimated whale position at the start of the approach. The
Table 6. Overview of the exposure runs for pilot/killer whales (PW/KW) and sperm whales (SW). The sonar source used will be either the CAPTAS (CAP) on KNM Otto Sverdrup (OSVE), or the SOCRATES source (SOC) on RV HU Sverdrup II (HUS). The source vessel will either do a Close approach starting at a distance of 4nmi from the whale, or a Distant approach starting at a distance of 8nmi. The duration of the exposures is always 40min, speed and course should always be kept constant.
Run/session Source/Ship Species Start range
Table 7. Order of exposure runs for sperm whales using the CAPTAS on OSVE as the source. No-sonar means no transmissions but the source ship will do a close approach as if it was
transmitting. XHPAS and HPAS transmissions mean 1000ms sonar transmission of 1280-1920 Hz HFM with 20spulse repetition time. Time vs source level is specified in Table 8. Maximum source level of HPAS is 214 dB re 1µPa·m and max source level of the XHPAS is 220 dB re 1µPa·m. The starting distance of the Close approaches will be 4 nmi, and the starting distance of the Distant approaches will be 8 nmi. Tow speed 8 knots, and source depth 100-120 m. At least two of the sonar runs have to be completed, otherwise the experiment has to be repeated.
Experiment 1st treatment 2nd treatment 3rd treatment 4th treatment
1 No Sonar Close XHPAS-Distant XHPAS-Close HPAS-Close
2 No Sonar Close XHPAS-Close XHPAS-Distant HPAS-Close
3 No Sonar Close XHPAS-Distant HPAS-Close XHPAS-Close
4 No Sonar Close XHPAS-Close HPAS-Close XHPAS-Distant
5 No Sonar Close HPAS-Close XHPAS-Distant XHPAS-Close
6 No Sonar Close HPAS-Close XHPAS-Close XHPAS-Distant
Table 8. Sonar transmission scheme for the XHPAS and HPAS transmissions of the CAPTAS on OSVE.
The transmitted signal will always be 1000ms sonar transmissions of 1280-1920 Hz HFM with 20s pulse repetition time. The approach speed should be 8 knots, constant course, tow depth 100-120m. Time vs source level is specified in the table as attenuation from full powered source level. Time T0 is the time of the first ping. Only the time of changes of the source level is given. Maximum source level of HPAS is 214 dB re 1µPa·m and max source level of the XHPAS is 220 dB re 1µPa·m.
TIME
After an exposure there is a post-exposure period of 1 hrs 20 min, during which the frigate will reposition for the next run. The post/pre-exposure time may be extended if the whale does not appear to recover to post-exposure baseline level after exposure or if we have not managed to relocate the focal whale.
The first CEE approach will be a no-sonar control approach where the source is towed, but not transmitting. Each sonar run will include 20min of dose-escalation and 20 min of full SL transmission.
Pilot/killer whales exposures with SOCRATES on HUS
The pilot/killer whale exposures (see table 9) will be done in much the same way as the sperm whales exposures, except that all runs are Close runs. Another important
difference is that tracking of the pilot/killer whales will be done from the MOBHUS and HUS will be the source vessel. The pilot/killer whales will also be exposed to
continuous sonar.
The order of the four exposure sessions (see table 9) is determined to maximize the contrast between the different treatments with a minimum amount of data. No-sonar control approach is always conducted first to test the effect of ship on whale behaviour, before any sensitization by sonar can take place.
Table 9. Order of exposure runs for pilot and killer whales using the SOCRATES source on HUS. No-sonar means no transmissions but the source ship will do a close approach as if it was transmitting. MPAS and HPAS transmissions mean 1000ms sonar transmission of 1000-2000 Hz HFM with 20s pulse repetition time.
CAS means 19s transmission of 1000-2000 Hz HFM with 20s pulse repetition time. Time vs source level is specified in Table 10. Maximum source level of HPAS is 214 dB re 1µPa·m, MPAS is 201 dB and CAS is 201 dB re 1µPa·m. The starting distance of the Close approaches will be 4 nmi. Tow speed 8 knots, and source depth 100-120 m. At least two of the sonar runs have to be completed, otherwise the experiment has to be repeated
Experiment 1st treatment 2nd treatment 3rd treatment 4th treatment
1 No Sonar Close CAS-Close MPAS-Close HPAS-Close
2 No Sonar Close MPAS-Close CAS-Close HPAS-Close
3 No Sonar Close CAS-Close HPAS-Close MPAS-Close
4 No Sonar Close HPAS-Close CAS-Close MPAS-Close
5 No Sonar Close MPAS-Close HPAS-Close CAS-Close
6 No Sonar Close HPAS-Close MPAS-Close CAS-Close
Table 10. Sonar transmission scheme for the CAS, MPAS and HPAS transmissions of SOCRATES on HUS. The transmitted signal will always be either 1s (PAS) or 19s sonar transmissions of 1000-2000 Hz HFM with 20s pulse repetition time. The approach speed should be 8 knots, constant course, tow depth 100-120m. Time vs source level is specified in the table as attenuation from full powered source level. Time T0 is the time of the first ping. Only the time of changes of the source level is given. Maximum source level of HPAS is 214 dB re 1µPa·m, max source level of the MPAS and CAS are 201 dB re 1µPa·m.
TIME
After each 40min exposure session there is a post-exposure phase of minimum 1 h 20 min.
We might lose the track of the whale when HUS sails away to position for an approach on pilot/killer whales. It’s very important to try to relocate the animal as soon as possible during or after the approach using the DDF system and visual search. With sperm whales there is less risk that we will lose the track of the focal whales, since HUS will keep tracking it continuously during the exposures. Until we relocate the animal, the rest of the experiment has to be postponed. Once we have relocated HUS will again manoeuvre to track the whale as we did in the pre-exposure phase. After the end of the fourth exposure session, the final post exposure phase should be at least 1 h 20 min, but preferably longer.
It’s important that the frigate is instructed to keep a minimum distance from the whale of at least 2nmi, except during exposures. As soon as each tag releases MOBHUS I will be deployed with a team to pick up the tag and bring it back to HUS for data download. Some tags might be recovered by OSVE.