Pinger studies in Muara Pela, Mahakam River, Indonesia - Study executed by Yayasan Konservasi RASI Supported by
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Pinger studies in Muara Pela,
Mahakam River, Indonesia
Study executed by Yayasan Konservasi RASI
Supported by
Background • Pesut is a protected dolphin species in Indonesia since 1990 • Annual mortality between 1995-2019 = 4 dolphins/ year , whereas population was estimated at 80 dolphins in 2019 • Gillnet related mortality accounts for 67% of all known mortality causes. • Gillnets are legal fishing tools • RASI is lobbying to either 1) ban all gillnets inside the dolphin PA, or 2) ban gillnets with > 4 cm mesh size only. In both options, replace with alternative fishing gear • Meanwhile preliminary success with pinger trials seems like a potential alternative for the time being…
Pingers & willingness of fishermen to use them • Based on interviews with 97 fishermen who had gillnets, 71% often saw dolphins and 25% said dolphins had eaten fish from their gillnet and/or damaged their nets but only 2% admitted that dolphins had been entangled in their gillnets. • 96% of fishermen set gillnets at night as well as during the day. • 46% of gillnet fishermen have gillnets, which are potentially at high risk because it has a mesh size above 10 cm, which greatly increases the risk of fluke entanglement. • 91% of fishermen are willing to install pinger as a tool to expel dolphins from gillnets • Per 1 July 2020, 40 pingers were placed on gillnets with the consent of fishermen.
Goal • The aim of the initial pinger studies (Dec 2018-Dec 2019) were to design the pinger with a) the right frequency and volume to keep dolphins away from the pinger source with the preferred smallest possible radius, which is 10 to 20m; b) the pinger should not expel dolphins from the feeding area • The aim of the larger-scale pinger trial (July-December 2020) with 40 pingers attached to nets aimed to study the impact on fish catch and dolphin fish-predation behavior as well as fish predation by dolphins • The aim of the repeated dolphin-pinger interaction study conducted between 15-29 January2021 were to record habituation of dolphins towards pingers
Methods Study location: Confluence of Pela/ Mahakam River, East Kalimantan, Indonesia Study Period: • Study period 1: 5-18 December 2018; Study period 2: 9-18 January 2019 • Study period 3: 10-19 December 2019; Study period 4: 15-29 January 2021 Pinger specification: • Survey period 1 &2: frequency : 50-120kH & 115 dB output • Survey period 3 & 4: frequency : 50-120kH & 125 dB output Rotating observation teams Team 1) : 7:30-10:00; 12:30-15:00 Team 2): 10:00-12:30; 15:00-18:00 @team = 3 observers @ 10 hours of observation per day
Physical set up • Study 1: The pinger is attached on the head rope of a gillnet in Pela confluence in a usual fishing location. • Study 2, 3 & 4: The pinger is attached on a rope 2 m underneath the red buoy in high dolphin surfacing location, which is point 0. N, W, S, E of point 0 there are buoys with distance 0-10m; 10-20m; while buoys at horizontal positions are at 20-40m; 40-60m; 60-80m dan 80-100m from 0. • Pingers are running for 24 hours on and then 24 hours off and so on. • Pinger best placed in favorite surfacing area or second favorite if depth/current or traffic restraints
Visual study • Recording each surfacing and distance in relation to pinger • Recording each individual behavior also in relation to distance to pinger • Recording general group behaviors • Instead of using exact distances, distance ranges were used (too many dolphins surfacing to use theodolite)
Acoustic study • Recording surfacing and distance as well as behavior in relation to the pinger on a voice recorder while simultaneously recording underwater vocalizations and echolocation on a recorder device attached to the hydrophone.
Fish study • July 2020, daily study (5) nets): •Fish species, number of individual fish and weight were recorded from a gillnet where a pinger was attached to. Water levels and dolphin-fish predation were recorded too. • The fish pinger was attached 24 hours on the net and then 24 hours off. • July-Dec 2020, weekly study (35 nets) with pinger constant active
Water & observation condition • Three times a day water and observation condition was recorded during the dolphin-pinger observation trials
Results Survey periods 1 & 2: • No difference was found between the time spent in the confluence by pesut during days when pinger was ‘on’ or ‘off’. Indicating that dolphins were not expelled from the feeding area. • Pesut was observed more often in the 0-20m zone when pinger was 'on' than when pinger was 'off'. The difference between the two surveys is the difference in the frequency of occurrence between zones that do not depend on whether the pinger is on or not: In the first survey dolphins appear more often at a distance of 20-60m from the pinger (on and off) so for the second survey the pinger is deliberately installed at the most frequent surfacing point as observed in survey 1. • At the time of the second survey we examined whether there were differences in surfacing frequencies at distances from 0-10m and 10-20m. A significant result (Chi-square = 5.5, p
Survey period 1 (n=5041 surfacings)-
Pinger 115 dB output
Surfacing distances pesut towards pinger-December 2018
30.0
pinger on-dec 18
Frequency of surfacings (%)
25.0
pinger off- dec 18
20.0
15.0
10.0
5.0
0.0
0-20 m 20-40 m 40-60 m 60-80 m 80-100 mSurvey period 2 (n=3851 surfacings)
Pinger 115 dB output
60.0 Surfacing distances pesut towards pinger January 2019
Frequency of surfacings (%)
50.0
40.0 pinger on-Jan 19
pinger off- Jan 19
30.0
20.0
10.0
0.0
0-20 m 20-40 m 40-60 m 60-80 m 80-100 mSurvey period 2 (Pinger 115 dB output)
Surfacing distances pesut towards pinger
90
Frequency of surfacings (%)
80 pinger on-Jan 19
70 pinger off- Jan 19
60
50
40
30
20
10
0
0-10 m 10-20 m
Distance pesut to pinger (m)
The chi-square statistic is 22.4466. The p-value is .000002.
This result is significant at p < .01.Conclusion study period 1& 2 • Pesut seemed aware of the pinger and may have deliberately approached out of curiosity. But the approach applied to a 10- 20m while a decrease in surfacings of dolphins was observed for the distance 0-10m. • Dolphins were never observed feeding in the 0-10m zone when the pinger was on while they were observed at a distance of 0- 10m when pinger was off. Feeding behavior was observed in the 10-20m zone in both pinger on and off conditions. • One time within the 0-10m zone while pinger was active and while dolphins were playing, the jerrycan attached to the rope with pinger was observed to move. Also when dolphins enter the 0-10m zone while pinger was active, dolphins often were seen leisurely playing and waving their fins on the surface. • The third study was conducted to avoid net attraction and obtain more unambiguous results using a louder pinger as well as record behaviors per distance from pinger.
Survey period 3 (pinger output 125 dB)
(n=1822 dolphin surfacings)
35
Surfacing distances pesut towards pinger
pinger off-Dec 19
30
Frequency of surfacing (%)
pinger on- Dec 19
25
20
15
10
5
0
0-20 20-40 40-60 60-80 80-100
Distance towards pinger (m)Survey period 3
(pinger output 125 dB)
70.0
Surfacing distances pesut towards pinger
pinger on- Dec 19
60.0 pinger off- Dec 19
Frequency of surfacings (%)
50.0
40.0
30.0
20.0
10.0
0.0
0-10 m 10-20 m
Distance towards pinger (m)
The chi-square statistic is 19.6128. The p-value is < 0.00001. Significant at p < .01Survey period 3
Dominant group behavior < 10 m and >10Survey period 3
Water spitting behavior of pesut per distance to
pinger
80
% Water spits (n=63)
70
pinger on
60 pinger off
50
40
30
20
10
0
distance from pingerResults survey period 3 (pinger output 125 dB) • The pinger study significantly shows that when the pinger is on, dolphins occur more frequently in zones with a radius of 10-20m than in zones of 0-10m. Conversely, when pinger is off, dolphins surface more in the 0-10m zone than in the 10- 20m zone. • Behavioral observations indicate that dolphins never appear to forage in the 0-10m zone when the pinger is on even though they are still foraging in the 0-10m zone when the pinger is off. Foraging activities are still carried out at 20m distance or further away when pinger is active. • When the pinger is on, dolphins can only be seen spitting water (as an indicator of foraging) in a radius zone above 20m while when the pinger is off dolphins have also been seen spitting water and feeding in the 0-10m zone.
Results survey period 3 (continued) • Differences are also prominent when the pinger is on that dophins relatively more often do fast travel in the 0-10m zone than when pinger is off and compared to other zones. Fast traveling overall scored highest in all zones because during study period 3 there was less fish than usual and no feeding or milling was observed when pinger was active in the 0-10m distance range to pinger, which inherently increased the portion of fast travel here. • Dolphin's surface play behaviors are similar whether the pinger was active or not in the 0-10m zone. • During underwater listening, feeding click trains with jaw claps were only hard when the dolphins were further away from the pinger (at least >20m). • While socializing , dolphins would move in all zones just as much during pinger on than off. There was no evidence of increased aggressive behaviors when the pinger was on.
Fish catch study July 2020
Fish catch study results
(still ongoing)
• Less but larger fish was caught on pinger active days
• Total fish weight was 1.2 times larger on days with pinger on
than off with higher total market value
• There has been no fish
predation from gillnets
with pingers attached on
them from July until
December2020.Conclusions & recommendations for Mahakam
related to pingers
• Dolphin fish predation from gillnets and dolphin entanglement was regularly
recorded in the Mahakam.
• Initial pinger trial studies showed that dolphins would not feed within a 10m range
from a gillnet with active pinger but would when the pinger was off. Dolphins were
still feeding at 20m distance when pingers were active. This and the fact that an
equal amount of dolphin surfacings were recorded in the feeding area during all
study periods whether pingers were active or off, indicates that dolphins were not
excluded from their feeding area.
• Therefore, it is recommended for those gillnets that have been identified as high
risk to attach active pingers to reduce accidental gillnet entanglements.
• Ongoing evaluation studies should be done for the pingers already installed on 40
nets to see if the same results may be achieved over longer periods.
• Awaiting the 4th dolphin-pinger trial results, and if no habituation was
found, additional pingers may be considered to be attached to new nets.
• Alternative solutions to reduce fishermen’s dependence on gillnets need to
become part of government management program including alternative, safer
fishing gear or sustainable forms of fish-breeding
• New regulations that ban gillnets from confluence areas will be advocated for.Recommendations for other study site/ species
1. Order a prototype pinger that is developed for the dominant frequencies
of the species, river background noise and causing minimum loudness.
For pesut the effective pinger transmitted between 50-120 kHz with 125
dB loudness after the initial trials with a 115 dB pinger.
Decibel Estimated deterrent
distance
from Pinger(meters)
145 200
139 172
133 144
127 116
121 88
115 60
109 32Recommendations for other study site/ species 2. Conduct a trial observation study to assess differences in surfacing patterns, behavior, vocalizations and echolocation per distance zone towards pinger location 0 when the pinger is active or inactive. 3. Conduct a comparative fish catch study with alternating days pinger active or inactive
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