what we know about the effectiveness of the ‘pal ...€¦ · what we know about the effectiveness...
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What we know about the effectiveness of the ‘PAL’ (Porpoise Alert) application as an anti-bycatch measure
25th Meeting of the ASCOBANS Advisory Committee in Stralsund 17.09.2019
Dr. Andreas Ruser
Institute for Terrestrial and Aquatic Wildlife Research, Büsum
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Bycatch is the primary threat for the Baltic harbour porpoise
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Monthly probability of detection of harbour porpoises together with total hours fished (Jastarnia Plan, Fig. 8)
Situation in the Baltic Sea
• Bycatch in gillnet fisheries has been recognized as the primary threat for the survival of the Baltic harbour porpoise population
• Agreement on ‘Recovery Plan for Baltic Harbour Porpoises (Jastarnia Plan)’
(document: MOP8_2016-3_JastarniaPlan_inclAnnex.pdf)
• Number of annually bycaught animals is critically needed to evaluate and monitor threat from bycatch
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Bycatch is the primary threat for the Baltic harbour porpoise
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Situation in the Baltic Sea
• Bycatch in gillnet fisheries has been recognized as the primary threat for the survival of the Baltic harbour porpoise population
• Agreement on ‘Recovery Plan for Baltic Harbour Porpoises (Jastarnia Plan)’
• Number of annually bycaught animals is critically needed to evaluate and monitor threat from bycatch
SUMMER 2002-2018
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What are the measures to prevent bycatch?
According to ‘ASCOBANS Recovery Plan for Baltic Harbour Porpoises’
• Replacements of gillnets by alternative fishing gear with lower bycatch potential Hooks, seine nets, fish traps, …
• Use of acoustic deterrent devices Variety of ‘pingers’ available
• Protected areas or time area closures Reduction of fishing effort
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Situation in German Baltic Sea (Schleswig-Holstein)
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Voluntary agreement with fishermen in Schleswig-Holstein in Nov. 2015 Objectives
Maintain gillnet fisheries and economic efficiency in compliance with harbour porpoise and diving duck protection
• 219 of 280 fishermen in Schleswig-Holstein voluntarily signed agreement
• Report bycatches and participate in harbour porpoise monitoring
• Participate in scientific investigations on alternative fishery methods and anti-bycatch devices
• Avoid areas with diving duck aggregations from 16.11. – 01.03.
• Limitation of maximum net-row length to 4, 3 and 1.5 km for boats >8, <8 and <6m from 01.06 – 31.08.
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Ideal pinger from a porpoise conservation point of view
We critically need a (deterrent) device with… • High efficiency in reducing bycatch
• No habituation effects
• Very small exclusion zone
The PAL promises… • No deterring effect and therefore no habitat reduction
Supporting the harbour porpoise to detect the gillnet on its own
• No effect on catch rates of fisherman, maintain profitability
• 70 % bycatch reduction
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www.f3mt.net
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What is known about PAL effectiveness?
Outcomes of Culik et al. (2015) and pilot study in gillnet fisheries • PAL signal imitates aggressive call of harbour porpoise in human care
• Playback study in Denmark with PAL signal
Increase in echolocation activity of 10%
Comparably low deterrence of 23 m
• Test in commercial gillnet fisheries in Germany and Denmark in the Baltic Sea
3 participating fishing vessels
20 bycatches, 17 control nets, 3 PAL nets
70% bycatch reduction
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Uncertainties in PAL usage • No monitoring of harbour porpoise presence in the surrounding of gillnets
• Indication of increased gillnet detectability?
Meaning of PAL signals for porpoises?
Not tested: Reported deterrence of 23 m (Culik et al. 2015)
Detection range of set-nets between 3 – 26 m (Kastelein & Villardsgaards 2007)
• No effectiveness in preventing bycatches in the German North Sea
• No effectiveness in preventing bycatches in Iceland
Attractiveness for males suspected
• Number of reported bycaught animals is decreasing?
Less bycaught or less intension to deliver them?
Number of stranded animals in the Baltic Sea is not decreasing
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What we don‘t know about PAL effectiveness
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April 2017: • 1680 PAL devices bought for fishermen in Schleswig-Holstein
• 83 of 219 fishermen within voluntary agreement use PALs
• If fishermen use PALS no further limitations in length of net-rows
Observed effectiveness of PAL? • Indication of reduced bycatch?
Actually not
• Indication of reduced stranded porpoises?
NO
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Large scale usage of PALs in the German Baltic Sea
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Number of stranded porpoises
Stranded porpoises at the coast of Schleswig-Holstein (data: ITAW)
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Need for further studies on PAL effectiveness and application
Urgently needed investigations on… • How do harbour porpoises (seals, birds,…) react to the PAL signal?
Deterrence or behavioural change? • Indication for decrease in harbour porpoise detections during PAL
deployment found (Schaffeld 2016, master thesis) How do harbour porpoises react at a gillnet?
• Without and with the use of PALs • In what context do harbour porpoise approach nets? • Do PALs lead to a better detection of nets? • Do interactions with other interfering noises (ships, etc. . . ) occur? • Are there any indications of habituation?
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Need for further studies on PAL effectiveness and application
We request further investigations on… • Sound propagation along nets?
Acoustic coverage of gillnet row? • Is the signal in 200 m distance still loud enough to alarm porpoises?
– Directionality & attachment, battery-power, masking, etc.
• Acoustic gaps could lead to increased bycatches (Palka et al. 2008)
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Need for further studies on PAL effectiveness and application
We request further investigations on… • Sound propagation along nets?
Acoustic coverage of gillnet row? • Is the signal in 200 m distance still loud enough to alarm porpoises?
– Directionality & attachment, battery-power, masking, etc.
• Acoustic gaps could lead to increased bycatches (Palka et al. 2008)
Effect when net-rows are close to each other?
Further extensive investigation are needed!
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Thanks for your attention