Dampier. Archipelago. Monte Bello Is. Barrow Island. Leeuwin. Current .... Observer: Gavin Kewan, Geoff Diver. Nickol Bay Professional Fishermen's Association.
Incidental dolphin capture in a west Australian trawl fishery: mitigation and significance? Simon Allen, Vanessa Jaiteh, Neil Loneragan
Common bottlenose dolphins Tursiops truncatus
North West Shelf and Pilbara region 200 m Indonesian Throughflow
Leeuwin Current
Monte Bello Is. Barrow Island Dampier Archipelago
Ningaloo Reef
Chlorophyll-a (mg m3)
(CSIRO NW Shelf technical report)
Port Hedland
TW = Trawl TP = Trap
6
Zone 1 Zone 2
4 1
2
5
3
Port Samson
Human activities in the region
Port Headland
Onslow (Dept. Fisheries WA) Fishing - Trawl, trap, line
Lethrinids, Lutjanids
Butterfly bream
TW = Trawl TP = Trap
6
Zone 1 Zone 2
4 1
2
Human activities in the region
5
3
Port Samson
Port Headland
Oil and gas exploration Development projects Blue = existing; Red = proposed
Onslow (Dept. Fisheries WA) Fishing - Trawl, trap, line
(Dept Mines and Petroleum WA, 2011)
TW = Trawl TP = Trap
6
Zone 1 Zone 2
4 1
2
Human activities in the region
5
3
Port Samson
Port Headland
Oil and gas exploration Development projects Blue = existing; Red = proposed
Onslow (Dept. FisheriesWA) Fishing - Trawl, trap, line
4 species of dolphins Bottlenose, humpback, snub fin and spinner (Dept Mines and Petroleum WA, 2011)
Trawl effort Hours
Pilbara Fish Trawl Interim Managed Fishery (PTF) Interim managed since 1997 because of incidental catch of dolphins 17 - 50 dolphins per year
60,000
Foreign fleet Australian
30,000 10,000 1970
1980
1990
(CSIRO NW Shelf technical report)
2000
Trawl effort Hours
Pilbara Fish Trawl 60,000 Interim Managed Fishery (PTF) 30,000 • single, demersal otter trawl; 10,000 • 3-4 full time vessels 1970 • ~ 5,000 trawls p.a. • 1,200 tonnes p.a. ~75% of WA finfish • ~13,000 km2
Foreign fleet Australian
1980
1990
(CSIRO NW Shelf technical report)
2000
Incidental dolphin capture: Aims In 2002, DoFWA started research (Peter Stephenson) This research started in 2008: 3 components 1. Assess incidental catch of dolphins and effects of modifications to net designs (Simon Allen, Bejder, Tyne, Jaiteh, Loneragan) 2. Describe dolphin behaviour in trawl nets (Vanessa Jaiteh, Allen, Jessica Meeuwig, Loneragan) 3. Estimate “sub-population” (group) size of dolphins interacting with trawlers (Allen, et al. , Michael Krutzen, Ken Pollock)
Assessing incidental catch of dolphins (FRDC report Allen & Loneragan 2010)
Objectives 1. Examine spatial, seasonal and daily variation in fishing/ dolphin interactions (space/area closures as an option); 2. Evaluate changes in net designs, including the introduction of bycatch reduction devices Data sources (provided by DoFWA) 1. Logbooks from the fishery (2003 to 2009, ~ 30,000 trawls) 2. Data collected by observers (8% to 17% - 2005 to 2009, ~ 5,000 trawls); Nickol Bay Professional Fishermen’s Association
Fishing effort and dolphin captures
Observer Log book
Log books 2003 to 2009, ~ 30,000 trawls Observer 2005 to 2009, ~ 5,000 trawls
Analysis of factors affecting incidental dolphin capture Generalised Linear Models – main effects and interaction terms 1. 2. 3. 4. 5. 6.
Management area (1, 2, 4, 5) Water depth (10 m categories, 50 to 100 m) Season (northern wet, dry) Vessel (4 vessels) Time of day (6 h blocks) Net design Mean dolphin catch per 1,000 trawls
Mean catch per 1,000 trawls by vessel (~ 3, 000 h trawling) Number per 1,000 trawls 20
Logbook Observer
*
15
10
*
5
0 1
2
Vessel
3
4
Incidental catch and time of day Number per 1,000 trawls 15
Logbook Observer
10
5
* * 0 Morning Afternoon Evening Early morn. Time of Day (6 h blocks)
Net Design and incidental dolphin catch (modified orange roughy net) BRD 44 m BRD
Bottom opening
Major modifications to the nets Pre 2006 – No Grid 2006 - Bycatch reduction device fitted (Grid) 2008 - BRD moved forward (Grid forward) 2012 - Top opening escape hatch
Net Design and incidental dolphin catch Number per 1,000 trawls 25
Logbook Observer
10,933; 1, 064
20 15
10,785; 2, 141
10
5, 097; 521
5 0 No Grid
Grid
Grid forward
Net Design ~50% reduction in incidental catch of dolphins after the introduction of BRDs.
Analysis of fishery data Incidental catches are made throughout the area of the trawling grounds and the year (time/area closures not likely to be effective) Differences in incidental catch rates: - between vessels (skipper behaviour) - time of day (dolphin behaviour) - net design Observer incidental catches 1.6 to 3.7 times higher than logbook
Dolphin behaviour inside trawl nets Vanessa Jaiteh (Hons) Jaiteh et al. (2012) Marine Mammal Science Preliminary work by Alice MacKay Univ. St Andrews (MacKay, 2011 – PhD Thesis)
Nickol Bay Professional Fishermen’s Association
Camera 1 Camera 2 Exclusion grid Escape hatch
Behaviour inside trawl nets 1.
To quantify dolphin behaviour in and around trawl nets Ø
Interaction rates
Forward facing camera
2.
To assess implications of subsurface behaviour for bycatch mitigation
Rear facing camera
Quantifying Behaviour: Video Analyses
• Underwater, in-trawl video footage of 36 trawls (85 h)
• EventMeasure software • Recorded 18 behavioural events, 3 states (foraging, traveling, socialising)
• Developed a Photo- ID library Videos from trawls in Oct/Nov 2008 On-board observer data available for these trawls
Dolphin interactions 29 individuals identified from 36 trawls Interaction rates very high: - Inside: 81% of trawls (n=29), up to 98% of total trawl time - Outside: 94% of trawls (n=34), 99% of total trawl time
Mean = 2, range = 0 to 9
Mean Percent Frequency
Subsurface behaviour
Foraging Traveling Socialising Behavioural state and event
Resightings of identified individuals Area ≈12, 780 km²
Ndolphins = 29 Nresighted ind. = 7
Summary of video observaGons - Small numbers of dolphins interacted with nets (localised) - Dolphins are interacting with actively fishing nets almost all the time - High motivation for interaction: foraging, play and socialising Matched video with observer data (44 trawls) - From video 3 dolphins interacted with BRDs; all 3 died; only 1 was landed on deck - 34% of all bycatch either escaped or fell out the bottomopening escape hatch. Bycatch is under-reported by observers
Dolphin interactions with the fishery
What is the significance of incidental catch?
Estimation of dolphin numbers interacting with trawlers (Simon Allen et al., Australian Marine Mammal Ctr.)
• Two x one-week trips on a trawler in April 2011 • Twelve x 20-minute photo-ID sessions (Pollock robust design mark-recapture)
• Aerial survey of the fishery (4 zones)
Results from trawler Photo-identification Two fishing trips
• 151 dolphins identified, 100 found once or twice, 51 > 2 times (max = 7) • Group sizes following trawler Mean = 28, range = 17-46 • Estimated numbers around trawlers 183 ± 11 • Several individuals were seen in 2008/2009
Conclusions
• Video, photo-ID and preliminary genetic evidence give
consistent results – indicate a small community/sub-population of dolphins; has fidelity to foraging around trawlers
• Numbers interacting with trawlers are small; Current incidental catch may be significant.
• Further net modifications – top-opening hatch is being pursued
• Observer information is important This apparent habituation presents significant challenges to the mitigation of bycatch.
Acknowledgments
• Steering Committee : Lindsay Joll, Graeme Stewart, Shane Donoghue
• Funders :
Western Australian Department of Fisheries FRDC, Nickol Bay Professional Fishermen’s Association Australian Marine Mammal Centre
• Industry : • Observer:
PFTIMF licensees, skippers and crew Gavin Kewan, Geoff Diver
Australian Marine Mammal Centre Nickol Bay Professional Fishermen’s Association
References Allen SJ, Cagnazzi DD, Hodgson AJ, Loneragan NR & Bejder L 2012. Snubfin, humpback and bottlenose dolphins of north-western Australia: Unknown populations in a rapidly changing region. Pacific Conservation Biology 18: 56-63. Allen SJ & Loneragan N 2010. Reducing dolphin bycatch in the Pilbara Finfish Trawl Fishery. Final Report to the Fisheries Research and Development Corporation. Murdoch University, Perth, Australia. 59 pp. ISBN: 978-0-86905-926-5. Bejder L, Hodgson AJ, Loneragan NR & Allen SJ. 2012. Coastal dolphins in north-western Australia: The need for re-evaluation of species listings and shortcomings in Environmental Impact Assessments. Pacific Conservation Biology 18: 22-25. Brown A, Bejder L, Cagnazzi D, Parra G & Allen S. Accepted. The North West Cape, Western Australia: A potential hotspot for Indo-Pacific Humpback Dolphins Sousa chinensis? Pacific Conservation Biology Jaiteh VF, Allen SJ, Meeuwig JJ & Loneragan NR 2012. Subsurface behaviour of bottlenose dolphins (Tursiops truncatus) interacting with fish trawl nets in north-western Australia. Marine Mammal Science DOI: 10.1111/1748-7692.2012.00620.x