Development of marine mammal bycatch mitigation in European trawl fisheries

Transcription

1 Development of marine mammal bycatch mitigation in European trawl fisheries Presentation to FRDC workshop on mitigating marine mammal interactions in the SPF Alice Mackay 25 June 2015

2 Introduction Development of bycatch mitigation strategies in UK pair trawl fishery for European seabass (Dicentrarchus labrax) Led by Dr Simon Northridge, SMRU, University of St Andrews Funded by the Department of the Environment, Food and Rural Affairs (DEFRA), UK and the EU Necessity Project EU NECCESITY Project Objective: to develop effective and acceptable gear modifications (by-catch reduction devices or acoustic deterrents) to reduce the by-catch and mortality of cetaceans in pelagic trawl fisheries. Pelagic fisheries: 12 target species, 6 nations, 3 major gear types Denmark, France, Ireland, Netherlands, Spain, UK

3 Overview of UK bass pair trawl fishery November to April in Western English Channel 2-3 pairs of boats (15-38m vessels) Tows 6-7 hours Net length 250m, wing-end spread 90m* 18m (stretched mesh) at mouth, 8m at 125m along net At sharks teeth net is 40m wide with 1.6m mesh then get gradually smaller, ending in a tunnel to codend (~25m) Tow speed knots (through water) Headline at or near surface Footrope ~ 40m Annual fishing effort very variable; 10 s to 500 tows Also French sector of fishery ~ variable: few tens of pairs

4 Industry approached SMRU Autumn 2000 seeking way to mitigate high bycatch of common dolphins Location of observed bycatches

5 Initial pinger trials: 2001 Dukane pingers deployed 12 around headline and footrope Pingers Number of tows No of dolphins bycaught Deployed Not deployed Bycatch rate per tow 2002 Aquamark deployed 6 around sharks teeth 2 hauls without pingers took 20 animals All other observed hauls were WITH pingers Catch rate ~ 0.7 dolphins per tow

6 Development of exclusion grid(s) Season Initial grid: solid stainless steel with 1.7m escape hole with 22mm mesh net cover 31 tow trials observed with camera No dolphin bycatch during trial 2 caught after trial (reported by skipper) could not easily exit through escape hatch Also video of dolphins present in net not recorded bycaught Reason for apparent success? Grid acting as barrier (rather than exit)? Scanmar grid sensor acoustic deterrent?

7 Development of exclusion grid(s) Aimed to improve ability for dolphins to exit escape holes easily and improve ease of grid handling Two new grids and escape hatch covers Tubular stainless steel and flexipanel (rope and plastic tube) improve deck handling and concerns about steel grids 5mm mesh net, vinyl strips, bungee cord Enlarged escape hole from 1.7m to 2.4m in length Switched to smaller pair of boats (15m) Aimed to get real time monitoring of all tows (dolphin interactions and fish losses) Flexi-panel grid deployed in UK fleet Solid plastic grid developed by French

8 season Unprecedented level of bycatch bycatch event every 1 in 3 tows Change in seasonal pattern of bycatch and distribution of bycatches: earlier in season further inshore Problems with real time video footage cable breakages so no footage of bycatch events Grid type Hole size Escape hatch cover net type Tows Dolphins Dolphin bycatch tows Dolphins Per tow Proportion of tows with bycatch Steel 1.7m 22mm mesh Flexipanel Steel (tube) 2.4m 22mm mesh m 5mm mesh Indication that steel grid with large escape hole and small mesh cover reduced number of dolphins bycaught per tow (exiting mouth or escape hatch?)

9 season No functioning camera system:? exited Dolphin caught further forward in net than previously observed up to 55m forward of grid Presence of grid? Slightly smaller net thinner mesh from extension piece to sharks teeth

10 : trial of net grid 20cm mesh net panel in mid section of net Increased drag and reduced fish catches

11 Stainless tubular grid at extension piece 33 bycatches forward of grid Moved flexible grid 30m forward in net 5 dolphins exited escape hatch (with effort) 18 dolphins bycaught forward of grid Moved steel grid another 10m forward Four more dolphins exited through escape hole 15 bycaught forward of grid Estimates of dolphins exiting escape hatch is minimum not always observed Issues moving grid forward - ballooning of net, substantial fish losses

12 : Limited fishing effort 54 observed hauls ~ 90% of total fishing effort Most of observed hauls were with grids but number of technical issues with cameras and with the grids that are poorly documented 9 bycatch events totaling 77 dolphin bycatches Grid in similar location to previous season Lower proportion of tows with bycatch but higher group size (8.55 average to 3.9 other season) Trialed prototype acoustic deterrent device by Aquatec Interactive pinger Deployed on two tows bycatch of 15 dolphins

13 EU Necessity project ( ) Excluder devices Trials in the French sector of the bass fishery 400mm square-mesh barrier at 200mm mesh section of net, with two 3x3m escape openings with bungee cord cover 7 of 22 hauls has bycatch with most animals caught at level of net barrier Dolphins did exit through opening but others were observed in a passive state at the barrier Fish loss through the escape opening. Acoustic deterrent devices Direct playback / bow riding experiments Commercial fishing trials Aquatec Interactive acoustic deterrent device Cetasaver STM-DDD pinger

14 Pinger playback experiments Mixed results of playback experiments of Aquatec, DDD and Cetasaver devices Inter-species difference in reaction Intra-species difference in reaction in different geographical areas Trials in the bass fishery France - Cetasaver pinger deployed at sharks teeth 2 dolphins bycaught in 52 tows with pinger 11 dolphins in 61 tows without pinger UK bass fishery Start of trials with STM DDD-02F pinger Deployed two close to the shark s teeth (1 tow); tangled with net Afterwards deployed on footrope of trawl No bycatches in 18 tows when DDDs were working 8 in 2 tows where one/both pingers not working 14 in 3 events from 7 observed tows without pingers No trials in ; very low effort - high fuel cost and low bass

15 UK bass fishery Most tows equipped with either DDD-02F or DDD-03H 2 dolphins caught in 1 event out of 28 observed tows No control trials - no information on underlying bycatch rates UK bass fishery Two pairs of boats fishing Pair A DDD-02F on both nets 17 dolphins in 5 events from 131 observed tows with DDD-02f 1 dolphin in 1 event from 8 observed tows without pingers Pair B DDD-03H on one net Zero dolphins in 34 tows with DDD-03s 10 dolphins in 4 events out of 23 control tows

16 Started testing voltage of DDDs DDD-02Fs were no longer holding charge (3 years old) : 82 hauls observed, 3 dolphins in 2 events : 84 hauls observed, 6 dolphins in 3 events January 2015: European Union has banned trawling for bass during the spawning season Since 2011, DDDs (02F or 03H) have also been used in the Irish pelagic pair trawl fishery for Albacore tuna and on three pairs of pelagic trawlers in Italy. Background bycatch rates in these fishery very low

17 Conclusions Excluder devices Means to reduce cetacean bycatch Some dolphins observed exiting escape holes Others seen in a passive state when reaching excluder device Positioning within trawl is critical as far towards mouth will be best Issues with rigging, handling and increased drag Losses of commercial fish Acoustic devices Level of effect is likely to be species and fishery specific Deterrent or alerting? Will depend on signal of device and background noise of gear and vessel Interpretation of differences between playback experiments and fishery observations The use of DDDs led to a marked reduction in bycatch rates of common dolphins in the UK pair trawl fishery for bass. It is difficult to quantify the exact scale of this reduction due to the absence of control tows. Issues with longevity and performance of devices Need to be properly charged and working when deployed Need to be placed at appropriate depth Rechargeable batteries will not last indefinitely

18 Conclusions Testing the effectiveness of any mitigation measure in an operational fishery requires an understanding of: Variability in the distribution and abundance of marine mammals in the fishing area The underlying bycatch rate The nature of interactions and the behaviour of individuals interacting with trawl gear When and how bycatch occurs Considerations when testing any mitigation measure include Difficultly in obtaining sufficient data to draw conclusions when bycatches are sporadic Operational practicalities of any mitigation device Ability to monitor all tows (underwater video / passive acoustics) Ability to conduct control tows To date no measure to mitigate cetacean bycatch in trawls has been 100% effective

19 Acknowledgements The development of mitigation measures in the UK pair trawl fishery for bass was funded by DEFRA and the Necessity Project and led by Dr Simon Northridge at SMRU, University of St Andrews, Scotland. The project was facilitated by a team of observers and by the skippers and crews involved. Necessity Project members: AZTI (Spain) BFAFi (Netherlands) BIM and UCC (Ireland) DIFRES (Denmark) IFREMER and CRMM (France) IMARES (Netherlands) SMRU (UK)