Presentation outline slipping mortality in purse seine fisheries - PDF document

14.07.2014 Quantification and mitigation of Presentation outline slipping mortality in purse seine fisheries Part 1: Mortality of crowded and slipped herring and mackerel Part 2: Mortality causes of slipped herring Part 3: Slipping mortality mitigation Part 4: Future challenges and plans Maria Tenningen Purse seining method Norwegian Purse Seine Fisheries 1. Detect and evaluate school • Main species: Herring, mackerel and capelin (> 90% caught by purse 5. Catches pumped seine) on board • Catch: 827 000 t in 2013 (ca. 40% of all Norwegian catches) ~700 m ~150 m Ocean going (ca 1500 t) <15 m Coastal (ca 350 t) 2. The net is shot around the school (5 min) 3. The purse line is hauled and the net is closed (20 min) 4. The net is hauled on board (1 h) A major problem in these fisheries Part 1 Mortality of crowded and slipped is the mortality of slipped fish herring • Reasons for slipping: -Too large catches -Low value individuals or species - Regulated species or sizes According to norwegian legislation it is illegal to slip dead or dying fish. But how do we know wether the slipped fish will survive or die?? 1400 t herring FOTO: "LIBAS". 1

14.07.2014 Method Crowding experiments 3 net pens (2 crowded, 1 control) (North Sea herring, June 2008 and 2009) 10 min crowding phase 4-5 days monitoring phase Huse and Vold, 2010 North Sea and Norwegian Spring Spawning (NSS) Mortality of crowded NS herring Herring 4-5 days post crowding 60 60 Small individuals are more sensitive 50 50 40 40 Mortality (%) Mortality (%) North Sea 30 2008 Round 1 30 NSS 2011 2008 Round 2 NSS 2012 Round 1 2009 Round 1 20 20 Controls: careful slipping is ok! NSS 2012 Round 2 10 10 0 0 100 200 300 400 500 600 0 Crowding density (kg m -3 ) 0 100 200 300 400 500 600 Crowding density (kg m -3 ) NSS herring: unpublished data IMR Part 2 Herring and Mackerel Mortality causes 90 80 Density & Time Lack of 70 oxygen? 60 Physical Mortality (%) 50 exhaustion? 40 Herring Mackerel (small scale) 30 Mackerel (large scale) Skin injuries ? 20 10 0 0 100 200 300 400 500 600 -10 Crowding density (kg m -3 ) Small scale: Lockwood et al., 1983 Large scale: Huse and Vold, 2010 2

14.07.2014 Physiological stress response to crowding The role of scale loss Laboratory experiments where 25 and 50% of herring scales were removed. Initial stress response: Extended stress response: Mortality monitored for 7 days • Increasing cortisol • Continuously high cortisol levels • Increasing lactate • Loss of osmoregulatory balance • Increased chloride • Approaching energy exhaustion The role of hypoxia How much scales do herring lose during commercial fishing? 403 kg m-3, 52% mortality 478 kg m-3, 51% mortality 92 kg m -3 – mortality 10% 226 kg m -3 – mortality 28% Herring have been shown to tolerate oxygen levels to < 30% 393 kg m -3 – mortality 36% (Dommasnes et al., 1994; Domenici et al., 2000) (Svalheim, 2012) Part 3 Conclusions on mortality causes Slipping mortality mitigation • Scale loss is likely to explain some crowding mortality, but not all! • Hypoxia and physical exhaustion are likely to be important additional stressors • Mortality is a result of a combination of several ”stressors” • The main causes of mortality may vary under different conditions • Understanding the mortality causes is important! – It can help us understand variation in mortality (within an experiment, between experiments and between species) – Identify the best mitigation measures 3

14.07.2014 How late in a haul can slipping be accepted? Alternative 1 Quantify mortality and include the data in the assessment Alternative 2 Total ban on slipping  not feasible in practice (increased net bursts, increased illegal slipping ) Alternative 3 Slipping limit 90 Reduce the need for slipping  improved pre-catch identification 80 (development of sonar technology) 70 Mortality (%) 60 50 Alternative 4 Herring 40 Increase the survival of slipped fish  Careful slipping before 30 Mackerel (small scale) 20 Mackerel (large scale) densities get too high 10 0 0 100 200 300 400 500 600 Crowding density (kg m -3 ) How can we estimate fish densities? Monitoring net volume and fish shoal size during purse seining Fishery sonar Transponders Image: Simrad Challenges: • Large and flexible net and fish may be anywhere • Acoustics  cover large area, but airbubble noise from vessel is problematic • Camera technology  high resolution but short range, lack of light Results: Net volume Significant variation in net volume between sets Fitted a regression model to describe net volume as a function of hauling proportion The reconstructed 3D net and shoal shape. Part (a) shows the 3D point cloud created from the sonar data at several tilt angles. Parts (b-d) show the closed triangulated surface used for the volume estimates at 22, 44 and 50 % hauled net. The shoal is shown in red and the ship in blue. 4

14.07.2014 How to use the data into regulation? Results: a. Net volume available per fish in the catch (Catch biomass / net volume) 1. Further develop the methods for net and catch monitoring b. Density (catch biomass / shoal volume) (more accurate estimates and also from the last part of hauling) 12 kg 2. Net volume monitoring: Need to verify the assumption of even fish distribution at the point where density becomes harmful 3. Need to understand what factors and how these determine net volume (e.g. net design, vessel operation and environment)  Model net volume under different conditions and use it together 7/8 hauled net is at  87% with catch size to predict when critical densities can be expected.  Real time monitoring for density or net volume (with a catch Lowest registered value 0.07 Mackerel 30 kg m -3 or 0.01 m 3 per fish biomass estimate) for a flexible limit on slipping.  5-28% mortality Herring 100 kg m -3 or 0.002 m 3 per fish  0-10% mortality Part 4 Catch simulations Future work ? Mortality causes Improved gear and catch monitoring ? Slipping quantities Better mortality data for mackerel Expected volume available for individual fish (m 3 per fish) as a function of hauling proportion and catch weight, obtained from the linear regression model fitted to the net volume estimates. Catch and gear monitoring during Funding application 2015-2017 purse seining • Norwegian Research Council 3. September 2014 Title: Development of Tools to Reduce Slipping Mortality in Purse Seine Fishing Main objective : Reduce slipping mortality in mackerel and herring purse seine fisheries by improving the monitoring and control of the fishing operation 5

14.07.2014 Purse seine projects at the IMR Thank You  a reduced need for slipping and in situations where slipping is necessary it can be carried out in an early stage of hauling in a careful way 6