Observing halibut survival after trawler deck-release with satellite tags Craig S. Rose, FishNext Research Julie Nielsen, Kingfisher Marine Research John Gauvin, Alaska Seafood Cooperative Tim Loher, Int. Pacific Halibut Commission Paige Drobny, Spearfish Research Andrew Seitz & Michael Courtney, U of Alaska Fairbanks, SAFS Suresh Sethi, Alaska Pacific Univ. and Cornell Funded by grants from the North Pacific Research Board and NOAA’s Saltonstall-Kennedy program
Bering Sea flatfish (all Pleuronectidae) Biomass 4.9 million mt (2015 AFSC shelf survey) • Yellowfish sole Limanda aspera • Northern rock sole Lepidopsetta polyxystra • Flathead sole Hippoglossoides elassodon • Alaska Plaice Pleuronectes quadrituberculatus • Arrowtooth flounder Atherethes stomias • Pacific halibut Hippoglossus stenolepis Also: Greenland turbot, Kamchatka flounder, rex sole, Dover sole, Bering flounder, Sakhalin sole, butter sole, longnose dab, starry flounder
Trawl fisheries for flatfish in the Bering Sea • 225,000 - 250,000 mt / year recently (NMFS AKR) Other Flatfish Flathead Sole • Catcher / processor vessels Arrowtooth Flounder Alaska Plaice • Quotas allocated by vessel Pacific halibut Yellowfin Rock Sole Sole (bycatch, must be released) • Fixed halibut bycatch mortality limits - allocated between vessels • Significant constraint • Recently reduced • Catches sampled entering processing area (after holding)
Trawler deck-sorting to reduce halibut mortality • Deck-sort to release bycaught halibut as soon as possible • Much lower mortality than if put into holding tanks • Current survival estimates from onboard viability assessments • Structured set of reflex and injury observations • Scored Excellent, Poor, ‘Dead’ • Viability survival rates (E-80%, P-45%, D-10%) based on 1970 tag releases • Vessel specific mortality estimates for trials
Project Goals • Apply modern tag technology to validate and improve the foundation for halibut survival rates • Develop tag tools and metrics to monitor halibut survival (Julie Nielsen’s earlier talk) • Compare viability-based survival outcomes with those indicated by recorded halibut activity • Find conditions that improve survival • Guide further survival improvements
Deployment Trips Tags on: 160 trawl releases 20 Controls Flounder, turbot ATF/GTR_2 (25) Halibut Yellowfin sole Pac. Ocn. Perch longline (10) YFS_1 (39) POP_2 (8) YFS_3 (45) Trawl - June Flathead sole FHS_1 (34) Trawl - June Trawl - Aug Longline – Jul1
Halibut handling and data • Stratified halibut selection – Time on deck • 1 per 5 minute intervals – random time within • Video viability assessments • Reflex and injury scan, scored Excellent, Poor, or ‘Dead’ • Scored from videos by 5 experienced observers Camera • Fish and handling data recorded • fish length • humidity • time-on-deck • sand in catch • tow duration • sea state • deck temperature • trawl net • seafloor temperature • excluder use
Tags popped up and reported • Data reported from 5 – 14.9 days 0 – 4.9 days all 180 tags! (only one with too little data to use) • Some appeared to release from active fish (anchor failure?) • Most recoveries in 15 – 59.9 days 60+ days vicinity of release, at all durations • Some longer movements from full or near-full deployment periods
Classification of activity data: live or dead and when Alive all 60 days Died after 3 days • Scored by 6 reviewers • Majority outcome after reconciliation discussion (Nine dropped – still tied or too uncertain)
Analysis methods • Kaplan-Meyer survival curves – estimate probability of surviving by time since release (can account for early releases) Trip • Cox proportional hazards modelling to regress multiple factors against survival period.
Survival analysis Viability scores D P E .01 .45 .80 Key features of survival curves Nearly all deaths occurred in the first 2 weeks Variability by Trip-Target
Survival analysis Compare survival estimates between tagging results and from viability scores 100% Viability Survival 90% Tag Survival 80% Most Trip-Targets have reasonable matches 70% (POP only 8 fish) 60% 50% 40% 30% 20% 10% 0% ATF/GTR_2 FHS_1 POP_2 YFS_1 YFS_3 Trip 3 (YFS) high viability, Low tag survival
Survival by trip and viability Most trip/targets – Survival rates by • viability score similar to each other and standard rates YFS Trip 3 – Survival rates for Excellent • Poor excellent and poor scores ‘Dead’ substantially lower than other trips and standard rates
Third trip hypotheses Increased mortality due to: Surface/air temperatures Deck handling Assessment handling
Third trip hypotheses Viability assessments overestimated: Pre – assessment recovery tank Multiple potential differences unique to Trip 3 precluded isolating a single cause for the low survival of released halibut in spite of scoring high viabilities
Factors predicting mortality Handling, fish size, environmental Cox proportional hazards model AIC Measurement pvalue import. SpecimenLength 0.003 97% OnDeckTime 0.007 92% Trip1-FHS 0.862 Trip2-POP 0.149 96% Trip1-YFS 0.004 Trip3-YFS 0.012 TowDuration 0.010 92% Sediment in n.s. 27% catch DeckTemp* n.s. 37% CatchSize n.s. 26% * - Also Surface Temp, Surface Temp – Bottom Temp (all highly correlated)
Factors predicting mortality Model comparison (132 halibut with viabilities) R 2 Model structure Npars AIC Without Viability DaysSurvive ~ All factors except Viability 10 640 0.47 DaysSurvive ~ SpecimenLength 1 652 0.20 DaysSurvive ~ OnDeckTime 1 653 0.19 DaysSurvive ~ Trip/Catch 4 662 0.16 DaysSurvive ~ TowDuration 1 662 0.09 DaysSurvive ~ SpecimenLength + OnDeckTime + TowDuration 3 641 0.34 DaysSurvive ~ SpecimenLength + OnDeckTime + TowDuration + Trip/Catch 7 637 0.45 With Viability DaysSurvive ~ All factors including Viability 12 591 0.74 DaysSurvive ~ Viability 2 623 0.47 DaysSurvive ~ Viability + SpecimenLength + OnDeckTime + Tow Duration 5 601 0.64 DaysSurvive ~ Viability + SpecimenLength + OnDeckTime + TowDuration + Trip/Catch 9 591 0.72
Next steps • Better understand variation across fisheries/seasons/vessels • Viability scoring from deck sorts • More tagging? How to distribute? • Explore survival monitoring options • Viability? Length-TOD-Tow time? Both? • How much variability is acceptable? • Does monitoring motivate practices that increase survival? • Further tag developments for survival use
Summary • Acceleration-only tags measure survival and tell us a lot about what happens to halibut after deck release • Deck sort process greatly improves halibut survival (Time on deck <25 min. vs. hours) • Viability predicts survival well – except for trip 3 – Could not isolate specific cause • Fish size, time-on-deck and tow time all influence survival • Trip and Fishery variability is also significant
Questions? Discussion Viability reviewers Captains and crews of: • Thanks to: Elanor Wolfe F/V Constellation • Coauthors! Nicholas Rubino F/V Cape Horn Laura Mowczan • Sarah Webster F/V Arica Alisha Foster F/V Darlynne Christopher Kromm
Length composition of tagged halibut 25 ATF/GTR_2 (25) 20 FHS_1 (22) POP_2 (8) 15 Number YFS_1 (36) 10 YFS_3 (41) 5 0 50 60 70 80 90 Length (nearest 10 cm) 15 December 2017 IFS 10 21
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