An ecological risk assessment for the effect of the Korean tuna longline fishery in the Western and Central Pacific Ocean

Transcription

1 An ecological risk assessment for the effect of the Korean tuna longline fishery in the Western and Central Pacific Ocean You Jung Kwon 1,2, Doo Hae An 2, Chang Ik Zhang 1, Dae Yeon Moon 2 and Jae Bong Lee 2 1 Pukyong National University, Korea, 2 National Fisheries Research & Development Institute, Korea

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3 Ecological risk assessment Scoping Scoping Comprehensive (qualitative analysis) Uncertain Level 1 Level 1 (semi-quantitative analysis) Focused (quantitative analysis) Time & $$ Qualitative L H Time & $$ Level 2 L H More certain Level 3 Quantitative L H Risk Management Response L L L H Level 2 H Level 3 H Risk Management Response (Smith et al, 2007)

4 Level 2: PSA (Productivity and Susceptibility Analysis) db dt B = rb(1 ) K qeb Productivity, r - recovery rate after potential depletion or damage by the fishing activity Susceptibility, q - extent of the impact due to fishing activity

5 Purpose Assessment on the adverse impacts of the Korean tuna longline fishery in the Western and Central Pacific Ocean - target species, non-target species and dependent or associated with the target species Precautionary approach for the stock or ecosystem management and conservation - identification of non-target species for consideration of future research or management - protect biodiversity in the marine environment

6 Data Survey area N 60 o 40 o 20 o Period: Area: Western and Central Pacific Ocean Source: 0 o 20 o WCPO 2006 EPO - 20,157 catches in number - 48 species 40 o 60 o S Collected data by 7 scientific observers from NFRDI in Korea E 100 o 120 o 140 o 160 o 180 o 160 o 140 o 120 o 100 o 80 o W

7 Species Group English name Scientific name Tunas (5) Billfishes (6) Sharks (13) Albacore Thunnus alalunga Bigeye tuna Thunnus obesus Yellowfin tuna Thunnus albacares Skipjack tuna Katsuwonus pelamis Bluefin tuna Thunnus thynnus Swordfish Xiphias gladius Shortbill spearfish Tetrapturus angustirostris Blue marlin Makaira mazara Indo-Pacific sailfish Istiophorus platypterus Striped marlin Tetrapturus audax Black marlin Makaira indica Bigeye thresher shark Alopias superciliosus Blue shark Prionace glauca Galapagos shark Carcharhinus galapagensis Longfin mako Isurus paucus Shortfin mako Isurus oxyrinchus Oceanic whitetip shark Carcharhinus longimanus Grey reef shark Carcharhinus amblyrhynchos Smooth hammerhead Sphyrna zygaena Crocodile shark Pseudocarcharias kamoharai Scalloped hammarhead shark Sphyrna lewini Japanese velvet dogfish Zameus ichiharai Salmon shark Lamna ditropis Silky shark Carcharhinus falciformis

8 Species Group English name Scientific name Turtles (3) Other species (21) Green sea turtle Loggerhead sea turtle Olive ridley sea turtle Sickle pomfret Black pomfret Escolar Snake mackerel Wahoo Longnose lancetfish Pelagic stingray Ocean sunfish Great barracuda Opah Chelonia mydas Caretta caretta Lepidochelys olivacea Taractichthys steindachneri Taractes rubescens Lepidocybium flavobrunneum Gempylus serpens Acanthocybium solandri Alepisaurus ferox Dasyatis violacea Mola mola Sphyraena barracuda Lampris guttatus Dolphinfish Coryphaena hippurus Sharptail mola Masturus lanceolatus Manta ray Mobula japanica Oilfish Ruvettus pretiosus Rainbow runner Elagatis bipinnulata Slender sunfish Ranzania laevis Suck fish Flyingfish Crested oarfish Razorback scabbardfish Shortnose lancetfish Remora remora Prognichthys gibbifrons Lophotus lacepede Assurger anzac Alepisaurus brevirostris

9 Species composition catch in weight Shortfin Mako shark mako 22.9% Others 9.6% Bigeye thresher shark 6.6% Nontarget species 43% Blue shark 60.9% Sharks 28.8% Sickle pomfret 12.2% Billfishes 5.9% Others 27.9% Others 8.2% Opah Turtles 20.7% 0.3% Target species 57% Escolar 39.3% Tunas 56.8% Indo-Pacific sailfish 5.8% Shortbill spearfish 2.8% Striped marlin 16.5% Blue marlin 29.6% Black marlin 0.8% Swordfish 44.5% Yellowfin 10.6% Bigeye 59.4% Skipjack 1.3% Bluefin 0.1% Albacore 28.5% Proportion of captured species (weight) by 7 scientific observations from 2005 to 2008

10 Indicators for species components (Target, By-catch, Protected species) Productivity attributes Maximum age Age at maturity Size at maturity Annual fecundity Maximum size Reproductive strategy Trophic level Susceptibility attributes Overlap with fishing effort Global distribution Adult habitat overlap with juvenile Selectivity Post-capture mortality

11 Attribute Susceptibility Indicator Overlap with fishing effort 309m 25m Sea surface sp. B sp. A 0m 25m 167m Maximum hook depth Reference point Species A: High risk (2), 100% Species B: Medium risk (1), 50% Species C: Low risk (0), 0% sp. C 309m bottom

12 Attributes (CSIRO, 2005) Attributes Productivity Susceptibility Indicators Reference points Low (0) Medium (1) High (2) Maximum age (year) < < Age at maturity (year) < < Size at maturity (cm) < < Maximum size (cm) < < Reproductive strategy Broadcast spawners Demersal spawners Live bearer Trophic level < < Overlap with fishing effort (m) 309 < 167 < Global distribution Worldwide Hemisphere Locality Adult habitat overlap with juvenile Selectivity Low rate Medium rate High rate No selectivity for longline fishery Post-capture mortality Alive Barely alive Dead

13 Captured Indicator mean length Ⅱ Ecosystem risk assessment TypeⅠ High risk Low risk Length Indicator maturity Ⅰ Susceptibility Attribute Ⅱ Low risk TypeⅡ Medium risk High risk 1 2 Productivity Attribute Ⅰ

14 TypeⅠ 300 Tunas Sharks Captured mean length (cm) Billfishes Other species Others Length at maturity (cm)

15 TypeⅡ Tunas Billfishes Susceptibility Productivity

16 TypeⅡ

17 TypeⅡ 2 Oceanic Oceanic white-tip white-tip Shark Shark Galapagos shark sharks Susceptibility 1 tunas tunas billfishes Bigeye thresher shark turtles billfishes Blue shark sharks Shortfin mako Scalloped hammarhead shark Longfin mako turtles Productivity

18 Conclusion Not only target tuna species were influenced by the tuna longline fishery, but also non-target species were affected by the fishery WCPFC This study Blue shark- tunas: medium risk Galapagos shark Oceanic white-tip - billfishes: shark medium or high Longfin risk mako Shortfin mako - sharks: high risk Scalloped hammarhead shark Thresher shark Oceanic white-tip shark - turtles: : medium or high risk - others: medium or high risk

19 Conclusion For reducing non-target species I. Development and improvement of long-term data collection, monitoring and research programmes II. Enhancement and development of methodology - more robust assessment III.Identification of captured non-target species by other tuna fisheries such as purse seine or pole-and-line Provide wider scientific advices to the policy makers and stakeholders