Quantitative risk assessment of benthos & bycatch sustainability in a tropical shelf trawl fishery. Roland Pitcher

Transcription

1 Quantitative risk assessment of benthos & bycatch sustainability in a tropical shelf trawl fishery Roland Pitcher

2 Builds on GBR Seabed Biodiversity Project Conservation Planning: Comprehensive maps of distribution & abundance of seabed habitats & biodiversity in the GBRMP Provide information to assist with assessing protection afforded by the zoning developing monitoring strategies, planning of future multiple-uses Sustainable Fisheries: Assist with environmental assessments of the prawn trawl fishery Development of sustainability risk indicators and reference points Provide information to assist with the Trawl Management Plan

3 Benthic biodiversity Sampling AIMS RV Lady Basten: 24 hrs, 180 days BRUVS Acoustics Benthic Sled Towed Video

4 Demersal fish diversity sampling QDPI FRV Gwendoline May: Night hrs, 125 days Seabed fish & bycatch samples 8 fathom otter trawl

5 Trawl and benthic sites sampled GM trawl: ~125 days LB benthic: ~180 days 448 sites sampled 1340 sites sampled

6 Seabed habitat photos

7 >7,000 taxa identified, many new species Some GM sample specimens.

8 Collated 28 physical environment covariates eg.bathymetry, slope, current stress, sediments, turbidity, nutrients, fishing etc North GBR South GBR

9 log base 2 (mean estimate): grams /Ha Biomass scale (g/ha) 2D Colou Predicted species distribution maps 16384g 8192g 4096g 2048g 1024g 512g 256g 128g 64g 32g 16g 8g 4g

10 Trawl Exposure Indicators: for ~850 species Rank Class Genus Species %Protected %Exposed %EffortExp Rel_Catch %Caught M_est C/M 1 Crustacea Penaeus semisulcatus Crustacea Cryptolutea arafurensis Actinopterygii Brachirus muelleri Actinopterygii Pentaprion longimanus Actinopterygii Pelates quadrilineatus Actinopterygii Leiognathus leuciscus Actinopterygii Upeneus sundaicus Crustacea Portunus gracilimanus Actinopterygii Terapon puta Bivalvia Enisiculus cultellus Crustacea Metapenaeus ensis Crustacea Thenus parindicus Actinopterygii Psettodes erumei Bivalvia Amusium pleuronectes cf Crustacea Penaeus latisulcatus Crustacea Penaeus esculentus Crustacea Metapenaeus endeavouri Actinopterygii Saurida grandi/undo Bivalvia Amusium balloti Actinopterygii Leiognathus cf bindus Crustacea Portunus pelagicus Actinopterygii Trixiphichthys weberi Cephalopoda Sepia elliptica Actinopterygii Sillago burrus Actinopterygii Pomadasys maculatus Crustacea Portunus sanguinolentus Actinopterygii Fistularia petimba Crustacea Metapenaeopsis novaeguineae

11 Sensitivity of indicators Frequency distributions for species, by indicator Species biomass in management zones available to trawling Species biomass exposed to trawl grounds Biological (limit) Reference Point Species biomass exposed to trawl effort as swept coverage Species biomass estimated to be caught annually

12 Indicators without species distributions Frequency distributions for species, by indicator Species biomass in management zones available to trawling Species biomass exposed to trawl grounds Species biomass exposed to trawl effort as swept coverage Species biomass estimated to be caught annually

13 2009 update: trawl effort trends 200,000 km² Effort_hrs 264, ,277 Grid_Count 40,582 45,192 Swept_km² 38,849 21,756 Area_km² 17,240 14,029

14 2009 update: trawl effort comparison Difference

15 CLASS GENUS SPECIES %Protected %Exposed %EffortExp Rel_Catch Uncertainty BRD pcaught M_est C_REL_M pexposed peffortexp pcaught C_REL_M Crustacea Penaeus semisulcatus Crustacea Cryptolutea arafurensis Actinopterygii Brachirus muelleri Actinopterygii Pentaprion longimanus Actinopterygii Pelates quadrilineatus Actinopterygii Leiognathus leuciscus Actinopterygii Upeneus sundaicus Crustacea Portunus gracilimanus Actinopterygii Terapon puta Bivalvia Enisiculus cultellus Actinopterygii Brachaluteres taylori Crustacea Trachypenaeus anchoralis Crustacea Metapenaeus ensis Crustacea Erugosquilla woodmasoni Actinopterygii Leiognathus bindus Bivalvia Melaxinaea vitrea Actinopterygii Saurida argentea/tumbil complex Actinopterygii Terapon theraps Crustacea Myra tumidospina Actinopterygii Calliurichthys grossi Crustacea Thenus parindicus Gastropoda Nassarius cremmatus cf Actinopterygii Psettodes erumei Bivalvia Placamen tiara Actinopterygii Scolopsis taeniopterus Bivalvia Amusium pleuronectes cf Actinopterygii Yongeichthys nebulosus Actinopterygii Apogon poecilopterus Actinopterygii Euristhmus nudiceps Actinopterygii Tripodichthys angustifrons Anthozoa Sea pen sp Cephalopoda Sepia pharaonis Actinopterygii Nemipterus peronii Actinopterygii Saurida grandi/undo complex Crustacea Charybdis truncata Crustacea Portunus tuberculosus Actinopterygii Trixiphichthys weberi Cephalopoda Sepia elliptica Gastropoda Aplysia sp1_qms Gastropoda Lamellaria sp Actinopterygii Sillago burrus Crustacea Diogenidae sp Actinopterygii Pomadasys maculatus Actinopterygii Nemipterus furcosus Actinopterygii Nemipterus hexodon Actinopterygii Fistularia petimba Actinopterygii Chaetodermis penicilligera Actinopterygii Nemipterus sp juv/unident Cephalopoda Sepia whitleyana Chondrichthyes Dasyatis leylandi Cephalopoda Sepia smithi Actinopterygii Polydactylus multiradiatus Actinopterygii Pristotis obtusirostris

16 Seabed habitat photos

17 Seabed habitats %Protected %Exposed EffortExp% pexposed peffortexp

18 Seabed assemblages %Protected %Exposed EffortExp% pexposed peffortexp

19 Summary Distributions are critical for assessment Prediction from environmental variables is useful Quantitative risk indicators absolute sustainability Analogous to stock assessment of target species Proportion caught relative to demographic rate Compare against established biological reference points Very few of 100s of species appeared to be at risk Intensity & footprint decreasing reduced risk