Fisheries Stock Monitoring & Assessment in Western Australia PDF

Fisheries stock monitoring and assessment in Western Australia Alex Hesp Department of Primary Industries and Regional Development (DPIRD) September 2024 UWA “Fisheries Science: Foundation and Application” BIOL3305  Introduc...

Fisheries stock monitoring and assessment in Western Australia Alex Hesp Department of Primary Industries and Regional Development (DPIRD) September 2024 UWA “Fisheries Science: Foundation and Application” BIOL3305  Introduction to WA assessment approach Harvest strategies (Monitoring/Assessment/Management framework) Performance indicators and reference points Risk assessment Weight-of-evidence assessments Outline WA assessment levels (L1 – L5) (Lecture 1) Main types of data used in WA assessments & issues Catch CPUE data (catch rate) Fishery dependent vs fishery independent Age / size compositions  L1 Catch-MSY (Catch + assumptions) Example: Sea mullet L3 Catch curve & per recruit analysis (Age data + biological parameters) Catch curve extensions Example: Sea mullet Outline Per recruit analyses L2/L4 Production models (Catch + fishery (Lecture 2) dependent CPUE data) Example: Sea mullet Risk score for Sea mullet L5 Integrated model assessment Biomass dynamics models vs integrated models Example: Age-based integrated model for Gascoyne pink snapper Accessing Department publications Department of Primary Industries and Regional Development Fisheries Publications – view all publications Several report series: Ones I tend to look at most State of the Fisheries report Fisheries research reports Western Australian Marine Western Australian Fisheries Stewardship Council Report and Marine Research Series Laboratories (Hillarys) UN Convention on Law of the Sea (1982) : The coastal State, taking into account the best scientific evidence available to it, shall ensure through proper conservation and management measures that the maintenance of the living resources in the exclusive economic zone is not endangered by over-exploitation. Principle #15 from the Rio Conference or "Earth Summit" (1992) : In order to protect the environment, the precautionary approach shall be widely applied by States according to their capabilities. Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation. FAO Code of Conduct for Responsible Fisheries (1992) – Voluntary based on above : States should apply the precautionary approach widely to conservation, management and exploitation of living aquatic resources in order to protect them and preserve the aquatic environment. The absence of adequate scientific information should not be used as a reason for postponing or failing to take conservation and management measures. Supporting science-based decision-making Multiple sectors Ecosystem Based Management (EBM) EBFM Mining Marine Coastal Parks Development Cumulative impacts allocation Ecosystem Based Fisheries Management (EBFM) Environment Aquaculture Ecological Sustainable Development (ESD) assessment Single Fishery Management WA finfish and invertebrate species  What is stock assessment? “Stock assessments provide fisheries managers with the information that is used in the regulation of a fish stock” https://en.wikipedia.org/wiki/Stock_assessment “Stock assessment involves the use of various statistical and mathematical calculations to make quantitative predictions about the reactions of fish populations to alternative management choices” Hilborn and Walters (1992) – stock assessment textbook  What is a harvest strategy? Formal document including: 1. Objectives: What is to be achieved and why - ecological, + any agreed social, economic 2. Performance indicators and reference points: Measuring and interpreting performance against objectives based on achieving acceptable risk levels. 3. Monitoring and assessment strategy: Data collection and analysis needed to estimate performance indicators. 4. Harvest Decision Rules : Predefined rules for determining appropriate catch levels/other management based on current (or expected future) status to avoid breaching thresholds or limits and assist achieving targets. Objectives: Example: West Coast Demersal Resource Harvest strategy 2021-2025 Sustainability objective for target species To maintain spawning stock biomass of each retained species above BMSY to maintain high productivity and ensure the main factor impacting recruitment is the environment Economic and social benefits, e.g. To provide flexible opportunities to ensure commercial fishers can maintain or enhance their livelihood (economic and social), within the constraints of ecological sustainability and catch share allocations, while having regard for the objectives of other fishing sectors To maintain or improve cultural, recreational and lifestyle benefits for recreational fishing participants within the constraints of ecological sustainability and catch share allocations, while having regard for the objectives of other fishing sectors; And several other objectives … Performance indicators and reference points Overfishing Reference points Btarget and Ftarget = where you want to be, management not required (for sustainability) Overfished Bthreshold and Fthreshold = early warning management may be needed Blimit and Flimit = where you don’t want to be, management required Harvest strategy procedures Harvest decision rules – rebuilding stocks example Resource allocation DPIRD - fisheries risk-based approach Likelihood Levels Consequence Risk = Consequence X Remote Unlikely Possible Likely Levels Likelihood Minor Other risk assessment Moderate approaches exist (e.g. dose-response) High Major Risk-based approach - Consequence Levels Minor – Impacts on population either not detectable against background variability for this population; or if detectable, limited impact on population size and none on dynamics (Biomass > Target) Moderate – Impacts at maximum acceptable level of depletion (Biomass between Threshold and Target) High – Level of depletion unacceptable but still not affecting recruitment levels of stock (Biomass between Limit and Threshold) Major – Level of depletion is already affecting (or likely to affect) future recruitment (Biomass below Limit) Risk-based approach- Likelihood Levels Likelihood of a particular consequence level occurring within a defined time period Remote – The consequence has never been heard of in these circumstances, but it is not impossible within the time frame ( 60 species Inshore (20-250 m) and offshore waters Oceanic waters, off Shark Bay/Carnarvon 2 main ‘indicator species’ pink snapper and goldband snapper L5 Assessment - age-based integrated (statistical catch-at-age model) Catch history Catches since early 1950s Catches began to be reduced since mid 2000s (management) Fine scale (10x10 nm) catch/effort data since late 2000s Model is ‘driven’ by catch Model is ‘fitted’ to cpue and age data CPUE data Standardised CPUE (monthly data) since 1990 Standardised CPUE (daily data) since 2008 Account for fishing efficiency changes Exp vs Obs CPUE in log space (model assumes lognormal distn) Exp vs Obs CPUE in normal space Age data Observed proportions at age (histograms) Estimated proportions at age (model fit to data – red lines) Stock – Max age ~ 30y Few old (> 10 y) fish  Fishing mortality & relative female spawning biomass 2 model scenarios - with and without CPUE Elevated fishing mortality levels with CPUE - low ‘current’ female spawning biomass (near limit) without CPUE - higher ‘current’ female spawning biomass (near threshold) Risk Framework Risk – severe Strong management action taken  Model projections Used model to predict future fishing mortality/biomass based on different catch levels Model including CPUE (more precautionary) Stock increases more rapidly with future catch Current situation – very low catches being taken to allow rapid fishery rebuild + large spawning area closures  Updated age data When catches markedly reduced to facilitate rebuilding, can affect quality of stock monitoring data data rich fisheries can become data limited! Fishery independent surveys implanted to improve monitoring of stock recovery Survey catches – all sizes of fish measured – allowing better estimation of gear selection, re-estimation of biology.  Recent updated GDSF pink snapper assessment Industry supported marked reduction in catches to facilitate rebuilding Evidence that biomass is rebuilding Overall conclusion Stock assessment science fundamental providing sound scientific advice for aquatic resource management Fisheries data – data availability / quality varies markedly (often affect by resourcing constraints) Applying a variety of models for stock assessment (tailored to data) WA approach - risk-based assessments, weight-of-evidence framework. Models used to provide quantitative information on stock status. Stock assessment science requires: Understanding of biology of fish populations Maths!