Presentation on theme: "Pelagic Indicators EU INCO-DEV Knowledge Base for fisheries management (KNOWFISH) Tracey Fairweather & Carl van der Lingen Marine and Coastal Management."— Presentation transcript:
Pelagic Indicators EU INCO-DEV Knowledge Base for fisheries management (KNOWFISH) Tracey Fairweather & Carl van der Lingen Marine and Coastal Management
Why do we want indicators? UNCED (1992) & UN CSD (1994) - Indicators: decision-making in self-regulating system decision-making in self-regulating system convey crucial technical information to non-technical users convey crucial technical information to non-technical users framework for evaluating management framework for evaluating management SA committed to WSSD goal of implementing EAF: quantitative ecosystem indicators & define reference points quantitative ecosystem indicators & define reference points integrate ecological, environmental, social & economic perspectives integrate ecological, environmental, social & economic perspectives Challenges: Selection Selection Reference points Reference points Communicating Communicating Response time Response time
The SA Pelagic Case Study… Fishery overview Catches, products, management… Catches, products, management… Candidate indicators Selected examples Selected examples Conclusions Management implications… Management implications…
Fishery Overview Fish caught using a purse-seine net. Multi-species fishery 3 dominant species >95% of landings Other species: juvenile Cape horse mackerel (maasbanker) juvenile Cape horse mackerel (maasbanker) chub mackerel chub mackerel lantern fish lantern fish light fish light fish anchovy sardine redeye round herring
Catches & Variability Large volume fishery avg. ~ t p.a. avg. ~ t p.a = 4 th consecutive yr landings > t 2004 = 4 th consecutive yr landings > t Sardine catches have steadily increased in the last decade. Fishing predominantly inshore off the west and southwest coasts. Small pelagic species are subject to inherent, large- scale fluctuations in population size. Anchovy Sardine Catch distribution
Products & Socio-Economics Anchovy are reduced to fish oil and meal (70% caught are recruits ~ 6 months). sardine are canned - pet & human consumption, frozen or used for bait (adult fish). Redeye are reduced to fish oil and meal, some are canned. Value of the fishery ~ R1 billion in Fishery employs ~ workers full-time part-time 700 sea-going 7100 factory workers SA’s most transformed fishery.
Research & Management Fishery independent surveys conducted twice a year recruitment strength (May) recruitment strength (May) spawner biomass (Nov) spawner biomass (Nov) Hydro-acoustics used to estimate fish biomass. Multi-species fishery = significant by-catch problems. By-catch problem 1: juvenile anchovy & sardine school together. By-catch problem 2: adult sardine & redeye school together. Commercial catches sampled by inspectors, field station personnel and observers.
Candidate Indicators Mean length of catch Total mortality Exploitation rate Ratio of by-catch Length at 50% maturity Centre of gravity of catches Methods from literature Addressed stakeholder concerns
Length at 50% maturity L50 documented as declining following heavy exploitation and collapse of the sardine resource and increasing during stock recovery. Such plasticity could be caused by a number of factors in combination. Maturity ogives calculated for 5 periods within the time series. annual sardine L 50 & sardine spawner biomass = highly significant positive correlation (R 2 =0. 452, p<0.01, n=49).
L50 Each moving average data series for sardine provided increasingly better fits: 3yr R 2 =0.575 (0.715 polynomial) 3yr R 2 =0.575 (0.715 polynomial) 5yr R 2 =0.729 (0.818 polynomial) 5yr R 2 =0.729 (0.818 polynomial) 7yr R 2 =0.821 (0.870 polynomial) 7yr R 2 =0.821 (0.870 polynomial) Anchovy data collected during annual fisheries independent surveys since Annual anchovy L50 has no correlation (R 2 =0.008) to spawner biomass est. Annual anchovy L50 has no correlation (R 2 =0.008) to spawner biomass est. Shorter-lived species = less maneuverability in age at maturity. Shorter-lived species = less maneuverability in age at maturity. This indicator will be of limited use for monitoring anchovy. But suggested descriptive indicator for sardine.
RxBi Proportion of By-catch estimated separately for each of 3 target fisheries: anchovy, sardine & redeye. R s B A & R R B A will be discussed. R s B A = mainly juvenile sardine. NB management issue. R s B A & ratio of sardine SB to anchovy SB = strong correlation R 2 =0.791 & p<0.01 R R B A = mainly juvenile redeye. Similar pattern to R S B A R R B A & ratio redeye SB to anchovy SB = strong correlation R 2 =0.682 & p<0.01 R s B A & R R B A can be used as descriptive indicators. Sardine by-catch Redeye by-catch
RxBi – Management Implications Flowcharts intro in 1998 for catch categorization (adult TL>16.5cm). Revised in 2003 (adult TL>14cm). Given the annual L50 – only 16% of sardine directed catch (R S B S ) should be considered adult. Given TL cut off – 71% of sardine by-catch (R S B A ) should be considered adult sardine, NOT juvenile. Given the annual L50 – only 12% of R S B R should be considered adult. These results contradict what is known about the fishery.
Exploitation rate = F/Z Sardine Z calculated using von Bertalanffy parameters. Sardine E < 0.4 Sardine E not correlated to biomass. But sardine biomass has increased steadily since Conclude: sardine management successful. Target reference point E*=0.4 F=C/N & is assumed to include discards. Anchovy Z derived from ecosystem model. Anchovy E <0.4 Anchovy E weakly correlated to biomass Anchovy biomass has also increased since E = effective performance indicator for both species.
Centre of gravity To determine changes in the geographical location of catches between years. Centre of gravity = centroid + axes showing extent of CV. A centroid is the weighted mean location (longitude ; latitude) of catches for a year. Centroids of commercial catches of anchovy, sardine by-catch and directed sardine were calculated. The majority of catches are taken close inshore between Saldanha Bay and Gans Bay. The coastline and commercial catch position information was linearised to aid interpretation of this indicator. ECO-UP
Annual Catch ECO-UP
Conclusions… Indicator & what it measures Ecosystem - Biological Info Stakeholder Concern Potential Usefulness L50 – how big sardine are when they mature Large biomass = large L50 Indicates stock collapse Descriptive Indicator PSB A – proportion juv. sardine in anchovy catch Relative recruitment of the two species Catch juv = negative impact on adults Flexibility to deal with fluctuations Max 20% trade-off (sliding sigmoid curve) included in OMP-04 Z & E – prop of fish dying & how heavily fished Fishing at a low exploitation rate. Mgmt has been conservative to rebuild stocks. Impact of F ltd. Impact of F is low biomass
Conclusions… Indicator & what it measures Ecosystem - Biological Info Stakeholder Concern Potential Usefulness Lbar – mean length of catch Monitor fishery Change is size = problem Market implications NB Lbar + L50 Need to manage by-catch Centroids – mean location of catches Extended range = high biomass Expansion or contraction of fish distribution = fishery What does change in distribution mean? Has implications… Population structure = key issue – need to monitor TAB Few indicators were applicable to anchovy for two main reasons: the logistics of data collection and the implications of being a short-lived particularly small pelagic fish.
Can we incorporate KNOWFISH indicators into management ? Determine appropriate suite of indicators for management using refined selection criteria from a rigorous scoring procedure, e.g.: Rochet and Rice 2005: concreteness, theoretical basis, public awareness, cost, measurement, availability of historic data, sensitivity, responsiveness, specificity. Rochet and Rice 2005: concreteness, theoretical basis, public awareness, cost, measurement, availability of historic data, sensitivity, responsiveness, specificity. Degnbol & Jarre 2004: acceptability among stakeholders, observability, relation to fisheries management (traffic light approach). Degnbol & Jarre 2004: acceptability among stakeholders, observability, relation to fisheries management (traffic light approach). Assess if indicators are redundant, consider cost and ease of translation into practical management measures. Where possible, these indicators will be incorporated into Pelagic fisheries management in the coming year.