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Pelagic Indicators EU INCO-DEV Knowledge Base for fisheries management (KNOWFISH) Tracey Fairweather & Carl van der Lingen Marine and Coastal Management.

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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:

1 Pelagic Indicators EU INCO-DEV Knowledge Base for fisheries management (KNOWFISH) Tracey Fairweather & Carl van der Lingen Marine and Coastal Management

2 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

3 The SA Pelagic Case Study…  Fishery overview Catches, products, management… Catches, products, management…  Candidate indicators Selected examples Selected examples  Conclusions Management implications… Management implications…

4 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

5 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

6 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.

7 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.

8 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

9 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).

10 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.

11 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

12 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.

13 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.

14 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

15 Annual Catch ECO-UP

16 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

17 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.

18 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.

19 Thank you


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