FISH STOCK ASSESSMENT

1. Mrs Nafisat Bolatito IKENWEIWE (PhD)DEPARTMENT OF AQUACULTURE AND FISHERIES MANAGEMENTUNIVERSITY OF AGRICULTURE, ABEOKUTA FISH STOCK ASSESSMENT titobola2007@yahoo.com, 08033770265

2. FISH STOCK ASSESSMENT FIS 715 (3 UNITS) CORE COURSE

3. Course outline • Biostatistics. • Catch assessment and frame survey. • Estimation of growth parameters. • Sampling commercial catches. • Estimation of maximum sustainable yield. • Multi species/Multi fleet problems.

4. Biostatistics • This a contraction of biology and statistics; sometimes referred to as biometry or biometrics, • It is the application of statistics to a wide range of topics in biology.

5. The science of biostatistics encompasses • the design of biological experiments (especially in medicine and agriculture); • the collection, summarization, and • analysis of data from those experiments; • the interpretation of, and • inference from, the results

6. Background to Fisheries • Fisheries are based on stocks of wild aquatic animals living in their natural environment (Oceans, seas, lakes, rivers, swamps) • The fisheries depend entirely on the state of the fish stocks • Management of fisheries require scientific advice about the state of the fish stocks • Fisheries science is concerned with provision of this advice

7. The role of stock assessment in fisheries management • To provide what is in the resource envelope (How much fish is available, composition, distribution, and population structure) • How much is being harvested using which type of gears • To provide advice on optimum exploitation of a fishery • To predict consequences of various levels of fishing effort on yield and biomass

8. Basic elements of a fishery • The standing stock (biomass) • the input (fishing effort) • the output (fish landed) • the processes that link input and output (the biological processes and fishing operations)

9. The fish stock assessment process • Fish stock assessment aims at describing the link between input and output using models. INPUT PROCESS OUTPUT (observation) (model) (observation) • Biological and technical data on the fisheries are required • These data are obtained by sampling the catches of commercial fisheries and research fishing surveys • Fishery survey data are processed together to provide managers and policy makers with advice on exploitation/utilisation of aquatic resources.

10. Terminologies • Underexploited: Undeveloped or new fishery. Believed to have a significant potential for expansion in total production; • Moderately exploited : Exploited with a low level of fishing effort. Believed to have some limited potential for expansion in total production; • Fully exploited: The fishery is operating at or close to an optimal yield level, with no expected room for further expansion;

11. Overexploited : The fishery is being exploited at above a level which is believed to be sustainable in the long term, with no potential room for further expansion and a higher risk of stock depletion/collapse; • Depleted: Catches are well below historical levels, irrespective of the amount of fishing effort exerted; • Recovering: Catches are again increasing after having been depleted

12. Snapshot of the global situation • Of the 600 marine fish stocks monitored by FAO (2003): • 3% are underexploited • 20% are moderately exploited • 52% are fully exploited • 17% are overexploited • 7% are depleted • 1% are recovering from depletion

13. What Can Stock Assessment Tell Us? • What is in the resource envelope? • how much fish is available, • what is the potential productivity • distribution • population structure • How much is being harvested using which type of gears • To predict consequences of different harvest strategies • To provide advice on policy formulation and management plans for the long-term sustainability of the fishery Source:www.fao.org

14. Basic Elements of a Fishery • The standing stock (biomass) • The input (fishing effort) • The output (catch) • The processes that link input and output • Biological processes • Fishing operations Source:www.fao.org

15. Control Measures and Fishing Capacity Input Standing Stock & Processes Output No. of vessels Vessel size Fishing time Minimum size Meash size Gear type TAC Bag limit Bycatch limit Fishing Capacity Overcapacity vs Over-exploitation Source: FAO (1999), Arrizabalaga et al. (2009)

16. The Role of Stock Assessment in Fishery Management Fishing activity Data collection Stock Assess. Advice (SAG) Regulations Policy Formulation (SAC) Fish stock Source:www.fao.org

17. Indicators of Stock Abundance for Fishery Management Purposes • Landings < 50% of the peak-5 years’ average without a clear cut in effort • Abundance indices < 50% of the initial values (catch rates of commercial or research vessels) • Fishing mortality >natural mortality (length-based methods) • The use of indicators involves a great uncertainty • Such uncertainties can be dealt with by adaptive approaches for management purposes, but using indicators to determine sustainability is much more difficult as it requires a clear Reference Value www.fao.org

18. Further Readings • Halls, A.S., Arthur, R., Bartley, D., Felsing, M., Grainger, R., Hartmann, W., Lamberts, D., Purvis, J., Sultana, P., Thompson, P. Walmsley, S. (2005) Guidelines for Designing Data Collection and Sharing Systems for Co-Managed Fisheries. Part 1: A Practical Guide. FAO Fisheries Technical Paper. 494/1. Part II: Technical Guidelines. FAO Fisheries Technical Paper. 494/2. Rome, FAO. • Ita E. O. and M. Mdaihli (1997). The Current Status Of Fish Stock And Fisheries In Kainji Lake

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