Mrs Nafisat Bolatito IKENWEIWE (PhD) DEPARTMENT OF AQUACULTURE AND FISHERIES MANAGEMENT UNIVERSITY OF AGRICULTURE, ABEOKUTA FISH STOCK ASSESSMENT

FISH STOCK ASSESSMENT FIS 715 (3 UNITS) CORE COURSE

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.

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.

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

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

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

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)

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.

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

Overexploited 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 Depleted: Catches are well below historical levels, irrespective of the amount of fishing effort exerted; Recovering Recovering: Catches are again increasing after having been depleted

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 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: What Can Stock Assessment Tell Us?

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

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

17 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 Indicators of Stock Abundance for Fishery Management Purposes

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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