Sustainable exploitation of fisheries resources: impact of ... - Seafdec

Sustainable exploitation offisheries resources:impact of trawl gearAlias Man and Abu Talib AhmadDPPSPM, TerengganuJuly, 2008

INTRODUCTION

Total30000Average of Kepadatan ikan, kg/km²250002000015000T10000500001920 1970 1980 1990WCPMPantai Tempoh

depending on short-term objectives.Nonetheless, this argument does not imply that relationship financing is not profitablefor banks.As in Diamond (1991), monitoring generates valuable informationabout the type of the agent, which has a future value only in the case of relationshipfinancing. But in our model, the behavior of the agent is also affected by the currentbelief of the bank about his type. This change in behavior decreases the incentives tomonitor for the principal and it eventually overcomes the positive effect of informationgeneration. This is the trade-off analyzed in the current paper.This model may also be interpreted as an expert-agent type of game. Under thisinterpretation, monitoring effort is a costly state verification activity. As a matter of example,consider the game played between a spy and an agency 7 . The agency is unsurewhether the spy is a double agent and would like to crosscheck his reports. Nevertheless,if every report is required to be checked, the agent is of no value. Even more, if theagent is known to be a double agent, he is useless and the agency may not have accessto similar agents or sources of information. Thus, double agents tend to survive undercoveredlonger than would seem reasonable. This was the case of Juan Pujol, a Spanishspy working for both UK and Germany. Although, from the point of view of historicalevidence, he had given enough evidence to the Germans that he was a double agent,they maintained their confidence in his reports until the very end 8 .This paper contributes to the literature on reputation in dynamic games of asymmetricinformation. In particular, it contributes to a small but important literature thatshows the limits of reputation as a way to restrain the behavior of patient players. Thefirst paper to identify a shortcoming of the reputation effect is Morris (2001) who presentsa model where an advisor with long-run concerns and no intrinsic bias against any alternativehas an incentive to misreport his information in order to look "good". Thisincentive results in an equilibrium without any useful information provision. In a similarfashion, Ely and Välimäki (2003) study the sequential equilibrium of a dynamic gamewhere the interaction between reputation and the interest of the agent to maintain hisemployment status, leads to no trade in equilibrium. The source of the no-trade theoremis, as opposed to my paper, the fact that the principals are short-lived and there7 Our setup is similar to Sobel (1985) who illustrates his model with this example. The main difference isthat, in his model, there is perfect and exogenous monitoring.8 Indeed, Juan Pujol was key in the cover up of the D-Day. More information about him is to be found inAndrew (2009)5

Objectives: to investigate impact of smallcodend mesh size (22mm) ascompared to 38mm (Fisheries Act,1985) to investigate the length at firstcapture, Lc, for both codends minimum commercial size, length at first maturity, Lm

MATERIALS ANDMETHODS

Four types of trawlers were used to sample fish inthe zone B and C in Selangor and PerakFish and prawn trawlers for the zone B (Perakand Selangor)Fish trawler for the zone C. (Perak and Selangor)Sergestid shrimp trawler in Zone B (Perak).Two different codend mesh sizes, 38mm and22mm.Covered codend mesh (Sparre and Venema,1992).A total of 36 and 48 hauls

Study area

Gear SelectivityRetention, rLogistic curvelinearr = 1/(1+exp(a-bL)Ln (1/r – 1) = a-bLBody length can be used to calculate theselectivity for individual fish species.For this study, maximum girth, G was usedto calculate the selectivity instead of thebody length. G = 2π√0.5(a² + b²)

Perimeter of thecodend meshPerimeter of thefish body, or girthdbdMesh size, MS = 2daPerimeter, P = 4d Girth, G = 2π √ 0.5(a ² + b ²)Perimeter, P = 2 MSIf MS = 38mm, Perimeter, P = 2 X 38 = 76mmFish would be retained by the mesh when G > P

RESULTS

Catchrates:kg/km²

Composition:%

Selectivity:non-elongated fishes

Selectivity:non-elongated fishes

Selectivity:--- 22mm___ 38mm

Selectivity:all species22mm L50=35mm38mm L50=99mm

Commercial size:Commercial fish species1.000.75Commercial0.500.250.000 100 200 300 400Girth, mm

Commercial size:Commercial species1Commercial0.750.50.250praw ns, L50=16cephalopods, L50=62mantis shrimps, L50=85fishes, L50=125crabs, L50=2570 100 200 300 400Girth, mm

Selectivity-Commercial sizeG50W50Selectivity 22mm mesh 34.638mm mesh 98.9Comm. size Prawns 15.6 0.24Cephalopods 61.7 1.32Mantis shrimps 85.5 12.82Fishes 124.9 17.61proportion1.000.750.50Selectivity 22mm meshSelectivity 38mm meshCommercial size Praw nsCommercial size CephalopodsCommercial size Mantis shrimpsCommercial size FishesCommercial size Crabs0.250.000 100 200 300 400Girth, mm

Selectivity-MaturityG50 W50Cephalopods 128.9 7.42Prawns 105.1 16.20Crabs 352.4 65.65Fishes 250.8 97.11proportion1.000.750.50Selectivity 22mm meshSelectivity 38mm meshMaturity CephalopodsMaturity Praw nsMaturity CrabsMaturity Fishes0.250.000 100 200 300 400Girth, mm

Commercial-Maturityproportion1.000.750.50Commercial size Praw nsCommercial size CephalopodsCommercial size Mantis shrimpsCommercial size FishesCommercial size CrabsMaturity CephalopodsMaturity Praw nsMaturity CrabsMaturity Fishes0.250.000 100 200 300 400Girth, mm

Selectivity-Commercial-Maturityproportion1.000.750.50Selectivity 22mm meshSelectivity 38mm meshCommercial size Praw nsCommercial size CephalopodsCommercial size Mantis shrimpsCommercial size FishesCommercial size CrabsMaturity CephalopodsMaturity Praw nsMaturity CrabsMaturity Fishes0.250.000 100 200 300 400Girth, mm

Adult fish population8000001.00700000A b u n d a n c e C e p h a l o p o d sA b u n d a n c e C r a b sAbundance, nos/km²600000500000400000300000200000A b u n d a n c e F i s h e sA b u n d a n c e P r a w n sM a t u r i t y C e p h a l o p o d sM a t u r i t y C r a b sM a t u r i t y F i s h e sM a t u r i t y P r a w n s0.750.500.2510000000 100 200 3000.00Girth, mm

Discussion & ConclusionBy using 38mm mesh, more juvenile fisheswere released, but: catch drop from 20 to 90 %, depending onthe trawl type. catch of fish trawlers in Zone C drop by 20% catch of prawn & fish trawlers in Zone Bdrop by 50 % catch of sergestids shrimp trawl drop by90 %.

Although the fishermen’s incomedrops immediately, the long-termeconomic benefit through improvedfish population can be expected.

At present, majority of the commercial fishcaptured by 22mm codend wereundersized (

The high demand of trash fishespecially for cage culture hasresulted in high exploitation pressureon the smaller fishes, regardlesswhether they are commercial speciesor not.

Increase mesh size need to becompliment with: regulation on minimum commercialsize (MCS) regulation on exploitation andutilisation of trash fish regulation on fish processing thatrely on undersized commercial fishes

also not to forget to: improve access control improve enforcement improve public awareness

Wild fish population (W) supports: aquaculture (A) fish meals (FM) fish cakes (FC) livelihood (L) consumption (C) export (E) ...W = A + FM + FC + L + C + E + ...

W = A + FM + FC + L + C + E + ...Left = RightLeft = RightLeft = RightLeft = Right....at the end, nothing is left