Fishing grounds a) for trawlers: m in depth, but mainly m b) For boat seines: shallow waters up to 50 m in depth In the Gulf also purse seines, nets, long-lines and traps exist Species assessed by FL although sporadically: Hake, red mullet and picarel Hake is being caught by trawlers and nets-longlines, Red mullet by trawlers and boat seines Picarel by trawlers and boat seines

Data available 1.Catch data since 1988 (sources: NSSG, FL) 2.Effort data Trawlers fishing days since 1988 Number of boat seines since Sporadic length frequencies by trawlers, boat seines and gill-nets 4.Economic data for trawlers, boat seines and gill-nets

State of stocks since 1988 HAKE Trawlers dataTrawlers and gill-nets data : Overexploited (Fmax= 0.2) Overexploited (Fmax= 0.5) : Overexploited (Fmax= 0.72) 2004: Overexploited (Fmax= 0.42) 2006: Overexploited (Fmax= 0.32) RED MULLET Trawlers and boat seine data : Overexploited (Fmax= 0.48) : Overexploited (Fmax= 0.64) 2004: Overexploited (Fmax= 0.66) PICAREL Trawlers data 2004: Underfished

Management measures: 1998: Mesh change in trawlers codend (28 mm to 40 mm) 2002: Decrease of fishing season for boat seines by 2 months

Management problem Impact o f boat seine on stocks and Posidonia beds. ~ Fishermen do not agree with latter impact and underwater observation has shown the harmless boat seine effect on the Posidonia beds. EC insists that boat seines operate on nursery grounds. However, the juveniles for most of the target species are found during spring and summer, a period which is closed for the boat seines. Potential market effects due to withdrawl of beach seines, with negative effects on both fishermen and market. Trawlers catch younger hake, while boat seines catch younger red mullet than trawlers. The overall fishing effect of the different gears on these stocks is unknown. It should be also noted that the effect on the stocks of the enforcement of square mesh size in trawler codend by 2008 will be further unknown.

Research questions and Management questions The research question is: Can we predict a model for Saronikos fishery based on catch and effort data? How this model can be improved (e.g. Bayesian setting)? The management question is: Study the effect of square mesh size in trawler codend to hake, red mullet and picarel Find alternative measures so that boat seines can remain in fishery without economic losses and harmful effect on resources. Those alternative measures could be the prohibition of vegetated areas from the boat seine fishing grounds. It is expected that the losses of boat seine picarel catches will be compensated by the red mullet catches, which should further increase for boat seines after the implementation of square mesh in trawlers. Examine the possibility of boat seines operation during spring and summer by the use of other gears and how profitable is this activity. If profitable, study whether they can compensate the losses Examine the potential interaction between trawler and boat seine and the implications of changes in gear and fishing patterns on the status of shared resources, and the economics of the two fleets.

Scientific approach to the problem The absence of traditional stock assessments in the area and the uncertainty of the state of stocks after the management measures enforced since 1998 and the change in fishing tactics, while only catch and effort data coming from different sources are available, were the reason for applying the surplus production models. The management measure (increase of mesh size) enforced in the time period was the reason to apply the model in two periods, and CEDA Application As an initial attempt to assess the available fishery data, the CEDA package (see Hoggarth et al., 2006) was applied to the available catch and effort data from the fishery. Many trials were done using different estimates of initial proportion. Since no information exists regarding the virgin biomass and the stock is considered as heavy exploited the 0.15 value of initial population seemed more reasonable to run CEDA for the first data set, while the value of 0.3 had shown better fit to the second data set. Also time lag equal to 0 and 1 were used since juveniles are the main bulk of the catch. The production models such as Fox, Schaefer and Pella Tomlinson as well all the error models were used. For the Pella Tomlinson production model an extra parameter is needed, the shape parameter, z. The z used was 1.5. The results showed by the examination of the residuals (Figs 1-10) that no model fitted well to our data.

Fox log fit Init Prop0,15 Time Lag1 K6,02E+07 q1,10E-05 r5,10E-05 MSY1129,61 Final biomass5,33E+06 R^20,26 FOX Log fit Init Prop0.15 Time lag1 K6.02E+07 q1.1E-05 r5.1E-05 MSY1129,61 Final Biom5.33E+06 R^20.26

FOX Lsq Init Prop0.15 Time lag1 K1.33E+12 q5.95E-11 r9.52E-01 MSY4.65E+11 Final Biom1.59E+12 R^2-1.09

Proposed modelling approach The model will be developed using FLR, concentrating on the hake trawler fishery in the Saronikos Gulf. The modelling will be undertaken in two parts: 1)a bio-economic model looking at the impacts of proposed mesh (selectivity) changes in the trawl fishery; 2)a management strategy simulation of the application of effort management to achieve the World Summit on Sustainable Development (MSY by 2015). VIT length-based VPA modelling performed with alternative hypotheses for M etc., providing potential starting points for the FLR population model