Date

2016-10-10

Author

Akkuş, Gizem

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Economically the most important fish species in Turkey is the Black Sea anchovy (Engraulis encrasicolus). It provides 60% of the total fish catch amongst all Turkish fisheries. However this precious resource has, so far, been exploited recklessly disregarding the consequences. Moreover, the reasons for the dramatic fluctuations in the quantity of anchovy landings over the years are poorly known. A sound management plan targeting maximum sustainable yield therefore necessitates scientifically proven stock assessment. In general, there are two methodological approaches currently used in stock assessment, each with pros and cons. The analytical model, namely eXtended Survivor Analysis (XSA), takes the recruitment compartment into consideration explicitly and requires age structure of the stock being known. On the contrary, holistic production model, entitled A Stock-Production Model Incorporating Covariates (ASPIC), disregards the demographic structure of the stock and does not account for recruitment. The aim of this study is to carry out an assessment with only Turkish data to evaluate the current Black Sea anchovy stock condition. To achieve this goal two different models of ASPIC (1968-2014) and XSA (2005-2014) were used to assess the same stock using two different approaches and examine the conformity of these holistic and analytical models, respectively. These models have been chosen since they are the most widely used in stock assessment and for easy comparison of results from previous studies by ensuring the continuity. ASPIC estimates the carrying capacity (K) of Black Sea anchovy as 1.2 m tons and indicates that there should be 610 k tons (BMSY) of fish present in the sea to achieve the maximum sustainable yield of 244 k tons (MSY) fish from the system with the fishing mortality rate of 0.4 (FMSY) that targeted the MSY. According to the estimated biomass of 399 k tons (B2015) in 2015, there are now 35% less fish present in the sea. Hence, it can be said that the Black Sea anchovy is exposed to low overfishing. On the other hand; in XSA, the fishing mortality rate is calculated as Fcurrent=0.71, yet the stock- recruitment relationship of Black Sea anchovy cannot be established. Therefore; the current status of stock has been estimated from the Patterson’s (1992) precautionary exploitation rate of Etarget=0.4 as a reference point. Accordingly, the current exploitation rate is calculated as Ecurrent=0.5 which is 25% higher than the Etarget. Hence, XSA results also suggest that the Black Sea anchovy is exposed to low overfishing. This result and the other comparable parameters of fishing mortality rates for the two models show the concordance and comparability of holistic (ASPIC) and analytic (XSA) models with respect to each other.

Subject Keywords

Black Sea anchovy, Stock Assessment, Analytical Age Structure Model, XSA, Holistic Production Model, ASPIC

URI

https://hdl.handle.net/11511/95099

Collections

Graduate School of Marine Sciences, Thesis