Evaluating and optimizing stock enhancement of natural flatfish stock

• Main Author: Sparrevohn, C.R.
• Other Authors: Rijnsdorp, Adriaan, Støttrup, J.G.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2008
• Subjects: artificial rearing; fish stocks; fisheries; fisheries ecology; fishery biology; fishery resources; pleuronectiformes; population biology; release; turbot; kunstmatige opfok; populatiebiologie; tarbot; visbestand; visserij; visserij-ecologie; visserijbiologie; visstand; vrijgeven; Turbot
• Online Access: https://research.wur.nl/en/publications/evaluating-and-optimizing-stock-enhancement-of-natural-flatfish-s

The overall objective of this thesis is to evaluate and optimize a stock enhancement program of natural population offlatfish in which artificially reared fish are released in coastal areas using turbot (Psetta maxima) as model. Biologicaland ecological criteria are developed to evaluate the likelihood for success, i.e. increasing the stock size, based onecological knowledge. Special reference is given to processes involved in the regulation of the natural population, suchas density-dependent and density-independent mortality and growth. Field data on the temporal and spatial variation inthe abundance of age-0 turbot is analyzed and implications for stock enhancement are discussed. It is concluded thatthere is a solid theoretical background indicating that stock enhancement through releases of artificially reared juvenileindividuals is a viable option for the turbot stock.Support for the hypothesis that stock enhancement is a viable option is provided by the results of a series offiled experiments conducted under a stock enhancement program in the southern part of Denmark. The focus of theseexperiments was on the growth and mortality of released fish in comparison to wild fish, and the importance of thecharacteristics of the release habitat. The growth of the released fish was similar to, or higher than, that of their wildcounterparts, and the mortality, even though highly variable, was on a comparable level. No indication of replacementof the wild individuals with released ones was found. The importance of the release habitat was investigated byreleasing turbot into three areas that differed in wind exposure. The area with the highest degree of wind-exposure was,as predicted, the area where the highest abundance of wild juvenile turbot was found. The highest growth of releasedindividuals was not found in this area but was found in the one characterized by the lowest degree of wind-exposure, anatypical nursery ground for turbot. The effect of the release habitat on the growth could be related to the quality of ...