Evaluation and implementation of discards policies under catch-based fisheries management regimes

Nekane Alzorriz Gamiz

Research output: Thesisinternal PhD, WU


This thesis brings a contribution to the debate, formally recognising fishers as an integral part of the ecosystem, by investigating the implications of applying a policy of limiting discards at sea in complex mixed fisheries that are managed under catch limits for the well-being of both the ecosystem and humans.

Discard restrictions and discard management regimes have been implemented to different extents in a number of fisheries around the world (e.g., Chile, Norway, Faroe Islands, Iceland, New Zealand, Namibia, Canada, and the US). The implementation, monitoring and control of the landing obligation generates some new challenges. In particular, the focus of monitoring and control shifts from landing to activities at sea leading to potentially higher costs of enforcement as it might require, for successful implementation, full observer coverage or electronic video monitoring to validate a self-reporting system. In chapter 2, experiences from fisheries around the world show that choosing the right measures is not a simple process and therefore, management authorities need to simultaneously implement complementary measures which will support implementation and encourage compliance with discarding rules.

The need to adapt the regulatory framework does not just concern enforcement systems. Other measures, including adaptations to the technical measure’s framework, also need to be considered. Improved selectivity of fishing gears remains a primary and important tool to avoid discards. In chapter 3 I studied the selective properties of a bottom trawl fitted with a 70 mm diamond mesh codend and a 100 mm top square mesh panel (SMP) in the commercial Basque bottom otter trawlers in the Bay of Biscay. Results suggested that a 100 mm SMP potentially enable undersized and immature individuals to escape through the meshes. However, the selectivity cruises demonstrated that in practice, the SMP was largely ineffective at releasing undersized and the release potential for the diamond mesh codend was found to be significantly lower than the length-at-maturity and the legal minimum conservation reference size for hake, pouting and red mullet. The introduction of the obligation to land all catches will create new challenges for this trawl fleet and thereby an incentive to improve selectivity to avoid unwanted catches of undersized individuals.

Moving to using more selective gears (bigger mesh size codend) may provide a partial solution to mitigate the potential impact of the landing obligation. However, such a measure may also lead to losses in marketable catch and reductions in revenue that make the fishery unviable in the short-term and perhaps in the long-term. Hence, dynamic state variable models allow studying how fishers may respond to changing policies and what consequences this adaptive response may have for the economic and social performance of the fishery. The model results suggested that these negative short-term impacts could be alleviated by incorporation of inter-species quota flexibility in the implementation of the landing obligation. The results indicate that there will be a strong incentive to use this policy arrangement to alleviate the choke effect problem where species with limiting quotas constrain the fishery. To study the possible consequences on a longer time horizon, an MSE approach can be applied to evaluate the long-term consequences of the changes in exploitation pattern on the productivity of the exploited stocks. Combining the main CFP objectives: exploiting at MSY and no discarding allowance, the

MSE showed that quota species brought risk of changing exploitation patterns also for non-quota stocks. Fishing effort was constrained by one or two quota stocks, resulting in drastic reductions of effort over the short-term and mid-term.

Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
  • Rijnsdorp, Adriaan, Promotor
  • Poos, Jan Jaap, Co-promotor
  • Mosqueira, I., Co-promotor, External person
Award date4 Dec 2019
Place of PublicationWageningen
Print ISBNs9789463806206, 9789463952163
Publication statusPublished - 2019


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