Abstract
The aim of the two EMFF projects “Danish brown shrimp fishery in the North Sea” and “Bycatch reduction in the North Sea brown shrimp beam trawl fishery” was to improve the basis for evaluating the self-management of the brown shrimp fishery and to contribute to a sustainable fishery on the resource. This report focuses on three main topics from these two projects, the review of the biology of brown shrimp (Crangon crangon), tests of improved selectivity in fishing gear, and monitoring and surveys, the latter mainly relating to the trilateral self-sampling program for estimating the unwanted bycatch of TAC species, for the evaluation of the de minimis exemption from the landing obligation. Below is a short summary of each of these three main topics.
Biology and population matters of brown shrimp - “Danish brown shrimp fishery in the North Sea”
A review of the biology and population conditions of the brown shrimp up to 2020 has identified insufficient information on several basic life history parameters and biological conditions, which are listed below and should be investigated further.
Discrepancies in growth estimation methods and parameter values. Variation in growth potential where inverse trade-off with survival has not been considered. Reproduction, where it is not clear how growth and egg production as well as hatching of larvae and moulting are related. Larval development and mortality, where an internal consistent approach to the mechanisms is often lacking. Lack of estimates of natural mortality in juvenile and adult brown shrimp, as well as arbitrary non-linear scaling from larva to adults. In addition, unexplained biological conditions include a lack of knowledge about population structure, distribution and migration. Finally, adequate studies on growth or age related structures are missing.
Laboratory studies to investigate the effects of discard, performed within the project, demonstrated no difference in survival between injured and non-injured individuals. Furthermore, size-related cannibalism was demonstrated. Tests of video-based monitoring under natural conditions were also conducted but found to have limited quantitative potential.
Monitoring and surveys - both projects.
An in-depth analysis of data from the Danish bycatch monitoring of the brown shrimp fishery under the DCF was performed within the project “Danish brown shrimp fishery in the North Sea” to support development of a self-sampling program to estimate the bycatch of TAC species used in evaluating the de minimis exemption from the landing obligation.
The self-sampling program was executed as a trilateral collaboration between Denmark, Germany and the Netherlands under the project “Bycatch reduction in the North Sea brown shrimp beam trawl fishery” where a report for the Scheveningen Group documented that bycatches were within the limits set and a three-year extension of the exemption was granted.
A mesh size experiment comparing a 16mm cod-end to a 26 mm cod-end was completed but showed no statistically significant difference.
Development of selective fishing gears - “Bycatch reduction in the North Sea brown shrimp beam trawl fishery”
DTU Aqua carried out a series of sea-trials to reduce bycatch in the North Sea brown shrimp fishery. First, it was analysed how shrimp and juvenile fish are distributed within different sections of the beam trawl. Results showed that roundfish (like herring and sprat) tended to concentrate in the upper parts of the trawl, while flatfish and shrimp were mostly in the lower parts. Based on these findings, three escape-panel designs were tested to allow unwanted fish to exit the trawl while retaining shrimp. All panels reduced bycatch effectively, with one full-width top panel performing best.
Additionally, experiments adjusting footrope height revealed a mid-level setting optimised bycatch reduction without significantly reducing shrimp catch.
Finally, testing different mesh sizes in the rock-hopper section showed that smaller meshes improved bycatch reduction while maintaining shrimp retention.
Overall, the study demonstrated that targeted gear modifications and coordinated monitoring efforts can significantly improve selectivity and support the sustainable management of the brown shrimp fishery.
Overall achievements for both projects
(1) compiled and structured available information on the biology and ecological role of brown shrimp for use in fisheries management;
(2) designed and implemented an optimized monitoring and surveillance framework to support stock assessment and management decisions; and
(3) developed and tested selective fishing gear to reduce bycatch while maintaining shrimp catch efficiency.
Biology and population matters of brown shrimp - “Danish brown shrimp fishery in the North Sea”
A review of the biology and population conditions of the brown shrimp up to 2020 has identified insufficient information on several basic life history parameters and biological conditions, which are listed below and should be investigated further.
Discrepancies in growth estimation methods and parameter values. Variation in growth potential where inverse trade-off with survival has not been considered. Reproduction, where it is not clear how growth and egg production as well as hatching of larvae and moulting are related. Larval development and mortality, where an internal consistent approach to the mechanisms is often lacking. Lack of estimates of natural mortality in juvenile and adult brown shrimp, as well as arbitrary non-linear scaling from larva to adults. In addition, unexplained biological conditions include a lack of knowledge about population structure, distribution and migration. Finally, adequate studies on growth or age related structures are missing.
Laboratory studies to investigate the effects of discard, performed within the project, demonstrated no difference in survival between injured and non-injured individuals. Furthermore, size-related cannibalism was demonstrated. Tests of video-based monitoring under natural conditions were also conducted but found to have limited quantitative potential.
Monitoring and surveys - both projects.
An in-depth analysis of data from the Danish bycatch monitoring of the brown shrimp fishery under the DCF was performed within the project “Danish brown shrimp fishery in the North Sea” to support development of a self-sampling program to estimate the bycatch of TAC species used in evaluating the de minimis exemption from the landing obligation.
The self-sampling program was executed as a trilateral collaboration between Denmark, Germany and the Netherlands under the project “Bycatch reduction in the North Sea brown shrimp beam trawl fishery” where a report for the Scheveningen Group documented that bycatches were within the limits set and a three-year extension of the exemption was granted.
A mesh size experiment comparing a 16mm cod-end to a 26 mm cod-end was completed but showed no statistically significant difference.
Development of selective fishing gears - “Bycatch reduction in the North Sea brown shrimp beam trawl fishery”
DTU Aqua carried out a series of sea-trials to reduce bycatch in the North Sea brown shrimp fishery. First, it was analysed how shrimp and juvenile fish are distributed within different sections of the beam trawl. Results showed that roundfish (like herring and sprat) tended to concentrate in the upper parts of the trawl, while flatfish and shrimp were mostly in the lower parts. Based on these findings, three escape-panel designs were tested to allow unwanted fish to exit the trawl while retaining shrimp. All panels reduced bycatch effectively, with one full-width top panel performing best.
Additionally, experiments adjusting footrope height revealed a mid-level setting optimised bycatch reduction without significantly reducing shrimp catch.
Finally, testing different mesh sizes in the rock-hopper section showed that smaller meshes improved bycatch reduction while maintaining shrimp retention.
Overall, the study demonstrated that targeted gear modifications and coordinated monitoring efforts can significantly improve selectivity and support the sustainable management of the brown shrimp fishery.
Overall achievements for both projects
(1) compiled and structured available information on the biology and ecological role of brown shrimp for use in fisheries management;
(2) designed and implemented an optimized monitoring and surveillance framework to support stock assessment and management decisions; and
(3) developed and tested selective fishing gear to reduce bycatch while maintaining shrimp catch efficiency.
| Original language | English |
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| Place of Publication | Kgs. Lyngby, Denmark |
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| Publisher | DTU Aqua |
| Number of pages | 100 |
| ISBN (Electronic) | 978-87-7481-434-4 |
| DOIs | |
| Publication status | Published - 2025 |
| Series | DTU Aqua-rapport |
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| Number | 490-2025 |
| ISSN | 1395-8216 |