Do PearlNets reduce fish CPUE? R script for data analysis

• Main Authors: Gildas Glemarec, Lotte Kindt-Larsen, Mollie Elizabeth Brooks, Anne-Mette Kroner
• Format: Software
• Language: unknown
• Published: 2024
• Subjects: Fisheries sciences not elsewhere classified; GLMM model; alternative gear; Bycatch mitigation tools; Acrylic pearls; Cod; Gillnet; Harbour porpoise; Bycatch; CPUE; atlantic cod; Gadus morhua
• Online Access: https://doi.org/10.11583/dtu.25574055.v1; https://figshare.com/articles/software/Do_PearlNets_reduce_fish_CPUE_R_script_for_data_analysis/25574055

The mitigation trials took place onboard a Danish commercial set net vessel during three distinct periods, in November 2022, February 2023, and May-June 2023 in the Western Baltic Sea. All trials were conducted with a standard 3-folds trammel net used in this area to target Atlantic cod and flatfish. We used 18 identical net panels of approximately 60 m in horizontal length, of which 5 net panels were equipped with acrylic pearls on one of the outer net layers, resulting in 13 control and 5 treatment panels. The pearls were small acrylic glass spheres (Ø 8 mm) with a groove (4 mm long and 0.8 mm wide) into which to fit the net thread. Each fishing day during the course of the trial, the fisher set one string of nets consisting of 6 control nets, then 5 pearl nets, and lastly 7 control nets. As a result, control nets and pearl nets were always deployed on the same fishing grounds, at the same time, and soaked in the water for the same duration. The trials were recorded using electronic monitoring (EM). The EM system installed onboard (Black Box Video, Anchorlab, Denmark) consisted of a control unit, associated with a position sensor (GPS), and two waterproof CCTV (closed-circuit television) cameras. The data set is made on haul basis. For each haul the date, number of control-nets, number of pearl-nets, Kg of all fish catches and numbers of cod ( Gadus Morhua ) is registered. The catches of fish (in kg) was noted by the fisher carrying out the trials whereas the numbers of cod caught was registered from video analysis of all net hauls.