Data and code for "Altering gillnet soak duration and timing minimizes bycatch and maintains target catch"

AbstractSeabirds are one of the most at-risk avian groups worldwide, and incidental catch in fishing practices is one of the top threats for seabirds globally. Seabirds that forage on fish through surface feeding, pursuit-diving, or plunge-diving are particularly vulnerable to bycatch. Bycatch mitigation solutions are therefore a vital component of global seabird conservation, but owing to the episodic nature of bycatch and its involvement of match-mismatch contingencies, results from existing efforts involving gear additions (e.g., lights, flags, or buoys) are highly varied and, at times, reduce target catch. Altering the time during which gear remains in the water and modifying fishing practices based on the activity patterns of target fish and seabirds is a promising option for bycatch mitigation. We experimentally tested best practices for the soak timing and duration of shallow-set gillnets used in the Atlantic herring (Clupea harengus) bait fishery in Newfoundland and Labrador, Canada. We compared catch, bycatch, and seabird activity among control (ca. 24 h) and short (ca. 12 h) set durations that were left to soak overnight or only during daylight hours. Target catch did not differ between control and short overnight sets but was greatly reduced during short daytime sets. Nearly all bycatch, including all seabird bycatch, occurred during the control sets. Seabirds associated with fishing vessels throughout the day. Since the catch of herring in gillnets occurs at night outside of most coastal seabirds’ foraging period, we recommend that fishers continue to haul their nets early every morning to minimize the time where shallow-set nets are filled with prey during daytime hours, thereby limiting seabird bycatch risk.File DescriptionsMain_herring_fishery_2024 - Herring_sampling.csv - dataset of individual herring morphometricsTrip_ID - unique trip identifier composed of the location and trip numberPort - Fishing location, either Musgrave Harbour (MH) or Bay de Verde (BdV)Net_treatment - one of three experimental treatments for the duration and timing of gillnet soaksSample_herring_FK_cm - the fork length of individual herring in cmSample_herring_wt_g - the weight of individual herring in gMain_herring_fishery_2024 - Metadata - metadata for fishing trips, including trip details, gear information, and weatherTrip_ID - unique trip identifier composed of the location and trip numberPort - Fishing location, either Musgrave Harbour (MH) or Bay de Verde (BdV)Coordinates - Latitude and longitude of net deployment locationsNumber_nets - number of nets deployed per trip (either 1 or 2)Setting_time - Time and date that each net was set per trip; nets are separated with a semicolonPulling_time - Time and date that each net was hauled per trip; nets are separated with a semicolonSoak_duration - one of three experimental treatments for the duration and timing of gillnet soaksTarget_spc - the fish species targeted by fishers and gillnetsWater_depth_m - depth of the water in m from the surface to the ocean floorDepth_surface_fathom - depth of the water in fathoms from the surface to the ocean floorMesh_size - size of the holes in the mesh used for each net in mm and inchesNet_height_fathom - height of the net in fathomsNet_height_m - height of the net in mNet_length_m - length of the net in mNet_area_m2 - total area of the net in m2SST_set - sea surface temperature in degrees Celsius during net settingWind_speed_set - Wind speed in km/h during settingWind_direction_set - cardinal direction of the wind during settingPrevailing_weather_cond_set - description of the weather conditions during settingSST - sea surface temperature in degrees Celsius during net haulingWind_speed - wind speed in km/h during haulingWind_direction - cardinal direction of the wind during haulingPrevailing_weather_cond - description of the weather conditions during haulingNotesMain_herring_fishery_2024 - Bird_catch_BothSites2.csv - catch and bird counts for each net of each haulPort - Fishing location, either Musgrave Harbour (MH) or Bay de Verde (BdV)Trip_ID - ID of each tripNet_group - the ID of each net per tripNet_treatment - one of three experimental treatments for the duration and timing of gillnet soaksTime_setting - time and date nets were setTime_haul - time and date nets were hauledSoak_duration - number of hours nets were deployed in the waterTotal_net_area_m2 - Total area of each net in m2Total_catch_number - number of Atlantic Herring caught in the netTotal_catch_wt_kg - amount of herring caught in the net in kgAvg_herring_FK_cm - average fork length of individual herring from each net in cmAvg_herring_wt_g - average weight of individual herring from each net in gColumns M:P - number of individuals of each specified species incidentally caught in a netColumns Q:AI - Counts of birds and whales observed during setting/hauling eventsCommentsSoakTime.Rmd - R code used for data cleaning, analysis, and figure creation