1. Estimating Seabird Bycatch in Gillnet Fisheries in the Danish Øresund using REM
Authors: Glemarec, G. , Kindt-Larsen, L. , Larsen, F.
Introduction
Gillnet fisheries, although highly selective, are also responsible for the capture of thousands of seabirds each year in Denmark. Reliable data on the subject are scarce, since the fleet consists mostly of unmonitored small-scale vessels (<15 meters). Using remote electronic monitoring (REM), we highlight the areas of high risks of seabird bycatch in the Øresund, the Strait separating Sweden and Denmark - a very important region for numerous migrating avian species. This work is a contribution to the European Union Plan of Action to reduce the impact of fishing on seabirds, and is planned to be extended to the rest of Danish coastal waters.
Methods
Data Collection
REM with at least 2 cameras per vessel, filming the sorting table and the area where the net breaks the water
3 Danish gillnet vessels operating in the Øresund
Data spanning from 2010 to 2018
Data Exploration
Data for each haul includes position, soak time, mesh size, net colour…
Bycatch data consist of species, position of the bycatch, sex, breeding status…
Data Analysis
Effort per vessel, per time of the year and per area
Risk maps
Model highlighting the influence of operational and environmental factor to explain the observed amount of bycatch
Results
1607 days at sea analysed
8485 unique hauls recorded
490 of bird bycatch identified
Among the 490 seabirds captured during the monitored period, ducks (Anatidae) were by far the most represented family (335 individuals, 68% of all catches), with the Eider duck Somateria mollissima alone making up nearly 80% of this amount. Cormorants (Phalacrocoracidae) came second (52 individuals, 11%), while guillemots and razorbills (Alcidae) closed the podium (39 individuals, 8%). Other birds , including 2 gulls (Laridae), 1 loon (Gavidae) and 1 grebe (Podicipedidae) were also captured (4 bycatch, <1%). Additionally, 60 birds (12%) could not be formally identified due to video failure.
Seabird bycatch was higher in fall and winter (83% of all catches), than in spring and summer (17%). The highest bycatch rates were observed in few areas (aka hotspots) in the fall-winter period, where ducks gather at sea in large numbers to feed on mussel banks.
Discussion
Remote Electronic Monitoring of small-scale gillnet vessels in the Øresund ensures the collection of high resolution data. Seabird bycatch would otherwise likely remain unnoticed in this fishery. REM is cost-effective and allows to obtain realistic estimates of bird bycatch in the area. By extrapolating our current findings to the rest of the fleet, we will determine the magnitude of seabird bycatch species-wise in the entire Øresund, and identify the spatial and temporal overlap (hotspots) between gillnet fisheries and seabirds.
Conclusion
This pilot study demonstrate the interest of using REM monitoring to assess the magnitude of seabird bycatch in Danish gillnet fisheries. Specifically, we could:
Assess the magnitude of bycatch of seabirds on a sample of three gillnet vessels operating in the Øresund, using data spanning from 2010 to 2018.
Identify the main factors to explain the observed levels of bird bycatch in gillnets in the Øresund (work in progress).
Smoothed mean fishing effort Fishing effort = net length (km) multiplied by soak time (hour).
Spring/Summer,
Fall / Winter.
The observations were made using remote electronic monitoring and cover the period for 3 gillnet vessels operating in the Øresund.
Raw bycatch rates
Bycatch rate = ratio of observed bird bycatch to fishing effort.
Spring / Summer,
Fall / Winter.
The observations were made using remote electronic monitoring and cover the period for 3 gillnet vessels operating in the Øresund.
Smoothed bycatch rates
Bycatch rate = ratio of observed bird bycatch to fishing effort.
Spring / Summer,
Fall / Winter.
The observations were made using remote electronic monitoring and cover the period for 3 gillnet vessels operating in the Øresund. The smoothing was done using spline interpolation and gives a first estimates of the areas of high/low risks of bird bycatch.