Spatial and temporal variations in seabird bycatch: Incidental bycatch in the Norwegian coastal gillnet-fishery

Abstract

The general decline of seabird populations worldwide raises large concerns. Although multiple factors are interacting to cause the observed trends, increased mortality from incidental bycatch in fisheries has proven to be important for many species. However, the bulk of published knowledge is derived from longline fisheries, whereas bycatch in gillnet fisheries is less studied and even overlooked in some areas. We present seabird bycatch data from a 10-year time-series of fishery data from the large fleet of small-vessels fishing with gillnets along the Norwegian coast—a large area and fishery with no prior estimates of seabird bycatch. In general, we document high rates of incidental bycatch (averaging 0.0023 seabirds/net, or approximately 0.08 seabirds/fishing trip). This results in an estimated annual bycatch between 1580 and 11500 (95% CI) birds in this fishery. There was a surprisingly high percentage (43%) of surface-feeding seabirds in the bycatch, with northern fulmar being the most common species. Among the diving seabirds caught, common guillemot was most numerous. Our findings suggest that coastal gillnet fisheries represent a more general threat to a wider range of seabird populations, as opposed to longline fisheries where surface-feeding seabird species seem to dominate the bycatch. The bycatch estimates for the Norwegian gillnet-fishery varied in time, between areas, and with fishing depth and distance from the coast, but we found no clear trends in relation to the type of gillnets used. The results enabled us to identify important spatio-temporal trends in the seabird bycatch, which can allow for the development and implementation of more specific mitigation measures. While specific time closures might be an efficient option to reduce bycatch for diving seabirds, measures such as gear modification and reduction in release of wastewater during fishing operation are probably a more effective mitigation approach for reducing bycatch of surface-feeding seabirds.

Using GIS and stakeholder involvement to innovate marine mammal bycatch risk assessment in data-limited fisheries

“…Still, variation in the final weighted average of exposure criteria scores highlight how much risk estimates posed by one gear can vary over space and time (e.g., 1.71 to 2.81 range of exposure scores for nets within SBTI). Spatial planners and managers can benefit from this insight by mapping fishing gears and at-risk marine species [ 46 , 65 , 91 ] and then applying ByRA to identify bycatch hotspots where mitigation is needed to reduce bycatch risk.…”

“…Species risk assessment is one approach to support sustainable resource use and conservation by evaluating the risk-reduction potential of different fisheries management options in marine fish stocks, habitats, and ecosystems [ 41 – 43 ]. With a similar goal in mind, geographers and spatial ecologists have developed tools to map and measure the probability of exposure, and resulting vulnerabilities to marine species, from offshore wind farm impacts and vessel noise to fisheries bycatch [ 44 – 46 ]. Studies that use GIS to evaluate risk of these incidental interactions can help address the marine mammal bycatch problem because they present frameworks for the analysis of biodiversity and its susceptibility to one or more threats.…”

Applying global best practices for estimating unreported catches in Norwegian fisheries under a discard ban

“…Use of the fisheries and stock tables (Gullestad et al 2017) should help to prioritise studies depending on their demand for estimates of unreported catches. Various studies have estimated unreported catches in Norway for commercial species as both target species (Aanes et al 2011) and bycatch (Breivik et al 2017), as well as incidental catches of species with high conservation importance (Bjørge et al 2013;Fangel et al 2015;Baerum et al 2019). They have utilised a wide variety of data sources and estimation procedures to extrapolate directly from sampled catches or infer from indirect sources.…”

“…Similarly, inspections by the Norwegian Coast Guard or passive observations by the MSS are done by independent observers and could therefore offer a suitable comparison. Nevertheless, qualitative evidence of reliability is available through multiple studies estimating the bycatch of species of high conservation importance, namely seabirds (Fangel et al 2015;Baerum et al 2019) and porpoises (Bjørge et al 2013) in coastal gillnet fisheries. Reporting of seabirds and sea mammals by the Norwegian Reference Fleet is notably higher than through official reporting channels, indicating a greater willingness to record sensitive data for scientific purposes.…”

Bycatch in local fishery disrupts natural reestablishment of Eurasian otter in western Norway

“…Stricter fisheries regulations would also reduce unwanted bycatch of local and migratory seabird species in western Norway. Northern fulmars (Fulmarus glacialis) and black guillemot (Cepphus grylleaso) often fall victim to commercial gillnetting operations in Norway (Baerum et al, 2019;Fangel et al, 2015). Incidences of cormorants (Phalacrocorax spp.)…”