Different bottom trawl fisheries have a differential impact on the status of the North Sea seafloor habitats

Abstract

Fisheries using bottom trawls are the most widespread source of anthropogenic physical disturbance to seafloor habitats. To mitigate such disturbances, the development of fisheries-, conservation-, and ecosystem-based management strategies requires the assessment of the impact of bottom trawling on the state of benthic biota. We explore a quantitative and mechanistic framework to assess trawling impact. Pressure and impact indicators that provide a continuous pressure–response curve are estimated at a spatial resolution of 1 × 1 min latitude and longitude (∼2 km2) using three methods: L1 estimates the proportion of the community with a life span exceeding the time interval between trawling events; L2 estimates the decrease in median longevity in response to trawling; and population dynamic (PD) estimates the decrease in biomass in response to trawling and the recovery time. Although impact scores are correlated, PD has the best performance over a broad range of trawling intensities. Using the framework in a trawling impact assessment of ten métiers in the North Sea shows that muddy habitats are impacted the most and coarse habitats are impacted the least. Otter trawling for crustaceans has the highest impact, followed by otter trawling for demersal fish and beam trawling for flatfish and flyshooting. Beam trawling for brown shrimps, otter trawling for industrial fish, and dredging for molluscs have the lowest impact. Trawling is highly aggregated in core fishing grounds where the status of the seafloor is low but the catch per unit of effort (CPUE) per unit of impact is high, in contrast to peripheral grounds, where CPUE per unit of impact is low.

Seine fishing on the Dutch and German parts of the Dogger Bank, 2013-2019 : Overview of the economic importance and the ecologic impact of the Belgian, British,Danish, Dutch, French, German and Swedish fleets

“…This theoretical estimate of 10% from Eigaard et al (2016) might be an overestimation for the area swept by the Danish seine, based on the lower empirical estimates (∼1% groundgear path) by Noack et al (2019). However, no empirical studies have been conducted on how the seines affect sea bed and benthic organisms (Rijnsdorp, 2015;Rijnsdorp et al, 2015;Bureau Waardenburg, 2017;Rijnsdorp et al, 2020). As empirical data is lacking, the impact of seine fishery has been assessed relative to other bottom trawl gear by Rijnsdorp and colleagues (Rijnsdorp, 2015;Rijnsdorp et al, 2015;Rijnsdorp et al, 2020).…”

“…In the RBS function the fishing effort is multiplied with a depletion rate (fraction of benthic biomass lost due to mortality). The depletion rate of flyshoot fisheries is taken from (Rijnsdorp et al, 2020)with a depletion rate of Danish seines (0.009) that is lower than that of Scottish seines (0.016). As the depletion rate of Danish seines is estimated based on otter trawl gears we used the depletion rate for SSC for for both SSC and DSN in this study.…”

“…However, no empirical studies have been conducted on how the seines affect sea bed and benthic organisms (Rijnsdorp, 2015;Rijnsdorp et al, 2015;Bureau Waardenburg, 2017;Rijnsdorp et al, 2020). As empirical data is lacking, the impact of seine fishery has been assessed relative to other bottom trawl gear by Rijnsdorp and colleagues (Rijnsdorp, 2015;Rijnsdorp et al, 2015;Rijnsdorp et al, 2020). The trawling intensity is estimated as the average annual swept area ratio (sum of the swept area of the trawling activities over the surface area of the grid cell) of the corresponding grid cell for all or specific bottom trawl metiers in a certain period (Rijnsdorp et al, 2018).…”

Reducing fisheries impacts on the seafloor: A bio-economic evaluation of policy strategies for improving sustainability in the Baltic Sea

“…It is difficult to find areas that not affected by any fishing (e.g., Bolam et al 2017). To gain a broader understanding of the dynamics of the ecosystems, however, more effort in collecting benthos data across different habitat types will be required, including information on various benthic life-history traits, survival and recoverability, in addition to environmental and physical habitat conditions (Rijnsdorp et al 2020). New data will enable the better fitting of different models that account for these effects (Nielsen et al in prep).…”

“…We compared the bio-economic effects along a gradient of restrictions relating to fishing and area closures in different locations, seafloor habitat types, and exclusive economic zones (EEZ). The impact of these spatial measures was quantified by inferring pressure-state relationships with the resulting change in the relative benthic status (RBS) of the seafloor (ICES 2019a, Rijnsdorp et al 2020) as well as the difference in the economic performance of the different fisheries when attempting to improve the state of the seafloor in the Baltic Sea.…”