SEAwise Report on changes in the spatiotemporal benthic effects of fishing on benthic habitats relative to suggested reference levels, both with respect to area impacted and impact intensity in response to spatial management

The SEAwise project works to deliver a fully operational tool that will allow fishers, managers, and policy makers to easily apply Ecosystem Based Fisheries Management. This SEAwise report describes assessments of the impact of fishery on the benthic ecosystem using the Relative Benthic State (RBS) indicator for four case study areas (Baltic Sea, North sea, Western Waters, Eastern Mediterranean Sea). The RBS indicator determines the risk of fisheries impacting on the benthic habitat based on the fishery footprint (SAR, metier specific depletion) and the sensitivity of the habitat (longevity composition). First assessments were reported in the previous deliverable of task 4.3 and here updates are added along with expected changes in response to management measures. In the updated model for the Danish EEZ in the Baltic and North Sea, the impact of hypoxia is included in the assessment. The Western waters has developed one integrated model for predicting the sensitivity of the habitats. For the Ionean Sea (Western and Eastern part), an integrated assessment is executed by expanding the models based on different data sources (macrofauna versus epifauna).

The model-based assessment results of benthic impact offer valuable support for evaluating fisheries management measures and their effect on the assessment outcome. The types of fishery management scenarios investigated were: (1) change in fishering effort within the area; (2) spatial restrictions to fishery and/or related effort displacement. The aim is to evaluate benefits to RBS of effort or spatial restriction fishery management scenario and several case study area specific scenarios were tested. Most scenarios focused on spatial restrictions, based on actual, planned or theoretical MPA placement, sometimes combined with decreasing effort (no displacement considered). The MPA scenarios are tested at different scales (entire area, ices subareas, member state EEZ, certain habitats). These spatial scenarios have a very small effect on the mean RBS value in most cases, especially on large scale. The effect strongly depends on the RBS score before implementation of the scenario, and the change of closing areas has least effect in areas with high mean RBS. The effect is different when taking fishery displacement into account, where in some case the RBS of certain habitats even decrease with MPA implementation (poorer status after implementation). In contrast, a theoretical spatial restriction scenario executed in Western waters showed that creating MPAS and relocating fishing effort leads to a strong dichotomy in the distribution of fishing effort and impact. The results show a portion of habitats that are potentially very healthy, and a portion where the accumulation of effort leads to increased and sometimes very pronounced impacts. In general, decreasing the overall fishing effort will slowly increase the overall mean RBS value of a habitat or area. Therefore, a combination of management actions are needed to improve seafloor health, but it is not yet possible to estimate how much effort needs to be reduced or how large an area must be protected to reach a specific status of the seafloor. The Impact of management action is furthermore area, habitat and fisheries history dependent.

The RBS approach is a risk based indicator, and as such estimates the risk of deteriorating the benthic state under a certain fishing pressure rather than the actual impact on habitat quality. Further, no overall threshold has been agreed for when the impact of fishing is negative. In this report, a threshold of 0.8 of the RBS was used but this does not reflect if an RBS below this is really causing adverse impacts on the benthic seafloor and hence is not necessarily reflecting GES or non-GES states. Therefore, the effect of fishery management actions still need to be confirmed by benthic state indicators.

The report provides further updates on methodological developments in assessing the impact of fishery on the benthic community composition and ecological functioning. As part of this work, the generic trait-based method (Beachard et al., 2021) to estimate vulnerability of seabed habitats and their associated benthic communities to fisheries-induced physical disturbance was tested in the North Sea Plaice box. This index estimates the vulnerability of the habitat, based on traits judging the sensitivity and recoverability of the species. The analysis explored the responsiveness over time after the (partial) closure of the plaice box in the North Sea, where the fishery patterns inside and outside changed over time.

In relation to ecosystem functioning, fishery is changing the fauna and species composition, which can change in the functional capacity of the seabed to contribute to ecosystem services. A study explores whether ecosystem functioning can be incorporated more explicitly into the FBIT seafloor assessment methodology, through the ICES FBIT working group. To do so, two steps were considered: (1) determining the relationship between macrofauna and ecosystem functioning (e.g., sediment biogeochemistry) mostly through the use of functional traits and how those traits mediate biogeochemical metrics (oxygen, organic carbon content) and (2) develop a model to predict changes in species composition due to trawling to estimate the change of bioturbation potential of a community.

Read more about the SEAwise project at www.seawisproject.org