Original publication: July 2014
Author: Michel J. KAISER
Short link to this post: http://bit.ly/2uRkx0a

Background

Inshore fisheries comprise the majority of vessels in terms of numbers across Europe. As a result they have an important socio-economic function particularly in rural economies. The range of fishing gears used by the inshore sector (small scale coastal fleets) is diverse and makes spatial management complex, particularly when fishers pursue the same species, or different species in the same area of the sea or seabed. This intense competition among different sectors, combined with the pressure of other users (e.g. windfarms) can lead to direct conflict resulting in damage to the fishing gear of one sector or another. Damaged, lost or otherwise discarded fishing gear can continue to fish to over one year, however the probability of lost gear continuing to ghost fish is idiosyncratic and highly dependent upon the circumstances. Pot and trap gear have the potential to ghost fish for the longest periods of time. Fishing gear zoning regimes have proved effective at minimising conflict among different sectors in a number of different circumstances. However, such arrangements are not common. These management systems are most vulnerable to violation by itinerant fishers from distant ports.

 

The natural environmental context of a location shapes the seabed and determines the organisms that can exist in that habitat. The intensity, frequency and extent of natural disturbance determine the degree to which a habitat and its associated species are likely to be affected by additional disturbance from fishing activities. In some circumstances fishing disturbance may have minimal effect compared to natural disturbance. In other circumstances fishing may cause long-lasting or irreversible changes. Understanding the distribution of habitats and their extent, and the overlying physical processes, provides the basis to evaluate the potential effects of fishing disturbance. Such an understanding enables the formulation of effective spatial management policies.

All fishing gears have the potential to affect or result in change to marine habitats and communities. Towed mobile bottom fishing gears have the largest environmental footprint, but often are used in areas that are resilient to fishing disturbance. Static fishing gears have a small environmental footprint, but when fished in areas of high species diversity and topographic relief they have the potential to have local impacts on those assemblages. Static fishing gears are more likely to ghost fish when lost or discarded and are associated with a wider range of negative interactions with endangered, threatened and protected species such as turtles and cetaceans. All fishing gears have the potential to be modified to improve their environmental performance to reduce bycatches of all species while maintaining catches of target species.

The effects of towed mobile fishing gear on seabed communities are well understood as a result of 25 years of research. Our ability to understand the effects of these fishing gears relies heavily upon a good understanding of the distribution, frequency and intensity and identity of these fishing activities, coupled with a detailed understanding of habitat distribution and overlying environmental parameters. It is possible to rank towed mobile bottom fishing gear based on their initial impacts which would indicate that scallop dredges and hydraulic dredges have the most negative instantaneous effects while otter trawls are the least damaging of these fishing gears. The development of policies that maintain fishing activities in currently productive fishing grounds would minimise negative environmental impacts on the seabed. The implementation of areas closed to fishing can result in a net negative outcome for seabed habitats and the associated animal communities.

The effects of static fishing gear on the seabed are poorly understood compared to the effects of towed mobile fishing gear. The majority of studies have focused on the effects of pots or traps. Studies to date indicate that these fishing gears have limited or no effects on seabed biota, however there remains the potential for cumulative effects if fishing activity was intense and coincided with habitats that are sensitive to disturbance. A single study outside Europe suggests that gill nets can have very localised effects on seabed biota. The effects of ghost fishing and issues related to the entanglement of endangered, threatened and protected species would appear to be a more serious issue in relation to static gears.

Depending on the environmental context, seabed habitats and their associated fauna can take from 100 days to >12 years to recover. It is important to understand the distribution of those habitats most sensitive and vulnerable to bottom fishing activities such that these may be protected appropriately. There exist many areas of the seabed that are highly resilient to the effects of fishing due to the environmental context in which they occur. Some areas of the seabed and their associated biology are so sensitive that they should be fished rarely if ever depending on the intended gear type proposed for use in those areas.

A number of recommendations are made for consideration by policy makers that encompass a wide range of issues from further research to fill knowledge gaps, innovation and incentives to adopt gear technology to mitigate environmental impacts, to investment in communication technologies among fishers and new experimental approaches to management.

Aim

The aim of the present study was to undertake an in-depth analysis and revision of the literature and scientific evidence of impacts, direct and long term, that different mobile gear like otter trawl, beam trawl, mussel and scallop rakes and clam dredgers have on the bottom ecosystem. It will also analyse what the main differences with the damage made by static gear to catch similar species are.

The note reviews the types of conflict in fisheries shared by mobile and static gear and how both systems perform in terms of selectivity and performance across Europe. The suitability of the different gears to be species-specific and to be size-selective is considered.

The note examines the political choices for the resolution of the conflict between static and mobile gear and makes substantiated recommendations for the management and conservation of the coastal waters in Europe and the steps that should be taken at European level.

Link to the full study: http://bit.ly/529-070

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