Fisheries Sciences to Policy

Trawling: Finding common ground on the scientific knowledge regarding best practices

Michel J. Kaiser, Bangor University and IUCN-Fisheries Expert Group

An international collaboration between experts in the field of impacts of fishing on the marine environment has generated new insights into the global footprint of trawling on the seabed. The project  (https://trawlingpractices.wordpress.com/) has five main components: understand the frequency and extent of trawling on the seabed, understand the relationship between trawling pressure and changes in seabed communities, develop a risk assessment methodology to understand the relative status of the seabed communities in trawled areas, understand secondary effects on fish production and finally to recommend possible best practices to mitigate the effects of trawling on the seabed.

The project has compiled vessel monitoring system data from 23 different marine areas confined mainly to North and South America, Europe and Australasia. The data has been analysed to provide insights into the extent and frequency of trawling activity in each area. For some areas of the world (e.g. Australia) the extent of trawling is <5% of the continental shelf, whereas for other areas (e.g. the Skagerrak/Kattegat) the extent of fishing is >50% of the continental shelf. The project has analysed data on the continental shelf and upper slope areas down to 1000m deep. When VMS data is aggregated at coarse spatial scales this gives a misleading over-estimation of fishing footprint. For many areas of the world >50% of the shelf seabed was never fished which far exceeds the amount of seabed suggested for protection from fishing.

Using a systematic review methodology the project has been able to establish the relationship between fishing gear penetration depth and the mortality of seabed animals and plants. This information coupled with the footprint of fishing informed a risk assessment approach to estimate the relative status of seabed communities. This latter part of the project is on-going but will provide insight into the resultant effect of current levels of fishing activity on seabed biota. The project has also established a link between recovery rate and animal longevity. This generic relationship would enable the methodology to be applied to other areas of the seabed such as Vulnerable Marine Ecosystems and Ecologically and Biologically Sensitive Areas in the deep sea and elsewhere.

The approach has considerable promise to provide objective and evidence-based methodologies to understand the best approaches to mitigating the wider ecosystem effects of trawling on the seabed.

Kaiser M.J., Hilborn R., Jennings S., Amaroso R., et al., & Sutherland W.J. (2016) Prioritisation of knowledge needs to achieve best practices for bottom-trawling in relation to seabed habitats. Fish and Fisheries doi:10.1111/faf.12134

Hiddink J.G., Jennings S., Sciberras M., Szostek C.L., Hughes K.M., Ellis N., Rijnsdorp A.D., McConnaughey R.A., Mazor T., Hilborn R., Collie J.S., Pitcher C.R., Amoroso R.O., Parma A.M., Suuronen P. & Kaiser M.J. 2017. Depletion and recovery of seabed biota following bottom trawling disturbance. Proceedings of the National Academy of Sciences.

Pitcher C.R., Ellis N., Jennings S., Hiddink J.G., Mazor T., Kaiser M.J., Kangas, M., McConnaughey R., Parma A.M., Rijnsdorp A.D., Suuronen P., Collie J.S., Amaroso R., Hughes K.M. & Hilborn R. 2016. Estimating the sustainability of towed fishing-gear impacts on seabed habitats: a simple quantitative risk assessment method applicable to data-poor fisheries. Methods in Ecology and Evolution

Mazor T., Pitcher R., Ellis N., Rochester W., Jennings S., Hiddink J.G., McConnaughey R.A., Kaiser M.J., Parma A., Suuronen P., Kangas M. & Hilborn R. in press. Trawl exposure and protection of seabed fauna at large spatial scales. Diversity and Distributions