ICES Technical Guidelines Published 26 March 2019

16.3.3.3 Spatial distribution of fishing effort and physical disturbance of benthic habitats by mobile bottom trawl fishing gear using VMS

Current basis of VMS advice

The coupling of VMS (vessel monitoring systems) data with logbook data is currently the most practical and cost-effective way to describe the spatial dynamics of fishing activities. ICES requests VMS and logbook data from ICES Member via an annual data call (ICES Data call for VMS/Log book data 2019). Within the EU, EU Member Countries are obliged to make such data available to end-users to support scientific analysis, as a basis for advice to fisheries management.

The primary data consist of a geographical position every two hours (as a minimum) for all vessels carrying VMS1, combined with logbook information on fishing vessel gear used, catch landed, effort, and vessel size. Due to data confidentiality issues, VMS/logbook data are anonymized and aggregated in a 0.05 × 0.05 degree grid prior to submission to ICES, using the C-square system (see Rees, 2003).

ICES has an agreed VMS/logbook access and use policy for data resulting from this type of data call (ICES, 2014); this policy governs the process of who is given access and what they can do with the data. The ICES Data Centre works closely with the Working Group on Spatial Fisheries Data (WGSFD) to analyse data to estimate spatial distribution of fishing activity and impact on the seabed. In addition, WGSFD also develops new methods and quality check indices that represent fishing intensity and frequency on different spatial scales developed in support of scientific advice.

As some countries do not submit data to ICES, some regions have incomplete data. Information is also lacking on smaller vessels that operate mainly in the coastal, nearshore waters and are not equipped with VMS (< 12 m) or logbooks (< 10 m, < 8 m in the Baltic Sea). For the data that ICES does receive, the ICES Data Centre performs a quality check and further harmonizes the individual countries’ submissions into one data set.

Technical description of fishing effort and physical disturbance of benthic habitats maps

ICES uses VMS data in a number of its advisory products, including the recurrently updated ecosystem overviews and fisheries overviews. These overviews contain the two types of maps explained below.

Spatial distribution of average annual fishing effort

Spatial distribution of average fishing effort maps show the distribution of effort (mW fishing hours) by vessels > 12 m having vessel monitoring systems (VMS). The number of hours fished is provided with the data call. Average fishing speed is either supplied by the submitting the data or estimated from other vessels using similar fishing gears. Fishing effort by vessels < 12 m may be significant, especially in the inshore areas. However, these vessels are not required to have VMS and ICES does not have information on the spatial distribution of their effort. Data on effort by vessels < 12 m are therefore not included.

Average annual surface and subsurface disturbance by mobile bottom-contacting fishing gear, expressed as average swept-area ratios (SAR)

Swept area is calculated as hours fished × average fishing speed × gear width. The gear width, expressed as surface and subsurface bottom contact, is estimated based on relationships between average gear widths and average vessel length or engine power (kW), as stated in Eigaard et al. (2015) and using ICES expert input.

The swept-area ratio is calculated for all 0.05 × 0.05 degree grid cells in the ecoregion and is the sum of the swept area divided by the area of each grid cell. The resultant values indicate the theoretical number of times the entire grid cell area would have been swept if effort were evenly distributed within each cell. The swept-area ratio is calculated separately for surface and subsurface contact.

1 As from 1 January 2012, the system is compulsory for EU vessels exceeding a length of 12 m.

ICES Advice 2019 – https://doi.org/10.17895/ices.advice.4683 1 ICES Technical Guidelines Published 22 March 2019

Surface abrasion is defined as the pressure to seabed surface features. Subsurface abrasion concerns the penetration and/or disturbance of the substrate beneath the seabed surface as the various gear types penetrate the seabed in different ways, causing different levels of physical disturbance.

Mobile bottom-contacting fishing gear groupings are bottom otter trawls, bottom seines, dredges, and beam trawls.

Sources and references

Eigaard, O. R., Bastardie, F., Breen, M., Dinesen, G. E., Hintzen, N. T., Laffargue, P., et al. 2015. Estimating seabed pressure from demersal trawls, seines, and dredges based on gear design and dimensions. ICES Journal of Marine Science, 73(Suppl. 1): 27–43. https://doi.org/10.1093/icesjms/fsv099 ICES. 2014. Conditions for VMS data use: Access and use conditions for Vessel Monitoring System (VMS) data made available through ICES Data calls. June 2014. Available at http://www.ices.dk/marine- data/Documents/VMS_DataAccess_ICES.pdf Rees, T. 2003. “C-squares”, a new spatial indexing system and its applicability to the description of oceanographic datasets. Oceanography, 16(1): 11–19.

Recommended citation: ICES. 2019. Spatial distribution of fishing effort and physical disturbance of benthic habitats by mobile bottom trawl fishing gear using VMS; Technical Guidelines. In Report of the ICES Advisory Committee, 2019. ICES Advice 2019, Section 16.3.3.3, https://doi.org/10.17895/ices.advice.4683

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