Estimating fishing effort and LPUE for the Scottish brown crab (Cancer pagurus) trap fishery using VMS and observer data

Information on fishing effort by vessels fishing with traps in Scotland is limited. The recent availability of VMS data combined with landings information from vessel logbooks provides new opportunities to describe the spatial distribution of effort and catch for data-limited fisheries. This study evaluates the use of VMS data applied to trap fisheries and estimates an indicator of fishing effort for the offshore brown crab fishery in Scotland. VMS data seem to provide a valid basis for calculating effort (time fishing), assuming that fishing can be distinguished from other activities by selecting an appropriate speed range. Comparisons between high and low temporal resolution data show that the standard 2-hour transmission interval of VMS data introduces substantial uncertainty into effort estimates. Assumptions related to the relationship between fishing time and the number of creels fished, and on assigning catch data to VMS positions, were explored. The areas to the north of Scotland are the main target of the offshore brown crab fleet. Landings and effort by offshore crab vessels have generally increased up to 2016-2018 followed by a clear reduction in the last 3-5 years. The brown crab LPUE trend in this study was found to be similar with that obtained from indices based on survey data. Effort and LPUE estimates may be used to identify and inform managers of the main fishing areas for offshore vessels targeting brown crab and can also be applied to fisheries for other data-limited species, provided that VMS or other GPS logger systems are available. The methodology implemented in this study is sensitive to the temporal resolution of the data collection systems. Systems capable of providing higher temporal resolution data would be desirable, to obtain more accurate estimates of fishing effort.