Fisheries Independent Data

Fisheries independent data are collected independently of the commercial fisheries and can be used to examine stock status. In the Isle of Man, fisheries independent data are collected by both scientists and industry (in collaboration with scientists). There are currently two main fishery independent surveys for king and queen scallops undertaken annually on the Isle of Man. In contrast, fisheries independent data collection methods for static gear fisheries are under development.
Examples of our approaches to fisheries independent data collection and how these data are used include:

Long-term, Coarse-Scale, scallop Survey
Spring surveys of scallops within Isle of Man territorial waters have been undertaken annually since 1992 and take place each spring. Approximately 60 fixed stations are surveyed each year with a ‘standard survey dredge bar’ with four dredges, two King and two Queen dredges interspersed along the bar. At each station the dredges are towed at 2.6 knots for 20 minutes with the direction of the tow dependent on tidal state and current condition. The total biomass of king and queen scallops is recorded by dredge and a subsample of 90 queen scallops and 90 king scallops from each dredge are then weighed and measured (king scallops are also aged). The results from this long-term, coarse-scale survey enable territorial sea trends to be assessed and are suitable for undertaking quantitative stock assessments.

Short-term, Fine-Scale, scallop Survey
In recent years, changes to the way scallop fisheries are managed within Isle of Man territorial waters, which include managing at a finer spatial resolution, have required additional finer resolution survey data to be acquired. In 2019 a new fine scale survey was designed and analysed by Bangor University which is completed on two industry fishing vessels with sampling coordinated by the MFPO. It is a fine resolution survey (survey cells: 1 min (longitude) x 0.5 min (latitude) with each vessel towing a ‘standard survey dredge bar’ with four dredges, two King and two Queen dredges interspersed along the bar and a ‘juvenile survey dredge bar’ of the same design but using Queen dredges with 17 teeth with a smaller mesh. These dredges are designed to enable smaller king and queen scallops to be sampled. Survey cells are sampled randomly within each ground strata (strata were defined predominately by depth) with approximately equal effort to ensure relatively even distribution of survey effort across the entire fished ground. Within each survey cell a 10 minute tow was undertaken at ~ 2.5 knots. This finer-scale survey enables ground specific trends to be more accurately assessed and managed.


Baited Remote Underwater Videos (BRUVs)
In collaboration with UK partners, as part of a Fisheries Industry Science Partnerships (FISP) scheme project, we are developing BRUV systems and methods for providing fisheries independent estimates of abundance for lobster to aid with stock assessment of this data poor fishery. During 2022, the BRUV systems were developed and trialled and have successfully been adapted to run for 24 hour deployments which enable lobster presence and activity to be recorded during a full light and dark cycle. For 2023, the project will focus on increasing the number of deployments and spatial and temporal coverage. Further validation of BRUVs for use as indicators of abundance will also be explored as part of this project using a 360 degree camera system deployed alongside the BRUVs to address some of the key questions on understanding the movement of individual lobsters in and out of the BRUV field of view.

Gear Trials for whelk surveys
In 2022 we collaborated with the Sustainable Fisheries Wales team in Bangor to deploy BRUVs during mark-recapture abundance surveys for whelk. This allowed us to trial the BRUVs as a method for assessing whelk abundance, while comparing results with commercial pot CPUE (catch per unit effort) and population density estimated from mark-recapture. The surveys took place at two commercial fishing sites, where strings of whelk pots were repeatedly fished at the same locations, with 1 BRUV unit added on the end of 5 random strings at each site. A total of 50 BRUV deployments were achieved across the two survey sites, and whelk abundance was assessed for each deployment using still images at 15-minute intervals. In total, 3,000 images were analysed and 35,000 whelks counted, with individual image counts ranging from 0 to 68 whelks. Whelk abundance differed considerably between the two sites, and there was also spatial variation within each site which remained consistent throughout the survey. As well as exploring temporal trends in abundance at each survey site, potential stock indices were calculated for each deployment: maxN (maximum abundance in one image); meanN (average abundance across all images); and T0 (time of first arrival). Preliminary results show a significant relationship between BRUV abundance indices and CPUE from pot strings.