No abstract

All fish stocks should be managed sustainably, yet for the majority of stocks, data are often limited and different stock assessment methods are required. Two popular and widely used methods are Catch-MSY (CMSY) and Surplus Production Model in Continuous Time (SPiCT). We apply these methods to 17 data-rich stocks and compare the status estimates to the accepted International Council for the Exploration of the Sea (ICES) age-based assessments. Comparison statistics and receiver operator analysis showed that both methods often differed considerably from the ICES assessment, with CMSY showing a tendency to overestimate relative fishing mortality and underestimate relative stock biomass, whilst SPiCT showed the opposite. CMSY assessments were poor when the default depletion prior ranges differed from the ICES assessments, particularly towards the end of the time series, where some stocks showed signs of recovery. SPiCT assessments showed better correlation with the ICES assessment but often failed to correctly estimate the scale of either F/FMSY of B/BMSY, with the indices lacking the contrast to be informative about catchability and either the intrinsic growth rate or carrying capacity. Results highlight the importance of understanding model tendencies relative to data-rich approaches and warrant caution when adopting these models.

Three plankton collection methods were used to gather plankton samples in the Celtic Sea in October 2016. The Plankton Image Analysis (PIA) system is a high-speed color line scan-based imaging instrument, which continuously pumps water, takes images of the passing particles, and identifies the zooplankton organisms present. We compared and evaluated the performance of the PIA against the Continuous Automatic Litter and Plankton Sampler (CALPS) and the traditional ring net vertical haul. The PIA underestimated species abundance compared to the CALPS and ring net and gave an image of the zooplankton community structure that was different from the other two devices. There was, however, good agreement in the spatial distribution of abundances across the three systems. Our study suggests that the image capture and analysis step rather than the sampling method was responsible for the discrepancies noted between the PIA and the other two datasets. The two most important issues appeared to be differences in sub-sampling between the PIA system and the other two devices, and blurring of specimen features due to limited PIA optical depth of field. A particular advantage of the CALPS over more traditional vertical sampling methods is that it can be integrated within existing multidisciplinary surveys at little extra cost without requiring additional survey time. Additionally, PIA performs automatic image acquisition and it does remove the need to collect physical preserved samples for subsequent analysis in the laboratory. With the help of an expert taxonomist the system in its current form can also integrate the sampling and analysis steps, thus increasing the speed, and reducing the costs for zooplankton sampling in near real-time. Although the system shows some limitation we believe that a revised PIA system will have the potential to become an important element of an integrated zooplankton monitoring program.

We compared and evaluated the performance of a Continuous Automatic Litter and Plankton Sampler (CALPS) against the traditional ring net vertical haul. CALPS is a custom-made semi-automatic sampler, which collects water using a pump system at a single depth along a predetermined transect as the ship sails. CALPS underestimated species abundance compared to the ring net by a factor 1.61, but both datasets illustrated a similar species composition, community size structure and good agreement in the spatial distribution of abundance. Our analysis suggests that avoidance of the CALPS is likely to be the main factor responsible for the observed difference in sampling efficiency, but other factors, such as depth, area sampled and zooplankton patchiness, are also likely to play their part. We conclude that whilst the CALPS is not suitable for investigations that require accurate measures of abundance, it is an ideal tool to identify and quantify changes in plankton communities and diversity. A particular advantage over more traditional vertical sampling methods is that it can be integrated within existing multidisciplinary surveys at little extra cost, thus making the CALPS particularly valuable as part of integrated monitoring programmes to underpin policy areas such as the EU Marine Strategy Framework Directive.

No abstract