PhD Quantifying the environmental impacts of bottom trawling for Nephrops

This multidisciplinary PhD is based at Heriot-Watt University in Edinburgh (Prof Michel Kaiser and five other colleagues) in collaboration with University of Essex (Dr Anna Sturrock). The PhD is structured around four key questions:

1. What is the environmental footprint of the Nephrops fishery on benthic habitats and biota?

The Nephrops fishery uses otter trawls, which have the lowest impact of all towed bottom fishing gear (Hiddink et al. 2017). Nevertheless, the habitat-specific nature of Nephrops means that some grounds are still fished at high intensities (Hinz et al. 2009). The impact of trawling on sedimentary habitats is well understood, allowing computation of the relative benthic status (RBS) of seafloor environments subjected to different levels of fishing intensity. The student will use publicly available vessel monitoring system (VMS) and automatic identification system (AIS) data to compute fishing intensity footprints within and among years across a 10-year period to highlight consistent hotspots of fishing activity. The student will further estimate the seabed RBS in defined Nephrops fishing grounds and evaluate the economic returns across the gradient of fishing intensity. Finally, using a ratio of Nephrops catch to environmental disturbance, the student will develop a novel ‘environmental efficiency score’ for resulting food production.

2. What are the ‘risks’ associated with fishery encounters with protected features and species?

Nephrops live in mud and sand habitats that are associated with protected species (e.g., quahogs) and sensitive habitat features, and likewise represent important carbon stores. The student will evaluate risks of bottom trawl fisheries encountering and damaging protected species and habitats by mapping fishing activity onto known Nephrops distributions, developing valuable skills in GIS and data visualisation. The student will also develop a risk index to identify areas that may require additional management intervention, such as the use of less impacting gear (e.g., semi-pelagic otter doors) or the use of area closures.

3. Does by-catch vary across space and through time?

By-catch is a large concern in Nephrops fisheries. The student will evaluate existing observer data to evaluate spatio-temporal trends in by-catch. The Scottish Whitefish Producers Association (SWFPA) has its own observer programme, which submits data to the Marine Directorate. Working with the SWFPA will give the student access to a unique dataset collected over more than a decade to evaluate trends in by-catch composition and abundance in relation to fishing effort, season and habitat type. Geostatistics and AI analytics will be used to discover and model multivariate patterns in this spatio-temporal data. This information will inform management policies that might avoid ‘by-catch hotspots’ (e.g., seasons or locations with problematic levels of by-catch) and catches of endangered species such as flapper skate.

4. Can stable isotope signatures offer insights into the trophic status of Nephrops or detect ‘cultivation effects’?

It is unknown whether by-catch and incidental mortality of other species provides ‘food pulses’ to the seabed below, thereby increasing the productivity of the Nephrops fishery. This ‘cultivation effect’ is unproven; however, we do know that Nephrops are opportunistic predators and scavengers that often feed on bait in creel fisheries. But, Nephrops also feed on suspended particulate organic matter and microbial communities lining their sediment burrows, which can create distinctive isotopic fingerprints in their body tissues. The student will analyse bulk stable isotopic signatures in soft tissues (hepatopancreas and muscle) of Nephrops collected from North and Irish Sea fisheries across seasons and years to investigate whether carbon, nitrogen and sulphur isotopic signatures co-vary with the spatio-temporal patterns in by-catch identified in Question 3.

The research will feed into a Fishery Improvement Project and will expose the student to a wide network of industry stakeholders and fishery managers. The PhD is funded by the Marine Alliance for Science and Technology Scotland (MASTS), Fishmonger’s Company, Whitby Seafoods, Scottish Whitefish Producers Organisation, MarFishEco Ltd., and NatureScot.

References

• Hiddink, J. G., Jennings, S., Sciberras, M., Szostek, C. L., Hughes, K. M., Ellis, N., ... & Kaiser, M. J. (2017). Global analysis of depletion and recovery of seabed biota after bottom trawling disturbance. Proceedings of the National Academy of Sciences, 114(31), 8301-8306.
• Hinz, H., Prieto, V., & Kaiser, M. J. (2009). Trawl disturbance on benthic communities: chronic effects and experimental predictions. Ecological Applications, 19(3), 761-773.