Application of the European Regional Seas Ecosystem Model (ERSEM) to assessing the eutrophication status in the OSPAR Maritime Area, with particular reference to nutrient discharges from Scottish salmonid aquaculture

Aquaculture production of salmonids in Scotland has grown over the last 15 years, exceeded 150,000 tonnes in 2001. There have been conflicting views as to the likely ecological impact of nutrient discharges from this activity. Whilst quantitative assessments of aquaculture nutrient discharges have been carried out, the debate regarding possible eutrophication impacts of these discharges has so far been largely speculative. In order to provide a quantitative basis for this discussion, a marine ecosystem model was used to simulate the consequences of a 50% reduction in aquaculture nutrient discharges, and the results are presented here

Modelling the behaviour of nutrients in the coastal waters of Scotland

The overall goal of this project was to provide Scotland with a strategic ecosystem simulation tool for identifying maritime areas which could be at risk of eutrophication. The tool should provide spatially resolved output, and be capable of discriminating between different types and locations of nutrient inputs, so as to enable scenario analyses of different reduction options. The specific aims of the project were firstly to simulate the annual cycles of nutrients and ecological properties of Scottish waters and advise on areas which might suffer from eutrophication, and secondly, to determine the contribution of Scottish nutrient discharges to eutrophication in the OSPAR maritime area as a whole

Modelling the behaviour of nutrients in the coastal waters of Scotland - an update on inputs from Scottish aquaculture and their impact on eutrophication status

A previous study estimated that salmon farming contributed approximately 6% of Scotland's nitrogen-nutrient input to coastal waters, and 13% of phosphorus (based on 2001 production figures). However, in some areas of the west of Scotland with small freshwater catchment areas and low levels of human habitation, aquaculture inputs represented greater than 80% of the total. In 2002, FRS published results from an ecosystem modelling study involving a collaboration with the Institute for Marine Research, University of Hamburg, and the Macaulay Land Use Research Institute in Aberdeen, to assess the eutrophication impact of various nutrient inputs to Scottish waters. The results suggested that a 50% reduction in aquaculture salmon production would have only a small impact on water quality which would be undetectable against the background of natural variability due to climate variations. Estimating aquaculture nutrient discharge is a difficult task. The 2002 study was based on data relating to the consented biomass of fish at farm sites in sea lochs. Since then, new data have become available on the actual harvest of fish at all sites in Scotland. In this report, we re-assess the salmon production in Scotland in 2001 and the consequent nutrient discharge, and repeat the ecosystem model runs to estimate the impact of reduction scenarios on eutrophication status. The new data indicate that the previous study had overestimated salmon production and nutrient discharge by approximately 18% Scotland wide. Production and discharge at Shetland and in the Southern Hebrides had been under-estimated, whilst that in the Minches had been over-estimated. New runs of the ecosystem model show that the original conclusions on eutrophication impact were sound. A scenario of 50% reduction in salmon production produced regional changes in water quality which were less than 25% of the natural variability due to climate. New runs simulating a cessation of aquaculture showed that even this extreme reduction scenario produced changes in water quality that were less than half the natural variability

Disentangling habitat concepts for demersal marine fish management

Fishing and other anthropogenic impacts have led to declines in many fish stocks and modification of the seabed. As a result, efforts to restore marine ecosystems have become increasingly focused on spatially explicit management methods to protect fish and the habitats they require for survival. This has led to a proliferation of investigations trying to map ‘habitats’ vulnerable to anthropogenic impacts and identify fish resource requirements in order to meet conservation and management needs. A wide range of habitat-related concepts, with different uses and understandings of the word ‘habitat’ itself has arisen as a consequence. Inconsistencies in terminology can cause confusion between studies, making it difficult to investigate and understand the ecology of fish and the factors that affect their survival. Ultimately, the inability to discern the relationships between fish and their environment clearly can hinder conservation and management measures for fish populations. This review identifies and addresses the present ambiguity surrounding definitions of ‘habitat’ and habitat-related concepts currently used in spatial management of demersal marine fish populations. The role of spatial and temporal scales is considered, in addition to examples of how to assess fish habitat for conservation and management purposes

Cross-shelf processes north of Scotland in relation to the southerly migration of Western mackerel

A combined acoustic and hydrographic survey was conducted west of Shetland in January 1995. The temperature salinity structure at the shelf edge north of Scotland was characterised by a narrow (30 kill) core of warm, saline water embedded within a broader distribution of Atlantic Water; this would generally mark the area of the shelf-edge current. Current measurements recorded during the period of this survey demonstration that uncharacteristically, the core did not mark the area of maximum transport along the shelf break but lay inshore of it. Hence larger scale processes associated with the north-west European shelf edge are important in determining the intermediate scale physical environment encountered by mackerel during their southerly migration to the spawning areas. Acoustic survey data revealed that a large number of the mackerel schools were located in, or close to, this warm saline core at the shelf edge, the reminder being found further inshore. Mackerel school structure varied dramatically between the large affected by this core and other parts of the survey area. In general, mackerel form large distinct schools in mid-water, and these were seen during the survey in the shelf waters. In the area of the warm core, schools were found deeper, were more diffuse and tended to form elongated thin layers. We present the hypothesis that the change in schooling behaviour reflects whether or not the schools are actively migrating, and that those schools observed in the warm water core were stationary, and those in cooler water were actively migrating

Eddies and a mesoscale deflection of the slope current in the Faroe-Shetland Channel

The mesoscale dynamics of the Scottish side of the Faroe-Shetland Channel have been investigated using synoptic in situ and remote sensing observations. A cold core cyclonic eddy, identified from an AVHRR image, had a diameter of about 50 km and surface current speeds of up to 50 cm s; it appeared to be attached to the 800 m isobath as it moved north-eastward along the edge of the channel at about 8 cm s. Speeds in the slope current were about 50 cm s but increased to 70 cm s where the current was compressed by the eddy. Offshore, over the 1000 m isobath in the cooler water, speeds in the current were slower (ca. 20 cm s). North-west of the Shetlands the offshore edge of the slope current was deflected across the channel for a distance of about 70 km from the shelf edge. The speed of drifters in the slope current increased to over 60 cm s as they moved anti-cyclonically around this deflection. CTD profiles suggest that the movement of the surface waters was mirrored in the deep water of the channel. The deflection carried a very large quantity of North Atlantic Water into the central part of the channel; its cause and ultimate fate are not known, although it is likely to have had a significant impact on the dynamics of the channel

Clarifying the role of inorganic carbon in blue carbon policy and practice

Since the term “blue carbon” was coined by the report of Nellerman et al. (2009) the marine carbon cycle has firmly entered the realm of marine policy alongside its terrestrial neighbour, “green carbon” (Crooks et al., 2018). Many marine policy decisions rely on accurate information concerning the stocks of blue carbon in a region, the annual sequestration rates associated with those stocks and the threats posed to those stocks by human activities, and especially recently by bottom-trawling (e.g., Sala et al., 2021). Hence policy officials are reliant on accurate blue carbon scientific advice. However, at the present moment there is one topic that is contributing confusion to policy-science understanding, and that is the topic of organic vs. inorganic carbon. The aim of this short note is to clarify the differences between these two types of blue carbon and to recommend how they are treated in policy formulation and the provision of scientific advice.PostprintPeer reviewe

Clarifying the role of inorganic carbon in blue carbon policy and practice

Since the term “blue carbon” was coined by the report of Nellerman et al. (2009) the marine carbon cycle has firmly entered the realm of marine policy alongside its terrestrial neighbour, “green carbon” (Crooks et al., 2018). Many marine policy decisions rely on accurate information concerning the stocks of blue carbon in a region, the annual sequestration rates associated with those stocks and the threats posed to those stocks by human activities, and especially recently by bottom-trawling (e.g., Sala et al., 2021). Hence policy officials are reliant on accurate blue carbon scientific advice. However, at the present moment there is one topic that is contributing confusion to policy-science understanding, and that is the topic of organic vs. inorganic carbon. The aim of this short note is to clarify the differences between these two types of blue carbon and to recommend how they are treated in policy formulation and the provision of scientific advice