Scottish Marine and Freshwater Science Volume 6 Number 1: Loch Linnhe and Firth of Lorn MASTS Case Study Workshop Report
Report on a case study workshop on the Loch Linnhe and Firth of Lorn (LL&FL) system.
DOI: 10.7489/1539-1
The Loch Linnhe System: What do we know about it?
Three invited speakers provided a background to the physical environment (Dr Andy Dale), the aquatic ecosystem (Prof Mike Heath) and the management (Dr Ted Schlicke) of the Loch Linnhe system. These overviews were supplemented by contributed presentations from other attendees. All contributions have been listed on the agenda. A brief overview will follow, and there is a plan to publish a more comprehensive report in the near future.
The Physical Environment
Loch Linnhe has a fjordic nature where sea bed topography (with shallow sills), freshwater input and meteorological forcing drive the circulation. Freshwater inflows are a key control of the dynamics of the Loch Linnhe system through determining surface stratification and controlling deep water renewal. Pulsed releases of freshwater from Upper Loch Linnhe through the Corran Narrows travel along the northern side out of the loch (due to rotation) as a bore. Understanding entrainment and mixing is key to understanding the dynamics of the inflows of coastal water and deep-water renewal. Hydrodynamic models of the area perform reasonably well, although the accurate representation of salinity gradients, exchange at the open boundary, and local topographic steering of winds are important processes which need to be included in the models. Circulation patterns in the Firth of Lorn have been less well studied but freshwater influence is apparent in the upper and central parts of the Firth. Towards the seaward end Atlantic and Irish Sea origin waters become more influential. There are also important oceanographic features such as the Corryvreckan tidal race which leads to pulses of water exchange between the Firth of Lorn and the Sound of Jura.
The Aquatic Ecosystem
Studies have been conducted in the upper parts of the Loch into nutrients and algal production ( Grantham, 1981). More intense ecosystem studies were conducted in the early 1990s. Recent ecosystem research in LL& FL has largely focused on quantifying the potential impact of anthropogenic contributions to the nutrient cycle (from local factories and fish farms). The upper and outer loch can be considered distinct in their biogeography: significant differences have been observed in the nutrient cycles and plankton communities.
Benthic surveys have been limited in spatial extent within Loch Linnhe (focused on Loch Creran), although a survey of the Firth of Lorn has recently been completed. Several species of marine mega-fauna, including porpoise and seals, are often recorded in the Firth of Lorn but become less frequent moving up the loch. There is a Special Area of Conservation ( SAC) on Lismore for seals. Research at SAMS suggests there is a link between state of tide at the Great Race (Corryvreckan) and its use as a foraging site by seabirds and harbour porpoises (Andy Dale, SAMS).
Several ecosystem models have been developed for the area, focusing on representing the nutrient cycle through the loch and the contribution of fish farms and effluent to the nutrient budget ( Ross et al, 1993). More recently, connectivity modelling has been used to assess the potential of sea lice transmission and the impact of additional habitat provision from man-made structures (such as man-made reefs or local wind farm developments).
Uses and Management
The management of LL& FL focuses on supporting local aquaculture developments and regulating the disposal of waste via the system (industrial effluent and waste water). There are also local fisheries management issues, and a number of Marine Protected Areas ( MPAs) have been created in the region. Several legislative directives drive management initiatives in the region, focusing on reducing adverse impacts to the system from human pressures.
In total, there are approximately 20 active salmonid farms in the LL& FL region divided in to 2 disease management areas (or three industry-planned farm management areas). Sea lice ( Lepeophtheirus salmonis) are one of the industry's main parasite challenges. Recently, a large multi-disciplinary project has focused on quantifying potential farm connectivity and sea lice dispersal within the system. Several flooding events have occurred in the upper loch and new methods for flood forecasting have been developed for the region.
A Meta-Data Catalogue for LL& FL
Presentations in the first two sessions of the workshop highlighted that LL& FL is a relatively data-rich region. As datasets are held by a number of different institutions/individuals, a meta-data catalogue of these data would be beneficial. An initial listing was drafted during the workshop (see Table 1 below) although attendees agreed that a more thorough overview should be collected after the meeting.
One particular application of data in LL& FL could be to provide a test-bed of ecosystem function assessment criteria: if ecosystem assessment tools do not work for relatively confined, data-rich ecosystems such as LL& FL, then can they be expected to work in larger regional assessments (such as North Sea scale)? However, LL& FL are clearly not fully self-contained systems and so their status will be linked to that of the wider Irish Sea and West of Scotland. The degree to which the LL& FL systems could be evaluated in isolation requires further discussion.
Initial listing of available data within LL& FL.
| Physical Environment | |
|---|---|
| Bathymetry |
|
| Freshwater Inputs (nutrients/suspended matter) |
|
| Temperature/Salinity |
|
| Atmospheric inputs (hydrodynamic modelling) |
|
| Tides |
|
| Circulation |
|
| Aquatic Ecosystem | |
| Chemistry |
|
| Plankton |
|
| Benthos |
|
| Fish & Shellfish |
|
| Birds |
|
| Mammals | Seal data Sea Mammal Research Unit and SNH (not much in way of cetacean activity although increasing numbers of harbour porpoise have been observed by wildlife tour operators in Firth of Lorn in recent years, David Ainsley pers. comm.) Could be supplemented by data holdings at SMRU and MS Licensing (seal shooting) |
| Uses and Management | |
| Urban input |
|
| Aquaculture |
|
| Human Pressures |
|
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