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[obanographers]

Is Fish Farming Suitable in Loch Etive?

Loch Etive, in Argyll and Bute Scotland, is a 30km sea loch with a maximum depth of 150m. Non-commercial fishing is common within the loch and there are several small scale fish farms which are currently in operation.

Fancy Words:

Sill: Sea flow barrier that restricts water flowing into an area.

Hypoxia: Deficiency of oxygen reaching the tissue.

BOD: Biochemical Oxygen Demand.

Are the physical, oceanographic features suitable for fish farming?

The short answer is yes. The loch system does provide a suitable area for fish breeding. When water is renewed, plenty of nutrients and oxygen are inputted into the loch for the local marine ecosystem. The waters in the loch are calm with little run off, this suggests that nutrients brought into the loch are likely to stay there. In addition, if run off from the loch is low, water renewal is more likely to occur (A Edwards et al., 1977).

In addition, there are fast currents described at the sill of the loch as well as by the coastline which would suggest that favourable fish farm locations would be away from these more turbulent conditions.

Are there any possible issues?

The main issue arises from a process known as hypoxia. Loch Etive has an incredibly long renewal time. This suggests that there is a possibility for the water within the loch to reach hypoxic conditions. (PA Gillibrand et al., 2007) states that lochs with the longest renewal times are at the greatest risks from reaching hypoxic conditions.

Why does this cause Hypoxia?

During water renewal, sea water contains fresh, oxygenated water which replaces the old, stagnant water in the loch. If the water is not renewed at a fast enough rate, the conditions become hypoxic for the marine organisms as oxygen is no longer readily available for respiration by the organisms.

Issues with Hypoxia theory

It is said that this model is an over-prediction. (PA Gillibrand et al., 1997) explains how lochs are just considered as rectangles which increases the uncertainty within the model. The over simplification of the model is described as causing an over prediction in hypoxic conditions. Large scale Salmon farming in some predicted hypoxic lochs occurs without hypoxic conditions ever being reached. In addition, it is stated that only 2 of the lochs out of 135 in the study may possibly reach hypoxic conditions, Loch Etive not being one of them (See Figure 7, Loch Etive is not in the highest percentage).

 Final Thoughts

There is no concrete evidence which suggests that conditions at Loch Etive have reached hypoxic conditions. The only issues that are currently present with fish farms in the loch are pollution caused by fish feed and faeces. Some of the fish farms that have been recently checked for pollution levels have been reported as dealing with the pollution in an unsatisfactory manner. As long as fish farming is approached in a sustainable way that does not pollute the water, the oceanographic features of Loch Etive should favour small scale, sustainable fish farming.

 References:

 1 A Edwards, DJ Edelsten, 1977, Deep water renewal of Loch Etive: a three basin Scottish fjord - Estuarine and Coastal Marine Science

2 PA Gillibrand, WR Turrell, 1997, The use of simple models in the regulation of the impact of fish farms on water quality in Scottish Aquaculture Elsevier

3 PA Gillibrand, CJ Cromey, KD Black, ME Inall 2007, Identifying the Risk of Deoxygenation in Scottish Sea Lochs with Isolated Deep Water Final report Scottish Association for Marine Science, Oban

4 Friends of Loch Etive, 2014, Dawnfresh’s Record on Loch Etive and Loch Awe, http://www.lochetive.org/docs/DawnfreshRecord.pdf (Last Accessed 17/09/16).

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I’M BACK YO

Took a mental break while I was abroad/returning from being abroad. For a million and one reasons, it was super important that I stepped away from Tumblr. Buuuut I miss it and feel like I’m finally in a good headspace and ready to get back into the grooove. Yahooo <3