I see the light! Using submerged lights to control salmon swimming depths. What are the applications?

Light is a very interesting thing.  The most common general uses for lighting in aquaculture include altering photoperiods are used for breeding and increasing the photoperiod for increased feeding and hence, growth. In Artemia culture, it is used to separate the cysts from the newly hatched nauplii by using light to attract them to your dispenser. But did you know that salmon can be coaxed to do the same thing? This article talks about its application to improve salmon growth. But what about this other application?

When I was working in Tasmania as a fish pathologist, almost every summer, at least some salmon pens would be hit by jellyfish stingers. The jellyfish tend to float along the top during the day and waft along with the water currents. Sometimes the water currents direct them towards the fish pens and their stingers come into contact with the fish, either directly or like a carrot through the grater, they break up as they pass through the nets. It is not always possible or practical to move the pens away from the arriving jellyfish. What else could we do? In such events, could you use light to attract the salmon to the depths and thus avoid contact with the jellyfish?  It’s definitely worth a try.

Aquaculture
Volume 391, Number 2 (April 2013)
	Modelling of Atlantic salmon (Salmo salarL.) behaviour in sea-cages: Using artificial light to control swimming depth
	Authors:	Martin Føre, Tim Dempster, Jo Arve Alfredsen, Frode Oppedal
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 391, Number 2 (April 2013)
	Page Numbers:	137 – 146
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	Submerged artificial light sources are commonly used to control sexual maturation in farmed Atlantic salmon, but may also be a tool to steer salmon to swim at depths which are optimal for production. In this study, we used an individual-based model of the behaviour of salmon toward environmental variability to simulate the swimming depths of salmon in different seasons, production environments and artificial light regimes. Model outputs agreed with direct observations of salmon swimming depths from literature, suggesting that the model accurately simulated the behavioural mechanisms behind responses toward artificial lights superimposed upon different environmental conditions. We used the model in a series of in silico experiments to predict the behavioural effects of submerged artificial lights placed at different depths in environmental conditions typical for coastal waters in winter, spring and summer. The model indicated that artificial lights controlled salmon swimming depths most efficiently in winter. Further, lights may be more efficient in sites with a more homogeneous environment throughout the water column (e.g. open coast) than sites that are thermally stratified (e.g. fjords). Placing submerged lights at the right depths could produce better culture conditions, ultimately resulting in increased growth. With standard measurements of temperature at several depths as a sole user input, the model could act as a tool to inform farmers of which depths to place their lights on any given day or season.
	Citation:	Martin Føre, Tim Dempster, Jo Arve Alfredsen, Frode Oppedal . Modelling of Atlantic salmon (Salmo salarL.) behaviour in sea-cages: Using artificial light to control swimming depth. Aquaculture, Volume 391, Number 2 (April 2013), pp. 137-146, <http://ejournals.ebsco.com/direct.asp?ArticleID=4764ABC6CAF1C6005D07&gt;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=4764ABC6CAF1C6005D07