Tracking salmon from the journals to the sea

SCENE has been a part of many collaborations over the years, including the IBIS project, which is coming to an end this summer. IBIS spanned Ireland and Scotland, creating many opportunities for high quality research focusing on freshwater and marine environments. Masters student Angus Lothian is hoping to carry on that tradition as he travels to northern Scotland to follow the Atlantic salmon. In this month’s Behind the SCENE, Angus writes about the preparation work he’s doing before jumping in the deep end.

Atlantic salmon are well known and make an ideal study species. nemilar [CC BY-NC 2.0], via Flickr.
Atlantic salmon are well known and make an ideal study species. nemilar [CC BY-NC 2.0], via Flickr.

Tracking salmon from the journals to the sea

Since 2011, SCENE has been the Scottish home for the IBIS project. This project focused on understanding and improving the aquatic ecosystems in the Republic of Ireland, Northern Ireland, and Scotland. PhD and Masters students across these regions worked to answer questions related to environmental change and ecosystem health.

Many of the IBIS projects looked at the impacts of barriers in rivers on fishes, including eels, lamprey, trout and salmon. My project will expand on this research by using similar tracking techniques to determine the cause of mortality in migrating Atlantic salmon (Samlo salar).

Before any project can get underway, a large amount of groundwork is required to thoroughly understand the topic, with current knowledge being summed up in an extensive literature review. This also forms the basis of my first MRes report. A good literature review entails searching for peer-reviewed papers related to my study topic, extracting important information from them, and critiquing this information so that I can design my study.

As my project focuses on Atlantic salmon migration and mortality, my literature review incorporated three major areas: understanding salmon migration and associated mortality, advances in acoustic telemetry used for tracking movements, and modeling sound waves traveling in water.

Salmon enter the smolt stage as they begin their journey to sea. Image from US Fish and Wildlife Service. Public domain, via Wikimedia Commons.
Salmon enter the smolt stage as they begin their journey to sea. Image from the National Digital Library of the United States Fish and Wildlife Service. Public domain, via Wikimedia Commons.

Salmon have a very predictable and well studied migration pattern, traveling from freshwater rivers to marine feeding grounds before returning to the same river to reproduce. Despite this, there is still a lot to learn about the species movements, because very few studies have focused on the estuary or marine stages of the migration because of the difficulty in monitoring salmon in those areas. But with advances in telemetry these areas are more accessible.

I will be implanting acoustic, rather than radio or satellite, transmitters into migrating fish; these devices are the smallest in size (a good thing as migrating salmon smolts are generally around 14cm in length) and the sound waves they produce can be transmitted through the saltwater of the estuary.

The transmissions will be recorded on acoustic receivers placed throughout my study site—the Cromarty Firth—in strategic positions. The positions are then determined by understanding how sound waves travel through water, which is achieved by using a mathematical model that includes local environmental conditions, such as wind.

The model determines the probability of detecting a transmission at different distances. By doing this, I will increase my chances of recording a fish with a transmitter. This model formed part of my preliminary data analyses to justify the design of my experiment. I haven’t conducted any actual fieldwork yet because I am currently waiting on the salmon migration to start in the Cromarty Firth. The migration should begin around mid- to late-April, so any time soon.

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My fieldwork will involve spending seven weeks in the Cromarty Firth region, tracking the migration of 120 salmon. Fish will be tagged with transmitters at one location in a tributary river, and then I will track them throughout the Firth. The receivers in the Cromarty Firth will essentially form gates that the fish have to swim through; when we stop detecting a fish or start to notice unexpected behaviour, then we know it has either died or been eaten.

We are also going to attempt something new by actively tracking fish out of the Firth and into the North Sea! This will be a great adventure, but will involve long and tiresome days. This project is going to be one of the largest ever attempted in the UK in terms of tagging and tracking fish with receivers, and I am really excited to be a part of it!

Angus and his teammates prepare to test their equipment out in the Cromarty Firth. ©James Barry
Angus and his teammates prepare to test the equipment out in the Cromarty Firth. ©James Barry

Before the fieldwork starts, and after several months of solid work on my report and models, as well as our taught modules at the main campus in Glasgow, we decided to have a little break. We were rewarded with a day of sunshine after handing in our first MRes report, and so took this opportunity to take the canoe out on the Dubh Lochan to see a beautiful sunset. Living and working here at SCENE is really rewarding, providing so many amazing opportunities to learn new skills and take part in some awesome work!


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