The Electronic Aire

Brown trout after being tagged below Newlay weir

Lockdown. Restriction. Isolation. Are a few of the many words used to describe 2020. However, these words may also be used to refer to our river systems and the challenges faced by many of the fish populations that reside within them. Whilst many of us were house bound in 2020, construction of four fish passes to help reconnect habitats for river resident and migratory fish species in the River Aire commenced. Here I hope to give you all an insight into how I tagging fish by implanting electronic tags allows us to find out what is going on beneath the water surface, and what difference these fish passes are having on the lives of our fish.

The effect of weirs on wildlife

Barriers such as weirs and dams disrupt fish migration routes, fragment fish populations, and are a major contributing factor to the extinction of fish species globally. In 2020, a scientific paper (Belletti et al., 2020) highlighted how there are over 1 million barriers that fragment European rivers, with an estimated 48,293 barriers in UK waterways, each restricting or halting the movements of native fishes in some form.

The River Aire has 34 major weirs situated along its 114-km length that are barriers to resident and migratory fish. Fish passage solutions (fish passes) have been installed on many of these weirs to help improve movements of fish along the River Aire. The DNAire project is constructing fish passes on another four weirs (Armley, Newlay, Kirkstall & Saltaire), with the major aim of enabling upstream migrating adult Atlantic salmon to reach spawning grounds at Skipton.

These fish passes do not just open up migration routes for the iconic salmon, they will hopefully provide passage routes for river-resident coarse and salmonid fish species too.

How efficient are fish passes?

In conjunction with the DNAire project, the University of Hull International Fisheries Institute (HIFI) together with the Environment Agency are investigating the movements of fish in the Aire.

One of the key aims of this investigation is to assess the efficiency of the DNAire fish passes at Newlay and Saltaire weirs. To achieve this aim, HIFI have spent the last three years capturing and tagging fish (brown trout, barbel, roach and chub) between Armley and Hirst Mill. In addition, efforts are being made to capture and tag Atlantic salmon in the lower Aire that will hopefully migrate upstream and pass through the DNAire fish passes. Passive Integrated Transponder (PIT) tags, similar to those put in cats and dogs, enable us to identify individual tagged fish.

These tags do not have a battery – and thus last the life of the fish – and emit a unique ID when activated by an electromagnetic antennas installed inside the fish passes. The antennas are strategically located to detect when fish approach, enter and ascend each fish pass. With this data, we can calculate the fish pass performance as well as provide additional information on environmental conditions when particular species move through the catchment.

Saltaire fish pass during construction. The baffles in the Larinier fish pass (left) can be seen with PIT antennas mounted on wooden beams across them. The plastic eel pass can also be seen (right).

Building knowledge for the future

Investigating fish pass performance and factors influencing passage is key to understanding effectiveness of fish passes constructed during the DNAire project and for developing future fish passes. We are all working towards a more natural and healthy River Aire that both fish and society can benefit from. We will continue to collect data in the coming months and will hopefully share results with you in a future blog.