Reflecting on the 2018 smolt run working with the GWCT

By Adele Green, Bournemouth University

In April 2018 I completed a placement on the River Frome, Wareham, Dorset, as a research assistant from Bournemouth university in collaboration with the GWCT for SAMARCH. From late March to mid-May, the team aim to recapture a percentage sample of the previous years tagged fish. An acoustic bubble is positioned on the main river to divert fish down through the RST on the Mill Stream.

The shifts were run by a supervising fisheries scientist and one research assistant (i.e. myself). Day shifts began at 08:00 and night shifts at 20:00. At the start of the shifts, we entered the fluvarium to check water flow and ensure the trap was running correctly. The RST was then lowered into the river and environmental data and timings entered in the recording sheet. We set up the laptop to record any tagged fish caught, and a tub of anaesthetic solution to temporarily and humanely sedate the fish for efficient processing.

The RST was checked every 30 minutes for salmon (WSSM) and trout (TSM) which would then be netted out into a tub of freshwater. Any other species found were noted and released downstream. The salmon and trout were then put into the anaesthetic solution and the fisheries scientist would check them individually for a tag. Any tagged fish had their details entered onto the computer and scale samples taken; different sides for smolt and parr. Any that weren’t tagged, had their measurements logged, and scale samples were taken from one of each size. Multiple fish caught of the same size were recorded but had no scales samples taken. The scales are sent off to Exeter University and used to determine the sex of the fish and the growth and lifecycles at sea. The fish were placed back into the freshwater tub to readjust to conditions and then released safely downstream.

Going into this placement, I had no experience of working with fisheries and was eager to learn more about research processes and sampling techniques. I expected the night shifts to be busier than they were, with capture rates barely reaching 20, however this was likely due to the temperature not reaching 12°C. As the placement had many quiet periods, opportunities arose to learn more from the fisheries scientist of the biology and physiology of salmon and trout, and the small morphological differences to assess when identifying the species.

Catching the occasional minnow and roach prompted discussions of the ecology of the river, with eels, perch and dace also caught throughout the run. I learnt more about the lifecycles of salmon and trout, their migration patterns, and their evolutionary responses to risk and challenges. For example, how the majority of smolt migration occurs during the night, likely due to adaptation or behavioural decision making to decrease predation risk and/or increase feeding due to a higher abundance of food, and so day shifts are likely to be much quieter.

Whilst working with supervising scientist, Bill Beaumont, I gained further knowledge of tagging techniques used to track fish. For example, the functional differences between acoustic and radio tagging, how they collect the data, and the environmental conditions that affect them. Whilst visiting the lab between processing times, I was shown how to read the information contained in the fish scales; analysing scales is similar to observing tree rings with aging and growth, condensed lines indicate winter growth, spread/spacious lines indicate summer growth and erosion on these lines indicate spawning. These quiet periods between trap checks also gave opportunity to engage with other scientists in the field to learn more about their careers. This provided me with important directional knowledge and contacts for experience in fisheries ecology and management.

Source: SAMARCH Blog