"Movements and temperature experience of adult salmon transported from estuary nets directly to the lower R.Avon".
During the 2005 seine netting season CEFAS plan to carry out a study of the habitats used by salmon in the Avon estuary , their temperature experience and their subsequent upstream migration For some years now, netted salmon have been transported past Christchurch Harbour, to the lower Avon at very low residual flows (<6 cumecs) because it is known that a large proportion of salmon can be lost in this estuary under these conditions , with high water temperatures implicated in the causation of losses.
The Environment Agency and Wessex Salmon and Rivers Trust are promoting an extension to the CEFAS project to include 20 extra tagged salmon to be tagged in the same way as the other 20 CEFAS salmon and transported to the lower river for comparison. An extra 4 fixed receivers in the river Avon are also proposed.
CEFAS will be responsible for the extra tagging, collection of telemetry data, and analysis and reporting of the whole project. The additional tagged salmon and fixed receivers will ,as well as casting light on the value of transportation , potentially add to data on subsequent upstream movement and any obstructing influences.
It is proposed that fish for transportation and those intended for Immediate release are tagged concurrently for optimum comparability , over a period of falling flows and that transportation is to an area of the lower river where the chance of recapture by anglers is minimal. This location is consistent with an approach minimising disruption of natural behaviour .
Projected residual Avon flows are extremely low, with 7 cumecs or less likely at the commencement of netting.
The transported salmon will be floy tagged and anglers asked to report their capture (and release). As all data will be downloaded directly from the acoustic receivers all the fish will be able to play out their normal migrations and spawning the project is unlikely to attract adverse reaction.
Methodology
Water temperature/behaviour recordings
The research will use telemetry/tracking techniques to determine the relationship between water temperature, the behaviour of adult Atlantic salmon in the River Avon estuary and entry into freshwater. The tracking programme will use the VEMCO Ltd. (Halifax, Canada) coded acoustic temperature tags and VR2 acoustic receivers which CEFAS is presently using successfully to determine the behaviour of adult salmon in a number of UK river estuaries (e.g. Fowey, Tyne and Tees). The tags have a range in the estuarine environment of ~500 metres and operate at a frequency of 69kHz and up to 4000 individual coded tags can be identified by the receivers. The tags also provide information on the ambient water temperatures being experienced by the individual salmon. The movements and locations of the tagged fish together with the water temperature will be detected using VR2 acoustic receivers, which will log the presence of the individual fish and the water temperature. Once the adult fish have been tagged there is no need to handle the fish again to retrieve any data – all temperature information is recorded remotely by the VR2 receivers. This methodology has many advantages over previous studies where Data Storage Tags attached to the fish collected the data but then had to be retrieved from the fish after spawning to down load the results from the study. Using the proposed VEMCO equipment temperature data will be downloaded from the receivers straight to a lap-top PC for analyses. Additional information on the precise positions of the fish within the Avon estuary, will obtained using a VEMCO VR60 acoustic receiver and hydrophone.
The VR2 receivers will be deployed throughout the length of the River Avon estuary and their strategic positioning within the study area will determine where the fish may hold or rest during estuarine migration. The VR2 receivers will also indicate the relationship between the behaviour of the adult salmon within the estuary and water temperature. The initial deployment of the equipment will be undertaken during early summer and will need to be tested under variable flow and tidal conditions to maximise the detection rates of migrating fish. The placement of the receivers will be undertaken after full consultation with the Environment Agency and the Harbour Authorities. Sufficient receivers will be deployed at each site in order to "gate" the estuary. CEFAS has used this "gate" method of tracking on a number of occasions to successfully monitor the upstream and downstream movements of adult salmonids in estuaries. The strategic positioning of the receivers normally results in a 100% detection rate of the tagged fish. Additional receivers will be placed in the freshwater sections of the River Avon to determine successful river entry.
Fish capture and tagging
Adult salmon will be obtained close to the mouth of the estuary by commercial nets-men, operating under licence. Numbers of fish caught will be dependant upon the availability of sufficient numbers of returning adult salmonids and by the conditions within the river permitting fish entry and capture. Fish will be released after recovery from handling and tagging and their subsequent movements within the estuary monitored. The adult tracking study will commence in June 2005 and a maximum of 20 salmon will be tagged and released. After tagging these fish will not be handled again and will be expected to spawn normally later in the season once they have entered freshwater. It should be noted that salmon caught at the mouth of any river estuary may not be destined to spawn in that particular river system. Salmon are known to enter a number of different river systems before finally spawning in their river of origin. Fish caught in the lower Avon may subsequently migrate to their adjacent river of origin. Therefore, unsuccessful entry into the freshwater section of the River Avon may not be the result of adverse environmental conditions within the river, but the subsequent movement of the fish to spawn in their home river.
Individual fish will be anaesthetised with 2-phenoxyethanol (0.4 ml l-1) and the coded temperature tags (54 mm in length, 16 mm in diameter) will be inserted into the stomach of Atlantic salmon. All work will be carried out under Home Office Project Licence PPL 80/1753 held by Dr Andrew Moore (CEFAS).