Solving fisheries problems in Wester Ross: to stock or not to stock?
Posted: Friday 4 June, 2010 @ 17:55:33
Summary from WRFT Workshop, 28th May 2010, Poolewe Village Hall
Many of the rivers and lochs in the Wester Ross area have been subject to stocking programmes over the past 50 years or more. These have usually been aimed at restoring or enhancing salmon and sea trout fisheries within the area. What good has this done?
This workshop, attended by 25 people comprising geneticists, fishery managers, and a range of other interested people, considered the role of stocking as a means of restoring and supporting fish populations and wild fisheries within the context of Wester Ross.
Peter Cunningham highlighted differences between and within salmon rivers in Wester Ross in terms of their habitat suitability for wild salmon populations. In contrast to the East of Scotland, rivers in Wester Ross are typically short, steep and infertile. There are extensive areas of stable, productive water in some of the larger rivers, particularly in areas downstream of lochs where densities of juvenile salmon have been consistently high (e.g. rivers Gruinard, Little Gruinard and Ewe). These areas represent ‘core’ habitat for the production of wild salmon. However, small headwater streams, especially those above waterfalls, and some smaller rivers (such as the little Tournaig river) provide shallow, less stable habitat, where wild salmon have a more difficult struggle to complete their life cycle, especially when rates of marine survival fall. Juvenile salmon populations were extirpated from some ‘marginal’ areas in the 1990s; some of these waters have since been recolonised by straying salmon (see WRFT Review May 2010).
Dr Alistair Duguid (from SEPA) summarised the remarkable genetic diversity of Brown trout (Salmo trutta) across the range of the species. Wild trout have even greater genetic diversity than salmon; and much of this is likely to be adaptive. Studies have shown that some Scottish lochs, including Loch Awe and Loch Laggan, support two or more distinct ‘sympatric’ trout populations. ‘Ferox’ trout spawn in the outflows of these lochs; their progeny must be adapted to swim upstream into the loch from nursery areas in contrast to the other trout populations which spawn in streams which feed the loch. Within the Loch Maree catchment Loch na h’ Oidhche trout are already know to be genetically quite distinct from other trout in the area; there may be geneticly different sea trout producing populations within lower parts of the system.
Mark Coulson (RAFTS geneticist) presented the results of the initial DNA analyses of wild salmon (Salmo salar) samples collected from the WRFT area. Differences between rivers were identified, however assignment tests were unable to separate fish into their respective samples with high levels of confidence. Mark warned against the assumption that differences between populations may therefore be small: further analyses using different genetic markers could clarify the extent of genetic variation within the area and levels of genetic introgression (e.g. with non-native fish).
Ross Gardiner (Marine Scotland) summarised legal aspects of stocking and the process by which decisions are made regarding stocking applications. In much of Wester Ross, the Wester Ross Area Salmon Fishery Board assesses applications to stock salmon or sea trout; this aims to achieve a level of consistency with the Marine Scotland process in the best interests of the wild fish populations concerned.
The afternoon session focussed on examples of stocking programmes. Simon McKelvie (Cromarty Firth Fisheries Trust) stressed that the Conon River system’s stocking programme, supported by Scottish and Southern Energy, was entirely the result of the unique situation that existed in the past. To compensate for the loss of extensive areas of nursery habitat for salmon as hydropower reservoirs were developed in the 1950s, an agreement was reached to stock the upper Bran, and support Conon hatchery operations. Only areas affected by hydropower schemes within the catchment were stocked. Production of salmon within the Blackwater system had been maintained through the stocking programme. By working in collaboration with scientists from Marine Scotland and further a field, many pioneering research studies had been undertaken.
Jon Gibb (River Lochy) also stressed that anthropomorphic impacts were the main reason behind the need for a stocking programme in the Lochy. Recent spates (?climate change) had led to destabilisation and large scale redd washout within the river; in some years eggs, fry and parr had disappeared after extreme spates, the most recent of which was in 2007. Of greater concern was the sea lice problem. During the 8 years up to 2008, in the year following ‘year 2’ of the production cycle of salmon farms in Loch Linnhe, grilse catches were very low. In intervening years, grilse catches were very much higher. Sea lice levels on sea trout sampled in the sea nearby by the Lochaber Fisheries Trust were much higher in ‘year 2’ of the production cycle. To maintain a productive fishery, a salmon smolt ranching programme was being initiated where a proportion of fish would be treated to give them greater resistance to sea lice infection prior to release.
Bob Kindness (River Carron restoration programme) outlined how from very low levels, rod catches of salmon and sea trout in the River Carron had recovered to their highest levels for many years. Bob described how, from early this century, catches had initially increased in parallel to the numbers of juvenile salmon stocked. More recently, with many more wild fish in the system, the majority of smolts leaving the system were thought to be progeny of wild spawned fish. However, to off-set against possible redd washout, Bob felt that the fishery still benefited from the stocking programme. Smolts leaving the system have been monitored using a rotary screw trap; using mark and recapture methods, data on repeat rod-capture rates for adult salmon had been collected indicating that in some years 10% or more of salmon are caught more than once.
The discussion that followed addressed two issues:
should stocking be used to restore wild salmon populations in a ‘marginal’ headwater stream above a difficult water fall [e.g. the upper Bruachaig (Ewe system)]
should stocking be used to restore the Loch Maree sea trout fishery?
- Restoration of salmon production in headwater streams
To safeguard wild salmon populations, almost all delegates supported the view put forward by geneticists that rivers should if possible not be stocked, and every effort should be made to allow wild fish to recolonise naturally. However, to support production of fish for fisheries, most delegates accepted that a different option might be worth investigating. For the Bruachaig, the development of a captive broodstock using, where available, early running Ewe fish as well as Kinlochewe River fish might pose least risk to existing wild salmon populations within the system (assuming those fish could be kept alive through the summer until spawning time and that their removal would not be detrimental to an existing population elsewhere within the system). It was suggested that such a broodstock, to produce 100k+ eggs or fry per year, could be grown on for much the same cost as the existing stocking programme (around £5k per year). Advice from geneticists should be sought at all stages.
- Loch Maree sea trout fishery restoration
The priority action should be further clarification of genetic status of wild populations. Trout show greater genetic variation than salmon populations, and lochs such as Loch Maree are likely to have more than one distinct trout population. It was suggested that until problems at sea were resolved there would be little benefit from a stocking programme in any case. Ranching sea trout smolts and feeding them on a diet to include anti sea lice infection prophylactic was proposed as an option if lice problems were to recur, but would only give short-term protection from sea lice. This was also judged to be of high risk to the genetic integrity of the native sea trout population.
Thank you to all participants for very useful meeting for WRFT and for contributing to the resolution of complex issues. The meeting was part funded by the Scottish Government via RAFTS.