Nith District Salmon Fishery Board
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Conservation

9

It is important that we think of the fisheries within the Nith catchment as an entire ecosystem rather than as individual entities.  The River Nith is a maternity ward and nursey for salmon, sea trout, sea lamprey and river lamprey; a premanent home for grayling, brown trout, brook lamprey, minnow, stone loach and stickleback; and a youth club for eels! No matter what type of fish inhabits the Nith, they all require clean, cool water and a natural food source in order to survive and thrive.


Catch and Release in the Nith Catchment

The primary aim of any fishery manager is to ensure that stocks of fish are present in sufficient numbers, or if numbers are below the natural carrying capacity of the river, to try to increase stocks. There are a variety of different methods that can be used to improve the freshwater habitat that salmon and sea trout utilise. For instance, barriers to migration can be taken down, the amount of diffuse pollution entering watercourses can be reduced, access by farm stock can be restricted, trees can be planted and hatcheries can be used to stock juveniles. All of these methods work with varying levels of success but it is not just down to fishery managers to ensure the future conservation of salmon stocks. Fishermen and women can certainly do their bit by returning salmon and sea trout that they catch back to the river. This is a well-recognised conservation method and on some rivers a total catch and release policy has been adopted. However, the actual impact that this conservation measure can have on a river is often not fully appreciated. A document was recently produced by the Association of Salmon Fishery Boards (ASFB) that illustrates the benefits that can be derived from returning salmon back to the river. Using the ASFB model and applying it to the Nith using our own catch data, we have calculated the impact that increasing catch and release could have on the Nith’s stocks of salmon. All of the assumptions used are those commonly used by fishery managers throughout Scotland and are based on research carried out on various rivers. Please note that all of the figures used are very conservative and should be seen as a minimum benefit.

On average, 3322 salmon and grilse were caught in the Nith over the last 10 years and it is generally assumed that this is approximately 10% of the total number of salmon entering the river. So, for ease, we can assume that 30,000 salmon and grilse enter the River Nith and its tributaries every year to spawn. If we assume that 50% of these are females that means that 15,000 hen salmon are depositing eggs in the Nith every year and that if each of these females laid an average of 4500 eggs each then 67.5 million eggs are being laid down naturally in the Nith catchment every year.

In 2010, 30% of the salmon and grilse that were caught in the Nith were returned. If we assume that 85% of these salmon survive to spawn and that 50% of them are hens (bearing in mind that most fish returned are females), then we can calculate that an additional 1.7 million eggs were laid down last year due to anglers returning their fish. If every fisherman or woman returned just one extra salmon per year it can easily be seen that this would have a significant impact on the number of salmon eggs being deposited in the Nith catchment. Table 1 below shows the number of additional eggs that could be laid down if catch and release figures was to increase.

Table 1: Percentage of salmon release and the additional number of eggs that could be laid down

Percentage C&R to eggs laid down copy

These numbers are not insignificant and can certainly make a difference to the number of returning salmon and grilse in future years. Unfortunately, the percentage of salmon that are caught and released within the Nith catchment is very low compared to other rivers around Scotland (Figure 1).

Figure 1

Comparision

An average river in Scotland is returning 70% of the total number of salmon and grilse caught each year. However, Figure 2 shows that in the last 10 years the number of salmon returned in the Nith has increased to 30% compared to 2000 when only 10% of salmon were returned.

Figure 2.

Percentage cath and release in Nith

If every angler returned one more fish a year it would benefit salmon and grilse stocks in the long term. Rather than thinking about returning one salmon, why not think of it as returning 4500 eggs instead? As it is illegal to sell salmon and sea trout caught by rod and line in the UK, if we only took what we could eat this would assist in ensuring that our fishery was sustainable in the long term and that future generations will be able to enjoy the benefits of salmon and sea trout.

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