Multi-captures of Rod Caught Salmon on the River Carron

The following article was written by Bob Kindness and published in the January 2010 issue of Trout & Salmon Magazine.

Once bitten, twice shy?

Salmon catch statistics for Scotland, covering both net and rod fisheries, have been produced since 1952. Over the period for which there are data, there has been a continual decline in catches indicating a progressive reduction in the number of salmon returning to Scottish waters. This decline has been reflected most in the net fishery where the catch has dropped from over 500,000 salmon and grilse in a single season during the 1960's to less than 16,000 in 2008.

In contrast, the rod and line catch shows no clear decline. However, it is undoubtedly the case that the number of salmon entering our rivers is hugely influenced by the decrease in the number taken by net fisheries. 

“To date, the decline in the netting industry has acted as a buffer for the rod fishery as marine survival has declined. However, net catches are now around 5% of those taken at the peak of the fishery and thus the buffering afforded to the numbers of salmon entering fresh water by the decline in net catch has been almost completely utilised. If marine survival continues to decrease, then rod catches may decline and ultimately spawning populations may be put at risk.”
— Marine Scotland's Statistical Bulletin of Scottish Salmon and Sea Trout Catches, 2008:

As a consequence of this concern for the current and future status of Scottish salmon stocks, certain management practices have been adopted in an attempt to at least preserve, if not enhance, the number of salmon available to rod fisheries. The key is to maximise smolt output. One such practice designed to increase spawning escapement and thereby increase the potential for smolt production, is the act of ‘catch and release'. This practice, whereby anglers release their quarry back into the river after its capture, maintains angling and therefore the financial viability of salmon fisheries while ensuring that enough fish reach the spawning grounds to produce the next generation.

Catch and release has been adopted on many salmon fisheries throughout Scotland and can be either total catch and release, where every salmon is returned to the river, or partial with a percentage of the fish being retained. The level chosen will normally depend on the status of the stocks within the individual river. Taking Scotland as a whole, the number of salmon being released has increased steadily since numbers were first recorded in the annual Statistical Bulletin in 1994. The most recent catches in 2008 had the highest percentage of released to date at 62%.

In the case of the River Carron in Wester Ross, a complete collapse in the salmon stocks prompted the introduction of a 100% catch and release policy in the mid-1990's. On the back of a major restoration programme based on stocking, the salmon stocks have shown a dramatic recovery in recent years with the 5-year rod caught average increasing from 6.2 in 2001 to 211 in 2009, the highest figure ever recorded. Although it seems clear that the increase in catches is mainly due to the stocking programme, with catch and release in place some of the increase could be due to released fish being caught again. From a stock management point of view, it was important to investigate this possibility

At 17 miles long, the Carron, although short by east coast standards, is one of the biggest rivers in Wester Ross. The fishing on the river is controlled by 6 riparian owners who are all fully committed to the stock management programme including strict adherence to the catch and release policy. All anglers follow a protocol for fishing the river which includes the use of a specially designed keep-net. This keep-net must be carried at all times so that every salmon when caught is retained to be examined before being released. The nets are easily set up in the river in a gentle flow once a salmon has been inserted ( photo 1). The salmon can be left long enough in the net to ensure complete recovery before being released. The net also gives ‘bleeders', which have been hooked in the gills, a chance to recover. Normally these fish would automatically be killed on the assumption that they would not survive if released. However, during the last two seasons several ‘bleeders' on the Carron have recovered fully having been left for several hours in keep-nets. Indeed one of these fish went on to be caught twice more before being retained as a brood fish.

To ascertain the frequency of multi-captures of salmon on the Carron, a marking programme was established in 2005 and has continued each year since. This consisted of marking as many salmon as possible that were caught on the lower one-third of the river where most of the fishing effort takes place. The upper part of the fishery, much of which consists of two lochs, is relatively unproductive although it usually holds good numbers of fish. The keep-nets are essential to the marking operation, allowing salmon to be retained anywhere within the river before being marked prior to release. This enables all the marking to be done by one person.

In choosing a method of marking fish, two considerations are important. Firstly, the method must not compromise the fish in any way and secondly, the method must leave a recognisable mark for individual fish for a substantial time after the fish is released. For these reasons the use of external tags was discounted since, not only can they compromise the fish, but they can also be lost and fin-clipping was not considered since this would not allow individual fish to be recognised and any fin damage could lead to saprolegnia infections. In view of this, the method chosen was to mark fish by applying the biological stain alcian blue as specific spots on the ventral surface.

The method involved a panjet that uses compressed air to inject the blue stain through the skin of the fish ( photo 2). The stain is held in a glass reservoir and several applications can be made from each fill of the reservoir. Ten locations were available on each fish for marking (see diagram) and by selecting 3 of these locations on each fish a total of 120 combinations is possible making it possible to identify 120 different fish. The first fish marked is 1,2,3 the second is 1,2,4 and so on with the final fish being 8,9,10. A keep-net makes the marking process easy since a salmon will lie quietly under a collapsed net ( photo 3). Without the need for anaesthetic, the fish can simply be drawn back out of the net, marked and then slipped back into the net. The process is then repeated for the other 2 spots before the fish is released ( photo 4).

Between 2005 and 2009 a total of 362 rod caught salmon were marked before being released. The majority of the fish were marked during August and September when the peak of the Carron's salmon run takes place. No marking was done after early October since from that time until the end of the season most of the salmon caught were retained as broodstock. Also, with fish caught close to the end of the season, there would be little time left to realistically have the opportunity of catching fish a second time.

In each of the years of the trial to date, marked salmon have appeared in the rod catch. Details for each year are as follows:

2005 

34 salmon were marked between 18/08/05 and 05/10/05.

3 salmon were caught a second time with one of them caught a third time as a kelt the following spring having been used as a brood fish after its second capture and then returned to the river.

2006

  • 79 salmon were marked between 08/07/06 and 26/09/06.
  • 11 salmon were caught a second time.

2007

  • 120 salmon were marked between 25/05/07 and 24/09/07.
  • 13 salmon were caught a second time.
  • 1 salmon was caught a total of 4 times before being kept as a brood fish.

2008

  • 75 salmon were marked between 04/04/08 and 06/10/08.
  • 11 salmon were caught a second time.
  • 5 salmon were caught 3 times.

2009

  • 54 salmon were marked between 08/05/09 and 25/09/09.
  • 15 salmon were caught a second time.
  • 2 salmon were caught 3 times.

Because this type of marking allows individual salmon to be recognised, interesting information on the movements of fish between captures and the time gap can be gathered. The patterns were similar for each of the years of the trial. There was a fairly even mix between fish being caught in exactly the same place (3 months between captures in the case of one fish), fish moving up the river and those moving down the river. In the latter case, one salmon was caught in Loch Dughaill on 20/08/09 and was then caught again on 02/09/09 having moved about 6 miles back down the river. The time gap between captures also varied considerably with the shortest being 2 days and the longest in the same season being 113 days. This fish was of particular interest. It was the first salmon of the season, caught as a ‘sea licer' on 08/05/09 in the lower part of the river. It was caught a second time on 29/08/09 having moved up 7 pools and was then caught a third time on 19/10/09 having gone back down 3 pools. It was obviously an early running fish that had no intention of leaving the lower part of the river. Ironically, it was the same angler who caught it on the first and third occasions.

However, the most significant result from the marking trials is the number of times that marked salmon were re-captured and not only twice but three and even four times. Despite the fact that the Carron is a very lightly fished river (on average less than 4 rods per day for the entire river during the peak of the season) and that only the lower third of the river is fished effectively, a surprising number of salmon were caught more than once. This was especially the case for the 2008 and 2009 seasons. Evidence of such a high re-capture rate is not only significant for the Carron but provides valuable information for all rivers where catch and release is practised.

Catch and release allows a greater spawning escapement and should generate more young stock, although this may be debatable given the level of spates that are now being experienced in many rivers and their ability to wash out redds. Perhaps of more certainty is the likelihood that catch and release will be generating increased catches through multi-captures. This leads to individual fish giving greater value to a fishery by providing sport for more than one angler and, given that it is only possible to tell if a salmon has been caught before if it is marked, then no successful angler in these circumstances will be disappointed.

However, the problem arises when rod catches are used to provide an indication of the size of a river's salmon run and particularly when comparisons are made with seasons before catch and release was practised. If re-captures are not taken into consideration then it is extremely doubtful whether it is still legitimate to use rod catches in this way. While it is not appropriate to apply the percentages of re-captures found on the Carron to other rivers, given the consistency of the results over five years, it is quite clear that something similar will be happening wherever catch and release is practised.  If this is indeed the case, then, with 53,038 salmon released by Scottish rod fisheries in 2008, the optimism currently being expressed on salmon stocks may not be well founded.