In the Tay catchment we are fortunate compared to the other major Scottish salmon rivers in having five fish counters to assess the strength of salmon runs. The counters are all located on spring salmon tributaries, mostly on hydro electric installations. Two of the counters, Pitlochry Dam and the Ericht, are situated in the lower reaches of the two most productive spring salmon tributaries in the district. Thus probably more than half the Tay spring run is counted, providing valuable insights into the status of spring salmon.
Pitlochry Dam
(Data kindly supplied by Scottish & Southern Energy plc)
Annual “net” upstream counts (that is down counts are subtracted from upcounts on a daily basis), 1953 – 2006
Net monthly upstream counts, Pitlochry Dam, 1997 to 2006 (final year incomplete). Monthly data are not available before 1997.
Pitlochry Dam spans the River Tummel, one of the major tributaries of the Tay. All salmon ascending must pass through a fish pass within which a fish counter is located. Also there are glass panels in the fish pass wall which allow salmon to be observed (see video clip). This facility is open to the public during the day.
The River Tummel is one of the main areas for producing spring salmon in the Tay district so this counter is particularly valuable for assessing spring salmon numbers, although there are some difficulties in interpreting the data which are explained in more detail by clicking here.
The count at Pitlochry Dam for 2006 at 6650 was the highest count since 1979, and head and shoulders above anything in recent years. The spring run was relatively late in passing through the dam in 2006 owing to a colder spring and many “springers” probably did not ascend until June or even later. Yet the count to the end of June was one of the best in recent times. Some grilse are always present in June counts, but since the grilse were late in ‘06 it is likely this count reflected the good spring run as reflected by catches generally. Another major boost in the counts resulted from considerably increased grilse counts but these mainly ascended in August and September reflecting the apparently delayed run in Scotland and Ireland in 2006. However, as a caution, at the end of 2004 a new counter was installed at Pitlochry replacing one which was known to undercount small grilse, though was accurate with salmon. It may partly be that grilse are now being counted more accurately, but even so, it would still mean that the ‘06 grilse run was much stronger than ‘05.
Clunie Dam
(Data kindly supplied by Scottish & Southern Energy plc)
Annual net upstream counts through Clunie Dam fish ladder, 1953 to 2006.
(note: counter malfunction occurred in 2005)
In 2006 counts at Clunie Dam were again up at the historic high levels seen in recent years, following a counter malfunction giving low counts in 2005. Counts at Clunie Dam increased in the 1990s after improvements in smolt passage at the dam led to an expansion of the population in the western part of the catchment.
Up to the mid 1980s smolts were prevented from passing through the turbines by means of mesh screens but it was found that smolts could not readily find the fish pass and so were stuck in the loch. Researchers from the Freshwater Fisheries Laboratory found with tagging experiments that, although there was still a significant loss, it was preferable for smolts to pass through the turbines at Clunie Power Station. As a result the screens were removed and have never been replaced.
Electrofishing surveys in the western part of the Tummel catchment have shown a recolonisation by salmon of the Rannoch / Gaur area, despite the fact that some fish have ascended through five sets of hydro fish ladders. Juvenile salmon have been found in places where they were practically absent 20 years ago. This recolonisation has taken place purely by natural spread and has not been assisted by artificial stocking. Although the increase in counts seems to have stabilised, it is hoped that further recent improvements in access at Gaur Dam in the far west of the catchment will result in renewed increase.
Lochay Falls
(Data kindly supplied by Scottish & Southern Energy plc)
Annual net upstream counts, Lochay Falls, 1960 to 2006
The Lochay Falls are a naturally insurmountable barrier to salmon on the lower reaches of the River Lochay near Killin. As compensation for the loss former spawning areas on the Lyon through damming, the North of Scotland Hydro Electric Board installed a borland fish lift to allow salmon access to the Lochay. In contrast to the other counters, the 2006 count was lower than for several years.
However, the count has never been very high and it is suspected that the Lochay has never been fully colonised by salmon, and this has been proven by electrofishing surveys. It has been suggested that inadequacies of the original design of the fish lift may be partly to blame, although there may be other factors. As part of the EU funded Conservation of Atlantic Salmon in Scotland project significant improvements to the Lochay lift are in the process of being undertaken in early 2007.
Stronuich Dam
(Data kindly supplied by Scottish & Southern Energy plc)
Annual net upstream counts, Stronuich Dam, 1961 to 2006
Stronuich Dam is situated near the head of the River Lyon, about three miles downstream from the larger Lubreoch Dam which is the highest point to which salmon can ascend the Lyon. Salmon can ascend Stronuich Dam into this short length of river by a borland fish lift. The fish which reach this area are mainly a mixture of spring salmon and summer grilse. The majority of fish tend to pass through this counter in July and August though they may have entered much earlier. The long term average total counts have been pretty steady but when the effects of de-netting in the Firth of Tay in the 1990s is factored in it will mean that a real long term decline in abundance has occurred.
However, it was particularly encouraging that 2006 was one of the best counts there has ever been, but as the fish pass was completely refurbished in 2006 it is not clear yet whether this may have been due to improved efficiency of fish passage. The biggest counts in 2006 were in fact in July, which might have reflected the better spring run in ‘06, since the grilse run on the Lyon was late, as elsewhere. Spring salmon, of course, take some time to ascend this far.
River Ericht
Annual upstream counts, River Ericht, 1990 - 2006. Blue additions
represent possible additional counts in years of counter malfunction (1998, 2000 and 2001) but in 2003 is indicative of fish which were unable to ascend past the counter because of a drought late in the autumn but were rescued and transported upstream by TDSFB staff
Monthly upstream counts, Rove Ericht, 1993 - 2006. No data are available for 1996 nor before 1993. No spring counts are available for 1998 or 2000 when the counter malfunctioned.
The River Ericht counter is situated at Blairgowrie, only a few miles above the confluence with the River Isla. However it is situated upstream of a waterfall, Cargill’s Leap, which like Pitlochry Dam, acts as a temperature barrier. Therefore the timing of spring counts especially is no reflection on when the fish might actually have entered the Tay.
Since the counter was installed in 1990 the average level has remained pretty stable at around 8000 fish. However, the removal of the nets after 1996 will have helped the Ericht since most Ericht fish came in during the netting season. Had there been a level playing field the true abundance in the early 1990s would most likely have been greater than that seen more recently.
It was particularly encouraging that 2006 saw another excellent count on the Ericht, at 11,500, the third biggest count since the counter was installed in 1990. Counts to mid June and end June were at their highest recorded levels again reflecting the improved spring run. Again, like elsewhere, the main grilse run occurred late in the season reflecting the lateness of their arrival in the Tay and a period of low water. As in ‘05 grilse numbers were relatively good however.
Conclusions from Counters
The general conclusion from the fish counters in the Tay District is of a spawning stock which appears to have been pretty steady for some decades with no really apparent recent decrease. However, this has occurred over a period when there has been a major decrease in fishing as a result of the remove of net fisheries, the advent of catch and release and restrictions on angling methods (e.g. the shrimp and prawn ban). Therefore the counters hide the fact there has been a considerable decline in numbers of salmon entering the Firth of Tay over the last 20 or 30 years.
The Clunie Dam experience is especially interesting since this part of the Tummel has been recolonising despite formidable obstacles in the form of hydro dams which the fish have to pass. What it shows is that if numbers of juvenile salmon are low, the much better survival experienced by these few fish (because of low competition) can compensate for increased problems later in the life-cycle, and even though adult numbers in long established populations may have reduced, populations can still increase in poorly stocked areas. What this suggests is that the general decline which has occurred in salmon numbers is not necessarily a gradual spiral to extinction but a fall to a lower but nevertheless stable equilibrium. It has also been found in other rivers that removal of obstacles in recent times have resulted in rapid colonisation by salmon. In the case of the River Tyne, for example, it has been contended that this has been aided by hatchery operations (though the extent of this is the source of some debate) but on the Tweed there has been rapid recolonisation of big tributaries such as the Whiteadder after the removal of weirs even in the absence of stocking.
|
