Speyducer
Advisory Board
Release to spawn another day
Posts: 4,123
|
Post by Speyducer on Mar 18, 2008 8:09:37 GMT
Spring Salmon Rod Catches 1994 to 2006: These figures have been generated from the official Salmon returns published for Scotland from the FRS @ Pitlochry, converted to Excel spreadsheets, and the graphical presentations kindly converted for presentation here by another forum member - djb - with thanks! Shown for the big 4 rivers (Dee, Spey, Tay & Tweed), and the points on each of the graphs shown as a particular year is the5 year average ie, 1994 to 1998 average is shown as 1996, 1995 to 1999 average is shown as 1997 etc. Click on the graph to expand this to show clearer detail: Throughout this series of data, the Dee is shown in dark blue, the Spey in pink, the Tay in yellow and the Tweed in light blue. Whereas all four rivers had shown a distinct dip in spring salmon rod catches in the middle of the period, all have recovered; the best recovery exceeding the earliest period has been shown for the Tweed and the Dee, also for the Spey with a more modest recovery & increase over the earliest numbers, but the Tay's latest 5 year average for these rod catches has also shown recovery, but only to the same 5 year average seen in the 1994 to 1998 period. Mike
|
|
Speyducer
Advisory Board
Release to spawn another day
Posts: 4,123
|
Post by Speyducer on Mar 18, 2008 8:23:01 GMT
Here are the 5 year averages for the weights of rod caught spring salmon for the same period: The average weight of these rod caught springers have remained reasonably steady, with only some reduction in the average Tay spring fish from 10.5 to 10lbs, the other rivers remaining very steady over the period, the Spey average springer being just over 9lb, and around 9lb for the average Dee springer, and around 8.5lbs for the Tweed. Mike
|
|
Speyducer
Advisory Board
Release to spawn another day
Posts: 4,123
|
Post by Speyducer on Mar 18, 2008 8:32:47 GMT
Spring salmon C&R rates for the big 4: Again, the points on the graphs represent the 5 year averages, and not actual yearly figures. Click on the graph to show better detail: Hearteningly, all 4 rivers show a very good increase in springer release rates for the period, the Spey with the very lowest starting point has progressed most recently to over 60% released for the latest 5 year averaged period; steady improvement is observed for the Tay and the Tweed, but the most outstanding improvement (but from a good starting point) is the Dee, with over 90% of springers released for the latest 5 year averaged period. Mike
|
|
hornet
Active Member
Posts: 1,120
|
Post by hornet on Mar 18, 2008 10:51:29 GMT
Excellent info Mike,
Cheers
Hornet
|
|
owen
Active Member
Posts: 184
|
Post by owen on Mar 18, 2008 13:18:42 GMT
Mike, Looking at the figures for the Tay.....if in 1996 time only around 5% of springers were returned, yet today we are catching the same number as then but returning just under 40% does this mean: a) returning 5% or 40% results in no appreciable differences in catches. (probably not..) Or b) the 'harvestable stock' of springers in the Tay has dropped so significantly into the negative that we now have to return 40% to maintain a catch number equivalent to 1996. Makes me also think that looking back we can see that we were in fact overharvesting in 1996. Can this data be used to show a point 'x' when we are in fact 'over harvesting', based on a combination of catch numbers and return rates? If it could then we could work out a catch figure which would inform conservation measures required. I bet this is already done and I havent just had a eureka moment. Nolon.
|
|
Speyducer
Advisory Board
Release to spawn another day
Posts: 4,123
|
Post by Speyducer on Mar 18, 2008 17:37:48 GMT
Mike, Looking at the figures for the Tay.....if in 1996 time only around 5% of springers were returned, yet today we are catching the same number as then but returning just under 40% does this mean: a) returning 5% or 40% results in no appreciable differences in catches. (probably not..) Or b) the 'harvestable stock' of springers in the Tay has dropped so significantly into the negative that we now have to return 40% to maintain a catch number equivalent to 1996. Makes me also think that looking back we can see that we were in fact overharvesting in 1996. Can this data be used to show a point 'x' when we are in fact 'over harvesting', based on a combination of catch numbers and return rates? If it could then we could work out a catch figure which would inform conservation measures required. I bet this is already done and I havent just had a eureka moment. Nolon. The '1996' figures, as stated earlier, are the five year average for the years 1994 to 1998. In that period, the Tay C&R of springers averaged ~5% (was less for the Spey in the same period), and this C&R rate for the spring fish has increased substantially up to the latest 5 year averaged figures of a tad less than 40%; Yet the actual numbers of spring fish landed from the Tay (again 5 year averages shown) has shown 'no change' - apart from the dip in numbers in the middle period (the same dip seen in the other rivers) - There could be many reasons for this, not really 'explained' by looking at the graphs here. I think it unlikely that a sustained 5% C&R rate for springers over the whole period from 1994 to 2006 would have resulted in the same number of springers landed in the last period compared to the first, but.... ....there are other factors which may have changed over the period affecting catches of spring fish. These factors (on the negative side - ie possible reduction in fish returning as springers) include water abstraction, dams & hydro schemes, agricultural and other industrial pollutants which may leech into the waters, habitat issues for the redds, and the nursery areas for parr & smolts, predation on smolts, smolts feeding in the estuarine waters and on the high seas, and commercial harvesting operations..... ...and on the positive side (ie possible increase of springers being rod-caught) would be increased angling pressure over the period. Unfortunately, there are no hard data for many of these factors, and thus we tend to make assumptions based on the available (limited) data. However, it may be assumed that, all other factors being equal (when we have an idea that they may not all be equal!), the 'recovery' of fish numbers, as measured by rod-caught springers over the period looked at, has been less in evidence for the Tay compared to the other 3 rivers analysed. I think you are absolutely right to point out that we should (or need!) to know the numbers of fish needed in a system from which a 'sustainable harvest' can be extracted without affecting subsequent years' numbers of fish returning to the system to spawn. Unfortunately, it may be the case that rod-caught catches alone may be a very crude indicator of the overall 'health' of the system, and that more detailed scientific data would be needed regarding habitat, parr numbers, smolt health & feeding, and accurate counts of total numbers of returning fish, and perhaps a comprehensive tagging (including radio-tagging) of caught fish. Mike
|
|
conwyrod
Advisory Board
Autumn on the Conwy
Posts: 4,659
|
Post by conwyrod on Mar 18, 2008 20:03:18 GMT
Excellent work Mike.
The graphs only show data to 2004, not 2006?
|
|
Speyducer
Advisory Board
Release to spawn another day
Posts: 4,123
|
Post by Speyducer on Mar 18, 2008 20:30:16 GMT
Excellent work Mike. The graphs only show data to 2004, not 2006? John, As stated in the opener, the points (or years) on each graph represents the average of five years, ie that year and the two years on either side (so as to smoothe out any year-by-year significant fluctuations), so what appears as 2004 is the latest five year average which includes the figures for 2002 through to 2006, averaged to give the '2004' figure on the graph. Hope that explains it better. Mike
|
|
|
Post by victorclem2 on Mar 18, 2008 20:34:47 GMT
Here are 2 questions that jump out at me:
Why are Tay spring fish consistently the heaviest, and Tweed the lowest?? Age of fish, habitat, where they feed in the ocean?? Interested in views.
What happened on the Spey that it increased it's C & R rate so effectively, overtaking two of the other rivers? Whatever they are doing, can it be copied elsewhere?
VC
|
|
conwyrod
Advisory Board
Autumn on the Conwy
Posts: 4,659
|
Post by conwyrod on Mar 18, 2008 21:10:20 GMT
Excellent work Mike. The graphs only show data to 2004, not 2006? John, As stated in the opener, the points (or years) on each graph represents the average of five years, ie that year and the two years on either side (so as to smoothe out any year-by-year significant fluctuations), so what appears as 2004 is the latest five year average which includes the figures for 2002 through to 2006, averaged to give the '2004' figure on the graph. Hope that explains it better. Mike Doh - thanks Mike, must stop speed reading threads!
|
|
|
Post by builnacraig on Mar 18, 2008 22:08:11 GMT
Why are Tay spring fish consistently the heaviest, and Tweed the lowest?? Age of fish, habitat, where they feed in the ocean?? Interested in views. Hi Victor, There could be many explanations including: Age and size at smolting:- likely to be older and bigger smolts from the Tay, a more highland river, which may result in Tay fish being larger for the same sea age. Evolutionary selection for bigger salmon on the Tay to combat what is a very powerful river in comparison to the Tweed. Higher proportion of msw salmon in the Tay, which will boost average weights considerably. Bigger mesh in the poachers nets in the Tay estuary! Builnacraig
|
|
owen
Active Member
Posts: 184
|
Post by owen on Mar 19, 2008 12:39:30 GMT
Mike,
Thanks for your (as always) comprehensive reply above. Is the lack of a full body of data due to funding limitations within the TDSFB? Presumably the more data they have the mroe effectively they could monitor and address issues affecting any of the many influencing factors which you list and thereby ensure the overall health of the river in terms of not just salmon numbers but habitat generally.
Nolon.
|
|
|
Post by victorclem2 on Mar 19, 2008 20:37:26 GMT
Owen,
It is FRS who are responsible for collecting data in all rivers in Scotland, not the individual river board, and I think the info collected on all the main ones is pretty consistent.
I will be asking them shortly for info in our three survey glens, and am interested to see what level of detail they can give us. Ultimately, info is only as good as the owners return. I am expecting info to be fairly good.
2007 data will be out September (almost a year from the end of the season!!) I think this is the main weak point.
VC
VC
|
|
|
Post by victorclem2 on Jun 15, 2008 12:04:14 GMT
Now that spring season is over for another year, anyone want to set he ball rolling with educated comment??
VC
|
|
Speyducer
Advisory Board
Release to spawn another day
Posts: 4,123
|
Post by Speyducer on Jun 22, 2008 15:06:03 GMT
Next batch of info: This graph shows the totals of rod and commercially landed spring salmon for the 94 to 06 period; Mike
|
|
Speyducer
Advisory Board
Release to spawn another day
Posts: 4,123
|
Post by Speyducer on Jun 22, 2008 15:07:34 GMT
and now for the summer rod-caught salmon stats for the period for the big 4 rivers: Mike
|
|
Speyducer
Advisory Board
Release to spawn another day
Posts: 4,123
|
Post by Speyducer on Jun 22, 2008 15:08:52 GMT
and the average weights for the rod-caught summer salmon for the 'big 4' rivers: Mike
|
|
Speyducer
Advisory Board
Release to spawn another day
Posts: 4,123
|
Post by Speyducer on Jun 22, 2008 15:10:17 GMT
and the catch & release rates (obviously for rod-caught fish) for the summer salmon in the big 4 rivers systems from 94 to 06 Mike
|
|
Speyducer
Advisory Board
Release to spawn another day
Posts: 4,123
|
Post by Speyducer on Jun 22, 2008 15:14:59 GMT
and finally at this time, the combined rod & commercial catches of summer salmon from the big 4 river systems for the period 1994 to 2006 Please note that ALL of the graphical data so released represents, for each year shown, the 5 year averages, ie, that shown as 1996 is the 5 year average between 1994 and 1998, that shown as 1997 is the 5 year average between 1995 and 1999 etc... This 5 year averaging is meant to even out the fluctuations between years, and thus gives a better overall picture of the trends in catches. Further views, opinions & commentary welcomed. Mike
|
|
Speyducer
Advisory Board
Release to spawn another day
Posts: 4,123
|
Post by Speyducer on Jun 23, 2008 18:47:28 GMT
No comments, then???
Mike
|
|