A statistical summary review of the NRW technical conservation case for introducing THE WALES ROD AND LINE (SALMON AND SEA TROUT) BYELAWS 2017 THE WALES NET FISHING (SALMON AND SEA TROUT) BYELAWS 2017 Mike Ashwin, Chris White & John Eardley presenting Objections for CPWF
In the short window period (20-30 years) since formal stock assessments were introduced, scientists and fisheries have yet to monitor or experience the longer span climatic and ecological impacts on our migratory stocks. We are only now beginning to see the major 1SW & MSW component transitions emerging and predicted over 50 – 60 year cycles . Our monitoring of migratory life cycle populations are at best incomplete and we have major resourcing issues to overcome. Parties need to work together. Monitoring and stock assessments reporting systems must be reviewed, tune in and adapt to these big trend changes if individual river stock performance & health can be used with confidence to guide and set Regulatory measures .
Significant trend changes reported in the 2017 Cefas (NRW & EA) National Assessment & Fisheries Statistics report “True” exploitation by Net & Rod fisheries ( salmon caught and killed) has reduced by 90% since 1970 In Wales the number of rod caught salmon released annually has improved dramatically from 7% in 1993 to 86% in 2017. Anglers have been guided by peer pressure and are observing and adopting conservation codes Over that same period Angler Days fished for Salmon & Sea Trout in Wales has dropped by 60% from 118,862 (1994) to 47,092 in 2017 Yet over the long term angler Rod licence sales in England & Wales have remained reasonably constant 37,728 in 1994 compared with 35,162 in 2017 Most noticeably marine smolt survival rates have crashed by 90% - WHY ? 1970`s 1SW - 25% & MSW - 15% 2017 1SW - 2-4% & MSW - 1-2% (Dee, Tamar, Frome estimates) A tenfold decrease
CPWF Objections and concerns are presented in four sections. In simple terms the four stages of determining a rivers stock assessment 1. the principles and methods adopted for setting and monitoring conservation targets - Conservation limit setting (CL), salmon stock dynamics and River smolt deficits 2. identifying and highlighting concerns with the capture and use of core data for reporting Annual River egg deposition estimates to Conservation limit (CL) 3. explaining weaknesses and flaws in the methodology and systems procedures where the national River Classification model is used to designate River Stock status 4. the final decision structure process and measures applied The report will conclude with presentational issues and a short analysis of alternate modelled systems - summarising recommendations made to Defra and Welsh Ministers to improve and harmonize Welsh & English systems and introduce a single conservation strategy
1. Conservation Limits, salmon stock dynamics and River smolt deficits Conservation Limit (CL) principles for setting Biological Reference Points (BRP) for managing and maintaining sustainable salmon stocks were adopted in England & Wales for monitored salmon rivers, following transportation of the River Bush statistical model in the 1990`s. Revised model principles being adopted from the 1997 EA commissioned Wyatt & Barnard Technical reports The setting of BRP`s established minimum sustainable CL targets (River egg depositions and juvenile recruitment from spawning stock) above which stocks should be maintained in the long term with higher advisory Management Targets (MT) for managers to aim for. In terms of physically assessing stocks we are unable to actually monitor or estimate whole river smolt output and Actual Spawning River egg depositions are estimates, either :- - from declared Welsh rod angler catches (21 of 23 individual Rivers) based on estimates and assumptions that the declared rod catch is a rod exploitation factor of the total spawning run - or for two Welsh rivers, that the “efficiency” of counters or traps is accurately monitoring a “validated “ proportion of the adult run
The conservation model in England & Wales used was introduced in the 1990`s and a River Classification trend model added to this in 2003. The 2003 trend model did not undergone Validation and its use for designating five year forward River “trends” and a Rivers stock status in the proposed regulatory measures is hotly contested and under scrutiny Today the Conservation model uses Sea Survival (Replacement Line) estimates that are out of alignment and Annual River assessments that use rod catch and exploitation estimates that require significant correcting or do not correct for important seasonal factors (e.g. rod effort, river flows, closed season runs) The challenges that our salmon stocks face are set out in the NRW conservation case BUT the Technical case document does not assess or quantify “Life Cycle” stage challenges or prioritise these in terms of their total impact on stocks. Doing so would identify strategies that should be prioritised above others Rod exploitation (retained fish) would appear well down that list (1- 2% of spawning stocks) and might not appear at all - given the negative impact mandatory measures would have on rod fisheries activities - fisheries do guard and improving stocks and habitat, and contribute socio/economic benefits
An example Conservation model illustrating the SR curve (blue line) and replacement line (red line) to derive Conservation Limits This graph is unusual in that it depicts more tangible spawning adult numbers on the X axis rather than the normal spawning egg deposition values In the SR curve the River Maximum smolt output of 160,000 smolts would be produced from 11,500 spawning adults 200 Management Target Conservation Limit = 6,200 adults = 5,000 adults Max smolt prod Smolts (thousands) = 11,500 adults 150 Replacement point = 15,000 adults 100 Max sustainable catch = 7,700 adults 50 0 0 5,000 10,000 15,000 20,000 25,000 Adults
The conservation model illustrating how changing sea survival trends impact on a rivers smolt output requirement The strong red line being 10% sea survival (e.g. 50,000 smolts provide 5,000 adults) As sea survival diminishes and the RL steepens we reach a point at 2.5% sea survival (red dotted line – far left) where the smolt output to meet the same 5,000 adults at CL is now 200,000 smolts. And exceeds the Rivers optimum or maximum smolt output - 160,000 smolts
At the example CL target of 5,000 spawning adults the rivers smolt output requirement to meet estimated sea survival losses has increased from 1990`s - 25,000 smolt output (average 20% sea survival) 2000 - 50,000 “ “ “ 10% “ “ 2016 - 200,000 “ “ “ 2.5% “ “ Even with 12,500 spawning adults and a River at pristine juvenile condition the River only has a maximum carrying capacity to produce 160,000 smolts. Sea survival losses are outstripping the Rivers ability to compensate even at its optimum carrying capacity It is widely accepted that sea survival has now reached levels where migratory populations are at risk and may not be sustained even at CL targets.
2. Capture and use of core data in reporting Annual River egg deposition estimates to Conservation limit (CL) A complex matrix of River datasets and variables are used to produce a Rivers final total estimate of spawning eggs deposited. These include :- • Rod catch estimates from angler declared catches (or counter/trap data for Dee & Taff) • Corrections applied for angler under reporting • Rod exploitation rate multipliers for rod catch derived Rivers • Mortality adjustments for natural River losses and C & R handling • Age/weight scale calculations to estimate the proportion of 1SW & MSW component stocks • proportions of female spawners in each 1SW & MSW class • Fecundity or female egg depositions calculated from the estimated age/weight of rod caught fish We will look at the first three of these as they form the core data or building blocks for stock estimates and directly relate to angler & fisheries activities
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