COMHAIRLE CONTAE ÁTHA CLIATH THEAS
SOUTH DUBLIN COUNTY COUNCIL

MEETING OF SOUTH DUBLIN COUNTY COUNCIL

Monday, November 14, 2011

QUESTION NO. 11

QUESTION: Councillor W. Lavelle

To ask the Manager to seek an update from Inland Fisheries Ireland (IFI) on the latest finding of surveys on fish stocks in the River Liffey similar to the recent publicised surveys which indicated that sea salmon have returned to spawning in the River Tolka and to further seek details of habitat rehabilitation projects being undertaken by IFI along the Liffey?

REPLY:

The following information has been supplied by Inland Fisheries Ireland:

The Conservation Limit (CL) for the River Liffey is 4391 fish; the Inland Fisheries Ireland Standing Scientific Committee (SSC) currently estimate that the River Liffey is reaching 31% of its CL, this is mainly based on counter information.  Over the past 3 years significant effort has gone into catchment wide electro fishing.  This is a survey technique used to estimate juvenile salmon abundance.  An average of 14.3 Salfry/5min (salmon fry encountered per 5 minutes of electro fishing) over the three years was reported on the River Liffey.   If an average index of 17 Salfry/5min had been achieved the SSC would have recommended that the Liffey could be open for catch and release angling.

In relation to rehabilitation works in the Liffey catchment, IFI are working in collaboration with OPW, to design a fishery enhancement scheme for a reach of the Morell River in the Johnstown area, Naas, where a flood relief programme was carried out.   Over the past 15 years IFI, working closely with both Intel and OPW, have designed and overseen the implementation of several major riverine salmonid enhancement programmes in the Rye River in both the Kilcock and Leixlip areas.   IFI regional staff coordinate and partake in the review and maintenance of salmon spawning beds though-out the Liffey catchment.  IFI also work closely with the ESB and MI (Marine Institute) in relation to efficient operation of the fish pass and counters at Leixlip and Islandbridge dams.

River Liffey – Salmon Conservation Limit Attainment Status

 Introduction

The River Liffey has been closed as a salmon fishery since 2007. The salmon Conservation Limit (CL) on the Liffey is 4391 fish (primarily comprising 1 Sea Winter fish) and the Standing Scientific Committee estimates that it is achieving approximately 31% of its CL in 2010 (SSC, 2010). Since individual river management/conservation of salmon was introduced in 2007 it is estimated that the Liffey has achieved on average about 28 % (range 19 – 38%) of its conservation limit annually with no possible surplus for exploitation. Consequently the river is closed to angling apart from a one day concession on the traditional opening day of the season.

Counter data

Two main indices are used to assess the status of Liffey salmon. A direct count of upstream migrants is provided by the Islandbridge counter.  Counter data (Table 1) shows that the highest verified counts were recorded in 2006 and 2007. An actual count of 2,015 was recorded in 2010 which is the highest recorded in recent years.. Another counter is situated upriver of Islandbridge at Leixlip and counts here tend to be about 50% of the Islandbridge count.

Counters are installed on approximately 20 rivers nationally. Other assessment methods have to be used in catchments where stock indices are not available. One of the primary methods is catchment-wide electrofishing.

Table 1: River Liffey counter data

CW electrofishing data for the Liffey

Catchment-wide electrofishing of juveniles (salmon fry) is one indirect source of data to measure salmon abundance as the numbers of juveniles should be a good index of the number of adults which spawned them also in addition to providing information on the relative productive capacity of that river.

The establishment of a relative index of fry abundance based on these data provides a scientific basis to identify those rivers currently closed for angling where Catch and Release (C&R) could be operated. Since 2007, the National Fisheries Management Executive have advised that where a river is meeting more than 65% of its CL, it can be opened for a Catch and Release (C&R) fishery. 

In 2009 the Standing Scientific Committee determined that a catchment-wide average of 17 salfry/5min fishing was high and indicative of good catchment-wide spawning (SSC, 2009). This figure of 17 salfry/5mins was applied to the most recent national annual electro-fishing surveys as a threshold value to allow catch & release in previously closed salmon rivers.

The status of the Liffey salmon stocks has been monitored using the catchment-wide electro fishing technique to assess juvenile salmon fry abundance since 2008. The annual mean values recorded are shown in Table 2. The distribution of sites sampled in 2009 is shown in Fig. 1. 

Table 2: Catchment-wide electrofishing data for the Liffey 2008-2010 (data in red not published)

  

Figure 1: Catchment-wide electrofishing - salmon fry (0+) abundance in the Liffey catchment 2009. Circles indicate site locations and measure of abundance

A mean catchment abundance value of 20 salfry/5mins was recorded in 2010 on the Liffey, the highest for the Liffey since this technique was used on the river. In a national context, the Liffey catchment average was in the second quartile of the 41 rivers sampled in 2010.

The catchment-wide mean over the three year period is 14.3 which is below the set national threshold of 17 salfry/5min.   Catchment-wide surveys were also conducted in 2011, the results of this survey is currently under consideration by the Standing Scientific Committee on salmon, these date will be made available post this review.

Conclusion

As for all salmon rivers assessed under the annual SSC process, the modelled estimate of recruitment to the Liffey in 2011 is based on the preceding 5 years of best available data. The outputs from counter data show that the Liffey is substantially under its CL.

This is corroborated by CW electro fishing data which show that, despite exceeding the 17 salfry/5min threshold value in 2010, the average value for the three years of electrofishing data available is below the threshold.

These scientific outcomes result in management deciding that the Liffey is closed for a salmon harvest.