Wednesday, 29 October 2008

River Goyt Brown Trout Monitoring Programme - (29/10)

With kind permission of the Environment Agency we publish a report based on the Brown Trout monitoring program taking place in the River Goyt -

The Environment Agency started monitoring the brown trout population in the River Goyt, upstream of New Mills in 2007. This monitoring programme is in its infancy but as it progresses over the next few years it can be used to target future projects to improve the fishery if necessary.

This report provides a summary of our findings for angling clubs, landowners and other parties interested in the status of fish populations in the River.

Survey Sites
The Brown Trout monitoring programme covers 14 sites between New Mills and Fernilee Reservoir, and includes the River Sett, Black Brook and Kinder Brook tributaries.

Trout numbers and habitat quality were estimated at each site by electric fishing and Habscore assessment, between July and August 2007.

Annual electric fishing on six sites will help us to detect changes in the number of trout young over time.

Habscore looks at the in-stream trout habitat available to hold fish and compares it to the number of fish actually caught during a survey. These two pieces of information are then used to calculate how well a river meets its potential to support and hold trout.

Habscore assessments and further electric fishing will be carried out every six years, to see whether the river is reaching its full potential as a trout fishery.

Fish recorded
A total of 506 Brown Trout (Salmo trutta) were caught across the 14 combined sites.

Perch (Perca fluvialitilis) and Grayling (Thymallus thymallus) were also recorded, but

at only one site (Whaley Bridge). Brook lamprey were also recorded at one site, on the main River Goyt near to Lodge Wood.

Brown trout lengths, age and growth

The following length frequency histogram provides a good picture of the overall make up of the trout population on the Goyt.

The first peak in fish lengths was recorded between 50mm to 90mm, which corresponds to this years fry. Large numbers of one year old fish are also evident, showing that survival during the first year has been good. However, under normal conditions, we would expect more fry to be present than one year old fish.

River Goyt trout had an ‘average’ growth rate compared to our national standard for brown trout (National Fisheries Technical Team, unpublished data), with a Percentage Standard Growth (PSG) value of 107%.

This indicates normal growth rates within the trout populations surveyed and reflects a stable, sustainable upland river trout population.

In order to assess fish populations, The National Fisheries Classification Scheme splits brown trout densities into two categories, those that hatched this year (0+ fry) and those that are older. The density of these two groups recorded during our surveys shown below.

The maps clearly show low numbers of trout fry, though the numbers of older fish were distributed more naturally. Despite the low numbers of fry, the greatest numbers of trout were found in the upper reaches of the Sett and Black Brook. This is consistent with the trout’s use of the smaller brooks for spawning and nursery areas.

Our surveys found that the older fish were dominated by one-year-olds that had hatched in 2006. This distribution is also illustrated by the length frequency histogram shown on the previous page, where 1+ trout were the most common age class seen.

This suggests that the 2007 spawning season had not been as successful as the previous year. Though we don’t know why this happened, the heavy summer floods in the catchment may have displaced smaller fish downstream.

Overall our Habscore assessments showed that there are enough habitats within the river to support more fish.

Trout productivity in the Goyt could be limited by poor water quality, a lack of adult brood stock or the action of impassable weirs which stop adults reaching good spawning areas.

This is the first year that electric fishing surveys of the brown trout population have been carried out upstream of New Mills. Fish populations can be very variable and definite conclusions should not been drawn from a single years data.

Having said that, our surveys showed fewer brown trout fry than expected on the River Goyt. The numbers of fry recorded were below that predicted by Habscore and that suggested for the previous year by the numbers of one-year-olds identified.

The Habscore analysis indicated that there is potential for further improvement in fish stocks, but numbers are likely limited by water quality or barriers to movement.

As more surveys are carried over the following years a clearer understanding of the fisheries performance will be possible. Of particular interest will be the number of fry caught in 2008, as this will help us determine the significance of the low numbers recorded in 2007.

Angling clubs and members of the public should;

• Notify the Environment Agency of any pollution incidents or illegal fishing activity taking place in watercourses, or of any discharges that may cause pollution using our Free phone Incident Hotline number - 0800 807060.
• Notify the Environment Agency of any information you may have about poaching or illegal fishing activities using our intelligence email address or using the free phone number above.
• Take part in the new Environment Agency Angling log book scheme, which will provide more data to help us to accurately determine the health of our fish populations. For more information please contact Ian Wood on 08708 506 506.

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