Mawddach Hatchery update 2007-2008

February 23, 2008

Mawddach Hatchery 2007-2008 update.

It has been another eventful year for the Environment Agency’s Mawddach Hatchery at Dolgellau. As the Hatchery passes its twentieth anniversary of production there are a number of things to report on, both in terms of the fish production and the freshwater pearl mussel rearing project.

Over the years the Mawddach Hatchery has developed a number of close working relationships with a number of stakeholders involved with angling and conservation of rivers. In 2007 it is extremely pleasing to note that both the Dolgellau Angling Association and the Prince Albert Angling Society have both signed up to sponsoring the cost of rearing a tank of 4000 smolts each. The 4000 fish being sponsored by Prince Albert will be stocked into the semi-natural rearing site on the upper Eden, a tributary of the Mawddach, and the tank being sponsored by Dolgellau Anglers, will be stocked into the semi-natural rearing site on the upper Wnion.

Fish stocking 2007

A total of 105,000 salmon and sea trout fry, parr and smolts were stocked out in 2007. As in previous years, a number of rivers throughout England and Wales benefited from the Hatchery’s work.

The location and numbers of fish stocked out, together with their age and weight at the time of stocking are listed in appendix 1.

Broodstock collection and ova laid down 2007-2008

Generally speaking, the broodstock collection work in the Autumn of 2007 went extremely well. Collection of enough broodstock to produce the required number of ova, was, in most cases achieved successfully. Once all the broodstock have been stripped of their ova, they are returned to their river of origin. Full details of the numbers of fish collected and the total numbers of ova laid down are shown in appendix 2.

Fresh water pearl mussel rearing project

The freshwater pearl mussel rearing project is continuing well with some good results.  The first juvenile mussels collected in 2006 (approximately 70,000) were sampled and measured during 2007. Their growth rates were very good, but it is impossible to estimate their survival as the young mussels need to be left alone in the trays, and more importantly, the mussels are still very small, averaging 1.0mm in size, so they cannot easily be seen in the gravel in which they live.

In the spring of 2007 approximately 5000 juvenile mussels were collected as they fell off the fish’s gills.

Spatting in 2007, of the mussels held on site, gave some interesting results. The Eden and Afon Ddu mussels spatted well, giving an estimated 5-6,000,000 mussel larvae, whereas the Lledr mussels, which have produced the most larvae in the past, gave nothing! This could be due to a number of factors. It is to early to tell exactly what the reasons for the unpredictability of the mussel spatting are, as this project has only been running for two and half years, which in the lifespan of these mussels is a very short time!

In 2008 a new water filter is being installed at the Hatchery to supply the cleaner water to the mussels. In general the water quality at Mawddach Hatchery is very good, however, the mussels do require the best possible water quality, therefore the installation of this drum filter will be an excellent investment for the freshwater pearl mussel rearing project.

Energy costs and CO2 emissions.

As energy costs continue to rise, the decision has been made to change the submersible water pumps at the Hatchery. Two new variable speed drive submersible pumps are being installed.  Doing this will, reduce the Hatchery’s energy consumption by approximately 20%. In addition to these energy savings, it is estimated that with these improvements and others recently made, at the Hatchery, it will have reduced its CO2 emissions by 20% over the last four years.

	stripping a fine sea trout hen fish	developing alvins