Plankton associated with medusae of the freshwater jellyfish Craspedacusta sowerbyi (Lankester) in a Thames backwater

Samples of plankton were taken from Broom Water in August 1997 after a sighting of medusae on 11th August. Broom Water is about 8 m wide, and extends 250 m from the main channel of the Thames, above the weir at Teddington. On 11th August medusae were so abundant that it was possible to collect 20 in ten minutes. They were rising to the surface in bright sunlight, then sinking slowly down through the water. Examination of a medusa's tentacles under a microscope revealed the presence of a commensal protozoan, a ciliate Trichodina pediculus. Over 20 species of phytoplankton were found in Broom Water. Most of the species are common and widespread, but it was a surprise to find Errerella bornhemiensis with its characteristic pyramidal colonies, which is a relatively rare species. Zooplankters in Broom Water consisted of Rotifera and Crustacea. Zooplankton is the main food of Craspedacusta and it was found that the crustaceans but not the rotifers did undergo significant changes during the period 11-19th August. The major changes were a big increase in the percentage of cyclopoids, and a marked decrease in Bosmina. This could be because the delicate cuticle of Bosmina is much more susceptible to the stinging cells of the medusae compared with the tougher exoskeleton of the cyclopoid.

Effects of Cow Green Reservoir upon downstream fish populations

Post impoundment observations on the fish populations of the River Tees, downstream from the Cow Green Reservoir were made between 1971 and 1980. Both bullhead (Cottus gobio L.) and brown trout (Salmo trutta L.) population densities increased in the river after impoundment but changes in growth rate were small. Investigations into the stomach contents of the two species reflects the results of other work on increases of benthos in the river. Following regulation there was an increase in the quantity of Ephemerella ignita found in trout stomachs while in the bullhead, regulation caused an increase in the importance of Mollusca and a decrease in importance of Ephemeroptera and Plecoptera.

Aspects of the washout of salmonid eggs. 4. Effects of a standard mechanical shock, applied at different stage of development, upon survival and development of eggs of brown trout (Salmo trutta L.)

It is generally accepted by fish culturists that salmonid eggs are sensitive to mechanical shock and that the sensitivity varies with the stage of development of the eggs. In general, the period of greatest sensitivity is thought to occur between fertilization and ”eyeing”. However, it is reasonable to expect that, during a period (perhaps of several hours) following fertilization, sensitivity will be low because in nature during this period the eggs may be subject to some mechanical shock caused by the parent fish covering them with gravel. In 1983-4 and 1984-5 experiments were performed on brown trout (Salmo trutta L.) eggs to examine the effect of a standard mechanical shock (c. 2,500 eggs in 1983-4 and c. 8,400 eggs in 1984-5) at various stages of development upon survival to hatching and time of hatching.The results of these experiments are reported in this study.

The effects of a sand layer upon swim-up success in UK salmonids

There are two main ways in which gravel composition and changes therein arising from siltation, can influence the survival of young salmonids. First, the composition of the gravel will affect its permeability and, hence, may influence the survival of eggs and alevins through its effect upon the rate of supply of oxygen and the rate of removal of metabolic products. Second, the composition of the gravel may affect the ease, or otherwise, of emergence at the time of swim-up and alevins may become trapped in the gravel and perish. This aspect is the main concern of the present report. Experiments were conducted to examine the effects upon fry emergence of a sand layer deposited on the gravel surface. The study concludes that fry of brown trout and Atlantic salmon emerged through layers of sand up to 8 cm thick but the percentage emergence, even from the controls with no sand, was relatively low (5 - 68%). There was no firm evidence that the experimental treatments influenced percentage emergence, timing of emergence or weight of fry at the time of emergence.

Report upon the commercial fisheries in the Lancashire River Authority Area and their effect upon rod angling and spawning stock in the rivers and particularly the River Lune

The stock of salmon in any river is largely dependent upon the escapement of sufficient fish to ensure that an adequate quantity of ova is deposited and full use is made of all suitable spawning areas. At the present time, no accurate information is available on the numbers of fish entering rivers. Therefore, catch returns provide valuable information on fish stocks. This report summarises the catch returns for salmon in the Lancashire River Authority in the North of England for the years 1960-1964. Rivers included are the Lune, Ribble, Kent, Leven and Duddon.

The assessment and exploitation of eel (ANGUILLA ANGUILLA. L) stocks in the River Thames and its catchment.

This is the assessment and exploitation of eel (Anguilla anguilla. L) stocks in the River Thames and its catchment performed by the Polytechnic of Central London and The Thames Water Authority Research Project between April 1985 and April 1986. The report makes an examination of the pre-pollution history of the Thames eel fishing industry to permit an assessment of the recovery of the eel stock following the cleaning up of the Tideway. Archive material shows that the 19th Century stock was larger and more widely distributed than it is today, and the natural recruitment of elvers to the system is now much smaller. Sampling of commercial catches and trapping studies, including comparisons of different mesh sizes, have been undertaken in order to develop a statistical model of the Inner Estuary eel stock and its fishery. Local migrations and activity throughout the year are studied. Electro—fishing methods and eel traps are compared using mark-recapture techniques in order to develop an accurate means of assessing relative abundance and distribution. Work so far has concentrated mainly on the Rivers Darent and Roding but a preliminary distribution map for the whole catchment has been prepared. An experimental trapping site was established on the River Darent to investigate natural recruitment and up—river migration of elvers and juvenile eels. 1790 small eels were taken in 1985 providing information on the scale, timings and factors affecting the migration.