The environmental requirements of salmon and trout in fresh water

This article is a summary for the general reader, rather than an in-depth review, and attempts to define, as quantitatively as possible, the habitat requirements of salmon and trout and then to relate them to the main ways in which man's activity can influence the survival and growth of these fishes. Frequent text references to an extensive body of published work have been avoided, although a selective bibliography has been included which lists some of the main work upon which the text depends. This article deals only with the freshwater part of the life cycle, and the coverage has some bias towards England and Wales.

Regulation of the fitness of Atlantic salmon (Salmo salar) by intra-specific competition amongst the juveniles

Factors affecting the fitness of juvenile salmon are discussed. Although fitness from the genetic point of view is defined as the relative capacity of carriers of a given genotype to transmit their genes to the gene pool of the following generations, growth and survival of individuals are also components of fitness, and are influenced by responses to competition, which is the major topic of this article including implications for management. In order to better understand the relationships of density-dependent survival in Newfoundland, egg depositions were manipulated experimentally in the Freshwater River. Figures demonstrate the relationship between stock (number of eggs per 100 m2 of river) and recruitment (number of smolts per l00 m2 of Atlantic salmon, and also the percentage survival from egg to smolt stage related to potential egg depositions.

A fisheries management plan for the River Tweed in the Scottish Borders

The River Tweed is, in rod-catch terms, the second most important river in Britain for Atlantic salmon, with an annual rod catch of ca.10,000 fish. This article gives an outline of the second edition of the Tweed Fisheries Management Plan, which is defined as "The co-ordination of data collection and analyses with fundamental research into relevant topics to devise management actions that will beneficially affect the future state of fish stocks". Much of the work set down for the present is concerned with setting up recording and measuring systems for fish catches and exploitation rates, and for the operation of monitoring sites for juvenile densities and adult trout and salmon spawning runs. While surveys show the present state of affairs, the collection of records and regular monitoring of sites will mean that in the future, the past will be better known through a longer series of records. Two case histories are described. The first is concerned with setting aims for managing the brown trout of the Tweed and defining the present state of the fishery. The second is an investigation into the spring salmon of the Tweed.

Progress on the salmon investigation

An article detailing some of the conclusions of the salmon investigation undertaken by the author, on the River Eden and its tributaries, for the previous few years. It is proposed that seasonal changes in young salmon growth are related to water temperature variation. A figure is included showing length of fish compared to the average temperature of water in the River Eden over a two year duration. The article describes comparative work undertaken to date between three streams within the Thurso watershed and the River Eden. A table is included showing the average size of fish in each of the watercourses compared. Laboratory experiments on the effects of temperature on young salmon are outlined, as well as investigative work undertaken into the realtionship between fish scales and fish length.

Experiments on downstream movement of recently emerged trout and salmon parr in Grassholme channels, 1983-1985

A number of authors have described the manner in which young salmonids, soon after emergence from the gravel, set up and defend territories. This leads to mortality or downstream displacement of the individuals which are unable to acquire territories and is widely accepted as the main method of population regulation amongst young salmonids. In some field experiments the fish were constrained in screened reaches and the option of downstream dispersal for the surplus fry was thus excluded. In order to explore some aspects of downstream dispersal more closely under conditions which gave more control than is obtained in a natural stream, four experimental channels were set up at Grassholme reservoir in Teesdale. The report describes the results of investigations on the timing and rate of downstream movement of young brown trout (Salmo trutta L.) and Atlantic salmon (Salmo salar L.) out of experimental channels, with special reference to the effect of water velocity on the rate of ”emigration”.

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 water requirements of salmon in the River Lune

This report looks at the upstream movement in the River Lune of 9704 salmon which were monitored in the years 1960-1966. It explores the Broadraine Weir near Kirby Lonsdale with its fish monitoring station, the visual counting and trapping salmon, electronic monitoring of fish, and analysis of river flows.

Juvenile salmon investigations River Wenning catchment 1981-86

As part of the River Lune juvenile salmonid investigation, a number of sites on the River Wenning catchment were electrofished annually from 1981 - 1985. Particularly low Salmon parr populations were evident for much of the Wenning catchment which has caused some concern. All the Wenning catchment electrofishing results are reported in this paper and comparisons are made with designated groups of sites on the remainder of the Lune catchment. These groups of sites are: River Lune and tributaries, upstream Tebay, Upper Middle Lune, Lower Middle Lune, Lower Lune, Birk & Borrow Becks, Chapel & Crosdale Becks, Rawthey system, Barbon & Leek Becks and the Greta system. The general scarcity of Salmonids in large sections of the main river Wenning probably reflects the apparent limited natural spawning areas on the catchment. Details of Salmon fry and ova planting on the Wenning catchment since 1981 have been collated and whilst survival through the 0+ stage appears to be quite good, recruitment to the 1++ stage appears to be poor. Water quality does not appear to be responsible for the very low salmonid densities at some main river sites but is possibly a factor in apparently preventing any Salmon run in Keasden Beck. Recommendations for future Fisheries and Biological work are given.

A report on the population structure of adult salmon and sea trout in the River Lune using scale samples - with reference to historical data.

During 1993, a comprehensive data set of scale readings, length and weight measurements was established for migratory salmonids on the River Lune. This information was collected using three methods of fish capture: 1. The Lune estuary commercial nets. 2. River Lune Forge weir fish trap. 3. River Lune rod catch scale returns. Additional information was contributed by the Kent, Leven and Duddon rod and commercial fisheries. The data shows that the salmon stock in 1993 was dominated by two year old smolts. This varies from year to year. The sea trout population displays a normal population curve in terms of numbers of fish in each age and weight class. The growth rate of salmon and sea trout is very similar even though salmon have the benefit of high sea feeding.

Report on the collection of salmon creel census data from Rivers Ribble and Hodder

The River Ribble bailiff team completed a total of 377 salmonid creel censuses by interviewing anglers fishing on the banks of the Rivers Ribble and Hodder during 1994. The study was undertaken for a number of reasons: (i) , To determine which areas of the river were fished by anglers. (ii) To ascertain which fishing methods were used in these areas. (iii) To identify the success of each fishing method within each area of the River Ribble system. In a limited 1993 sampling programme, 55 censuses were carried out. Results from these indicated that fishing with worm as bait was the most common method (39% of anglers interviewed) and also resulted in the greatest number of salmon being caught (61% of all salmon). The 1994 census data were collected from all areas of the Ribble system during the months of June to October. The data presented here are for anglers fishing for salmon only or for those fishing for salmon and sea trout at the same time. All of the fish caught were salmon.

Report on the analysis of salmon scale samples returned by anglers on the Rivers Ribble and Hodder

Fisheries technical staff from the North West Central Area of the National Rivers Authority (NRA) currently provide a service for the ageing of salmon scales from fish caught by anglers on the Rivers Ribble and Hodder in order to gather information on the biological characteristics of the salmon population on the River Ribble system in terms of weight, freshwater age and sea age. At the beginning of each fishing season, scale envelopes are distributed by the NRA to angling clubs and some individual anglers. Scales taken from salmon caught on the rivers are returned to the NRA Central Area Office by the anglers, or more often, by NRA bailiffs. The age of each fish caught is then determined by the identification and counting of annuli for both the river and sea zones on the scale. Information is provided by the angler on the scale packet concerning the length and weight of the fish caught, and the date, location and method of capture. Both this information and the age of the fish is recorded on a database. These data can be used to investigate the distribution, and exploitation patterns of the different age classes of the salmon stock within the river system. This report is principally concerned with the scale samples received in 1994, although comparison is also made with samples from 1993 and 1992. References to data will all relate to that received in 1994 unless an alternate year is stated.

Report on the 1994 juvenile salmon stocking study of Foxhouses and Grizedale Becks, River Wyre

The aim of this study was to assess the suitability of Foxhouses and Grizedale Becks as nursery habitat for juvenile salmon. A comprehensive fish stock assessment survey of the Wyre catchment was carried out by the NRA in 1992. This survey found that juvenile salmon were absent from two sites studied in Foxhouses Beck. In one site in Grizedale Beck, 0+ salmon were found at very low densities. Juvenile trout were found in all three sites studied in 1992. On the basis of the results of the 1992 survey, these two becks were stocked in 1994 with 0+ salmon reared from Lune broodstock at the NRA's Witcherwell Hatchery. These salmon were stocked at a known density, following a pre-stocking survey. This report examines and compares the results of the pre-stocking survey consisting of fourteen sites in the two becks, carried out between 12/04/94 and 27/04/94 and a post- stocking survey of six sites, carried out between 12/10/94 and 19/10/94. Flow, habitat and in-river obstructions have been shown to affect juvenile salmonid densities. A habitat description is provided for each site surveyed during the course of this study.

River Wyre salmon and sea trout spawning habitat restoration / creation project. Final report April 1995

Adult salmon and sea trout rod catches in the River Wyre have been subject to considerable variability over the years. Annual rod catches ranging from 6 to 401 have been reported since records began in 1905. It has long been suspected that the physical nature of the catchment, combined with anthropogenic influences, has resulted in a deleterious effect on the Wyre fishery. Acidification problems in the head water streams (Marshaw Wyre and Tarnbrook Wyre) have been reported and are thought to threaten salmon juvenile survival. The construction of Abbeystead Reservoir and an increased tendency towards rapidly rising water levels during storms (flashiness) 1 are thought to have a significant impact on spawning gravel quality and quantity, both of which are thought to be deteriorating. As part of an overall desire to maintain and improve the migratory salmonid population in the River Wyre, this project has been commissioned to investigate remedial action which may improve and enhance spawning success, leading to an eventual improvement in the status of adult stocks. The primary objective is to establish whether the quantity and/or quality of available spawning gravels are limiting migratory salmonid productivity. The investigations undertaken confirm the general observation that useable spawning gravels appear to be in short supply in the River Wyre, and may be the limiting factor influencing returning adult stock.

Genetic differentiation between Atlantic salmon populations in the Windermere catchment

Genetic analysis, using single locus probes for genomic DNA, revealed that the juvenile Atlantic salmon populations in the Rivers Leven, Rothay and Troutbeck were related but genetically distinct. This genetic differentiation is greater than might be expected (by comparison with other salmon populations in the UK) and it is recommended that no action is taken which might promote genetic exchange between the three rivers. Thus, future fisheries management practices should treat the salmon from each site as separate genetic stocks. It is unlikely that any attempts to encourage fish currently spawning in the River Leven (downstream of Windermere) to utilize the upper catchment will be successful. The faster growth rate of juvenile salmon in the River Leven, compared with the River Rothay, probably results from a difference in temperature between the inflowing streams and the main outflow of Windermere. Precocious sexual maturation of some male parr was found in all three populations but the incidence (13-33%) is well within the range reported for other waters. Because of their enhanced growth rate, it is likely that some of the precocious males in the River Leven were 0+ fish. A very high incidence of hybridization (>18%) between Atlantic salmon and brown/sea trout was found in Troutbeck but not in the other rivers. Mitochondrial DNA analysis of these hybrids revealed them to be the product of several, independent cross-fertilizations involving both sexes of both species. The implications of this finding are discussed in relation to the availability of suitable spawning sites in Troutbeck.

Salmon action plan: River Kent, July 2001

The report presents the Environment Agency's 5 year Salmon Action Plan for the River Kent for the period from January 2001, providing the background to the plan, responses to the public consultation given, and proposed actions.