• Review of the Irish Salmon Industry

      Went, A. E. J. (Department of Agriculture and Fisheries [Fisheries Division], 1965)
      For centuries the salmon has been an important item of commerce in Ireland and in many parts of the country today it is still very important in the general economy of the people, who gain a living directly or indirectly from it. It is important from two points of view. It provides sport for the angler and it supports a commercial fishery. There are three other articles in this issue: II. SALMON OF THE RIVER SHANNON (1957 to 1962) - Eileen Twomey; III. THE EFFECTS OF ARTERIAL DRAINAGE WORKS ON THE SALMON STOCK OF A TRIBUTORY OF THE RIVER MOY - E.D. Toner, Ann O’Riordan & Eileen Twomey; IV. RECAPTURES OF IRISH TAGGED SALMON OFF GREENLAND - A.E.J. Went.
    • The Movement of Salmon (Salmo Salar) Through an Estuary and a Fish-Pass

      Jackson, P. A.; Howie, D. I. D. (Department of the Marine, 1967)
      In this paper we have attempted to analyze in quantitative terms the behaviour of the salmon of the River Erne during the important phase of migration when the fish first enter brackish and fresh water.
    • The Early Life of Brown Trout (Salmo Trutta L.)

      Kennedy, M.; Fitzmaurice, P. (Department of Agriculture and Fisheries [Fisheries Division], 1968)
      The programme of research included field and laboratory studies of certain aspects of the early life history of the trout that are considered below.
    • "Specimen" Brown Trout and Sea Trout From Irish Waters

      Went, A. E. J. (Department of the Marine, 1968)
      The present paper deals with all the material collected up to the end of the 1967 fishing season and relates to brown trout of 10 lb weight and upwards and sea trout of 6 lb and upwards.
    • Irish Pike Investigations

      Kennedy, M. (Department of Agriculture and Fisheries [Fisheries Division], 1969)
      The spawning of pike was studied in 1965 and 1966 in five large Irish limestone lakes-Loughs Sheelin, Ennell, Mask, Corrib and Arrow. The spawning period was found to be February to April. Spawning took place in shallow, sheltered situations where there was a carpet of dead or living vegetation on the bottom at a depth of 20 to 60 cm. Spawning took place by day, at a water temperature of at least 9-1O C, when lake levels were high or rising. Gill-net catches reached a peak during periods of spawning. Weather conditions in February and March were much milder in 1966 than in 1965, and spawning began about a month earlier than in 1965. The eggs of Irish pike are 2.7 to 3.0 cm in diameter. They are golden to honey coloured, with a great many minute oil-globules distributed through the yolk in numerous tiny clusters. The incubation period in the field is probably 8-14 days, and the newly hatched larva is 8.0-9.0 mm long. For the first 10 days or so, the larvae hang vertically from the vegetation by means of adhesive glands on the head. They then become free-swimming, and soon afterwards begin to feed. At this stage they measure 13.0-13.5 mm. Their first food consists of small cladocera and copepods. Later, they feed on larger cladocera, amphipods, isopods, young stages of aquatic insects, and fish fry.
    • Irish Kelt Tagging Experiments

      Went, A. E. J. (Department of Agriculture and Fisheries [Fisheries Division], 1969)
      Since the beginning of the century large numbers of salmon kelts have been tagged in Irish waters and the results have been given in a series of papers...a considerable number of kelts have been tagged since 1962 at a number of stations in Ireland and they form the basis of this paper.
    • Fluctuations in the Characteristics in Irish Salmon

      Went, A. E .J.; Twomey, E. (Department of Agriculture and Fisheries [Fisheries Division], 1971)
      Fluctuations in the catches and stocks of fish are exceedingly important and have interested scientific workers for years. As far as the salmon is concerned it is known that great fluctuations occur not only in the number of fish entering the rivers from year to year but also in their character. This paper is an attempt to put on record certain changes, some of which have already been recorded in papers on Irish salmon published in a very wide range of journals.
    • Water Quality Investigations in the River Blackwater and River Martin, Co. Cork--1966-1969

      Toner, P. F.; O'Connell, C. (Department of Agriculture and Fisheries [Fisheries Division], 1971)
      Investigations in the period 1966 to 1969 showed that the bulk of the waste discharged to the Blackwater and Martin is of an organic nature and arises mainly from industries processing milk, sugar-beet and other foods and to a smaller extent from domestic sewage. Pollution, indicated by increases in the biochemical oxygen demand and suspended solids and depletion in dissolved oxygen, was detected below the towns of Rathmore and Mallow on the main Blackwater, Mitchelstown, on a tributary of the Blackwater, the R. Funcheon, and Rathduff on the R. Martin. Depletion of dissolved oxygen sufficiently large to constitute lethal conditions for fish and other aquatic life was recorded only at Mitchelstown and it appears that the high rates of reaeration operating in most cases prevented more widespread deoxygenation and also reduced the extent of diurnal variation. The concentrations of suspended solids recorded in polluted reaches were well below those which are directly injurious to fish but the accumulation of this material as sludge in slow flowing stretches below outfalls constitutes an extra demand on dissolved oxygen which in combination with the B.O.D. of the water may lead to lethal conditions. In the Funcheon, the presence of this material and of sewage fungus on the substratum invalidates the application of the standard theoretical method for predicting the variation of dissolved oxygen. The partial or complete elimination of the normal flora and invertebrate fauna from riffles below the main waste outfalls, and replacement of these by biocoenoses typical of slow flowing silted reaches were recorded in each area. The extent of such changes seemed to be related more to the intensity of sewage fungus growth on the substratum than directly to the chemical quality of the water. Complete elimination of fish was only recorded at Mitchelstown, the stretch affected being half a mile in length. Trout and coarse fish were present in all af the other polluted stretches investigated though in some of these young salmon were absent and trout very few in number. Trout appeared to make better growth in polluted than in unpolluted water, especially at Rathmore, and this is due in part to a greater food supply in the former reaches. Short surveys of the Blackwater estuary indicated that this reach may be slightly polluted. While the investigations indicated that severe pollution occurred in several reaches of the Blackwater and Martin, it was considered that the overall productivity of fish in the rivers was unlikely, at that stage, to have been adversely affected by such pollution.
    • The Crayfish Astacus pallipes of an Irish Lake

      Moriarty, C. (Department of Agriculture and Fisheries [Fisheries Division], 1971)
      The population of a 30 hectare limestone lake was studied. The crayfish were most active from July to September. Females carrying eggs were present from November to June. Parameters describing the measurements of the stock available for trapping were determined.
    • The Distribution of Irish Char (Salvelinus Alpinus)

      Went, A. E. J. (Department of Agriculture and Fisheries [Fisheries Division], 1971)
      Char* (Salvelinus alpinus) are rare in most places in Ireland to-day but they were formerly more widespread and abundant. About twenty-five years ago the Fisheries Division of the Department of Agriculture and Fisheries started to offer rewards for char submitted for examination and this has had the result of providing specimens which would otherwise have been lost. Many of these specimens wcre taken on rod and line but in recent years considerable numbers have been obtained in connection with either the improvement schemes of the Inland Fisheries Trust, Inc. or investigations concerned with the effects of drainage operations on Lough Conn.
    • Temperature and Oxygen Determinations in some Irish Lakes

      Fitzmaurice, P. (Department of Agriculture and Fisheries [Fisheries Division], 1971)
      Information about temperature and dissolved oxygen profiles in Irish lakes has hitherto been lacking. During the period 1966 to 1969 data on temperature and dissolved oxygen content at various depths were determined for a number of Irish lakes. The results are summarised in this paper.
    • Studies of the Eel Anguila Anguila in Ireland

      Moriarty, C. (Department of Agriculture and Fisheries [Fisheries Division], 1972)
      A total of 1,722 immature eels of lengths 25 to 95 cm and ages 5 to 33 years were collected in summer by fyke netting. It was shown that migration upstream was very slow, few eels of less than 9 years old being found upstream of Lough Corrib. Eels of less than 50 cm fed mainly on invertebrates, larger individuals brcoming piscivorous. Differences in the diets in the various lakes were observed and some evidence of selective feeding was found.
    • The Ecology of Brown Trout and Juvenile Salmon in the River Owena, Co. Donegal

      McCarthy, D .T. (Department of Agriculture and Fisheries [Fisheries Division], 1972)
      The growth rate and population structure of brown trout and juvenile salmon in two oligotrophic nursery streams in County Donegal in the North west of Ireland are compared, as well as data on sex ratios and sexual maturity. Details of the food of brown trout and salmon and the smolt run in 1967 are discussed. Estimates of fish population density and biomass for these rivers have been made and related to estimates made in two other rivers of similar terrain, one oligotrophic and the other eutrophic. Pre-migratory mortality rates in the salmon populations are discussed.
    • Insect Emergence Data from Four Small Lakes in the South and Southwest of Ireland

      Bracken, J. J.; Murray, D A. (Department of Agriculture and Fisheries [Fisheries Division], 1973)
      Emerging insects from four small lakes in Counties Cork and Kerry were captured using floating Mundie emergence traps during the period from late April to early November 1969. The data obtained are examined to provide information on distribution, emergence periods and seasonal fluctuations in numbers of insects present. The traps were serviced at weekly intervals and the weekly maximum/minimum temperature fluctuation was observed. Chironomids were the dominant forms emerging during the period of investigation, 51 species were recorded but only five were present in significant numbers; 19 Trichopteran species were taken, but only four in significant numbers; one species each of Chaoboridae and Ephemeroptera was taken. There does not appear to be a direct correlation between high temperatures and peak emergence within the Chironomidae, however the peak emergence of Chaoborus flavicans in Lough Avaul coincides with the maximum temperature recorded (15 C). Differences in peak emergence periods of some similar species in different lakes are apparent.
    • Studies of the Eel Anguila Anguila in Ireland No. 2. In Lough Conn, Lough Gill, and North Cavan Lakes

      Moriarty, C. (Department of Agriculture and Fisheries [Fisheries Division], 1973)
      A total of 843 immature eels of length 27 to 86 em and ages 5 to 28 years were collected in summer by fyke netting. The North Cavan eels formed a distinct population of large, fast-growing eels, most of which matured before 12 years. The eels of the other lakes were slower in growth and in maturing, substantial numbers of 13 years and older being found. Principal food organisms in the Cavan eels were fish and chironomid larvae; in Lough Gill fish for eels of over 50 cm and Gammarus and Ephemeroptera larvae for smaller; in Lough Conn, Gastropoda for all sizes.
    • The Age and Growth of Pike Esox Lucius from Four Irish Trout Rivers

      Bracken, J .J. (Department of Agriculture and Fisheries [Fisheries Division], 1973)
      Age and growth of pike Esox lucius L. taken by electrical fishing in four typical Irish trout rivers were determined,using isometric axis of scales. Age data showed that young pike dominated in catches in all four rivers. Very few pike older than four years were captured. Growth of pike in these rivers was compared with earlier results obtained for lake pike. River pike were much smaller than fish of similar age from the larger limestone lakes. Tag and recapture data from the Camlin river, confirmed that mean growth results were very similar to back-calculated means per year class. Data showed little movement of pike within this system and that electrical fishing was reasonably efficient for clearance of coarse fish in shallow trout waters. Stomach contents of pike taken in Robe and Camlin rivers were qualitatively analysed.
    • Studies of the Eel Anguila Anguila in Ireland No. 3. In the Shannon Catchment

      Moriarty, C. (Department of Agriculture and Fisheries [Fisheries Division], 1974)
      A sample of 1,637 immature eels of length 28 to 91 em and age 5 to 26 years was collected in summer seasons from 1969 to 1973 by fyke netting. The growth rate was similar to that of eels in many other Irish lakes but the age at maturity in the eels of the main Shannon was several years more than in similar waters. The food was almost exclusively invertebrate. In the Fergus system lakes earlier maturity was noted and fish was the principal food of eels of over 50 cm. A preliminary study of eels migrating upstream at Parteen Weir in 1973, 15 km above the tidal boundary, showed that few, if any, elvers travelled that distance in their first year.
    • Studies of the Eel Anguila Anguila in Ireland No. 4. In the Munster Blackwater River

      Moriarty, C. (Department of Agriculture and Fisheries [Fisheries Division], 1974)
      Yellow eels from estuarine and freshwater populations were sampled by fyke netting: in 1965 and 1966 2,221 specimens from the estuary and in 1972 and 1973 826 specimens from freshwater. It was the first extensive study of eels in an Irish river and the population was found to be more dense than that recorded in lakes. Growth in the estuary was relatively fast and spawning migration began at 9 years while in the freshwater growth was slower and migration began about four years later. One specimen of 36 years old was found and more than 17% of the freshwater sample were over 19 years. Eels of less than 40 cm fed largely on invertebrates whereas eels of 50 cm and over fed mainly on fish, cyprinids being taken to a much greater degree than salmonids. It was calculated that fyke netting of the unexploited fishery could yield a catch of 21 tonne of eels of over 50 em length in the lowland freshwater portion of the river.
    • The Effects of Drainage on the Trimblestown River

      McCarthy, D. T. (Department of Agriculture and Fisheries [Fisheries Division], 1977)
      The effects of arterial drainage on the macro-invertebrates and flora of a salmon nursery stream are described. A section of the Trimblestown River, Co. Meath was sampled from 1968 to 1974. In drainage operations of this kind the substratum where insect life predominates is removed, also fish and salmonid ova and fry life is affected by mechanical disturbance. A Surber stream-bottom sampler covering an area of 1 square ft (O.093m2) was used to take 107 samples. Wet and dry weights of the fauna were determined. A survey of the aquatic flora, pre- and post-drainage is also described. The fauna and flora were seriously depleted after drainage but recovered rapidly both in numbers and biomass a year after drainage was completed. There was an increase in the growth of emergent vegetation after drainage. Filamentous algae and Chara sp. recolonised the bed of the river replacing two submerged species (Fontinalis sp and Rorippa nasturtium) which had been abundant prior to drainage.
    • A Comparitive Limnological Study of Two Irish Lakes (Lough Sillan, Co. Cavan and Lough Dan, Co. Wicklow).

      O'Connor, J. P.; Bracken, J .J. (Department of Agriculture and Fisheries [Fisheries Division], 1978)
      A comparative study of Lough Sillan (Co. Cavan) and Lough Dan (Co. Wicklow) revealed that these two Irish lakes differ markedly in their physicoRchemical and faunal characteristics. The possible causes of these observed dissimilarities are reviewed and discussed. Lough Sillan may be classified as moderately eutrophic while Lough Dan is both humic and oligotrophic.