• Some Problems and Methods in Dublin Bay Prawn (Nephrops norvegicus) Research

      Hillis, J P (Department of Agriculture and Fisheries (Fisheries Division), 1972)
      Much is in the process of being learned about the Dublin Bay Prawn or Norway Lobster Nephrops norvegicus (referred to simply as the prawn hereafter) but compared with many other commercially fished species much still remains a mystery. This paper describes methods of examination of its biology and ecology designed to yield information on habits, movements and especially growth and death-rates, these being the two most important factors in the prosperity of the fishery.
    • Studies on Dublin Bay Prawns (Nephrops norvegicus) in the Irish Sea

      Hillis, J P (Department of Agriculture and Fisheries (Fisheries Division), 1971)
      The fishery for Dublin Bay prawns (Nephrops norvegicus) is carried on in a number of areas around the coast of Ireland, but the bulk of the catch comes from the Irish Sea north of Dublin, where the greatest landings, excluding County Down, are at Skerries, It is of recent origin, having been negligible prior to 1955, since when it had risen with some fluctuations to nearly 18,000 cwt in Counties Dublin and Louth in 1968. In research on prawns, there is no known means of ageing the animals, which makes estimates of their mortality and growth rate difficult. Sampling is complicated by the fact that they make burrows in the sea bed, into which they retreat when conditions are not suitable, thus sometimes giving small catches on grounds where the population may be large. This activity is governed by light conditions and the strength of bottom currents. In addition, females carrying external eggs disappear from the catch soon after becoming buried, due to either burrowing or emigration - most research workers believe the former to be the case. Work carried out in 1968 included:- (i) a survey of the commercial catch to find the size of prawns marketed and of those discarded at sea in order to compare their sizes with those taken in former years and (ii) with the aid of the research vessel, Cú na Mara, a comparison of the numbers, average size and sex-ratio of prawns from different depths and at different times of day. The aim of this research programme is to ascertain the facts governing the reproduction, growth rates and economic yield of this important stock of prawns.