Elements of ecology (1954) Elements of ecology elementsofecolog00clar Year: 1954 492 Dynamics of the Ecosystem other basis, and depends among other things upon the size of the standing crop. Thus one aspect of productivity affects another aspect. These relationships may be iHustrated by data for the total yield of haddock caught on the Icelandic fishing grounds in compari- son with the catch per unit effort (as measured by the landings per day's absence from port) and the total hours of fishing by British trawlers (Fig. ). The total yield of haddock declined slowly 1910 1930 1905 1910
Elements of ecology (1954) Elements of ecology elementsofecolog00clar Year: 1954 492 Dynamics of the Ecosystem other basis, and depends among other things upon the size of the standing crop. Thus one aspect of productivity affects another aspect. These relationships may be iHustrated by data for the total yield of haddock caught on the Icelandic fishing grounds in compari- son with the catch per unit effort (as measured by the landings per day's absence from port) and the total hours of fishing by British trawlers (Fig. ). The total yield of haddock declined slowly 1910 1930 1905 1910 1915 1920 1925 1930 1935 Fig. (Upper) Total catch of haddock from Icelandic Fishing Grounds by all countries. (Lower) Catch per day's absence from port (solid Hne) and total hours of fishing (broken line) by British First Class Trawlers. (Modified from Russell, 1942, The Overfishing Problem, Cambridge Univ. Press.) from 1905 to 1915, and the catch per unit effort declined regularly after 1911. During the war period 1914-1918 the haddock population had an opportunity to recover, and, with the resumption of fishing by the British trawlers in 1919, the catch per unit effort reached an all-time high. The total yield reached a peak in 1920 and a some- what higher peak during 1927-1929, owing in part to the increase in fishing time and in part to the adoption of a new type of trawl. From 1924 to 1937 the hours of fishing were doubled, but the catch per unit effort exhibited a downward trend to a value in 1937 less than one quarter of that obtained in 1919. The explanation is found in the fact that the standing crop of haddock in Icelandic waters became progres- sively depleted, as a result of the intense fishing, and consequently a
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