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A Study of the Mortality, Population Numbers, Year Class Strengths, Production and Food Consumption of Pike, Esox lucius L., in Windermere from 1944 to 1962

Charlotte Kipling and Winifred E. Frost
Journal of Animal Ecology
Vol. 39, No. 1 (Feb., 1970), pp. 115-157
DOI: 10.2307/2892
Stable URL: http://www.jstor.org/stable/2892
Page Count: 43
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
A Study of the Mortality, Population Numbers, Year Class Strengths, Production and Food Consumption of Pike, Esox lucius L., in Windermere from 1944 to 1962
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Abstract

(1) Pike have been caught in fine flax gill nets (mesh 6.4 cm, bar) each winter from 1944-45 to 1964-65. The total catch was 7751 pike, in 1944-45 756 were caught, and from 1945-46 to 1964-65 the average annual catch was 350. The age and growth of all pike were determined. (2) Pike were tagged every year from 1949 to 1965. At first tags were attached to the opercular bones, but this method proved unsatisfactory, so from 1953 all tags were attached to the jaw. Up to 70% of tagged pike were recaptured, mostly by gill nets and anglers. (3) Natural instantaneous mortality rates in the third year of life were estimated from recaptured tagged fish as 0.42 (both sexes), and in the fourth and subsequent years as 0.30 for females and 0.35 for males from age frequencies of pike caught in 1944-45. (4) Instantaneous mortality rates in the south basin due to gill netting varied from 0.24 to 0.45 in the years 1954-64 (ignoring the years of reduced nettings) as estimated from recaptured tagged fish. (5) Anglers caught from 2 to 23% of the pike tagged from perch traps and gill nets in the years 1949-62. (6) The total instantaneous mortality rate of females in the south basin was estimated from gill net catches to be 0.75 (53% per annum). In the north basin the mortality was 4% higher than in the south basin, and male mortality was 3% higher than female. (7) In 1944 the estimated population of adult pike in Windermere was 2300 fish. The virtual population (i.e. those fish which were in the lake in 1944 and were subsequently caught) was 1343 fish. The maximum estimated population of adult pike was 4600 and the minimum 1400. (8) In 1944 there were almost equal numbers of pike in the north and south basins, and almost equal numbers of males and females. (9) The largest year class was five times as numerous as the smallest. (10) From 1944 to 1965 the proportion of male pike caught in gill nets has varied from 49 to 64% of the total catch. These variations are associated with the selective action of the gill nets, and differences from year to year in year class strengths and growth, and the slower growth of male pike. (11) Pike inhabit the shallow water and in Windermere there are 550 ha of depth 10 m and less. In 1944 the population density of adult pike in this area was 8.4 kg/ha and 4.2 fish/ha. From 1945 to 1962 the maximum density was 9.5 kg/ha and 8.3 fish/ha and the minimum 3.6 kg/ha and 2.5 fish/ha. (12) Total production of adult pike was estimated as 2.2 metric tons in 1944-45. From 1945-46 to 1962-63 the maximum was 3.7 metric tons and minimum 1.3 metric tons. (13) The biomass of adult pike was estimated as 4.6 metric tons in 1944, from 1945 to 1962 the maximum was 5.2 metric tons, minimum 2.0 metric tons. (14) Total food consumption of adult pike was estimated as 10.9 metric tons in 1944-45. From 1945-46 to 1962-63 the maximum was 14.7 metric tons, minimum 6.1 metric tons. (15) In the first year of life mean production was estimated as 3.2 metric tons, and food consumption as 8.7 metric tons. (16) In the second year of life maximum production of year classes 1942-62 was 6.7 metric tons and minimum 1.0 metric tons. Maximum food consumption was 20.0 metric tons and minimum 3.0 metric tons. (17) Production and food consumption in the first 2 years of life formed respectively 72 and 63% of the totals estimated for the 1951 year class. (18) Year class strengths of pike hatched from 1944 to 1962 were very significantly correlated with temperature conditions in the first year of life, and significantly correlated with first year growth. They were not significantly correlated with either the numbers or biomass of the parent stock. (19) Correlations of year class strengths against temperatures in the separate months were very significant in September and October, significant in July and August, and not significant in May and June. (20) From laboratory experiments, which were carried out to find possible causes of mortality in eggs and alevins, it was found that contact with sand or silt did not kill the eggs. In the first feeding stage (lengths from 11 to 24 mm) mortality and growth were related to amounts of zooplankton provided. Cannibalism occurred among fry. (21) Variations in year class strengths (which were greatly influenced by temperature) were found to be very important in determining the amount of production and food consumption.

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