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Population dynamics of perch, Perca fluviatilis L. in Slapton Ley, Devon
Author(s) -
CRAIG J. F.
Publication year - 1974
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/j.1365-2427.1974.tb00107.x
Subject(s) - perch , biology , homogeneous , zoology , population , fish <actinopterygii> , body weight , ecology , fishery , demography , mathematics , combinatorics , sociology , endocrinology
Summary The age of perch. Perca fluviatilis L. was determined from the annual bands laid down on the opercular bone. Year class monthly mean lengths were based on this ageing. The opercular bones have also been used for back‐calculating growth. It was found that back‐calculated mean lengths per age were similar to those calculated by direct measurement. There was little difference in growth between the sexes for the first 2 or 3 years of life. The investigation was too short for a correlation to be found between growth increments and degree days above 14°C although Slapton Ley was found to be warm in comparison to other British waters and the perch grew fast. Ford‐Walford plots gave L ∞ = 22.0 cm for males and L ∞ = 25.0 cm for females. In length‐weight relationships, fry and immature females were homogeneous between their monthly subgroups, and fry obeyed the cube law throughout. Mature males and females were heterogeneous between monthly subgroups. Growth has been expressed in weight form and instantaneous growth rates are given. These rates are higher for fry than older fish. Condition was closely related to gonad development in mature fish. Condition fell sharply after spawning and then rose rapidly in May and June. A sudden drop in condition was noted in males during August which cannot be fully explained.