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The critical‐period concept for juvenile survival and its relevance for population regulation in young sea trout, Salmo trutta
Author(s) -
Elliott J. M.
Publication year - 1989
Publication title -
journal of fish biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.672
H-Index - 115
eISSN - 1095-8649
pISSN - 0022-1112
DOI - 10.1111/j.1095-8649.1989.tb03049.x
Subject(s) - salmo , biology , brown trout , trout , juvenile , fishery , population , zoology , population density , estuary , ecology , fish <actinopterygii> , demography , sociology
An example of density‐dependent regulation is provided by a long‐term investigation (1966‐present) of a population of migratory trout (estuarine and sea trout), Salmo trutta L., in a Lake District stream. Evidence for the concept of a critical period for the survival of young fish is briefly reviewed and found to be rather equivocal. The concept is, however, relevant to the trout population. Loss rates were high before but low after a critical survival time ( t c days after fry emergence) that varied between year‐classes (range 33‐70 days) and was inversely density‐dependent on egg density. Survivor density and loss rates were strongly density‐dependent on egg density before t c , but proportionate survival with stable loss‐rates occurred after t c . Some trout established feeding territories soon after emergence and the number of fish without territories decreased from a high initial value to a negligible value at t c . Fish size at t c was not constant but increased as t c increased. The range of t c for the different year‐classes was similar to that for survival times of unfed fry in the laboratory. A new stock‐recruitment model, incorporating t c , has been developed for the trout population and shown to be related to the model (Ricker curve) used in the long‐term study. The critical time can also be regarded as the critical age for survival in young trout; this concept may be relevant to other fish species.