The changes in growth processes of the European grayling from the Timan stream in conditions of non-controlled exploitation
E.I. Boznak, A.B. Zakharov
Section: Population ecology
The work deals with the retrospective analysis of linear growth dynamics for the European grayling in one of the Middle Timan streams (the Vym River, the Northern Dvina basin) under continuous unsustainable exploitation. The European grayling grows relatively fast indicating favorable environmental conditions. In contrast with the data of 1970-1990-ies, the specimens from generations formed in unsustainable fishing years (born in 2003-2012) increase in the segmented body length value (by 15%), absolute increments (by 19%), and specific growth rate (on the second-fourth living year – by 12%). Then, the grow rate slows down. The following five years do not much differ by the considered parameters. The growth slowdown seems to be related to the active commercial catching of quickly-growing fish specimens as they early reach the right size. The accelerated growth processes are accompanied by accelerated sexual development. The grayling normally becomes mature on the fifth-sixth living year (in 1980-1990-ies). From the early 2000-s, we regularly face sexually mature four-year-old (3+) specimens. There are no true correlation between mean annual temperatures and body length of five-to-seven-year-old specimens. The food resources of grayling also hold stable. Thus, the continuous over-exploitation of fish population results in visible changes in population parameters (population decrease, age structure degradation) and invisible aftereffects (growth and sexual maturation acceleration).
Keywords: the European grayling, linear growth, sexual maturation, non-commercial fishing, over-exploitation