Can stocking with advanced European grayling fry strengthen its populations in the wild?
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Date
2024
Journal Title
Journal ISSN
Volume Title
Publisher
PENSOFT
Abstract
European grayling, Thymallus thymallus (Linnaeus, 1758) (Actinopterygii: Salmoniformes: Salmonidae), represents one of the
highly attractive riverine fishing species in Europe. Its populations have declined in the Czech Republic due to various adverse
factors. Current approaches for strengthening these populations based on restocking with artificially reared 1+ or 2+ old individuals
have proven to be ineffective. This study focuses on the possibilities of supporting or restoring these populations by reintroducing
two-month-old, fast-growing fry reared in ponds. In June 2021, 5400 advanced fry marked with Alizarin Red (ARS) were introduced
into three free-flowing South Bohemian streams. The recapture rates and biometric data (length and weight) of stocked
grayling were assessed at the release sites as well as further downstream. The first electrofishing monitoring was conducted at the
end of the growing season (October) and after their first winter (March). Water temperature and flow rate at the stocking sites were
monitored throughout the growing season. The substantial number of recaptured individuals across all monitored sites suggests
that the fry successfully adapted to their new habitat and significantly contributed to the composition of local fish communities.
Downstream movement of stocked fry correlated with lower water temperatures and higher flows. Our findings demonstrate that
some introduced individuals successfully overwintered at all three reintroduction sites. Marking with ARS has proven to be a very
effective non-invasive method of group marking juvenile fish and is suitable for monitoring stocking programs. The production
and stocking of fast-growing advanced fry of European grayling is thus a promising strategy for revitalizing and strengthening the
populations of this threatened fish in running waters.
Description
Keywords
adaptability of stocked fish, ARS marking, grayling stocks production, natural discharge,, restocking grayling