OBSERVATIONS OF THE SIGNAL CRAYFISH PACIFASTACUS LENIUSCULUS (DANA) IN A LAKE IN THE EASTERN SUWAŁKI LAKE DISTRICT
Tadeusz Krzywosz, Wanda Krzywosz
The Stanisław Sakowicz Inland Fisheries Institute in Olsztyn, Poland
ABSTRACT. The aim of the study was to identify the characteristics of a population of signal crayfish Pacifastacus leniusculus (Dana) which were introduced into the lake eleven years ago. In 1992, 1,100 one-year-old signal crayfish specimens were released into the lake. The lake has a surface area of 57.6 ha, an average depth of 5.9 m and a maximum depth of 15.4 m and is currently in a moderately advanced trophic state. The lake was inhabited by numerous populations of the noble crayfish Astacus astacus (L.) until 1988 when they were poisoned. The catch rate statistics of crayfish fishermen have indicated that the growth in the signal crayfish populations has been progressive since 1996. In 1998, the sixth year they inhabited the lake, the size of the catch population, which occurred in that and in following years, was formed. Specimens measuring from 11 to 14 cm dominated in this population, while only a very few crayfish specimens reached a length of approximately 16 cm. As the crayfish specimens increased in body length, the male body weight predominance over female body weight also increased. While for specimens 10 cm long this figure was as high as 17.5%, for 16 cm long specimens it peaked at 33.6%. Noble and narrow-clawed crayfish have also been observed in control catches since 1999. The signal crayfish had similar weights at the same body lengths to those of the noble and narrow-clawed crayfish Astacus leptodactylus Esch. and were heavier than the spiny-cheek crayfish Orconectes limosus (Raf.). The signal crayfish reproduce in late September and early October, which is at least two weeks earlier than indigenous crayfish.
Key words: SIGNAL CRAYFISH (PACIFASTACUS LENIUSCULUS), INTRODUCTION, GROWTH, AGE, SEXUAL DIMORPHISM
Tadeusz Krzywosz, Instytut Rybactwa Śródlądowego, Zakład Rybactwa Jeziorowego, ul. Rajska 2, 11-500 Giżycko, Tel./Fax: + 48 87 4283881; e-mail: firstname.lastname@example.org