CO-OCCURRENCE OF THE SIGNAL CRAYFISH (PACIFASTACUS LENIUSCULUS (DANA)) AND THE SPINY-CHEEK CRAYFISH (ORCONECTES LIMOSUS (RAF.)) IN A FOOTHILL-LIKE RIVER (NORTHERN POLAND)
Department of Lake Fisheries, The Stanisław Sakowicz Inland Fisheries Institute in Olsztyn, Poland
ABSTRACT. The aim of the study was to determine the current state of the crayfish in a foothill-like river, Naryjska Struga, in northern Poland, where the noble crayfish, Astacus astacus L., occurred until the 1950s. The spiny-cheek crayfish, Orconectes limosus (Raf.), was noted to inhabit the Naryjska Struga River in the 1960s, while the signal crayfish, Pacifastacus leniusculus (Dana), escaped into the river from a nearby cultivation facility in the 1979-1981 period. The Naryjska Struga River connects two lakes that to date remain inhabited by the spiny-cheek crayfish. The signal crayfish was discovered to inhabit the river in 2000. During the period from 2002 to 2005, annual crayfish observations were conducted along the entire length of the river, and Evo traps were used to make monitoring catches on an approximately 500-m length of the river. The effectiveness of monitoring catches, measured as the quantity of specimens caught trap-1 night-1 in each year of the study ranged from 1.58 to 6.18 and was dependent on the intensity of previous poaching. The share of signal crayfish in the monitoring catches in each of the study years ranged from 98.8 to 100.0%. The remaining share was comprised of the spiny-cheek crayfish. During the study period, the male specimens of the signal crayfish game population had a total length range of 7.2 to 12.3 cm, (average of 9.86 ± 0.98 cm) at a weight range of 12.6 to 83.5 g (average of 39.3 ± 14.0 g). The length of the female specimens ranged from 7.1 to 12.2 cm (average of 9.71 ± 0.96 cm) at a weight range of 11.2 to 57.8 g (average 29.9 ± 8.6 g). Specimens longer than 9.0 cm comprised 83.2% of the sample caught. The habitat conditions in Naryjska Struga River proved to be advantageous for the signal crayfish, and this species limited the previously-occurring spiny-cheek crayfish to a 1.2% share of the entire crayfish game population in the river.
Key words: SIGNAL CRAYFISH (PACIFASTACUS LENIUSCULUS), SPINY-CHEEK (ORCONECTES LIMOSUS), COMPETITION, TRAP CATCHES
Dr hab. Tadeusz Krzywosz, Instytut Rybactwa Śródlądowego w Olsztynie, Zakład Rybactwa Jeziorowego, ul. Rajska 2, 11-500 Giżycko; Tel./Fax: +48 87 4283882;