Population characteristics of the narrow-clawed crayfish (Astacus leptodactylus Eschscholtz, 1823) in the Treće jezero of the Maksimir Park

Uskoškari rak (Astacus leptodactylus Eschscholtz, 1823) pripada porodici Astacidae te je autohtona europska slatkovodna vrsta koja naseljava stajaćice i spore vodotoke. Cilj ovog rada je opisati populacijske značajke uskoškarog raka u Trećem jezeru parka Maksimir u kojem je prisutnost ove vrste preliminarno zabilježena kao i utvrditi postoje li razlike morfometrijskih značajki, kondicije, udjela ozljeda i faza životnog ciklusa između spolova, te između veličinskih klasa. Uzorkovanje je provedeno od 7. - 16. lipnja 2016., vršama i ručnim lovom. Ulovljena su 153 raka, određen je spol, izmjereno do 25 morfometrijskih značajki po jedinki, zabilježene su vidljive ozljede, fiziološka faza godišnjeg ciklusa i aktivnost cementnih žlijezda kod ženki. Gustoća populacije određena je CPUE (ulov po jedinici napora) i metodom označavanja i ponovnog ulova. Analizom je dokazana statistički značajna razlika među spolovima u 8 morfometrijskih značajki, kao i odsustvo statistički značajne razlike u kondiciji i udjelu ozljeda. Temeljem ukupne dužine jedinki populacija uskoškarih rakova podijeljena je u 6 veličinskih klasa. Rezultati analize varijanci morfometrijskih značajki pokazali su da se mužjaci značajno razlikuju u svim mjerenim parametrima između klasa, a ženke se razlikuju u svima osim u širine areole. Nije zabilježena značajna razlika u kondiciji među klasama, ali je zabilježena u udjelu ozljeda (veće jedinke imaju veći udio ozljeda od manjih). Relativna gustoća populacije za istraživanu lokaciju CPUE metodom je 0,10 jedinki/vrši/noći, odnosno, 15,61 jedinki/osobi/h (23 jedinke/m2). Brojnost populacije je procijenjena na 2303 jedinke Schnabel metodom i 2279 jedinki Schumacher - Eschmeyer metodom. Istraživanjem je pokazano da je populacija uskoškarog raka Trećeg jezera velika, stabilna i vijabilna, te pod pritiskom predatora. Kako uskoškari rakovi imaju karakteristike invazivne vrste, potrebno je nastaviti pratiti populacijske značajke ove vrste na području parka Maksimir te pokušati spriječiti njeno širenje.Narrow-clawed crayfish (Astacus leptodactylus Eschscholtz, 1823) within the family Astacidae is a native European species that inhabits lakes and slow streams. The objective of this study is to examine population characteristics of narrow-clawed crayfish in Treće jezero of park Maksimir where its presence has been preliminary recorded as well as determine if there are differences in morphometric characteristics, condition, injury percentage and life cycle phases between sexes and between size classes. Sampling took place from 7th till 16th of June 2016, by both traps and hand. 153 crayfish were caught, their sex was determined, 25 morphometric characteristics per unit were measured, visible injuries, life cycle phases and cement gland activity (in females) were recorded. Population density was determined with CPUE (catch per unit effort) and mark - recapture method. Analysis has shown significant difference in 8 morphometric characteristics between sexes, and its lack in condition and injury percentage. Population of narrowed-clawed crayfish was divided into 6 size classes. Results of variance analysis of morphometric characteristics showed that males siginificantly differ in all parameters between classes while females differ in all, except in areolal width. There was no significant difference in condition between classes, but it was recorded in injury percentage (larger individuals have more injuries than smaller ones). Relative population density for investigated location using CPUE is 0.10 units/trap/night and 15.61 units/person/hour (23 units/m2). Population size was estimated by Schnabel (2303 units) and Schumacher - Eschmeyer (2279 units) method. The study has shown that narrow-clawed crayfish of Treće jezero make a large, stable and viable population under predator pressure. Since narrow-clawed crayfish have characteristics of invasive species, it is necessary to continue monitoring population characteristics of this species in the area of park Maksimir and try to prevent it from spreading