UTJECAJ PTICA MOČVARICA NA PROIZVODNJU RIBA U RIBNJAČARSTVU "JELAS"

• Main Author: Šetina, Mirko; Agrokombinat "Jasinje" Slavonski brod
• Format: Text
• Language: Croatian
• Published: Faculty of Agriculture, University of Zagreb 1990
• Subjects: ptice močvarice; proizvodnja riba; ribnjačarstvo "Jelas"; wetland birds; fish production; fish farm "Jelas"; Common tern; Sterna hirundo; Black-headed Gull; Larus ridibundus
• Online Access: http://hrcak.srce.hr/77124; http://hrcak.srce.hr/file/114470

Ribnjačarstvo »Jelas« s 2305 ha vodenih površina, od čega je 12% obraslo trskom i rogozom (Phragmites sp. i Typha sp.) mnogim vrstama ptica močvarica u vrijeme seobe pruža vrlo povoljne uvjete za gnježđenje, prehranu i odmor. Neke su od tih vrsta gotovo potpuno ili u većoj mjeri ihtiofagi, t j . hrane se ponajviše ribom i tako štete ribljoj proizvodnji u ovom ribnjačarstvu. U pokušaju da se utvrdi stupanj utjecaja spomenutih vrsta riba na riblju proizvodnju odabrali smo za istraživanje deset vrsta ihtiofagnih ptica, i to: Ćubasti gnjurac Podiceps cristatus (L.) Veliki vranac Phalacrocorax carbo (L.) Gak Nycticorax nycticorax (L.) Žuta čaplja Ardeola ralloides Scopoli Velika bijela čaplja Egretta alba (L.) Mala bijela čaplja Egretta garzetta (L.) Siva čaplja Ardea cinerea (L.) Čaplja danguba Ardea purpurea (L.) Riječni galeb Larus ridibundus (L.) Obična čigra Sterna hirudno (L.) te samo jednu vrstu iz grupe omnivora i to lisku (Fulica atra /L./). Kriterij za izbor tih deset vrsta ihtiofaga osnivao se na podatku o udjelu ribe u dnevnom obroku i o brojnosti populacije. Na osnovi želučanih sadržaja odraslih i mladih ptica utvrđene su približne količine pojedine ribe za svaku od deset istraživanih vrsta, a na osnovi utvrđene brojnosti svake populacije i dužine zadržavanja na ribnjačarstvu u toku godine utvrđene su ukupne količine pojedine ribe. Istraživanja su provedena od god. 1976. do 1985. Dobiveni rezultati upućuju na podnošljive štete u razdoblju od 1976. do 1980. jer je u to vrijeme broj vrsta koje se gnijezde znatno manji nego u razdoblju od 1980. do 1985. godine, kada se na gniježđenju javljaju nove ihtiofagne vrste, i to s vrlo brojnim populacijama tako da enormno štete rastu. Posebna šteta nije utvrđivana. Mogućnosti zaštite cjelokupnog ribnjačarstva ili pojedinih ribnjaka vrlo su ograničene, a djelomično ili potpuno uništenje pojedinih vrsta ptica ne može biti prikladno rješenje. Mjere moraju biti kompleksne i treba da teže smanjenju broja pojedinih vrsta (posebno onih kojih se populacija povećava), i to upotrebom aktivnih i pasivnih plašila pa sve do naknade za učinjenu štetu. The fish farm »Jelas« with a 2305 ha water expanse, 12% of which is overgrown with reeds and bull-rushes (Phragmites sp. and Typha sp.), offer favourable conditions for nesting, nutrition and rest to many different species of wading birds. Some of these species are either completely or only partially ichthyophagous birds, i.e. they feed either exclusively or only partially on the fish thus, damaging the fish production in the fish ponds. To determine the degree of their influence on the fish production 10 species of ichthyophagous birds were investigated: Great Crested Grebe Podiceps cristatus (L.) Cormorant Phalacrocorax carbo (L.) Night Heron Nycticorax nycticorax (L.) Squacco Heron Egretta alba (L.) Great White Egret Ardeol aralloides (Scopoli) Little Egret Egretta garzetta (L.) Grey Heron Ardea cinerea (L.) Purple Heron Ardea purpurea (L.) Black-headed Gull Larus ridibundus (L.) Common Tern Sterna hirundo (L.) Only one species of herbivorous birds, the Coot (Fulica atra), was investigated of the 13 species which feed on fish from fish ponds. The decisive criterion for chosing these 10 species was their participation in their daily portion of food and the size of the population. Based on the gizzard contents of both the grown-up and the young birds the approximate quantity of the consumed fish was determined for each of the investigated species, while the approximate total quantity of the consumed fish was determined according to the recorder number of each population and the duration of its sojourn at the fish ponds. The investigations were Carried from 1976-1985. The obtained results show that damage was tolerable in the interval from 1976-1980 because the number of nesting species was then considerably smaller than in 1985 when some new ichthyophagous species were observed to nest at the fish ponds in very numerous populations, causing a great increase of damage. Indirect damage has not been investigated. Possibilities are very limited for the protection of either the complete area of the fish ponds or separate ponds. On the other hand, partial or total extinction of a single species will not give adequate solution. The meausres have to be complex and should include a decrease in the number of single species (particularly those in expansion like the cormorant), use of both active and passive scarecrows and damage compensation for the overpopulated but endangered species.