Merkingar og heimtur urriða í Grenlæk á árunum 1995 –2003

Ágrip

Hér er greint frá merkingum á urriða á vatnasvæði Grenlækjar sem er hluti af sjóbirtingsrannsóknum á vatnasvæði Grenlækjar sem hófust árið 1995. Á árunum 1995 – 2003 voru merktir 1.345 sjóbirtingar og 206 staðbundnir urriðar. Alls voru 1.195 sjóbirtingar merktir að vorlagi fyrir sjógöngu. Langflestir urriðanna voru veiddir í Fitjarflóði á veiðisvæði 4. Sjóbirtingarnir voru 29 – 80 cm langir og staðbundnu urriðarnir 19 – 68 cm. Aldur sjóbirtinganna við merkingu var 3 – 11 ára og staðbundinna urriða var 4 – 10 ár. Mikill meirihluti sjóbirtinga 50 cm og stærri bar merki um fyrri kynþroska í hreistri, eða 72,8%. Í veiði í Grenlæk heimtust 273 sjóbirtingar (20,3%). Heimtur í veiði minnkuðu eftir 1999. Sjötíu og fjórir (27,1%) heimtust í vorveiði og 195 (71,4%) í haustveiði. Sjóbirtingurinn sýndi góða ratvísi, 90,8% heimtust aftur á vatnasvæði Grenlækjar. Af sjóbirtingum sem gengið höfðu í sjó milli merkinga og heimta komu 25 (8,8%) fram í öðrum ám og einn heimtist í sjó, í Hornafjarðarósi. Allir fiskar sem heimtust í fersku vatni komu fram í nálægum ám, flestir á vatnasvæði Skaftár. Af þeim fiskum sem heimtust utan vatnasvæðis Grenlækjar voru flestir minni en 50 cm við merkingu. Innan vatnasvæðis Grenlækjar heimtust flestir í haustveiði á svæði 6 (29,8%) og á svæði 4 (26,5%) flestir að vori. Meðallengdarvöxtur á sumri í sjó var breytilegur milli ára eða frá 2,6 – 7,8 cm. Vöxtur dróst saman eftir því sem vaxtarsumrin í sjó voru fleiri. Reiknuð árleg meðaldánartala frá fyrsta til sjötta sumri í sjó var 66%. Af staðbundnum urriðum heimtust 27,2% og hjá þeim kom fram 3,69 cm meðalársvöxtur.

Abstract

Trout tagging in the R. Grenlækur watershed was a part of the sea trout research in the R. Grenlækur watershed that began in 1995. During the years 1995 – 2003, 1.345 sea trout and 206 resident brown trout were tagged. 1.195 sea trout were tagged in the spring before sea migration. By far the most trout were caught in the Fitjarflóð in fishing area 4. The sea trout were 29 – 80 cm long and the resident trout 19 – 68 cm. The age of the sea trout at tagging was 3 – 11 years and the resident trout was 4 – 10 years. The vast majority of sea trout 50 cm and larger showed signs of sexual maturity in their scales, or 72.8%. In angling in R. Grenlækur, 273 sea trout (20.3%) were caught. Recaptures in angling decreased after 1999. Seventy-four (27.1%) were caught in the spring fishery and 195 (71.4%) in the autumn fishery. The sea trout showed low straying rate to other rivers. Of the sea trout that had migrated to sea between tagging and catching (8.8%) were caught in other rivers and one in the sea at Hornafjarðarós, 90.8% were recaptured in the R. Grenlækur watershed. All recaptures in fresh water were in nearby rivers, most of them in the R. Skaftár watershed. The bulk of recaptures outside the R. Grenlækur watershed were smaller than 50 cm at tagging. Within the Grenlækur watershed, most were caught in the autumn fishery in area 6 (29.8%) and in area 4 (26.5%) mostly in the spring. Average growth during the summer in the sea was from 2.6 – 7.8 cm. Growth rate decreased with the number of growing seasons in the sea. The calculated instantaneous death rate from the first to the sixth summer at sea was 66%. Of the resident trout, 27.2% were harvested and their average annual growth was 3.69 cm.