Improved fish detection in data from split-beam sonar

Hydroacoustic split-beam techniques have been applied to enumerate salmon migrating in the river Tana (northern Norway) during the summers 1998 and 1999. Analysing data by single echo detection and tracking was difficult. Missing echoes in tracks from fish, combined with noise in the output from the single echo detector was seen as reasons for this. An improved counting method is presented. Contours from moving targets are detected by image analysis. Then, detected single echoes within these contours are combined into tracks. This procedure reduces problems related to noise, and to tracking fish with few accepted single echoes

Target strength of tiny roach

Seven frozen specimens of surface-adapted roach (Rutilus rutilus), of lengths 32-40 mm and masses 0.20-0.49 g, have been sectioned with a precision microtome. The swimbladder contours have been digitized and the swimbladder volumes determined. For ordinary ultrasonic frequencies the wavelength is much longer than the particular characteristic swimbladder dimensions. However, it is shorter than the wavelength at resonance. The sound scattering is computed according to a resonant swimbladder model

Hydroakustisk overvåkning og styring av lakseproduksjon

Efficient and "clean" cage-rearing of Atlantic salmon requires good monitoring- and controlroutines. Fullscale tests of a the combined monitoring and feeding system "CageEye", indicated that active use of the system will reduce food waste (incl. antibiotics). Automatic demand-feeding, based on hydroacoustic measurements of the feeding response, worked well both in very large (12000 m3) and small cages (125 m3 and is thus widely applicable. "CageEye" was also found to be very useful for routine monitoring of fish behaviour, especially in deep cages. For example, die1 and seasonal rhythms in swimming depth related to changes in temperature and light was recorded in a l5 m deep cage holding up to 100 tons of fish. Automatic logging of sea temperature (five depths), wildfish- and theftalarm. as well as remote monitioring have been implemented during the project period. NORSK SAMMENDRAG:Effektiv og miljøvennlig merdproduksjon av laks krever gode overvåknings- og kontrollrutiner. Utprøving av det kombinerte overvåknings- og fôringsystemet "Merdøye" indikerte at aktiv bruk av systemet i komrnersiellt oppdrett reduserer sjansen for forspill (og spill av antibiotika). Systemets automatiske appetiforing, basert på hydroakustisk kvantifisering av laksens beiterespons, fungerte både i spesielt store (12 000 m3) og små (125 m3 merder og har dermed et bredt anvendelsesområde. Systemet er videre spesielt nyttig for generell overvåkning av fisken i store og dype enheter. Ved overvåkning av 18-70 tonn laks i stormerd ble det for eksempel registrert døgn- og årstidsvariasjoner i svømmedyp relatert til endringer i lys og temperatur. Informasjon om fiskens atferd kan lagres som døgnfiler og systemet logger en rekke produksjonsparametere. I prosjektperioden har det blitt utført en betydelig videreutvikling som har gjort systemet mer brukervennlig og fleksibelt. Systemet er reprogrammert fka DOS til WINDOWS for blant annet å kunne styre seniralfôringsanlegg på en effektiv måte. Videre er det implementert automatisk temperaturlogging (fem dyp), tyveri- og villfiskalarm, samt mulighet til fjernovervåkning via telefonlinje (modem)

Lake Päijänne Symposium

Lake Päijänne Symposium. Jyväskylä (Finland), March 19-20, 1987. The first Symposium on Lake Päijänne was arranged during the 150th anniversary of the City of Jyväskylä and its protector was Mr. Matti Ahde, Minister for the Environment. The meeting was arranged by the Departments of Biology and Chemistry and by the Institute for Environmental Research at the University of Jyväskylä. Financial support for the arrangements was received from the Academy of Finland, University of Jyvaskyla, City of Jyväskylä, Merck Ltd., Millipore and the Savings Bank of Central Finland. About 120 persons participated in the symposium, and the program consisted of 26 lectures and 9 posters. Most of the original papers have been collected in this publication