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Egg stocking in rivers and streams is a common measure to support and re-introduce salmonid populations. To ensure the success of egg stocking programs, knowledge of the early life stages of juveniles including dispersal ability and habitat preferences of fry is a prerequisite. This study was conducted to investigate downstream dispersal patterns and habitat use of young of the year brown trout in a mid-sized, channelized, boreal river in Sweden. Eyed trout eggs were stocked in February of 2021. During August of the same year, 2-3 months after emergence, trout were sampled by electrofishing within 1 km downstream of the stocking sites and each individual point of capture was recorded by GPS. In addition, data on riverbank slope, shoreline irregularity, stream bed substrate, water velocity and water depth were collected for each of the sampling sections. The results showed that trout fry were distributed throughout the 1 km long sampled sections and that the density of fry did not increase towards the stocking points. The observed variation in the distribution of trout fry was best explained by the riverbank slope. Approximately twice as high fry densities were found in reaches with gentle compared to medium and steep bank slopes. The differences are suggested to be an effect of 1) stream marginal water velocity differences during high flows affecting fry occupancy, and 2) that gentle slopes were often accompanied by shallow water, preferred by fry. These findings may provide helpful knowledge for fisheries managers to optimize the outcome of egg stocking and river restoration activities regarding fry recruitment. Romutsättning i vattendrag är en vanlig åtgärd för att stärka och återetablera populationer av laxartade fiskar. För att lyckas med romutsättningar krävs kunskap om ynglens spridningsförmåga och habitatpreferenser. Denna studie genomfördes för att undersöka spridningsmönster och habitatval av ensomrig öring i en medelstor kanaliserad älv i Sverige. Ögonpunktad rom sattes ut i februari 2021. Under augusti samma år, 2-3 månader efter att ynglen lämnat lekgruset elfiskades 1 km långa sträckor direkt nedströms utsättningsplatserna. De fångade individernas position registrerades med GPS. Data över strandkantens lutning, strandzonens flikighet, bottensubstrat, vattenhastighet och djup samlades in för varje elfiskesträcka. Resultatet visade att öringyngel spridit sig över hela de 1 km långa elfiskesträckorna, och att tätheterna av yngel inte ökade med minskat avstånd till utsättningspunkterna. Den observerade variationen i fördelningen av öringyngel förklarades bäst av strandkantens lutning. Ungefär dubbelt så hög täthet av yngel förekom i sträckor med flack jämfört med medel och brant lutning. Skillnaderna föreslås vara en effekt av 1) skillnader i vattenhastighet under höga vattenflöden som påverkar ynglens möjligheter till att bibehålla sin position i habitatet, och 2) att flack lutning av strandkanten ofta åtföljdes av grunt vatten vilket föredras av yngel. Dessa upptäckter kan bidra med värdefull kunskap för att optimera romutsättningar och restaureringar i avseende på rekrytering av årsyngel.

Kysttorsk er en viktig ressurs i Norge av høy kommersiell- og rekreasjonell verdi. De siste tiårene har flere populasjoner av kysttorsk hatt en drastisk nedgang i forekomst, men årsaken til dette er usikkert. For å beskytte kysttorsken for ytterligere populasjonsnedgang, er det nødvengig å forstå dens behov gjennom ulike stadier av dens livssyklus. Formålet med denne oppgaven var å undersøke yngelfasen (< 26,5 cm) til kysttorsken og se hvilke bunnforhold den forekommer i, slik at en kan beskytte viktige oppvekstområder. Feltundersøkelser ble gjennomført i perioden etter bunnslåing av fjorårets yngel, i august-september 2020, og foregikk både langs kysten ved Frøya og i indre deler av Trondheimsfjorden ved Verdal. Bunnforhold hvor torskeyngel ble funnet ble undersøkt med hensyn på type bunn, tilstedeværelse av alger og ålegress, i tillegg til fysiokjemiske faktorer (dybde, bølgeeksponering, temperatur, salinitet, turbiditet og pH). Innsamlingen ble utført ved hjelp av undervannsvideo, leppefiskteiner og minisnurrevad, og målinger av vannkvaliteten ble undersøkt med CTD, secchiskive og pH-måler. Bølgeeksponering ble modellert. Totalt 822 torskeyngel ble registrert, hvor det ble funnet signifikant flere yngel i indre fjord ved Verdal. Signifikante mengder torskeyngel oppholdt seg her på åpen sandbunn, mens sandbunn i tilknytning til vegetasjon forekom oftere på Frøya. For ålegress, ble det påvist signifikante funn på at det ikke utgjør et viktig oppvekstområde i Verdal. Disse funnene gjelder dog kun for aktivitet på dagtid, ettersom det ikke ble foretatt egne målinger på natten, og det kan dermed ikke utelukkes at ålegress har en viktigere rolle på nattestid. Martaum ble funnet å ha en signifikant positiv effekt på yngelforekomsten, og det kan dermed spekuleres i om den utgjør et godt gjemmested for predatorer i strandsonen i en kort tid på året, ettersom den kan bli veldig lang på kort tid og ofte dekker store deler av overflaten på grunne steder. Av de fysiokjemiske variablene målt, var det grad av bølgeeksponering som hadde stor signifikant påvirkning på forekomsten av yngel, hvor yngelen ser ut til å oppsøke steder med lav eksponering. Dette gir mening i lys av størrelse på yngelen og mengde bølgebevegelse i vannet, hvor yngelen lettere og mer energibesparende kan manøvrere seg frem. Det ble funnet høyest forekomst av yngel i fjorden, men det kan derimot ikke antas at dette gjelder i alle fjorder ettersom enhver fjord er unik. Fjorder med god rekruttering av egg og larver, som også er utsatt for antropogene påvirkninger, burde overvåkes for å unngå at vannkvaliteten når verdier som påfører yngelen stress utover dens toleransegrense. På denne måten kan en sørge for at tidlige livsstadier av kysttorsk får gode muligheter til å vokse opp, og dermed sørge for videre rekruttering av den nedgående bestanden.

Gäddan (Esox lucius) är en toppredator och nyckelart som är beroende av grunda och vegetationsrika rekryteringsmiljöer. Dessa miljöer hyser risk att minska i sjöar med mänsklig påverkan, vilket i sin tur skulle kunna leda till lägre överlevnad hos gäddlarver och yngel till följd av intraspecifik konkurrens av föda. Under två veckors tid undersöktes överlevnaden hos gäddyngel (< 30 mm, medellängd = 20 mm) i relation till täthet, för tätheter mellan 2-20 individer/m2, fördelat i 10 burar placerade i en naturlig uppväxtmiljö. Jag fann ett signifikant negativt samband mellan täthet och överlevnad i burarna, där en ökad täthet miskade överlevnaden av gäddyngel. Täthetsberoende tillväxt kunde inte konstateras hos gäddynglen, men de två längsta individerna och individerna med högst individuell tillväxt återfanns vid högst- respektive näst högst initial täthet. Mina resultat stöder hypotesen att överlevnaden är täthetsberoende för gäddlarver i en naturlig rekryteringsmiljö, och bidrar med kunskap att ta hänsyn till vid förvaltning av gäddpopulationer. Pike (Esox lucius) is a top predator keystone species dependent on shallow, vegetated areas for recruitment. These types of habitats stand at risk of reduction in human impacted lakes, which in turn could lead to lower survival of pike fry and -larvae due to intraspecific competition for food. During a time period of two weeks, the survival of pike fry (< 30 mm, mean length = 20 mm) was studied in relation to fry densities between 2-20 pike/m2, in 10 enclosures placed in a natural nursery habitat. I found that survival of pike-fry within the enclosures was significantly negatively correlated to initial stocking density, where an increase in density led to lower survival of pike fry. No evidence of density dependence was found for growth of pike fry, although the two longest fry and fry with the highest individual length increase were found at the highest- and second highest initial densities. The results support my hypothesis that the survival of pike fry is density dependent in a natural nursery habitat, and provides further knowledge for consideration in population management of pike.

Pregnant eelpout were exposed via the water to known endocrine disrupting compounds (EDCs) to clarify if EDCs could be causing the increased eelpout fry malformation frequencies observed in coastal areas receiving high anthropogenic input. The presence of a teratogenic window for estrogen-induced malformations was also investigated by starting the exposure at different times during eelpout pregnancy.Both 17α-ethinylestradiol (EE2) (17.8 ng/L) and pyrene (0.5 μg/L) significantly increased fry malformation frequency whereas 4-t-octylphenol (4-t-OP) up to 14.3 μg/L did not. Vitellogenin was significantly induced by EE2 (5.7 and 17.8 ng/L) but not by 4-t-OP and pyrene. A critical period for estrogen-induced fry malformations was identified and closed between 14 and 22 days post fertilization (dpf). Exposure to 17β-estradiol (E2) between 0 and 14 dpf caused severe malformations and severity increased the closer exposure start was to fertilization, whereas malformations were absent by exposure starting later than 14 dpf. Data on ovarian fluid volume and larval length supported the suggested teratogenic window. Larval mortality also increased when exposure started right after fertilization.

Å forflytte seg mellom biologisk viktige områder er en viktig del av hverdagen til en rekke dyr. Dette krever evnen til å sanse, prosessere og memorere informasjon fra omverdenen, som er fylt med enorme mengder potensielle ledetråder. Skal man på en fest kan man få beskjeden «Ta til høyre ved den store eika, følg lyden og lukten, jeg har bakt boller», en rekke ulike ledetråder som leder fram til moroa. For unglaks som lever i elva er ledetrådene annerledes, og så svømmer de ikke så ofte til fest, men det å finne veien krever det samme; sanse, prosessere og memorere, prosesser som krever kognitive evner. Det er lett å legge merke til morfologiske tilpasninger f.eks. giraffens hals, men naturlig seleksjon har også formet dyrs kognitive evner. I møtet med et komplekst og varierende miljø er romlig læring og fleksibilitet viktige egenskaper. Romlig læring har hos fisk blitt knyttet opp mot en del av forhjernen (Braithwaite, 2006). Det er høye energetiske- kostnader ved å utvikle hjernen, derfor er det grunn til å tro at forstørring kan være en følge av erfaringer. Fisk som ikke blir utsatt for strukturer og får erfaring med det, vil dermed ikke allokere energi til like mye hjerneutvikling. Forhold som fisk erfarer tidlig i livet, kan gi varige endringer i morfologi, livshistorie, adferd og vekstrate (Jonsson and Jonsson, 2014). Når effekten av en viss type erfaringer er spesielt sterk i en periode av hjernens utvikling blir dette kalt sensitive perioder (Knudsen, 2004). I dette studiet har vi undersøkt om strukturell beriking av oppvekstmiljøet ved to ulike tidspunkt har gitt ulike utslag i evnen til romlig læring hos unglaks. To grupper unglaks har blitt eksponert for beriking ved ulike tidspunkt, ved begge tidspunkt ble også en gruppe unglaks fra samme kull holdt i tomt miljø (kontroll). Læring ble testet i en labyrint der ett av kamrene var innredet som et «optimalt habitat», med tilgang på mat og vann i bevegelse. Laks fra ulik bakgrunn ble testet en gang om dagen i 7 dager. Denne metoden avdekket ingen tegn til sensitive perioder, dette skyldes trolig at kammeret som var innredet som «optimalt habitat» ikke var attraktivt for testfisken. Dermed kan forsøkene hverken avkrefte eller bekrefte om det finnes sensitive perioder for romlig læring hos unglaks. Det ble derimot funnet store forskjeller i utforskende adferd for 31 uker gamle unglaks og ikke 18 uker gamle. Testfisk fra møblert bakgrunn startet utforskningen av labyrinten raskere enn individer fra uberiket bakgrunn, forskjellen mellom gruppene økte ut over i uken, noe som tyder på at fisk fra beriket bakgrunn var mer fleksible. Når det er kamp om resursene kan utforskende adferd være avgjørende for overlevelse, det kan føre til at man oppdager nye mulige habitater og kan utvide territoriet. Master i Biologi MAMN-BIO BIO399

I detta examensarbete görs en praktisk undersökning av några utvalda faktorer i habitatet som antas påverka yngel av öring under deras första månader. Studien har genomförts i anslutning till en utsättning av ca 30 000 yngel i Gysingeforsarna vid Nedre Dalälven som Länsstyrelsen i Gävleborg utförde under sommaren 2014 och som sedan under hösten följdes upp med hjälp av elfiske. Fältdata har samlats in från fem lokaler under perioden 29 oktober 2014 till 9 januari 2015. Resultatet från denna kartering och litteraturstudier i ämnet visar på goda förutsättningar i habitatet vid två av lokalerna, vilka även är de två platser där flest yngel återfångades. Vid två andra lokaler återfångades inga yngel. Detta kan för det ena fallet (Sevedskvarn, södra) förklaras med för litet djup under sommarens lågvattenflöde och alltför höga vattenhastigheter vid normalflöde. Den andra platsen där yngel saknades (Granön, ovan bron) erbjuder bättre förutsättningar för predatorer (både fisk och fågel) samt har en bottenstruktur som vid en jämförelse erbjuder färre skyddade platser. En föreslagen hypotes utifrån studiens resultat är att bottensubstrat i storleksintervallet 60-200 mm har stor betydelse i öringynglens habitat vid närvaro av predatorer då där skapas skydd (hålor/springor) i lämplig storlek för öringyngel. The purpose of this project was to examine important parameters for juvenile brown trout habitat selection in their first months after hatching. The study was carried out after approximately 30 000 fry had been released by the County Administrative Board of Gävleborg. Data on habitat selection was collected from five different localities at the river Dalälven, near Gysinge, Sweden. The method of estimating preferred habitat was to determine remaining fry after a period of seven weeks by electrofishing. This study confirms that the optimal local habitat choice for juvenile trout is where the substrate size 60- 200 mm is present and a hypothesis is proposed that this substrate is of importance for juvenile trout survival as it gives shelter in the presence of predators. Based on previous research the study gives some suggestions to which important habitat characteristics that were missing where no trout were recaptured.

Working Document # 7 WKROUND, 9-16 February 2010 NEA saithe 0-group indices from observers along the coast does not seem to reflect the dynamics in year class strength very well and is therefore probably not suitable for improving future recruitment estimates for this stock.

Annual development of density and mean weight of juvenile plaice Pleuronectes platessa was examined at 2 nursery grounds (Port Erin Bay, Isle of Man, Irish Sea and Admucknish Bay, Firth of Lorne, west coast of Scotland) over a number of years. In both cases there was evidence of 'self-thinning' in the populations when the density was high, although in Port Erin Bay the slope suggested a relationship different from the standard - 4 ⁄3 rule proposed for animal populations. The site specific dynamic thinning lines (dynamic carrying capacities) were consistent with the dynamic thinning line (-4⁄3 rule) for both populations. The 2 nursery grounds were different, with growth rates and densities generally higher on the Ardmucknish Bay nursery ground compared with Port Erin Bay. Similarly, the estimated total biomass of plaice was higher in Ardmucknish Bay than Port Erin Bay, but there was considerable inter-annual variation. Maximum plaice biomass generally occurred from August to September for both sites. In Port Erin Bay this coincided with the maximum consump- tion rates. The size structure was described using the Gini coefficient (G) and the timing of size struc- ture development by the centre of gravity (CG). The size structure of the populations differed and in both cases varied during the season in response to settlement and mortality. Over the study periods, population density was only occasionally high enough to reach the site specific self-thinning line. This suggests that these populations rarely approached the carrying capacity of the nursery grounds.

poster

only The growth-mortality hypothesis, where survival during the larval stage is positively related to size, is tested for Norwegian spring spawning herring (Clupea harengus L.). The daily increment width in the otoliths is compared between larvae sampled in May-June along the Norwegian shelf and the surviving population of 0-group juveniles sampled in fjords and inlets along the coast and in the Barents Sea in autumn (August-December). In order to select juveniles from the same cohort as the larvae sampled on the Norwegian shelf (May-June), a numerical model was used to simulate the drift of larvae from the shelf areas to the nursery areas where 0-group juveniles had been sampled. Samples from years with low high recruitment and from different areas are compared. The results are discussed in relation to variations in environmental conditions

only.

Presented at "First international symposium on stock enhancement and sea ranching, Bergen 8-11 September 1997"

The year class strength of Arcto-Norwegian cod (Gadus morhua L.) in the Barents Sea is extremely variable. One of the key indicators for a possible strong year class is water temperature since good year classes may be produced in warm years while they seldom if ever occur in cold years. Water temperature alone is not sufficient to produce a good year class. Thus it is conjectured that when there is a strong flow of Atlantic water from the Norwegian Sea into the Barents Sea it not only warms the water but transports large quantities of zooplankton and hence provides better survival conditions for cod. Survey data from the Barents Sea for the years 1977 through 1984 are examined to determine the relation between zooplankton abundance and the spatial distribution of juvenile cod and to investigate if zooplankton abundance is associated with the flow of Atlantic water. For all years, more zooplankton on average were found in areas with cod than in those without cod. Total zooplankton abundance increased significantly in the Barents Sea concurrently with an increased inflow of Atlantic waters in 1981.

The bycatch of juvenile fish can be a major problem in fisheries with small meshed trawls, such as fisheries for shrimp, (Pandalus borealis). A sorting grid that effectively removes most of the undersized fish has been developed for shrimp trawls and it is not legal to fish for shrimp in the Barents Sea without the use of this sorting grid. Apart from this, the existing catch-regulation of shrimp fishery in the Barents Sea is closing of shrimp fisheries on fishing-grounds, where the bycatch of juvenile fish exceeds the criteria for allowable bycatch in numbers per ton of shrimp set by The Notwegian- Russian Fishery Commission. In this paper a new method for calculation of a criteria for closing shrimp fisheries based on both biological and economic considerations is established. This bio-economic approach is an alternative to the existing biological approach. The main concept in the bio-economic approach is that if the expected future value of the bycatch exceeds the value of the shrimp catches, the shrimp fishery should be closed. In this paper a joint criteria for allowable bycatch is developed and calculated, including all the commercially interesting species, (cod; Gadus morhua, haddock; Melanogrammus aeglefinus, redfish; Sebastes mentella and Greenland halibut; Reinhardtius hippoglossoides) whose juveniles are caught as bycatch in the shrimp fisheries in the Barents Sea.

I syfte att förbättra tillväxt och överlevnad hos framförallt kommersiellt intressanta varmvattenarter släpptes ca 70 m3/s kylvatten från Forsmarks kärnkraftverk ut i grunda, kustnära vattenområden. På så sätt värmdes ett 6—8 km2 stort område upp under april—oktober 1990 och 1991. Övertemperaturen avtog snabbt från utsläppspunkten och i varmvattenartemas huvudsakliga rekryteringsområden uppgick temperaturöverskottet som mest till 4—5 °C under vår och sensommar. I genomsnitt var dock överskottet ett par grader lägre och under juni, juli och fram till mitten av augusti förekom inget överskott. Vattentemperaturen var t om lägre än i opåverkat område vissa perioder under sommaren såsom en effekt av kraftverkets reducerade elproduktion i kombination med förhållandevis låga intagstemperaturer. Negativa effekter av utsläppen i form av grumlingar kunde inte visas, och ökadalgpåväxt förekom endast i ett begränsat område inom ett par hundra meter frånutsläppspunkten. Tillväxtsäsongen hos vattenväxterna var dock förlängd ävenpå någon kilometers avstånd. Abborre var den art som i fråga om tillväxt och överlevnad studerades mest intensivt under första levnadsåret. Hos denna art åstadkoms en tidigare lek som resulterade i en produktionstopp av nykläckta larver ungefär en månad tidigare än i opåverkade områden. Den förbättrade tillväxt som denna förlängning av tillväxtsäsongen borde inneburit reducerades emellertid av avsaknaden av övertemperatur under en stor del av sommaren. Effekten på tillväxten blev dock slutligen positiv, eftersom temperaturöverskottet var relativt stort under sensommar och höst. Abborrynglet blev därmed inom det påverkade området nära dubbelt så stort som inom det opåverkade vid tillväxtsäsongens slut. Eftersom även mörtynglens tillväxt gynnades, kan man anta att de flesta varmvattenarter reagerar likartat. Konsumtionsberäkningar för abborrynglet visade att födointaget var nära maximalt under såväl påverkade som opåverkade förhållanden. Det första året med kylvattenuppvärmning, vilket även naturligt var varmt, uppstod de högsta yngeltätheter av abborre som noterats på 14 år inom experimentområdet. Efterföljande år var däremot ovanligt kallt och borde enligt tidigare erfarenhet lett till mycket låga yngeltätheter. Utsläppens uppvärming åstadkom emellertid normala sådana. Tätheten av karpfiskamas yngel ökade inte på motsvarande sätt. Den definitiva slutsatsen kan man emellertid dra först om några år, då dessa årsklasser rekryterats till den vuxna populationen. Effekterna på kallvattenartemas tillväxt och tätheter kunde inte bedömas. Sikens tidiga utvecklingsstadier tycktes dock ha påverkats negativt av den snabba temperaturhöjningen på vårvintern. Effekterna på de vuxna fiskpopulationema var marginella. Störst effekt kunde noteras på strömming, vilken anlockades till det kylvattenpåverkade området på våren i samband med lek och som under de varmaste perioderna syntes undvika utsläppsområdet i större utsträckning än normalt. För att optimera effekterna av kylvattnet på rekryteringen hos varmvattenarter bör utsläppen i större utsträckning än som här varit fallet ske i direkt anslutning till lämpliga rekryteringsområden. För att minska utdrift av fisklarver bör också strömhastigheten anpassas till de lokala förhållandena. Discharges of cooling water from a nuclear power plant, situated in the SW partof the Gulf of Bothnia, have been used in an attempt to improve recruitment of commercially interesting warm water species. In the experiment about 70 m3/s ofcooling water, normally elevated about 10 °C above ambient, was discharged into shallow water areas from April until October in two consecutive years. This resulted in the warming up of an area of 6—8 km3. There was, however, a sharp temperature decrease from the point of discharge and the temperature increase was much reduced when reaching the actual nursery areas of the warm waterspecies. The highest increase was 4—5 °C during spring and late summer. In general it was a few degrees lower and during June, July up to the middle of August there was no increase at all in these areas. In fact, water temperature was even lower as compared to unaffected areas due to a combination of small temperature increases within the power plant and relatively low temperatures within the intake area. Effects on the turbidity of the water in the affected area could not be documented. Increased algal coverage was shown within some hundred meters from the point of discharge. The length of the growth season was, however, increased for the vegetation submerged at greater distances. Perch {Perea fluviatilis) was studied most thoroughly concerning growth and survival during the first year of life. Earlier spawning resulted in a peak of abundance of newly hatched larvae about a month earlier than in unaffected areas. This event should have increased first year growth, but due to some temperature deficiencies during the summer this growth effect was reduced. The overall effect of the discharges on the growth was positive, however, since temperatures were relatively high in late summer and autumn. Thus, 0+ perch was about double the size at the end of the growth season in the most affected areas in comparison with unaffected areas. The growth of 0+ roach [Rutilus rutilus) was affected in a similar manner. Calculations of consumption in perch using abioenergetics model, demonstrated that feeding was close to maximal in affected as well as in unaffected areas. During the first experimental year, which also was a naturally very warm year, the highest abundance of 0+ perch for a period of 14 years was documented within the experimental area. The next year was, on the contrary, extremely cold and should, based on earlier experiences in the area, have resulted in very low abundances within the affected area. However, normal abundances appeared.The abundances of 0+ cyprinids did not increase in a similar manner. It is not possible, however, to draw a final conclusion concerning these observations until these year-classes are recruited to the adult stock. The effects of the coolingwater discharges on the adult stocks were small. Herring {Clupea harengus) was most greatly affected, since it was observed to spawn within the cooling water plume. Also, there were some indications that this species avoided the affected areas during the warmer parts of the year to a larger extent than normal. To maximize the effects of the cooling water discharges on recruitment of warmwater species, the cooling water should be discharged closer to the actual recruitment areas than was possible in this experiment. To reduce drifting of pelagic fish larvae, the velocity of the cooling water should also be adjusted to thel ocal conditions.

Contributors: Øivind Bergh, N. Finn, I. Haaland, I. Holmefjord, I. Lein, Terje van der Meeren, Anders Mangor-Jensen, O. Nielsen, Victor Øiestad, Karin Pittman

The main question that has to be raised when planning to enhance natural fish populations is whether reared fish are fitted for a life in the wild, or more specifically, whether there are differences between reared and indigenous fish. There are many published examples of observed differences between reared and wild individuals. The causes and effects of these differences are discussed. Results from the Norwegian enhancement programme, comparing reared and wild individuals of Atlantic salmon, Salmo salar L., Atlantic cod, Gadus morhua L., and European lobster, Homarus gammarus L. are discussed in the light of other results in the literature.

In the northeast Atlantic Ocean catch rates of juvenile fish from pelagic trawls are used to calculate indices of relative abundance which are applied as a first indication of year class strength. A major constraint for a reliable time series of these indices may arise from a varying vertical fish distribution, particularly near the surface due to sampling gear behaviour. In this paper a new three level trawl, which samples three separate depths simultaneously, is described in detail and catches are compared with catches from a standard juvenile survey trawl. The new trawl was highly more efficient in catching small juveniles in the near surface layers than the standard trawl. We concluded that changes in densities in this layer could significantly affect the reliability of the catch data from the standard trawl.

Using a new method for determining the stage of spawning in batch spawners, a positive correlation between the length of Arcto-Norwegian cod females, having spawned 25-75% of their eggs, and the egg diameter was established. This was not found in 1992 when egg groups from cod females in all stages of spawning were used. The maternal effect of cod female size was compared to the effect of stage of spawning. This comparison revealed the following tentative conclusions: 1) The egg diameter is less affected by the length of the cod female than by its stage of spawning. 2) The fertilization percentage and larval activity are correlated with the stage of spawning of the cod female, but not to its length. The present results indicate that the maternal effect of individual changes in egg characteristics during spawning is larger than the maternal effect of cod female size. In addition investigations on egg mortality, larval feeding ability, genetics, bacteriology, biochemistry and rearing of selected larvae groups to metamorphosis were carried out. The project will be terminated in 1994.

(Sluttrapport NFFR prosjekt nr. 1701-701.353) Hovudmålsetninga har vore å fremskaffe nye og supplerande kunnskaper for eit breiare fagleg grunnlag omkring skadeeffektar på egg, larvar og yngel frå seismisk arbeid med luftkanoner. Dette skal medverke til å styrke forvaltninga av oljeleitingsaktivitetar i forhold til fiskeriressursforvaltninga og fiskeriaktivitetar. Feltforsøka har vore utførte ved Havbruksstasjon Austevoll med utgangspunkt i veleigna anlegg og innretningar og personell som meistra metodikkane som er utvikla for yngelproduksjon av marin fisk.

Contributors: G. Adoff, Øivind Bergh, S. Bolla, Didrik S. Danielssen, A. Folkvord, K. Gravning, J. Gulbrandsen, K. Hamre, I. Holmefjord, Ingvar Huse, E. Kjørsvik, T. Kleppe, I. Lein, Anders Mangor-Jensen, Gro van der Meeren, Erlend Moksness, Kjell Emil Naas, Y. Olsen, Ingjerd Opstad, T. Pedersen, H. Reinertsen, G. Rosenlund, A. Skadsheim, Snorre Tilseth, Victor Øiestad.

Fisk används i ökande utsträckning i miljöövervakningen utmed våra kuster, och medvetenheten om kustfiskets utvecklingsmöjligheter tilltar. Denna situation ställer krav på långsiktig övervakning av och prognoser över fiskbeståndens storlek och produktionskapacitet samt en fortlöpande kontroll av deras hälsotillstånd i vid mening. Föreliggande arbete beskriver ett basprogram utformat för att möta dessa krav. Systemet utgör också en bas för specialundersökningar av t ex fysiologi och miljögiftshalter. Såväl beståndsövervakningen som insamlingen av fisk för provtagning sker genom fiske med etablerad metodik—-nät och ryssjor. För en utförlig presentation av principerna bakom systemet hänvisas till Neuman (1985). Övervaknings- och prognossystemet är utformat för kustbundna arter. Dessa uppträder huvudsakligen nära botten; de dominerande pelagiska fiskarna uppehåller sig främst längre ut till havs. För att det skall vara möjligt att koppla fiskens reaktioner till miljösituationen i undersökningsområdet, prioriteras stationära arter; i synnerhet gäller detta mätningar på individnivå. Vidare är systemet inriktat på relativt storvuxna arter, eftersom de ofta är av intresse för fisket, medger individuell kemisk och biologisk analys och är lätta att fånga med etablerad metodik. De arter som övervakas, dvs bottenlevande, någorlunda storvuxna fiskarter, kan vid Östersjöns kuster grupperas i två samhällen: littorala, i huvudsak stationära varmvattenarter samt kallvattenarter, som lever djupare och är mindre stationära. I den förra gruppen är abborre, mört och gers vanligast, medan den senare främst består av skrubbskädda, torsk, simpor, tånglake och sik. Vid svenska västkusten dominerar kallvattenarter som torsk, plattfiskar, tånglake och rötsimpa även på grunt vatten; ål utgör här det enda starka inslaget av varmvattenfisk. Uppläggningen av provfiskena, liksom all annan kontroll av mellanårsvariationer i biologiska förlopp, stälier hårda krav på statistisk planering. De metoder som här beskrivs har utvecklats efter mångåriga förstudier och statistiska prövningar. Genom stratifiering vad gäller val av art- och storleksgrupper, djupintervall, stationer och årstid har det varit möjligt att till rimliga kostnader skapa statistiskt tillfredsställande program. En klar skiljelinje har alltså dragits mot inventering; en sådan bredare insats bör dock ingå i den förundersökning som måste ligga till grund för varje enskilt övervakningsprogram.

Föreliggande arbete utgör slutrapport från projektet ’Tånglaken som indikator på effekter av giftiga ämnen". Avsikten har varit att utveckla ett miljökontrollsystem där tånglaken (Zoarces viviparus (L.)) används som indikatorart för förekomst av giftiga ämnen i havet och ekologiska effekter av sådana ämnen. Systemet skall kunna användas inom såväl utsläpps- och recipientkontroll som inom långtidsövervakning i referensområden (PMK). Flera enartssystem har utvecklats för att i laboratoriet söka mäta biologiska effekter av giftiga ämnen. Observerade reaktioner är dock ofta svåra att överföra till ekologiskt väsentliga störningar i naturen. Ett enartssystem för såväl utsläpps- som recipientkontroll bör innefatta inte bara mätande av effekter på individnivå i laboratorium och fält utan även kontroll av beståndsvariationer samt, om aktuella ämnen är persistenta och bioackumulerande, även kemisk analys. Väljer man att arbeta med fisk, bör arten ifråga ha följande egenskaper: ■ 1 .Ett stationärt levnadssätt under hela livscykeln, vilket är nödvändigt för koppling av observationerna till det kontrollerade områdets föroreningar. ■ 2.Tillräckligt storvuxen för att ge prover stora nog för individuell kemisk och fysiologisk analys. ■ 3.Lättfångad, även som yngel. ■ 4.Rik förekomst, helst inom ett stort utbredningsområde. ■ 5.Lång livslängd, vilket gör det möjligt att integrera effekter över tiden och undersöka betydelsen av långtidsexponering. ■ 6.Möjlighet att bestämma åldern krävs för analys av dos/effekt och för studier av beståndets åldersfördelning, vilken kan indikera störning av fortplantningen eller ökad mortalitet. ■ 7.Lämplighet för utsläppskontroll, vilket innebär att det skall vara möjligt att registrera ekologiskt betydelsefulla effekter av ett utsläpp inte bara under kontrollerade laboratorieförhållanden utan att det också skall tänkas gå att göra motsvarande observationer i fält. Jacobsson et al. (1986) har visat att tånglaken besitter de ovan uppräknade egenskaperna. Författarna baserar detta konstaterande på tidigare befintlig kunskap vad gäller de sex första kraven och på ett i uppsatsen beskrivet experiment vad gäller det sjunde. Också flera sötvattenfiskar har de nödvändiga egenskaperna men knappast någon annan i svenska vatten förekommande marin art. Detta innebär att Västsveriges och Skånes kuster saknar goda alternativa indikatorarter; PMK:s miljögiftsprogram utnyttjar t ex i sin kustlokal i Västerhavet den icke stationära skrubbskäddan. Även relativt våra sötvattenfiskar har tånglaken en väsentlig fördel: den föder levande ungar efter en långdräktighet (4-6 månader). Härigenom elimineras ett generellt problem vid studier av reproduktionsparametrar hos fisk, nämligen svårigheten att klargöra individuell kulltillhörighet och reproduktionsframgång hos individer.

Gjengitt med tillatelse av Nordisk Ministerråd

The aim of this work was to see if a shallow, enriched seawater basin was a suitable location for scallop culture. Growth of great scallop juveniles (Pecten maximus L.) was compared with two open sea locations, and the mean growth rate is described for 23.1-29.5 mm juveniles in three intervals from early April to late September 1989. In 1990 the mean of individual growth rate is described for 30-65 mm juveniles in April, May, June and July. Growth was measured as increase in shell height. Temperature, salinity and particulate organic material, POM, (1990) were recorded twice every week Phytoplankton (1989) was observed weekly. Mean growth rate per individual (mm/30 days) in 1989 was, relative to the other locations, higher in the basin in April-May, approximately equal in May-July and lower in July-September. The relative high growth rate in April-May coincided with relative higher temperature and phytoplankton biomass. The low growth rate in the basin was observed in a period of equal temperature relative to the other locations, higher phytoplankton biomass, but with large variations in salinity (25-31 ppt). In 1990 there were no significant difference in mean of individual growth rate between the locations, except for in June. The low growth rate and high mortality observed in the basin this month coincided with very high POM values (mean=17 mg/l, maximum =31 mg/l). The conclusion so far is that the seawater basin is suitable for culturing scallop juveniles, given a certain manipulation with salinity, fertilization and water circulation.

Halibut yolk sac larvae were kept at different light intensities from Day 1 posthatch. Measurements of activity and swimming speed showed that larvae that were kept in darkness were more active, but had lower swimming speed than those kept in light. Larvae kept at 1000 lux had lower yolk sac utilization than larvae kept at lower light intensities, probably due to stress caused by light. Larvae kept at 1 and 10 lux had higher body dry weight when the experiment was terminated. Differences in pigmentation were found. An autecological model is discussed, suggesting that halibut yolk sac larvae are distributed in relatively shallow waters during the first week posthatch, thereafter sink into deeper waters, and rise again when the time of first feeding approaches.

Contributor: Odd M. Smedstad Introduction: The results from the International Young Fish survey become available in successive steps. During the survey the numbers of 1-group fish, based on fish below a certain length, are exchanged between the participating research vessels. Immediately after the survey the length compositions of the seven standard species are sent to ICES (in IYFS exchange format), to be used by the different assessment working groups, together with all age-length keys which are available by then. Final data, including length compositions for all species and age-length data, should be submitted to ICES before 15 April. These data are then checked and stored in the ICES IYFS data base, in order to be able to run the final analysis in time for the May meeting of ACFM. This report is based on the analysis done in May 1990.

Contributor: John Lahn-Johannessen

Merket "begrenset distribusjon" For å finne ut om bruk av seismiske energikilder kan skade fisk, eksponerte vi egg, larver og yngel av torsk (Gadus morhua L.) med en liten luftkanon (Bolt 600B) og yngel med en stor luftkanon (Bolt 1500C) og med en vannkanon (Seismic Systems P400). Egg, larver og små yngel ble plassert i en polyethylen plastpose (40 µ)i omlag 5 l vann under avfyring av luftkanon, og den større yngelen (lengde 9-11 cm) ble plassert i et finmasket notbur. Avstanden mellom plastposen og energikilden var 1m til 10 m og mellom buret og energikilden 2m til 6 m. Vi avdekka ingen skader på egg, larver og liten yngel belastet med den lille luftkanonen. Luftboblene som blir dannet av luftkanonen kan kanskje forårsake noe skade. Den eldre yngelen som ble belastet med luftkanon fikk problemer med balansen, men kom seg innen få minutter. Vannkanonen drepte 90% av yngelen ved en avstand på 2 m. Ved en avstand på 6 m fikk yngelen problem med balansen, men de kom seg.

Contributors: Erling Bakken, Are Dommasnes, Olav Dragesund, Stein Hjalti Jakupsstovu, Lars Midttun, Ingold Røttingen, Roald Sætre, Øyvind Ulltang.

Eggs, larvae and the larvae's first search for food are the most critical stages in a fish life, both to threats from natural causes and pollution. Based on experimental studies of several species of fish eggs, larvae and zooplankton, and their in situ abundance, calculations of potential reduction of the affected year class or stock are demonstrated. The organisms exposed to oil concentrations likely to be found in the marine environment show considerably variation from species to species. While our experiments show little or no impact on herring eggs and larvae, eggs of saith and cod do not tolerate even short term (2-24 hour) exposure to low oil concentrations (50 ppb WSF). In some areas the majority of the years spawning products are restricted both in time and space, and therefore the potential for reduction in the recruitment of these stocks is considerable. Based on registered distributions of fish eggs and larvae, our calculations show a fairly low percentage of potential reduction using a worst case concept. Although the statistically calculated risk for an accident resulting in serious oil pollution is very low, real and severe accidents remind us that this may happen every so otten regardless of the statistics. It is our hope that the experimental results presented can be used in predicting and assessing the impact of serious oil spills.

This paper describes tlte Norwegian investigations on juvenile herring (0-, I- and II-group) of the Norwegian spring spawning stock. The investigations were carried out in Norwegian coastal areas and in the Barents Sea in the period June 1984 - May 1985. Empahasis is made on the distribution of the strong 1963 year class, and the distribution and migration of this year class is compared with an earlier strong yearclass. that of 1959.

Since 1959 the Norwegian sprat investigations have been considerably intensified. In this connection extensive hydrographical investigations have also been carried out. In this paper an account is given of the distribution and movement of the different water masses in the area shown in Fig. 1. The distribution of sprat eggs and larvae in relation to the hydrographical conditions has also been discussed. A warm surface layer with high content of oxygen, and a low phosphate content was separated from the underlying water masses by a transition layer in which the stability was particularly high. A core of Atlantic water with relatively high salinity, temperature and oxygen content, and a low content of phosphate, penetrated into the Skagerak along the edge of the North Sea Plateau, continuing along the Swedish and Norwegian coasts, constantly losing its original character (Fig.s 2 and 3). Current measurements were made at an anchor station (St. 410 on Fig.s G and 7). During the summers of 1960 and 1961 drift-bottle-experiments were carried out. The assumed drift is shown in Fig.s 8 and 9. The number of days drift is indicated at the point of recovery. The investigations indicate the existence of a cyclonic vortex in Skagerak. Persuming dynamic equilibrium this vortex is in good accordance with the depth of the boundary surface between the upper layers and the deep-water masses found by Dietrich ( 1950). Sprat eggs and larvae were collected in vertical hauls with a one-meter egg net. Examples of their distribution in the area are given in Fig.s 10 and 11. During the last 10 years sprat larvae have been caught in much smaller numbers outside western Norway than one might expect in relation to the concentration of eggs and larvae in Skagerak. The present author is of the opinion that because of the cyclonic vortex mentioned above, the larvae are forced to remain in the Skagerak for a relatively long period. When they finally are carried to the area off western Norway, they have grown large enough to avoid the plankton nets used.