Protection from fishing improves body growth of an exploited species

Hunting and fishing are often size-selective, which favours slow body growth. In addition, fast growth rate has been shown to be positively correlated with behavioural traits that increase encounter rates and catchability in passive fishing gears such as baited traps. This harvest-induced selection should be effectively eliminated in no-take marine-protected areas (MPAs) unless strong density dependence results in reduced growth rates. We compared body growth of European lobster (Homarus gammarus) between three MPAs and three fished areas. After 14 years of protection from intensive, size-selective lobster fisheries, the densities in MPAs have increased considerably, and we demonstrate that females moult more frequently and grow more during each moult in the MPAs. A similar, but weaker pattern was evident for males. This study suggests that MPAs can shield a wild population from slow-growth selection, which can explain the rapid recovery of size structure following implementation. If slow-growth selection is a widespread phenomenon in fisheries, the effectiveness of MPAs as a management tool can be higher than currently anticipated.publishedVersio

Protection from fishing improves body growth of an exploited species

Hunting and fishing are often size-selective, which favours slow body growth. In addition, fast growth rate has been shown to be positively correlated with behavioural traits that increase encounter rates and catchability in passive fishing gears such as baited traps. This harvest-induced selection should be effectively eliminated in no-take marine-protected areas (MPAs) unless strong density dependence results in reduced growth rates. We compared body growth of European lobster (Homarus gammarus) between three MPAs and three fished areas. After 14 years of protection from intensive, size-selective lobster fisheries, the densities in MPAs have increased considerably, and we demonstrate that females moult more frequently and grow more during each moult in the MPAs. A similar, but weaker pattern was evident for males. This study suggests that MPAs can shield a wild population from slow-growth selection, which can explain the rapid recovery of size structure following implementation. If slow-growth selection is a widespread phenomenon in fisheries, the effectiveness of MPAs as a management tool can be higher than currently anticipated.publishedVersionPaid open acces

Protection from fishing improves body growth of an exploited species

Hunting and fishing are often size-selective, which favours slow body growth. In addition, fast growth rate has been shown to be positively correlated with behavioural traits that increase encounter rates and catchability in passive fishing gears such as baited traps. This harvest-induced selection should be effectively eliminated in no-take marine-protected areas (MPAs) unless strong density dependence results in reduced growth rates. We compared body growth of European lobster (Homarus gammarus) between three MPAs and three fished areas. After 14 years of protection from intensive, size-selective lobster fisheries, the densities in MPAs have increased considerably, and we demonstrate that females moult more frequently and grow more during each moult in the MPAs. A similar, but weaker pattern was evident for males. This study suggests that MPAs can shield a wild population from slow-growth selection, which can explain the rapid recovery of size structure following implementation. If slow-growth selection is a widespread phenomenon in fisheries, the effectiveness of MPAs as a management tool can be higher than currently anticipated.publishedVersio

Kunnskapsinnhenting Leppefisk – biologi og fiskeri 2013-2018: Rapport til Fiskeridirektoratet for 2018 sesongen

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Kunnskapstøtte og råd for regulering av fisket etter leppefisk i 2021

Fiskeridirektoratet har i en bestilling datert 07.09.2020 bedt Havforskningsinstituttet (HI) om kunnskapsstøtte for regulering av totaluttak, fartøykvoter, artsbegrensninger i fisket etter leppefisk. Det bes også om ny kunnskap om effekten av mindre innganger i teiner. Fiskeridirektoratet ønsker også kunnskap om hvordan fiske etter stamfisk av berggylte kan gjennomførers på en bærekraftig måte, kunnskap om oppdretternes behov for stamfisk, og kunnskapsstøtte knyttet til fangsten av stamfisk med hensyn på fangsttid, antall, redskaptype, røkting og bifangst.publishedVersio

Goldsinny wrasse (Ctenolabrus rupestris) have a sex-dependent magnetic compass for maintaining site fidelity

The goldsinny wrasse (Ctenolabrus rupestris) is a commercially important fish that inhabits coastal areas across the eastern Atlantic. This species moves from a shallow home territory along the coast into deeper waters in the autumn and winter and then returns to that same territory in the spring. Only male goldsinny wrasse exhibit strong territorial behavior, which may manifest as sexual differences in the ability or motivation to return to home territories. The orientation mechanism underlying the homing migration of goldsinny wrasse males and females is unknown. In this study, we hypothesized that goldsinny wrasse use the magnetic field of the Earth to follow a compass-based path toward their home territory. To test this hypothesis, we collected 50 adult goldsinny wrasse, approximately half males and half females, in a harbor in Austevoll, Norway. Fish were translocated to a magnetoreception laboratory situated north of the site of capture, in which the magnetic field was artificially rotated. In the laboratory, males oriented toward the magnetic south taking a mean direction of 201°, which is the approximate direction that they would have had to take to return to the site at which they were captured. Females oriented in random magnetic directions. There was no difference in swimming kinematics between males and females. These results show that male goldsinny wrasse have a magnetic compass that they could use to maintain site fidelity, an ability that could help them and other coastal fish undertake repeatable short-range migrations.publishedVersio

Mind the depth: The vertical dimension of a small-scale coastal fishery shapes selection on species, size, and sex in wrasses

Small‐scale fisheries (SSFs) tend to target shallow waters, but the depth distributions of coastal fish can vary depending on species, size, and sex. This creates a scope for a form of fishing selectivity that has received limited attention but can have considerable implications for monitoring and management of these fisheries. We conducted a case study on the Norwegian wrasse fishery, a developing SSF in which multiple species are caught in shallow waters (mean depth = 4.5 m) to be used as cleaner fish in aquaculture. Several of these wrasses have life histories and behaviors that are sensitive to selective fishing mortality, such as sexual size dimorphism, paternal care, and sex change. An experimental fishery was undertaken over three sampling periods in 2018. Data on catch, length, and sex of wrasses across a depth gradient (0–18 m) were collected and analyzed. We found that depth distributions were species specific and the vertical overlap with the fishery was high for Corkwing Wrasse Symphodus melops and Ballan Wrasse Labrus bergylta, which were most abundant at depths less than 5 m. Three other wrasse species had invariant or increasing abundance with depth and were therefore less likely to be negatively impacted by this fishery. Body size was positively correlated with depth for these wrasses, and sex ratio became more male biased for the Corkwing Wrasse, the only species that could be visually sexed. This study demonstrates that depth can have strong effects on fishing selectivity at multiple scales and that such knowledge is necessary to develop management strategies that balance fishing mortality sustainably across species, sizes, and sexes. We recommend that management priorities be directed toward the Ballan and Corkwing wrasses—the species having the highest vertical overlap with the fishery. Furthermore, CPUE was strongly affected by seasonality and positively correlated with increasing wave exposure for one of the species. This underscores the general importance of standardizing catch data for several environmental covariates when monitoring species that are affected by SSFs.publishedVersio

Kunnskapsbasert innovasjon for optimal ressursutnyttelse i leppefiskeriet — Sluttrapport i prosjekt 272202 - Regionalt forskningsfond Agder

Rensefisk benyttes for å kontrollere mengden lakselus i oppdrett av laksefisk i sjø i Norge. Behovet for rensefisk har økt markant siden 2010 på grunn av resistensutvikling mot medikamentelle behandlinger hos lakselus (Skiftesvik et al. 2014; Aaen et al. 2015; Rueness et al. 2019). På tross av at produksjonen av oppdrettet rensefisk, primært rognkjeks, har økt kraftig de siste årene, så har det ikke redusert behovet for villfanget leppefisk som rensefisk. Leppefiskeriet har blitt en svært viktig næring for kystfiskere i Agder. Da ålefisket ble forbudt i 2006, gikk mange over til å fiske leppefisk som kan utføres med samme redskap og fartøy. På Sørlandet har fiskerne leveringsavtaler med oppkjøpere som transporterer og videreselger leppefisken til oppdrettsanlegg hovedsakelig i Midt- og Nord-Norge. Fiskeriet på Skagerrakkysten er ikke jevnt fordelt, hoveddelen (ca 80 %) av fangsten tas i Agder (Figur 1). Fiskepresset på leppefisk anses å være lavt fra Telemark og til Svenskegrensen. Ytterligere informasjon om fangsttall, verdi og fartøy i de ulike regionene finnes på Fiskeridirektoratets nettsider: https://www.fiskeridir.no/Yrkesfiske/Tall-og-analyse/Fangst-ogkvoter/Fangst-av-leppefisk. Man har inntil nylig hatt lite kunnskap om hvor mye beskatning leppefiskbestandene tåler og hvilke økologiske konsekvenser et eventuelt overfiske kan medføre. På Skagerrakkysten fangstes det på tre ulike leppefiskarter, bergnebb (Ctenolabrus rupestris), grønngylte (Symphodus melops) og berggylte (Labrus bergylta). Grasgylt (Centrolabrus exoletus) og Rødnebb/Blåstål (Labrus mixtus) regnes som bifangst på Sørlandet siden de ikke egner seg for langdistansetransport. Det forekommer noe bruk av disse artene lokalt på Vestlandet. I tillegg tas det en del bifangst av andre fisk og skalldyr, som kan forårsake skade på leppefisken, samt av kyst-torsk og hummer, ikoniske arter som er truet av overfiske på Skagerrak-kysten (Fernández-Chacón et al. 2015; Sørdalen et al. 2018). Taskekrabbe brukes som agn i leppefisket, men må fiskes med egne krabbeteiner. Regelverket pålegger at all bifangst som fanges i Kunnskapsbasert innovasjon for optimal ressursutnyttelse i leppefiskeriet 1 - Bakgrunn for prosjektet 4/21 leppefiskredskap skal slippes ut på fangststedet. I Agder er det dokumentert høyere forekomster av leppefisk innad i bevaringsområder sammenliknet med nærliggende områder med åpent fiske, noe som tyder på at fiskeriet kan ha en bestandsregulerende effekt (Figur 2; Halvorsen et al. 2017). HIs råd om kvoter og reguleringer har vært basert på en føre-var-tilnærming for å stoppe en videre ekspansjon i fiskeriet før man har tilstrekkelig kunnskap om bestandenes tåleevne og svingninger. Fiskeridirektoratet forvalter bestandene ved bruk av flere ulike reguleringer, herunder gytetidsfredning, fluktåpninger, artsspesifikke minstemål, fartøykvoter og totalkvoter for ulike regioner. På Sørlandet er totalfangsten begrenset til fire millioner leppefisk årlig. For å gi råd om forsvarlig uttak av bestandene etablerte HI i 2011 et nettverk av referansefiskere som leverte fangstrapporter. Bestandsutviklingen ble representert ved regionale trender i fangst-per-enhet-innsats (Catch per unit effort; CPUE, heretter), men datagrunnlaget var for variabelt til å kunne konkludere med at endringer i CPUE reflekterte faktiske endringer i bestandsstørrelse. I dette prosjektet har vi fokusert på å ta i bruk ny teknologi og forbedre rapporteringsrutiner i fiskeriavhengig datainnsamling for å få kunnskap om leppefiskens romlige økologi. For fiskeriet på Skagerrak vil dette kunne bidra til mer kunnskap om ressursfordelingen og hvordan de kan utnyttes bedre og mer effektivt, samtidig som at dette muliggjør en bedre bestandsovervåking og grunnlag for å gi mer presise kvoteråd. I Prosjektet har vi også utnyttet tilgjengelige dataserier for å få en oversikt over bestandsutviklingen i Skagerrak. Merkeforsøk har blitt gjennomført for å få bedre kunnskap om romlig adferd og fangbarhet. Resultatene har blitt fortløpende inkludert i HIs kunnskapsstøtte til Fiskeridirektoratet, og det nasjonale referansefiskernettverket har tatt i bruk metodene for fangstrapportering som er utviklet i dette prosjektet. Det arbeides med å ferdigstille publikasjoner for fagfellevurderte tidsskrifter, og i denne rapporten vil det kun gis en kort oppsummering av disse studiene.publishedVersio

Temperate fish detection and classification: a deep learning based approach

A wide range of applications in marine ecology extensively uses underwater cameras. Still, to efficiently process the vast amount of data generated, we need to develop tools that can automatically detect and recognize species captured on film. Classifying fish species from videos and images in natural environments can be challenging because of noise and variation in illumination and the surrounding habitat. In this paper, we propose a two-step deep learning approach for the detection and classification of temperate fishes without pre-filtering. The first step is to detect each single fish in an image, independent of species and sex. For this purpose, we employ the You Only Look Once (YOLO) object detection technique. In the second step, we adopt a Convolutional Neural Network (CNN) with the Squeeze-and-Excitation (SE) architecture for classifying each fish in the image without pre-filtering. We apply transfer learning to overcome the limited training samples of temperate fishes and to improve the accuracy of the classification. This is done by training the object detection model with ImageNet and the fish classifier via a public dataset (Fish4Knowledge), whereupon both the object detection and classifier are updated with temperate fishes of interest. The weights obtained from pre-training are applied to post-training as a priori. Our solution achieves the state-of-the-art accuracy of 99.27% using the pre-training model. The accuracies using the post-training model are also high; 83.68% and 87.74% with and without image augmentation, respectively. This strongly indicates that the solution is viable with a more extensive dataset.publishedVersio

Kunnskapsstøtte og råd for regulering av fisket etter leppefisk i 2022

Havforskningsinstituttets råd om reguleringer av leppefisk har bygget på føre-var-prinsippet. Det er en målsetning å minimere risikoen for at fiskeriet fører til betydelige endringer i arts, størrelse- og kjønnssammensetning av leppefisk i lokale bestander. Artene bør her kunne opprettholde et naturlig rekrutteringspotensial, samt at deres økologiske funksjon blir minst mulig endret i forhold til en naturlig tilstand uten fiske. Fisket etter leppefisk er et flerartsfiskeri på arter med ulik biologi. Dette er nøkkelarter i kystøkosystemet, og de ulike artene fyller forskjellige økologiske nisjer som predatorer og byttedyr.publishedVersio