Multiple paternity assessment and paternity assignment in wild european lobster (Homarus gammarus) : comparing a no-take reserve and an exploited area

Understanding the mechanisms driving mating systems is intricate for wild populations of species where behavioral observations are difficult, but nonetheless imperative for harvested species. This study investigated the occurrence and frequency of multiple paternity for the European lobster (Homarus gammarus) in a marine reserve (MPA) and in a heavily exploited control area on the Norwegian Skagerrak coast. Also, this study is the first to conduct a parental assignment in a wild lobster population. With three to six microsatellite loci genotyped, 81 females and ten offspring from each brood, high level of multiple paternity was discovered in both reserve (27 and 96%) and control area (3 and 90%) with no significances in regards to body size. However, significantly more cases of multiple paternity was observed in the reserve area using the most parsimonious estimate. These results demonstrate that females in all size categories may mate with more than one male after pre-molt insemination, perhaps due to altered mating behavior as result of decades of overharvest or due to high density of individuals. Of the 475 candidate males genotyped for six loci, 13 of them were assigned to offspring of 14 females but with no clear patterns for assortative mating, although 71% of the pairs consisted of a male bigger than the female. As five of the mated pairs have crossed the boundaries of the reserve in either direction there are tendencies of spill-over effects. However, eight of the pairs resided in the marine reserve which also indicating a high site fidelity. Further research to unveil the genetically significance of multiple paternity and what drives the females’ choice is important for management of this high valued species

Multiple paternity assessment and paternity assignment in wild european lobster (Homarus gammarus) : comparing a no-take reserve and an exploited area

Understanding the mechanisms driving mating systems is intricate for wild populations of species where behavioral observations are difficult, but nonetheless imperative for harvested species. This study investigated the occurrence and frequency of multiple paternity for the European lobster (Homarus gammarus) in a marine reserve (MPA) and in a heavily exploited control area on the Norwegian Skagerrak coast. Also, this study is the first to conduct a parental assignment in a wild lobster population. With three to six microsatellite loci genotyped, 81 females and ten offspring from each brood, high level of multiple paternity was discovered in both reserve (27 and 96%) and control area (3 and 90%) with no significances in regards to body size. However, significantly more cases of multiple paternity was observed in the reserve area using the most parsimonious estimate. These results demonstrate that females in all size categories may mate with more than one male after pre-molt insemination, perhaps due to altered mating behavior as result of decades of overharvest or due to high density of individuals. Of the 475 candidate males genotyped for six loci, 13 of them were assigned to offspring of 14 females but with no clear patterns for assortative mating, although 71% of the pairs consisted of a male bigger than the female. As five of the mated pairs have crossed the boundaries of the reserve in either direction there are tendencies of spill-over effects. However, eight of the pairs resided in the marine reserve which also indicating a high site fidelity. Further research to unveil the genetically significance of multiple paternity and what drives the females’ choice is important for management of this high valued species

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.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

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

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

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

Biometric Fish Classification of Temperate Species Using Convolutional Neural Network with Squeeze-and-Excitation

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