Corkwing Research Articles

Trajectory-based fish event classification through pre-training with diffusion models

This study contributes to advancing the field of automatic fish event recognition in natural underwater videos, addressing the current gap in studying fish interaction and competition, including predator-prey relationships and mating behaviors. We used the corkwing wrasse (Symphodus melops) as a model, a marine species of commercial importance that reproduces in sea-weed nests built and cared for by a single male. These nests attract a wide range of visitors and are the focal point for behavior such as spawning, chasing, and maintenance. We propose a deep learning methodology to analyze the movement trajectories of the nesting male and classify the associated events observed in their natural habitat. Our approach leverages unsupervised pre-training based on diffusion models, leading to improved feature learning. Additionally, we introduce a dataset comprising 16,937 trajectories across 12 event classes, making it the largest in terms of event class diversity. Our results demonstrate the superior performance of our method compared to several deep architectures. The code for the proposed method and the trajectories can be found at https://github.com/NoeCanovi/Fish_Behaviors_Generative_Models.

The genome sequence of the corkwing wrasse, Symphodus melops (Linnaeus, 1758)

We present a genome assembly from an individual Symphodus melops (the corkwing wrasse; Chordata; Actinopteri; Labriformes; Labridae). The genome sequence is 636.4 megabases in span. Most of the assembly is scaffolded into 23 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 16.5 kilobases in length.

A contrastive learning approach for individual re-identification in a wild fish population

In both terrestrial and marine ecology, physical tagging is a frequently used method to study population dynamics and behavior. However, such tagging techniques are increasingly being replaced by individual re-identification using image analysis. This paper introduces a contrastive learning-based model for identifying individuals. The model uses the first parts of the Inception v3 network, supported by a projection head, and we use contrastive learning to find similar or dissimilar image pairs from a collection of uniform photographs. We apply this technique for corkwing wrasse, Symphodus melops, an ecologically and commercially important fish species. Photos are taken during repeated catches of the same individuals from a wild population, where the intervals between individual sightings might range from a few days to several years. Our model achieves a one-shot accuracy of 0.35, a 5-shot accuracy of 0.56, and a 100-shot accuracy of 0.88, on our dataset.

Habitat associations of juvenile Atlantic cod (Gadus morhua L.) and sympatric demersal fish communities within shallow inshore nursery grounds

Resolving the relationship between demersal fish and sublittoral biotic habitats and substrates is a key element in the protection of important nursery grounds for strengthening fish recruitment. In Norway, coastal Atlantic cod (Gadus morhua L.) is a commercially and culturally important demersal fish for Norwegian coastal communities, and in recent decades the stock has declined to such an extent that a plan to rebuild the stock to biologically safe limits has been implemented. Yet, little is known about the specific biotic and abiotic habitat associations of the early-life stages of coastal cod, which is important for the management and protection of the species. The same shallow, sublittoral zones are inhabited by juveniles and adults of other commercial demersal gadoids and wrasses. This study presents novel findings on associations between juvenile coastal cod and other demersal fish species with seafloor substrates and biological habitats, inferred from five years of extensive fyke net surveys. Newly settled 0-group cod were typically associated with eel grass and red algae biotic habitats on sand and shell sand substrates. However, there was an ontogenic habitat shift amongst one year old (1-group) individuals that became more ubiquitous with their biotic habitat or substrate type choices. The juvenile gadoids saithe (Pollachius virens) and pollack (Pollachius pollachius), were most associated with hard bottom dominated sites with saithe being more abundant at exposed sites, compared to pollack. Goldsinny wrasse (Ctenolabrus rupestris) and corkwing wrasse (Symphodus melops) appeared to favor sugar kelp forests and red algae. Overall, the study identifies the specific sublittoral biotic habitats and substrates important to different early life stages of juvenile coastal cod and other commercially important demersal fish, providing critical information needed for identifying candidate coastal habitats for protection.

Population Status, Breeding Biology and Diet of Norwegian Great Cormorants

Two subspecies of the Great Cormorant breed in Norway, the continental Phalacrocorax carbo sinensis in the south, along the Skagerrak coast, and the marine P. c. carbo from central Norway and northwards. Here we review the information existing until 2017 on population status and trends, breeding performance and diet of these two subspecies in Norway. The most recent national population estimates are approximately 2500 (in 2012) and 19,000 (in 2012–2014) breeding pairs of sinensis and carbo, respectively. The sinensis population established itself in 1996 in Rogaland at the south-western tip of Norway, and in 1997 in Østfold close to the Swedish border; in both areas it increased for about ten years. Since then, the numbers have stabilised. For carbo, the population increased from 21,000 pairs in the early 1980s to 27,000 in 1995, and then decreased to the current number of 19,000 pairs. Significant annual variations in clutch size and reproductive output have been observed, but the drivers of these changes have not been identified. Unidentified gadoids and Atlantic Cod Gadus morhua were the most common prey of carbo, whereas inshore species such as Corkwing Wrasse Symphodus melops, Rockcook Centrolabrus exoletus, Goldsinny Wrasse Ctenolabrus rupestris and Black Goby Gobius niger were the most common prey in the eastern Skagerrak caught by sinensis. Carbo took very large numbers of 1–3-year-old gadoids during the year, and we cannot exclude the possibility this can have local effects on fish mortality rates.

Combining population genomics with demographic analyses highlights habitat patchiness and larval dispersal as determinants of connectivity in coastal fish species.

Gene flow shapes spatial genetic structure and the potential for local adaptation. Among marine animals with nonmigratory adults, the presence or absence of a pelagic larval stage is thought to be a key determinant in shaping gene flow and the genetic structure of populations. In addition, the spatial distribution of suitable habitats is expected to influence the distribution of biological populations and their connectivity patterns. We used whole genome sequencing to study demographic history and reduced representation (double‐digest restriction associated DNA) sequencing data to analyse spatial genetic structure in broadnosed pipefish (Syngnathus typhle). Its main habitat is eelgrass beds, which are patchily distributed along the study area in southern Norway. Demographic connectivity among populations was inferred from long‐term (~30‐year) population counts that uncovered a rapid decline in spatial correlations in abundance with distance as short as ~2 km. These findings were contrasted with data for two other fish species that have a pelagic larval stage (corkwing wrasse, Symphodus melops; black goby, Gobius niger). For these latter species, we found wider spatial scales of connectivity and weaker genetic isolation‐by‐distance patterns, except where both species experienced a strong barrier to gene flow, seemingly due to lack of suitable habitat. Our findings verify expectations that a fragmented habitat and absence of a pelagic larval stage promote genetic structure, while presence of a pelagic larvae stage increases demographic connectivity and gene flow, except perhaps over extensive habitat gaps.

Not that clean: Aquaculture-mediated translocation of cleaner fish has led to hybridization on the northern edge of the species' range.

Translocation and introduction of non‐native organisms can have major impacts on local populations and ecosystems. Nevertheless, translocations are common practices in agri‐ and aquaculture. Each year, millions of wild‐caught wrasses are transported large distances to be used as cleaner fish for parasite control in marine salmon farms. Recently, it was documented that translocated cleaner fish are able to escape and reproduce with local wild populations. This is especially a challenge in Norway, which is the world's largest salmon producer. Here, a panel of 84 informative SNPs was developed to identify the presence of nonlocal corkwing wrasse (Symphodus melops) escapees and admixed individuals in wild populations in western Norway. Applying this panel to ~2000 individuals, escapees and hybrids were found to constitute up to 20% of the local population at the northern edge of the species’ distribution. The introduction of southern genetic material at the northern edge of the species distribution range has altered the local genetic composition and could obstruct local adaptation and further range expansion. Surprisingly, in other parts of the species distribution where salmon farming is also common, few escapees and hybrids were found. Why hybridization seems to be common only in the far north is discussed in the context of demographic and transport history. However, the current lack of reporting of escapes makes it difficult to evaluate possible causes for why some aquaculture‐dense areas have more escapees and hybrids than others. The results obtained in this study, and the observed high genomic divergence between the main export and import regions, puts the sustainability of mass translocation of nonlocal wild wrasse into question and suggests that the current management regime needs re‐evaluation.

Wrasse fishery on the Swedish West Coast: towards ecosystem-based management

Abstract Fishing and translocation of marine species for use in aquaculture is widespread. Corkwing, goldsinny, and ballan wrasse (Symphodus melops, Ctenolabrus rupestris, and Labrus bergylta) are fished on the Swedish west coast for use as cleaner-fish in Norwegian salmon farms. Here, we aim to provide knowledge and recommendations to support ecosystem-based management for wrasse fisheries in Sweden. We compared fished and non-fished areas to test if current fishery levels have led to stock depletion. To gain insight on the role of wrasse in the algal belt trophic chain, we analysed the gut contents of goldsinny and corkwing using metabarcoding. Finally, we analysed the trophic interactions of wrasse and potential prey in a mesocosm study. We could not detect any signs of stock depletion or altered size structure in fished areas compared to the protected control area. Gut analyses confirmed both goldsinny and corkwing as non-specialized, omnivorous opportunists and revealed, with 189 prey taxa detected, a broader spectrum of prey than previously known. Common prey items included mesoherbivores such as small gastropods and crustaceans, but also insects and algae. We conclude that there are no visible signs of stock depletion at the current removal level of wrasses by the fishery. However, this emerging fishery should be closely monitored for potential cascading effects on the algal belt ecosystem, and our study could provide a baseline for future monitoring.

Predator presence affects activity patterns but not food consumption or growth of juvenile corkwing wrasse (Symphodus melops)

Indirect effects of predators can manifest themselves as changes in prey behaviour and physiology. Given that digestion requires energy, it has been suggested that prey will choose to eat smaller meals under predation risk to reserve a larger portion of the aerobic metabolic scope they have available for energetically demanding tasks more critical than digestion, such as escape. To test this prediction, we quantified food consumption and growth of juvenile corkwing wrasses (Symphodus melops) over 11 days in the presence or absence of a predator (Atlantic cod, Gadus morhua). We then quantified behaviour and food consumption of the same wrasses in behavioural arenas with a predator. All food consumption was examined in the context of the aerobic scope that would have been available during the digestive period. Overall, there was no effect of predator exposure on food consumption or growth, yet predator-exposed wrasses were more consistent in their daily food consumption, lending some support to our prediction of prey bet-hedging on meal size under predation risk. The lack of a clear pattern may have resulted from a relatively low percentage of aerobic scope (~ 20–27%) being occupied by digestion, such that fish retained ample capacity for activities other than digestion. In the subsequent behavioural trials, predator-exposed wrasses were more active and spent more time near the cod than predator-naive wrasses, suggesting the former had habituated to predation threat and were more risk-taking. Our results highlight the complex and often counter-intuitive effects that predator presence can have on prey populations beyond direct consumption. Predators affect the behaviour of prey species by simply being present in the environment. Such intimidation by predators can change activity patterns of prey and be as important as direct predation for ecosystem dynamics. However, compared to behavioural changes, we know little about how predators indirectly affect prey physiology. We investigated if fish deliberately eat less food when a predator is present, in order to retain sufficient physiological capacity for avoiding a potential attack, on top of the energetically costly process of digesting. While our study confirms that predator encounters reduce prey activity, prey fish appeared to rapidly habituate to predator presence and we did not see reduced food consumption in predator-exposed fish; these were, however, more consistent than unexposed fish in their daily food consumption, suggesting that fish may still be mindful about protecting their aerobic capacity under predation risk.

First Report of Symphodus melops (Linnaeus, 1758) with Maximum Length in the Black Sea

An individual of corkwing wrasse Symphodus melops (female) was captured by trammel nets on May 15, 2020, at 20 m depths from Ordu, the southern Black Sea coast. The total length and weight were measured as 320 mm and 520 g. The specimen was female with a gonad weight of 42 g and it was determined to be eight years old. This is the first record for the S. melops from the Black Sea. Its total length and weight were the maximum observed values for the species for the World. The paper is considered to contribute to fisheries biology and international scientific literature.

Mind the Depth: The Vertical Dimension of a Small‐Scale Coastal Fishery Shapes Selection on Species, Size, and Sex in Wrasses

AbstractSmall‐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.

Sound production in male and female corkwing wrasses and its relation to visual behaviour

ABSTRACT In fish, social interactions are commonly accompanied by acoustic signalling. Males have been found to produce sounds in a large range of species, but female sounds have received considerably less attention. But even in males, there remain significant taxonomical gaps, e.g. in one of the largest fish families, the wrasses. Here, we investigate sound production in territorial males and females of the corkwing wrasse in a field study in Norway. We complemented an in-depth analysis of the visual and acoustic behavioural repertoire of territorial males by descriptions of female behaviours. Males as well as females produced sounds in courtship and agonistic contexts. We recorded four types of sounds and found significant differences between male and female sound properties. We hereby provide one of the first descriptions of sound production in wrasses and, to our knowledge, the first one to also investigate female sound production. Our study shows that wrasses are an underappreciated family when it comes to sound production. With a repertoire of four different calls, corkwing wrasses are remarkably versatile among fishes. Our results highlight the potential and importance of future research about sound communication in neglected taxa, and in both sexes.

The consequences of size‐selective fishing mortality for larval production and sustainable yield in species with obligate male care

AbstractSize‐based harvest limits or gear regulations are often used to manage fishing mortality and ensure the spawning biomass of females is sufficiently protected. Yet, management interactions with species’ mating systems that affect fishery sustainability and yield are rarely considered. For species with obligate male care, it is possible that size‐specific harvest of males will decrease larval production. In order to examine how size‐based management practices interact with mating systems, we modelled fisheries of two species with obligate care of nests, corkwing wrasse (Symphodus melops, Labridae) and lingcod (Ophiodon elongatus, Hexigrammidae) under two management scenarios, a minimum size limit and a harvest slot limit. We simulated the population dynamics, larval production and yield to the fishery under a range of fishing mortalities. We also modelled size‐dependent male care to determine its interaction with management. In both species, the slot limit decreased yield by <12% (relative to minimum size limits) at low fishing mortalities; at higher mortalities, individuals rarely survived to outgrow the slot and spawning potential decreased substantially relative to unfished levels, similar to minimum size limits. Spawning potential decreased less when managed with a slot limit if we included a positive feedback between male size, care and hatching success, but the benefit of implementing the slot depended both on the relative proportions of each sex selected by the fishery and on our assumptions regarding male size and care. This work highlights that the effects of size‐ and sex‐selective fisheries management can be nuanced and produce counter‐intuitive results.

Comments on "The marine teleost fishes of the Sea of Marmara; an updated and annotated checklist" by Artüz amp; Fricke (2019).

The recent paper by Artüz Fricke (2019) is focused on the analysis of marine teleost fishes of the Sea of Marmara, where they have tried to correct doubtful species occurrences and presented an annotated checklist. In a few cases, the authors have provided convincing data for the removal of some species from the regional inventory, such as Apogon imberbis (Linnaeus, 1758), Scomberesox saurus (Walbaum, 1792) and Polyprion americanus (Bloch Schneider, 1801), and pointed out revision-seeking genera (i.e. Alosa spp., Pegusa spp., etc.), which should certainly be taken into consideration. However, the paper also raises several doubts resulting from mistranslations of some previous research, misinterpretation and incomplete examination of certain published biodiversity data related to the Sea of Marmara. Despite the authors presented a number of mistaken first record data (for example Sardinella aurita Valenciennes, 1837, for full account see Bilecenoglu et al. 2002), included some unsubstantiated/questionable species (such as Symphodus melops (Linnaeus, 1758), Gobius vittatus Vinciguerra, 1883, etc.), and unexpectedly neglected the occurrence of some common coastal and deepsea species from the area, such as Arnoglossus kessleri Schmidt, 1915, Gobius bucchichi Steindachner, 1870, Labrus merula Linnaeus, 1758, Parablennius zvonimiri (Kolombatović, 1892) and Argyropelecus hemigymnus Cocco, 1829, I herein concentrate solely on the erroneous/invalid records (totaling 42 fish species) with appropriate explanations.

Sea lice prevention strategies affect cleaner fish delousing efficacy in commercial Atlantic salmon sea cages

Over the last 2 decades, cleaner fishes have been employed to remove external sea lice parasites from Atlantic salmon Salmo salar in sea cages. Norway, Scotland, Ireland, and the Faroe Islands combined now use ~60 million cleaner fish per year. While small-scale experiments demonstrate the efficacy of cleaner fishes, industrial-scale sea cages have multiple structures and conditions that create different environments, which may impact cleaner fish efficacy and welfare. Here, in commercial sea cages, we investigated if 4 different anti-lice strategies impacted the delousing efficacy, physical condition, and behaviour of cleaner fish (corkwing wrasse Symphodus melops). The strategies tested were: (1) cleaner fishes only; (2) cleaner fishes and functional feed; (3) cleaner fishes, functional feed, and deep lights and feeding; and (4) cleaner fishes, functional feed, deep lights and feeding, and lice skirts. Corkwing wrasse were sampled from 3 cage-level replicates of each anti-lice strategy 3 times over 2 mo. Lice levels on salmon were recorded every 3 to 4 wk. Only 11% of corkwing wrasse had salmon lice in their gut, with individual wrasse having up to 72 lice in their stomach. Wrasse in cages encircled by lice skirts consumed one-ninth as many lice as those in other anti-lice treatments and had less overall impact on the number of lice per salmon. Fin, skin, mouth and eye condition, K factor, and observed cleaning behaviours of corkwing wrasse were similar across all anti-lice strategies. Our results demonstrate that different in-cage anti-lice strategies altered the magnitude of lice consumption in corkwing wrasse at this site and for this production period. Moreover, while a small proportion of corkwing wrasse appear to target lice as prey, most individual corkwing wrasse were ineffective biological control agents in a full-scale farm setting.

Demographic history has shaped the strongly differentiated corkwing wrasse populations in Northern Europe.

Understanding the biological processes involved in genetic differentiation and divergence between populations within species is a pivotal aim in evolutionary biology. One particular phenomenon that requires clarification is the maintenance of genetic barriers despite the high potential for gene flow in the marine environment. Such patterns have been attributed to limited dispersal or local adaptation, and to a lesser extent to the demographic history of the species. The corkwing wrasse (Symphodus melops) is an example of a marine fish species where regions of particular strong divergence are observed. One such genetic break occurred at a surprisingly small spatial scale (FST ~0.1), over a short coastline (<60km) in the North Sea-Skagerrak transition area in southwestern Norway. Here, we investigate the observed divergence and purported reproductive isolation using genome resequencing. Our results suggest that historical events during the post-glacial recolonization route can explain the present population structure of the corkwing wrasse in the northeast Atlantic. While the divergence across the break is strong, we detected ongoing gene flow between populations over the break suggesting recent contact or negative selection against hybrids. Moreover, we found few outlier loci and no clear genomic regions potentially being under selection. We concluded that neutral processes and random genetic drift e.g., due to founder events during colonization have shaped the population structure in this species in Northern Europe. Our findings underline the need to take into account the demographic process in studies of divergence processes.

Interbreeding between local and translocated populations of a cleaner fish in an experimental mesocosm predicts risk of disrupted local adaptation.

Translocation of organisms within or outside its native range carries the risk of modifying the community of the recipient ecosystems and induces gene flow between locally adapted populations or closely related species. In this study, we evaluated the genetic consequences of large‐scale translocation of cleaner wrasses that has become a common practice within the salmon aquaculture industry in northern Europe to combat sea lice infestation. A major concern with this practice is the potential for hybridization of escaped organisms with the local, recipient wrasse population, and thus potentially introduce exogenous alleles and breaking down coadapted gene complexes in local populations. We investigated the potential threat for such genetic introgressions in a large seminatural mesocosm basin. The experimental setting represented a simulated translocation of corkwing wrasse (Symphodus melops) that occurs on a large scale in the Norwegian salmon industry. Parentage assignment analysis of mesocosm's offspring revealed 30% (195 out of 651 offspring) interbreeding between the two populations, despite their being genetically (F ST = 0.094, p < 0.05) and phenotypically differentiated. Moreover, our results suggest that reproductive fitness of the translocated western population doubled that of the local southern population. Our results confirm that human translocations may overcome the impediments imposed by natural habitat discontinuities and urge for immediate action to manage the genetic resources of these small benthic wrasses.

Embryonic development in corkwing wrasse, Symphodus melops

AbstractCorkwing wrasse, Symphodus melops, is one of the main species used as cleaner fish to combat sea lice infestation in salmon aquaculture; however, there is little knowledge about its biology. Here, we describe the embryonic development of this species and examine the viability of the eggs under three temperature regimes. The experiments were conducted at three water temperature regimes, 12, 15, and 18°C, which resemble common sea water temperatures registered during the spawning season of corkwing wrasse at different latitudes along the Norwegian coast. Corkwing wrasse spawn small spherical eggs of 0.75–0.80 mm in diameter (mean 0.78, CV = 3.6%) with several oil droplets and go through eight developmental stages until hatching. The shortest hatching time was registered after 144 hr at 18°C and after 222 and 372 hr at 15 and 12°C, respectively. These observations provide important baseline biological information to advance the establishment of commercial rearing techniques and sustainable fishing management practices for this heavily exploited species.

On the presence of a well-established population of Symphodus melops (Linnaeus, 1758) in the central Mediterranean Sea with notes on its habitat and ecology

The presence of a well-established population of the corkwing wrasse, Symphodus melops (Linnaeus, 1758), is reported for the first time from the central Mediterranean Sea (southwestern Sicily). We discuss about the presence of the species in the area, with notes on its habitat, ecology and distribution.

A continuous genome assembly of the corkwing wrasse (Symphodus melops)

The wrasses (Labridae) are one of the most successful and species-rich families of the Perciformes order of teleost fish. Its members display great morphological diversity, and occupy distinct trophic levels in coastal waters and coral reefs. The cleaning behaviour displayed by some wrasses, such as corkwing wrasse (Symphodus melops), is of particular interest for the salmon aquaculture industry to combat and control sea lice infestation as an alternative to chemicals and pharmaceuticals. There are still few genome assemblies available within this fish family for comparative and functional studies, despite the rapid increase in genome resources generated during the past years. Here, we present a highly continuous genome assembly of the corkwing wrasse using PacBio SMRT sequencing (x28.8) followed by error correction with paired-end Illumina data (x132.9). The present genome assembly consists of 5040 contigs (N50 = 461,652 bp) and a total size of 614 Mbp, of which 8.5% of the genome sequence encode known repeated elements. The genome assembly covers 94.21% of highly conserved genes across ray-finned fish species. We find evidence for increased copy numbers specific for corkwing wrasse possibly highlighting diversification and adaptive processes in gene families including N-linked glycosylation (ST8SIA6) and stress response kinases (HIPK1). By comparative analyses, we discover that de novo repeats, often not properly investigated during genome annotation, encode hundreds of immune-related genes. This new genomic resource, together with the ballan wrasse (Labrus bergylta), will allow for in-depth comparative genomics as well as population genetic analyses for the understudied wrasses.