Fishery Species Research Articles

Oyster reef recovery: Impacts of rotational management and restoration efforts on public fishing grounds.

Coastal ecosystems are degraded worldwide and oyster reefs are among the most threatened coastal habitats. Oysters are a critical ecosystem engineer and valuable fishery species, thus effective management strategies must balance tradeoffs between protecting reef ecosystems and continued human use. Management practices for oysters commonly incorporate shell replenishment (provisioning hard substrates to increase reef relief) and spatial management (rotational harvest areas or sanctuaries); however, the impact of these practices on reef dynamics and fisheries outcomes are poorly understood, particularly on harvested reefs. This project examines the efficacy of shell replenishment and spatial management practices on public fishing grounds by analyzing long term datasets available for the Rappahannock River in the Chesapeake Bay, USA. Using generalized linear mixed effects models, we examine how oyster reef metrics (brown shell substrate L m-2, recruit density m-2, market density m-2) and fisheries efficiency (meeting daily bushel harvest limit or not) respond to management actions. Our results indicate that a 3y rotation maintains the underlying reef structure, enhances recruitment, and increases market sized oyster density by 1.23 oysters m-2 on average. Sanctuaries and harvested reefs had comparable brown shell and recruit density; however, sanctuaries had higher market oyster density on average. Shell replenishment practices directly enhanced harvester efficiency, particularly in harvest areas with poor reef condition. Our results indicate that low levels of replenishment (∼1000 bushels acre-1) provide substantial benefits to oyster reefs and the fishery. This study is the first to evaluate the marginal benefits of replenishment activities for biological and fisheries outcomes, and a novel, real world assessment for oyster restoration practices on public fishing grounds. Cumulatively, our findings show that spatial management and replenishment practices enhance oyster reefs in temperate estuaries and offers a framework applicable to other degraded ecosystems worldwide.

Validation and otolith-mass prediction of age and growth for cardinal snapper Pristipomoides macrophthalmus of the Caribbean Sea

Cardinal snapper Pristipomoides macrophthalmus is a commercially important, but commonly misidentified, deepwater species in artisanal and semi-industrial fisheries throughout the Caribbean Sea. As with many tropical deepwater fishes, little is known about the biology or ecology of the species. Bomb radiocarbon (14C) dating was applied to cardinal snapper sagittal otoliths collected from the waters of Belize and Honduras during 2015–2019 to investigate the lifespan of the species from thin-sectioned otoliths with an evaluation of otolith mass as a proxy for age. Ages estimated from 28 thin-sectioned otoliths ranged from 7 to 68 years for fish that covered the range lengths and otolith masses available. Radiocarbon values were measured for each cardinal snapper otolith core, and two fish (one each from Belize and Honduras) had 14C signatures consistent with pre-bomb values, effectively validating a lifespan of at least 60 years. A curvilinear relationship between otolith mass and estimated age was robust (r2 = 0.95) and is likely to produce age estimates with similar margins of error to traditional, more labor-intensive methods, such as counting increments from thin-sectioned otoliths. The otolith mass-to-age relationship is a well-supported method that provides a simple, low-cost approach that can be used by fishers, managers, and other stakeholders to assess the age composition of the cardinal snapper stock in the western Caribbean Sea for present and long-term monitoring.

Fatty Acids of European Sardine (Sardina pilchardus) White Muscle Can Discriminate Geographic Origin Along the Iberian Atlantic Coast.

The European sardine (Sardina pilchardus) ranks among the most valuable species of Iberian fisheries, and the accurate tracing of its geographic origin, once landed, is paramount to securing sustainable management of fishing stocks and discouraging fraudulent practices of illegal, unreported, and unregulated (IUU) fishing. The present study investigated the potential use of S. pilchardus white muscle fatty acids (FAs) to successfully discriminate the geographic origin of samples obtained in seven commercially important fishing harbors along the Iberian Atlantic Coast. While 35 FAs were identified using gas chromatography-mass spectrometry in the white muscle of S. pilchardus, the following, as determined by the Boruta algorithm, were key for sample discrimination: 14:0, 22:6n-3, 22:5n-3, 18:0, 20:5n-3, 16:1n-7, 16:0, and 18:1n-7 (in increasing order of relevance). An average 83% correct allocation of landed specimens was achieved, with some landing locations presenting 100% correct allocation (e.g., Ría de Pontevedra in northern Spain and Peniche in central Portugal). Linear discriminant analysis revealed a separation of samples from northern Spain and Peniche, and a partial overlap of all other locations. The present results highlight the potential of using FAs of S. pilchardus white muscle to reliably discriminate the geographic origin of landed individuals along the Iberian Atlantic coast.

Environmental DNA metabarcoding reveals the presence of invasive and cryptic species in the Mweru-Luapula fishery

Environmental DNA metabarcoding reveals the presence of invasive and cryptic species in the Mweru-Luapula fishery

Angler catch data as a monitoring tool for European barbel Barbus barbus in a data limited recreational fishery

Large bodied freshwater fishes can be important target species for recreational anglers, with some species introduced intentionally to diversify angling experiences. European barbel Barbus barbus is an important target species in many riverine fisheries, including the River Severn and its River Teme tributary, western England, where it has supported a catch-and-release recreational fishery for approximately 50 years. The River Teme was renowned for the quality of its barbel angling from the 1980s. Since 2007, angler dissatisfaction has increased substantially in this fishery, being associated with alleged declines in the number of barbel being captured and in their population abundances. As there were few data available at that time to investigate these declines, data from periodic electric fishing surveys and some angler catch data were sourced. Analyses revealed temporal declines in the number of sampled barbel during electric fishing surveys, although the number of surveys was low, varied between years and did not target barbel specifically. Analyses of four angler catch data sets (1995–2022) involving more than 1000 captured barbel of 0.5–5.3 kg also revealed significant temporal declines in barbel catches (by number and catch-per-unit-effort). These catch declines were generally coincident with reductions in angler presence and effort on the river, suggesting low catches were a driver of angler dissatisfaction. These results provide empirical support for angler claims of substantial declines in barbel catches and abundances, and emphasise that even limited volumes of angler catch data are useful for understanding temporal changes in exploited but data limited fish populations.

Genetic identification of zoonotic parasite Anisakis pegreffii (Nematoda: Anisakidae) parasitizing the shortfin squid Illex argentinus under commercial exploitation in the Southwestern Atlantic Ocean.

Despite the shortfin squid, Illex argentinus, is one of the most important commercial species for the Argentine fisheries, being the third frozen product exported to Europe, the occurrence and distribution of zoonotic anisakid nematodes is scarcely reported. A total of 712 I. argentinus distributed in 17 samples, corresponding to its three main commercial stocks, caught along its distribution range in Argentine waters were examined for anisakid parasites. In total, 360 nematodes were detected in the viscera, however no infestations in the mantle were observed. According to their morphology, all the larvae (L3) were assigned to the genus Anisakis. Genetic identification was performed by sequence analysis of the mitochondrial (mtDNA cox2) gene loci resulting in the record of only Anisakis pegreffii. Distance-based multiple linear regressions (DistLM) evidenced that dorsal mantle length (ML) and date of capture (as surrogate of cohort) were the most important predictors of parasite abundance across infrapopulations in I. argentinus. At component population, DistLM analysis showed that ML and latitude (indirectly representing a gradient in water temperature) were the most important variables determining the prevalence of parasites, however, its mean abundance was only influenced by ML. Parasite burdens were temporally inestable, due to variability in recruitment to host populations, being associated with changing hydrographic conditions and the opportunistic feeding behaviour and annual life cycle of the hosts. The genetic identification of A. pegreffii is relevant for both human health and the fishery industry, given its importance as an etiological agent of human anisakiosis. Due to the restriction of larvae to internal organs, the risk of anisakiosis by the consumption of edible parts of I. argentinus is low.

Multiple Dimensions Define Thresholds for Population Resilience of the Eastern Oyster, Crassostrea virginica.

A species' distribution depends on its tolerance to environmental conditions. These conditions are defined by a minimum, maximum, and optimal ranges of single and combined factors. Forays into environmental conditions outside the minimum or maximum tolerance of a species (i.e., thresholds) are predicted to have large effects on a species' population and may help predict population resilience in the face of changing conditions. Here, we explore ecological thresholds for an important fisheries species and ecosystem engineer, Crassostrea virginica (eastern oyster). In coastal Louisiana, extreme freshwater inputs from rivers and precipitation events impact estuarine salinity, which is a key driver of oyster population dynamics. Using daily salinity and monthly oyster abundance monitoring data across Louisiana estuaries, we explore low salinity exposure threshold levels for oysters. Two statistical approaches were applied, with each model highlighting a different operational definition of a threshold: random forest models identified a threshold as an abrupt change in the oyster abundance- salinity relationship, while Bayesian models identified an increased probability of oysterabundance dropping below a critical threshold, defined here as less than 50% of the 5-year mean. All model results indicate oysters in coastal Louisiana experience low salinity exposure thresholds, defined as the number of consecutive summer days of salinity levels less than 5. However, actual number of days and salinity threshold differed by statistical approach, oyster life stage, and estuary highlighting the multiple dimensions defining ecological thresholds. While thresholds are considered important benchmarks to inform management and assess population or ecosystem vulnerability, our results reveal the need to carefully relate threshold definition to management goals and to acknowledge that thresholds may be highly context dependent.

Species Composition of Crustaceans of Korapuzha Estuary, Kerala, India

The Korapuzha estuarine ecosystem, acting as a link between the freshwater expanse of Akalapuzha and the seawater at Elathur, is characterized by delicate and fragile features. Besides its ecological importance, scientific studies on faunal diversity of Korapuzha is very scarce which emphasizes the necessity of elaborate studies. The present study focusses on species composition of crustaceans, playing a vital role in biogeochemical cycles. The study aims to undertake comprehensive study on crustaceans of Korapuzha estuary, thus minimizing the critical gap in understanding the estuarine ecosystem. Sampling efforts were from 2021 to 2023 involving local participation using various gears. 30 crustaceans were identified under 21 genera, 11 families and two orders, showcasing the complexity in faunal diversity of crustaceans. Shrimps (Fenneropenaeus indicus) and crabs (Scylla serrata) were the dominant species of commercial fisheries. The study highlighted the non-commercial species like Clibanarius infraspinatus (hermit crabs), Balanus Amphitrite and Balanus balanoides (Barnales) and Oratosquilla sp (mantis shrimp). The present study focused on understanding of Korapuzha estuary in detail, thus generating baseline data for conservation and management of estuary. The study also stresses on the economic importance of commercial crustaceans and shows the need for long-term effective conservational measures.

Multiplex panels of SNP markers based on single-base primer extension in the west Pacific pen shell Atrina lischkeana (Clessin, 1891).

As part of stock enhancement programs for marine fishery species, the stocking of hatchery-produced seedlings into sea areas has been implemented worldwide. DNA markers are vital for responsible stock enhancement practices that aim to conserve the genetic diversity of recipient wild populations. We report novel single-nucleotide polymorphism (SNP) markers and multiplex SNP panels developed for the west Pacific pen shell Atrina lischkeana (Clessin, 1891), a large bivalve that is expected to be a subject of stock enhancement activity as the natural resource has dwindled, especially in Japan. On the basis of single-base primer extension combined with MALD-TOF/MS analysis, we developed 218 SNP markers across eight multiplex SNP panels, which allowed genotyping of specimens from two wild A. lischkeana populations. However, our parentage analysis for a captive-bred population sample revealed that 21 of the 218 markers exhibited non-Mendelian patterns of allelic transmission in parent-offspring trios. We verified that the inheritance of undetectable null alleles caused almost all the aberrant allelic transmissions. The developed markers will be of significant use in dealing with issues related to the stock enhancement of A. lischkeana, such as the monitoring of genetic diversity of hatchery stocks and the evaluation of impacts of stocking upon the genetic makeup of recipient wild populations, although caution is warranted especially when the 21 markers with unexpected patterns of allelic segregation are applied to field samples. Additionally, the markers can be analyzed in other targeted genotyping platforms.

Length–Weight Relationships of Commercial Species in the Eastern Australian Sea Cucumber Fishery

Biological data, such as length–weight relationships, are essential for the management and stewardship of harvested individuals. Sea cucumbers are a lucrative industry globally but many of the associated fisheries lack species-level biological data, which reduces the effectiveness of any management strategy. The Queensland Sea Cucumber Fishery (QSCF) on the Great Barrier Reef is managed through various controls: primarily catch limits, effort limits, zoning, and size restrictions. Over 20 species may be harvested but there is a lack of comprehensive biological data for many of these species, particularly important life history characteristics. This study addresses this knowledge gap by assessing 2621 individual length–weight relationships of key-target sea cucumber species associated with the fishery across the range of the distribution of the species and covering a variety of habitats, depths, sampling times, and management zones. Linear models with log transformations were used to analyse the relationships between length and weight. Results revealed significant positive relationships for all assessed species, with Holothuria atra having the clearest relationship between length and weight (R2 = 0.45). Only negative allometric relationships were observed, as is the case for many species of holothurians. Despite challenges associated with measuring and weighing these soft and elastic animals, results will be useful for understanding length–weight dynamics across species. This research underscores the importance of robust biological data for the effective management of sea cucumber fisheries and ultimately reef health.

Pejerrey (Odontesthes bonariensis) Under Siege: Main Infectious Diseases and Their Role in Aquaculture and Wild Populations Amidst Environmental Change.

The pejerrey (Odontesthes bonariensis) is a key species for recreational and commercial fisheries in Argentina and holds significant aquaculture potential. It has been introduced to various countries worldwide, including Japan, where intensive aquaculture has developed. However, infectious diseases present major challenges to its cultivation, as pejerrey is susceptible to diverse pathogens, including bacteria, fungi and parasites. The primary bacterial pathogens affecting pejerrey include the genera Aeromonas, Pseudomonas and Mycobacterium (M. piscida). Fungal-like pathogens such as Saprolegnia spp., and fungal pathogens such as Achyla racemosa and Fusarium species (F. solani and F. semitectum) are also prevalent. Additionally, pejerrey hosts external and internal parasites, primarily Lernaea cyprinacea and members of the genera Cangatiella, Gyrodactylus, Contracaecum and Diplostomum. This review explores the primary infectious diseases affecting pejerrey, focusing on their symptoms, epidemiology and causative pathogens, based on literature from multiple countries and languages. Although no new diseases have emerged, we have identified persistent challenges that have remained unsolved for decades, highlighting the need for further research. Understanding the biology and epidemiology of these pathogens is crucial for expanding the aquaculture of pejerrey. Moreover, we examine how environmental changes, such as global warming, pollution and alien species, may influence disease dynamics in wild populations, stressing the need for management measures to preserve this valuable resource.

The challenge of harvesting common sole (Solea solea) in highly selective trawl fisheries

Common sole (Solea solea) is an economically important species in several European trawl fisheries, yet little is known about the size selective properties of codends used in bottom trawl fisheries targeting sole. This study presents results from a sea trial conducted in the inner Danish waters where common sole is fished in a seasonal trawl fishery using a 90 mm diamond mesh codend with a mandatory large mesh escape panel. To improve understanding of the selectivity in this gear, we in addition tested a plain 90 mm diamond mesh codend without an escape panel. This combination of codend mesh size and large mesh escape panel is part of an ambitious management plan aimed at eliminating bycatch of cod (Gadus morhua) in trawl fisheries in the inner Danish waters. In the fishery for common sole, we found a severe mismatch between gear regulations and minimum conservation reference size of the target species. The outcome is a highly inefficient fishery in which only 22 % (CI: 18–27 %) by weight of the marketable sole is retained in the 90 mm diamond mesh codend. Further, we estimated that 25 % (CI: 16–35 %) of the sole entering the codend would contact the mandatory escape panel and escape, resulting in a total loss of 83 % (CI: 79–87 %) of marketable sole through the mandatory gear. The inefficiency in this fishery demonstrates the need for other means than gear specifications to regulate this type of fishery.

Diving into the fish pathology of an important commercial fish species: the case of the European hake (Merluccius merluccius Linnaeus, 1758) in the northwest Mediterranean Sea.

The gross pathology and the histopathological alterations identified in juvenile specimens of the European hake (Merluccius merluccius), one of the most important target species of commercial fisheries in the northwest Mediterranean, are described. A qualitative and semi-quantitative histological approach was performed in specimens from 2007 and 2019. Prevalence and mean intensity of parasites and histopathological changes were calculated in both years. No macroscopic alterations were found in any organ but several parasites (e.g., copepods, nematodes, digeneans) were detected. Microscopically, alterations identified in gills included foci of inflammation and hyperplasia (present in 77.38% of hakes from both years), extensive hyperplasia (33.33%), and inflammation (16.65%) that were potentially related to the mechanical effects of monogeneans and copepods, cysts of unknown etiology (62.69%), and lamellar inflammation associated to Aporocotyle spinosicanalis eggs (8.33%). Granulomas and inflammatory focus were detected in the liver, spleen, and stomach, apparently associated with the presence of nematodes. Coelozoic myxosporean parasites were detected within the renal tubules (66.66%). Most of the pathologies detected were similar to those described in other gadoid species (i.e., Gadus morhua) and were usually related to the presence of ecto and endoparasites. The potential impact of parasites on the health of this fish species is discussed for improving the knowledge and management of these valuable fishing stocks.

Limited Evidence Base for Determining Impacts (Or Not) of Offshore Wind Energy Developments on Commercial Fisheries Species

ABSTRACTThe coexistence between offshore wind and fisheries has raised questions about potential impacts on species that are fished. We systematically evaluated the offshore wind farm (OWF) literature for evidence of effects leading to impacts on commercial fisheries species. First, we collated evidence of environmental effects of OWFs on fisheries species and then determined whether these could be interpreted as impacts using fishery‐scale and organism‐scale parameters for pelagic finfish, demersal and reef‐associated roundfish, demersal flatfish, elasmobranchs and shellfish. We appraised consistency and level of agreement of direct evidence and explored the body of indirect evidence. A total of 1268 documents featured evidence of OWF effects on fisheries species, with only 60 documents (274 species records) providing direct evidence. Evidence on finfish far outweighed that for shellfish. Demersal and reef‐associated roundfish were the best‐studied group, while elasmobranchs were poorly evidenced. Most studies considered population rather than stock parameters. There was limited evidence of impacts, owing to inconclusive results and inconsistent effects within the parameters assessed—illustrating the importance of looking across the evidence base rather than focussing on individual studies. Hence, there is currently insufficient direct evidence to confidently determine OWF impacts on fisheries species. Overwhelmingly, the evidence deals with indirect effects, although these should not be disregarded as they can highlight plausible impacts on fisheries species, which could guide research and monitoring targeted at understanding the impacts of OWF—a pressing concern given the increased policy commitment of many nations to these two marine sectors sharing marine space.

Using species-specific behavior to improve catch efficiency of target species in mixed trawl fisheries

Demersal trawl fisheries are increasingly challenged by new and more ambitious gear regulations alongside rising fuel costs. However, knowledge of behavioral differences between species are yet poorly integrated and exploited in commercially operated trawl designs. In the demersal mixed species trawl fishery for Nephrops (Nephrops norvegicus), many fish species are herded by the netting and actively avoid contact with the meshes as opposed to Nephrops, for which most individuals are tumbling along the bottom panel of the gear towards the codend. By reducing the mesh size of the entire lower half of the trawl we reduced the loss of marketable sized Nephrops through the bottom panels significantly by 47.2 % (CI: 33.6–60.2 %) in the North Sea. The unchanged catches of the round fish, cod (Gadus morhua) and hake (Merluccius merluccius) confirm that these species do not come in physical contact with the bottom panel. In contrast, witch flounder (Glyptocephalus cynoglossus) escapes through the bottom panel of the baseline trawl as the treatment gear caught 65.1 % (CI: 39.5–104.9 %) more marketable-sized individuals and 259.7 % (CI: 144.4–459.5 %) more undersized individuals. Our results confirm known species-specific behavior in the forward part of the trawl and demonstrate how this can be exploited with simple design changes to increase the catch efficiency for Nephrops and likely other species without affecting the catches of roundfish. The undersized individuals captured will largely escape through the meshes used in commercial codends.

Black abalone status in Baja California. Are there recovery signals for a sustainable harvest?

The black abalone (Haliotis cracherodii) is an important fishery species in Baja California, México; however, in the 1980s, fishing pressure and drastic mortalities due to the wasting syndrome caused the populations to become apparently extinct. Because of population decline, in 1996, the fishing cooperatives agreed to cease the catch. Recently, signs of recovery of the species were observed in some sites, hence, some cooperatives and fishing permit holders obtained catch quotas, which were based on the evaluation of the abalone stock from which extraction permission was requested. Given the risk of the reopening of the fishery, it is vitally important to assess the status of the black abalone populations in Baja California and identify priority sites for the conservation and recovery of the species. In this study, black abalone populations were studied at 22 sites from Tijuana to El Faro San José. Although the observed densities were low (0.0009 to 0.23 abalones/m²), some sites showed moderate densities of juveniles, suggesting recent recruitment. At other sites, we found adults distributed in clusters forming groups of 5 individuals on average, suggesting some probabilities of reproductive success in these populations. We found that juvenile and subadult abalone were associated with moderate habitats, and adults with good habitat. Some sites showed that five or more adults per group were common, suggesting that at these sites successful reproduction might be possible. Our results indicate a high relationship between human disturbance and density, suggesting that this is the main threat to the species in this region. It is imperative that the government, academia, NGO’s and stakeholders work together to propose a recovery plan that assures that enough numbers of individuals are surviving to contribute to healthy and stable populations.

Evaluation of a Wisconsin-type bioenergetics model to estimate brook charr (Salvelinus fontinalis) growth and food consumption under two salinity conditions.

In Québec, Canada, brook charr (Salvelinus fontinalis) is the most sought-after species for recreational fisheries, which makes it economically important. To improve population monitoring and better anticipate climate change impacts on brook charr, bioenergetics models can be useful. The objective of this research was to evaluate the performance of a resident brook charr Wisconsin Energy Budget (WEB) model applied to an anadromous strain under two salinity treatments. Growth and food consumption were predicted by the model and compared to the observed values obtained after a 60-day experiment in the laboratory on fish reared in fresh or brackish water. Predictions for fish reared in fresh water better estimated growth rate and consumption than for fish reared in brackish water, for which growth was overestimated and consumption was underestimated. Overall, these results suggest that there is a difference for the WEB model’s predictions depending on the salinity and that observed food consumption is predicted more accurately than growth.

Characterization of the sex determining region and development of a molecular sex identification method in a Salangid fish

BackgroundThe short-snout icefish, Neosalanx brevirostris, a member of the Salangidae family, is an economically important fishery species in China. Understanding the mechanisms underlying sex determination in this species has crucial implications for conservation, ecology and evolution. Meanwhile, there is a shortage of rapid and cost-effective genetic methods for sex identification, which poses challenges in identifying the sex of immature individuals in sex determination mechanism studies and aquaculture breeding applications.ResultsBased on whole genome resequencing data, sex-specific loci and regions were found to be concentrated in a region on chromosome 2. All sex-specific loci exhibited excess heterozygosity in females and complete homozygosity in males. This sex determining region contains seven genes, including cytochrome P450 aromatase CYP19B, which is involved in steroidogenesis and is associated with 24 sex-specific loci and two W-deletions. A haploid female-specific sequence was identified as paralogous to a diploid sequence with a significant length difference, making it suitable for rapid and cost-effective genetic sex identification by traditional PCR and agarose gel electrophoresis, which were further validated in 24 females and 24 males with known phenotypic sexes.ConclusionsOur results confirm that N.brevirostris exhibits a female heterogametic sex determination system (ZZ/ZW), with chromosome 2 identified as the putative sex chromosome containing a relatively small sex determining region (~ 48 Kb). The gene CYP19B is proposed as a candidate sex determining gene. Moreover, the development of PCR based method enables genetic sex identification at any developmental stage, thereby facilitating further studies on sex determination mechanisms and advancing aquaculture breeding applications for this species.

Ultimate Fighting Crab: Agonistic Behaviour, Dominance, and Recognition in the Edible Crab, Cancer pagurus (L.)

Edible crabs (Cancer pagurus) are an economically important species for Scottish inshore fisheries, with an estimated annual landing value of GBP 16 million (2023). Research into the behaviour, particularly agonistic behaviour, of this species is currently lacking. This paper aims to investigate behaviour, social interactions, potential hierarchies, and the impact of claw size on the outcomes of agonistic interactions of male C. pagurus through behavioural trials and retrials. Crabs were semi-randomly assigned to pairs (based on allocated condition index rating) and introduced to one another in trial tanks. Each pair underwent two trials, 24 h apart (the “trial” and “retrial”). Analyses of video records of agonistic bouts revealed that 77% of retrials were won by the initial victors, with a significant decrease in fight time between trials and retrials. Fight time was not correlated with weapon size (claw length, height, and depth). There were no differences in weapon size of winners and losers of bouts. Winners exhibited a significantly higher frequency of aggressive and dominant behaviours (approach, aggressive contact, threat displays, and mounting), and losers exhibited higher frequencies of submissive behaviours (withdrawal, retracting limbs, and remaining motionless). These results suggest that individual behaviour may play more of a role in dominance than size or other morphometric characteristics.

Population genomics informs the management of harvested snappers across north-western Australia

Failure to consider population structure when managing harvested fishes increases the risk of stock depletion, yet empirical estimates of population structure are often lacking for important fishery species. In this study, we characterise genetic variation in single nucleotide polymorphisms (SNPs) to assess population structure for three harvested species of tropical snappers across the broad (up to 300 km wide) and extensive (~ 4000 km) continental shelf of north-western Australia. Comparisons across ~ 300 individuals per species, showed remarkably similar patterns of genetic structure among Lutjanus sebae (red emperor), L. malabaricus (saddletail snapper) and Pristipomoides multidens (goldband snapper) despite subtle differences in biological and ecological traits. Low levels of genetic subdivision were reflected in an isolation by distance relationship where genetic connectivity increased with geographic proximity. This indicates extensive but not unlimited dispersal across the north-western Australian shelf. Our findings provide evidence of connectivity between current management areas, violating the assumption of multiple independent stocks. Spatial stock assessment models may be more suitable for the management of these species however demographic connectivity rates cannot be accurately estimated from the conventional population genetic approaches applied in this study. We recommend that managers aim to maintain adequate spawning biomass across current management areas, and assess stocks at finer scales, where practical.