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Abstract: Background: Many ecologically and commercially important species occur in the epipelagic marine environment and have been observed to spend a considerable amount of time associating with surface structure. The bottom depth of this habitat often exceeds transmission (~ 500-1000 m) and receiver (500–750 m) range specifications for commonly used acoustic telemetry methods that rely on an array of receivers deployed on the seafloor with overlapping fields of detection to provide positioning of acoustically tagged individuals. This poses logistical challenges for tracking the fine-scale movements, behaviors, and associations to moored and free-floating structure of these species. Acoustic telemetry can provide high resolution positioning data for tagged animals within an array of receivers with overlapping fields of detection; however, this technique has not been applied in deep open-ocean environments off the benthos. Results: Herein, we detail the development of a novel vertical acoustic telemetry array that can be mounted on, or suspended from, various moored and free-floating structures in the open ocean, thus facilitating high resolution tracking of structure-associated epipelagic animals. This new ‘vertical acoustic array’ (VAR) allows for the calculation of a transmitter’s distance from the array and depth with average error around these metrics ranging from 16.2 to 54.8 m (distance error) and 8.6 to 61.5 m (depth error) within the tested range (~ 500 m radius around the array, ~ 300 m deep). We also validated the ability of the VAR to inform the association of an epipelagic species to surface structure by calculating fine-scale positioning for a great barracuda around a fish aggregating device (FAD), which on average was 27.9 ± 2.9 m away at a depth of 9.3 ± 0.4 m over a 9-day tracking period, demonstrating high association with the structure. Conclusions: This new array is able to provide two-dimensional (distance away and depth) animal behavior data around natural and anthropogenic moored and free-floating structures in open-ocean environments where bottom depths often exceed transmission (~ 1000 m) and receiver (~ 500 m) range specifications of traditional bottom moored positioning arrays. This array can also be used to quantitatively assess associations of epipelagic species beyond presence/absence using a single receiver, advancing the potential to improve understanding of the interactions between pelagic fauna and anthropogenic structures such as wind turbines, oil rigs, and fish aggregation devices.

Unprecedented warm river temperatures in July 2023 in Labrador, a subarctic region of Canada, were the highest since monitoring began (1994–2023) and ranged from 19.4°C (Hunt River) to 22.5°C (Eagle River). Incipient lethal water temperatures were exceeded for adult Atlantic salmon and brook trout (≥25°C) on 14 days in five of seven rivers and Arctic charr (≥24°C) on 17 days in six of seven rivers. Consequently, Labrador had the greatest number of angling restrictions and closures in 2023. Recent warming serves as a warning to fishery managers of regions historically unaffected by heat waves of the need to prepare action plans that mitigate the effects of a warming climate on fishes. [ABSTRACT FROM AUTHOR]

Human activities have the potential to accelerate population-level decline by contributing to climate warming and decreasing the capacity of species to survive warming temperatures. Here we build a predictive model to test interactions between river warming and catch and release mortality in recreational fisheries for Atlantic salmon (Salmo salar) by compiling and analyzing published data. We then test whether warming has occurred in rivers where angling occurs and whether angling opportunities have been restricted through increased river closures due to high water temperatures. We find that catch and release mortalities are low ( Les activites humaines ont le potentiel d'accelerer les declins de populations en participant au rechauffement climatique et en reduisant la capacite des especes de survivre a des temperatures en hausse. Nous elaborons un modele predictif pour examiner les interactions entre le rechauffement des rivieres et la mortalite associee a la peche avec remise a l'eau dans la peche sportive au saumon atlantique (Salmo salar), en compilant et en analysant des donnees publiees. Nous verifions ensuite si un rechauffement s'est produit dans les rivieres ou une peche a lieu et si les occasions de peche ont ete restreintes par l'augmentation du nombre de fermetures de riviere en raison de temperatures de l'eau elevees. Nous constatons que les taux de mortalite associes a la peche avec remise a l'eau sont faibles (, Introduction Average global air temperature has increased 0.74 [degrees]C since 1906, with 17 of the 18 warmest years on record occurring since 2001 (IPCC 2018) and with projections of further [...]

Species extinction and population extirpation are now widespread across aquatic ecosystems with many diadromous species, including Atlantic salmon (Salmo salar), in decline throughout much of the North Atlantic. Declines can occur simultaneously at both large and small regional scales rendering factors driving the decreases more elusive. On the south coast of Newfoundland abundance of Atlantic salmon at Conne River fell by 92% over a period of almost four decades in contrast with most other populations in the region suggesting local factors may be contributing to the decline. Here factors potentially contributing to the long-term decline of salmon are reviewed by (1) examining long-term trends in abundance and survival at different life stages, (2) presenting a synopsis on the presence and absence of factors impacting survival and productivity of this population, (3) using a semi-quantitative two dimensional classification system, based on expert opinion, to rank factors potentially contributing to the decline, and (4) utilizing a quantitative Random Forest analysis to complement the expert opinion approach in identifying factors possibly affecting salmon abundance in this south coast Newfoundland population. Results from both qualitative and quantitative analyses identified factors associated with salmon aquaculture as a possible driver of the decline. Additional factors include the influence of both climate change and predation in freshwater and marine habitats. As various Atlantic salmon populations across the native range approach extirpation, the results further highlight the necessity of river-specific analyses in addition to long-term monitoring and fine-scale demographic and threat information in the prioritization of research necessary for conserving or restoring endangered populations. [ABSTRACT FROM AUTHOR]

The pelagic zone of the ocean can be a challenging environment in which to conduct research and as a result we lack the robust baseline abundance and diversity data, compared to what is available in more accessible coastal habitats, to be able to track changes or stressors to the biota in this environment. Many large‐scale fisheries target pelagic fish, and much of the information available on these species is based on fisheries‐dependent data that may be biased towards hotspots and commercially valuable fishes. Here, a long‐term video and visual fish survey was conducted on two subsurface moored fish aggregating devices (FADs) in the pelagic waters of the central Bahamas to determine the feasibility of using moored pelagic FADs as tools for collecting fish abundance and diversity data. A wide range of species was documented, including large migratory fish that are the focus of commercial and recreational fisheries, and smaller often overlooked species on which little abundance or seasonality information exists. We found that FADs colonize quickly and reach a peak stable (albeit seasonally cyclical) abundance and diversity within the first several months after deployment. Species richness was higher in video surveys, but abundance was higher in visual surveys, except for sharks. Our results highlight the need to tailor survey methods to fit the context and study objective, and provide further evidence for the importance of fisheries‐independent data in monitoring pelagic species. [ABSTRACT FROM AUTHOR]

Resource user compliance is a key element in effective fisheries management. Herein, we examine two decades of enforcement records pertaining to Atlantic salmon from Newfoundland and Labrador, Canada. Illegal incidents were negatively correlated with the number of licensed anglers but not salmon abundance. Over two decades, illegal incidents declined by 66%, even after correcting for the positive relationship between enforcement effort and illegal incidents. This decline was primarily driven by a 67% reduction in netting and jigging‐related violations, which were likely to impose the highest levels of mortality on adult salmon among violations examined. Additionally, illegal incidents and violation types did not increase as a result of management changes. While Newfoundland and Labrador remains one of the last strongholds for Atlantic salmon, we encourage other jurisdictions to monitor fisheries compliance to better understand the social‐ecological landscape that is crucial to supporting healthy fisheries. [ABSTRACT FROM AUTHOR]

Partial migration, in which some individuals of a population migrate while other individuals remain resident, is generally associated with ontogenetic shifts to better feeding or as a response to adversity, but its underlying mechanisms remain relatively unknown. Brown trout (Salmo trutta) exhibit partial migration, with some individuals remaining in fresh water (freshwater-resident) while others undertake an anadromous migration, gain most of their adult size at sea, and then return to fresh water to spawn. The option adopted by an individual trout is thought to be partly determined by its growth performance in early life, which in the stochastic and dynamic environment of freshwater streams may be dependent on its flexibility. To examine potential effects of parent type on phenotypic flexibility, we measured the metabolism, growth, and morphology of full-sibling groups of offspring from freshwater-resident and anadromous parents both before and after a switch in diet. We found that fry had a higher growth rate and a more rounded head and body shape when reared on chironomid larvae compared with when they were reared on Daphnia, but diet had no effect on standard metabolic rate. Interestingly, offspring of anadromous parents were less able to maintain their growth rate when fed on Daphnia than were those of freshwater-residents and showed a correspondingly greater increase in growth following a switch from Daphnia to chironomid larvae. Offspring of anadromous parents also showed less morphological flexibility in response to diet than did the offspring of freshwater-residents. We discuss how the migration history of the parents might interact with phenotypic flexibility in early life to influence the migration probability of the offspring. La migration partielle, selon laquelle certains individus d'une population migrent alors que d'autres demeurent residents, est generalement associee a des changements ontogeniques visant une meilleure alimentation ou a une reaction a l'adversite. Les mecanismes de la migration partielle demeurent toutefois meconnus. Les truites de mer (Salmo trutta) font preuve de migration partielle, certains individus demeurant en eau douce (residents d'eau douce), alors que d'autres entreprennent une migration anadrome, la majeure partie de leur croissance jusqu'a la taille adulte s'effectuant en mer avant qu'ils ne retournent en eau douce pour frayer. L'option adoptee par une truite donnee serait en partie determinee par sa performance de croissance au debut de la vie qui, dans le milieu stochastique et dynamique des cours d'eau douce, pourrait dependre de sa flexibilite. Afin d'examiner les effets potentiels du type parental sur la flexibilite phenotypique, nous avons mesure le metabolisme, la croissance et la morphologie de groupes de pleine fratrie de progeniture de parents residents d'eau douce et anadromes, avant et apres un changement de regime alimentaire. Nous avons constate que les alevins se nourrissant de larves de chironomides presentaient un taux de croissance plus grand et avaient des tetes et des corps plus arrondis que ceux se nourrissant de Daphnia, mais le regime alimentaire n'avait pas d'effet sur le metabolisme standard. Fait interessant, la progeniture de parents anadromes etait moins en mesure de maintenir son taux de croissance quand elle se nourrissait de Daphnia que la progeniture de residents d'eau douce, et elle presentait une augmentation consequente de sa croissance quand elle passait d'une alimentation a base de Daphnia a un regime de larves de chironomides. La progeniture de parents anadromes presentait egalement une moins grande flexibilite morphologique en reponse a l'alimentation que la progeniture de residents d'eau douce. Nous abordons l'influence possible de l'interaction de l'historique de migration des parents avec la flexibilite phenotypique au debut de la vie sur la probabilite de migration de la progeniture. [Traduit par la Redaction], Introduction Phenotypic flexibility, an organism's ability to match its morphology and physiology to current environmental conditions, is fundamental to adaptability and occurs when complementary combinations of traits change in response [...]

Territoriality is one of the best examples of interference competition and generally results in larger, dominant individuals gaining preferential access to food. However, the expectation of higher growth of dominant individuals among juvenile salmonids has received only mixed support. We used outdoor semi-natural stream channels stocked with varying sizes of young of the year juvenile salmonids under high and low food rations (i) to examine the mechanisms underlying variation in the benefits of dominance and (ii) to demonstrate that inconsistencies in the apparent benefits of dominance are a logical outcome of the allometry of growth and differential energy intake among fish of different size in a dominance hierarchy. Growth of dominants exceeded that of subordinates when food was abundant, but subordinates grew faster than dominants in low food treatments and when dominant fish increased in size and approached the capacity of their habitat. In general, size disparity within a dominance hierarchy may promote higher growth of subdominants because of the lower energetic requirements of smaller individuals, and the allometry of fish growth, relative to habitat capacity, can reverse the expected growth and condition of dominant and subordinate fish. La territorialite est l'un des meilleurs exemples de la competition par interference et elle produit generalement des individus plus grands et dominants qui ont un acces preferentiel a la nourriture. Bien qu'on s'attende a une croissance accrue chez les individus dominants parmi les jeunes saumons, les donnees n'appuient pas clairement cette attente. Nous avons utilise des canaux semi-naturels empoissonnes de jeunes salmonides de l'annee de tailles diverses dans des conditions elevees et basses de nourriture afin (i) d'examiner les mecanismes qui expliquent la variation dans les benefices de la dominance et (ii) de demontrer que les incoherences dans les benefices apparents de la dominance sont le resultat logique de l'allometrie de la croissance et de l'incorporation differentielle de l'energie chez les poissons de tailles differentes dans une hierarchie de dominance. La croissance des dominants depasse celle des subordonnes lorsque la nourriture est abondante, mais les subordonnes croissent plus vite que les dominants en conditions de nourriture restreinte et lorsque les poissons dominants augmentent en taille et s'approchent du stock limite de leur habitat. En general, la disparite des tailles dans une hierarchie de dominance peut promouvoir une croissance plus forte des subordonnes a cause des besoins plus faibles en energie des individus plus petits; l'allometrie de la croissance, en relation avec le stock limite de l'habitat, peut inverser la croissance et la condition auxquelles ont s'attend chez les poissons dominants et subordonnes. [Traduit par la Redaction], Introduction Territoriality is one of the best examples of interference competition and generally results in larger dominant individuals gaining preferential access to food, shelter, or mates. Territoriality occurs across a [...]

We describe observations of sea lamprey (Petromyzon marinus) and striped bass (Morone saxatilis) incursions into Labrador, Canada. While P. marinus have been periodically observed in similar latitudes, their numbers have conspicuously increased in estuarine environments in 2020. In contrast, M. saxatilis were not observed from Labrador until 2017 but appear to be declining after the initial surge in abundance that peaked in 2018. It remains unclear whether spawning populations of either species exist. Given the potential to negatively affect species of commercial and cultural importance through predation, follow‐up surveys are warranted. [ABSTRACT FROM AUTHOR]

Warming water temperatures, combined with increased mortality following catch and release, could have synergistic consequences if rivers remain open to catch and release at high water temperatures, and catchability of fish remains similar across water temperatures. Here archived data for Atlantic salmon, Salmo salar L., were used to (a) quantify the influence of water temperature on catchability and (b) refine estimates of absolute catch and release mortality to incorporate the relationship between temperature and catchability. A significant decline in the number of Atlantic salmon caught at warmer water temperatures was found after accounting for the effects of river water height, fishing effort, run duration and year‐to‐year differences in fish abundance. Overall, absolute catch and release mortalities were predicted to be infrequent at cool river temperatures. At river temperatures sometimes associated with fishing closures, mortality due to the catch and release ranged from 6% to 14%. Although post‐release mortality increases with water temperature, it is somewhat compensated by the reduced catchability of Atlantic salmon. Thus, the catchability component of catch and release is an integral consideration when evaluating the effectiveness of river closure temperature thresholds when managing catch and release angling. [ABSTRACT FROM AUTHOR]

ABSTRACT The red rock crab, Cancer productus, is primarily harvested by a recreational fishery, with a small commercial harvest in California. Although relatively large, meat yields are low because the legs are small, and meat is largely confined to the claws. We investigated the potential for a claw‐only harvest for this species. Although hand removal is used in the stone crab fishery, it caused > 90% post‐harvest mortality in red rock crabs. Inducing autotomy by inserting a spike into the arthrodial membranes or by cutting into the autotomy plane resulted in a high post‐harvest survival. We recommend a minimum harvest size of 35 mm claw height to produce a claw size similar to medium‐sized stone crabs and standard‐sized brown and Jonah crabs and to ensure that severed claws are unlikely to have come from female crabs, which is important for regions that mandate a male‐only harvest. [ABSTRACT FROM AUTHOR]

Gecarcinid land crabs are ecosystem engineers playing an important role in nutrient recycling and seedling propagation in coastal forests. Given a predicted future decline in precipitation for the Caribbean, the effects of dehydration on feeding preferences of the black land crab Gecarcinus ruricola were investigated. G. ruricola were offered novel food items of lettuce, apple, or herring to test for food choice based on water and nutritional (energetic) content in single and multiple choice experimental designs. The effect of dehydration was incorporated by depriving crabs of water for 0, 4, or 8 days, leading to an average body water loss of 0%, 9%, and 17%, respectively, (crabs survived a body water loss of 23% + 2% and 14–16 days without access to water). The results were consistent between the single and multiple choice experiments: crabs consumed relatively more apple and fish and only small amounts of lettuce. Overall, no selective preferences were observed as a function of dehydration, but crabs did consume less dry food when deprived of water and an overall lower food intake with increasing dehydration levels occurred. The decrease in feeding was likely due to loss of water from the gut resulting in the inability to produce ample digestive juices. Future climatic predictions suggest a 25–50% decline in rainfall in the Caribbean, which may lead to a lower food intake by the crabs, resulting in compromised growth. The subsequent reduction in nutrient recycling highlights possible long-term effects on coastal ecosystems and highlights the importance of future work on climate relative behavioral interactions that influence ecosystem function. [ABSTRACT FROM AUTHOR]

Large and long‐lived piscivorous brown trout, Salmo trutta, colloquially known as ferox trout, have been described from a number of oligotrophic lakes in Britain and Ireland. The "ferox" life history strategy is associated with accelerated growth following an ontogenetic switch to piscivory and extended longevity (up to 23 years in the UK). Thus, ferox trout often reach much larger sizes and older ages than sympatric lacustrine invertebrate‐feeding trout. Conventional models suggest that S. trutta adopting this life history strategy grow slowly before a size threshold is reached, after which, this gape‐limited predator undergoes a diet switch to a highly nutritional prey source (fish) resulting in a measurable growth acceleration. This conventional model of ferox trout growth was tested by comparing growth trajectories and age structures of ferox trout and sympatric invertebrate‐feeding trout in multiple lake systems in Scotland. In two of the three lakes examined, fish displaying alternative life history strategies, but living in sympatry, exhibited distinctly different growth trajectories. In the third lake, a similar pattern of growth was observed between trophic groups. Piscivorous trout were significantly older than sympatric invertebrate‐feeding trout at all sites, but ultimate body size was greater in only two of three sites. This study demonstrates that there are multiple ontogenetic growth pathways to achieving piscivory in S. trutta and that the adoption of a piscivorous diet may be a factor contributing to the extension of lifespan. [ABSTRACT FROM AUTHOR]

Dominance hierarchies, where they exist, affect individual food acquisition ability and fitness, both of which have the potential to influence life history pathways. Juvenile salmonids exhibit clear dominance hierarchies in early life. As one of the drivers for the adoption of alternative life histories in salmonids is the relative rate of resource acquisition, there is potential for juvenile behaviour to influence the subsequent life history strategy of the individual. Lacustrine brown trout, Salmo trutta, exhibit a multitude of life histories which includes among others the piscivorous (ferox) life history where individuals grow to large size and have delayed maturity and benthivorous and pelagic life histories where individuals grow to much smaller sizes, however mature earlier. Using a number of observable characteristics of dominance, this study compared differences in behaviour between size-matched pairs of progeny, reared under common garden conditions which are derived from alternative, co-existing life history strategy parents. We found that first-generation progeny of ferox trout were more aggressive, acquired more food, had lighter skin pigmentation and held more desirable positions than the progeny of benthivorous brown trout in an experimental stream system. Ferox trout progeny were dominant over benthivorous brown trout progeny in 90% of trials in dyadic contests. Given such clear differences in dominance, this study indicates that parentally acquired dominance-related differences, passed through either, or both, of genetic and nongenetic (e.g. maternal effects) means, are likely a contributing factor to the continued maintenance of distinct life history strategies of brown trout. [ABSTRACT FROM AUTHOR]

Partial migration, in which some individuals of a population migrate while other individuals remain resident, is generally associated with ontogenetic shifts to better feeding areas or as a response to environmental instability, but its underlying mechanisms remain relatively unknown. Brown trout ( Salmo trutta) exhibit partial migration, with some individuals remaining in freshwater (freshwater resident) while others undertake an anadromous migration, where they spend time at sea before returning to breed in freshwater (migrant). We reared full-sibling groups of offspring from freshwater-resident and anadromous brown trout from the same catchment in the laboratory under common garden conditions to examine potential differences in their early development. Freshwater-resident parents produced eggs that were slower to hatch than those of anadromous parents, but freshwater-resident offspring were quicker to absorb their yolk and reach the stage of exogenous feeding. Their offspring also had a higher conversion efficiency from the egg stage to the start of exogenous feeding (so were larger by the start of the fry stage) than did offspring from anadromous parents despite no difference in standard metabolic rate, maximal metabolic rate or aerobic scope. Given these differences in early development, we discuss how the migration history of the parents might influence the migration probability of the offspring. [ABSTRACT FROM AUTHOR]

Partial migration, in which some individuals of a population migrate and others remain sedentary, is a phenomenon that occurs across a wide range of taxa, but the factors that predispose particular individuals to one or the other strategy are usually unknown. Brown trout (Salmo trutta) initially compete for feeding territories in freshwater streams, but while some individuals remain resident in fresh water throughout their lives, others undertake an anadromous migration. Because one of the drivers for migration is the relative rates of resource acquisition in different habitats, we compared the ability of juvenile offspring from freshwater-resident and anadromous parents to compete for feeding territories; we also tested how this depended on the quality of the environment previously experienced. Brown trout derived from freshwater-resident or anadromous parents were reared for ~7 months under high-, mid-, or low-food regimes and were then induced to compete for feeding territories in a seminatural stream channel. We found that the parental type had a significant effect on dominance status in territorial interactions, with offspring of anadromous fish being dominant over sizematched offspring of freshwater residents, but only when both had been raised under intermediate levels of food availability. The results suggest that the migration strategy of the parents interacts with the environmental conditions experienced by the offspring to potentially influence its motivation to compete for feeding territories and hence its probability of migration. [ABSTRACT FROM AUTHOR]

In many taxa there is considerable intraspecific variation in life history strategies from within a single population, reflecting alternative routes through which organisms can achieve successful reproduction. Atlantic salmon Salmo salar (Linnaeus) show some of the greatest within-population variability in life history strategies amongst vertebrates, with multiple discrete male and female life histories co-existing and interbreeding on many spawning grounds, although the effect of the various combinations of life histories on offspring traits remains unknown. Using crosses of wild fish we show here that the life history strategy of both parents was significantly associated with a range of offspring traits. Mothers that had spent longer at sea (2 versus 1 year) produced offspring that were heavier, longer and in better condition at the time of first feeding. However, these relationships disappeared shortly after fry had begun feeding exogenously. At this stage, the juvenile rearing environment (i.e. time spent in fresh water as juveniles) of the mother was a better predictor of offspring traits, with mothers that were faster to develop in fresh water (migrating to sea after two rather than three years of age) producing offspring that had higher maximal metabolic rates, aerobic scopes, and that grew faster. Faster developing fathers (1 year old sneaker males) tended to produce offspring that had higher maximal metabolic rates, were in better body condition and grew faster. The results suggest that both genetic effects and those related to parental early and late life history contribute to offspring traits. [ABSTRACT FROM AUTHOR]

Acoustic telemetry is an important tool for studying the behaviour of aquatic organisms in the wild.VEMCO high residence (HR) tags and receivers are a recent introduction in the field of acoustic telemetry and can be paired with existing algorithms (e.g. VEMCO positioning system [VPS]) to obtain high-resolution two-dimensional positioning data.Here, we present results of the first documented field test of a VPS composed of HR receivers (hereafter, HR-VPS). We performed a series of stationary and moving trials with HR tags (mean HR transmission period = 1.5 s) to evaluate the precision, accuracy and temporal capabilities of this positioning technology. In addition, we present a sample of data obtained for five European perch Perca fluviatilis implanted with HR tags (mean HR transmission period = 4 s) to illustrate how this technology can estimate the fine-scale behaviour of aquatic animals.Accuracy and precision estimates (median [5th-95th percentile]) of HR-VPS positions for all stationary trials were 5.6 m (4.2-10.8 m) and 0.1 m (0.02-0.07 m), respectively, and depended on the location of tags within the receiver array. In moving tests, tracks generated by HR-VPS closely mimicked those produced by a handheld GPS held over the tag, but these differed in location by an average of ≈9 m.We found that estimates of animal speed and distance travelled for perch declined when positional data for acoustically tagged perch were thinned to mimic longer transmission periods. These data also revealed a trade-off between capturing real nonlinear animal movements and the inclusion of positioning error.Our results suggested that HR-VPS can provide more representative estimates of movement metrics and offer an advancement for studying fine-scale movements of aquatic organisms, but high-precision survey techniques may be needed to test these systems.