Monitoring post-spawning movement, habitat use, and survival of adult anadromous rainbow smelt using acoustic telemetry in a New Hampshire estuary.

Anadromous rainbow smelt (Osmerus mordax, [Mitchill 1814]) are found along the northeast Atlantic coastline of North America, with their range now limited to north of Cape Cod, Massachusetts, USA. Although their anadromous life cycles are described broadly, gaps remain regarding how adult rainbow smelt use estuaries post-spawning, including movement behaviors, habitats used, and specific timing of emigration to coastal waters. In spring 2021, we used acoustic telemetry to characterize movements during and after the spawning season of rainbow smelt captured in tributaries to Great Bay, New Hampshire, USA, a large estuarine system near the southern edge of their range. Forty-four adult rainbow smelt (n = 35 male, n = 9 female) were tagged with Innovasea V5 180-kHz transmitters and an array of 22,180 kHz VR2W receivers were deployed throughout Great Bay to detect movements of tagged fish from March to October 2021. Rainbow smelt were detected 14,186 times on acoustic telemetry receivers, with 41 (93%) of the tagged individuals being detected at least once post-tagging. Individuals were detected moving between tributaries, revealing that rainbow smelt can use multiple rivers during the spawning season (March-April). Mark-recapture Cormack-Jolly-Seber models estimated 83% (95% confidence interval 66%-92%) of rainbow smelt survived to the mainstem Piscataqua River, and a minimum of 50% (22 of 44) reached the seaward-most receivers and were presumed to have survived emigration. Most individuals that survived remained in the estuary for multiple weeks (average = 19.47 ± 1.99 standard error days), displaying extended use of estuarine environments. Downstream movements occurred more frequently during ebb tides and upstream movements with flood tides, possibly a mechanism to reduce energy expenditures. Fish emigrated from the estuary by mid-May to the coastal Gulf of Maine. Our results underscore that rainbow smelt need access to a variety of habitats, including multiple tributaries and high-quality estuarine habitat, to complete their life cycle.

Bottlenose dolphin distribution in a Mediterranean area exposed to intensive trawling.

The Adriatic Sea is one of the areas most exposed to trawling, worldwide. We used four years (2018-2021) and 19,887 km of survey data to investigate factors influencing daylight dolphin distribution in its north-western sector, where common bottlenose dolphins Tursiops truncatus routinely follow fishing trawlers. We validated Automatic Identification System information on the position, type and activity of three types of trawlers based on observations from boats, and incorporated this information in a GAM-GEE modelling framework, together with physiographic, biological and anthropogenic variables. Along with bottom depth, trawlers (particularly otter and midwater trawlers) appeared to be important drivers of dolphin distribution, with dolphins foraging and scavenging behind trawlers during 39.3% of total observation time in trawling days. The spatial dimension of dolphin adaptations to intensive trawling, including distribution shifts between days with and without trawling, sheds light on the magnitude of ecological change driven by the trawl fishery.

The movement ecology of fishes.

Movement of fishes in the aquatic realm is fundamental to their ecology and survival. Movement can be driven by a variety of biological, physiological and environmental factors occurring across all spatial and temporal scales. The intrinsic capacity of movement to impact fish individually (e.g., foraging) with potential knock-on effects throughout the ecosystem (e.g., food web dynamics) has garnered considerable interest in the field of movement ecology. The advancement of technology in recent decades, in combination with ever-growing threats to freshwater and marine systems, has further spurred empirical research and theoretical considerations. Given the rapid expansion within the field of movement ecology and its significant role in informing management and conservation efforts, a contemporary and multidisciplinary review about the various components influencing movement is outstanding. Using an established conceptual framework for movement ecology as a guide (i.e., Nathan et al., 2008: 19052), we synthesized the environmental and individual factors that affect the movement of fishes. Specifically, internal (e.g., energy acquisition, endocrinology, and homeostasis) and external (biotic and abiotic) environmental elements are discussed, as well as the different processes that influence individual-level (or population) decisions, such as navigation cues, motion capacity, propagation characteristics and group behaviours. In addition to environmental drivers and individual movement factors, we also explored how associated strategies help survival by optimizing physiological and other biological states. Next, we identified how movement ecology is increasingly being incorporated into management and conservation by highlighting the inherent benefits that spatio-temporal fish behaviour imbues into policy, regulatory, and remediation planning. Finally, we considered the future of movement ecology by evaluating ongoing technological innovations and both the challenges and opportunities that these advancements create for scientists and managers. As aquatic ecosystems continue to face alarming climate (and other human-driven) issues that impact animal movements, the comprehensive and multidisciplinary assessment of movement ecology will be instrumental in developing plans to guide research and promote sustainability measures for aquatic resources.

Infected juvenile salmon can experience increased predation during freshwater migration.

Predation risk for animal migrants can be impacted by physical condition. Although size- or condition-based selection is often observed, observing infection-based predation is rare due to the difficulties in assessing infectious agents in predated samples. We examined predation of outmigrating sockeye salmon (Oncorhynchus nerka) smolts by bull trout (Salvelinus confluentus) in south-central British Columbia, Canada. We used a high-throughput quantitative polymerase chain reaction (qPCR) platform to screen for the presence of 17 infectious agents found in salmon and assess 14 host genes associated with viral responses. In one (2014) of the two years assessed (2014 and 2015), the presence of infectious haematopoietic necrosis virus (IHNv) resulted in 15-26 times greater chance of predation; in 2015 IHNv was absent among all samples, predated or not. Thus, we provide further evidence that infection can impact predation risk in migrants. Some smolts with high IHNv loads also exhibited gene expression profiles consistent with a virus-induced disease state. Nine other infectious agents were observed between the two years, none of which were associated with increased selection by bull trout. In 2014, richness of infectious agents was also associated with greater predation risk. This is a rare demonstration of predator consumption resulting in selection for prey that carry infectious agents. The mechanism by which this selection occurs is not yet determined. By culling infectious agents from migrant populations, fish predators could provide an ecological benefit to prey.

Predation landscapes influence migratory prey ecology and evolution.

Migratory prey experience spatially variable predation across their life cycle. They face unique challenges in navigating this predation landscape, which affects their perception of risk, antipredator responses, and resulting mortality. Variable and unfamiliar predator cues during migration can limit accurate perception of risk and migrants often rely on social information and learning to compensate. The energetic demands of migration constrain antipredator responses, often through context-dependent patterns. While migration can increase mortality, migrants employ diverse strategies to balance risks and rewards, including life history and antipredator responses. Humans interact frequently with migratory prey across space and alter both mortality risk and antipredator responses, which can scale up to affect migratory populations and should be considered in conservation and management.

Migratory coupling between predators and prey.

Animal migrations act to couple ecosystems and are undertaken by some of the world's most endangered taxa. Predators often exploit migrant prey, but the movements taken by these consumers are rarely studied or understood. We define such movements, where migrant prey induce large-scale movements of predators, as migratory coupling. Migratory coupling can have ecological consequences for the participating prey, predators and the communities they traverse across the landscape. We review examples of migratory coupling in the literature and provide hypotheses regarding conditions favourable for their occurrence. We also provide a framework for interactions induced by migratory coupling and demonstrate their potential community-level impacts by examining other forms of spatial shifts in predators. Migratory coupling integrates the fields of landscape, movement, food web and community ecologies, and represents an understudied frontier in ecology.

Whale and dolphin behavioural responses to dead conspecifics.

The scientific study of death across animal taxa-comparative thanatology-investigates how animals respond behaviourally, physiologically and psychologically to dead conspecifics, and the processes behind such responses. Several species of cetaceans have been long known to care for, attend to, be aroused by, or show interest in dead or dying individuals. We investigated patterns and variation in cetacean responses to dead conspecifics across cetacean taxa based on a comprehensive literature review. We analysed 78 records reported between 1970 and 2016, involving 20 of the 88 extant cetacean species. We adopted a weighted comparative approach to take observation effort into account and found that odontocetes (toothed cetaceans) were much more likely than mysticetes (baleen whales) to attend to dead conspecifics. Dolphins (Delphinidae) had the greatest occurrence of attentive behaviour (92.3% of all records), with a weighed attendance index 18 times greater than the average of all other cetacean families. Two dolphin genera, Sousa and Tursiops, constituted 55.1% of all cetacean records (N=43) and showed the highest incidence of attentive behaviour. Results of analyses intended to investigate the reasons behind these differences suggested that encephalisation may be an important predictor, consistent with the "social brain" hypothesis. Among attending individuals or groups of known sex (N=28), the majority (75.0%) were adult females with dead calves or juveniles (possibly their own offspring, with exceptions), consistent with the strong mother-calf bond, or, in a few cases, with the bond between mothers and other females in the group. The remaining records (25.0%) involved males either showing sexual interest in a dead adult or subadult, or carrying a dead calf in the presence of females. Because an inanimate individual is potentially rescuable, responses to dead conspecifics-especially by females-can be explained at least in part by attempts to revive and protect, having a clear adaptive value. In some cases such responses are followed by apparently maladaptive behaviour such as the long-term carrying of, or standing by, a decomposed carcass, similar to observations of certain terrestrial mammals. Among the possible explanations for the observed cetacean behavioural responses to dead conspecifics are strong attachment resulting in a difficulty of "letting go"-possibly related to grieving-or perhaps individuals failing to recognise or accept that an offspring or companion has died. Our current understanding is challenged by small sample size, incomplete descriptions, and lack of information on the physiology and neural processes underpinning the observed behaviour. We provide research recommendations that would improve such understanding.

Tracking wild sockeye salmon smolts to the ocean reveals distinct regions of nocturnal movement and high mortality.

Few estimates of migration rates or descriptions of behavior or survival exist for wild populations of out-migrating Pacific salmon smolts from natal freshwater rearing areas to the ocean. Using acoustic transmitters and fixed receiver arrays across four years (2010-2013), we tracked the migration of > 1850 wild sockeye salmon (Oncorhynchus nerka) smolts from Chilko Lake, British Columbia, to the coastal Pacific Ocean (> 1000 km distance). Cumulative survival to the ocean ranged 3-10% among years, although this may be slightly underestimated due to technical limitations at the final receiver array. Distinct spatial patterns in both behavior and survival were observed through all years. In small, clear, upper-river reaches, downstream migration largely occurred at night at speeds up to 50 km/d and coincided with poor survival. Among years, only 57-78% of smolts survived the first 80 km. Parallel laboratory experiments revealed excellent short-term survival and unhindered swimming performance of dummy-tagged smolts, suggesting that predators rather than tagging effects were responsible for the initial high mortality of acoustic-tagged smolts. Migration speeds increased in the Fraser River mainstem (~220 km/d in some years), diel movement patterns ceased, and smolt survival generally exceeded 90% in this segment. Marine movement rates and survival were variable across years, with among-year segment-specific survival being the most variable and lowest (19-61%) during the final (and longest, 240 km) marine migration segment. Osmoregulatory preparedness was not expected to influence marine survival, as smolts could maintain normal levels of plasma chloride when experimentally exposed to saltwater (30 ppt) immediately upon commencing their migration from Chilko Lake. Transportation of smolts downstream generally increased survival to the farthest marine array. The act of tagging may have affected smolts in the marine environment in some years as dummy-tagged fish had poorer survival than control fish when transitioned to saltwater in laboratory-based experiments. Current fisheries models for forecasting the number of adult sockeye returning to spawn have been inaccurate in recent years and generally do not incorporate juvenile or smolt survival information. Our results highlight significant potential for early migration conditions to influence adult recruitment.

Piscivorous fish exhibit temperature-influenced binge feeding during an annual prey pulse.

Understanding the limits of consumption is important for determining trophic influences on ecosystems and predator adaptations to inconsistent prey availability. Fishes have been observed to consume beyond what is sustainable (i.e. digested on a daily basis), but this phenomenon of hyperphagia (or binge-feeding) is largely overlooked. We expect hyperphagia to be a short-term (1-day) event that is facilitated by gut volume providing capacity to store consumed food during periods of high prey availability to be later digested. We define how temperature, body size and food availability influence the degree of binge-feeding by comparing field observations with laboratory experiments of bull trout (Salvelinus confluentus), a large freshwater piscivore that experiences highly variable prey pulses. We also simulated bull trout consumption and growth during salmon smolt outmigrations under two scenarios: 1) daily consumption being dependent upon bioenergetically sustainable rates and 2) daily consumption being dependent upon available gut volume (i.e. consumption is equal to gut volume when empty and otherwise 'topping off' based on sustainable digestion rates). One-day consumption by laboratory-held bull trout during the first day of feeding experiments after fasting exceeded bioenergetically sustainable rates by 12- to 87-fold at low temperatures (3 °C) and by  Ëœ1·3-fold at 20 °C. The degree of binge-feeding by bull trout in the field was slightly reduced but largely in agreement with laboratory estimates, especially when prey availability was extremely high [during a sockeye salmon (Oncorhynchus nerka) smolt outmigration and at a counting fence where smolts are funnelled into high densities]. Consumption by bull trout at other settings were lower and more variable, but still regularly hyperphagic. Simulations demonstrated the ability to binge-feed increased cumulative consumption (16-32%) and cumulative growth (19-110%) relative to only feeding at bioenergetically sustainable rates during the  Ëœ1-month smolt outmigration period. Our results indicate the ability for predators to maximize short-term consumption when prey are available can be extreme and is limited primarily by gut volume, then mediated by temperature; thus, predator-prey relationships may be more dependent upon prey availability than traditional bioenergetic models suggest. Binge-feeding has important implications for energy budgets of consumers as well as acute predation impacts on prey.

Predator swamping reduces predation risk during nocturnal migration of juvenile salmon in a high-mortality landscape.

Animal migrations are costly and are often characterized by high predation risk for individuals. Three of the most oft-assumed mechanisms for reducing risk for migrants are swamping predators with high densities, specific timing of migrations and increased body size. Assessing the relative importance of these mechanisms in reducing predation risk particularly for migrants is generally lacking due to the difficulties in tracking the fate of individuals and population-level characteristics simultaneously. We used acoustic telemetry to track migration behaviour and survival of juvenile sockeye salmon (Oncorhynchus nerka) smolts released over a wide range of conspecific outmigration densities in a river associated with poor survival. The landscape was indeed high risk; smolt survival was poor (˜68%) over 13·5 km of river examined even though migration was rapid (generally <48 h). Our results demonstrate that smolts largely employ swamping of predators to reduce predation risk. Increased densities of co-migrant conspecifics dramatically improved survival of smolts. The strong propensity for nocturnal migration resulted in smolts pausing downstream movements until the next nightfall, greatly increasing relative migration durations for smolts that could not traverse the study area in a single night. Smolt size did not appear to impact predation risk, potentially due to unique characteristics of the system or our inability to tag the entire size range of outmigrants. Movement behaviours were important in traversing this high-risk landscape and provide rare evidence for swamping to effectively reduce individual predation risk.

Variability in Migration Routes Influences Early Marine Survival of Juvenile Salmon Smolts.

Variability in animal migratory behavior is expected to influence fitness, but few empirical examples demonstrating this relationship exist. The initial marine phase in the migration of juvenile salmon smolts has been identified as a potentially critical life history stage to overall population productivity, yet how fine-scale migration routes may influence survival are unknown. Large-scale acoustic telemetry studies have estimated survival rates of outmigrant Pacific salmon smolts through the Strait of Georgia (SOG) along the British Columbian coastline to the Pacific Ocean, but these data have not been used to identify and characterize fine-scale movements. Data collected on over 850 sockeye salmon (Oncorhynchus nerka) and steelhead (Oncorhynchus mykiss) smolts detected at an array in the Strait of Georgia in 2004-2008 and 2010-2013 were analyzed to characterize migration routes and link movements to subsequent survival at an array 250 km further along the marine migration pathway. Both species exhibited disproportionate use of the most eastern route in the Strait of Georgia (Malaspina Strait). While many smolts moved across the northern Strait of Georgia acoustic array with no indication of long-term milling or large-scale east-to-west movements, large proportions (20-40% of sockeye and 30-50% of steelhead) exhibited a different behavior, apparently moving in a westward or counterclockwise pattern. Variability in migratory behavior for both species was linked to subsequent survival through the Strait of Georgia. Survival for both species was influenced by initial east-to-west location, and sockeye were further influenced by migration timing and duration of time spent near the northern Strait of Georgia array. Westward movements result in a net transport of smolts from Malaspina Strait to the Strait of Georgia, particularly for steelhead. Counterclockwise movements may be due to the currents in this area during the time of outmigration, and the higher proportion of steelhead smolts exhibiting this counterclockwise behavior may reflect a greater exposure to wind-altered currents for the more surface-oriented steelhead. Our results provide an empirical example of how movements can affect migration survival, for which examples remain rare in movement ecology, confirming that variability in movements themselves are an important part of the migratory process.

Distribution and habitat associations of billfish and swordfish larvae across mesoscale features in the Gulf of Mexico.

Ichthyoplankton surveys were conducted in surface waters of the northern Gulf of Mexico (NGoM) over a three-year period (2006-2008) to determine the relative value of this region as early life habitat of sailfish (Istiophorus platypterus), blue marlin (Makaira nigricans), white marlin (Kajikia albida), and swordfish (Xiphias gladius). Sailfish were the dominant billfish collected in summer surveys, and larvae were present at 37.5% of the stations sampled. Blue marlin and white marlin larvae were present at 25.0% and 4.6% of the stations sampled, respectively, while swordfish occurred at 17.2% of the stations. Areas of peak production were detected and maximum density estimates for sailfish (22.09 larvae 1000 m(-2)) were significantly higher than the three other species: blue marlin (9.62 larvae 1000 m(-2)), white marlin (5.44 larvae 1000 m(-2)), and swordfish (4.67 larvae 1000 m(-2)). The distribution and abundance of billfish and swordfish larvae varied spatially and temporally, and several environmental variables (sea surface temperature, salinity, sea surface height, distance to the Loop Current, current velocity, water depth, and Sargassum biomass) were deemed to be influential variables in generalized additive models (GAMs). Mesoscale features in the NGoM affected the distribution and abundance of billfish and swordfish larvae, with densities typically higher in frontal zones or areas proximal to the Loop Current. Habitat suitability of all four species was strongly linked to physicochemical attributes of the water masses they inhabited, and observed abundance was higher in slope waters with lower sea surface temperature and higher salinity. Our results highlight the value of the NGoM as early life habitat of billfishes and swordfish, and represent valuable baseline data for evaluating anthropogenic effects (i.e., Deepwater Horizon oil spill) on the Atlantic billfish and swordfish populations.

AMP-activated protein kinase (AMPK) in the rock crab, Cancer irroratus: an early indicator of temperature stress.

Exposure of marine invertebrates to high temperatures leads to a switch from aerobic to anaerobic metabolism, a drop in the cellular ATP concentration ([ATP]), and subsequent death. In mammals, AMP-activated protein kinase (AMPK) is a major regulator of cellular [ATP] and activates ATP-producing pathways, while inhibiting ATP-consuming pathways. We hypothesized that temperature stress in marine invertebrates activates AMPK to provide adequate concentrations of ATP at increased but sublethal temperatures and that AMPK consequently can serve as a stress indicator (similar to heat shock proteins, HSPs). We tested these hypotheses through two experiments with the rock crab, Cancer irroratus. First, crabs were exposed to a progressive temperature increase (6 degrees C h(-1)) from 12 to 30 degrees C. AMPK activity, total AMPK protein and HSP70 levels, reaction time, heart rate and lactate accumulation were measured in hearts at 2 degrees C increments. AMPK activity remained constant between 12 and 18 degrees C, but increased up to 9.1(+/-1.5)-fold between 18 and 30 degrees C. The crabs' reaction time also decreased above 18 degrees C. By contrast, HSP70 (total and inducible) and total AMPK protein expression levels did not vary significantly over this temperature range. Second, crabs were exposed for up to 6 h to the sublethal temperature of 26 degrees C. This prolonged exposure led to a constant elevation of AMPK activity and levels of HSP70 mRNA. AMPK mRNA continuously increased, indicating an additional response in gene expression. We conclude that AMPK is an earlier indicator of temperature stress in rock crabs than HSP70, especially during the initial response to high temperatures. We discuss the temperature-dependent increase in AMPK activity in the context of Shelford's law of tolerance. Specifically, we describe AMPK activity as a cellular marker that indicates a thermal threshold, called the pejus temperature, T(p). At T(p) the animals leave their optimum range and enter a temperature range with a limited aerobic scope for exercise. This T(p) is reached periodically during annual temperature fluctuations and has higher biological significance than earlier described critical temperatures, at which the animals switch to anaerobic metabolism and HSP expression is induced.