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In recent decades, the relative proportion of female sockeye salmon (Oncorhynchus nerka) on spawning grounds of several British Columbia populations has declined. Coincident with the decline has been large changes to oceanic, estuarine, and river migration environments. Over the past 30 years, numerous telemetry tracking and laboratory studies have examined mortality of adult Fraser River sockeye salmon during ocean and freshwater migrations. We reviewed 19 studies that provided 40 situations where male and female mortality could be directly compared. Female mortality averaged 2.1 times greater than that of males and up to eightfold higher. High female mortality was also evident in migrating coho salmon (Oncorhynchus kisutch) and Chinook salmon (Oncorhynchus tshawytscha) and for sockeye salmon in other systems. Female mortality was highest when migration conditions were challenging (e.g., high or turbulent flows, high temperatures, confinement, or handling) and towards end of river migration. We review mechanisms for differential mortality, including energy exhaustion, cardiac performance, physiological stress, and immune factors. Female-specific mortality will become even more pronounced in coming years as ocean and riverine conditions continue to change.

Many of the world’s rivers are dammed, altering the physiology, behaviour, ecology and survival of fish. Integrative research has the potential to improve our understanding of these impacts and could enable environmental managers to develop effective solutions for population conservation. Such approaches, however, are not yet prevalent. We use a case study on Pacific salmon (Oncorhynchus spp.) in British Columbia, Canada, to demonstrate how regulated rivers may be used as experimental systems, allowing for applied research that can advance our understanding of the biology of migratory fish as well as our ability to manage them. Through the integration of multiple research approaches (i.e. biotelemetry, behavioural tests, physiological and molecular analyses, and hydraulic monitoring), we characterized the effects of natal water dilution and dam flow releases on upstream navigation, passage success and post-passage survival of returning adult salmon. Our findings confirmed previously established operational guidelines for natal water dilution and informed the adoption of new operational conditions for dam flow releases, providing an example of the successful application of integrative research to the management of a fisheries resource in a regulated river. We encourage researchers to consider using an experimental approach that integrates multiple research disciplines to inform science-based management action.

Expression of 12 olfactory genes was analysed in adult sockeye salmon Oncorhynchus nerka nearing spawning grounds and O. nerka that had strayed from their natal migration route. Variation was found in six of these genes, all of which were olfc olfactory receptors and had lower expression levels in salmon nearing spawning grounds. The results may reflect decreased sensitivity to natal water olfactory cues as these fish are no longer seeking the correct migratory route. The expression of olfactory genes during the olfactory-mediated spawning migration of Pacific salmon Oncorhynchus spp. is largely unexplored and these findings demonstrate a link between migratory behaviours and olfactory plasticity that provides a basis for future molecular research on salmon homing.

Most Pacific salmon Oncorhynchus spp. migrate to their natal sites to spawn. Some, however, stray into nonnatal habitats and interact (e.g., reproduce) with individuals from other populations. Pacific salmon straying has been heavily studied for several decades, particularly from the perspective of the populations that donate the stray migrants. Conservation consequences are experienced primarily by the populations that receive strays, though, and there is recent evidence of significant levels of genetic introgression in small recipient populations, which could contribute to the loss of local adaptations. Straying may also provide the benefit of a demographic rescue effect that could save declining recipient populations from extirpation. We highlight the influence of population abundances on the magnitude of straying into recipient populations and demonstrate this using evidence we collected from a small population of Sockeye Salmon O. nerka in British Columbia, Canada. We also review potential factors th...

Effective dam management requires an understanding of the ecological impact of a facility and its operations on individual fish and fish populations. Traversing high flows downstream of dams is an energetically challenging activity that could influence survival and spawning success following passage. Carryover effects, however, are an underappreciated consequence of dam passage that have been overlooked by researchers and natural resource managers. We conducted a large-scale management experiment to determine if the operation of dam attraction flows could be changed to reduce high sockeye salmon Oncorhynchus nerka mortality following passage and increase spawning success. We tested two flow conditions: (i) a baseline condition—currently used by managers—that released high attraction flows directly adjacent to the entrance to a vertical-slot fishway and (ii) an alternative condition that released attraction flows 10 m away from the fishway entrance to reduce the flows fish swim through while approaching the passage structure. We tagged 637 sockeye salmon with telemetry tags to monitor dam passage, post-passage survival to spawning grounds and spawning success under the two flow conditions. Validated fish counters at the exit of the fishway and on spawning grounds were used to generate population level estimates of survival to spawning grounds. Individuals exposed to baseline flow conditions spent two times longer recovering from dam passage and exhibited 10% higher mortality following passage than those exposed to alternative flows. Release of alternative flows for 10 days assisted approximately 550 fish (or 3% of total spawners) in reaching spawning grounds. Once on spawning grounds, female spawning success was strongly influenced by individual spawning characteristics (longevity and date of arrival on spawning grounds) and not dam flow condition. Our findings highlight a cost-effective solution that decreases mortality following passage simply by altering the location of dam flow releases and not reductions in discharge. Copyright © 2016 John Wiley & Sons, Ltd.

Migrations are characterized by periods of movement that typically rely on orientation towards directional cues. Anadromous fish undergo several different forms of oriented movement during their spawning migration and provide some of the most well-studied examples of migratory behaviour. During the freshwater phase of the migration, fish locate their spawning grounds via olfactory cues. In this review, we synthesize research that explores the role of olfaction during the spawning migration of anadromous fish, most of which focuses on two families: Salmonidae (salmonids) and Petromyzontidae (lampreys). We draw attention to limitations in this research, and highlight potential areas of investigation that will help fill in current knowledge gaps. We also use the information assembled from our review to formulate a new hypothesis for natal homing in salmonids. Our hypothesis posits that migrating adults rely on three types of cues in a hierarchical fashion: imprinted cues (primary), conspecific cues (secondary), and non-olfactory environmental cues (tertiary). We provide evidence from previous studies that support this hypothesis. We also discuss future directions of research that can test the hypothesis and further our understanding of the spawning migration.

Directed animal movement, which drives behaviors such as natal philopatry or dispersal, is guided by the input of sensory information. Anadromous salmonids are philopatric (they return to their natal habitat to reproduce), and their upstream movements during the spawning migration are directed by olfactory cues. Two main sources of olfactory cues have been identified—imprinted natal cues and pheromones—although the relative importance of these cues is unresolved. We tested the response of migratory adult sockeye salmon (Oncorhynchus nerka) to conspecific odors in the presence of, and in the absence of, imprinted natal cues. The results indicate that sockeye salmon are attracted to conspecifics when imprinted natal cues are absent, but not when they are present. This suggests that pheromones may provide a directional cue that is secondary to the primary cue of imprinted chemicals. The finding follows the hierarchical navigation hypothesis and is supported by previous findings in salmonid research. There are several potential benefits to this method of navigation that could increase the reproductive success of stray migrants, which could promote dispersal and increase genetic diversity within populations.

Pacific salmon (Oncorhynchus spp.) navigate towards spawning grounds using olfactory cues they imprinted on as juveniles. The timing at which imprinting occurs has been studied extensively, and there is strong evidence that salmon imprint on their natal water during the parr-smolt transformation (PST). Researchers have noted, however, that the life histories of some species of Pacific salmon could necessitate imprinting prior to the PST. Juvenile pink salmon (O. gorbuscha) spend less time in fresh water than any other species of Pacific salmon, and presumably must imprint on their natal water at a very young age. The time at which imprinting occurs in this species, however, has not been experimentally tested. We exposed juvenile pink salmon as alevins to phenethyl alcohol (PEA) or control water, reared these fish to adulthood, and then tested their behavioural responses to PEA to determine whether the fish successfully imprinted. We found that pink salmon exposed to PEA as alevins were attracted to the chemical as adults, suggesting that imprinting can occur during this stage. Our finding provides some of the first evidence to support the long-standing belief that imprinting can occur in pink salmon prior to the PST.

Many fish that are exposed to a threat release disturbance cues, which are chemicals that alert conspecifics to the presence of the threat. The release of disturbance cues has been well demonstrated in various species of laboratory-reared fish. Migratory fish species often exhibit increased cortisol levels and are exposed to numerous stressors during their migrations, which could trigger the release of disturbance cues. We tested the responses of wild migrating sockeye salmon (Oncorhynchus nerka) and pink salmon (O. gorbuscha) to the odours of disturbed and undisturbed conspecifics to determine whether these fish release disturbance cues following exposure to a simulated stressor. Furthermore, we tested the responses of sockeye salmon to water-borne cortisol, following evidence from past studies that this chemical is excreted through the gills of stressed fish, and speculation that endogenous correlates of stress might function as disturbance cues. We found that sockeye salmon avoid the odour of disturbed conspecifics, whereas pink salmon do not. Avoidance occurred in both female and male sockeye salmon, and was associated with an increase in plasma cortisol levels in females, but not in males. We also found no behavioural response to water-borne cortisol, which suggests this chemical does not act as an exogenous disturbance cue in sockeye salmon. Avoidance of disturbed conspecifics could limit exposure to risks during the sockeye salmon spawning migration, but could also delay the rate of migration and thereby accrue reproductive costs.

The impressive diversity and unique distribution of primate taxa in Southeast Asia creates a region of interesting biogeography and evolutionary history that remains poorly understood. The three species in the Asian colobine genus Pygathrix (P. cinerea, P. nemaeus, and P. nigripes) appear to follow the unique distribution pattern, replacing one another along the north–south axis. However, the evolutionary history and taxonomic status within Pygathrix is currently debated. We constructed climate-based ecological niche models (ENMs) for the three species, using six environmental variables, to confirm that the bioclimate envelopes of Pygathrix cinerea, P. nemaeus, and P. nigripes follow the north–south gradient. We also used the ENMs to test whether the three species lack ecological exchangeability, meaning differentiation among factors that define the fundamental niche, and whether they exhibit ecological niche conservatism, or the tendency for related species to differ less ecologically than might be expected by the climate available to each species. Our ENMs for Pygathrix followed a north–south gradient as expected, with P. nemaeus extending from ca. 14°N to 21°N, P. cinerea from 14°N to 16°N, and P. nigripes from 11°N to 13.5°N. This study presents the first use of ENMs for doucs that yield significant predictive ability based only on climatic variables. The models are significantly different for all three species, supporting a lack of ecological exchangeability between them, as well as the recent elevation of Pygathrix cinerea to species status. Importantly, Pygathrix cinerea and P. nemaeus show evidence of ecological niche conservatism, which lends support to the occurrence of an allopatric speciation event. This result also suggests that the current overlapping distribution of Pygathrix cinerea and P. nemaeus is the result of secondary contact. The north–south distribution gradient, which exists in similar form among other groups of sister taxa in the region, may be attributed to a zoogeographic barrier, vicariance, or current or historical climatic shifts.

Migrations are characterized by periods of movement that typically rely on orientation towards directional cues. Anadromous fish undergo several different forms of oriented movement during their spawning migration and provide some of the most well-studied examples of migratory behaviour. During the freshwater phase of the migration, fish locate their spawning grounds via olfactory cues. In this review, we synthesize research that explores the role of olfaction during the spawning migration of anadromous fish, most of which focuses on two families: Salmonidae (salmonids) and Petromyzontidae (lampreys). We draw attention to limitations in this research, and highlight potential areas of investigation that will help fill in current knowledge gaps. We also use the information assembled from our review to formulate a new hypothesis for natal homing in salmonids. Our hypothesis posits that migrating adults rely on three types of cues in a hierarchical fashion: imprinted cues (primary), conspecific cues (secondary), and non-olfactory environmental cues (tertiary). We provide evidence from previous studies that support this hypothesis. We also discuss future directions of research that can test the hypothesis and further our understanding of the spawning migration.

For many people, the combination of the words ‘fish’ and ‘smell’ has a negative connotation. As defined in the Oxford English Dictionary, ‘smell’ is Ba quality in something that is perceived by the faculty of smell^, andwhen the word ‘fish’ is attached, that quality is an unpleasant one. But for some people, at least in the world of fish biology, their minds jump to a different definition in the OED: Bthe faculty or power of perceiving odours or scents by means of the organs in the nose^. This book will appeal to such people. More specifically, the book focuses on ‘pheromones’, a term that was first coined in 1959 (Karlson and Luscher 1959). The study of pheromones, however, pre-dates the word itself, and can be traced back to at least the 1800’s. The field reached a wider audience within the scientific community in the middle of the 20th century, following Karl Von Frisch’s pioneering studies on communication in honey bees. Von Frisch also documented the release of chemical alarm signals by injured minnows, and this discovery presaged a major focus on pheromone research in the aquatic environment. A cursory look through the book’s reference sections suggests there has been another, more recent surge in studies on fish pheromones over the past two decades. Despite the long history and recent advances in this field, however, the Preface notes that this is the first book of its kind, which puts it in the unique position of being both timely and over-due. The first chapter defines several relevant terms and seeks to create a common framework for the sections that follow. Chief among these terms are those found in the book’s title—‘pheromones’ and ‘related cues’. ‘Pheromones’ are identified as adaptive chemical cues that elicit a specific response in conspecifics. They also communicate information that is shared by all individuals of a species (Sorensen describes them as Banonymous^). ‘Related conspecific cues’, on the other hand, are learned or highly context dependent, and can vary significantly among individuals (they can act as an individual fish’s Bsignature^). The distinction between these two categories is not always clear, however, and the use of these terms in later chapters is not uniform. In one chapter, for example, Wisenden warns that many of the fish ‘pheromones’ currently studied are not truly pheromones (because there is no apparent selective pressure on the sender of the cues), but in the next chapter the term ‘pheromone’ is used for precisely these types of chemicals. This does not detract from the quality of the book’s content, but perhaps indicates a missed opportunity to provide a unified framework for terminology. A main focus early in the book is the species-specific properties of pheromones and their related cues. Sorensen and Baker introduce the term ‘pheromone complexes’, which could be Bmixtures of relatively common metabolic products^ that are combined in different ways to create species-specific pheromones. From an evolutionary standpoint, this might provide a simpler alternative to the adaptation of uniquely specialized pheromones within Environ Biol Fish (2015) 99:169–170 DOI 10.1007/s10641-015-0460-y

An improved understanding of bycatch mortality can be achieved by complementing field studies with laboratory experiments that use physiological assessments. This study examined the effects of water temperature and the duration of net entanglement on physiological disturbance and recovery in coho salmon (Oncorhynchus kisutch) after release from a simulated beach seine capture. Heart rate was monitored using implanted electrocardiogram biologgers that allowed fish to swim freely before and after release. A subset of fish was recovered in respirometers to monitor metabolic recovery, and separate groups of fish were sacrificed at different times to assess blood and white muscle biochemistry. One hour after release, fish had elevated lactate in muscle and blood plasma, depleted tissue energy stores, and altered osmoregulatory status, particularly in warmer (15 vs. 10°C) and longer (15 vs. 2 min) capture treatments. A significant effect of entanglement duration on blood and muscle metabolites remained after 4 h. Oxygen consumption rate recovered to baseline within 7–10 h. However, recovery of heart rate to routine levels was longer and more variable, with most fish taking over 10 h, and 33% of fish failing to recover within 24 h. There were no significant treatment effects on either oxygen consumption or heart rate recovery. Our results indicate that fishers should minimize handling time for bycatch and maximize oxygen supply during crowding, especially when temperatures are elevated. Physiological data, such as those presented here, can be used to understand mechanisms that underlie bycatch impairment and mortality, and thus inform best practices that ensure the welfare and conservation of affected species.