Results for “Predator” — Page 48

USGS2011

Food webs and fishing affect parasitism of the sea urchin Eucidaris galapagensis in the Galápagos

In the Galápagos Islands, two eulimid snails parasitize the common pencil sea urchin, Eucidaris galapagensis . Past work in the Galápagos suggests that fishing reduces lobster and fish densities and, due to this relaxation of predation pressure, indirectly increases urchin densities, creating the potential for complex indirect interactions between fishing and parasitic snails. To measure indirect effects of fishing on these parasitic snails, we investigated the spatial relationships among urchins, parasitic snails, commensal crabs, and large urchin predators (hogfish and lobsters). Parasitic snails had higher densities at sites where urchins were abundant, probably due to increased resource availability. Commensal crabs that shelter under urchin spines, particularly the endemic Mithrax nodosus , preyed on the parasitic snails in aquaria, and snails were less abundant at field sites where these crabs were common. In aquaria, hogfish and lobsters readily ate crabs, but crabs were protected from predation under urchin spines, leading to a facultative mutualism between commensal crabs and urchins. In the field, fishing appeared to indirectly increase the abundance of urchins and their commensal crabs by reducing predation pressure from fish and lobsters. Fished sites had fewer snails per urchin, probably due to increased predation from commensal crabs. However, because fished sites also tended to have more urchins, there was no significant net effect of fishing on the number of snails per square meter. These results suggest that fishing can have complex indirect effects on parasites by altering food webs.

Ecology↗

USGS2020

Co-occurence of Chiricahua leopard frogs (Lithobates chiricahuensis) with sunfish (Lepomis)

Invasive species are a major threat to the persistence of native species, particularly in systems where ephemeral aquatic habitats have been replaced by permanent water and predators, such as fish, have been introduced. Within the Altar Valley, Arizona, the invasive American bullfrog, Lithobates catesbeianus (formerly Rana catesbeianus ), has been successfully eradicated to help recover Chiricahua leopard frogs ( Lithobates chiricahuensis ). However, other nonnative predators including sunfish ( Lepomis ) are present in some permanent water bodies. During four consecutive years (2014–2017), we detected both the federally threatened Chiricahua leopard frog and sunfish at one permanent water body in the Altar Valley. This suggests that despite the potential negative effect of predatory fish on amphibians, there may be conditions where the Chiricahua leopard frog can co-occur with this nonnative predator. A better understanding of rare situations of co-occurrence with nonnative predators may contribute to our understanding of why co-occurrence happens in some, but not all, systems and whether conservation strategies can be developed in situations where eradication of nonnative predators is infeasible.

Arizona↗

USGS2010

Strategies for nest-site selection by king eiders

Nest site selection is a critical component of reproduction and has presumably evolved in relation to predation, local resources, and microclimate. We investigated nest-site choice by king eiders (Somateria spectabilis) on the coastal plain of northern Alaska, USA, 2003-2005. We hypothesized that nest-site selection is driven by predator avoidance and that a variety of strategies including concealment, seclusion, and conspecific or inter-specific nest defense might lead to improved nesting success. We systematically searched wetland basins for king eider nests and measured habitat and social variables at nests (n = 212) and random locations (n = 493). King eiders made use of both secluded and concealed breeding strategies; logistic regression models revealed that females selected nests close to water, on islands, and in areas with high willow (Salix spp.) cover but did not select sites near conspecific or glaucous gull (Larus hyperboreus) nests. The most effective nest-placement strategy may vary depending on density and types of nest predators; seclusion is likely a mammalian-predator avoidance tactic whereas concealment may provide protection from avian predators. We recommend that managers in northern Alaska attempt to maintain wetland basins with islands and complex shorelines to provide potential nest sites in the vicinity of water. ?? The Wildlife Society.

Journal of Wildlife Management↗

USGS2007

Depredation of common eider, Somateria mollissima, nests on a central Beaufort Sea barrier island: A case where no one wins

Along the central Beaufort Sea, Pacific Common Eiders ( Somateria mollissima v-nigra ) nest on unvegetated, barrier islands; often near nesting Glaucous Gulls ( Larus hyperboreus ). Nest-site choice likely reflects a strategy of predator avoidance: nesting on islands to avoid mammalian predators and near territorial gulls to avoid other avian predators. We observed a nesting colony of Common Eiders from first nest initiation through nesting termination on Egg Island near Prudhoe Bay, Alaska (2002 – 2003). Resident gulls depredated many eider nests, mostly during initiation. All nests failed when an Arctic Fox ( Alopex lagopus ) visited the island and flushed hens from their nests, exposing the eggs to depredation by the fox and gulls (resident and non-resident). Common Eiders actively defended nests from gulls, but not from foxes. Likely all three species (i.e., eiders, gulls, and foxes) ultimately achieved negligible benefit from their nest-site selection or predatory activity: (a) island nesting provided no safety from mammalian predators for eiders or gulls, (b) for Common Eiders, nesting near gulls increased egg loss, (c) for Glaucous Gulls, nesting near colonial eiders may have reduced nest success by attracting the fox, and (d) for Arctic Foxes, the depredation was of questionable value, as most eggs were cached and probably not recoverable (due to damage from fall storms). Thus, the predator-prey interactions we observed appear to be a case where little or no fitness advantage was realized by any of the species involved.

Canadian Field-Naturalist↗

USGS1995

Caribou calf mortality in Denali National Park, Alaska

Calf mortality is a major component of caribou (Rangifer tarandus) population dynamics, but little is known about the timing or causes of calf losses, or of characteristics that predispose calves to mortality. During 1984-87, we radiocollared 226 calves (≤3 days old) in the Denali Caribou Herd (DCH), an unhunted population utilized by a natural complement of predators, to determine the extent, timing, and causes of calf mortality and to evaluate influences of year, sex, birthdate, and birth mass on those losses. Overall, 39% of radio-collared calves died as neonates (≤15 days old), and 98% of those deaths were attributed to predation. Most neonatal deaths (85%) occurred within 8 days of birth. Few deaths occurred after the neonatal period (5, 10, and 0% of calves instrumented died during 16-30, 31-150, and >150 days of age, respectively). Survival of neonates was lower (P = 0.038) in 1985, following a severe winter, than during the other 3 years. In years other than 1985, calves born during the peak of calving (approx 50% of the total, born 5-8 days after calving onset) experienced higher (P < 0.001) neonatal survival than did other calves. Grizzly bears (Ursus arctos), wolves (Canis lupus), and unknown large predators (i.e., grizzly bears or wolves) accounted for 49, 29, and 16% of the neonatal deaths, respectively. The rate of bear-caused mortalities declined (P < 0.001) with calf age, and bears killed few calves >10 days old. Wolf predation was not related (P > 0.05) to calf age and peaked 10 days after onset of calving. Grizzly bear and wolf predation on neonates during the calving season was a limiting factor for the Denali Caribou Herd.

Journal of Wildlife Management↗

USGS2022

Assessing the efficacy of using a parentage-based tagging survival model to evaluate two sources of mortality for juvenile Chinook salmon (Oncorhynchus tshawytscha) in Lookout Point Reservoir, Oregon

We conducted a study to assess the efficacy of using a parentage-based tagging survival model (PBT N-mixture model) to evaluate two sources of mortality for juvenile Chinook salmon ( Oncorhynchus tshawytscha ) in Lookout Point Reservoir, Oregon. The model was originally developed to evaluate reservoir mortality because of predation from piscivorous fish. However, recent studies have also found that juvenile Chinook salmon experience high infection rates from parasitic copepods ( Salmincola californiensis ), which are known to negatively affect performance and survival. Our study was conducted to determine if the PBT N-mixture model could separately estimate mortality because of predation from non-native fish and mortality resulting from copepod infection. This assessment was conducted in two parts: (1) data collected in Lookout Point Reservoir during 2018 were re-analyzed; and (2) a simulation was conducted to evaluate a multi-year study that included inter-annual variation in copepod infection rate and two subsampling strategies (10 fish per month, 30 fish per month) to characterize monthly copepod infection rate. Results from each of these efforts suggest that the survival model is unlikely to provide reliable survival estimates for the two mortality sources that we evaluated. The re-analysis of 2018 data showed that “predation only” and “copepod only” models estimated a negative coefficient for the respective covariate, but the model that included both covariates provided coefficient estimates that differed from the other models and were highly uncertain. Similarly, the simulation results showed that most models failed to correctly estimate the magnitude and direction of mortality due to predation and copepods. These results suggest that additional data will be required if a model is desired that can separately estimate mortality effects due to both predation and copepods in the future. The existing data are limited by factors including low detection probabilities from previous field studies, existing uncertainties about copepod effects on mortality in a natural setting and expected limitations in the number of years that a field study could realistically be expected to receive funding.

Oregon↗

USGS2016

Effects of Coralliophila violacea on tissue loss in the scleractinian corals Porites spp. depend on host response

We investigated interactions between the corallivorous gastropod Coralliophila violacea and its preferred hosts Porites spp. Our objectives were to experimentally determine whether tissue loss could progress in Porites during or after Coralliophila predation on corals with and without tissue loss and to histologically document snail predation. In 64% of feeding scars, tissue regenerated within 3 wk, leaving no trace of predation. However, in roughly 28% of scars, lesions progressed to subacute tissue loss resembling white syndrome. In feeding experiments, scars from snails previously fed diseased tissue developed progressive tissue loss twice as frequently as scars from snails previously fed healthy tissue. Scars from previously healthy-fed snails were 3 times as likely to heal as those from previously diseased-fed snails. Histology revealed marked differences in host responses to snails; P. cylindrica manifested a robust inflammatory response with fewer secondary colonizing organisms such as algae, sponges, and helminths, whereas P. rus showed no evident inflammation and more secondary colonization. We conclude that lesion progression associated with Coralliophila may be associated with secondary colonization of coral tissues damaged by predator-induced trauma and necrosis. Importantly, variation at the cellular level should be considered when explaining interspecific differences in host responses in corals impacted by phenomena such as predation.

Diseases of Aquatic Organisms↗

USGS2004

Effects of marine reserves and urchin disease on southern Californian rocky reef communities

While the species level effects of marine reserves are widely recognized, community level shifts due to marine reserves have only recently been documented. Protection from fishing of top predators may lead to trophic cascades, which have community-wide implications. Disease may act in a similar manner, regulating population levels of dominant species within a community. Two decades of data from the Channel Islands National Park Service's Kelp Forest Monitoring database allowed us to compare the effects of fishing and urchin disease on rocky reef community patterns and dynamics. Different size-frequency distributions of urchins inside and outside of reserves indicated reduced predation on urchins at sites where fishing removes urchin predators. Rocky reefs inside reserves were more likely to support kelp forests than were fished areas. We suggest that this results from cascading effects of the fishery on urchin predators outside the reserves, which releases herbivores (urchins) from predation. After periods of prevalent urchin disease, the reef community shifted more towards kelp forest assemblages. Specific groups of algae and invertebrates were associated with kelp forest and barrens communities. The community dynamics leading to transitions between kelp forests and barrens are driven by both fishing and disease; however the fishery effect was of greater magnitude. This study further confirms the importance of marine reserves not only for fisheries conservation, but also for the conservation of historically dominant community types.

Marine Ecology Progress Series↗

USGS2024

Effect of invasive plant removal on the density of Peromyscus sonoriensis (western deer mice) in Point Reyes National Seashore, California, USA.

Non-native plants can affect communities through direct competition, and by providing refuge to seed predators, creating apparent competition with native plants. Ammophila arenaria (European beachgrass) has been introduced to coastal dune habitats throughout the western United States where it forms dense monocultures, stabilizes dunes, and alters abiotic and biotic conditions. The dominance of European beachgrass has been linked to declines of Lupinus tidestromii (Tidestrom’s lupine), an herb endemic to coastal dune communities in central and northern California. Peromyscus sonoriensis (western deer mice), a native seed predator, use beachgrass as refuge from predators. Tidestrom’s lupine plants near European beachgrass stands experience greater predation pressure from deer mice. At Point Reyes National Seashore, California, USA (PRNS), mechanical removal, manual pulling, and herbicide treatment have been used to reduce the density of European beachgrass near Tidestrom’s lupine populations. We trapped deer mice at five sites in PRNS that experienced different management regimes and used spatially-explicit capture-recapture models to estimate deer mouse density as a function of site and habitat treatment. We found that deer mouse density was lowest in areas where European beachgrass was mechanically removed and in herbicide-treated foredunes, and highest in areas highly invaded by European beachgrass and Carpobrotus spp. (iceplant). The density of deer mice increased from 2021 to 2022 at every site except one that underwent extensive mechanical removal of European beachgrass from 2010-2011. This study shows enduring effects of European beachgrass removal on the density of a native seed predator and highlights the importance of habitat management for conservation of Tidestrom’s lupine.

California↗

USGS2009

Learning to be different: Acquired skills, social learning, frequency dependence, and environmental variation can cause behaviourally mediated foraging specializations

Question: How does the ability to improve foraging skills by learning, and to transfer that learned knowledge, affect the development of intra-population foraging specializations? Features of the model: We use both a state-dependent life-history model implemented by stochastic dynamic programming (SDPM) and an individual-based model (IBM) to capture the dynamic nature of behavioural preferences in feeding. Variables in the SDPM include energy reserves, skill levels, energy and handling time per single prey item, metabolic rate, the rates at which skills are learned and forgotten, the effect of skills on handling time, and the relationship between energy reserves and fitness. Additional variables in the IBM include the probability of successful weaning, the logistic dynamics of the prey species with stochastic recruitment, the intensity of top-down control of prey by predators, the mean and variance in skill levels of new recruits, and the extent to which learned Information can be transmitted via matrilineal social learning. Key range of variables: We explore the effects of approaching the time horizon in the SDPM, changing the extent to which skills can improve with experience, increasing the rates of learning or forgetting of skills, changing whether the learning curve is constant, accelerating (T-shaped) or decelerating ('r'-shaped), changing both mean and maximum possible energy reserves, changing metabolic costs of foraging, and changing the rate of encounter with prey. Conclusions: The model results show that the following factors increase the degree of prey specialization observed in a predator population: (1) Experience handling a prey type can substantially improve foraging skills for that prey. (2) There is limited ability to retain complex learned skills for multiple prey types. (3) The learning curve for acquiring new foraging skills is accelerating, or J-shaped. (4) The metabolic costs of foraging are high relative to available energy reserves. (5) Offspring can learn foraging skills from their mothers (matrilineal social learning). (6) Food abundance is limited, such that average individual energy reserves are low Additionally, the following factors increase the likelihood of alternative specializations co-occurring in a predator population: (1) The predator exerts effective top-down control of prey abundance, resulting in frequency-dependent dynamics. (2) There is stochastic Variation in prey population dynamics, but this Variation is neither too extreme in magnitude nor too 'slow' with respect to the time required for an individual forager to learn new foraging skills. For a given predator population, we deduce that the degree of specialization will be highest for those prey types requiring complex capture or handling skills, while prey species that are both profitable and easy to capture and handle will be included in the diet of all individuals. Frequency-dependent benefits of selecting alternative prey types, combined with the ability of foragers to improve their foraging skills by learning, and transmit learned skills to offspring, can result in behaviourally mediated foraging specialization, and also lead to the co-existence of alternative specializations. The extent of such specialization is predicted to be a variable trait, increasing in locations or years when intra-specific competition is high relative to inter-specific competition. ?? 2009 M. Tim Tinker.

Evolutionary Ecology Research↗

USGS2012

Loss and modification of habitat

Amphibians live in a wide variety of habitats around the world, many of which have been modified or destroyed by human activities. Most species have unique life history characteristics adapted to specific climates, habitats (e.g., lentic, lotic, terrestrial, arboreal, fossorial, amphibious), and local conditions that provide suitable areas for reproduction, development and growth, shelter from environmental extremes, and predation, as well as connectivity to other populations or habitats. Although some species are entirely aquatic or terrestrial, most amphibians, as their name implies, lead a dual life and require a mosaic of habitats in both aquatic and terrestrial ecosystems. With over 6 billion people on Earth, most species are now persisting in habitats that have been directly or indirectly influenced by human activities. Some species have disappeared where their habitats have been completely destroyed, reduced, or rendered unsuitable. Habitat loss and degradation are widely considered by most researchers as the most important causes of amphibian population decline globally (Barinaga 1990; Wake and Morowitz 1991; Alford and Richards 1999). In this chapter, a background on the diverse habitat requirements of amphibians is provided, followed by a discussion of the effects of urbanization, agriculture, livestock grazing, timber production and harvesting, fire and hazardous fuel management, and roads on amphibians and their habitats. Also briefly discussed is the influence on amphibian habitats of natural disturbances, such as extreme weather events and climate change, given the potential for human activities to impact climate in the longer term. For amphibians in general, microhabitats are of greater importance than for other vertebrates. As ectotherms with a skin that is permeable to water and with naked gelatinous eggs, amphibians are physiologically constrained to be active during environmental conditions that provide appropriate body temperatures and adequate water balance (Thorson and Svihla 1943; Brattstrom 1963; Tracy 1976). Hence, individuals require and seek specific microhabitats that maintain their preferred body temperature while at the same time reducing water loss or allowing individuals to re-hydrate. Amphibians also possess relatively few physical attributes that protect them from predators. Although they may avoid predators behaviourally or deter them by skin toxins, amphibians lack defensive shells or hardened cuticles, do not have protective teeth or claws, and most are insufficiently fast to escape predators. Hence, they are relatively dependent on sites that conceal or protect them from predation. Most amphibians also differ significantly from other vertebrates in possessing a complex two-phase life cycle: the pre-metamorphic larval (tadpole) stage and the post-metamorphic juvenile and adult stage (Wilbur 1980, 1984). Most amphibian species have two distinct econes (Heatwole 1989), each with different habitat requirements, the larvae being aquatic and the post-metamorphic animals more terrestrial. The habitats required by the two phases can differ greatly, but both are essential to the survival of a species. However, amphibian diversity is great and exceptions to this general pattern exist. For example, some species have direct development without going through a larval stage and are fully terrestrial, whereas the larvae of other species can reach sexual maturity without going through metamorphosis (i.e., neoteny) and are fully aquatic.

Book chapter↗

USGS2014

Research, monitoring, and evaluation of emerging issues and measures to recover the Snake River fall Chinook salmon ESU, 1/1/2012 – 12/31/2013: Annual report, 1991-029-00

The portion of the Snake River fall Chinook Salmon Oncorhynchus tshawytscha ESU that spawns upstream of Lower Granite Dam transitioned from low to high abundance during 1992–2014 in association with U.S. Endangered Species Act recovery efforts and other Federally mandated actions. This annual report focuses on (1) numeric and habitat use responses by natural- and hatchery-origin spawners, (2) phenotypic and numeric responses by natural-origin juveniles, and (3) predator responses in the Snake River upper and lower reaches as abundance of adult and juvenile fall Chinook Salmon increased. Spawners have located and used most of the available spawning habitat and that habitat is gradually approaching redd capacity. Timing of spawning and fry emergence has been relatively stable; whereas the timing of parr dispersal from riverine rearing habitat into Lower Granite Reservoir has become earlier as apparent abundance of juveniles has increased. Growth rate (g/d) and dispersal size of parr also declined as apparent abundance of juveniles increased. Passage timing of smolts from the two Snake River reaches has become earlier and downstream movement rate faster as estimated abundance of fall Chinook Salmon smolts in Lower Granite Reservoir has increased. In 2014, consumption of subyearlings by Smallmouth Bass was highest in the upper reach which had the highest abundance of Bass. With a few exceptions, predation tended to decrease seasonally from April through early July. A release of hatchery fish in mid-May significantly increased subyearling consumption by the following day. We estimated that over 600,000 subyearling fall Chinook Salmon were lost to Smallmouth Bass predation along the free-flowing Snake River in 2014. More information on predation is presented in Appendix A.3 (page 51). These findings coupled with stock-recruitment analyses presented in this report provide evidence for density-dependence in the Snake River reaches and in Lower Granite Reservoir that was influenced by the expansion of the recovery program. The long-term goal is to use the information covered here in a comprehensive modeling effort to conduct action effectiveness and uncertainty research and to inform fish population, hydrosystem, harvest, hatchery, and predation and invasive species management RM&E.

Oregon, Washington↗

USGS2015

Research, monitoring, and evaluation of emerging issues and measures to recover the Snake River fall Chinook salmon ESU, 1/1/2014 - 12/31/2014

The portion of the Snake River fall Chinook Salmon Oncorhynchus tshawytscha ESU that spawns upstream of Lower Granite Dam transitioned from low to high abundance during 1992–2014 in association with U.S. Endangered Species Act recovery efforts and other Federally mandated actions. This annual report focuses on (1) numeric and habitat use responses by natural- and hatchery-origin spawners, (2) phenotypic and numeric responses by natural-origin juveniles, and (3) predator responses in the Snake River upper and lower reaches as abundance of adult and juvenile fall Chinook Salmon increased. Spawners have located and used most of the available spawning habitat and that habitat is gradually approaching redd capacity. Timing of spawning and fry emergence has been relatively stable; whereas the timing of parr dispersal from riverine rearing habitat into Lower Granite Reservoir has become earlier as apparent abundance of juveniles has increased. Growth rate (g/d) and dispersal size of parr also declined as apparent abundance of juveniles increased. Passage timing of smolts from the two Snake River reaches has become earlier and downstream movement rate faster as estimated abundance of fall Chinook Salmon smolts in Lower Granite Reservoir has increased. In 2014, consumption of subyearlings by Smallmouth Bass was highest in the upper reach which had the highest abundance of Bass. With a few exceptions, predation tended to decrease seasonally from April through early July. A release of hatchery fish in mid-May significantly increased subyearling consumption by the following day. We estimated that over 600,000 subyearling fall Chinook Salmon were lost to Smallmouth Bass predation along the free-flowing Snake River in 2014. More information on predation is presented in Appendix A.3 (page 51). These findings coupled with stock-recruitment analyses presented in this report provide evidence for density-dependence in the Snake River reaches and in Lower Granite Reservoir that was influenced by the expansion of the recovery program. The long-term goal is to use the information covered here in a comprehensive modeling effort to conduct action effectiveness and uncertainty research and to inform fish population, hydrosystem, harvest, hatchery, and predation and invasive species management RM&E.

Oregon, Washington↗

USGS2012

Loss and modification of habitat

Amphibians live in a wide variety of habitats around the world, many of which have been modified or destroyed by human activities. Most species have unique life history characteristics adapted to specific climates, habitats (e.g., lentic, lotic, terrestrial, arboreal, fossorial, amphibious), and local conditions that provide suitable areas for reproduction, development and growth, shelter from environmental extremes, and predation, as well as connectivity to other populations or habitats. Although some species are entirely aquatic or terrestrial, most amphibians, as their name implies, lead a dual life and require a mosaic of habitats in both aquatic and terrestrial ecosystems. With over 6 billion people on Earth, most species are now persisting in habitats that have been directly or indirectly influenced by human activities. Some species have disappeared where their habitats have been completely destroyed, reduced, or rendered unsuitable. Habitat loss and degradation are widely considered by most researchers as the most important causes of amphibian population decline globally (Barinaga 1990; Wake and Morowitz 1991; Alford and Richards 1999). In this chapter, a background on the diverse habitat requirements of amphibians is provided, followed by a discussion of the effects of urbanization, agriculture, livestock grazing, timber production and harvesting, fire and hazardous fuel management, and roads on amphibians and their habitats. Also briefly discussed is the influence on amphibian habitats of natural disturbances, such as extreme weather events and climate change, given the potential for human activities to impact climate in the longer term. For amphibians in general, microhabitats are of greater importance than for other vertebrates. As ectotherms with a skin that is permeable to water and with naked gelatinous eggs, amphibians are physiologically constrained to be active during environmental conditions that provide appropriate body temperatures and adequate water balance (Thorson and Svihla 1943; Brattstrom 1963; Tracy 1976). Hence, individuals require and seek specific microhabitats that maintain their preferred body temperature while at the same time reducing water loss or allowing individuals to re-hydrate. Amphibians also possess relatively few physical attributes that protect them from predators. Although they may avoid predators behaviourally or deter them by skin toxins, amphibians lack defensive shells or hardened cuticles, do not have protective teeth or claws, and most are insufficiently fast to escape predators. Hence, they are relatively dependent on sites that conceal or protect them from predation. Most amphibians also differ significantly from other vertebrates in possessing a complex two-phase life cycle: the pre-metamorphic larval (tadpole) stage and the post-metamorphic juvenile and adult stage (Wilbur 1980, 1984). Most amphibian species have two distinct econes (Heatwole 1989), each with different habitat requirements, the larvae being aquatic and the post-metamorphic animals more terrestrial. The habitats required by the two phases can differ greatly, but both are essential to the survival of a species. However, amphibian diversity is great and exceptions to this general pattern exist. For example, some species have direct development without going through a larval stage and are fully terrestrial, whereas the larvae of other species can reach sexual maturity without going through metamorphosis (i.e., neoteny) and are fully aquatic.

Book chapter↗

USGS2017

Research, monitoring, and evaluation of emerging issues and measures to recover the Snake River Fall Chinook Salmon ESU, 1/1/2016 - 12/31/2016

The portion of the Snake River fall Chinook Salmon Oncorhynchus tshawytscha ESU that spawns upstream of Lower Granite Dam transitioned from low to high abundance during 1992–2016 in association with U.S. Endangered Species Act recovery efforts and other federally mandated actions. This annual report focuses on (1) numeric and habitat use responses by natural- and hatchery-origin spawners, (2) phenotypic and numeric responses by natural-origin juveniles, and (3) predator responses in the Snake River upper and lower reaches as abundance of adult and juvenile fall Chinook Salmon increased. Spawners have located and used most of the available spawning habitat and that habitat is gradually approaching redd capacity. Timing of spawning and fry emergence has been relatively stable; whereas the timing of parr dispersal from riverine rearing habitat into Lower Granite Reservoir has become earlier as apparent abundance of juveniles has increased. Growth rate (g/d) and dispersal size of parr also declined as apparent abundance of juveniles increased. Passage timing of smolts from the two Snake River reaches has become earlier and downstream movement rate faster as estimated abundance of fall Chinook Salmon smolts in Lower Granite Reservoir has increased. In 2016, we described estimated the consumption rate and loss of subyearlings by Smallmouth Bass before, during, and after four hatchery releases. Before releases, Smallmouth Bass consumption rates of subyearling was low (0–0.36 fish/bass/d), but the day after the releases consumption rates reached as high as 1.6 fish/bass/d. Bass consumption in the upper portion of Hells Canyon was high for about 1–2 d before returning to pre-release levels, but in the lower river consumption rates were reduced but took longer to return to pre-release levels. We estimated that most of the subyearlings consumed by bass were of hatchery origin. Smallmouth Bass predation on subyearlings is intense following a hatchery release, but the predation pressure is relatively short-lived as subyearlings quickly disperse downstream. This information will allow us to better estimate subyearling loss to predation from our past efforts at time intervals less than 2 weeks. These findings coupled with stock-recruitment analyses presented in this report provide evidence for density-dependence in the Snake River reaches and in Lower Granite Reservoir that was influenced by the expansion of the recovery program. The long-term goal is to use the information covered here in a comprehensive modeling effort to conduct action effectiveness and uncertainty research and to inform Fish Population, Hydrosystem, Harvest, Hatchery, and Predation and Invasive Species Management RM&E.

Snake River basin↗

USGS2014

Offshore pelagic fish community

Lake Ontario’s offshore zone, as defined by Stewart et al. (2013), comprises all waters of the lake where the bottom depth is greater than 15 m excluding those in embayments. When the lake is thermally stratified during June-October, the offshore pelagic zone includes the upper-warm and middle-cool layers of water which serve as important habitat for Alewife and other prey fishes, and for predators like salmon and trout. Early changes in the fish community of the offshore pelagic zone are well documented elsewhere (e.g., Smith 1972; Christie 1973) as are more recent changes (e.g., Owens et al. 2003; Mills et al. 2003). Currently the offshore fish community consists of a mix of native and non-native species. Native species are those that were present prior to European colonization and for the offshore pelagic zone, include predators like Atlantic Salmon and prey fish like Cisco, Emerald Shiner, and Threespine Stickleback. Non-native species are those that were introduced unintentionally like Alewife and Rainbow Smelt, or that were introduced intentionally like Chinook Salmon, Coho Salmon, Rainbow Trout, and Brown Trout. Non-native salmon and trout were introduced originally by fisheries managers to provide fishing opportunities and later to reduce an overabundance of Alewife. Alewife is the most abundant prey fish in the offshore pelagic zone and it dominates the diets of native and introduced predators (Brandt 1986; Lantry 2001). Alewife can have direct and indirect negative effects on other fishes through competition for food and/or predation on their larvae (Madenjian et al. 2008). Alewife also contain thiaminase, an enzyme that catalyzes the breakdown of thiamine, and fish that eat mainly Alewife can become thiamine deficient which impairs their reproduction (Honeyfield et al. 2005). Except for that of the Alewife, prey fish populations in the offshore pelagic zone are depressed, and not large enough to sustain the zone’s predators. Alewife remain necessary for a functional ecosystem that is required to sustain a highly-valued, trophy sport fishery (Stewart et al. 2013). Wild production of trout and salmon occurs in Lake Ontario tributaries, contributing to in-lake populations (Rand et al. 1993; Connerton et al. 2009; Connerton et al. 2014c). Stocking hatchery-reared fish (Fig. 1), however, remains an essential tool for managing Lake Ontario’s diverse trout and salmon fisheries and achieving the Offshore Pelagic Zone Goal (Stewart et al. 2013): Maintain the offshore pelagic fish community, that is characterized by a diversity of trout and salmon species including Chinook Salmon, Coho Salmon, Rainbow Trout, Brown Trout, and Atlantic Salmon, in balance with prey-fish populations and lower trophic levels. Here we review the fish-community objectives (FCOs) for Lake Ontario’s offshore pelagic zone (Stewart et al. 2013) and evaluate whether those objectives were met during this reporting period (2008-2013) by assessing the status of the objectives’ indicators. We also compare the status of indicators in this reporting period with those in the previous reporting period (2003-2007) (Connerton et al. 2014b). Specific objectives are in italics at the start of each major section and associated indicators of progress are given in Progress and Outlook subsections.

Lake Ontario↗

USGS2023

First investigations on lamprey responses to elevated total dissolved gas exposure and risk of gas bubble trauma

A flexible spill program in the federal Columbia River power system increased the total dissolved gas (TDG) water quality standards (i.e., the gas cap) from 120% to 125%. Spill is used to pass juvenile salmon (Oncorhynchus spp.) over dams, but it can generate elevated TDG, and exposed fish can develop gas bubble trauma (GBT) or experience mortality. Juvenile salmon are monitored for GBT through the Fish Passage Center’s (FPC), and under the flexible spill program, native non-salmonid fishes are also monitored. Pacific Lamprey (Entosphenus tridentatus) are exposed to elevated TDG, but nothing is known about their risk for GBT. This project is the first to evaluate GBT in lamprey, beginning with larval and juvenile lamprey in a controlled laboratory setting. These early life stages were chosen for this initial work because they have been shown to be more sensitive to GBT in other fish species. We modified the FPC protocol for GBT exams to be specific to lamprey and ranked bubbles in the mouth, eyes (juveniles only), gill pores, first and second dorsal fins, caudal fin, anal fin, vent, and body. We followed the FPC ranking criteria and assigned rank based on the proportion of the area occluded with bubbles, as 0=no bubbles, 1=1-5%, 2=6-25%, 3=26-50%, and 4=>50%. Four experiments were completed with larval lamprey from January to September 2022 using small (70 mm total length or less) and large (86 mm total length or greater) larvae in approximately equal proportions. Experiments included: (1) 130% TDG for 31 d, (2) 125% TDG for 91 d, (3) 130% TDG for 20 d with assessments of burrowing performance, and (4) 128-138% TDG for 3-4 d with assessments of predator avoidance ability and the corresponding untreated control groups. The first and second experiments had similar study designs and findings. First, we tested an acute exposure at 130% TDG and then we tested a chronic exposure at 125%, to represent a full spill season. None of the controls (exposed to normally saturated water) experienced mortality or showed GBT signs. Few lamprey in the treatment groups (5% in Experiment 1; 0% in Experiment 2) showed GBT signs, and there were no mortalities (n=200 fish experiment 1; n=100 fish Experiment 2). Lamprey with GBT signs had bubbles on the body, with low severity ranks. During external exams for Experiment 2, we observed bubbles in the gut of several lamprey. The light coloration and transparency of the body made these observations possible, and we confirmed the finding with internal exams. From day 9 to day 91, 70.8% of the lamprey examined had bubbles in the gut. We observed five lamprey that were positively buoyant in the test tanks, and we likely underestimated the prevalence of floating as our procedures were not initially designed to document this sign. In our third experiment, burrowing performance was not significantly different between lamprey exposed to 130% TDG and controls. Mortality was 4.2% in the treatment group, but no GBT signs were observed. The proportion of lamprey with positive buoyancy increased through time, with 87.5% of fish floating on day 20 (end of the test). Bubbles in the gut were observed for some lamprey on each of five sampling dates (day 2 to 20), with prevalence ranging from 50-100%. Median burrow times ranged from 28 to 154 sec for treatment fish and from 40 to 100 sec for controls. We noted some atypical behaviors during burrow performance tests, including lamprey that were positively buoyant and unable to descend through 0.5 m of water to reach the sediment as well as lamprey that were unable to complete burrowing (within 10 min test period). These lamprey were so buoyant that they repeatedly floated to the surface of the water when they stopped or slowed their burrowing movements. Predator avoidance ability was assessed in our fourth experiment by exposing lamprey with GBT signs (floating) and controls to sculpin (Cottus spp.) until about 50% of the fish had been consumed or 2 h had passed. We completed five predation trials, testing the hypothesis that an equal proportion of treatment and control lamprey would be consumed. Treatment groups were generated by exposing 15 lamprey to 128-138% TDG for 3-4 d, until at least 10 lamprey were floating. Overall, 41 treatment and 46 control fish were eaten and there was no evidence that sculpin preferentially preyed upon lamprey with GBT signs. Additional tests with another predator are recommended. Two experiments were completed with juvenile lamprey from March to November 2022: Experiment 5 exposed fish to 125% TDG for 10 d and Experiment 6 exposed fish to 125% for 16 d. Mortality rates for the treatment groups were 21.7% and 20.0% for these experiments, respectively, and few lamprey (4 per experiment) showed GBT signs. With the results from experiments pooled, bubbles were observed in all body areas with low severity ranks (means 0-1). We observed some exophthalmia and bubbles behind the gill pores, in addition to bubbles in the gut and fish floating. The presence of bubbles in or near the gill pores was the likely cause of death as exam findings included enlarged gill pore areas and restricted openings. This project provided the first insights into lamprey responses to elevated TDG, but substantial learning opportunities remain. Our findings highlight that lamprey are vulnerable to GBT, but the effects are generally sublethal and would not be detected using FPC exam procedures. For example, we observed larval and juvenile lamprey that had bubbles in the gut and/or were floating, although these conditions were not consistently linked. More data are needed, but we surmise that it takes some time for bubbles to form in sufficient quantity to create the floatation required to overcome the mass of the lamprey. Positive buoyancy in natural settings could have substantial impacts to the risk of mortality for lamprey. Future studies could test GBT risk for larval lamprey in burrows, investigate the influence of lamprey size, measure performance (e.g., burrowing, swimming, predator avoidance ability) after elevated TDG exposure, and describe the rate that GBT signs dissipate when lamprey are returned to normally saturated water.

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USGS2023

Gopherus Agassizii (Mojave Desert Tortoise). nest depredation

Nest site selection is an important determinant of clutch success and hatchling sex ratios in Gopherus agassizii, Mojave Desert tortoises (Spotila et al. 1994. Herpetol. Monogr. 8:103-116). G. agassizii lay eggs in or near the entrance of their burrows (Ennen et al. 2012. Copeia 2012:222-228) and females of both G. agassizii and G. morafkai, may reduce egg predation risk by remaining at their burrows for days or weeks after oviposition, potentially protecting them from predators (Murray et al. 1996. Herpetological Natural History 4(1):83-88., Agha et al. 2013. Southwest. Nat. 58(2):254-257). Numerous species are known or suspected predators of desert tortoise eggs, including Vulpes macrotis (kit foxes), Spilogale gracilis (western spotted skunks), Mephitis mephitis (striped skunks), Taxidea taxus (badgers), Ammospermophilus leucurus (white-tailed antelope squirrels), Lynx rufus (bobcats), Canis latrans (coyotes), Masticophis flagellum (coachwhips), and Heloderma suspectum (Gila monsters) (Ernst & Lovich 2009. Johns Hopkins University Press, Baltimore 2:827). Here we report visitation and nest depredation at a Mojave Desert tortoise nest by multiple predators, and add a new documented species, the Urocyon cinereoargenteus (gray fox), to the list of known predators on desert tortoise eggs.

Herpetological Review↗