Leptocottus Armatus Research Articles

Morphology of skin armament of the diadromous and freshwater sculpins (Actinopterygii, Scorpaeniformes, Cottidae) of Eurasia

The morphology of skin armament has long been studied in some of freshwater sculpins, but has not found wide use in the taxonomy of this group. To assess the taxonomic value and determine the patterns of variability of this character, alizarin-stained skin samples of 19 diadromous and freshwater sculpins from Eurasia and one ancient North American species, Leptocottus armatus, were examined for the morphology of prickles. Three morphological types of prickles were ascertained. The largest prickles with a wide basal plate having an uneven anterior edge and a short, strong spine should be considered as the ancestral state. On a series of prickles examined a successive process of reduction was revealed from the ancestral type to the prickles that represent a thin, elongated, fusiform spine extending from a barely visible rounded basal plate with a smooth anterior edge, usually specific for younger freshwater species. The types of skin armament are not strictly consistent with the current concepts on the phylogeny of the studied freshwater Cottidae in view of the phenotypic parallelisms in this group. It is tentatively indicated insignificant intraspecific variation of the prickles shape in Mesocottus haitej, Cottus amblystomopsis, C. czerskii, and C. volki. Identification of most species studied using a single prickle is quite a challenge, although some species are easily identified this way. The species-specificity of prickles is shown to be the greatest in deeply divergent lineages, providing the opportunity to use these structures for diagnosing species and revealing hidden species richness. The skin armament morphology may also become an accessible and useful tool for testing taxonomic, biogeographical, and evolutionary hypotheses.

Invasive European green crab (Carcinus maenas) predation in a Washington State estuary revealed with DNA metabarcoding.

Predation by invasive species can threaten local ecosystems and economies. The European green crab (Carcinus maenas), one of the most widespread marine invasive species, is an effective predator associated with clam and crab population declines outside of its native range. In the U.S. Pacific Northwest, green crab has recently increased in abundance and expanded its distribution, generating concern for estuarine ecosystems and associated aquaculture production. However, regionally-specific information on the trophic impacts of invasive green crab is very limited. We compared the stomach contents of green crabs collected on clam aquaculture beds versus intertidal sloughs in Willapa Bay, Washington, to provide the first in-depth description of European green crab diet at a particularly crucial time for regional management. We first identified putative prey items using DNA metabarcoding of stomach content samples. We compared diet composition across sites using prey presence/absence and an index of species-specific relative abundance. For eight prey species, we also calibrated metabarcoding data to quantitatively compare DNA abundance between prey taxa, and to describe an 'average' green crab diet at an intertidal slough versus a clam aquaculture bed. From the stomach contents of 61 green crabs, we identified 54 unique taxa belonging to nine phyla. The stomach contents of crabs collected from clam aquaculture beds were significantly different from the stomach contents of crabs collected at intertidal sloughs. Across all sites, arthropods were the most frequently detected prey, with the native hairy shore crab (Hemigrapsus oregonensis) the single most common prey item. Of the eight species calibrated with a quantitative model, two ecologically-important native species-the sand shrimp (Crangon franciscorum) and the Pacific staghorn sculpin (Leptocottus armatus)-had the highest average DNA abundance when detected in a stomach content sample. In addition to providing timely information on green crab diet, our research demonstrates the novel application of a recently developed model for more quantitative DNA metabarcoding. This represents another step in the ongoing evolution of DNA-based diet analysis towards producing the quantitative data necessary for modeling invasive species impacts.

Growth of Pacific staghorn sculpin (Leptocottus armatus) is reduced at contaminated sites in the Lower Duwamish River, Washington

The Lower Duwamish River is a highly industrialized waterway flowing into the densely urbanized Puget Sound waterfront of Seattle, Washington, USA. The river has been profoundly altered from its natural state following more than a century of channelization, recurrent dredging, shoreline armoring, and pollution discharges. As part of a Natural Resource Damage Assessment addressing historical pollution at three designated Superfund sites (i.e., the assessment area), juvenile Pacific staghorn sculpin (Leptocottus armatus) were sampled throughout the lower river in order to evaluate injury from exposure to polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDTs), and butyltins (BTs). Sculpin live in close association with the river sediments within and upriver of the assessment area. Fish were collected for analysis of contaminant concentrations in composited whole bodies and stomach contents, as well as individual fish health metrics including daily somatic growth rates measured from otoliths. Sediment contaminant concentrations were also measured at sites near to fishing locations. Fish growth rates varied from 0.65 to 1.05 mm/day, and were significantly lower at unremediated downriver sites compared to upriver and remediated locations. Sculpin growth rates were negatively correlated with concentrations of PCBs in fish bodies, PAHs in stomach contents, as well as PCBs, DDTs and PAHs in sediment. Mixed effects models for whole-body and stomach content contaminants showed positive correlations between growth rate and water temperature. Temperature was not a significant confounding variable for the relationship between growth rate and sediment contaminants. Overall, these results show that juvenile sculpin are harmed by contaminant exposure in the Lower Duwamish River. Furthermore, this study demonstrates the utility of using paired biological and chemical indicators of pollutant-induced injury in a resident fish to inform a complex Natural Resource Damage Assessment and associated restoration efforts.

The physiological consequences of a very large natural meal in a voracious marine fish, the staghorn sculpin (Leptocottus armatus).

Little information exists on physiological consequences when wild fish eat natural food. Staghorn sculpins at 10-13°C voluntarily consumed 15.8% of their body mass in anchovies. Gastric clearance was slow with >60% of the meal retained in the stomach at 48 h, and was not complete until 84 h. At 14-24 h post-feeding, pH was depressed by 3 units and Cl- concentration was elevated 2-fold in gastric chyme, reflecting HCl secretion, while in all sections of the intestine, pH declined by 1 pH unit but Cl- concentration remained unchanged. PCO2and total ammonia concentration were greatly elevated throughout the tract, whereas PNH3and HCO3- concentration were depressed. Intestinal HCO3- secretion rates, measured in gut sacs in vitro, were also lower in fed fish. Whole-animal O2 consumption rate was elevated approximately 2-fold for 72 h post-feeding, reflecting 'specific dynamic action', whereas ammonia and urea-N excretion rates were elevated about 5-fold. Arterial blood exhibited a modest 'alkaline tide' for about 48 h, but there was negligible excretion of metabolic base to the external seawater. PaCO2and PaO2remained unchanged. Plasma total amino acid concentration and total lipid concentration were elevated about 1.5-fold for at least 48 h, whereas small increases in plasma total ammonia concentration, PNH3and urea-N concentration were quickly attenuated. Plasma glucose concentration remained unchanged. We conclude that despite the very large meal, slow processing with high efficiency minimizes internal physiological disturbances. This differs greatly from the picture provided by previous studies on aquacultured species using synthetic diets and/or force-feeding. Questions remain about the role of the gastro-intestinal microbiome in nitrogen and acid-base metabolism.

Northeast Pacific eelgrass fish communities characterized by environmental DNA represent local diversity and show habitat specificity

AbstractFish biodiversity is an important indicator of ecosystem health and a priority for the National Park Service in Drakes Estero, a shallow estuary within Point Reyes National Seashore, Marin County, California. However, fish diversity has yet to be described following the removal of oyster aquaculture infrastructure within Drakes Estero from 2016 to 2017. We used environmental DNA (eDNA) to characterize fish biodiversity within Drakes Estero. We amplified fish eDNA with MiFish primers and classified sequences with a 12S rRNA reference database. We identified 110 unique operational taxonomic units (OTUs, at 97% similarity) within the estuary from 40 samples across 4 sites. From these 110 OTUs, we identified 9 species and 13 taxonomic groups at the genus, family, order, or class level within the estuary. Species‐level assignments are limited by a lack of representative sequences targeted by the MiFish primers for 42% of eelgrass fishes in our region that we identified from a literature review in the Northeast Pacific (NEP) from Elkhorn Slough to Humboldt Bay. Despite this limitation, we identified some common Drakes Estero fishes with our eDNA surveys, including the three‐spined stickleback (Gasterosteus aculeatus), Pacific staghorn sculpin (Leptocottus armatus), surfperches (Embiotocidae), gobies (Gobiidae), and a hound shark (Triakidae). We also compared fish biodiversity within the estuary with that from nearby Limantour Beach, a coastal site. Limantour beach differed in community composition from Drakes Estero and was characterized by high relative abundances of anchovy (Engraulis sp.) and herring (Clupea sp.). Thus, we can distinguish estuarine and non‐estuarine sites (<10 km away) with eDNA surveys. Further, eDNA surveys accounted for greater fish diversity than seine surveys conducted at one site within the estuary. Environmental DNA surveys will likely be a useful tool to monitor fish biodiversity across eelgrass estuaries in the Northeast Pacific, especially as reference databases become better populated with regional species.

PTEROBDELLA OCCIDENTALIS N. SP. (HIRUDINIDA: PISCICOLIDAE) FOR P. ABDITOVESICULATA (MOORE, 1952) FROM THE LONGJAW MUDSUCKER, GILLICHTHYS MIRABILIS, AND STAGHORN SCULPIN, LEPTOCOTTUS ARMATUS, AND OTHER FISHES IN THE EASTERN PACIFIC.

Pterobdella occidentalis n. sp. (Hirudinida: Piscicolidae) is described from the longjaw mudsucker, Gillichthys mirabilis Cooper, 1864, and the staghorn sculpin, Leptocottus armatus Girard, 1854, in the eastern Pacific, and the diagnosis of Pterobdella abditovesiculata (Moore, 1952) from the 'o'opu 'akupa, Eleotris sandwicensis Vaillant and Sauvage, 1875, from Hawaii is amended. The morphology of both species conforms with the genus Pterobdella in possessing a spacious coelom, well-developed nephridial system, and 2 pairs of mycetomes. Originally described as Aestabdella abditovesiculata, P. occidentalis (present along the U.S. Pacific Coast), can be distinguished from most congeners by its metameric pigmentation pattern and diffuse pigmentation on the caudal sucker. Based on mitochondrial gene sequences, including cytochrome c oxidase subunit I (COI) and NADH dehydrogenase subunit I (ND1), P. occidentalis forms a distinct polyphyletic clade with Pterobdella leiostomi from the western Atlantic. Based on COI, ND1, and the 18S rRNA genes, other leech species most closely related to P. occidentalis include Pterobdella arugamensis from Iran, Malaysia, and possibly Borneo, which likely represent distinct species, and Pterobdella abditovesiculata from Hawaii, one of only a few endemic fish parasites in Hawaii. Like P. abditovesiculata, P. arugamensis, and Petrobdella amara, P. occidentalis is often found in estuarine environments, frequently infecting hosts adapted to a wide range of salinity, temperature, and oxygen. The physiological plasticity of P. occidentalis and the longjaw mudsucker host, and the ease of raising P. occidentalis in the lab, make it an excellent candidate for the study of leech physiology, behavior, and possible bacterial symbionts.

Escaping from multiple visual threats: modulation of escape responses in Pacific staghorn sculpin (Leptocottus armatus).

Fish perform rapid escape responses to avoid sudden predatory attacks. During escape responses, fish bend their bodies into a C-shape and quickly turn away from the predator and accelerate. The escape trajectory is determined by the initial turn (stage 1) and a contralateral bend (stage 2). Previous studies have used a single threat or model predator as a stimulus. In nature, however, multiple predators may attack from different directions simultaneously or in close succession. It is unknown whether fish are able to change the course of their escape response when startled by multiple stimuli at various time intervals. Pacific staghorn sculpin (Leptocottus armatus) were startled with a left and right visual stimulus in close succession. By varying the timing of the second stimulus, we were able to determine when and how a second stimulus could affect the escape response direction. Four treatments were used: a single visual stimulus (control); or two stimuli coming from opposite sides separated by a 0 ms (simultaneous treatment), 33 ms or 83 ms time interval. The 33 ms and 83 ms time intervals were chosen to occur either side of a predicted 60 ms visual escape latency (i.e. during stage 1). The 0 ms and 33 ms treatments influenced both the escape trajectory and the stage 1 turning angle, compared with a single stimulation, whereas the 83 ms treatment had no effect on the escape trajectory. We conclude that Pacific staghorn sculpin can modulate their escape trajectory only between stimulation and the onset of the response, but the escape trajectory cannot be modulated after the body motion has started.

Environmental Drivers of Nearshore Fish Community Composition and Size Structure in Glacially Influenced Gulf of Alaska Estuaries

Coastal ecosystems in Alaska are undergoing rapid change due to warming and glacier recession. We used a natural gradient of glacierized to non-glacierized watersheds (0–60% glacier coverage) in two regions along the Gulf of Alaska—Kachemak Bay and Lynn Canal—to evaluate relationships between local environmental conditions and estuarine fish communities. Multivariate analyses of fish community data collected from five sites per region in 2019 showed that region accounted for the most variation in community composition, suggesting that local effects of watershed type were masked by regional-scale variables. Seasonal shifts in community composition were driven largely by the influx of juvenile Pacific salmon (Oncorhynchus spp.) in late spring. Spatiotemporal differences among fish communities were partly explained by salinity and temperature, which accounted for 19.5% of the variation in community composition. We used a multi-year dataset from Lynn Canal (2014–2019) to examine patterns of mean length for two dominant species. Generalized additive mixed models indicated that Pacific staghorn sculpin (Leptocottus armatus) mean length varied along site-specific seasonal gradients, increasing gradually through the summer in the least glacially influenced sites and increasing rapidly to an asymptote of ~ 150 mm in the most glacially influenced sites. Starry flounder (Platichthys stellatus) mean length was more strongly related to environmental conditions, increasing with temperature and turbidity. Together, our findings suggest that community compositions of estuarine fishes show greater variation at the regional scale than the watershed scale, but species-specific variation in size distributions may indicate differences in habitat quality across watershed types within regions.

Effects of Estuary-Wide Seagrass Loss on Fish Populations

Globally, habitat loss in coastal marine systems is a major driver of species decline, and estuaries are particularly susceptible to loss. Along the United States Pacific coast, monospecific eelgrass (Zostera marina) beds form the major estuarine vegetated habitat. In Morro Bay, California, eelgrass experienced an unprecedented decline of > 95%, from 139 ha in 2007 to < 6 ha by 2017. Fish populations were compared before and after the eelgrass decline using trawl surveys. Beach seines surveys were also conducted during the post-decline period to characterize species within and outside of remnant eelgrass beds. While the estuary-wide loss of eelgrass did not result in fewer fish or less biomass, it led to changes in species composition. The post-eelgrass decline period was characterized by increases in flatfish (mainly Citharichthys stigmaeus) and staghorn sculpin (Leptocottus armatus), and decreases in habitat specialists including bay pipefish (Syngnathus leptorhynchus) and shiner perch (Cymatogaster aggregata). There were similar trends inside and outside of remnant eelgrass patches. These findings support evidence across multiple ecosystems suggesting that the predominance of habitat-specialists predicts whether or not habitat loss leads to an overall decline in fish abundance. In addition, loss of critical habitats across seascapes can restrict population connectivity and lead to range contraction. For bay pipefish, the loss of eelgrass in Morro Bay is likely to create a population biogeographic divide. Currently, Morro Bay is dominated by flatfish and sculpins, and the longevity of this new ecosystem state will depend on future eelgrass recovery dynamics supported by ecosystem-based management approaches.

Temporal and habitat differences in the juvenile demersal fish community at a marine-dominated northeast Pacific estuary

The role that west coast estuarine habitats play in the early life history of many nearshore marine fishes is poorly understood, in part due to the limited temporal sampling of estuarine habitats. To begin to understand this role, we compared the juvenile demersal fish community between two habitat types at a marine-dominated estuary on the northeast Pacific coast and examined how community structure changed temporally. Sampling occurred in Yaquina Bay, Oregon during 2008–2009, 2012–2013, and 2016–2017 at eleven sites, comprised of anthropogenic (dock) and natural (eelgrass) habitats. The juvenile fish assemblage was dominated by a few highly abundant species, including saddleback gunnel (Pholis ornata), Pacific staghorn sculpin (Leptocottus armatus), and rockfishes (Sebastes spp.), with the majority of species being marine associated. Community structure varied among years and between habitat types, with greater differences seen between habitat types than years. Docks appear to be a specialized habitat, supporting some species but with greater change in community structure over time and lower overall abundances than eelgrass. Use of docks by commercially and recreationally-exploited species, though, indicates potential importance. Community structure differences were best described by a combination of regional (Pacific Decadal Oscillation) and local (upwelling, temperature, salinity) climate variables, but correlation values are considered weak. Greater abundances and reduced change in communities over time at eelgrass sites suggests that maintaining these habitats is potentially critical for many estuary-rearing species, and temporal changes in these communities highlight the importance of long-term monitoring.

Transmission of a Freshwater Isolate of Ichthyophonus (Clade C) to Two Marine Fish Species.

The ingestion of infected prey is the most recognizable mode of transmission for Ichthyophonus, but because this mode of transmission is unidirectional from small prey fish to larger predators, it cannot sustain the parasite within or among populations nor does it explain transmission to planktivores. Recently, waterborne transmission was demonstrated in cultured Rainbow Trout Oncorhynchus mykiss, which could explain how the parasite is transmitted without piscivory. However, it is possible that this is an adaptation to aquaculture conditions, and may not occur among wild fish. To address this question, experiments were conducted to determine if a freshwater isolate of Ichthyophonus is infectious and pathogenic to marine species, as well as if transmission is possible between different marine species. Pacific Staghorn Sculpins Leptocottus armatus were fed a freshwater isolate of Ichthyophonus (clade C) and then housed with susceptible sentinel Rock Soles Lepidopsetta bilineata. Ninety two percent of the orally exposed sculpins and 30% of the sentinel soles were Ichthyophonus-positive at the end of the study, with 0% infected controls. These results demonstrate that a freshwater isolate of Ichthyophonus is infectious and pathogenic to marine species and can be transmitted in seawater in the absence of piscivory. It also provides a plausible mechanism for transmission to small prey fish and planktivores, as well as within a population of piscivores when infected prey is not available.

Spatiotemporal Variation and Size‐Selective Predation on Hatchery‐ and Wild‐Born Juvenile Chum Salmon at Marine Entry by Nearshore Fishes in Southeast Alaska

AbstractJuvenile Pacific salmon Oncorhynchus spp. experience high mortality at marine entry, yet our quantitative understanding of predation during this critical period is limited. We evaluated spatial, temporal, and size‐based patterns of predation on hatchery‐ and wild‐born juvenile Chum Salmon O. keta by two abundant predators in Southeast Alaska estuaries: the Pacific Staghorn Sculpin Leptocottus armatus and Dolly Varden Salvelinus malma. For the predators we sampled, Chum Salmon comprised 4.5% of the diet by weight for Pacific Staghorn Sculpin (n = 937) and 19.6% of the diet by weight for Dolly Varden (n = 448), with 88% of the individual Chum Salmon consumed originating from hatcheries. Variation in occurrence of Chum Salmon in diets was driven by date, site, and local Chum Salmon density. The quantity of Chum Salmon consumed by Pacific Staghorn Sculpin varied with predator length, Chum Salmon density, and the proportion of hatchery fish present; however, date was the only important predictor for Dolly Varden. The mean length of Chum Salmon in the diets of both predators was significantly shorter than that of concurrent hatchery releases or seine catches, suggesting size‐selective predation on smaller individuals. This pattern indicates that hatchery strategies of releasing larger individuals may reduce the initial vulnerability of hatchery salmon to estuarine predators.

Assessing the use of vibrations and strobe lights at fish screens as enhanced deterrents for two estuarine fishes.

The role of vision and the lateral-line system in fish-screen avoidance behaviours was investigated in shiner surfperch Cymatogaster aggregata and staghorn sculpin Leptocottus armatus. Avoidance experiments were conducted in front of water-diversion-type wedge-wire fish screens in a laboratory flume with a 0.3 m s-1 water velocity. Fish contacted the screens less frequently during the day than night, indicating that fish screen avoidance is visually mediated during the day. Input from the fishes' lateral-line systems was also blocked with streptomycin-sulphate treatments during the night to determine if these fishes use mechanoreceptive cues to guide screen avoidance in darkened conditions. Streptomycin-treated and untreated fish had similar contact rates suggesting that mechanoreceptive guidance was not increasing the fishes' abilities to avoid contact with non-vibrating screens at night. Fishes were stained with 2-(4-(dimethylamino)styryl)-N-ethylpyridinium iodide (DASPEI) to assess the streptomycin treatment's effectiveness. We also tested the fishes' ability to avoid contact with the screens at night, when a strobe light or industrial vibrator was operated on the screens, to respectively increase the screen's visual and mechanoreceptory guidance potential. Cymatogaster aggregata contacted the screens significantly less frequently when they were vibrating, compared with their night-time controls, suggesting useful mechanoreceptive guidance. Leptocottus armatus contacted the screens significantly less frequently under strobe-light illumination, compared with their night-time controls, suggesting useful visual guidance. This research should benefit fishery and water-resource managers, regarding the development of future fish-protection decisions at screened water diversions.

Variable gene transcription underlies phenotypic convergence of hypoxia tolerance in sculpins

BackgroundThe degree by which mechanisms underlying phenotypic convergence are similar among taxa depends on the number of evolutionary paths available for selection to act upon. Likelihood of convergence will be influenced by an interplay of factors such as genetic architecture, phylogenetic history and population demography. To determine if there is convergence or divergence in mechanisms underlying phenotypic similarity, we assessed whether gene transcription patterns differed among species with similar levels of hypoxia tolerance.ResultsThree species of marine fish from the superfamily Cottoidea (smoothhead sculpin [Artedius lateralis], sailfin sculpin [Nautichthys oculofasciatus] and Pacific staghorn sculpin [Leptocottus armatus]), all of which have previously been shown to share the same level of hypoxia tolerance, were exposed to short-(8 h) and longer-term (72 h) hypoxia and mRNA transcripts were assessed using a custom microarray. We examined hypoxia-induced transcription patterns in metabolic and protein production pathways and found that a high proportion of genes associated with these biological processes showed significant differences among the species. Specifically, the data suggest that the smoothhead sculpin, unlike the sailfin sculpin and the Pacific staghorn sculpin, relied on amino acid degradation rather than glycolysis or fatty acid oxidation to generate ATP during hypoxia exposure. There was also variation across the species in the transcription of genes involved in protein production (e.g. mRNA processing and protein translation), such that it increased in the smoothhead sculpin, decreased in the sailfin sculpin and was variable in the Pacific staghorn sculpin.ConclusionsChanges in metabolic and protein production pathways are part of the key responses of fishes to exposures to environmental hypoxia. Yet, species with similar overall hypoxia tolerance exhibited different transcriptional responses in these pathways, indicating flexibility and complexity of interactions in the evolution of the mechanisms underlying the hypoxia tolerance phenotype. The variation in the hypoxia-induced transcription of genes across species with similar hypoxia tolerance suggests that similar whole-animal phenotypes can emerge from divergent evolutionary paths that may affect metabolically important functions.

A walking behavior generates functional overland movements in the tidepool sculpin, Oligocottus maculosus

Tidepool sculpins (Oligocottus maculosus) have been observed moving overland in the rocky intertidal, and we documented the terrestrial walking behavior that they use to accomplish this. We quantified the terrestrial movements of O. maculosus and compared them to (1) their aquatic locomotion, (2) terrestrial locomotion of closely-related subtidal species (Leptocottus armatus and Icelinus borealis), and (3) terrestrial movements of walking catfishes (Clarias spp.). We recorded sculpin movements (210 fps) on a terrestrial platform and in a water tank and tracked body landmarks for kinematic analysis. The axial-appendage-based terrestrial locomotion of O. maculosus is driven by cyclic lateral oscillations of the tail, synchronized with alternating rotations about the base of the pectoral fins, a behavior that appears similar to a military “army crawl.” The pectoral fins do not provide propulsion, but act as stable points for the body to rotate around. In contrast, individuals of O. maculosus use primarily axial undulation during slow-speed swimming. The army crawl is a more effective terrestrial behavior (greater distance ratio) than the movements produced by L. armatus and I. borealis, which use rapid, cyclic oscillations of the tail, without coordinated pectoral fin movements. Relative to Clarias spp., O. maculosus rotated the body about the base of the pectoral fin, rather than the tip of the fin, which may cause O. maculosus to have a lower distance ratio. Since O. maculosus lack major morphological adaptations for terrestrial locomotion, instead relying on behavioral adaptations, we propose behavioral adaptations may evolutionarily predate morphological adaptations for terrestrial locomotion in vertebrates.

Axial morphology and 3D neurocranial kinematics in suction-feeding fishes.

ABSTRACTMany suction-feeding fish use neurocranial elevation to expand the buccal cavity for suction feeding, a motion necessarily accompanied by the dorsal flexion of joints in the axial skeleton. How much dorsal flexion the axial skeleton accommodates and where that dorsal flexion occurs may vary with axial skeletal morphology, body shape and the kinematics of neurocranial elevation. We measured three-dimensional neurocranial kinematics in three species with distinct body forms: laterally compressed Embiotoca lateralis, fusiform Micropterus salmoides, and dorsoventrally compressed Leptocottus armatus. The area just caudal to the neurocranium occupied by bone was 42±1.5%, 36±1.8% and 22±5.5% (mean±s.e.m.; N=3, 6, 4) in the three species, respectively, and the epaxial depth also decreased from E. lateralis to L. armatus. Maximum neurocranial elevation for each species was 11, 24 and 37°, respectively, consistent with a hypothesis that aspects of axial morphology and body shape may constrain neurocranial elevation. Mean axis of rotation position for neurocranial elevation in E. lateralis, M. salmoides and L. armatus was near the first, third and fifth intervertebral joints, respectively, leading to the hypothesis of a similar relationship with the number of intervertebral joints that flex. Although future work must test these hypotheses, our results suggest the relationships merit further inquiry.

Prey fish returned to Forster's tern colonies suggest spatial and temporal differences in fish composition and availability.

Predators sample the available prey community when foraging; thus, changes in the environment may be reflected by changes in predator diet and foraging preferences. We examined Forster’s tern (Sterna forsteri) prey species over an 11-year period by sampling approximately 10,000 prey fish returned to 17 breeding colonies in south San Francisco Bay, California. We compared the species composition among repeatedly-sampled colonies (≥ 4 years), using both relative species abundance and the composition of total dry mass by species. Overall, the relative abundances of prey species at seven repeatedly-sampled tern colonies were more different than would be expected by chance, with the most notable differences in relative abundance observed between geographically distant colonies. In general, Mississippi silverside (Menidia audens) and topsmelt silverside (Atherinops affinis) comprised 42% of individuals and 40% of dry fish mass over the study period. Three-spined stickleback (Gasterosteus aculeatus) comprised the next largest proportion of prey species by individuals (19%) but not by dry mass (6%). Five additional species each contributed ≥ 4% of total individuals collected over the study period: yellowfin goby (Acanthogobius flavimanus; 10%), longjaw mudsucker (Gillichthys mirabilis; 8%), Pacific herring (Clupea pallasii; 6%), northern anchovy (Engraulis mordax; 4%), and staghorn sculpin (Leptocottus armatus; 4%). At some colonies, the relative abundance and biomass of specific prey species changed over time. In general, the abundance and dry mass of silversides increased, whereas the abundance and dry mass of three-spined stickleback and longjaw mudsucker decreased. As central place foragers, Forster’s terns are limited in the distance they forage; thus, changes in the prey species returned to Forster’s tern colonies suggest that the relative availability of some fish species in the environment has changed, possibly in response to alteration of the available habitat.

Adverse metabolic effects in fish exposed to contaminants of emerging concern in the field and laboratory.

Several metabolic parameters were assessed in juvenile Chinook salmon (Oncorhynchus tshawytscha) and staghorn sculpin (Leptocottus armatus) residing in two estuaries receiving wastewater treatment effluent and one reference estuary. We also conducted a laboratory study with fish dosed for 32 days with 16 of the most common contaminants of emerging concern (CECs) detected in feral fish. Several blood chemistry parameters and other indicators of health were measured in fish from the field and laboratory study that were used to assess potential metabolic disruption. The blood chemistry values observed in feral juvenile Chinook salmon were relatively consistent among fish collected from effluent-impacted sites and substantially different compared to reference site fish. These responses were more pronounced in Chinook salmon, which is supported by the disparity in accumulated CECs. The blood chemistry results for juvenile Chinook salmon collected at effluent-impacted sites exhibited a pattern generally consistent with starvation because of similarities to observations from studies of food-deprived fish; however, this response is not consistent with physical starvation but may be contaminant induced. The altered blood chemistry parameters are useful as an early indicator of metabolic stress, even though organismal characteristics (lipid content and condition factor) were not different among sites indicating an early response. Evidence of metabolic disruption was also observed in juvenile Chinook salmon that were exposed in the laboratory to a limited mixture of CECs; however, the plasma parameters were qualitatively different possibly due to exposure route, season, or the suite of CECs. Growth was impaired in the high-dose fish during the dosing phase and the low- and medium-dose fish assayed after 2 weeks of depuration. Overall, these results are consistent with metabolic disruption for fish exposed to CECs, which may result in early mortality or an impaired ability to compete for limited resources.

Spatial and Temporal Variation in the Diets of Pacific Staghorn Sculpins Related to Hydrological Factors in a Glacially Influenced Estuary

AbstractIn southeastern Alaska, a large volume of freshwater flows into estuaries from thinning and retreating glaciers and from high rainfall in the surrounding coastal temperate rainforest. Freshwater runoff to the coast affects the physical and chemical properties of estuarine habitats and, in turn, the structure and dynamics of biological communities. This study quantified temporal and spatial variation in the diets of Pacific Staghorn Sculpins Leptocottus armatus as an important step toward understanding how climate‐driven changes in freshwater runoff may translate into shifts in the feeding ecology of a highly abundant consumer in estuaries along the west coast of North America. Stomach contents of Staghorn Sculpins were collected monthly (April–September 2014) from three intertidal sites at the mouths of rivers that differ in their headwater hydrology. Staghorn Sculpins (N = 402) consumed a variety of marine prey items including epibenthic invertebrates, juvenile fishes, and terrestrial and aquatic insects. Based on a multivariate analysis of similarity, diet composition showed weak to moderate differences across sampling months and sites. Diet differences reflected seasonal shifts in the contributions of freshwater‐tolerant marine invertebrates and young of the year fishes. The greatest site differences were observed between the Cowee Creek estuary and Mendenhall River estuary, the watersheds with the lowest and highest glacial coverage, respectively. Overall, the generalist feeding behavior of Staghorn Sculpins and their consumption of prey items that are well adapted to brackish and freshwater conditions suggest that these fish are resilient to changes in estuarine conditions associated with increasing freshwater runoff.

Effects of Hypoxia on Fish Survival and Oyster Growth in a Highly Eutrophic Estuary

Human land use activities around estuaries can result in high levels of eutrophication. At Elkhorn Slough estuary, a highly eutrophic California estuary, we investigated the effects of impaired water quality on two stress-tolerant estuarine species, a common fish, the staghorn sculpin, Leptocottus armatus and a foundational invertebrate, the Olympia oyster, Ostrea lurida. We caged the two indicator species at six wetlands with different levels of water quality impairment, four of which had restricted tidal flow. We also recorded water quality parameters simultaneously at all sites using YSI sondes, and sampled nutrients and chlorophyll-a monthly, building on the National Estuarine Research Reserve System-wide Monitoring Program. We found that the monitored environmental variables predicted ecological responses by the indicator species. In particular, we found that the duration and severity of hypoxia were negatively correlated with fish survival and oyster growth. Further, our results corroborate previous studies that artificial tidal restriction leads to increased hypoxia stress. We conclude that large diurnal fluctuations in dissolved oxygen and extended nighttime hypoxia can have lethal and sub-lethal effects even on stress-tolerant organisms in the estuary. While laboratory experiments have often shown such effects, it is relatively rare to demonstrate negative effects of oxygen variation with in situ experiments, which provide stakeholders with concrete evidence for impaired water quality at local wetlands. Tidally restricted sites, which experience the largest fluctuations in dissolved oxygen and longest periods of hypoxia, harbor conditions harmful to vertebrates and invertebrates in the estuary. Reversing the anthropogenically induced low oxygen levels, by restoring more natural tidal exchange and by decreasing agricultural runoff, could improve the survival and growth of important estuarine organisms.