Geology topics

William E. Brown

Publications and source records attributed to William E. Brown.

4 recordsLinked to original sources

USGS2021

Virulence and infectivity of UC, MD and L strains of infectious hematopoietic necrosis virus (IHNV) in four populations of Columbia River Basin Chinook salmon

Infectious Hematopoietic Necrosis Virus (IHNV) infects juvenile salmonid fish in conservation hatcheries and aquaculture facilities, and in some cases, causes lethal disease. This study assesses intra-specific variation in the IHNV susceptibility of Chinook salmon ( Oncorhynchus tshawytscha ) in the Columbia River Basin (CRB), in the northwestern United States. The virulence and infectivity of IHNV strains from three divergent virus genogroups are measured in four Chinook salmon populations, including spring-run and fall-run fish from the lower or upper regions of the CRB. Following controlled laboratory exposures, our results show that the positive control L strain had significantly higher virulence, and the UC and MD strains that predominate in the CRB had equivalently low virulence, consistent with field observations. By several experimental measures, there was little variation in host susceptibility to infection or disease. However, a small number of exceptions suggested that the lower CRB spring-run Chinook salmon population may be less susceptible than other populations tested. The UC and MD viruses did not differ in infectivity, indicating that the observed asymmetric field prevalence in which IHNV detected in CRB Chinook salmon is 83% UC and 17% MD is not due to the UC virus being more infectious. Overall, we report little intra-species variation in CRB Chinook salmon susceptibility to UC or MD IHNV infection or disease, and suggest that other factors may instead influence the ecology of IHNV in the CRB.

Columbia River Basin↗

USGS2021

Endangered Australian top predator is frequently exposed to anticoagulant rodenticides

Anticoagulant rodenticides (ARs) used to control mammalian pest populations cause secondary exposure of predatory species throughout much of the world. It is important to understand the drivers of non-target AR exposure patterns as context for assessing long-term effects and developing effective mitigation for these toxicants. In Australia, however, little is known about exposure and effects of ARs on predators. We detected AR residues in 74% of 50 opportunistically collected carcasses of the Tasmanian wedge-tailed eagle ( Aquila audax fleayi ), an endangered apex predator. In 22% of birds tested, or 31% of those exposed, liver concentrations of second generation ARs (SGARs) were >0.1 mg/kg ww. Eagles were exposed to flocoumafen, a toxicant only available from agricultural suppliers, at an exceptionally high rate (40% of birds tested). Liver SGAR concentrations were positively associated with the proportion of agricultural habitat and human population density in the area around where each eagle died. The high exposure rate in a species not known to regularly prey upon synanthropic rodents supports the hypothesis that apex predators are vulnerable to SGARs. Our results indicate that AR exposure constitutes a previously unrecognized threat to Tasmanian wedge-tailed eagles and highlight the importance of efforts to address non-target AR exposure in Australia.

Tasmania↗

USGS2021

Morphometric sex identification of nestling and free-flying Tasmanian Wedge-tailed Eagles (Aquila audax fleayi)

The endangered Tasmanian Wedge-tailed Eagle ( Aquila audax fleayi ) is the focus of continued research and conservation efforts. A tool for accurate and efficient identification of the sex of individuals would be a valuable aid to research and management. However, plumages are monomorphic between the sexes, making sex identification difficult without molecular analyses. Our aim was to assess whether Tasmanian Wedge-tailed Eagles of different age classes could be sexed accurately using morphological measurements. We took measurements of 25 live late-stage eagle nestlings and 108 carcasses of free-flying birds found opportunistically throughout Tasmania. Sex of all individuals was confirmed via genetic analyses. Free-flying birds were larger than nestlings; thus, we used age-specific statistical tools to distinguish the sexes. For both nestlings and free-flying birds, females were significantly larger than males, but overlap between the sexes prevented accurate sex identification using any single measurement. We used stepwise linear discriminant function analyses to select morphometric measurements necessary for accurate sex identification. Free-flying birds could be sexed with 97.6% accuracy using a combination of measurements of the forearm length, tarsus width (i.e., lateromedial width), and hallux length. Late-stage nestlings (9–10 wk old) could be sexed with 95.4% accuracy using measurements of the hallux width (i.e., lateromedial width), hallux breadth (i.e., anteroposterior width of hallux), and tarsus breadth (i.e., anteroposterior width of the tarsometatarsus at the narrowest point). The discriminate functions we present also allow the identification of sex in cases where morphological sex identification may be in doubt and molecular analyses should be prioritized. These equations provide a valuable research tool for studies of sexual differences in behavior and causes of mortality of this endangered subspecies.

Tasmania↗

USGS2020

High frequency of lead exposure in the population of an endangered Australian top predator, the Tasmanian wedge-tailed eagle (Aquila audax fleayi)

Lead poisoning, mainly through incidental ingestion of lead ammunition in carcasses, is a threat to scavenging and predatory bird species worldwide. In Australia, shooting for animal control is widespread, and a range of native scavenging species are susceptible to lead exposure. However, the prevalence of lead exposure in Australia's scavenging and predatory birds is largely unknown. We evaluated the degree to which the Tasmanian wedge‐tailed eagle ( Aquila audax fleayi ), an endangered Australian raptor and facultative scavenger, showed evidence of lead exposure. We detected lead in 100% of femur and liver tissues of 109 eagle carcasses opportunistically collected throughout Tasmania between 1996 and 2018. Concentrations were elevated in 10% of 106 liver (> 6 mg/kg dw) and 4% of 108 femur (> 10 mg/kg dw) samples. We also detected lead in 96% of blood samples taken from 24 live nestlings, with 8% at elevated concentrations (> 10 μg/dL). Of the liver samples with elevated lead, 73% had lead 207/206 isotope ratios within the published range of lead‐based bullets available in Tasmania. These first comprehensive data on lead exposure of an Australian raptor are comparable to those for raptor studies elsewhere that identify lead‐based ammunition exposure as a conservation threat. Our findings highlight the importance of further research and efforts to address lead contamination throughout the Tasmanian ecosystem and in other Australian regions.

Environmental Toxicology and Chemistry↗