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At least 829 records · Page 46Linked to original sources

USGS2010

Trip report: pilot study of factors linking watershed function and coastal ecosystem health in American Samoa

Coral reef resources in the territory of American Samoa face significant problems from overfishing, non-point source pollution, global warming, and continuing population growth and development. The islands are still relatively isolated relative to other parts of the Pacific and have managed to avoid some of the more devastating invasive species that have reached other archipelagoes. As a result, there are opportunities for collaborative and integrative research and monitoring programs to help restore and maintain biodiversity and functioning natural ecosystem in the archipelago. We found that the “Ridge to Reef” paradigm already exists in American Samoa, with a high degree of interagency cooperation and efficient use of limited resources already taking place in the Territory. USGS may be able to make contributions as a partner organization in the Coral Reef Advisory Group (CRAG) through deployment of sediment monitoring instrumentation to supplement stream monitoring by the American Samoa Environmental Protection Agency, by providing high resolution vegetation and land-use maps of main islands, by providing additional support to the American Samoa Department of Marine and Wildlife Resources and the National Park Service for monitoring of invasive species, by working with members of CRAG to initiate sediment transport studies on Samoan reefs, and by developing new projects on the effects of bacterial contamination and pollutants on coral reef physiology and demography.

Open-File Report↗

USGS2022

Multi-year, spatially extensive, watershed-scale synoptic stream chemistry and water quality conditions for six permafrost-underlain Arctic watersheds

Repeated sampling of spatially distributed river chemistry can be used to assess the location, scale, and persistence of carbon and nutrient contributions to watershed exports. Here, we provide a comprehensive set of water chemistry measurements and ecohydrological metrics describing the biogeochemical conditions of permafrost-affected Arctic watersheds. These data were collected in watershed-wide synoptic campaigns in six stream networks across northern Alaska. Three watersheds are associated with the Arctic Long-Term Ecological Research site at Toolik Field Station (TFS), which were sampled seasonally each June and August from 2016 to 2018. Three watersheds were associated with the National Park Service (NPS) of Alaska and the U.S. Geological Survey (USGS) and were sampled annually from 2015 to 2019. Extensive water chemistry characterization included carbon species, dissolved nutrients, and major ions. The objective of the sampling designs and data acquisition was to characterize terrestrial–aquatic linkages and processing of material in stream networks. The data allow estimation of novel ecohydrological metrics that describe the dominant location, scale, and overall persistence of ecosystem processes in continuous permafrost. These metrics are (1) subcatchment leverage, (2) variance collapse, and (3) spatial persistence. Raw data are available at the National Park Service Integrated Resource Management Applications portal (O'Donnell et al., 2021, https://doi.org/10.5066/P9SBK2DZ ) and within the Environmental Data Initiative (Abbott, 2021, https://doi.org/10.6073/pasta/258a44fb9055163dd4dd4371b9dce945 ).

Alaska↗

USGS2016

Should fatty acid signature proportions sum to 1 for diet estimation?

Knowledge of predator diets, including how diets might change through time or differ among predators, provides essential insights into their ecology. Diet estimation therefore remains an active area of research within quantitative ecology. Quantitative fatty acid signature analysis (QFASA) is an increasingly common method of diet estimation. QFASA is based on a data library of prey signatures, which are vectors of proportions summarizing the fatty acid composition of lipids, and diet is estimated as the mixture of prey signatures that most closely approximates a predator’s signature. Diets are typically estimated using proportions from a subset of all fatty acids that are known to be solely or largely influenced by diet. Given the subset of fatty acids selected, the current practice is to scale their proportions to sum to 1.0. However, scaling signature proportions has the potential to distort the structural relationships within a prey library and between predators and prey. To investigate that possibility, we compared the practice of scaling proportions with two alternatives and found that the traditional scaling can meaningfully bias diet estimators under some conditions. Two aspects of the prey types that contributed to a predator’s diet influenced the magnitude of the bias: the degree to which the sums of unscaled proportions differed among prey types and the identifiability of prey types within the prey library. We caution investigators against the routine scaling of signature proportions in QFASA.

Ecological Research↗

USGS2014

Estuarine removal of glacial iron and implications for iron fluxes to the ocean

While recent work demonstrates that glacial meltwater provides a substantial and relatively labile flux of the micronutrient iron to oceans, the role of high-latitude estuary environments as a potential sink of glacial iron is unknown. Here we present the first quantitative description of iron removal in a meltwater-dominated estuary. We find that 85% of “dissolved” Fe is removed in the low-salinity region of the estuary along with 41% of “total dissolvable” iron associated with glacial flour. We couple these findings with hydrologic and geochemical data from Gulf of Alaska (GoA) glacierized catchments to calculate meltwater-derived fluxes of size and species partitioned Fe to the GoA. Iron flux data indicate that labile iron in the glacial flour and associated Fe minerals dominate the meltwater contribution to the Fe budget of the GoA. As such, GoA nutrient cycles and related ecosystems could be strongly influenced by continued ice loss in its watershed.

Geophysical Research Letters↗

USGS2016

Estimation of time-variable fast flow path chemical concentrations for application in tracer-based hydrograph separation analyses

Mixing models are a commonly used method for hydrograph separation, but can be hindered by the subjective choice of the end-member tracer concentrations. This work tests a new variant of mixing model that uses high-frequency measures of two tracers and streamflow to separate total streamflow into water from slowflow and fastflow sources. The ratio between the concentrations of the two tracers is used to create a time-variable estimate of the concentration of each tracer in the fastflow end-member. Multiple synthetic data sets, and data from two hydrologically diverse streams, are used to test the performance and limitations of the new model (two-tracer ratio-based mixing model: TRaMM). When applied to the synthetic streams under many different scenarios, the TRaMM produces results that were reasonable approximations of the actual values of fastflow discharge (±0.1% of maximum fastflow) and fastflow tracer concentrations (±9.5% and ±16% of maximum fastflow nitrate concentration and specific conductance, respectively). With real stream data, the TRaMM produces high-frequency estimates of slowflow and fastflow discharge that align with expectations for each stream based on their respective hydrologic settings. The use of two tracers with the TRaMM provides an innovative and objective approach for estimating high-frequency fastflow concentrations and contributions of fastflow water to the stream. This provides useful information for tracking chemical movement to streams and allows for better selection and implementation of water quality management strategies.

Water Resources Research↗

USGS2013

Tidally influenced alongshore circulation at an inlet-adjacent shoreline

The contribution of tidal forcing to alongshore circulation inside the surfzone is investigated at a 7 km long sandy beach adjacent to a large tidal inlet. Ocean Beach in San Francisco, CA (USA) is onshore of a &sim;150 km2 ebb-tidal delta and directly south of the Golden Gate, the sole entrance to San Francisco Bay. Using a coupled flow-wave numerical model, we find that the tides modulate, and in some cases can reverse the direction of, surfzone alongshore flows through two separate mechanisms. First, tidal flow through the inlet results in a barotropic tidal pressure gradient that, when integrated across the surfzone, represents an important contribution to the surfzone alongshore force balance. Even during energetic wave conditions, the tidal pressure gradient can account for more than 30% of the total alongshore pressure gradient (wave and tidal components) and up to 55% during small waves. The wave driven component of the alongshore pressure gradient results from alongshore wave height and corresponding setup gradients induced by refraction over the ebb-tidal delta. Second, wave refraction patterns over the inner shelf are tidally modulated as a result of both tidal water depth changes and strong tidal flows (&sim;1 m/s), with the effect from currents being larger. These tidally induced changes in wave refraction result in corresponding variability of the alongshore radiation stress and pressure gradients within the surfzone. Our results indicate that tidal contributions to the surfzone force balance can be significant and important in determining the direction and magnitude of alongshore flow.

California↗

USGS2002

Heavy mineral provinces of the Palos Verdes margin, southern California

Natural sources of sediment for the Palos Verdes margin, southern California, have been augmented by effluent discharged from Los Angeles County Sanitation District's sewage-treatment facility and by the reactivation of the Portuguese Bend landslide. Heavy minerals in very fine and fine sand (63-250 ??m) from beach and shelf sites off the Palos Verdes Peninsula distinguish effluent-affected sediment from unaffected deposits, and track the sediment contributed by the Portuguese Bend landslide. Heavy minerals also identify heterogeneous sediment sources for the nearshore zone and relate outer-shelf sediment to depositional cells north and south of the area.

Continental Shelf Research↗

USGS1998

Erosional valleys in the Thaumasia region of Mars: Hydrothermal and seismic origins

Analysis of erosional valleys, geologic materials and features, and topography through time in the Thaumasia region of Mars using co-registered digital spatial data sets reveals significant associations that relate to valley origin. Valleys tend to originate (1) on Noachian to Early Hesperian (stages 1 and 2) large volcanoes, (2) within 50–100 km of stages 1 and 2 rift systems, and (3) within 100 km of Noachian (stage 1) impact craters >50 km in diameter. These geologic preferences explain observations of higher valley-source densities (VSDs) in areas of higher elevations and regional slopes (>1°) because the volcanoes, rifts, and craters form high, steep topography or occur in terrain of high relief. Other stage 1 and stage 2 high, steep terrains, however, do not show high VSDs. The tendency for valleys to concentrate near geologic features and the overall low drainage densities in Thaumasia compared to terrestrial surfaces rule out widespread precipitation as a major factor in valley formation (as is proposed in wann, wet climate scenarios) except perhaps during the Early Noachian, for which much of the geologic record has been obliterated. Instead, volcanoes and rifts may indicate the presence of shallow crustal intrusions that could lead to local hydrothermal circulation, melting of ground ice and snow, and groundwater sapping. However, impact-crater melt would provide a heat source at the surface that might drive away water, fonning valleys in the process. Post-stage 1 craters mostly have low nearby VSDs, which, for valleys incised in older rocks, suggests burial by ejecta and, for younger valleys, may indicate desiccation of near-surface water and deepening of the cryosphere. Later Hesperian and Amazonian (stages 3 and 4) valleys originate within 100–200 km of three young, large impact craters and near rifts systems at Warrego Valles and the southern part of Coprates rise. These valleys likely developed when the cryosphere was a couple kilometers or more thick, inhibiting valley development by hydrothermal circulation. However, eruption of groundwater may have occurred from impact-induced fracturing and lateral and perhaps minor upward transport of water due to seismic pumping. The two smaller craters formed along the plateau margin where the highest potential hydraulic head would occur in aquifers beneath the plateau. In the case of the larger crater (Lowell, 200 km in diameter), potential aquifers would likely be at depths of kilometers below the cryosphere. Seismic energy generated by the Lowell impactor would have been much greater, pumping both groundwater and perhaps fluidized slurry to the surface from beneath the cryosphere to form the young valleys and flow deposit. Along the margin of Thaumasia, tectonic pressurization of groundwater also may have contributed to valley formation. Dissection of rim materials of the Argyre impact may relate to tectonic activity and the unconsolidated state of basin ejecta.

Journal of Geophysical Research E: Planets↗

USGS2012

The glass transition in basalt

The glass transition has been experimentally detected in basalt as (1) an increase in the aggregate linear thermal expansion coefficient α L , (2) an abrupt change in the temperature dependence of Young's modulus dE / dT , and (3) a change in stress relaxation behavior that effectively separates the T > T G and T < T G creep regimes. Transition temperatures determined by the respective experimental methods are (1) 730° ± 15°C, by expansion dilatometry, (2) 725° ± 10°C, by acoustic spectroscopy, and (3) 725° ± 25°C, by stress relaxation. For olivine tholeiite from Kilauea Iki lava lake, Hawaii, thermal expansivity rises through the glass transition interval, attaining α υ = 39.0 × 10 −6 °C −1 at 850°C. For olivine tholeiites with moderate glass contents, the temperature dependence of the Young's modulus changes on either side of the inferred T G of 725°C, and dE / dT = −0.071 kbar °C −1 for T < T G , while dE / dT = − 0.21 kbar °C −1 for T > T G . Collectively, the mechanical results suggest that for Hawaiian olivine tholeiite at 1-atm pressure, the principal material responses are (1) elastic ( T ≤ 600°C), (2) reduced creep (600 < T < 725°C), (3) glass transition ( T ≃ 725°C), (4) enhanced creep (725 < T < 980°C), and (5) partial melt ( T > 980°C). Fracture surface morphologies developed during solidification suggest that the presence of the supercooled melt grain boundary phase may participate in the regulation of the thermal cracking process. Well-preserved fracture surfaces formed by incremental crack growth are found to be covered with striations that correspond to the inferred sequential stopping positions of the advancing fracture front. These striae may be rationalized in terms of experimental analogues that have been produced in viscoelastic polymers by cyclic tension-tension loading. The fracture surface morphology, mechanical data, and the controlled crack growth analogues suggest that thermal fracture in solidifying basalt is an incremental and cyclic process, involving three steps: (1) the accumulation of elastic strain energy in cooling rock at temperatures below that required for stress relaxation due to viscous flow in the intercrystalline liquid phase, (2) fracture at a Δ T determined primarily by the aggregate thermal expansion coefficient α υ and Young's modulus E , (3) the penetration by the advancing crack tip, of the thermal horizon capable of relaxing stress due to the creep of intercrystalline supercooled melt, producing the rough surface texture associated with the termination of a striation. Further crack growth must now await the migration of the solidus. The cycle then repeats. Striations measured in deep Hawaiian lava lakes have been compared with the crack advance increments expected in the vicinity of the glass transition, based on two tests: (1) thermal gradients measured in Kilauea Iki, combined with the mechanical properties of olivine tholeiite evaluated near T G , and (2) the crack advance required to match the recorded seismic stopping phases for prexisting cracks of the dimensions expected for Kilauea Iki. The observed versus predicted comparisons are (1) 31 versus 36 cm; and (2) 31 versus 30 cm. We envision this incremental crack growth process as contributing to the control on the downward movement of the thermal cracking front—and its associated hydrothermal circulation zone—in the upper portions of solidifying subaerial and submarine ponded basalt.

Journal of Geophysical Research Solid Earth↗

USGS2020

Very‐long‐period (VLP) seismic artifacts during the 2018 caldera collapse at Kīlauea, Hawaii

Throughout the 2018 eruption of Kīlauea volcano (Hawai‘i), episodic collapses of a portion of the volcano’s summit caldera produced repeated M w "> M w 4.9–5.3 earthquakes. Each of these 62 events was characterized by a very‐long‐period (VLP) seismic signal ( ⁠ > 40    s "> > 40 s ⁠ ). Although collapses in the later stage of the eruption produced earthquakes with significant amplitude clipping on near‐summit broadband seismometers, the first 12 were accurately recorded. For these initial collapse events, we compare average VLP seismograms at six near‐summit locations to synthetic seismograms derived from displacements at collocated Global Positioning System stations. We show that the VLP seismic signal was generated by a radially outward and upward ramp function in displacement. We propose that at local distances the period of the VLP seismic signal is solely dependent on the duration of this ramp function and the instrument transfer function, that is, the seismic VLP is an artifact of the bandlimited instrument response and not representative of real ground motion. The displacement ramp function imposes a sinc‐function velocity amplitude spectrum that cannot be fully recovered through standard seismic instrument deconvolution. Any near‐summit VLP signals in instrument‐response‐corrected velocity or displacement seismograms from these collapse events are subject to severe band limitation. Similarly, the seismic amplitude response is not flat through the low‐frequency corner, for example, instrument‐response‐uncorrected seismograms scaled by instrument sensitivity are equally prone to band limitation. This observation is crucial when attempting to clarify the different contributions to the VLP source signature. Not accounting for this effect could lead to misunderstanding of the magmatic processes involved.

Hawaii↗

USGS2009

PAGER-CAT: A composite earthquake catalog for calibrating global fatality models

We have described the compilation and contents of PAGER-CAT, an earthquake catalog developed principally for calibrating earthquake fatality models. It brings together information from a range of sources in a comprehensive, easy to use digital format. Earthquake source information (e.g., origin time, hypocenter, and magnitude) contained in PAGER-CAT has been used to develop an Atlas of Shake Maps of historical earthquakes (Allen et al. 2008) that can subsequently be used to estimate the population exposed to various levels of ground shaking (Wald et al. 2008). These measures will ultimately yield improved earthquake loss models employing the uniform hazard mapping methods of ShakeMap. Currently PAGER-CAT does not consistently contain indicators of landslide and liquefaction occurrence prior to 1973. In future PAGER-CAT releases we plan to better document the incidence of these secondary hazards. This information is contained in some existing global catalogs but is far from complete and often difficult to parse. Landslide and liquefaction hazards can be important factors contributing to earthquake losses (e.g., Marano et al. unpublished). Consequently, the absence of secondary hazard indicators in PAGER-CAT, particularly for events prior to 1973, could be misleading to sorne users concerned with ground-shaking-related losses. We have applied our best judgment in the selection of PAGER-CAT's preferred source parameters and earthquake effects. We acknowledge the creation of a composite catalog always requires subjective decisions, but we believe PAGER-CAT represents a significant step forward in bringing together the best available estimates of earthquake source parameters and reports of earthquake effects. All information considered in PAGER-CAT is stored as provided in its native catalog so that other users can modify PAGER preferred parameters based on their specific needs or opinions. As with all catalogs, the values of some parameters listed in PAGER-CAT are highly uncertain, particularly the casualty numbers, which must be regarded as estimates rather than firm numbers for many earthquakes. Consequently, we encourage contributions from the seismology and earthquake engineering communities to further improve this resource via the Wikipedia page and personal communications, for the benefit of the whole community.

Seismological Research Letters↗

USGS2018

Raptor interactions with wind energy: Case studies from around the world

The global potential for wind power generation is vast, and the number of installations is increasing rapidly. We review case studies from around the world of the effects on raptors of wind-energy development. Collision mortality, displacement, and habitat loss have the potential to cause population-level effects, especially for species that are rare or endangered. The impact on raptors has much to do with their behavior, so careful siting of wind-energy developments to avoid areas suited to raptor breeding, foraging, or migration would reduce these effects. At established wind farms that already conflict with raptors, reduction of fatalities may be feasible by curtailment of turbines as raptors approach, and offset through mitigation of other human causes of mortality such as electrocution and poisoning, provided the relative effects can be quantified. Measurement of raptor mortality at wind farms is the subject of intense effort and study, especially where mitigation is required by law, with novel statistical approaches recently made available to improve the notoriously difficult-to-estimate mortality rates of rare and hard-to-detect species. Global standards for wind farm placement, monitoring, and effects mitigation would be a valuable contribution to raptor conservation worldwide.

Journal of Raptor Research↗

USGS2011

Recent and historic drivers of landscape change in the Everglades ridge, slough, and Tree Island mosaic

More than half of the original Everglades extent formed a patterned peat mosaic of elevated ridges, lower and more open sloughs, and tree islands aligned parallel to the dominant flow direction. This ecologically important landscape structure remained in a dynamic equilibrium for millennia prior to rapid degradation over the past century in response to human manipulation of the hydrologic system. Restoration of the patterned landscape structure is one of the primary objectives of the Everglades restoration effort. Recent research has revealed that three main drivers regulated feedbacks that initiated and maintained landscape structure: the spatial and temporal distribution of surface water depths, surface and subsurface flow, and phosphorus supply. Causes of recent degradation include but are not limited to perturbations to these historically important controls; shifts in mineral and sulfate supply may have also contributed to degradation. Restoring predrainage hydrologic conditions will likely preserve remaining landscape pattern structure, provided a sufficient supply of surface water with low nutrient and low total dissolved solids content exists to maintain a rainfall-driven water chemistry. However, because of hysteresis in landscape evolution trajectories, restoration of areas with a fully degraded landscape could require additional human intervention.

Critical Reviews in Environmental Science and Tech↗

USGS2009

Food habits of American black bears as a metric for direct management of humanbear conflict in Yosemite Valley, Yosemite National Park, California

The management of human-American black bear (Ursus americanus) conflict has been of significant concern for Yosemite National Park (YNP) personnel since the 1920s. Park managers implemented the YNP Human-Bear Management Plan in 1975 in an effort to reduce human-bear conflicts, especially in the extensively developed Yosemite Valley (YV). We used scat analysis to estimate annual and seasonal food habits of black bears in YV during 2001-02. We assessed the success of efforts to reduce the availability of anthropogenic foods, including garbage, by examining changes in the diet compared to a study from 1974-78 (Graber 1981). We also quantified consumption of non-native fruit to address its possible contribution to human-bear conflicts. The annual percent volume of human-provided food and garbage in black bear scats in YV decreased from 21% to 6% between 1978 and 2002, indicating YNP efforts have been effective. We found high use of non-native apples by bears throughout YV. Non-native food sources could be contributing to habituation and food conditioning, given their proximity to developed areas of YV. We recommend that YNP managers continue to (1) adapt and improve their management tools to address changing circumstances, (2) quantify the success of new management tools, and (3) reduce the availability of non-native food sources. ?? 2009 International Association for Bear Research and Management.

Ursus↗

USGS2011

Objectives, priorities, reliable knowledge, and science-based management of Missouri River interior least terns and piping plovers

Supporting recovery of federally listed interior least tern (Sternula antillarum athalassos; tern) and piping plover (Charadrius melodus; plover) populations is a desirable goal in management of the Missouri River ecosystem. Many tools are implemented in support of this goal, including habitat management, annual monitoring, directed research, and threat mitigation. Similarly, many types of data can be used to make management decisions, evaluate system responses, and prioritize research and monitoring. The ecological importance of Missouri River recovery and the conservation status of terns and plovers place a premium on efficient and effective resource use. Efficiency is improved when a single data source informs multiple high-priority decisions, whereas effectiveness is improved when decisions are informed by reliable knowledge. Seldom will a single study design be optimal for addressing all data needs, making prioritization of needs essential. Data collection motivated by well-articulated objectives and priorities has many advantages over studies in which questions and priorities are determined retrospectively. Research and monitoring for terns and plovers have generated a wealth of data that can be interpreted in a variety of ways. The validity and strength of conclusions from analyses of these data is dependent on compatibility between the study design and the question being asked. We consider issues related to collection and interpretation of biological data, and discuss their utility for enhancing the role of science in management of Missouri River terns and plovers. A team of USGS scientists at Northern Prairie Wildlife Research Center has been conducting tern and plover research on the Missouri River since 2005. The team has had many discussions about the importance of setting objectives, identifying priorities, and obtaining reliable information to answer pertinent questions about tern and plover management on this river system. The objectives of this presentation are to summarize those conversations and to share insights about concepts that could contribute to rigorous science support for management of this river system.

Missouri River↗

USGS2018

U.S. Department of the Interior Climate Science Centers and U.S. Geological Survey National Climate Change and Wildlife Science Center—Annual report for 2017

Introduction The year 2017 was a year of review and renewal for the Department of the Interior (DOI) Climate Science Centers (CSCs) and the U.S. Geological Survey (USGS) National Climate Change and Wildlife Science Center (NCCWSC). The Southeast, Northwest, Alaska, Southwest, and North Central CSCs’ 5-year summary review reports were released in 2017 and contain the findings of the external review teams led by the Cornell University Human Dimensions Research Unit in conjunction with the American Fisheries Society. The reports for the Pacific Islands, South Central, and Northeast CSCs are planned for release in 2018. The reviews provide an opportunity to evaluate aspects of the cooperative agreement, such as the effectiveness of the CSC in meeting project goals and assessment of the level of scientific contribution and achievement. These reviews serve as a way for the CSCs and NCCWSC to look for ways to recognize and enhance our network’s strengths and identify areas for improvement. The reviews were followed by the CSC recompetition, which led to new hosting agreements at the Northwest, Alaska, and Southeast CSCs. Learn more about the excellent science and activities conducted by the network centers in the 2017 annual report.

Open-File Report↗

USGS2017

Vulnerability of coral reefs to bioerosion from land-based sources of pollution

Ocean acidification (OA), the gradual decline in ocean pH and [ ] caused by rising levels of atmospheric CO 2 , poses a significant threat to coral reef ecosystems, depressing rates of calcium carbonate (CaCO 3 ) production, and enhancing rates of bioerosion and dissolution. As ocean pH and [ ] decline globally, there is increasing emphasis on managing local stressors that can exacerbate the vulnerability of coral reefs to the effects of OA. We show that sustained, nutrient rich, lower pH submarine groundwater discharging onto nearshore coral reefs off west Maui lowers the pH of seawater and exposes corals to nitrate concentrations 50 times higher than ambient. Rates of coral calcification are substantially decreased, and rates of bioerosion are orders of magnitude higher than those observed in coral cores collected in the Pacific under equivalent low pH conditions but living in oligotrophic waters. Heavier coral nitrogen isotope (δ 15 N) values pinpoint not only site-specific eutrophication, but also a sewage nitrogen source enriched in 15 N. Our results show that eutrophication of reef seawater by land-based sources of pollution can magnify the effects of OA through nutrient driven-bioerosion. These conditions could contribute to the collapse of coastal coral reef ecosystems sooner than current projections predict based only on ocean acidification.

Hawaii↗

USGS2021

Diet composition of the African manatee: Spatial and temporal variation within the Sanaga River Watershed, Cameroon

The present study aimed to investigate the diet of African manatees in Cameroon to better inform conservation decisions within protected areas. A large knowledge gap on diet and seasonal changes in forage availability limits the ability to develop informed local management plans for the African manatee in much of its range. This research took place in the Sanaga River Watershed, which includes two protected areas in the Littoral Region of Cameroon: the Douala-Edea National Park and the Lake Ossa Wildlife Reserve. We analyzed 113 manatee fecal samples and surveyed shoreline emergent and submerged vegetation within the Sanaga River Watershed. We used microhistological analyses to determine the relative contribution of each plant species to African manatee diets and compared across locations and across seasons (wet vs. dry season). We found that the shoreline vegetation is diverse with over 160 plant species, unevenly distributed across space and season, and dominated by emergent vegetation mostly represented by the antelope grass ( Echinochloa pyramidalis ). We recorded a total of 36 plant species from fecal samples with a spatial and temporal distribution mostly reflecting that of the corresponding shoreline vegetation. African manatees appear to be primarily opportunistically feeding on available vegetation across the seasons and habitat. This work documents the current, but changing, state of plant availability in the Sanaga River Watershed and reports the African manatee diet in Cameroon for the first time. This information can play a critical role in successfully managing the species and these protected areas. If we wish to protect the African manatee and the aquatic ecosystems within the Sanaga River Watershed, we must understand how forage availability changes over time, especially as its waters become nutrient enriched, eutrophic, and exposed to invasive species of plants in a changing world.

Douala-Edea National Park, Lake Ossa Wildlife Rese↗