Geology topics

Anton D. Tucker

Publications and source records attributed to Anton D. Tucker.

6 recordsLinked to original sources

USGS2023

Monitoring population-level foraging distribution of a marine migratory species from land: Strengths and weaknesses of the isotopic approach on the Northwest Atlantic loggerhead turtle aggregation

Assessing the linkage between breeding and non-breeding areas has important implications for understanding the fundamental biology of and conserving animal species. This is a challenging task for marine species, and in sea turtles a combination of stable isotope analysis (SIA) and satellite telemetry has been increasingly used. The Northwest Atlantic (NWA) loggerhead ( Caretta caretta ) Regional Management Unit, one of the largest sea turtle populations in the world, provides an excellent opportunity to investigate key biological patterns as well as methodological aspects related to the use of stable isotopes to infer spatial distribution of turtles in foraging areas. We provide the first comprehensive assessment of the annual distribution of NWA adult female loggerheads among foraging areas and investigate the efficacy of various analytical approaches as well as the effect of sample size in these types of studies. A total of 5168 individual females were sampled from seven Management Units (MUs) between 2013-2018. We provide the first estimate of the proportion of females originating from each MU that uses each foraging area and show how this proportion varies over time. We also estimate the relative importance (in terms of number of turtles) of each foraging area to the overall loggerhead breeding aggregation nesting in Florida and in the NWA for each year of the study. The foraging area used by reproductively active females differs considerably across MUs. One of these, the Subtropical NWA, is by far the most important foraging area in terms of both number of individuals and genetic diversity, and therefore this region may be considered as a conservation priority. Through simulations, we show that limited sizes of sample groups (unknowns; training; priors) may result in false geographic differentiation and consequently mislead interpretations. We provide thresholds and methodological recommendations for future studies. This study establishes a fundamental baseline for monitoring the annual contribution of foraging area to a terrestrial-based breeding aggregation of a marine animal in a cost-effective way. This type of monitoring allows for early detection of changes in foraging distributions—a possible effect of climate change on marine ecosystems or of area-specific anthropogenic threats.

Frontiers in Marine Science↗

USGS2016

Biomarkers reveal sea turtles remained in oiled areas following the Deepwater Horizon oil spill

Assessments of large-scale disasters, such as the Deepwater Horizon oil spill, are problematic because while measurements of post-disturbance conditions are common, measurements of pre-disturbance baselines are only rarely available. Without adequate observations of pre-disaster organismal and environmental conditions, it is impossible to assess the impact of such catastrophes on animal populations and ecological communities. Here, we use long-term biological tissue records to provide pre-disaster data for a vulnerable marine organism. Keratin samples from the carapace of loggerhead sea turtles record the foraging history for up to 18 years, allowing us to evaluate the effect of the oil spill on sea turtle foraging patterns. Samples were collected from 76 satellite-tracked adult loggerheads in 2011 and 2012, approximately one to two years after the spill. Of the 10 individuals that foraged in areas exposed to surface oil, none demonstrated significant changes in foraging patterns post spill. The observed long-term fidelity to foraging sites indicates that loggerheads in the northern Gulf of Mexico likely remained in established foraging sites, regardless of the introduction of oil and chemical dispersants. More research is needed to address potential long-term health consequences to turtles in this region. Mobile marine organisms present challenges for researchers to monitor effects of environmental disasters, both spatially and temporally. We demonstrate that biological tissues can reveal long-term histories of animal behavior and provide critical pre-disaster baselines following an anthropogenic disturbance or natural disaster.

Ecological Applications↗

USGS2016

Development of a Kemp’s ridley sea turtle stock assessment model

We developed a Kemp’s ridley ( Lepidochelys kempii ) stock assessment model to evaluate the relative contributions of conservation efforts and other factors toward this critically endangered species’ recovery. The Kemp’s ridley demographic model developed by the Turtle Expert Working Group (TEWG) in 1998 and 2000 and updated for the binational recovery plan in 2011 was modified for use as our base model. The TEWG model uses indices of the annual reproductive population (number of nests) and hatchling recruitment to predict future annual numbers of nests on the basis of a series of assumptions regarding age and maturity, remigration interval, sex ratios, nests per female, juvenile mortality, and a putative ‘‘turtle excluder device effect’’ multiplier starting in 1990. This multiplier was necessary to fit the number of nests observed in 1990 and later. We added the effects of shrimping effort directly, modified by habitat weightings, as a proxy for all sources of anthropogenic mortality. Additional data included in our model were incremental growth of Kemp’s ridleys marked and recaptured in the Gulf of Mexico, and the length frequency of stranded Kemp’s ridleys. We also added a 2010 mortality factor that was necessary to fit the number of nests for 2010 and later (2011 and 2012). Last, we used an empirical basis for estimating natural mortality, on the basis of a Lorenzen mortality curve and growth estimates. Although our model generated reasonable estimates of annual total turtle deaths attributable to shrimp trawling, as well as additional deaths due to undetermined anthropogenic causes in 2010, we were unable to provide a clear explanation for the observed increase in the number of stranded Kemp’s ridleys in recent years, and subsequent disruption of the species’ exponential growth since the 2009 nesting season. Our consensus is that expanded data collection at the nesting beaches is needed and of high priority, and that 2015 be targeted for the next stock assessment to evaluate the 2010 event using more recent nesting and in-water data.

Gulf of Mexico Science↗

USGS2015

Determining origin in a migratory marine vertebrate: a novel method to integrate stable isotopes and satellite tracking

Stable isotope analysis is a useful tool to track animal movements in both terrestrial and marine environments. These intrinsic markers are assimilated through the diet and may exhibit spatial gradients as a result of biogeochemical processes at the base of the food web. In the marine environment, maps to predict the spatial distribution of stable isotopes are limited, and thus determining geographic origin has been reliant upon integrating satellite telemetry and stable isotope data. Migratory sea turtles regularly move between foraging and reproductive areas. Whereas most nesting populations can be easily accessed and regularly monitored, little is known about the demographic trends in foraging populations. The purpose of the present study was to examine migration patterns of loggerhead nesting aggregations in the Gulf of Mexico (GoM), where sea turtles have been historically understudied. Two methods of geographic assignment using stable isotope values in known-origin samples from satellite telemetry were compared: 1) a nominal approach through discriminant analysis and 2) a novel continuous-surface approach using bivariate carbon and nitrogen isoscapes (isotopic landscapes) developed for this study. Tissue samples for stable isotope analysis were obtained from 60 satellite-tracked individuals at five nesting beaches within the GoM. Both methodological approaches for assignment resulted in high accuracy of foraging area determination, though each has advantages and disadvantages. The nominal approach is more appropriate when defined boundaries are necessary, but up to 42% of the individuals could not be considered in this approach. All individuals can be included in the continuous-surface approach, and individual results can be aggregated to identify geographic hotspots of foraging area use, though the accuracy rate was lower than nominal assignment. The methodological validation provides a foundation for future sea turtle studies in the region to inexpensively determine geographic origin for large numbers of untracked individuals. Regular monitoring of sea turtle nesting aggregations with stable isotope sampling can be used to fill critical data gaps regarding habitat use and migration patterns. Probabilistic assignment to origin with isoscapes has not been previously used in the marine environment, but the methods presented here could also be applied to other migratory marine species.

Ecological Applications↗

USGS2012

Common coastal foraging areas for loggerheads in the Gulf of Mexico: Opportunities for marine conservation

Designing conservation strategies that protect wide-ranging marine species is a significant challenge, but integrating regional telemetry datasets and synthesizing modeled movements and behavior offer promise for uncovering distinct at-sea areas that are important habitats for imperiled marine species. Movement paths of 10 satellite-tracked female loggerheads ( Caretta caretta ) from three separate subpopulations in the Gulf of Mexico, USA, revealed migration to discrete foraging sites in two common areas at-sea in 2008, 2009, and 2010. Foraging sites were 102–904 km away from nesting and tagging sites, and located off southwest Florida and the northern Yucatan Peninsula, Mexico. Within 3–35 days, turtles migrated to foraging sites where they all displayed high site fidelity over time. Core-use foraging areas were 13.0–335.2 km 2 in size, in water <50 m deep, within a mean distance to nearest coastline of 58.5 km, and in areas of relatively high net primary productivity. The existence of shared regional foraging sites highlights an opportunity for marine conservation strategies to protect important at-sea habitats for these imperiled marine turtles, in both USA and international waters. Until now, knowledge of important at-sea foraging areas for adult loggerheads in the Gulf of Mexico has been limited. To better understand the spatial distribution of marine turtles that have complex life-histories, we propose further integration of disparate tracking data-sets at the oceanic scale along with modeling of movements to identify critical at-sea foraging habitats where individuals may be resident during non-nesting periods.

Florida↗

USGS1997

Perceptions of species abundance, distribution, and diversity: Lessons from four decades of sampling on a government-managed reserve

We examined data relative to species abundance, distribution, and diversity patterns of reptiles and amphibians to determine how perceptions change over time and with level of sampling effort. Location data were compiled on more than one million individual captures or observations of 98 species during a 44-year study period on the US Department of Energy’s (DOE) Savannah River Site National Environmental Research Park (SRS-NERP) in South Carolina. We suggest that perceptions of herpetofaunal species diversity are strongly dependent on level of effort and that land management decisions based on short-term data bases for some faunal groups could result in serious errors in environmental management. We provide evidence that acquiring information on biodiversity distribution patterns is compatible with multiyear spatially extensive research programs and also provide a perspective of what might be achieved if long-term, coordinated research efforts were instituted nationwide. To conduct biotic surveys on government-managed lands, we recommend revisions in the methods used by government agencies to acquire and report biodiversity data. We suggest that government and industry employees engaged in biodiversity survey efforts develop proficiency in field identification for one or more major taxonomic groups and be encouraged to measure the status of populations quantitatively with consistent and reliable methodologies. We also suggest that widespread academic cooperation in the dissemination of information on regional patterns of biodiversity could result by establishment of a peer-reviewed, scientifically rigorous journal concerned with status and trends of the biota of the United States.

Environmental Management↗