Publications by authors named "Joshua D Stewart"

The prevalence and intensity of marine heatwaves is increasing globally, disrupting local environmental conditions. The individual and population-level impacts of prolonged heatwaves on marine species have recently been demonstrated, yet whole-ecosystem consequences remain unexplored. We leveraged time series abundance data of 361 taxa, grouped into 86 functional groups, from six long-term surveys, diet information from a new diet database, and previous modeling efforts, to build two food web networks using an extension of the popular Ecopath ecosystem modeling framework, Ecotran.

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Understanding population connectivity and genetic diversity is of fundamental importance to conservation. However, in globally threatened marine megafauna, challenges remain due to their elusive nature and wide-ranging distributions. As overexploitation continues to threaten biodiversity across the globe, such knowledge gaps compromise both the suitability and effectiveness of management actions.

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Article Synopsis
  • Climate change is causing rapid transformations in polar ecosystems, impacting various species, particularly at lower trophic levels.
  • Long-lived and mobile species like gray whales might cope better with short-term changes, but their survival still depends on the availability of prey in warming Arctic conditions.
  • Significant mortality events in gray whales, linked to low prey biomass and high ice cover, indicate that even adaptable species are vulnerable to the changing Arctic environment.
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Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species.

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Background: Expanding fisheries in developing nations like Sri Lanka have a significant impact on threatened marine species such as elasmobranchs. Manta and devil (mobulid) rays have some of the most conservative life history strategies of any elasmobranch, and even low to moderate levels of bycatch from gillnet fisheries may lead to significant population declines. A lack of information on life history, demographics, population trends, and fisheries impacts hinders effective management measures for these species.

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Whales are now largely protected from direct harvest, leading to partial recoveries in many previously depleted species. However, most populations remain far below their historical abundances and incidental human impacts, especially vessel strikes and entanglement in fishing gear, are increasingly recognized as key threats. In addition, climate-driven changes to prey dynamics are impacting the seasonal foraging grounds of many baleen whales.

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The whale shark (Rhincodon typus) is an endangered species with a declining global population. The South Ari Atoll Marine Protected Area (SAMPA), Maldives, is one of few locations globally where year-long residency of individuals occurs. This SAMPA aggregation appears to consist almost exclusively of immature males.

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Article Synopsis
  • The study focuses on conserving manta and devil rays, which are facing global threats, but face challenges due to their similar physical traits and recent changes in their classification.
  • Researchers generated genome-wide SNP data to clarify the evolutionary relationships and species boundaries of these rays, revealing that current species classifications may not reflect distinct evolutionary lineages.
  • The findings suggest the existence of a new manta ray species in the Gulf of Mexico and highlight the importance of detailed genetic analysis for effective conservation strategies, including managing genetic diversity below the species level.
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A floating plastic monitoring program was conducted for two years on a weekly basis in Banderas Bay, Mexico. A total of 94 samples were collected from May 2016 to April 2018 in the southern part of the bay. Half (57%) of them contained plastic debris; 79% of it being <5 mm in length.

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Objective: To test a novel method to select spermatozoa with high chromatin integrity.

Design: Specimens with high sperm chromatin fragmentation (SCF) were selected by density gradient selection (DGS) and microfluidic sperm sorting (MSS).

Setting: Academic medical center.

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In the eastern Pacific Ocean, the tropical tuna purse-seine fishery incidentally captures high numbers of five mobulid bycatch species; all of which are classified as mortalities by the Inter-American Tropical Tuna Commission due to uncertainties in post-release mortality rates. To date, the factors (operational or environmental) leading to the capture of these species by the fishery have not been well studied. Here, we developed Generalized Additive Models for fisheries observer data to analyze the relationships between the presence/absence of Mobula mobular bycatch and oceanographic conditions, the spatial and temporal variability in fishing location, and the set type (associated with dolphins, free-swimming tuna schools or floating objects).

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Infertility is estimated to affect about 10% to 15% of couples. Most cases of infertility have etiologies that can be attributed to tubal factors, ovulatory dysfunction, endometriosis, uterine factor, male factor, or diminished ovarian reserve, while the remainder often do not have a known attributable cause, that is, unexplained infertility. The current manuscript summarizes the contemporary management of unexplained infertility.

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Purpose: Fragile X premutation (PM) carriers may experience difficulties conceiving a child probably due to fragile X-associated diminished ovarian reserve (FXDOR). We investigated which subgroups of carriers with a PM are at higher risk of FXDOR, and whether the number of AGG interruptions within the repeat sequence further ameliorates the risk.

Methods: We compared markers of ovarian reserve, including anti-Müllerian hormone, antral follicle count, and number of oocytes retrieved between different subgroups of patients with a PM.

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Mobulid rays have a conservative life history and are caught in direct fisheries and as by-catch. Their subsequent vulnerability to overexploitation has recently been recognized, but fisheries management can be ineffective if it ignores habitat and prey preferences and other trophic interactions of the target species. Here, we assessed the feeding ecology of four mobulids (, , , ) in the Bohol Sea, Philippines, using stomach contents analysis of fisheries specimens landed between November and May in 2013-2015.

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Foraging drives many fundamental aspects of ecology, and an understanding of foraging behavior aids in the conservation of threatened species by identifying critical habitats and spatial patterns relevant to management. The world's largest ray, the oceanic manta (Manta birostris) is poorly studied and threatened globally by targeted fisheries and incidental capture. Very little information is available on the natural history, ecology and behavior of the species, complicating management efforts.

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Objective: To compare IVF outcomes between women undergoing frozen transfers of blastocysts verified as euploid by preimplantation genetic screening (PGS) with patients undergoing fresh nonbiopsied blastocyst transfers.

Design: Retrospective cohort study.

Setting: Academic medical center.

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Purpose: The purpose of this study is to investigate if female patients with lymphoma demonstrate diminished ovarian reserve prior to initiation of the lymphoma treatment.

Methods: Sixty-four patients with newly diagnosed lymphoma undergoing controlled ovarian hyperstimulation for fertility preservation were compared with 365 healthy controls undergoing elective oocyte cryopreservation (controlled ovarian hyperstimulation (COH)) and 128 patients with other types of malignancy prompting fertility preservation. The data of all lymphoma patients, all elective, and all the patients with other types of malignancy who met the inclusion criteria and underwent COH for fertility preservation during the study period were retrospectively analyzed.

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Objective: To assess the availability and capacity of US-based integrated centers for the management of Lynch syndrome.

Methods: A cross-sectional survey of practice patterns in the care of patients with Lynch syndrome was conducted at 33 National Cancer Institute-designated cancer centers in the USA from March 1 to June 1, 2013. Each cancer center was contacted by telephone and the caller used a uniform scripted greeting and survey format.

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