The sand tiger shark Carcharias taurus is a highly migratory coastal species with declining populations worldwide. This species exhibits many behaviors that make coastal sharks difficult to manage, including aggregatory behavior, sexual segregation, and large-scale migrations through shallow coastal waters with many opportunities for human interactions. Sand tigers from the Western North Atlantic subpopulation are known to seasonally inhabit Delaware Bay and surrounding coastal waters. This region has been recommended as a habitat area of particular concern for the Western North Atlantic sand tiger population, and increased understanding of their movements and habitat requirements will facilitate management efforts. We developed models to predict sand tiger occupancy using spatially dynamic environmental predictors. Our models predicted sand tiger (juveniles, adult males, adult females, and all sharks combined) occurrences in 2 study regions, the Delaware Bay and the western Mid-Atlantic coastal ocean. Sea surface temperature, day of year, water depth, and remote sensing reflectance at 555 nm were the most important environmental predictors of occurrence, and correctly predicted 80−89% of sand tiger acoustic telemetry records in the 2 study regions. Our models predicted differences in the timing and location of occurrences among juveniles and adults, as well as areas where these life history stages overlap in the Mid-Atlantic coastal ocean. Our hope is that a daily forecast of sand tiger occurrence from our modeling efforts could be useful for conservation and management efforts in this important region, as well as for studying the spatial and behavioral ecology of this important top predator.

Quantifying habitat selection in marine organisms is challenging because it is difficult to obtain species location information with multiple corresponding habitat measurements. In the ocean, habitat conditions vary on many spatiotemporal scales, which have important consequences for habitat selection. While macroscale biotic and abiotic features influence seasonal movements (spatial scales of 100−1000 km), selectivity of conditions on mesoscales (1−100 km) reflects an animal's response to the local environment. In this study, we examined habitat selectivity by pairing acoustic telemetry with environmental habitat parameters measured by an autonomous underwater vehicle (AUV), and demonstrate that migrating sand tiger sharks Carcharias taurus along the East Coast of the USA did not randomly use the coastal environment. Of the variables examined, we found evidence to suggest that sand tigers were selecting their habitat based on distance to shore, salinity, and colored dissolved organic matter (CDOM). Notably, temperature was not predictive of habitat use in our study. We posit that during their coastal migration, sand tigers select for specific mesoscale coastal habitats that may inform navigation or feeding behaviors. To our knowledge, this is the first empirical measure of mesoscale habitat selection by a coastal marine organism using an AUV. The applications of this method extend beyond the habitat selectivity of sand tigers, and will prove useful for future studies combining in situ observations of marine habitats and animal observations.

Animals utilize various habitats throughout their life to optimize growth, fitness, and survival. Identifying environmental conditions and locations where animals exhibit different movement behaviors can be used to infer the relative importance of habitat types. In the case of threatened and endangered species, such as the Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus, critical habitat designations are a tool used to promote conservation and recovery. We utilized an extensive passive acoustic telemetry array, observed atmospheric conditions and river flow, modeled seawater conditions, and used generalized additive mixed modeling to determine environmental predictors of Atlantic Sturgeon movement and residency in the Delaware Bay on the U.S. East Coast. Our results suggested that shallower waters, warmer bottom temperatures, and areas toward the eastern portion of the Delaware Bay were predictive of residency, while movement was predicted by increased depth, cooler bottom temperatures, and areas toward the western portion of the bay. Our findings add to a growing body of evidence highlighting habitats at the Delaware Bay mouth, where Atlantic Sturgeon occur at heightened concentrations from late spring through fall. The Delaware River estuary once supported the largest population of Atlantic Sturgeon in North America, but that population is now critically imperiled (or endangered). Atlantic Sturgeon spend the vast majority of their life in marine, polyhaline waters, and without enhanced protection for these habitats, their recovery may never be realized.

Encogiendo el pajar: utilización de un Vehículo Autónomo Submarino en un Observatorio Oceánico Integral para Mapear el Esturión del Atlántico en el Océano Costero RESUMEN: los procesos físicos que ocurren en zona costera del Atlántico medio generan un paisaje complejo y dinámico. La comprensión de cómo los peces costeros responden a tal complejidad ha sido una motivación importante para establecer un arreglo de biotelemetría en la franja costera. Muchos de los arreglos costeros maximizan la probabilidad de detectar peces mediante el uso de hidrófonos cerca de los cuellos de botella geofísicos. El desarrollo de un observatorio oceánico de monitoreo en tiempo real permite un mapeo sincrónico de estructuras hidrográficas dinámicas que son relevantes para los peces costeros. Estas observaciones bindan el contexto para interpretar el impacto que tienen ciertos rasgos oceanográfi-cos en el comportamiento de animales rastreados mediante telemetría. En una misión diseñada para probar este concepto, se desplegó el deslizador Slocum en un observatorio oceánico para demostrar cómo los aparatos móviles de monitoreo pueden ser reubicados de forma dinámica en respuesta a procesos físicos de mesoescala que ocurren en el océano costero. El deslizador Slocum detectó cuatro especímenes de esturión del Atlántico Acipencer oxyrinchus oxyrinchus encontrados en una masa de agua fresca, somera y relativamente cálida en una región en la que históricamente el esturión del Atlántico ha sido parte de la captura incidental.ABSTRACT: Physical processes in the coastal Mid-Atlantic create a complex and dynamic seascape. Understanding how coastal fishes respond to this complexity has been a major motivation in establishing coastal biotelemetry arrays. Most coastal arrays maximize the probability of fish detection by positioning hydrophones near geophysical bottlenecks. The development of a real-time ocean observatory allows for synchronous mapping of dynamic hydrographic structures important to coastal fishes. These observations provide important context for interpreting the impact of oceanographic features on the behavior of telemetered animals. In a proof-of-concept mission, we deployed a Slocum glider in a real-time ocean observatory to demonstrate how mobile listening assets could be dynamically reallocated in response to the mesoscale physics of the coastal ocean. The Slocum glider detected four Atlantic Sturgeon Acipencer oxyrinchus oxyrinchus that were in a shallow, well-mixed, and relatively warm and fresh water mass in a region of historic Atlantic Sturgeon bycatch.

The Hudson River currently supports the largest population of Atlantic Sturgeon (Acipenser oxyrinchus oxyrinchus) in the United States despite currently supporting less than a percent of historic abundance. Listed as Endangered throughout much of their range, Atlantic Sturgeon are still impacted by multiple threats, resulting in habitat destruction or direct mortality that has inhibited a population rebuild despite 20+ years without directed fishing pressure. To assist in management and reduction in anthropogenic impacts to adult Atlantic Sturgeon in the Hudson River we have examined sex specific patterns related to spawning. Utilizing hundreds of adult Atlantic Sturgeon, telemetered along the Atlantic Coast, and an extensive passive acoustic array from 2010-2016 we were able to estimate arrival, departure, and duration of occupancy for four segments of the Hudson River for male, female, and unknown sex individuals. Male Atlantic Sturgeon arrived above river kilometer 100 at an average date of May 27, 12 days prior to females on June 8. While there were only few significant differences in the timing of departure, the average date from RKM 100 was July 11 for males, June 29 for females and July 23 for unknown sex individuals, as such occupancy was significantly longer for male Atlantic Sturgeon. This study shows female Atlantic Sturgeon often spawn in consecutive years and had much shorter mean intervals between spawning appearances (females 1.66 years, males 1.28 years) than the historical literature suggests. While the timing of spawning is consistent with the historic record, we provide a much greater detail and finer resolution timeline for adults in the Hudson Accepted Article This article is protected by copyright. All rights reserved River as well as update the historic estimate of spawning return rates. Conservation measures to reduce direct impacts to spawning habitat and mature Atlantic Sturgeon would likely provide the most benefit if conducted between mid-May through the end of July.