Information about spawning migration and spawning habitat is essential to maintain and ultimately restore populations of endangered and threatened species of anadromous fish. We used ultrasonic and radiotelemetry to monitor the movements of 35 adult Gulf sturgeon Acipenser oxyrinchus desotoi (a subspecies of the Atlantic sturgeon A. oxyrinchus) as they moved between Choctawhatchee Bay and the Choctawhatchee River system during the spring of 1996 and 1997. Histological analysis of gonadal biopsies was used to determine the sex and reproductive status of individuals. Telemetry results and egg sampling were used to identify Gulf sturgeon spawning sites and to examine the roles that sex and reproductive status play in migratory behavior. Fertilized Gulf sturgeon eggs were collected in six locations in both the upper Choctawhatchee and Pea rivers. Hard bottom substrate, steep banks, and relatively high flows characterized collection sites. Ripe Gulf sturgeon occupied these spawning areas from late March through early May, which included the interval when Gulf sturgeon eggs were collected. For both sexes, ripe fish entered the Choctawhatchee River significantly earlier and at a lower water temperature and migrated further upstream than did nonripe fish. Males entered the Choctawhatchee River at a lower water temperature than females. Results from histology and telemetry support the hypothesis that male Gulf sturgeon may spawn annually, whereas females require more than 1 year between spawning events. Upper river hard bottom areas appear important for the successful spawning of Gulf sturgeon, and care should be taken to protect against habitat loss or degradation of known spawning habitat.

Globally, population declines for the sand tiger shark (Carcharias taurus) have resulted in calls for informed management of populations, including in the western North Atlantic, where they have been listed as a Species of Concern by NOAA Fisheries. However, information on movements and habitat use, critical for informed management of this sand tiger population, is limited. We investigated horizontal and vertical movements of sand tigers along the US east coast using pop-up archival satellite transmitters, supplemented by acoustic telemetry. Thirteen sand tiger sharks were tagged with satellite and acoustic transmitters in Delaware Bay in late August and early September 2008. Ten of these provided satellite data for horizontal tracks using a Kalman filter. Males left Delaware Bay in autumn and moved south along the continental shelf until reaching waters off North Carolina. Females moved east to waters near the edge of the continental slope. Average depth of males was positively correlated with shark size. All individuals spent at least 95% of their time in waters of 17–23°C. Sand tiger sharks appear most susceptible to fisheries in November and December. Slight expansion of the boundaries and timing of an existing shark-directed bottom longline area closure would likely reduce by-catch of sand tiger sharks and enhance recovery of the stock.

Multibeam imaging sonars have considerable potential for use in fisheries surveys because the video-like images are easy to interpret, and they contain information about fish size, shape, and swimming behavior, as well as characteristics of occupied habitats. We examined images obtained using a dual-frequency identification sonar (DIDSON) multibeam sonar for Atlantic sturgeon Acipenser oxyrinchus oxyrinchus, striped bass Morone saxatilis, white perch M. americana, and channel catfish Ictalurus punctatus of known size (20–141 cm) to determine the reliability of length estimates. For ranges up to 11 m, percent measurement error (sonar estimate – total length)/total length × 100 varied by species but was not related to the fish's range or aspect angle (orientation relative to the sonar beam). Least-square mean percent error was significantly different from 0.0 for Atlantic sturgeon (x̄  =  −8.34, SE  =  2.39) and white perch (x̄  = 14.48, SE  =  3.99) but not striped bass (x̄  =  3.71, SE  =  2.58) or channel catfish (x̄  = 3.97, SE  =  5.16). Underestimating lengths of Atlantic sturgeon may be due to difficulty in detecting the snout or the longer dorsal lobe of the heterocercal tail. White perch was the smallest species tested, and it had the largest percent measurement errors (both positive and negative) and the lowest percentage of images classified as good or acceptable. Automated length estimates for the four species using Echoview software varied with position in the view-field. Estimates tended to be low at more extreme azimuthal angles (fish's angle off-axis within the view-field), but mean and maximum estimates were highly correlated with total length. Software estimates also were biased by fish images partially outside the view-field and when acoustic crosstalk occurred (when a fish perpendicular to the sonar and at relatively close range is detected in the side lobes of adjacent beams). These sources of bias are apparent when files are processed manually and can be filtered out when producing automated software estimates. Multibeam sonar estimates of fish size should be useful for research and management if these potential sources of bias and imprecision are addressed.

No abstract

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.

The popularity of recreational shark fishing appears to be on the rise in recent years, with current policies often failing to address the direct targeting of protected species in this sector. Examination of catch trends from the past decade revealed that more than 66 million sharks were caught by recreational anglers along the U.S. eastern coast alone, including more than 1.2 million prohibited species. Using Sand Tigers Carcharias taurus captured by volunteer anglers as a case study to evaluate post‐release mortality, 33 individuals were fitted with external acoustic tags and passively tracked using an array of acoustic receivers. Although rates of internal hooking and gear retention were high (57% and 60%), short‐term post‐release mortality was relatively low (6%) and was heavily influenced by hook location and retention. Given the dramatic increase in the range and extent of recreational fishing targeting prohibited species, even relatively low mortality rates may still pose a significant threat to recovery.