Dewayne A. Fox

Gulf Sturgeon Spawning Migration and Habitat in the Choctawhatchee River System, Alabama-Florida

Abstract 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 Mar...

Responses of resident marsh fishes to stages of Phragmites australis invasion in three mid atlantic estuaries

Modification of brackish marshes by nonindigenousPhragmites australis has occurred across a broad geographical area in eastern North America. Among its effects on marsh processes,Phragmites may be increasingly unfavorable to marsh surface fishes as its invasion progresses within an estuary. We assessed the effect of thePhragmites invasion on resident marsh surface fishes by examining the population response ofFundulus heteroclitus (mummichog, 5–48 mm TL) andF. luciae (spotfin killifish, 5–41 mm TL) to four distinct invasion stages in three estuaries of the U.S. mid Atlantic region (New Jersey, Delaware, and Maryland). We documented precipitous declines in mean catch per unit effort ofF. heteroclitus in pit traps from natural marsh (51.6), through initial (33.8), early (12.3), and late invasion stages (2.4) across all sites. A similar pattern was documented forF. luciae, with mean catch per unit effort in pit traps declining from natural marsh (48.9), through initial (39.1), early (9.3), and late invasion stages (2.7). Population structure of both species also changed somewhat across invasion stages such that we collected a narrower size range of individuals of both species from late invasion stages. Patterns suggest that as thePhragmites invasion progresses, there is a decline in habitat function for larval and juvenileF. heteroclitus and an increased risk of extirpation ofF. luciae from brackish marshes along the east coast of the U.S.

Shrinking the Haystack: Using an AUV in an Integrated Ocean Observatory to Map Atlantic Sturgeon in the Coastal Ocean

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 offish 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 proofofconcept 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 r...

Origin of Atlantic Sturgeon Collected off the Delaware Coast during Spring Months

AbstractAtlantic Sturgeon Acipenser oxyrinchus oxyrinchus was federally listed under the U.S. Endangered Species Act as five distinct population segments (DPS). Currently, at least 18 estuaries coastwide host spawning populations and the viability of these vary, requiring differing levels of protection. Subadults emigrate from their natal estuaries to marine waters where they are vulnerable to bycatch; one of the major threats to the rebuilding of populations. As a result, identifying the population origin of Atlantic Sturgeon in coastal waters is critical to development of management plans intended to minimize interactions of the most imperiled populations with damaging fisheries. We used mitochondrial DNA control region sequencing and microsatellite DNA analyses to determine the origin of 261 Atlantic Sturgeon collected off the Delaware coast during the spring months. Using individual-based assignment (IBA) testing and mixed stock analysis, we found that specimens originated from all nine of our referen...

Dynamic seascapes predict the marine occurrence of an endangered species: Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus

Summary Categorical landscapes are powerful environmental partitions that index complex biogeochemical processes that drive terrestrial species distributions. However, translating landscapes into seascapes requires that the dynamic nature of the fluid environment be reflected in spatial and temporal boundaries such that seascapes can be used in marine species distribution models and conservation decisions. A seascape product derived from satellite ocean colour and sea surface temperature partitioned mid-Atlantic coastal waters on scales commensurate with the Atlantic Sturgeon migration. The seascapes were then matched with acoustic telemetry records of Atlantic Sturgeon to determine seascape selectivity. To test for selectivity, we used real-time satellite seascape maps to normalize the sampling of an autonomous underwater vehicle that resampled similar geographic regions with time varying seascape classifications. Our findings suggest that Atlantic Sturgeon prefer one seascape class over those available in the coastal ocean, indicating selection for covarying environmental properties rather than geographical location. The recent listing of Atlantic Sturgeon as Endangered throughout much of their United States range has highlighted the need for improved understanding of marine habitat requirements to reduce interactions with anthropogenic stressors. Narrow dynamic migration corridors may enable seascapes to be used as a daily decision tool by industry and managers to reduce interactions with this imperilled species during coastal migrations.

Reliability of Fish Size Estimates Obtained From Multibeam Imaging Sonar

Abstract 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, ...

Diversity in destinations, routes and timing of small adult and sub-adult striped bass Morone saxatilis on their southward autumn migration.

Almost three-quarters of the 46 young adult and sub-adult striped bass Morone saxatilis that were acoustically tagged in Plum Island Estuary, Massachusetts, U.S.A., in the summer of 2006 were detected in one or more southern coastal arrays during their autumn migration. On the basis of the trajectories along which these M. saxatilis moved from feeding to overwintering areas, three migratory groups emerged. After leaving Plum Island Estuary, about half of the fish were detected only in a mid-latitude array, Long Island Sound. The other half of the tagged fish were detected during autumn and winter in a more southern array, the Delaware Estuary. This latter group of fish may have used two routes. Some travelled to the Delaware Estuary through Long Island Sound while other fish may have taken a second, more direct, coastal route that did not include Long Island Sound. Consequently, a seemingly homogeneous group of fish tagged at the same time in the same non-natal feeding location exhibited a diversity of southward movement patterns that could affect population-level processes. These three groups that differed in overwintering location and migration route could be movement contingents with migratory connectivity.

Shifting distributions of adult Atlantic sturgeon amidst post-industrialization and future impacts in the Delaware River: a maximum entropy approach.

Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) experienced severe declines due to habitat destruction and overfishing beginning in the late 19th century. Subsequent to the boom and bust period of exploitation, there has been minimal fishing pressure and improving habitats. However, lack of recovery led to the 2012 listing of Atlantic sturgeon under the Endangered Species Act. Although habitats may be improving, the availability of high quality spawning habitat, essential for the survival and development of eggs and larvae may still be a limiting factor in the recovery of Atlantic sturgeon. To estimate adult Atlantic sturgeon spatial distributions during riverine occupancy in the Delaware River, we utilized a maximum entropy (MaxEnt) approach along with passive biotelemetry during the likely spawning season. We found that substrate composition and distance from the salt front significantly influenced the locations of adult Atlantic sturgeon in the Delaware River. To broaden the scope of this study we projected our model onto four scenarios depicting varying locations of the salt front in the Delaware River: the contemporary location of the salt front during the likely spawning season, the location of the salt front during the historic fishery in the late 19th century, an estimated shift in the salt front by the year 2100 due to climate change, and an extreme drought scenario, similar to that which occurred in the 1960’s. The movement of the salt front upstream as a result of dredging and climate change likely eliminated historic spawning habitats and currently threatens areas where Atlantic sturgeon spawning may be taking place. Identifying where suitable spawning substrate and water chemistry intersect with the likely occurrence of adult Atlantic sturgeon in the Delaware River highlights essential spawning habitats, enhancing recovery prospects for this imperiled species.

Large Nektonic Fishes in Marsh Creek Habitats in the Delaware Bay Estuary

Abstract Larger nektonic fishes, many of which are economically important, comprise a large portion of the biomass in estuaries and may influence energy flow through their migrations and feeding, yet we know relatively little of this faunal component. To elucidate the patterns of species composition, distribution, and abundance in Delaware Bay, we sampled (n = 2298 sets) nektonic fishes (n = 3693 individuals, mean length = 261.4 mm, range = 53–600 mm) with multi-mesh gill nets in near-shore bay and marsh creek habitats during the summer and fall (June-November 2001) when fishes are more abundant in temperate estuaries. For the most abundant species, the older and larger individuals (age 1+) often dominated the catches. Patterns of assemblage structure were influenced by spatial gradients in salinity and dissolved oxygen and temporal changes in temperature. Many of the large nektonic fishes that dominate in Delaware Bay are also found in other temperate estuaries from the Gulf of Maine to Chesapeake Bay, in part, because these species are highly migratory.

Social Network Analysis Reveals Potential Fission-Fusion Behavior in a Shark.

Complex social networks and behaviors are difficult to observe for free-living marine species, especially those that move great distances. Using implanted acoustic transceivers to study the inter- and intraspecific interactions of sand tiger sharks Carcharias taurus, we observed group behavior that has historically been associated with higher order mammals. We found evidence strongly suggestive of fission-fusion behavior, or changes in group size and composition of sand tigers, related to five behavioral modes (summering, south migration, community bottleneck, dispersal, north migration). Our study shows sexually dimorphic behavior during migration, in addition to presenting evidence of a potential solitary phase for these typically gregarious sharks. Sand tigers spent up to 95 consecutive and 335 cumulative hours together, with the strongest relationships occurring between males. Species that exhibit fission-fusion group dynamics pose a particularly challenging issue for conservation and management because changes in group size and composition affect population estimates and amplify anthropogenic impacts.