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No description available.

Natural resource mangers may find themselves in a conflict of interest over the management of shallow subaqueous bottom when they attempt to promote both hard clam (Mercenaria mercenaria) aquaculture and the growth of submersed aquatic vegetation (SAV) (Zostera marina and Ruppia maritima). This project examines the issue of bottom use conflict along the Lower Eastern Shore of the Chesapeake Bay in a managerial and scientific context in an attempt to develop a solution to this conflict. First, it examines historical trends in clam aquaculture and SAV growth in the study area. Habitat suitability models are then developed to predict optimal habitat for clam aquaculture and SAV and through these, potential conflict between these resources. Comparable Western Shore sites are used for validation of ceratin models. The laws and policies of Virginia and the neighboring states of Maryland and North Carolina are then examined to understand the political reasons for this conflict. Finally, the historical, scientific, and political information is summarized and potential solutions to this conflict are recommended. Results show bottom use by clam aquaculture in Cherrystone Creek along the lower Eastern Shore of the Chesapeake Bay often increased between 1989 and 1997. SAV beds were also generally expanding during this time both in Cherrystone Creek as well as in creeks north of cherrystone where no clam culture was occurring. Habitat models, incorporating biological factors (SAV spreading rates, exposure tolerance, and light requirements) and management factors (water depth and bottom hardness for tending clams, exposure to prevent smothering of clam nets) show large areas of both suitable clam and SAV habitat in the lower portions of the study creeks. Consequently, conflict models show large areas of potential conflict in study creeks where these habitats overlap. Study of the policies, laws, and regulations of Virginia and adjacent states shows that none of these states have adequately addressed this issue. The primary management recommendation of this project is to annually define existing SAV beds and a 50 meter buffer surrounding these beds and restrict use of this area to clam aquaculture. Habitat models which placed “no clam” buffers of 50, 100, 150, and 200 meters around an SAV bed suggested a 50 meter buffer would adequately protect SAV bed expansion while minimizing areas legally restricted but otherwise suitable for clam aquaculture.

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Striped bass (Morone saxatilis) and white perch (M. americana) are two common species residing within Chesapeake Bay and its tributaries. These congeners are both commercially and recreationally important species. White perch are permanent residents in the Bay, while striped bass are only residents during the first few years of their life. During these initial years, striped bass co-occur with white perch. There is very little known about white perch and resident striped bass site fidelity and home range. This acoustic tagging study aims to examine site fidelity and home range of both species and determine if there is any spatial competition between these congeners. Sixteen white perch and sixteen striped bass residing in two small tributaries of the York River were utilized for this experiment. White perch exhibited a high degree of site fidelity along with a small home range. The minimum convex polygon (MCP) and minimum stream polygon (MSP) methods were utilized to measure home range size. The average MCP/MSP was 0.114 km2. Kernel densities were also examined to understand their utilization distribution within their home range. The output contours considered were the 95% contour (total home range) and the 50% contour (core area of activity). The kernel method areas were 0.0128 km2 and 0.0021 km2, respectively. White perch, in the Poropotank River, typically had two core areas of activity which often correlated to the tidal stage. They were often found during high tide upon the flooded marsh or up in shallow creeks and in the relatively deep main channels during low tide. However, white perch in the Queen Creek only had one core area of activity and they were always associated with submerged structure. White perch did not show any movement with sudden changes in salinity and/or temperature resulting from tropical depressions or Hurricane Isabel. They also did not display any change in behavior associated with episodic hypoxia within the creeks. Striped bass did not exhibit a high degree of site fidelity. In the Poropotank River, 58% of the striped bass displayed site fidelity, while zero striped bass exhibited it in Queen Creek. Local hypoxia events could explain the lack of site fidelity within Queen Creek. The home range data might be under-estimated due to the inability to track in the York River. The average MCP/MSP was 0.36 km.2 and the average 95% and 50% kernel densities were 0.02 km2 and 0.002 km2, respectively. Only two striped bass displayed a tidal interaction, utilizing the slack high water to flood up upon marsh corners or sandy beaches. Two other striped bass also displayed a lunar periodicity. Both fish would enter and leave the Poropotank River during the days surrounding new and full moons. Striped bass also did not display any change in behavior associated with sudden changes in temperature and/or salinity due to tropical depressions or Hurricane Isabel. There was very little space competition between these two congeners. White perch occupied 8.5% of the striped bass overall home range. The spatial overlap did increase when only core areas were examined. The two species shared a common core area in a small rivulet of the Poropotank River. This common core area was one third of the striped bass cumulative core area. Nevertheless, there very little evidence of spatial competition or resource partitioning between white perch and striped bass.

The Chesapeake Bay blue crab is in decline. One of the threats to it is the loss of its once plentiful nursery habitat, seagrass, due to baywide eutrophication and climate change. The emergence of the non-native benthic macroalga Gracilaria vermiculophylla may offer the blue crab an alternative nursery if it can provide juvenile crabs a refuge from predation. The ability of Gracilaria to protect juvenile blue crabs was investigated in mesocosm and field survival studies, which were combined into a larger dataset. All of these studies used tethering and therefore a tethering validation study in mesocosms accompanied these experiments. In the validation study, there was no evidence for treatment specific-bias due to tethering, and mortality of free crabs was approximately half that of tethered crabs. In mesocosms, survival in a large algal patch of 80-cm diameter was 42-69 % greater than that of crabs in a 10-cm algal patch or unvegetated habitat. In the field, the survival benefits of a 40-cm-diameter Gracilaria patch varied with the size of juvenile blue crabs. In the combined data, larger algal patches increased the survival of smaller juvenile crabs. This survival benefit of macroalgae decreased with increased crab size such that survival of larger juveniles was inversely related to Gracilaria patch diameter. Consequently, the non-native Gracilaria may serve as a nursery for the blue crab, but its benefits will depend on crab and algal patch size.

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Detectability, the probability that a species is encountered if it inhabits a site, is often overlooked in fisheries research despite its potential to obscure habitat use inferences. Detectability can be estimated using models that also provide an estimate of occupancy (Ψ), the probability that a species inhabits a site. I used these models to estimate both probabilities, and to examine factors affecting detectability and occupancy for three fishes in Chesapeake Bay tributaries: young-of-the-year striped bass (Morone saxatilis), yearling Atlantic croaker (Micropogonias undulatus), and spottail shiner (Notropis hudsonius). Occupancy models were fitted to data from a seine survey conducted during summer, 2008 and 2009, in two Chesapeake Bay tributaries. Key assumptions of occupancy models relate to the extent and timing of fish movement: sites are independent, and no site-specific emigration or immigration occurs. A mark-recapture study of striped bass, and previously published studies of Atlantic croaker and spottail shiner, suggested that these assumptions were reasonable. Detectability differed among species and variation was explained by both gear-related and environmental factors. Effective net length (i.e., the distance from shore the seine was deployed) explained variation in detectability for all species; generally, when the effective seine length exceeded 12 m, detectability was higher and less variable. Detectability varied from early to late summer for Atlantic croaker and spottail shiner but not for striped bass. This variation may be attributed to increased net avoidance by Atlantic croaker during late summer and increased relative abundance of spottail shiner due to recruitment of individuals to the gear. Occupancy of striped bass and Atlantic croaker, both of which are transient species, was high (Ψ>0.80), whereas the resident spottail shiner occupied fewer sites (Ψ=0.59±0.21; mean±SE) and occupancy varied by river (ΨMattaponi=0.36±0.11; ΨPamunkey=0.82±0.10). Occupancy models are useful to identify factors affecting detectability of fishes captured by seines in Chesapeake Bay tributaries, but other fisheries studies would benefit from sampling design modifications that maximize detectability and improve habitat-use inferences.

Aquaculture of the hard clam Mercenaria mercenaria is a valuable industry on the east coast. At high planting densities, cultured bivalves can become limited by food availability, resulting in reduced growth. Centric diatoms are considered the dominant food source to cultured bivalves. Alternative sources may also be important, including resuspended benthic microalgae (pennate diatoms) and detritus from macroalgae growing on predator exclusion nets. This study measured (1) the availability of different food sources in clam beds at Cherrystone Inlet in Chesapeake Bay, including the effects of macroalgae on food availability, and (2) the clearance rates and absorption efficiencies by cultured clams on individual and mixed food treatments in laboratory feeding experiments. Abundances of benthic microalgae (pennate diatoms) were similar to or greater than centric diatoms. Detritus availability under nets was related significantly to macroalgal abundance. Mass-specific clearance rates and absorption efficiencies were similar among food sources, but differences in the percentage of clams feeding on each treatment suggest macroalgal detritus was less utilized by clams than either phytoplankton or benthic microalgae. Both phytoplankton and benthic microalgae appeared to be valuable food sources to clams, both in terms of in situ abundance and relative food value indices calculated from feeding studies. Though food value was lower for macroalgal detritus, the high availability of this source to clams during blooms suggests it may be important seasonally. Lower diatom concentrations under nets compared to above during a macroalgal bloom suggest dense blooms may limit diatom availability to clams. Future modeling of cultured bivalve carrying capacity should consider the importance of multiple food sources in aquaculture environments.

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