J. Christopher Taylor

Physiological performance of juvenile southern flounder, Paralichthys lethostigma (Jordan and Gilbert, 1884), in chronic and episodic hypoxia

Dissolved oxygen (DO) is proving to be one of the most important abiotic factors determining growth and survival of juvenile estuarine fish. In shallow, throughout estuarine systems, low DO can occur in two broad categories: a diel oscillating pattern resulting in repeated nocturnal hypoxia due to the photosynthesis-respiration cycle of algal populations, or as prolonged bottom water hypoxia or anoxia caused by stratification. A series of laboratory experiments was conducted to characterize the physiological performance of juvenile southern flounder, Paralichthys lethostigma, (55-65 mm TL) exposed to four treatments of DO: (1) constant normoxia (6.50+/-0.50 mg O(2) l(-1)), (2) constant hypoxia (2.79+/-0.19 mg O(2) l(-1)), (3) constant intermediate hypoxia (4.74+/-0.18 mg O(2) l(-1)), and (4) an oscillating oxygen environment cycling dielly between the normoxic and hypoxic levels (2.8-6.2 mg O(2) l(-1), daily mean=4.40 mg O(2) l(-1)). Routine respiration was positively correlated with DO level and increased significantly during the day in the oscillating treatment in response to increasing DO. Ventilation rates were negatively correlated with the DO level in the constant treatments and increased significantly at night in the oscillating treatment in response to nocturnal hypoxia. Similarly, hematocrit levels were negatively related to DO levels in the constant treatments after 5 and 26 days of exposure to the treatments. Hematocrit levels also increased significantly the oscillating treatment, apparently in response to the episodic nocturnal hypoxia. Growth was significantly reduced in the 2.8 mg O(2) l(-1) treatment and the oscillating treatment but not in the 4.7 mg O(2) l(-1) treatment. Acclimation was evident by an increase in growth rates from week 2 to week 3 and a decrease in hematocrit levels between 5 and 26 days of exposure in the 2.7 and 4.5 mg O(2) l(-1) treatments but was not evident in the normoxic or oscillating treatments. These results suggest that a juvenile fish must remain in even moderately low DO in order for acclimation to occur. The research presented demonstrates that correctly assessing habitat quality in terms of DO requires knowledge of a fishs physiological and environmental history.

Spatial overlap and distribution of anchovies (Anchoa spp.) and copepods in a shallow stratified estuary

Juvenile pelagic fishes are integral members of many coastal river communities. Many of these systems are strongly influenced by variable wind stress and freshwater inputs that can increase heterogeneity in estuarine habitat for fishes. We use mobile sonar surveys within the Neuse River Estuary System, NC, USA to assess the distribution and behavioral patterns of juvenile anchovies, Anchoa spp. 25-65 mm TL, over a broad range of spatial scales in relation to diel and seasonal changes in water quality including stratification, hypoxic events and copepod distribution. Results from our study indicate that episodic stratification-induced hypoxic events can reduce suitable habitat volume for anchovies by more than 50%. Furthermore, our sampling suggests that hypoxia causes spatial separation between plankton and the grazing fishes. Under stratified oxygen conditions, we observe higher densities of copepods in hypoxic bottom water. Finally, we report that reductions in available habitat caused an increase in local densities of fishes and may result in increased competition for resources. These spatially explicit data are critical for developing trophic dynamic models that predict the response of fish communities to natural and anthropogenic impacts on the system.

Mapping Reef Fish and the Seascape: Using Acoustics and Spatial Modeling to Guide Coastal Management

Reef fish distributions are patchy in time and space with some coral reef habitats supporting higher densities (i.e., aggregations) of fish than others. Identifying and quantifying fish aggregations (particularly during spawning events) are often top priorities for coastal managers. However, the rapid mapping of these aggregations using conventional survey methods (e.g., non-technical SCUBA diving and remotely operated cameras) are limited by depth, visibility and time. Acoustic sensors (i.e., splitbeam and multibeam echosounders) are not constrained by these same limitations, and were used to concurrently map and quantify the location, density and size of reef fish along with seafloor structure in two, separate locations in the U.S. Virgin Islands. Reef fish aggregations were documented along the shelf edge, an ecologically important ecotone in the region. Fish were grouped into three classes according to body size, and relationships with the benthic seascape were modeled in one area using Boosted Regression Trees. These models were validated in a second area to test their predictive performance in locations where fish have not been mapped. Models predicting the density of large fish (≥29 cm) performed well (i.e., AUC = 0.77). Water depth and standard deviation of depth were the most influential predictors at two spatial scales (100 and 300 m). Models of small (≤11 cm) and medium (12–28 cm) fish performed poorly (i.e., AUC = 0.49 to 0.68) due to the high prevalence (45–79%) of smaller fish in both locations, and the unequal prevalence of smaller fish in the training and validation areas. Integrating acoustic sensors with spatial modeling offers a new and reliable approach to rapidly identify fish aggregations and to predict the density large fish in un-surveyed locations. This integrative approach will help coastal managers to prioritize sites, and focus their limited resources on areas that may be of higher conservation value.

Relationships between Larval and Juvenile Abundance of Winter-Spawned Fishes in North Carolina, USA

Abstract We analyzed the relationships between the larval and juvenile abundances of selected estuarine-dependent fishes that spawn during the winter in continental shelf waters of the U.S. Atlantic coast. Six species were included in the analysis based on their ecological and economic importance and relative abundance in available surveys: spot Leiostomus xanthurus, pinfish Lagodon rhomboides, southern flounder Paralichthys lethostigma, summer flounder Paralichthys dentatus, Atlantic croaker Micropogonias undulatus, and Atlantic menhaden Brevoortia tyrannus. Cross-correlation analysis was used to examine the relationships between the larval and juvenile abundances within species. Tests of synchrony across species were used to find similarities in recruitment dynamics for species with similar winter shelf-spawning life-history strategies. Positive correlations were found between the larval and juvenile abundances for three of the six selected species (spot, pinfish, and southern flounder). These three species have similar geographic ranges that primarily lie south of Cape Hatteras. There were no significant correlations between the larval and juvenile abundances for the other three species (summer flounder, Atlantic croaker, and Atlantic menhaden); we suggest several factors that could account for the lack of a relationship. Synchrony was found among the three southern species within both the larval and juvenile abundance time series. These results provide support for using larval ingress measures as indices of abundance for these and other species with similar geographic ranges and winter shelf-spawning life-history strategies.

Sampling and Statistical Considerations for Hydroacoustic Surveys Used in Estimating Abundance of Forage Fishes in Reservoirs

Abstract An understanding of the spatial distribution of forage fish resources is required to make informed fishery management decisions. We used mobile hydroacoustics to assess the distribution and abundance of forage fish in Badin Lake, a reservoir in central North Carolina. By sampling a series of cross-channel and longitudinal transects and analyzing the data using geostatistics, we characterized both large- and small-scale spatial patterns in forage fish density. Forage fish were observed in higher densities in upstream regions of the reservoir and were seen only in surface waters during July 2000 owing to the existence of a strong thermo–oxycline and in two layers (surface and near bottom) during mixed conditions in December 2001. We observed differences in the scale of patchiness (200–700 m) in forage fish distribution depending on the region of the reservoir where sampling took place, and we infer that these patterns are governed by prevailing limnological conditions. Modeling the spatial variatio...

Flat and complex temperate reefs provide similar support for fish: Evidence for a unimodal species-habitat relationship

Structural complexity, a form of habitat heterogeneity, influences the structure and function of ecological communities, generally supporting increased species density, richness, and diversity. Recent research, however, suggests the most complex habitats may not harbor the highest density of individuals and number of species, especially in areas with elevated human influence. Understanding nuances in relationships between habitat heterogeneity and ecological communities is warranted to guide habitat-focused conservation and management efforts. We conducted fish and structural habitat surveys of thirty warm-temperate reefs on the southeastern US continental shelf to quantify how structural complexity influences fish communities. We found that intermediate complexity maximizes fish abundance on natural and artificial reefs, as well as species richness on natural reefs, challenging the current paradigm that abundance and other fish community metrics increase with increasing complexity. Naturally occurring rocky reefs of flat and complex morphologies supported equivalent abundance, biomass, species richness, and community composition of fishes. For flat and complex morphologies of rocky reefs to receive equal consideration as essential fish habitat (EFH), special attention should be given to detecting pavement type rocky reefs because their ephemeral nature makes them difficult to detect with typical seafloor mapping methods. Artificial reefs of intermediate complexity also maximized fish abundance, but human-made structures composed of low-lying concrete and metal ships differed in community types, with less complex, concrete structures supporting lower numbers of fishes classified largely as demersal species and metal ships protruding into the water column harboring higher numbers of fishes, including more pelagic species. Results of this study are essential to the process of evaluating habitat function provided by different types and shapes of reefs on the seafloor so that all EFH across a wide range of habitat complexity may be accurately identified and properly managed.

Developing Fishery-Independent Indices of Larval and Juvenile Gag Abundance in the Southeastern United States

Abstract We developed an index describing the abundance of gags Mycteroperca microlepis at the planktonic postlarval stage, and we assessed the indexs potential for use in stock assessment. Data on postlarval gags were collected weekly at the Pivers Island bridge near Beaufort Inlet, North Carolina, during the National Oceanic and Atmospheric Administrations bridgenet program (ichthyoplankton sampling, November–May 1986–2008); additionally, ichthyoplankton were sampled nightly during spring in 2007 and 2008. Catch of juvenile gags was examined in relation to several factors to assist in developing and refining fishery-independent surveys; juveniles were sampled with a small trawl in seagrass beds at 15–20 randomly selected stations near Beaufort Inlet every 2 weeks during June–September 2007 and 2008. Catches of postlarval and juvenile gags were low in both gear types. From 1986 to 2008, weekly concentrations of postlarval gags were highest from mid-April to mid-May, and peak ingress coincided with new ...