Browsing by Author "Kenneth H. Pollock, Committee Member"

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Assessing the Effects of Scale and Habitat Management on the Residency and Movement Rates of Migratory Shorebirds at the Tom Yawkey Wildlife Center, South Carolina.
(2007-12-17) Obernuefemann, Kelsey Piper; Jaime A. Collazo, Committee Chair; James E. Lyons, Committee Member; Kenneth H. Pollock, Committee Member; Theodore R. Simons, Committee Member
I evaluated the influence of inter-wetland distance and the timing of drawdowns on local daily survival (residency) and movement probability of Semipalmated Sandpipers (Calidris pusilla) during the springs of 2006 and 2007 at the Tom Yawkey Wildlife Center (YWC), South Carolina. There is growing interest in determining the scale at which coastal wetlands are functionally connected and how management influences their use by migrant shorebirds. Parameters of interest were estimated using multi-state models and encounter histories obtained from resight and telemetry data. Data were collected in the spatial context of three clusters of multiple wetland units each separated by distances of 2.6 to 4.1 km and two hydrologic treatments--a slow and fast draw down. Mean length of stay was 2.99 d (95% CIs = 2.45 - 3.52) in 2006 and 4.57 d (95% CIs = 2.59 — 8.92) in 2007. Residency probability was influenced by a negative and significant interaction between estimated percent fat at capture and southerly wind speed. This meant that differences in departure rates by birds with varying body conditions were minimized. Sixty-five percent of all marked birds stayed within 2 km from their banding location. Movement probabilities were negatively related to inter-cluster distance and bird density. In the spatial context of YWC there was functional connectivity among the clusters that were ˜2.5 km apart; movement was negligible between units at nearly twice that distance (4.1 km). Contrary to expectations, the average probability of surviving and not moving for birds in slow-managed units was higher than birds in fast-managed units (PhiSS 2006 = 0.488, PhiSS 2007 = 0.654). On average, birds marked in fast-managed units moved out at high rates (Psi 2006 = 0.399, Psi 2007 = 0.467). Higher prey biomass and bird density in slow-managed units influenced observed residency and movement rates. My findings advocate for conservation strategies that identify functionally connected wetland units and suggested that habitat supplementation for shorebirds during peak migration can be met by carefully planned staggered, slow drawdowns. The effectiveness of fast drawdowns is vulnerable to differential prey base quality, presence of birds on previously exposed habitat, failure of water control structures to operate properly, and the possibility of mismatching peak migration and rapid drawdown implementation.
Avian conservation in north-central Puerto Rico: Assessing the conservation value of shaded coffee plantations and the influence of nest location and habitat on nest predation rates
(2006-01-23) Gleffe, Jessica Dawn; Jaime A. Collazo, Committee Chair; James F. Gilliam, Committee Member; Kenneth H. Pollock, Committee Member
As size and number of undisturbed forests dwindle due to human encroachment, the importance of disturbed areas, such as secondary forests and shaded coffee plantations, for conservation of avifauna has risen. These 'functional substitutions' are not only recognized and valued at present, but in some cases, they may have played important conservation roles in the past. It is hypothesized that shaded coffee plantations in Puerto Rico played such a role by minimizing extinction rates of resident forest avifauna during periods of widespread deforestation during the 19th and 20th centuries. Implicit in this refugia hypothesis is that shaded coffee plantations harbored successful breeding populations. Data to evaluate this possibility, however, were not available. Likewise, data on breeding productivity and other measures of reproduction were not available for secondary forests, which as of 1992 totaled 41% of the island's forest cover. These measures are intimately related to fitness and, therefore, provide a useful basis to guide habitat conservation initiatives and management. In this study, I report on the reproductive activity and productivity of resident avifauna in shaded coffee plantations and compare them with similar data from secondary forests in Puerto Rico from 1997 to 1999. During that period, 253 nests were found in coffee plantations (12 ha) and 97 in secondary forests (45 ha). The composition of resident species found nesting in shaded coffee plantations and secondary forests was similar. Some of the most common nesting species were endemics. Predation and nest abandonment each accounted for 38% of nest failures. Nest success did not differ between secondary forest and shaded coffee plantations for vireos, tanagers, and hummingbirds. Similarly, breeding productivity did not differ between habitat types for four species for which sufficient data were available. Although the fate of fledglings (e.g., dispersal, survival) was not followed, documenting successful reproduction in shaded coffee plantations confirmed a fundamental assumption of the refugia hypothesis. This finding, coupled with the fact that shaded coffee plantations were more widespread in the past and were managed as rustic plantations and traditional polycultures (resembling primary forests), lends considerable support to the notion that shaded coffee plantations have served as a refuge for resident avian species during periods of widespread deforestation. The production capacity of shaded coffee plantations was dependent on nesting substrates provided by the shade vegetation (canopy) layer, not the coffee tree layer. Nesting activity in secondary forests also occurred primarily in the canopy layer. To investigate the basis of this pattern, I tested whether the observed nesting patterns were influenced by differential predation pressure between the understory and canopy layers. I also tested whether predation pressure differed between canopy layers of plantations and secondary forests to further assess the conservation value of shaded plantations. Tests were conducted using a series of carefully designed artificial nest experiments during the breeding season of 2005. I found that predation rates ranged from 0.44 to 0.77 (average = 0.65 ± 0.06 SE) for understory and from 0.45 to 0.80 (average = 0.65 ± 0.05 SE) for canopy nest heights. Predation rates ranged from 0.67 to 1.0 (average = 0.84 ± 0.06 SE) in shaded coffee plantations, and from 0.63 to 0.97 (average = 0.81 ± 0.06 SE) in adjacent secondary forest. Rates for both experiments were not significantly different (P > 0.05). Based on photographic evidence, avian and mammalian nest predators can prey upon nests regardless of height. Experiments and data from natural nests suggest that birds nesting in shaded plantations are not at a disadvantage compared to those nesting in secondary forests. Moreover, the pervasive nature of nest predation reported in this work, and its influence on habitat quality, affirmed the need to identify and manage habitat features associated with nest success.
Breeding Biology of Swainson's Warblers in a Managed South Carolina Bottomland Forest
(2005-07-22) Thompson, Jennifer Laurie; Richard A. Lancia, Committee Chair; Kenneth H. Pollock, Committee Member; Heather M. Cheshire, Committee Member; Phillip D. Doerr, Committee Member
Conservation plans for the southeastern U.S. have identified Swainson's Warblers (Limnothlypis swainsonii) to be among the more vulnerable Neotropical migrants. However, a lack of life history information, in particular breeding, jeopardizes sound management decisions. My study examined a population in Britton's Neck, South Carolina on timberland owned by International Paper Co. From 1999-2001, I conducted a breeding biology study that examined nesting, territory, vegetative, and landscape characteristics. I discovered 98 SWWA nests, 63 of which were active. SWWA nesting success equaled 60% using the Mayfield success estimator. Contrary to the notion of SWWA requiring mature forests to breed, SWWA bred successfully in 20-year old regenerating clearcuts. Multiple brooding, where a pair initiates nesting attempts after their first is successful, was detected in 20% of the pairs. An individual's seasonal fecundity was doubled by multiple brooding, increasing the young per female from 1.5 to 3.7. Brown-headed Cowbirds (Molothrus ater) parasitized only 10% of nests. No SWWA chicks were observed fledging in the presence of Cowbirds. Apparent population density was 17 territories/km2, equaling the highest density ever recorded for SWWA. One-fifth the site contained 59 territories/km2, compared to the remaining four-fifths with 12 territories/km2. I examined vegetative differences between nests built in high- versus low-density areas using a discriminant function analysis (DFA). The DFA results indicated understory thickets accounted for the largest difference between high- and low-density nest sites. Nests in the high-density area were more associated with understory thickets.
Effects of Age-1 Striped Bass Predation on Juvenile Fishes in Western Albemarle Sound
(2005-05-15) Tuomikoski, Jack Esa; Kenneth H. Pollock, Committee Member; Joseph E. Hightower, Committee Co-Chair; Jeffrey A. Buckel, Committee Co-Chair
Historically, adult river herring (Alosa pseudoharengus, Alosa aestivalis) and American shad (Alosa sapidissima) fisheries were economically important in Albemarle Sound. Stocks of these species are currently in decline while stock estimates for striped bass (Morone saxatilis) have increased 10-fold for the Albemarle Sound-Roanoke River stock since the early 1990s. The primary goal of this study was to quantify the diet, prey selectivity and the predatory impact of age-1 striped bass on juvenile river herring and American shad in 2002 and 2003. Similar estimates were produced for juvenile yellow perch (Perca flavescens), a species with an expanding fishery. Striped bass and prey samples were obtained from 443 beach seine and 171 purse seine hauls from May through October in 2002 and 2003. Age-1 striped bass were primarily piscivorous from May onward in both years. Alosa spp. were a small component of age-1 striped bass diet in summer months but dominated diet in early fall months. Age-1 striped bass fed randomly with respect to Alosa spp. abundance during the summer and selected for them during early fall months. During summer 2003, selectivity for yellow perch decreased with concomitant decreases in importance as a prey item. Field estimates of consumption rates ranged from 3 to 8 % body weight per day while bioenergetics model estimates of consumption ranged from 4 to 12 % in 2002 and 3 to 10% in 2003. Age-1 striped bass density, diet, prey sizes eaten, and consumption rates were used to calculate loss rates due to predation and were compared with total loss rates from catch curves. There was interannual variation in the effects of predation. Age-1 striped bass predation had a marked effect on juvenile American shad densities in 2002 but had little influence on their numbers in 2003. Conversely, age-1 striped bass predation explained none of the loss in juvenile yellow perch in 2002 but accounted for nearly all of the loss in 2003. Thus, predation by striped bass may explain at least some of the variability in year class strength for these species. In most cases, age-1 striped bass predation did not have a strong influence on juvenile alewife numbers. Juvenile blueback herring were preyed on but the relative predatory impact could not be determined because of apparent emigration into the study area. To better understand striped bass impacts on Alosa spp., future work should address movement of juvenile Alosa spp into and out of Albemarle Sound estuary.
Factors Affecting Reproduction in the Red Wolf (Canis rufus).
(2009-07-20) Rabon, David Reid Jr.; Nicholas M. Haddad, Committee Member; Kenneth H. Pollock, Committee Member; Harold F. Heatwole, Committee Chair; Phillip D. Doerr, Committee Member
The endangered red wolf (Canis rufus) was preserved in captivity with just 14 founders following its planned extirpation in the wild. Longitudinal reproductive events were investigated to determine whether inbreeding, parental age, and breeding experience were factors in reproductive performance and fitness. A behavioral preference study using olfactory presentations of conspecific and congeneric social odors also was conducted to determine those factors that are important in the selection of mates. Over 30 years of managed breeding, the level of inbreeding in the captive population has increased, and litter size has declined. Inbreeding levels were lower in sires and dams that reproduced than in those that did not reproduce, but there was no difference in the level of inbreeding of actual and predicted litters. Litter size was negatively affected by offspring and paternal levels of inbreeding, but the effect of inbreeding on offspring survival was restricted to a positive influence. Younger wolves were more likely to reproduce, and were more likely to produce larger litters, than were older individuals. The age of the dam, but not the sire, had a significant negative effect on pup survival. Sires and dams that had prior experience in the production of offspring were more likely to reproduce again than were individuals without prior reproductive success, but prior sexual experience alone was not a factor in the production of offspring. Parental breeding experience had a significant negative effect on pup survival, but no apparent relationships with size or sex ratio of the litter. In general, females responded to the presentation of social odors of conspecific males more quickly than did males, and males responded more quickly to social odors of conspecific females than did females. There were no differences in the proportion of time males and females spent proximal to conspecific social odors. Males and females typically responded more quickly to and spent more time investigating social odors during the non-breeding season than during the breeding season. Species-specific responses to social odors were indeterminate.
Factors Influencing the Mortality and Distribution of Subadult Red Drum in North Carolina
(2008-08-13) Bacheler, Nathan Mitchell; Louis B. Daniel, III, Committee Member; James F. Gilliam, Committee Member; Kenneth H. Pollock, Committee Member; Joseph E. Hightower, Committee Co-Chair; Jeffrey A. Buckel, Committee Co-Chair
Subadult red drum Sciaenops ocellatus are ecologically and economically important in North Carolina, but little is known about factors influencing their mortality and distribution in estuaries. I first assessed the effect of fishing on red drum abundance using 24 years of tagging data. The tag-return model incorporated all first returns from fish caught-and-released and accounted for age-dependent selectivities that varied by fate of the fish. Estimated fishing mortality rates (F) were high and variable before regulation changes in 1991, but decreased in magnitude and variability after 1991. A dome-shaped selectivity pattern was estimated to account for migration of older fish into coastal waters. To quantify the natural mortality rate and seasonal Fs for red drum, I conducted the first field test of a combined telemetry – tag return approach. Estimated Fs were similar in seasonal pattern and magnitude between tagging and telemetry, but joint estimates were influenced primarily by tagging. Natural mortality rate was low and influenced primarily by telemetry. The combined approach provides a new tool to estimate mortality rates for myriad fish species. Next, habitat use of subadult red drum was quantified with a combination of fishery-independent sampling, telemetry, and generalized additive models. At a large scale, red drum were associated with shallow, nearshore waters, sometimes with seagrass. To determine the influence of prey, I examined red drum stomachs and used generalized additive models to relate physicochemical and prey attributes to telemetered red drum at a small scale. Telemetered red drum were negatively related to salinity and positively related to dissolved oxygen and total prey. Last, I used tagging and telemetry to quantify the large- and small-scale movements of subadult red drum. Movement rates and directions were influenced by age of fish and region and season of tagging, and suggest that the spatial scale of management and regulations currently employed in North Carolina are appropriate. Tagging and fishery-independent surveys have provided valuable information to improve red drum management.
Fall Migration and Vehicle Disturbance of Shorebirds at South Core Banks, North Carolina.
(2008-12-02) Tarr, Nathan Moloney; Kenneth H. Pollock, Committee Member; Jaime A. Collazo, Committee Member; Theodore R. Simons, Committee Chair
Anthropogenic disturbance has been implicated as a factor related to declines in shorebird populations because they depend upon coastal stopover sites, where human recreation is concentrated, for resting and refueling between long, energetically-expensive migration flights. We examined the use of South Core Banks, a barrier island on North Carolinaâ€™s Outer Banks, by migrating shorebirds and recreationists during fall and measured the effects of vehicle disturbance on shorebird behavior and habitat use. To describe spatial, temporal, and tidal patterns in shorebird and vehicle abundance, we performed weekly surveys of birds and vehicles from all-terrain vehicles, recording the species, numbers, and microhabitat locations (i.e. surf, swash zone, dry sand, and wet sand) of all individuals within half-mile ocean beach segments. We summarized survey data by week, tide, beach section, and daylight hour in order to identify patterns in abundance. Shorebird densities on South Core Banks were similar to those reported for other sites on the Outer Banks, and their numbers decreased slightly throughout the season, but peaked several times. Gull and vehicle numbers increased throughout the fall while tern numbers decreased. As a group, shorebirds were more or less evenly distributed along the southeast facing beach, but individual shorebird species showed unique spatial patterns in abundance. Several species, including Sanderlings (Calidris alba), Black-bellied Plovers (Pluvialis squatarola), Semipalmated Plovers (Charadrius semipalmatus), Red Knots (Calidris canutus), and Ruddy Turnstones (Arenaria interpres), were more abundant on the ocean beach during high tide than during low tide. They used a sand spit and a portion of the ocean beach on the southern half of the island as roosting sites at high tide. Shorebirds were abundant in areas where vehicle abundance was also relatively high, but their distribution among microhabitats was opposite that of vehicles; vehicles were primarily located on dry sand while shorebirds were typically found in the swash zone and wet sand microhabitats. Many environmental, habitat, and biological factors influence the distributions of nonbreeding shorebird, and they are often confounded. To examine whether or not vehicle disturbance is one of these factors, we employed a before-after-control-impact (BACI) experimental study design that isolated disturbance effects from spatial or temporal differences among sites. We manipulated disturbance levels within beach closures using paired control and impact plots and measured bird abundance and Sanderling behavior during before and after periods on both control and impact plots. Control plots were closed to vehicles during both the before and after periods. Treatment plots were closed to vehicles during the before period but subjected to a fixed level of vehicle disturbance during the after period. Differences in shorebird abundance and behavior between paired control and treatment plots provided an estimate of vehicle disturbance effects. We found that disturbance has a negative effect on site use by shorebirds, all birds, and Black-bellied Plovers. The two most abundant species of shorebird at our study sites, Sanderlings and Willets (Catoptrophorus semipalmatus), did not show a significant decrease in abundance in response to disturbance, but disturbance influenced Sanderling activity by decreasing the proportion of time that they spent roosting and increasing the proportion of time that they spent active. Microhabitat use shifted towards the swash zone when disturbance was introduced. We conclude that vehicle disturbance influences shorebirdsâ€™ use of ocean beach habitat for roosting during the nonbreeding season and that experimental BACI study designs provide a practical tool for measuring the effects of disturbance on wildlife without the confounding that affects purely observational approaches.
A Life History Assessment on the Reproduction and Growth of Striped Mullet, Mugil cephalus, in North Carolina
(2004-07-12) Bichy, John Brooke; Kenneth H. Pollock, Committee Member; Dr. Steve W. Ross and Dr. John Miller, Committee Co-Chair; Joseph E. Hightower, Committee Member
The striped mullet, Mugil cephalus, has supported a commercial fishery in North Carolina since the 1800s and today ranks in the top ten of commercially valuable fin- fisheries in the state worth over a million dollars annually. The species is a direct link between lower and higher trophic levels and thus serves an important role in the food web. Despite striped mullet's biological and economic importance, basic life history data from North Carolina are limited and the stock status is unknown. Objectives of this study were to describe striped mullet growth, reproductive seasonality, size and age at maturity, and fecundity. Monthly samples of striped mullet were collected using both fishery independent and dependent sampling strategies throughout North Carolina. Sagittae otoliths were removed and sectioned for age and growth analyses. Gonads were fixed and histologically prepared for maturity indices and fecundity estimation. Length was highly variable within age classes. Regional growth differences within North Carolina were found as fish collected from the southern sampling regions were smaller at age and lived longer than fish from the northern regions. Growth models suggest growth rates in North Carolina were greater than other areas in the species' range. Based on the presence of recently post-spawned fish and gonadal development, striped mullet spawn between late September and December. The collection of a hydrated female less than 1 km from an inlet, coupled with the presence of post-ovulatory follicles from fish sampled within the estuary, provided evidence for near-shore spawning. Males matured at a smaller length (L50) than females, 283 mm and 324 mm fork length, respectively. Fecundity correlated well with fork length (r2=0.88) and body weight (r2=0.91), and ranged from 1193 to 2535 eggs per gram of eviscerated body weight. This study provides the first life history assessment of striped mullet reproduction and growth from North Carolina and shows differences in growth, maturity, spawning location, reproductive seasonality, and fecundity compared to other areas in the species' range.
Maximizing the Impact of Field Borders for Quail and Early-succession Songbirds: What?s the Best Design for Implementation?
(2007-12-09) Riddle, Jason; Nicholas M. Haddad, Committee Member; Christopher E. Moorman, Committee Chair; David T. Cobb, Committee Member; Stacy A. C. Nelson, Committee Member; Kenneth H. Pollock, Committee Member; Peter T. Bromley, Committee Member
Nesting Ecology and Conservation of Least Terns in St. Croix, USVI
(2007-05-30) Lombard, Claudia Danielle; Theodore R. Simons, Committee Co-Chair; Kenneth H. Pollock, Committee Member; Nick Haddad, Committee Member; Jaime A. Collazo, Committee Co-Chair
Little is known about the Least Tern (Sterna antillarum antillarum) in the Caribbean, including the U.S. Virgin Islands. Concerns about predation rates and human disturbance on St. Croix prompted a study of their nesting ecology and a population viability analysis to determine their status and help formulate conservation strategies. From 2003 to 2006 I monitored 56 colonies (4,640 nests) built on salt ponds, sandy beaches, offshore cays, and an industrial park. Daily nest survival rates averaged 0.92 ± 0.04. Rainfall significantly and negatively influenced daily survival rates. The impact was most severe when precipitation events exceeded 190 mm. In densely human populated areas, mammalian predation was more pervasive. Five colonies were protected from predation (exclosure) and flooding (elevated platform) to determine the gains in nest survival. These colonies yielded a daily nest survival of 0.957 ± 0.02, or a gain of ˜100% in nest survival (0.24 to 0.50). Chick survival rates were 0.30 ± 0.11 (n = 44). Estimated breeding productivity was 0.08 (i.e., female fledglings⁄female). Breeding productivity needs to be at least 0.33 to attain a   1. This threshold assumed daily nest survival rates of at least 0.957, chick survival rates  0.5, and medium survival rates (i.e., 0.56 for S1, 0.81 for S2 and S3 and 0.92 for S4). A viability analysis predicted persistence of the St. Croix population only under the most optimistic age-specific survival rates or when immigration from other populations was allowed. Increasing reproductive output by implementing nest protection measures was not an effective tool to reduce extinction risks. Implementing a 25% management effort improved time to quasi-extinction by only 8.4 months when compared to a scenario with no management. Applying management to all nests (100%) increased the time to quasi-extinction by only 6 years. The Least Tern population nesting on St. Croix is the largest known in the Caribbean. The annual number of nests ranged from 919 to 1341. Three explanations can be advanced to reconcile the observed level of breeding activity and outcomes generated by model scenarios. One is that the species is indeed facing a precarious outlook. Least Terns are long-lived species and time lags may mask the population's downward trend in persistence. A second is that observed levels of reproductive activity might be maintained by immigration from source populations elsewhere in the Caribbean. Both of these possibilities are consistent with a population acting as a sink. The third explanation is that the status of the species is not as precarious because age specific survival rates are higher than assumed in my "base" model (i.e., medium survival rates). This possibility is plausible because many survival estimates for Least Terns were based on return rates, which are biased-low. Conservation efforts in St. Croix should be aimed at protecting existing and historical Least Tern breeding habitat, particularly the most isolated sites, and at minimizing egg and chick mortality. Improved reproductive rates alone, however, will not prevent a trajectory of decreasing persistence. My work underscored the importance of immigration and age-specific survival rates in maintaining a viable population. Estimates for these parameters are not available in the Caribbean. Reducing parameter uncertainty is necessary to set local management targets and formulate an integrated, multi-scale conservation strategy. Initially, efforts should focus on colonies closest to St. Croix to generate estimates of age-specific survival and movement rates. A focal geographic area facilitates addressing important study design considerations (e.g., sample size, sampling frequency) necessary for precise estimates. Subsequently, similar efforts could be extended to other focal areas. Molecular genetic approaches could help discern patterns of population connectivity and areas of conservation importance.
Population Dynamics of Atlantic Croaker Occurring Along the U.S. East Coast, 1981 - 2002.
(2005-12-02) Lee, Laura Maleda; Kenneth H. Pollock, Committee Member; Peter S. Rand, Committee Co-Chair; Joseph E. Hightower, Committee Co-Chair
Atlantic croaker are one of the most plentiful inshore, demersal fishes from the Chesapeake Bay to Florida. A coastwide assessment of the stock based on landings, fishery-dependent and fishery-independent length data, and survey abundance information was performed using the stock synthesis model. Landings have generally increased since the 1950s, with most of the catch occurring in North Carolina and Virginia. Major commercial gears are gill net, trawl, haul seine, and pound net. The recreational fishery has become increasingly important over time. Indices of relative abundance generated from fishery-independent surveys show that year-class strength has varied considerably among years. Patterns for year-class strength were consistent within each state, and fairly consistent among states. There is evidence for a potential rebuilding of the stock from both the observed data and model predictions. Coastwide length samples from the recreational fisheries and length samples from NC commercial fisheries demonstrated an increase in the maximum length in recent years. Observed and predicted mean lengths for the gill net, trawl, and recreational fisheries also suggest an increase in the proportion of older and larger fish in recent years. Observed trends in relative abundance and model predictions of recruitment reflect the presence of several recent strong year classes. The model results suggest that the population is highly recruitment-driven and that recruitment is variable. This dynamic is likely reflected in the harvest as variability in catch, which has shown fluctuations for at least the past 50 years. Estimates of fishing mortality have been high, particularly during the late 1980s when abundance was estimated to be low. Evaluation of the uncertainty in model estimates demonstrated that the model was fairly insensitive to changes in source data, but did appear sensitive to changes regarding assumptions about M and assumptions about the error associated with survey abundance indices. The yield-per-recruit analysis results suggested that a significant gain in yield would result if age-at-entry was delayed, which, in turn, would allow for relatively higher Fs. Comparison of age-0 abundance indices between Virginia and North Carolina revealed similar patterns in annual recruitment. Age-0 abundance indices also exhibited significant spatial autocorrelation for both states. In general, sampling stations in close proximity tended to have more similar observations of age-0 abundance. Positive spatial autocorrelation typically occurred at distances less than 30-km, while negative spatial autocorrelation was more often detected at distances of 40-km or greater. Accounting for spatial patterns in recruitment indices should result in a better measure of recruitment for use in future stock assessments.
Population Ecology of Introduced Flathead Catfish
(2004-11-21) Pine, William Earl; Joseph E. Hightower, Committee Member; Thomas J. Kwak, Committee Co-Chair; Kenneth H. Pollock, Committee Member; James A. Rice, Committee Co-Chair
Invasive aquatic species are becoming increasingly problematic for aquatic ecologists and resource managers, as the ecological and economic impacts of introductions become better known. The flathead catfish Pylodictis olivaris is a large piscivorous fish native to most of the interior basin of the United States. Via legal and illegal introductions, they have been introduced into at least 13 U.S. states and one Canadian province primarily along the Atlantic slope. I used a variety of capture-recapture models to estimate flathead catfish population parameters in three North Carolina coastal plain rivers (Contentnea Creek, Northeast Cape Fear River, and Lumber River). My estimates using a Jolly-Seber model were hindered by low capture probabilities and high temporary emigration. Reasonable estimates were possible using a robust-design framework to estimate population size and temporary emigration with supplemental information from a radio-telemetry study to examine model assumptions. Population size estimates using a robust design model including temporary emigration ranged from 4 to 31 fish/km (>125-mm total length, TL) of sampling reach. Additional analyses showed high rates of temporary emigration (>90%), independently supported by radio-telemetry results. I also examined flathead catfish diet in these rivers and found that flathead catfish fed on a wide variety of freshwater fish and invertebrates, anadromous fish, and occasionally estuarine fish and invertebrates. Fish or crayfish comprised more than 50% of the stomach contents by percent occurrence, percent-by-number, and percent-by-weight in all rivers and years. A significant difference in the diet composition percent-by-number was found between Contentnea Creek and the Northeast Cape Fear River. Significant differences were not detected between years within Contentnea Creek but were found within the Northeast Cape Fear River. Feeding intensity (as measured by stomach fullness) was highest in the Northeast Cape Fear River associated with a lower mean size of feeding flathead catfish in this river than of those in Contentnea Creek or the Lumber River. A significant correlation between diet item length and flathead catfish total length was found for Contentnea Creek in 2001. This relationship was not significant in the Northeast Cape Fear River in either year. Based on the diet composition data collected in this study and those published on native and introduced flathead catfish populations, I am not able to support or refute the hypothesis that flathead catfish are preferentially feeding on specific species or families. However, the flathead catfish populations examined here are well established, and the greatest impact from selective predation may have occurred immediately following introduction. Based on my findings, flathead catfish could restructure or suppress native fish communities in coastal rivers through direct predation because of their primarily piscivorous food habits. To evaluate the potential ecosystem impact of this invasive species on the native fish community, I developed an ecosystem simulation model (including flathead catfish) based on empirical data collected for a North Carolina coastal river. Model results suggest that flathead catfish suppress native fish community biomass by 5-50% through both predatory and competitive interactions. However, these reductions could be mitigated through sustained exploitation of flathead catfish by recreational or commercial fishers at levels equivalent to those for native flathead catfish populations (6-25% annual exploitation). These findings demonstrate the potential for using directed harvest of an invasive species to mitigate the negative impacts to native species.
Population Estimates with Age and Genetic Structure of a Harvested Bear Population in Eastern North Carolina
(2007-03-11) Langer, Timothy Joseph; Bruce Weir, Committee Member; Kenneth H. Pollock, Committee Member; Phillip David Doerr, Committee Chair; David T. Cobb, Committee Member
Noninvasive genetic sampling (NGS) is appealing because it facilitates the use of more robust, capture-recapture models to estimate population size. NGS is expensive, however, and current sub-sampling approaches, though made a priori, are made with incomplete knowledge of the ramifications. I compared model selection and population estimates from all hair samples to those from subsets of samples chosen by simulating 4 published sub-sampling approaches. I used 4 weeks of samples collected from black bears (Ursus americanus) at scented DNA hair traps during Spring 2003 and again during Spring 2004 in Hyde County, North Carolina. I found that follicle filters deleted individuals from the data set without altering sex ratio, but random sub-sampling both deleted capture histories and altered the sex ratio. Collectively, these decisions biased population estimates low and produced inconsistent model selection among 10 replications. I also conducted a 13-week study in Spring⁄Summer 2004 to investigate effects of using food and scent to lure bears to DNA hair traps. Food and scent collected twice as many hair samples as just scent, but produced similar estimates. I do not recommend using follicle filters or sub-sampling; my data suggest they may reduce NGS to an expensive population index. Instead, I recommend using only scent to lure bears, identifying all samples for gender, and genotyping just female samples. This approach estimates the female population size and, combined with ages from trapped bears and ages with fecundity data from hunter harvested bears, allows estimation of reproductive rate, which are especially valuable for population monitoring. Model Mo fit females best and model Mb fit males best for both 2003 and 2004 and produced population estimates of 223 females and 160 males. Using reproductive tract data from hunter harvested bears and Spring estimates of breeding-age females, I estimated yearly cub production as 97 cubs of each sex for a total population estimate of 577 bears in our 404.3 mi2 (1,047.2 km2) study area. My study area has averaged about 120 hunter harvested bears the past 15 years. Because I estimated the net reproductive rate was 1.0, the maximum sustainable yield appeared to be 20.7 %.
Sampling Attributes of Puerto Rico Stream Fishes: Bias, Selectivity, and Environmental Influences
(2008-10-16) Brown, Christin Hambrick; Kenneth H. Pollock, Committee Member; Thomas J. Kwak, Committee Chair; James F. Gilliam, Committee Member
Puerto Rico, an island in the Caribbean Sea, is known for its marine sport and commercial fisheries, but the freshwater habitats of the island also support a substantial number of fishes, which provide recreational and subsistence fishery values. There are about 80 fish species that inhabit Puerto Rico freshwaters. Of those, there are fewer than 10 native fish species that reside within the rivers, and they are of primary management concern. Management of these stream fish resources would be enhanced by an understanding of gear catchability, a standardized sampling method, and accurate population estimates. My primary objectives for this study were to (1) quantitatively describe gear efficiency and selectivity relationships to estimate stream fish populations in Puerto Rico; (2) evaluate population models among species using electrofishing catch results analyzed with mark-recapture and removal methods to identify the most suitable parameter-estimating model; (3) use these findings to develop a standardized stream fish sampling protocol to be applied island-wide; and (4) develop empirical, hierarchical models that describe relationships between fish catchability and instream habitat and water quality parameters for each native fish species. In my first research component, I compared two fish sampling gear types (electrofishing and seining) and four models for estimating fish population parameters (Petersen mark-recapture and removal estimators of 2â€“4 sampling passes) to provide the quantitative basis for development of a standardized sampling protocol for Puerto Rico stream fish. I found electrofishing more efficient and logistically feasible for collecting fish in these environments. I determined that three- and four-pass removal models were more accurate than the Petersen mark-recapture model or a two-pass removal model, and that accuracy was similar between three- and four-pass removal models. I investigated variations of models that account for assumption violations and found model Mb, that adjusts for fish behavioral effects, to provide the overall best and most parsimonious fit for estimating population parameters. Based on these findings, I propose a standard fish sampling protocol for Puerto Rico wadeable streams that includes sampling stream reaches from 100 m to 200 m long, using the appropriate electrofishing gear (backpack or barge electrofishers) and conducting three sampling passes of equal effort. A Zippin-type, maximum-likelihood estimator will then be used to calculate estimates of fish population densities. I sampled fish in 81 wadeable stream reaches island-wide, totaling 105 sampling occasions, using the standardized sampling protocol with backpack or barge electrofishers. I estimated fish catchability using the standard maximum-likelihood removal estimator. At each sampling location, I measured seven instream habitat and 13 water quality parameters. I employed a correlation matrix to reduce 20 environmental parameters to seven, then developed hierarchical regression models and used AIC model selection to quantify the most parsimonious relationships between catchability and environmental variables. Mean catchability among six fish species ranged from 0.30 to 0.55. I found no trend relating environmental parameters to variation in catchability among benthic and water-column species. The most influential environmental parameters on fish catchability were mean column velocity, mean stream width, and percent cover. Catchability was negatively correlated to mean column water velocity and mean stream width and positively to percent cover. Turbidity was not closely associated with electrofishing catchability within the range of my sampling. The regression models that I developed can be used to better understand environmental variables that influence electrofishing catchability and may be applied to more efficiently estimate fish populations. Because these models correct for bias associated with varying sampling conditions, they can be utilized with single-pass electrofishing data to estimate stream fish populations. These models will enable fisheries researchers and managers in Puerto Rico to conduct fish population estimates with a single field sample, saving time and expense, with minimal bias. More complete, quantitative estimates of the fish community may then form the basis for improved stream fish and ecosystem management.
Short-term Hooking Mortality and Movement of Adult Red Drum (Sciaenops ocellatus) in the Neuse River, North Carolina.
(2003-08-21) Aguilar, Robert; Kenneth H. Pollock, Committee Member; Joseph E. Hightower, Committee Member; Peter S. Rand, Committee Chair
Despite the increasing importance of the red drum Sciaenops ocellatus recreational fishery, little is known about mortality rates of caught and released adult red drum. In this study, short-term hooking mortality rates (3-d) of adult red drum caught on 7/0 j-style hooks and 16/0 circle ('tuna') hooks from the Neuse River, North Carolina were determined via ultrasonic telemetry (2000) and confinement in field enclosures (2001). From June to September 2000, 22 red drum (928-1180 mm fork length; FL) were angled, tagged with ultrasonic transmitters, and released. An overall short-term mortality rate of 5.7% was determined for 17 fish. Due to the limited sample size, no attempt was made to model the factors associated with mortality. From June to September 2001, 112 red drum (880-1250 mm FL) were angled and held in net pens for 3 d to assess short-term mortality. An overall mortality rate of 6.7% was determined for 104 fish. Logistic regression analysis indicated that hook position (P = 0.012) and surface salinity (P = 0.002) were significantly related to mortality However, fish size (FL), sex, surface water temperature, depth, landing time, handling time, transport time, and hook type were not significantly related to mortality. Logistic regression analysis also indicated that hook position was dependent on hook type (P = 0.002) and sex (P = 0.015), but not fork length, surface water temperature, and depth. Approximately 52% percent of fish caught with j-style hooks were deep hooked, compared with 4.2% of those caught with circle hooks. A larger percentage of fish deep hooked with j-style hooks died compared to those deep hooked with circle hooks (15.9% vs. 0%, respectively). Necropsy analysis of five mortalities (all deep hooked) indicated extensive internal hemorrhaging and damage to tissues and organs. These data suggest the conservation goal of reducing post-release mortality on these fish can be achieved through directed efforts at either promoting or requiring certain terminal gear (particularly through the use of circle hooks) to reduce incidence of deep hooking. Movement information was collected for 18 of the 22 (81.8%) red drum angled and tagged with ultrasonic transmitters in 2000. Biotelemetry proved to be an effective method for examining adult red drum movement. Red drum appeared to exhibit seasonal fidelity to the lower Neuse River during the summer and fall months, but not to specific locations within this system. Most adult red exhibited a noticeable upriver-downriver ('longshore') pattern of movement, which was supported by Rayleigh's tests of individual fish movement. There was no significant difference between the mean angles (Watson's two-sample U2 test: 0.2 < P < 0.5) and movement rates (Wilcoxon rank sum test; P = 0.4068) of male (3.25±0.62 km d-1) and female (5.50±2.08 km d-1) tagged and released red drum. Furthermore, the difference between day and night relocation depths for male and female red drum was not significantly different (Wilcoxon rank sum test: P = 0.5610). On 14 separate occasions, two red drum were located in close proximity to each other (~5 m to 300m), which was defined as a co-occurrence. Given the high number of co-occurrences, mobile nature of fish movement, seasonal residency, and apparent longshore movement pattern, adult red drum appear to form short-term loose aggregations within the Neuse River during the summer and early fall months. These data also indicate the lower Neuse River and similar areas of the western Pamlico Sound are important habitat for red drum in North Carolina.
White Perch Expansion and Life History Within a Southern Reservoir
(2002-11-24) Wong, Russell K.; Kenneth H. Pollock, Committee Member; James A. Rice, Committee Member; Richard L. Noble, Committee Chair
Concern has been raised regarding the effects of invasive fishes, among them white perch (Morone americana), in a variety of freshwater systems. Previous research on white perch as an invasive species has examined landlocked white perch in ponds, lakes and reservoirs throughout much of its geographic range. However, research has been lacking regarding the role of invasive white perch in southern reservoirs. A long-term data set of the Jordan Lake fish community indexed via gill nets was evaluated to assess the expansion of white perch in Jordan Lake, as well as concurrent declines in other fishes found in Jordan Lake from 1987 through 1998. White perch catch rates increased from zero fish per net night in 1987 to 16.1 fish per net night in 1994, surpassing catch rates for all other fish captured in gill nets. White perch were found to live to age 7 in Jordan Lake where they shift food habits seasonally from zooplankton and diptera larvae in the spring to young shad in the fall. Relative weights and mean calculated total lengths at annulus formation suggest that the Jordan Lake white perch population is in good condition, comparable to other landlocked white perch populations in North Carolina and surpassing white perch populations found in their native estuarine environs throughout the eastern seaboard. Young white perch were found to prefer cover-free primary points featuring hard sand and clay substrates, minimizing the likelihood that Jordan Lake white perch will impact centrarchids as has been suggested by research in other freshwater systems outside of the southeastern United States.