Browsing by Author "Joseph E. Hightower, Committee Member"

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Age, Growth and Reproduction of Dolphin (Coryphaena hippurus) Caught Off the Coast of North Carolina.
(2005-05-02) Schwenke, Kara Laurice; Joseph E. Hightower, Committee Member; Leonard A. Stefanski, Committee Member; Jeffrey A. Buckel, Committee Chair
The common dolphin (Coryphaena hippurus) supports economically important fisheries along the east coast of the United States. In recent years, landings of dolphin from the United States Atlantic have increased dramatically. For example, recreational landings in the US South Atlantic Bight have increased from 162,000 dolphin in the 1960s to over 1.3 million dolphin in recent years. The last age and growth study of North Carolina dolphin was conducted in the early 1960s. It is hypothesized that life history parameters may have changed due to increased exploitation. Age, growth and reproduction were studied on dolphin (n=802; size range=89 to 1451 mm FL) collected between May 2002 and May 2004 from commercial and recreational catches in North Carolina. Annual increments from scales (n=541) and daily increments from sagittal otoliths (n=126) were examined; estimated von Bertalanffy parameters were L∞ = 1299 mm FL and k = 1.08 yr ⁻¹. The maximum age observed was 3 years. No major change in length at age has occurred since the early 1960s. Daily growth increments for age-0 dolphin reduced much of the variability in length-at-age values for age-0 dolphin and provided an average growth rate of 3.78 mm/day in the first six months, which is extremely fast for a teleost fish. Growth of North Carolina dolphin is similar to that found in Florida and the Mediterranean, but differs from observed growth in the Caribbean and Gulf of Mexico. Age at 50% maturity was around 4 months for female dolphin and 6 months for male dolphin. Monthly length-adjusted gonadal weights suggest that peak spawning occurs from April through July off North Carolina; back-calculated hatch dates from age-0 dolphin along with prior studies on the east coast of Florida suggest that dolphin spawning occurs year round with highest levels from January through June. This study provides an updated and improved (year-round sampling and otolith daily ages) age-length function for dolphin caught off the coast of North Carolina using both scale annuli and daily growth increments and provides some of the first comprehensive data on North Carolina dolphin reproduction. The life history of dolphin, including fast growth and early maturity, allows for high levels of exploitation.
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.
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.
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.
Spatial Dynamics in an Estuarine System: Modeling Biophysical Components and Interactions to Advance Blue Crab Fishery Management
(2009-11-23) Durham, Christina Louise; David B. Eggleston, Committee Chair; Daniel Kamykowski, Committee Member; Amy Nail, Committee Member; Joseph E. Hightower, Committee Member
Estuaries are dynamic ecosystems with abiotic environments that exhibit extreme space-time variability. Cyclic variation is somewhat predictable, but hurricanes and large-scale atmospheric disturbances can rapidly and drastically alter anticipated conditions. These disturbances can induce rapid biological responses across large spatial scales and frequently shift distribution patterns of mobile species. Physical conditions recover relatively quickly from climactically driven perturbations, and most physically-induced animal migrations are also temporary and reversible. Nevertheless, in the case of a commercially valuable fish species, even short-term alterations can change their vulnerability (i.e., catchability) to fishery-independent surveys, which provide valuable data used in population assessment. We examined the effects of salinity and other physical forcing mechanisms on the spatial distribution of ecologically and economically important blue crabs (Callinectes sapidus) in Pamlico Sound, NC. Pamlico Sound is the second largest estuary in the U.S. and is prone to hurricane activity. The blue crab fishery, North CarolinaÃ¢â‚¬Ëœs most important, is managed using indices of spawning stock biomass (SSB) and catch-per-unit effort generated from a fishery-independent trawl survey that does not sample shallow (< 2 m deep) regions. If environmental conditions affect the proportion of the population located within the survey region at a given time, then these indices are susceptible to bias resulting from variations in crab catchability. When the majority of the population is distributed in the Pamlico Sound survey area, a relatively high catchability would inflate estimates of relative population size. Likewise, when the population is less aggregated in mainstem Pamlico Sound and distributed further up in shallow water tributaries, relative population size would be underestimated by a relatively low catchability. Our objectives, to investigate the potential existence of aggregations and their environmental causes and to develop ways to account for environmental variability to obtain unbiased estimates of relative population abundance, were accomplished in two parts using three different statistical models. First, we modeled salinity observations collected in Pamlico Sound over the past 20 years as a function of recent and long-term freshwater influx from four rivers, distance to nearby inlets, and hurricane incidence. Maps of salinity predictions generated by this model illustrated changes in spatial salinity patterns during 40 survey time periods that encompassed a variety of climatic conditions. Salinity predictions were used to characterize the relationship between salinity and the presence and spatial distribution of blue crab SSB to predict historic distribution patterns. Observed survey SSB was modeled as function of space-time variable environmental factors that likely affect crab catchability in order to estimate time period-specific SSB means that were adjusted for these environmental effects. The time series of estimated means comprise an environmentally-adjusted SSB index that is more suitable for tracking relative population size over time than the index currently used to manage the fishery. This adjustment validated conclusions drawn from previous analyses and field observations that blue crab SSB has decreased over the past 20 years, most notably since 1999. A second model, including factors that did not change over time but likely affected crab spatial distribution, allowed us to predict SSB at a given space-time location. Predictions revealed consistent SSB spatial distribution patterns over successive monthly time periods and under variable environmental conditions. This information could help managers station no-take marine reserves to better conserve the blue crab spawning stock. In addition to yielding results that will better inform blue crab fishery managers, this research significantly increases the knowledge base regarding the effects of abiotic forcing events on mobile estuarine species. Furthermore, these methods provide a rigorous and robust analytical template to create future adjustment indices to manage mobile species that change their spatial distribution in response to environmental variables.
Use of Natural Tags in Closed Population Capture-Recapture Studies: Modeling Misidentification
(2007-08-14) Yoshizaki, Jun; Nicholas M. Haddad, Committee Co-Chair; Cavell Brownie, Committee Member; Joseph E. Hightower, Committee Member; James D. Nichols, Committee Member; Kenneth H. Pollock, Committee Chair