Browsing by Author "David B. Eggleston, Committee Member"

Now showing 1 - 3 of 3

Evaluation of nursery habitat: an ecophysiological approach
(2008-11-11) Del Toro-Silva, Felix Manuel; David B. Eggleston, Committee Member; Jeffrey A. Buckel, Committee Member; Derek D. Aday, Committee Member; John M. Miller, Committee Chair
DEL TORO SILVA, FELIX M.: Evaluation of nursery habitat: an ecophysiological approach. Abiotic conditions can determine biomass production within habitats and this can influence the relative contribution of nursery habitats to adult populations, yet few studies have addressed how the interactions of abiotic parameters can influence production. Through a combination of laboratory experiments, simulation modeling, and field experiments the effects of abiotic dynamics on fish growth were examined. The objective of the study were to: (1) assess the effects of oxygen and temperature dynamics on growth; (2) test three indices of metabolic capacity (MMS, RMR, LOC) as indicators of fish performance relative to these dynamics; (3) develop a simulation model to predict growth based on abiotic conditions; (4) validate the model in four nursery areas within the Pamlico River Estuary; (5) compare habitat classification based on model results with juvenile abundance classification. Results showed significant individual and interaction effects of oxygen and temperature on growth. No significant abiotic effects on RMR were detected, but significant effects were detected for the other two indices (MMS and LOC). MMS indices showed a pattern similar to the observed growth rates in response to temperature and oxygen treatments. The model was successfully parameterized with laboratory data and validated through simulations of field trials. The model successfully reproduced growth rates in the field using environmental data (oxygen, temperature and salinity) as input variables and more importantly, it reproduced in a fine temporal scale dynamics of growth rate within the simulations. Comparisons of habitat classification between juvenile abundance and model simulations were not possible because environmental conditions during field experiments were so sever that most of the experiments resulted in negative growth rates. Overall, the study demonstrated the importance of abiotic dynamics on individual performance and resulting biomass production within a habitat and that the ecophysiological framework is an adequate model to develop and test hypothesis of mechanism affecting production within nursery habitats.
Implications of a Decrease in the Mature Size of Female Blue Crab, Callinectes sapidus
(2006-01-26) Davis, John Howell; David B. Eggleston, Committee Member; Donna L. Wolcott, Committee Chair; Thomas G. Wolcott, Committee Member
The size-at-maturity of female blue crabs is declining and the proportion of very small mature females (<100mm carapace width (CW)) is increasing North Carolina. Decreasing mature size of the female may have an effect on the mating success and mortality of size-disparate mating pairs. To test the effect of body size on mating behavior, I used controlled mating experiments comparing size-disparate mating pairs with similarly-sized mating pairs. Small males handled large females longer than any other mating pair combination; however, no increase in injury or mortality was found. Neither large nor small males transferred significantly different numbers of sperm to large and small females. Size-disparity appears to have no effect on mating success in blue crabs, suggesting that diversity of size-related genotypic traits can be preserved in the population. I also designed a mathematical model to estimate the lifetime spawning potential of different size-cohorts of female blue crabs subject to different mortality pressures. Cohorts of very small females (<100mm CW) that are not subject to fishery mortality produce 5.1 — 58.1% more eggs over two spawning seasons than larger, harvestable females (127-159mm CW), suggesting an evolutionary advantage to maturing at smaller sizes. I also used the model to estimate the efficacy of a proposed restriction on the commercial harvest of large females (>172mm CW), intended to increase the spawning potential of large females in order to increase population-wide recruitment, as well as the number of recruits that may possess a larger-size genotype. The proposed seasonal (Sept. — Apr.) commercial harvest of large females produced an estimated 23.2 — 35.1% increase in egg production over two spawning seasons. However, since the large females compose less than 2% of the population, on average, the estimated increase in spawning potential for the entire population was negligible (0.46%). Additionally, the 5% tolerance of the regulation allows for the harvest of the entire population of large females, suggesting that the proposed restriction will be ineffective.
Use of passive acoustic monitoring to resolve spatial and temporal patterns of spawning activity for red drum, Sciaenops ocellatus, in the Neuse River Estuary, North Carolina.
(2004-08-02) Barrios, Anna Teresita; Peter S. Rand, Committee Chair; David B. Eggleston, Committee Member; Adam S. Frankel, Committee Member; Thomas Wolcott, Committee Member; Tony F. Clark, Committee Co-Chair; Stacy A.C. Nelson, Committee Member
Spawning site selection by red drum within the Neuse River Estuary (NRE) was studied by locating vocalizing aggregations using traditional hydrophone surveys (involving deploying gear from a research vessel stationed over a sampling site) and submersible, autonomous sonobuoys. Sonobuoys allowed interval recording over multiple stations during a given night, and reduced the likelihood that boat noise would interfere with courtship and spawning behavior. The field season extended from 8 July to 30 September 2003. Sampling sites were selected at random, with replacement, from four possible categories: shallow—soft bottom (sandy, < 3 m), medium—soft bottom (transitional sand to mud, 3-5 m), deep-soft bottom (primarily mud, > 5 m), and deep-hard bottom (oyster reef or shell, > 5 m). Synoptic egg sampling at a subset of acoustic sampling sites confirmed a statistically significant relationship between probability of detecting vocalizing red drum and Sciaenid-type egg presence. On 30 dates between July and September 2003, vocalizing males were detected 43 (of 72) times with sonobuoys (multiple observations per site) and 35 (of 88) times while spot sampling (one observation per site). Most vocalizations (85 %) were observed at sites with water depths greater than 5 m, and 97 % occurred in August and September. Vocalization activity was most prevalent between 8 August and 17 September 2003, with the majority of vocalizations detected during a four hour period beginning at sunset.Highest vocalization activity varied between 1 and 3 hours after sunset with the average occurring 1 ½ hours after sunset over hard substrate sites, and 2 hours after sunset over soft substrate sites. I concluded that spawning aggregations were relatively spatially stationary once vocalizations began based on a high degree of vocalization persistence, and no significant shift in time of highest vocalization activity within the study area that would imply net movement of the aggregation over a given night's sampling period. Given the relatively fixed position of vocalizing aggregations, it was determined that depth and proximity to the river mouth were the dominant factors defining distribution of aggregations in the NRE during the 2003 field season. Drum appeared to have a strong affinity for deeper water during spawning. Vocalization activity and Sciaenid-type egg presence was more prevalent near the river mouth, suggesting that spawning activity was centered in this area. Higher received levels at the hydrophone (dB re 1 μPa 1- 1000 Hz, Bandwidth, P-P, as an indicator of vocalizing red drum presence) were found at sites containing greater than 2.5 mg/l dissolved oxygen in bottom waters. Egg presence was also positively associated with bottom waters containing greater than 3 mg/l dissolved oxygen. This evidence suggests that hypoxia may limit available spawning sites in the NRE. Egg presence was significantly related to day of year, with an increase in probability of presence occurring near the 12 August full moon, suggesting a link between spawning activity and the lunar calendar. The NRE presents a unique set of characteristics not previously noted in estuarine systems where red drum spawning has been confirmed. These include a meso-saline environment that experiences periodic water column stratification, often with hypoxic or anoxic bottom waters. Passive acoustic monitoring techniques offer a viable and non-invasive method to locate spawning aggregations, describe diel and seasonal spawning patterns, and determine affinities to particular habitats.