Browsing by Subject "Tursiops truncatus"

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    Determining the northern range of the NNCES stock of bottlenose dolphins (Tursiops truncatus) through photo-identification
    (2018-04-27) Young, Alaina
    The Roanoke Sound is an important summer habitat for coastal Atlantic bottlenose dolphins, including members of the Northern North Carolina Estuarine System (NNCES) stock. However, our understanding of the northern range of this stock is limited. It has been assumed that the stock occurs northward only as far as the NC/VA border, but there is considerable uncertainty in the location of this boundary. The objective of the present study was to better delineate this boundary by determining the northern range of individual dolphins sighted in Roanoke Sound. I matched individuals with high capture probabilities (n=59) in Roanoke Sound (NC-OBXCDR catalog) with individuals sighted in Norfolk, Virginia (VA-HDR catalog), the Potomac (MD-PCDP) catalog, and Cape May, NJ (NJ-CMWWRC catalog) through the MABDC. Five individuals, all likely females, were matched to VA-HDR, but none were matched to MD-PCP nor to NJ-CMWWRC. Four of the matched individuals were also sighted in the Pamlico Sound. The movements of these dolphins show some degree of seasonality, with sightings in the Roanoke Sound peaking in June but occurring from May to October, and in Virginia only in July and August. The results of my study indicate that the NC/VA border is not the northern boundary of the NNCES stock, but instead that the movement of these dolphins extends into the Chesapeake Bay. Thus, the management of this stock of dolphins should consider the threats, including by-catch, that may occur in this extended range.
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    Estimating the Lower Temperature Limit of Bottlenose Dolphins Along the North Carolina Coast
    (2004) Shoemaker, Mandy
    During winter, the coastal ecotype of bottlenose dolphins are at the northern limit of their range off the coast of North Carolina. In this study, the distribution of coastal bottlenose dolphins in North Carolina was evaluated in response to variation in sea surface temperature to determine whether the distribution of dolphins was limited directly or indirectly by winter temperature minima. Observations of dolphin distribution were obtained from monthly aerial surveys conducted along the North Carolina coast during February 2000 through July 2001. Sea surface temperatures were obtained for each survey from NOAA’s Pathfinder satellite, using PO.DAAC Ocean ESIP Tool (POET). Where necessary, the sea surface temperature data was interpolated (krigged) over areas of cloud cover. The northern latitudinal and lower temperature distribution was determined for each survey. During winter months bottlenose dolphins were not distributed throughout their known range of 10-32 °C. Dolphins may be limited directly by temperature, due to the limits of their thermal neutral zone, or indirectly by temperature, through distribution of their prey. To determine how temperature is affecting dolphin distribution in the Western North Atlantic, future research should focus on determining the thermal neutral zone of dolphins in this region. In addition, it would be useful to build a model including other dynamic factors that may affect dolphin distribution. Although results suggest that more research is necessary, there is potential for using results from this type of analysis for management.
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    Foraging with Trawlers May Blur the Boundaries Between Estuarine and Coastal Stocks of Common Bottlenose Dolphin (Tursiops truncatus) off South Carolina
    (2023-04-28) Meza-Fidalgo, Joshua
    In the western North Atlantic, common bottlenose dolphins (Tursiops truncatus) that forage in association with shrimp trawlers in ocean waters are widely assumed to be members of coastal rather than estuarine stocks. To test this assumption, I analyzed photo-identification (photo-id) images of common bottlenose dolphins collected by Justin Greenman in 2011 from North Carolina to Florida during surveys conducted aboard the South Carolina Department of Natural Resources Research Vessel Lady Lisa. I developed a dorsal fin catalog of 254 individual dolphins and compared this catalog to 14 regional photo-identification catalogs from North Carolina to Florida. I created a dataset with sightings records for matched dolphins seen 10 or more times (n=18) to examine their stock identities, based on criteria described in National Marine Fisheries Service (NMFS) Stock Assessment Reports (SARs). Only two of the 18 dolphins were sighted only in coastal waters, and four had the majority of their sightings in estuarine waters but also traveled into coastal waters to forage in association with trawlers. Two dolphins were first observed foraging in association with shrimp trawlers dating back to 1998. Overall, I found that dolphins from multiple stocks forage in association with shrimp trawlers in coastal waters of South Carolina. In addition, it appears that this behavior may attract estuarine dolphins into coastal waters outside their typical stock boundaries. The movement of dolphins across stock lines to engage in this foraging behavior raises concerns about our understanding of bycatch in this fishery. Misassignment of bycatch to the wrong stock could be particularly harmful to small stocks of bottlenose dolphins.
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    Occurrence of depredation by common bottlenose dolphins (Tursiops truncatus) on reef fish captured and released by rod and reel fisheries in the northeastern Gulf of Mexico
    (2021-04-30) Grewal, Corie E.
    In the northeastern Gulf of Mexico, depredation by common bottlenose dolphins (Tursiops truncatus) on rod and reel fishing gear leads to increased costs for anglers and serious injury and mortality for dolphins. I analyzed data collected from the Florida Fish and Wildlife Conservation Commission fisheries-dependent monitoring at-sea observer program to determine contributing factors to, spatial distribution of, and frequency of interactions for bottlenose dolphin depredation from 2009-2020. The dataset included 110,575 observations, of which 269 were recorded depredation events. I chose potential predictive factors from the dataset based on their known or hypothesized influence on dolphin behavior and used a generalized linear model to examine relationships between instances of depredation and these predictive factors. The number of anglers fishing, two geographic areas (Panama City and Destin, FL), years 2015 and 2017-2019, and captured fish families Lutjanidae (snapper family), Carangidae (jack family), and Serranidae (grouper and sea bass family) were significant predictive factors in the model. These results, as well as the results of a spatial analysis and an examination of the frequencies of these predictors suggest that food provisioning in the Florida panhandle is a driver of depredation and that the incidence of depredation is increasing over time. Bottlenose dolphins from the Gulf of Mexico northern and eastern coastal stocks have become conditioned to exhibit a range of low cost foraging techniques such as scavenging and begging, and depredation is an augmentation of those behaviors. Lutjanidae species were observed in 78% of depredation events and the family was the most significant factor in the model, revealing a regional prey preference for snapper. This study can help inform management and mitigation of bottlenose dolphin depredation in the Gulf of Mexico and provides a baseline for future scientific study.
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    Occurrence, Distribution and Reproductive Status of Female Bottlenose Dolphins (Tursiops truncatus) in Roanoke Sound, NC
    (2020-04-23) Reibel, Waverly
    I examined the spatial distribution of bottlenose dolphin (Tursiops truncatus) nursery groups in Roanoke Sound, NC, to gain insight into how environmental parameters affect site fidelity, and to determine whether habitat use patterns change based on the reproductive state of females. For mature females, I compiled information on interbirth intervals and length of calf dependency to obtain a more comprehensive picture of the ecology and life history of this age-sex class of estuarine dolphins. I analyzed photo-identification data from Roanoke Sound to compare the location and extent of kernel density estimates of home ranges for nursery groups, non-nursery groups and individual females. Many nursery groups are observed in this area during spring and summer, leading to the hypothesis that Roanoke Sound is an important nursery habitat. The importance of this area to lactating females may be attributable to its relatively shallow depth and abundant seagrass beds, which provide protection and a relatively plentiful supply of prey. In Roanoke Sound, nursery groups (n = 170) were significantly (p < 0.00001) larger than non-nursery groups (n = 68) with a mean of 12 individuals per sighting, while non-nursery groups averaged 4 individuals. Nursery groups and non-nursery groups had a high overlap percentage between ranging patterns, with home ranges overlapping 88%. This demonstrates that there is no specific “nursery area” within the Roanoke Sound, but coupled with the high numbers of large nursery groups sighted during the summer, the entire site itself may be of importance to these females. Four focal females had a mean interbirth interval of 7.5 years, and a mean length of calf dependency of 4.75 years. The females exhibited individual variation in ranging patterns, with habitat use overlap between nursery and non-nursery areas ranging from 11-79%. These females may be choosing areas based on their needs (and those of their calves), either for energetic purposes or protection. Documentation of nursery habitat can aid protection of these important areas through implementation of measures such as safe boating zones and increased water quality monitoring, as well as assist in the development of educational materials.
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    Population Genomics of Bottlenose Dolphins (Tursiops truncatus) in the Northwest Atlantic
    (2021-04-30) Shintaku, Nikki
    Bottlenose dolphins (Tursiops truncatus) are widely accepted as belonging to one of two ecotypes: offshore or inshore. These ecotypes exhibit remarkable differences in ecology, morphology, and genetic diversity. However, regional patterns of genetic differentiation and stock delineation remain poorly defined for both ecotypes. To improve our understanding of the population structures among these groups we investigated genome-wide genetic variation from 96 biopsy samples collected from bottlenose dolphins in inshore and offshore waters of the northwest Atlantic from North Carolina to Florida using restriction site associated DNA sequencing to infer population structure. Analysis of 14,783 single nucleotide polymorphisms revealed at least three genetically differentiated populations. Our results suggest an inshore population along North Carolina’s Outer Banks (n=32), an offshore population off the continental shelf break from North Carolina to Jacksonville, Florida (n= 38), and a shelf population off Jacksonville, Florida (n=26). Bayesian clustering showed significant admixture between the North Carolina and Jacksonville populations, providing potential evidence of historical or current gene flow. Most of the offshore samples were collected off Cape Hatteras, but this population also includes four individuals sampled beyond the continental shelf break off Jacksonville, FL, in close spatial proximity to shelf animals. This suggests a sharp distinction between shelf and offshore individuals structured by the shelf break itself. Such habitat heterogeneity is likely a driver in diversifying populations through influences on social behavior and foraging strategies. Our analyses provide fine-scale genetic resolution of bottlenose dolphin population differentiation in the Western North Atlantic. These results help inform conservation management and advance our understanding of processes that may drive the evolution of population genetic structure.