Browsing by Subject "Bottlenose dolphins (Tursiops truncatus)"

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Open Access
Bycatch and Biomass: Mitigating dolphin bycatch while maintaining fish catch in the Virginia Beach pound net fishery
(2008-04-18T22:24:11Z) Herman, Elia
Pound nets are traditional, passive fishing traps that have been used since the 1870s to catch estuarine fish species in the Chesapeake Bay. Most unwanted species captured in the actual pound net can be released alive; however, sea turtles and marine mammals may die if they become entangled in the leader of the net. In 2004, NOAA Fisheries required changes in the construction of pound net leaders in part of the Chesapeake Bay to reduce entanglement rates of sea turtles. To date no actions have been taken to address the bycatch of bottlenose dolphins in pound net leaders. In the summer of 2007, I conducted a pilot study to sample catches of butterfish (Peprilus alepidotus and Peprilus triacanthus) and Spanish mackerel (Scomberomorus maculatus) in a Virginia Beach pound net fishery considering modifications to their leaders to reduce dolphin bycatch. Using these observations, I worked with the Virginia Aquarium to design an experiment to test the new leaders during the 2008 fishing season. The primary goal of this experiment is to determine whether the experimental leader will affect the catch of target fish species. From an analysis of dolphin strandings in Virginia from 1997-2004, I found that pound nets accounted for the greatest percentage (50%) of all documented Human Interaction (HI) strandings. I also used geospatial analyses to examine the distribution of bottlenose dolphin strandings that may be associated with bycatch in pound nets. HI stranded dolphins were found significantly closer to the Virginia Beach pound nets than dolphins that stranded for another reason (No HI) or for an unknown cause (CBD). Together these analyses help to improve our understanding of interactions between bottlenose dolphins and the Virginia Beach pound net fishery, as well as the importance of community-based management efforts.
Open Access
CHARACTERIZATION OF BOTTLENOSE DOLPHIN (TURSIOPS TRUNCATUS) USE OF RESTRICTED AREAS IN THE PAMLICO SOUND, NC
(2003) Maher, Jessica
In two areas of the Pamlico Sound, NC, the U.S. Marine Corps and other branches of the military conduct training activities that involve airborne deployment of ordnance. Entry into these areas is restricted, and as such, they have not been included in previous surveys for marine mammals or other protected species. Since July 2002, however, we have been contracted by the Marine Corps to conduct photo-identification surveys for bottlenose dolphins in two bombing ranges (BT-9 near Brandt Island Shoal and BT-11 in Rattan Bay) and waters surrounding the ranges. We observed 261 dolphins (in 10 sightings) during eight surveys conducted between July and December, 2002. Of the 261 animals photographed, 100 met our criteria for distinctiveness; these 100 identifications represent 96 individual dolphins, as four were seen on two occasions. We matched 39 dolphins to the Duke University Marine Laboratory/University of North Carolina at Wilmington dorsal fin photo-identification catalog, and we made 57 new identifications. Many dolphins (185) were sighted inside the bombing range boundaries, sometimes in close proximity to the bombing targets. The BT-9 range had a daily occupancy of 0.17 sightings/survey day and an hourly occupancy of 0.09 sightings/hour; BT-11’s daily occupancy was 0.38 sightings/survey day and its hourly occupancy was 0.31 sightings/hour; waters adjacent to the bombing ranges had a daily occupancy of 0.88 sightings/survey day and an hourly occupancy of 0.45 sightings/hour. The combined (bombing ranges and adjacent waters) mean dolphin group size was 26.1 ± 27.4 SD. The mean density of BT-9 (75 km2) was 0.11 dolphins/km2 and the mean density of BT-11 (11 km2) was 1.50 dolphins/km2. This work represents the first systematic survey effort for bottlenose dolphins in restricted areas of the Pamlico Sound.
Open Access
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.
Open Access
Foraging Ecology and Maternal Transmission of Foraging Specializations of Bottlenose Dolphins (Tursiops truncatus)
(2004) Weiss, Jessica
Bottlenose dolphins use a variety of foraging specializations to detect and pursue prey. Like other mammals, individual dolphins may use specialized foraging techniques that are shaped in response to habitat or particular prey resources. The long duration of the mother-calf bond presents an opportunity for mothers to transmit such specializations to their calves, and cases of observational learning by dolphins are well known from captive colonies. This study explored how specializations may influence choices of habitat use and on how such specializations may spread within a community. A focal follow technique was used to document the foraging behavior of five resident females and their calves from June-August 2003 in Sarasota, FL. Females significantly differed in their selection of foraging habitats. Three of the five focal females used known foraging specializations, kerplunking and barrier feeding, and exhibited a preference for only one type. Females also increased the use of foraging habitats associated with their preferred foraging specializations. Limited observations, as well as anecdotal evidence from past studies, suggest that maternal transmission may play a role in the spread of kerplunking and barrier feeding within a community. Findings suggest that the use of foraging specializations is associated with foraging habitat preferences in Sarasota Bay as well as support the importance of incorporating knowledge of social behavior into the management structure for bottlenose dolphins. Many questions still remain concerning the prey specificity, stability, and sex-specific nature of foraging specializations and future studies should concentrate on these areas of research.
Open Access
Preliminary Observation of Depredation by Bottlenose Dolphins on the King Mackerel Troll Fishery in Florida
(2004) Zollett, Erika A
Conflicts between marine mammals and fisheries can be attributed to spatial overlap and resource competition between cetaceans and fisheries and/or behavioral learning among marine mammals. In the present study, I documented depredation by bottlenose dolphins (Tursiops truncatus) in Florida’s king mackerel troll fishery. Depredation refers to the behavior in which predator species remove or damage fish on fishing lines or in nets. I conducted twenty-six surveys of charter and commercial fishermen in Islamorada, Florida and twenty-three along Florida’s east coast from Fort Pierce south to Lake Worth Inlet, and I observed dolphin behaviors from working vessels in these two study sites. All survey respondents indicated they had observed bottlenose dolphins depredating bait or catch. Fishermen reported that king mackerel was the species most often taken by bottlenose dolphins. From behavioral observations, I found that dolphins took 6% of king mackerel caught by charter fishermen and 20% of fish caught by commercial fishermen. I attributed these differences to seasonal variation in fish distribution or gear differences between vessel types. Preliminary tests demonstrated that a modification to the outrigger planar will successfully deter bottlenose dolphins from engaging in depredation, without causing a reduction in catch.
Open Access
The effect of acoustic deterrent devices on bottlenose dolphin depredation in the Spanish mackerel gillnet fishery
(2005) Burke, Erin K
Bottlenose dolphins (Tursiops truncatus) reduce catches of Spanish mackerel (Scomberomorus maculatus) when they interact with coastal gillnets off Hatteras, North Carolina. Acoustic alarms, or pingers, are one means of potentially reducing these adverse interactions. We measured the effect of Save Wave alarms on the incidence of dolphin depredation and target fish catches. The study had two goals: (1) to quantify the effect of alarms on target species catch and (2) to quantify the effect of alarms on dolphin depredation. Fieldwork was conducted off Hatteras during June and August 2004. During this period, we attached alarms to 118 Spanish mackerel gillnet sets (63 active and 55 control). All catches were standardized for effort by incorporating measures of net length and soak duration. We collected data on total catch-per-unit effort (CPUE), Spanish mackerel CPUE, counts of fish discards, and evidence of depredation. There was no difference in total CPUE (p = 0.25) or Spanish mackerel CPUE (p = 0.94) between active and control sets. Net position (inshore, middle, offshore) also had no effect on total CPUE (p = 0.48) or Spanish mackerel CPUE (p = 0.35). We observed several dolphins interacting with nets with active alarms, but did not observe a sufficient amount of dolphin depredation to quantify their response to the Save Wave alarms. These results suggest that Save Wave alarms do not affect fish catches. Fieldwork for this project will continue during the summer of 2005 to determine whether or not the alarms reduce dolphin depredation.
Open Access
Top Predator Distribution and Foraging Ecology in Florida Bay, Florida
(2007-11-14) Torres, Leigh Gabriela
The heterogeneous landscape of Florida Bay provides habitats for a variety of predators and prey. This dissertation examined the bottom-up transfer of affects from environmental variability through prey composition up to competition and predation affects on top predator distribution and foraging ecology in Florida Bay. Line transect surveys for bottlenose dolphins and seabirds were conducted in Florida Bay during the summer months of 2002 - 2005. Photo-identification techniques were implemented to identify individual dolphins. Synoptic with this survey effort, habitat characteristics (temperature, salinity, dissolved oxygen, turbidity, chlorophyll a, depth and bottom type) and prey composition (bottom trawl or gillnet) were sampled. Comparison of envelope maps from generalized additive models determined that predictive capacity of dolphin habitat did not improve by incorporating fish distribution data. However, models of dolphin distribution based solely on environmental proxies of fish distribution resulted in high predictive capacity. During the 2005 summer, shark distribution was sampled using a longline. The abundance of sharks was only correlated to fish catch from trawls on a regional scale. Larger sharks, of species that may threaten dolphins, were only caught in the Gulf zone of the Bay. Analysis of dolphin distribution revealed high individual site and foraging tactic fidelity. Dolphins were spatially coincident with habitat characteristics that encouraged the use of each individual's preferred foraging tactic. Depth was identified as the primary variable determining dolphin foraging tactic choice. Depth plays a significant role in the benthic composition of Florida Bay, which subsequently impacts prey communities and affects dolphin distribution, foraging and social ecology. Ordinations determined that fish distribution was also principally affected by depth and bottom type. Shallow environments frequently corresponded with mudbank habitat (depth < 1m) where the sighting rates of seabirds (cormorants, osprey, pelicans, terns) and foraging dolphins peaked. In conclusion, subtle relief in South Florida's bedrock topography dramatically affect benthic composition within Florida Bay, providing patchy habitats for prey and predators. The Florida Bay ecosystem will change with expected sea level rise, including spatial shifts of mudbank habitats. Top predator populations in Florida Bay will be forced to modify their distribution and foraging ecology accordingly.
Open Access
USING PASSIVE ACOUSTICS TO MONITOR BOTTLENOSE DOLPHIN (TURSIOPS TRUNCATUS) USE OF TWO MILITARY RANGES IN PAMLICO SOUND, NORTH CAROLINA
(2009-04-24T03:09:34Z) Laura, Anna-Marie
A passive acoustic monitoring device to detect bottlenose dolphin (Tursiops truncatus) presence in two military ranges in Pamlico Sound, NC is being developed by researchers at the Duke University Marine Lab. Potential adverse effects of military activities in these ranges include temporary or permanent hearing loss, tissue damage, altered habitat use, and changes in behavior. The real-time passive acoustic monitoring system allows for automated detection of bottlenose dolphin whistles and alerts the Marine Core Air Station (MCAS) Cherry Point when dolphin whistles are detected. Passive acoustic monitoring relies on the detection of vocalizations, so I conducted focal follows coupled with acoustic monitoring to determine group vocalization rates. Dolphins near the ranges produced at least one detectable whistle in 25% of one-minute bins. Behavioral state and group size affected whistle production, and probability of whistle presence was significantly higher for socializing dolphins and groups of 1-2 and 11-20 dolphins. I examined focal follow tracks to determine rates of travel and calculated potential residence time for dolphins in the range. The average rate of travel for dolphins in the area was 0.871m/s, and rate of travel when traveling was significantly higher than any other behavior state. Residence time was also influenced by behavioral state and group size. The probability of whistle production is sufficient for an automated real-time passive acoustic detection device to detect bottlenose dolphins. Results of this study could be used by MCAS Cherry Point to establish procedures that will mitigate harmful effects to bottlenose dolphins without sacrificing military readiness. This type of system has potential for use at other coastal military ranges, bridge demolitions and other near shore activities posing threats to coastal dolphin populations and other marine mammals.