Browsing by Subject "Sharks"

Now showing 1 - 5 of 5
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    A Preliminary Delineation of Shark Nursery Grounds in Two South Carolina Estuaries
    (2004) Prosser, Christopher M
    I hypothesize that urbanization Murrells Inlet will affect the total number of elasmobranches present and the species diversity of elasmobranchs. I believe predation is the controlling factor for newborn sharks and young juveniles, and so I would expect to find those individuals in the areas least accessible to adult sharks. This idea is supported by Gilliam and Fraser (1987) who looked at foraging behavior in response to predation pressure. They found fishes will move to the habitats that afford them the greatest chances of survival. However, once animals grow in size, and the risk of being eaten becomes substantially less, they move to areas that are less environmentally stressful.
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    Freezing behaviour facilitates bioelectric crypsis in cuttlefish faced with predation risk.
    (Proc Biol Sci, 2015-12-07) Bedore, Christine N; Kajiura, Stephen M; Johnsen, Sönke
    Cephalopods, and in particular the cuttlefish Sepia officinalis, are common models for studies of camouflage and predator avoidance behaviour. Preventing detection by predators is especially important to this group of animals, most of which are soft-bodied, lack physical defences, and are subject to both visually and non-visually mediated detection. Here, we report a novel cryptic mechanism in S. officinalis in which bioelectric cues are reduced via a behavioural freeze response to a predator stimulus. The reduction of bioelectric fields created by the freeze-simulating stimulus resulted in a possible decrease in shark predation risk by reducing detectability. The freeze response may also facilitate other non-visual cryptic mechanisms to lower predation risk from a wide range of predator types.
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    Improving Protections for Threatened Shark Nursery Grounds Off the Pacific Coast of Northwest Mexico
    (2022-04-19) Anrig, Greg
    In 2021, The PEW Charitable trusts commissioned the Duke Marine Geospatial Ecology lab (MGEL) to conduct a literature review of existing scientific research on nursery and spawning grounds for a select group of threatened marine species. This project was developed with the following goals: A) Identify a set of focal marine species that are of conservation concern. B) Conduct a global-scale review of scientific literature to identify where nursery, pupping, and spawning grounds for these species are located, how these areas are impacted by fisheries and how they are protected by existing management measures. C) Use this information to develop recommendations for how these areas can be protected more effectively to prevent further population declines. Fundamentally, PEW intended this report to help determine how their own resources can be allocated most efficiently in the future to maximize conservation benefits, both in terms of where new initiatives should be located and what they will work to achieve. The following report is a supplementary document to the global MGEL study that helps further this underlying goal by providing a more focused analysis of an area with outstanding conservation importance identified in the global review: the coastal waters of northwest Mexico. By incorporating data from the literature review and additional research, this study develops more detailed recommendations for this area within the original project framework. The first section explains why protecting shark nursery grounds is a critical conservation concern, especially in the northwest Mexican Pacific (NMP). Nursery grounds facilitate growth and development of juveniles, allowing them to reach the spawning stage. However, when fishers land large volumes of juvenile sharks, they accelerate population declines by eliminating the specimens themselves and their potential offspring, a prevalent problem in the NMP. Because nursery grounds for multiple threatened shark species in this area are targeted directly by artisanal fishers, reducing or eliminating these fishing threats will be critical to ensuring the survival of underlying populations. The following two sections define the species composition and spatial distribution of focal shark nursery grounds in the NMP while identifying proximal fishing threats. Protecting juvenile shark aggregations requires a consideration of how they are distributed across the study area. Based on the literature review data, focal shark nursery grounds are concentrated in three specific regions of the NMP, which likely hold disproportionate conservation importance. While existing research is limited, available data suggests that all three regions are subject to concentrated fishing activity. The next section outlines the existing regulatory framework for the NMP shark fishery. Understanding this regulatory framework is necessary to develop realistic and effective management recommendations that are within the purview of existing regulatory bodies. Two central regulatory bodies are identified, both of which have authority to institute new protection measures for local shark nursery grounds. The final two sections synthesize the preceding research to provide recommendations for how the Mexican government can protect focal shark nursery grounds in the NMP more effectively. Recording the species composition and corresponding locations of juvenile shark landings in logbook reports can inform the placement of new, small-scale area closures, a feasible means of protecting these nursery grounds from artisanal fishing. The conclusion further outlines how non-governmental organizations (NGOs) like PEW can collaborate with the Mexican government to ensure the success of these new measures.
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    Shark Week and Public Perceptions of Sharks
    (2019-04-12) O'Donnell, Katie
    Perceptions of predators, and the type of language used when describing them, can influence a person’s decision whether or not to support wildlife conservation. Many shark species are important apex predators that are found in oceans worldwide, giving sharks a unique role in our society. This study investigated social conversations about sharks by using sentiment analysis of the social media platform, Twitter. We wanted to see if popular annual programming, such as Discovery Channel’s Shark Week, influences the language used in public social conversations and how that affects attitudes toward sharks. Sentiment and statistical analyses show that Shark Week affects the sentiment of language used in Twitter conversations about sharks from 2012-2017. This study builds on the growing literature that increases understanding of public sentiment of sharks, which can contribute to more informative and effective policies to better protect sharks.
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    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.