The influence of predation risk on bottlenose dolphin habitat use in the Neuse River Estuary
Damon Gannon’s Ph.D. thesis (Gannon 2003) described patterns of habitat use for bottlenose dolphins in the Neuse River estuary. The prey of dolphins is distributed evenly throughout the estuary, but dolphins are found almost exclusively along the shallow margins of the estuary. Therefore, bottlenose dolphin habitat use cannot be predicted solely by the distribution of their prey. Damon hypothesized that predation risk could be structuring the habitat use of estuarine dolphins. Bull sharks are euryhaline predators that inhabit both estuarine and coastal ecosystems. As top predators, they have the potential to directly and indirectly influence the distribution and abundance of their prey species, such as bottlenose dolphins. Approximately 34% of bottlenose dolphins in North Carolina have scars from predation attempts by sharks. We are using fishing and acoustic tracking to evaluate the habitat use of bull sharks in the Neuse River estuary. Understanding the movement patterns and habitat use of bull sharks will allow us to examine the influence of this predator on the habitat use of bottlenose dolphins. This project is funded by the Joseph F. Ramus Endowment Fund.
The value of marine reserves in protecting apex predators: does a spillover effect exist in the Northwestern Hawaiian Islands?
Marine reserves are frequently used to protect sensitive ecosystem components and are advocated as a buffer against overfishing. Additionally, marine reserves have been hypothesized to enhance adjacent fishery catches via “spillover” from reserves. Based on this hypothesis, the density and size of target species increase within a reserve, which results in the density-dependent emigration of fish outside the reserve and into fished areas. However, few studies have tested the spillover hypothesis with large pelagic fishes (e.g., sharks, tuna, billfish) and it is not clear whether marine reserves are effective for these species. Therefore, I will determine whether a spillover effect exists for apex predators in an already established marine reserve in the Northwestern Hawaiian Islands. Not only is this research original and unique, it will also evaluate current management practices and use conservation science to determine appropriate management decisions for apex predators.