Catherine M. McClellan

Understanding movement data and movement processes: current and emerging directions

Animal movement has been the focus on much theoretical and empirical work in ecology over the last 25 years. By studying the causes and consequences of individual movement, ecologists have gained greater insight into the behavior of individuals and the spatial dynamics of populations at increasingly higher levels of organization. In particular, ecologists have focused on the interaction between individuals and their environment in an effort to understand future impacts from habitat loss and climate change. Tools to examine this interaction have included: fractal analysis, first passage time, Lévy flights, multi-behavioral analysis, hidden markov models, and state-space models. Concurrent with the development of movement models has been an increase in the sophistication and availability of hierarchical bayesian models. In this review we bring these two threads together by using hierarchical structures as a framework for reviewing individual models. We synthesize emerging themes in movement ecology, and propose a new hierarchical model for animal movement that builds on these emerging themes. This model moves away from traditional random walks, and instead focuses inference on how moving animals with complex behavior interact with their landscape and make choices about its suitability.

Complexity and variation in loggerhead sea turtle life history

Juvenile loggerhead sea turtles spend more than a decade in the open ocean before returning to neritic waters to mature and reproduce. It has been assumed that this transition from an oceanic to neritic existence is a discrete ontogenetic niche shift. We tested this hypothesis by tracking the movements of large juveniles collected in a neritic foraging ground in North Carolina, USA. Our work shows that the shift from the oceanic to neritic waters is both complex and reversible; some individuals move back into coastal waters and then return to the open ocean for reasons that are still unclear, sometimes for multiple years. These findings have important consequences for efforts to protect these threatened marine reptiles from mortality in both coastal and open-ocean fisheries.

Using telemetry to mitigate the bycatch of long-lived marine vertebrates.

The unintended bycatch of long-lived marine species in fishing gear is an important global conservation issue. One suite of management approaches used to address this problem restricts or modifies fishing practices in areas where the probability of bycatch is believed to be high. Information on the distribution and behavior of the bycaught species is a desirable component of any such scheme, but such observations are often lacking. We describe a spatially explicit approach that combines data on the distribution of fishing effort and observations of the distribution of bycatch species derived from satellite telemetry. In a case study, we used a spatially explicit predator-prey model to investigate real-time interactions between three species of sea turtles (Caretta caretta, Chelonia mydas, and Lepidochelys kempii) and the fall large-mesh gill net fishery that targets southern flounder (Paralichthys lethostigma) in Pamlico Sound, North Carolina between 2002 and 2004. The model calculates a spatial overlap index, thereby allowing us to identify which fishing areas have the greatest risk of encountering bycatch. In this study, our telemetry deployments (n = 50) were designed specifically to address existing fisheries conservation measures in Pamlico Sound intended to reduce sea turtle bycatch. We were able to predict the spatial distribution of bycatch and evaluate management measures. This approach offers a powerful tool to managers faced with the need to reduce bycatch.

Understanding the distribution of marine megafauna in the English channel region: identifying key habitats for conservation within the busiest seaway on earth.

The temperate waters of the North-Eastern Atlantic have a long history of maritime resource richness and, as a result, the European Union is endeavouring to maintain regional productivity and biodiversity. At the intersection of these aims lies potential conflict, signalling the need for integrated, cross-border management approaches. This paper focuses on the marine megafauna of the region. This guild of consumers was formerly abundant, but is now depleted and protected under various national and international legislative structures. We present a meta-analysis of available megafauna datasets using presence-only distribution models to characterise suitable habitat and identify spatially-important regions within the English Channel and southern bight of the North Sea. The integration of studies from dedicated and opportunistic observer programmes in the United Kingdom and France provide a valuable perspective on the spatial and seasonal distribution of various taxonomic groups, including large pelagic fishes and sharks, marine mammals, seabirds and marine turtles. The Western English Channel emerged as a hotspot of biodiversity for megafauna, while species richness was low in the Eastern English Channel. Spatial conservation planning is complicated by the highly mobile nature of marine megafauna, however they are important components of the marine environment and understanding their distribution is a first crucial step toward their inclusion into marine ecosystem management.

Modeling and mapping isotopic patterns in the Northwest Atlantic derived from loggerhead sea turtles

Stable isotope analysis can be used to infer geospatial linkages of highly migratory species. Identifying foraging grounds of marine organisms from their isotopic signatures is becoming de rigueur as it has been with terrestrial organisms. Sea turtles are being increasingly studied using a combination of satellite telemetry and stable isotope analysis; these studies along with those from other charismatic, highly vagile, and widely distributed species (e.g., tuna, billfish, sharks, dolphins, whales) have the potential to yield large datasets to develop methodologies to decipher migratory pathways in the marine realm. We collected tissue samples (epidermis and red blood cells) for carbon (δ13C) and nitrogen (δ15N) stable isotope analysis from 214 individual loggerheads (Caretta caretta) in the Northwest Atlantic Ocean (NWA). We used discriminant function analysis (DFA) to examine how well δ13C and δ15N classify loggerhead foraging areas. The DFA model was derived from isotopic signatures of 58 loggerheads equipped with satellite tags to identify foraging locations. We assessed model accuracy with the remaining 156 untracked loggerheads that were captured at their foraging locations. The DFA model correctly identified the foraging ground of 93.0% of individuals with a probability greater than 66.7%. The results of the external validation (1) confirm that assignment models based on tracked loggerheads in the NWA are robust and (2) provide the first independent evidence supporting the use of these models for migratory marine organisms. Additionally, we used these data to generate loggerhead-specific δ13C and δ15N isoscapes, the first for a predator in the Atlantic Ocean. We found a latitudinal trend of δ13C values with higher values in the southern region (20–25 °N) and a more complex pattern with δ15N, with intermediate latitudes (30–35 °N) near large coastal estuaries having higher δ15N-enrichment. These results indicate that this method with further refinement may provide a viable, more spatially-explicit option for identifying loggerhead foraging grounds.

Phytoplankton forcing by a record freshwater discharge event into a large lagoonal estuary

We report here the response of the water column and phytoplankton biomass of a large lagoonal estuary to a record freshwater discharge event which followed from extraordinary hurricane activity. In the fall of 1999, three hurricanes passed over eastern North Carolina coast in a 7-wk period: Hurricane Dennis (August 24–September 5), Hurricane Floyd (September 14–17), and Hurricane Irene (October 13–16). The hurricanes delivered record rainfall to the watersheds of the Pamlico Sound, North Carolina, the second largest estuary in North America. Hurricane Floyd was followed by a 500-yr flood that displaced 80% of the volume of the Sound and delivered half the annual nitrogen (N)-nutrient load to this N-limited system.After Hurricane Floyd, buoyancy stratification restricted the mixed layer depth, dissolved inorganic nitrogen (DIN) in surface waters increased, and surface chlorophyll biomass increased up to 4-fold. Chlorophyll biomass did not increase to the potential indicated by residual DIN because of light-limitation attributable to suspended particulates, phytoplankton pigments, and colored dissolved organic material (CDOM).The discharge waters created hydrological conditions and supplied materials that we interpret to have both stimulated and restricted phytoplankton blooms. The effects of the discharge event on the hydrology and phytoplankton of the Pamlico Sound persisted about 6 months, after which it returned to its pre-event condition, attesting to the resilience of the system.