Multi-year tracking reveals extensive pelagic phase of juvenile loggerhead sea turtles in the North Pacific.

BACKGROUND: The juvenile stage of loggerhead sea turtles (Caretta caretta) can last for decades. In the North Pacific Ocean, much is known about their seasonal movements in relation to pelagic habitat, yet understanding their multi-year, basin-scale movements has proven more difficult. Here, we categorize the large-scale movements of 231 turtles satellite tracked from 1997 to 2013 and explore the influence of biological and environmental drivers on basin-scale movement. RESULTS: Results show high residency of juvenile loggerheads within the Central North Pacific and a moderate influence of the Earth's magnetic field, but no real-time environmental driver to explain migratory behavior. CONCLUSIONS: We suggest the Central North Pacific acts as important developmental foraging grounds for young juvenile loggerhead sea turtles, rather than just a migratory corridor. We propose several hypotheses that may influence the connectivity between western and eastern juvenile loggerhead foraging grounds in the North Pacific Ocean.

Active dispersal in loggerhead sea turtles (Caretta caretta) during the 'lost years'.

Highly migratory marine species can travel long distances and across entire ocean basins to reach foraging and breeding grounds, yet gaps persist in our knowledge of oceanic dispersal and habitat use. This is especially true for sea turtles, whose complex life history and lengthy pelagic stage present unique conservation challenges. Few studies have explored how these young at-sea turtles navigate their environment, but advancements in satellite technology and numerical models have shown that active and passive movements are used in relation to open ocean features. Here, we provide the first study, to the best of our knowledge, to simultaneously combine a high-resolution physical forcing ocean circulation model with long-term multi-year tracking data of young, trans-oceanic North Pacific loggerhead sea turtles during their 'lost years' at sea. From 2010 to 2014, we compare simulated trajectories of passive transport with empirical data of 1-3 year old turtles released off Japan (29.7-37.5 straight carapace length cm). After several years, the at-sea distribution of simulated current-driven trajectories significantly differed from that of the observed turtle tracks. These results underscore current theories on active dispersal by young oceanic-stage sea turtles and give further weight to hypotheses of juvenile foraging strategies for this species. Such information can also provide critical geographical information for spatially explicit conservation approaches to this endangered population.

Comparing effectiveness of experimental and implemented bycatch reduction measures: the ideal and the real.

Fishers, scientists, and resource managers have made substantial progress in reducing bycatch of sea turtles, seabirds, and marine mammals through physical modifications to fishing gear. Many bycatch-avoidance measures have been developed and tested successfully in controlled experiments, which have led to regulated implementation of modified or new fishing gear. Nevertheless, successful bycatch experiments may not translate to effective mitigation in commercial fisheries because experimental conditions are relaxed in commercial fishing operations. Such a difference between experimental results and real-world results with fishing fleets may have serious consequences for management and conservation of protected species taken as bycatch. We evaluated preimplementation experimental measures and postimplementation efficacy from primary and gray literature for three case studies: acoustic pingers that warn marine mammals of the presence of gill nets, turtle excluder devices that reduce bycatch of turtles in trawls, and various measures to reduce seabird bycatch in longlines. Three common themes to successful implementation of bycatch reduction measures are long-standing collaborations among the fishing industry, scientists, and resource managers; pre- and postimplementation monitoring; and compliance via enforcement and incentives.

Ecosystem impacts of three sequential hurricanes (Dennis, Floyd, and Irene) on the United States' largest lagoonal estuary, Pamlico Sound, NC.

Three sequential hurricanes, Dennis, Floyd, and Irene, affected coastal North Carolina in September and October 1999. These hurricanes inundated the region with up to 1 m of rainfall, causing 50- to 500-year flooding in the watershed of the Pamlico Sound, the largest lagoonal estuary in the United States and a key West Atlantic fisheries nursery. We investigated the ecosystem-level impacts on and responses of the Sound to the floodwater discharge. Floodwaters displaced three-fourths of the volume of the Sound, depressed salinity by a similar amount, and delivered at least half of the typical annual nitrogen load to this nitrogen-sensitive ecosystem. Organic carbon concentrations in floodwaters entering Pamlico Sound via a major tributary (the Neuse River Estuary) were at least 2-fold higher than concentrations under prefloodwater conditions. A cascading set of physical, chemical, and ecological impacts followed, including strong vertical stratification, bottom water hypoxia, a sustained increase in algal biomass, displacement of many marine organisms, and a rise in fish disease. Because of the Sound's long residence time ( approximately 1 year), we hypothesize that the effects of the short-term nutrient enrichment could prove to be multiannual. A predicted increase in the frequency of hurricane activity over the next few decades may cause longer-term biogeochemical and trophic changes in this and other estuarine and coastal habitats.

Indirect effects of fish on macrophytes in Bays Mountain Lake: evidence for a littoral trophic cascade.

We began this experiment to test specific hypotheses regarding direct and indirect effects of fish predation on the littoral macroinvertebrate community of Bays Mountain Lake, Tennessee. We used 24 m2 enclosures in which we manipulated the presence and absence of large redear sunfish (Lepomis microlophus>150 mm SL), and small sunfish (L. macrochirus and L. microlophus <50 mm SL) over a 16-mo period. Here we report on effects of fish predation on gastropod grazers that appear to cascade to periphyton and macrophytes.Both large redear sunfish and small sunfish maintained low snail biomass, but snails in fish-free controls increased significantly during the first 2-mo of the experiment. By late summer of the first year of the experiment, the difference in biomass between enclosures with and without fish had increased dramatically (>10×). Midway through the second summer of the experiment, we noted apparent differences in the abundance of periphyton between enclosures containing fish and those that did not. We also noted differences in the macrophyte distribution among enclosures. To document these responses, we estimated periphyton cover, biovolume and cell size frequencies as well as macrophyte distributions among enclosures at the end of the experiment. When fish were absent, periphyton percent cover was significantly reduced compared to when fish were present. Periphyton cell-size distributions in enclosures without fish were skewed toward small cells (only 12% were greater than 200 m3), which is consistent with intense snail grazing. The macrophyte Najas flexilis had more than 60 x higher biomass in the fish-free enclosures than in enclosures containing fish; Potamogeton diversifolius was found only in fish-free enclosures. These results suggest a chain of strong interactions (i.e. from fish to snails to periphyton to macrophytes) that may be important in lake littoral systems. This contrasts sharply with earlier predictions based on cascading trophic interactions that propose that fish predation on snails would enhance macrophyte biomass.