In this paper, we modified and updated a stage—based population model for loggerhead sea turtles (Caretta caretta) and used the model to project potential population—level effects of the use of turtle excluder devices (TEDs) in trawl fisheries of the southeastern US. We reduced the seven—stage model of Crouse et al. (1987) to a five—stage model and performed sensitivity analyses on the matrix. The most sensitive matrix parameters were those dealing with survival while remaining in a stage, rather than growth from one stage to the next or reproductive output. Population growth rate was most sensitive to survival in the large juvenile stage, followed by small juvenile survival. Large juveniles are the most common size class among stranded dead turtles found on beaches; 70—80% of strandings are thought to be related to trawl fisheries. Simulations of our loggerhead model based on estimated effects of TED regulations on stage—specific survivorship suggested that southeastern US loggerhead populations should increase, but rather slowly. If TEDs were required during the shrimping season in offshore areas only (as they were from 1990 to 1992), 70 yr or more would be required for the simulated population to increase by an order of magnitude. Recent estimates of TED effects from South Carolina strandings data suggest a similar recovery rate. Good compliance with regulations requiring TEDs year—round in all waters could allow the population to increase nearly twice as fast as that expected under the "seasonal offshore" regulations. We also used a Leslie matrix version of the model to illustrate the expected transient response in the numbers of females expected on nesting beaches (due to shifting age—size structures with TED use). Rather than a monotonic increase, we expect an initial increase in the number of nesting females, followed by a leveling off or slight decline (perhaps 10—15 yr from now), followed by another increase. The magnitude of the projected population increase will depend upon the actual increases in stage—specific survivorship due to TED regulations. New, or compensatory, sources of mortality could slow or reverse this projected recovery.

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 m 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 m), 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.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology. Abstract. We designed a field experiment to examine predator interactions-in particular, the effect of each predator on the growth and survival of the other, and to examine the effects of predation on prey assemblages-in particular, predation effects by each predator alone as well as together. Blue crabs (Callinectes sapidus) and the fish, spot (Leiostomus xanthurus), co-occur in Southeastern estuaries of the USA, and share many prey taxa and habitat types. We predicted that the blue crabs and spot would suffer both interference and exploitation competition when held together in enclosures. We also predicted that, as a consequence of the competitive interactions, their joint impact on prey assemblages would be different from that predicted based on the impact when held alone.We installed mesh enclosures in an existing earthen pond after allowing it to be filled with water from Bogue Sound, North Carolina, and to be colonized by the naturally occurring species assemblage. A factorial design was used to allow us to test for nonadditive effects of the two predators on their prey assemblage. Contrary to our predictions, we found that spot survival was enhanced in the presence of blue crabs. This enhancement was probably effected by removal of the alga Enteromorpha intestinalis by the crabs. The alga was positively affected by spot. The positive effect of spot on Enteromorpha, and the negative effect of crabs, was probably responsible for differences in densities and distributions of prey taxa within the enclosures. Significant interaction terms in our analysis suggest that community response to either predator is not independent of the other. Our data suggest that we cannot expect to explain adequately the effects of multi-species predator assemblages on their prey by combining information obtained through single-predator experiments.

The cueing program intervention is acceptable and participants feel they improve; however, this small feasibility study lacks statistical power to detect important changes in falls rates or FOG severity. A larger study is warranted to further investigate the potential to influence FOG and falls.Video Abstract available for more insights from the authors (Supplemental Digital Content 1, http://links.lww.com/JNPT/A105).