Animals aggregate to reduce predation risk, facilitate mating, and access resources with patchy distributions. During a long-term study of turtle populations in the Santa Fe River (SFR) ecosystem in northern Florida, we observed a large aggregation of turtles at Gilchrist Blue Springs Park (GBSP) in August–October 2013 and again in March–May 2014. On 8 September 2013, we hand-captured 496 turtles of 5 species in GBSP. The Suwannee cooter (Pseudemys concinna suwanniensis) was the most abundant species in the sample, with 477 individuals representing all demographic groups. Density of this species was 530 turtles/ha and biomass was 2242 kg/ha. We hypothesize that hydrological changes in the SFR basin contributed to the temporary turtle aggregations at GBSP. The 113-km SFR originates as a tannin-stained blackwater stream, but receives input of clear water from ≥ 45 artesian springs in its lower 37 km. Heavy rainfall in the upper SFR basin from Tropical Storm Debby in June 2012 resulted in a large influx of tannic water that overwhelmed the capacity of the springs to dilute the river water. This storm in combination with additional episodes of heavy rainfall and declining spring flows led to an unusually long (34-mo) tannic period in the typically clear lower 37 km of the SFR. The resulting loss of most submerged aquatic macrophytes in the river due to insufficient sunlight may have been the stimulus that led the herbivorous P. c. suwanniensis to seek food in one of the few locations that had abundant submerged aquatic vegetation in 2013 and 2014. Turtles previously marked upriver (to 16 km) and downriver (to 4.6 km) from GBSP were in the aggregation, suggesting the individuals gathered at GBSP represented a large portion of the SFR P. c. suwanniensis population.

The nesting ecology of Apalone spinifera in large North American rivers is largely unknown despite the wide distribution of the species in these naturally dynamic ecosystems. We describe the nesting locations, timing, behavior, and habitat of A. spinifera in relation to natural and anthropogenic factors in the Missouri River. Nesting followed annual peak river stage, mostly occurred in the afternoon when air temperatures were 25°–30°C, and did not occur when human activity was nearby. Apalone spinifera nested in June in a year with average discharge (2012), but nested 20 d later in a year with a large flood event (2011). During the average discharge year, 90% of nests were found on islands, but similar proportions of nests were found on island and mainland habitats during the flood year because many islands were inundated. Nests were mostly in mixed-gravel substrates where vegetation cover was sparse or absent. Depredation occurred only after the emergence of hatchlings (∼ 60 d after nesting) and more often on nests on the mainland than on islands. Emergence rates were ∼ 1.5 times higher in the average year than the flood year, and emergence rates were higher in mixed-gravel nests than in pure-sand nests in 2011. In artificial nests, incubation temperatures averaged ∼ 4.3°C higher in mixed-gravel than in sand substrates, and freezing temperatures in winter penetrated to depths greater than the mean egg chamber depth (7.5 cm) for up to 3 wks. Therefore, incubation might be accelerated in mixed-gravel substrates. Accelerated incubation would enhance reproductive success because freezing temperatures preclude hatchlings from overwintering in nests in our study area. Mountain snowmelt-driven hydrology, coupled with the onset of freezing temperatures in autumn, might create a temporal “runoff-freeze squeeze” that limits the successful reproduction of A. spinifera in some years. However, high runoff also scoured vegetation from shorelines where A. spinifera nested in subsequent years. Natural variation in annual discharge might therefore be crucial to conservation of A. spinifera in large rivers.

A spatially explicit participatory approach was used to collect fishing effort and sea turtle bycatch data from local fishers at 15 ports in the Yucatan Peninsula, Mexico. These data were combined with satellite telemetry data to define potential bycatch hotspots. This is the first participatory and spatially explicit study on sea turtle bycatch rates in the region. Hawksbill turtles (Eretmochelys imbricata) were the most frequently caught bycatch species, followed by loggerheads (Caretta caretta) and green turtles (Chelonia mydas). Gillnets were the most dangerous for sea turtles, with the greatest incidence of dead turtles caught. Three particular bycatch hotspots were identified at the northeast, northwest, and southwest coasts of the peninsula. Identification of bycatch hotspots is recognized worldwide as a key element for protecting these endangered species, particularly in a region such as the Yucatan Peninsula that harbors critical habitats for ≥ 4 sea turtle species, 2 of them categorized as critically endangered (hawksbills and Kemp's ridleys [Lepidochelys kempii]). The spatially explicit participatory approach is versatile, easy to implement, and strategic for generating information under marine spatial planning for endangered species conservation.

The hawksbill turtle (Eretmochelys imbricata) is a critically endangered species with a global distribution and is broadly distributed along the Yucatan Peninsula in the Gulf of Mexico. To complete its life cycle, this species uses sandy beaches with particular environmental conditions that facilitate nesting and hatching. This study aimed to identify if beach physical characteristics influence biological reproductive parameters (hatching and emergence success). Nesting activity was monitored along 18 km of beach in the state of Campeche, Mexico, during 2014. Seventy-eight nests were recorded, 12 physical and environmental variables were measured in the nests and contiguous areas, and the hatching and emergence success of each nest was determined. Beach slope and width had no significant relationship to nest site selection. Nest depth and nest distance to highest tide and vegetation, including vegetation type, did influence hatching and emergence success. Herbaceous and bushy plants were positively correlated with reproductive parameters, highlighting the importance of preserving beach vegetation cover. This parameter was a central structural component of hawksbill nesting habitat, possibly because it influenced nest shading, preventing egg overheating and possible embryo death. Preservation and restoration of vegetation structure on hawksbill nesting beaches is clearly vital to enhancing the reproductive success of this species.