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- Sex ratios of loggerhead sea turtles Caretta caretta during the juvenile pelagic stagePublication . Delgado, Cláudia; Canário, Adelino V. M.; Dellinger, ThomasSex ratios are a fundamental trait for species reproduction. In species with temperature-dependent sex determination (TSD), sex ratios are not necessarily even, which has important demographic consequences. We examined the sex ratio of juvenile pelagic stage loggerhead turtles Caretta caretta offshore Madeira Island, North Eastern Atlantic, using laparoscopy and histology. The overall sex ratio was 2:1 (F:M), significantly different from an even sex ratio. Although there was no apparent temporal variation, sex ratios among size classes were significantly different. The sex ratio of juveniles was compared with known sex ratios for the putative source rookery and found to be similar to the subadults’ sex ratio, but significantly less female-biased than the hatchlings sex ratio. This sug gests overestimation of hatchlings sex ratios and/or, less likely, differential mortality of females during the first months of life. Alternatively, the Madeira Island aggrega tion may be recruiting males from other geographical sources such as the Mediterranean and the Cape Verde.
- Compensatory growth in oceanic loggerhead sea turtles: response to a stochastic environmentPublication . Bjorndal, Karen A.; Bolten, Alan B.; Dellinger, Thomas; Delgado, Cláudia; Martins, Helen R.Compensatory growth (CG, accelerated growth that may occur when an organism that has grown at a reduced rate as a result of suboptimal environmental conditions is exposed to better conditions) is considered an adaptation to variable en vironments. Although documented thoroughly under captive conditions, CG has rarely been studied in wild populations. In their first years of life, oceanic-stage loggerhead sea turtles (Caretta caretta) have relatively little control over their geographic position or movements and thus have an extremely stochastic lifestyle with great variation in food availability and temperature. This environmental variation results in variable growth rates. We evaluate somatic growth functions of oceanic-stage loggerheads from the eastern Atlantic based on skeletochronology that allowed us to assign age and cohort to each individual. We demonstrate CG in these turtles based on three different analytical approaches: changes in coefficients of variation in size-at-age, generalized additive model regression analyses of somatic growth, and linear regression of age-specific growth rates. As a result of CG, variation in size-at-age in these juvenile loggerheads is substantially reduced. Thus, size is a better predictor of age than expected based on variation in growth rates. CG decreases with age, apparently as loggerheads gain greater control over their movements. In addition, we have evaluated for the first time in wild sea turtles the time-dependent nature of somatic growth by distinguishing among age, year, and cohort effects using a mixed longitudinal sampling design with assigned-age individuals. Age and year had significant effects on growth rates, but there was no significant cohort effect. Our results address critical gaps in knowledge of the demog raphy of this endangered species.
- Considerations on the biology of Plesionika narval (Fabricius, 1787) in the Northeastern AtlanticPublication . Sousa, Ricardo; Henriques, Paulo; Biscoito, Manuel; Pinto, Ana Rita; Delgado, João; Dellinger, Thomas; Pinho, Mário RuiLife history traits of Plesionika narval were studied in the Northeastern Atlantic, Madeira archipelago including growth, age, sexual maturity, recruitment pattern and mortality. A total of 28,262 specimens were sampled over a period of 8 years comprising two time series from 1991 to 1995 and 2004 to 2008. The relative growth pattern showed a negative allometric nature of growth for combined sexes, males, females, non ovigerous and ovigerous females. Estimated asymptotic carapace length (CL∞) and growth coefficient (K) showed higher values in females (CL∞=30.21 mm, K=0.450 year-1 ) comparatively to males (CL∞=28.61 mm, K=0.430 year-1 ), resulting in better overall growth performance in females. The maximum life span (tmax) was estimated at 6.81 years for combined sexes, 6.97 for males and 6.66 for females, however 99.95% of the individuals were younger than 3 years. Although a seasonal spawning season was evident from late summer to late autumn, reproduction may be prolonged throughout the year since ovigerous females are present in all months and achieving sexual maturity at 14.61 mm. The recruitment pattern was continuous throughout the year with a major peak occurring in spring. The total mortality (Z) and fishing mortality (F) were higher in females than in males while natural mortality (M) was similar between groups.
- Transatlantic developmental migrations of loggerhead sea turtles demonstrated by mtDNA sequence analysisPublication . Bolten, Alan B.; Bjorndal, Karen A.; Martins, Helen R.; Dellinger, Thomas; Biscoito, Manuel J.; Encalada, Sandra E.; Bowen, Brian W.Molecular markers based on mitochondrial (mt) DNA control region se quences were used to test the hypothesis that juvenile loggerhead sea turtles (Caretta caretta) in pelagic habitats of the eastern Atlantic are derived from nesting populations in the western Atlantic. We compared mtDNA haplotypes from 131 pelagic juvenile turtles (79 from the Azores and 52 from Madeira) to mtDNA haplotypes observed in major nesting colonies of the Atlantic Ocean and Mediterranean Sea. A subset of 121 pelagic samples (92%) contained haplotypes that match mtDNA sequences observed in nesting colonies. Maximum likelihood analyses (UCON, SHADRACQ) estimate that 100% of these pelagic juveniles are from the nesting populations in the southeastern United States and adjacent Yucatan Peninsula, Mexico. Estimated contributions from nesting populations in south Florida (0.71, 0.72), northern Florida to North Carolina (0.19, 0.17), and Quintana Roo, Mexico (0.11, 0.10) are consistent with the relative size of these nesting aggregates. No contribution was detected from nesting colonies in the Mediterranean (Greece) or South Atlantic (Brazil), although samples sizes are insufficient to exclude these locations with finality. The link between west Atlantic nesting colonies and east Atlantic feeding grounds provides a more complete scientific basis for assessing the impact of subadult mortality in oceanic fisheries. Demographic models for loggerhead turtles in the western Atlantic can now be improved by incorporating growth and mortality data from juvenile turtles in pelagic habitats. These data demonstrate that the appropriate scale for loggerhead turtle conservation efforts is vastly larger than the current scale of management plans based on political boundaries.
- Evidence for trophic differences between live and bycatch oceanic juvenile loggerhead sea turtlesPublication . Raposo, Cheila; Patrício, Ana Rita; Catry, Paulo; Dellinger, Thomas; Granadeiro, José P.The loggerhead sea turtle Caretta caretta is a vulnerable migratory species that spends its frst years of life in the open sea. During this developmental phase, loggerheads can be found foraging in the epipelagic zone of the waters surrounding the Madeira Archipelago, providing a rare opportunity to gather information on the ecology of its oceanic developmental stage. In this study, we characterized the isotopic niche of these juveniles, using stable isotope analysis. We assessed two groups of turtles, turtles captured alive (n=24) and turtles captured as bycatch on local longlines (n=12), and explored whether animals caught in the local fshing gear represented a random sample of the population, or whether there is some evidence for a specialized foraging behaviour. We found that turtle bycatch had a signifcantly higher mean stable nitrogen isotope value in whole blood (δ15N=8.5±0.6‰ SD) compared to the group of turtles captured alive in the same period (δ15N=7.6±0.5‰ SD), indicating that they had a diferent diet. While there was a tendency for turtle bycatch to be slightly larger, we found no efect of body size on δ15N values. We propose a distinct foraging behaviour strategy hypothesis, with a group of turtles being more susceptible to interactions with fsheries and thus having a higher mortality risk, which should motivate the implementation of existing guidelines to reduce sea turtle bycatch.
- Prospective study of the fishery of the shrimp Plesionika narval (Fabricius, 1787) in the Northeastern AtlanticPublication . Sousa, R.; Pinho, M. R.; Delgado, J.; Biscoito, M.; Pinto, A. R.; Dellinger, Thomas; Gouveia, L.; Carvalho, D.; Henriques, P.Several experimental surveys were carried out in the Northeastern Atlantic, Madeira archipelago from 1991 to 2008 to explore new fisheries resources. This study examined the selectivity of bottom and floating traps and the analysis of yield-per-recruit (YPR) and biomass-per-recruit (BPR) providing helpful insight to the management of the shrimp Plesionika narval. A total of 28,262 specimens were sampled and the analysis of length at first capture returned higher values when using floating traps indicating that these traps are more selective, exerting less pressure on the resource. The YPR and BPR analysis showed that the stock is under exploited for the studied area and suggests that the use of floating traps in the commercial fisheries of P. narval is recommended, which will allow a higher maximum allowable limit of exploitation and greater yield. The results suggest that P. narval has the potential to support a viable and sustainable fishery using floating traps.
- Fish prey of the sympatric Galápagos fur seals and sea lions: seasonal variation and niche separationPublication . Dellinger, Thomas; Trillmich, FritzAnalysis of fish otoliths in scats and vomits of Galápagos fur seals (Arctocephalus galapagoensis) and Galápagos sea lions (Zalophus californianus wollebaeki) was used to determine the numerical composition of the diets for the post-El Niño year 1983, the cold seasons in 1984 and 1985, and the warm season in 1986. Between 84 and 99% of all otoliths in fur seal scats were from myctophids and bathylagids. The fur seals’ diet included 26 species. Only 3 species contributed more than 1% of otoliths. No seasonal differences in diet were found. Sea lion samples contained a mean of 14 otoliths. Sardines (Sardinops sagax) contributed 75–85% of otoliths. Sea lions preyed on 24 species, but only 3 surpassed 1% abundance. Seasonality was not reflected in the sea lions’ diet. After the 1982–1983 El Niño, the diets of both species deviated from those in all other years of the study. Food-niche overlap between the two sympatric species was almost non-existent. This is hard to understand, based on our knowledge of the diving capabilities of the two species, but reflects the fact that Galápagos fur seals are nighttime foragers and sea lions are daytime foragers.
- Larval cestodes infecting the deep-water fish, Cataetyx laticeps (Pisces: Bythitidae) from Madeira Archipelago, Atlantic OceanPublication . Costa, Graça; Khadem, Mahnaz; Dellinger, Thomas; Biscoito, Manuel; Moreira, Egberto MeloParasites of deep-water fishes are less known in comparison to the parasites of fishes living in the demersal and epipelagic ocean zones. In the present research note we report the occurrence of larval trypanorhynch cestodes in a rare deep-water fish, the deep-water brotula, Cataetyx laticeps. Based on the 28S rDNA (region D1-D3) sequence homology and the phylogenetic analysis, the larval cestodes are putatively assigned to the genus Grillotia. It is suggested that the definitive host of this trypanorhynch is a batoid.
- Surface behavior of pelagic juvenile loggerhead sea turtles in the eastern North AtlanticPublication . Freitas, Carla; Caldeira, Rui; Dellinger, ThomasSea turtles bask at the ocean surface, but little is known about the patterns and ecological context of surface behavior in the wild. This study investigated the surface behavior of ten juvenile loggerhead sea turtles (34 - 58 cm straight carapace length) satellite tagged in Madeira, in the pelagic eastern North Atlantic. During a total of 2273 tracking days, turtles moved through oceanic areas with a mean depth of ~3400 m. On average, turtles spent one third of the time at the surface (0 - 1 m depth), spending 43% of the time at the surface during the day and 29% of the time during the night. Generalized linear mixed modelling showed that the proportion of time at the surface was significantly larger during the day, particularly during spring and summer. Time spent at the surface during the day increased with elevated air temperatures and weak winds, probably to maximize the benefits of solar absorption. Conversely, the probability of being at the surface during the day decreased as horizontal search effort increased, suggesting a trade-off between basking and daytime foraging activities. At night, time spent at the surface was not associated with air temperature or wind speed but was instead positively associated with moon illumination. As turtles tend to dive deeper during clear nights, increased surface time may be needed to recover from deeper dives. This study presents important aspects of the behavioral ecology of the species during the oceanic juvenile phase. The findings reported here may be relevant for species management and conservation, including correction of census data and management of interactions with surface fishing gear and other anthropogenic activities.
- Identification of likely foraging habitat of pelagic loggerhead sea turtles (Caretta caretta) in the North Atlantic through analysis of telemetry track sinuosityPublication . McCarthy, Abigail L.; Heppell, Selina; Royer, Francois; Freitas, Carla; Dellinger, ThomasChanges in the behavior of individual animals in response to environmental characteristics can provide important information about habitat preference, as well as the relative risk that animals may face based on the amount of time spent in hazardous areas. We analyzed movement and habitat affinities of ten log gerhead turtles (Caretta caretta) tagged with satellite transmitters in the spring and fall of 1998 near Madeira, Portugal for periods of 2–10 months. We analyzed the behavior of these individuals in relation to the marine environment they occupied. As a measure of behavior we calculated the straightness index (SI), the ratio of the displacement of the animal to the total distance traveled, for individual weekly seg ments of the 10 tracks. We then extracted information about chlorophyll a concentration, sea-surface temperature (SST), bathymetry, and geostrophic current of the ocean in a 20-km buffer surrounding the tracks, and examined their relationship to the straightness index using generalized linear models. Chlorophyll a value, bathymetry and SST were significantly related to the straightness index of the tracks of all ten animals, as was the circular standard deviation of the geostrophic current (Wald’s test: p = 0.001, p = 0.008, p = 0.025, and p = 0.049, respectively). We found a significant negative relationship between straightness index and chlorophyll, and positive relationships with ocean depth and SST indicat ing that animals are spending more time and searching more thoroughly in areas with high chlorophyll concentrations and in areas that are shallower, while moving in straight paths through very warm areas. We also found a positive relationship between straightness index and the circular standard deviation of surrounding geostrophic currents suggesting that these turtles are more likely to move in a straight line when in the presence of diffuse, less-powerful currents. Based on these relationships, we propose that conservation planning to reduce overlap of turtles with fishing operations should take into account the locations of bathymetric features such as seamounts and upwelling locations where chlorophyll concen trations are high. This analysis is an effective way to characterize areas of high-use habitat for satellite tagged marine vertebrates, and allows for comparisons of these characteristics between species and among individuals.