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- Sex ratios of loggerhead sea turtles Caretta caretta during the juvenile pelagic stagePublication . Delgado, ClĂĄudia; CanĂĄrio, 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 subadultsâ 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, ClĂĄudia; 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, JoĂŁo; Dellinger, Thomas; Pinho, MĂĄrio 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 (CLâ) and growth coefficient (K) showed higher values in females (CLâ=30.21 mm, K=0.450 year-1 ) comparatively to males (CLâ=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.
- Abundance and population structure of Plesionika narval (Fabricius, 1787) in the Northeastern AtlanticPublication . Sousa, R.; Pinho, M. R.; Delgado, J.; Pinto, A. R.; Biscoito, M.; Dellinger, T.; Henriques, P.Analysis of abundance and population structure of Plesionika narval was performed on data concerning 5,255 specimens obtained from 62 fishing sets carried out off the Madeira archipelago (Northeastern Atlantic) between 2004 and 2008 in a depth range from 101 to 350 m. Abundance ranged from 0.01 to 19.74 specimens-per-trap and significant differences were found between seasons, probably as a result of an increment of population in the spring during the recruitment season. The analysis of size distribution revealed that the carapace length (CL) ranged from 2.45 to 28.61 mm and that mean female size consistently exceeded that of males. Differences in mean CL were statistically significant between depth strata and seasons. Of the specimens sampled, 57.00% were males, 41.88% females and 1.42% undetermined. Sex ratio also differed significantly between seasons according to depth strata, consolidating the hypothesis of the existence of seasonal migrations related with the reproductive cycle of this species. Ovigerous females showed larger sizes and occurred all year around and remain in shallow waters in winter, summer and autumn and move to deeper waters in spring. The highest frequency of ovigerous females was recorded in summer, between 151 and 200 m deep supporting the hypothesis that spawning of this species occurs in shallow waters, especially in late summer.
- Estimating diet composition from scat analysis in otariid seals (Otariidae): is it reliable?Publication . Dellinger, T.; Trillmich, F.Analysis of teleost sagittal otoliths contained in scats has been widely used to determine the diet of seals. This method is based on the assumption that relative frequencies of otoliths in scats faithfully reflect those of fish in the diet. This assumption has rarely been tested experimentally. We compared the ratios of herring (Clupea harengus) to sprat (Sprattus sprattus) oto liths in faeces (output) of captive California sea lions (Zalophus calijornianus) and South American fur seals (Arctocephalus australis) with the ratios at feeding (input). Sea lions and fur seals showed no consistent differences in recovery rates and partial digestion of otoliths. Output ratios deviated only slightly from input ratios, the smaller sprat otoliths being underrepre sented in the output by 8%. Only about 40% of the otoliths fed to the seals were found in the scats. For both species partial digestion of otoliths led to a 16% underestimation of fish length and a 35% underestimation of fish mass.
- 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; PatrĂcio, Ana Rita; Catry, Paulo; Dellinger, Thomas; Granadeiro, JosĂ© 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 (ÎŽ15N=8.5±0.6â° SD) compared to the group of turtles captured alive in the same period (ÎŽ15N=7.6±0.5â° 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 ÎŽ15N 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.
- Foraging behavior of juvenile loggerhead sea turtles in the open ocean: from LĂ©vy exploration to area-restricted searchPublication . Freitas, C.; Caldeira, R.; Reis, J.; Dellinger, T.Most sea turtle species spend part of, or their entire juvenile stage in pelagic habitats. A key question is how pelagic turtles exploit their environment to optimize prey intake and max imize fitness. This study combined animal telemetry with remote-sensed environmental data to quantify the drivers and patterns of foraging behavior of juvenile loggerhead sea turtles in the pelagic eastern North Atlantic. Juveniles ranged in size from 34 to 58 cm straight carapace length. First-passage time (FPT) analysis, used to quantify search effort, indicated that turtles performed area-restricted searches at nested spatial scales of 10 and 50 to 200 km. High-usage areas, as quantified by FPT, were associated with increased dive activity and weak surface currents, as well as with oceanographic features (high chlorophyll a and shallower bathymetry) thought to stimu late prey availability. Conversely, low-usage areas (i.e. transit areas) were associated with deep, probably exploratory dives, typical from LĂ©vy movement patterns. Further interpretation of dive data indicates greater dive activity in shallow depths (0 to 10 m) during the night and during tran sit. Conversely, greater activity at intermediate depths (10 to 50 m) was observed during daytime, under strong lunar illumination and in high-usage areas, suggesting these depths are major day time foraging layers. This study clarifies the foraging ecology of sea turtles during their develop ment phase in the open sea, providing evidence that these pelagic predators can adjust their for aging strategies and effort in response to the local conditions of their dynamic environment.
- 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.
- Esforço, custos e benefĂcios da reprodução em iguanas marinhasPublication . Dellinger, Frank Thomas Ussener