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Background: Transcriptomic data has demonstrated utility to advance the study of physiological diversity and organisms' responses to environmental stressors. However, a lack of genomic resources and challenges associated with collecting high-quality RNA can limit its application for many wild populations. Minimally invasive blood sampling combined with de novo transcriptomic approaches has great potential to alleviate these barriers. Here, we advance these goals for marine turtles by generating high quality de novo blood transcriptome assemblies to characterize functional diversity and compare global transcriptional profiles between tissues, species, and foraging aggregations. Results: We generated high quality blood transcriptome assemblies for hawksbill (Eretmochelys imbricata), loggerhead (Caretta caretta), green (Chelonia mydas), and leatherback (Dermochelys coriacea) turtles. The functional diversity in assembled blood transcriptomes was comparable to those from more traditionally sampled tissues. A total of 31.3% of orthogroups identified were present in all four species, representing a core set of conserved genes expressed in blood and shared across marine turtle species. We observed strong species-specific expression of these genes, as well as distinct transcriptomic profiles between green turtle foraging aggregations that inhabit areas of greater or lesser anthropogenic disturbance. Conclusions: Obtaining global gene expression data through non-lethal, minimally invasive sampling can greatly expand the applications of RNA-sequencing in protected long-lived species such as marine turtles. The distinct differences in gene expression signatures between species and foraging aggregations provide insight into the functional genomics underlying the diversity in this ancient vertebrate lineage. The transcriptomic resources generated here can be used in further studies examining the evolutionary ecology and anthropogenic impacts on marine turtles. [ABSTRACT FROM AUTHOR]

Data characterizing somatic growth patterns and the ages and sizes at which organisms mature are fundamental to understanding population dynamics. However, obtaining this information for endangered leatherback sea turtles (Dermochelys coriacea) is particularly challenging due to unusual physiology and prevalence of remote oceanic habitat use, which limit direct observation. While inference has been made through indirect approaches such as captive, genetic, and/or skeletal growth mark (skeletochronology) studies, these diverse methods have yielded similarly varied results, limiting usefulness of available information for management and conservation. To address this data gap, we conducted refined skeletochronological analysis of Atlantic and Pacific leatherback scleral ossicle bones, allowing estimation of carapace length-at-age relationships throughout individual turtles' lives, including the juvenile life stage. In addition, this improved approach made it possible to estimate mean and range for age and size at sexual maturation (ASM and SSM, respectively), as well as post-maturation longevity. Updated mean ASM estimates from the current study of 17–19 years were lower than those previously proposed using skeletochronology and more similar to predictions from captive growth and genetic data. Maximum estimates of reproductive longevity (18–22 years) were consistent with the 16–19 years reported previously from mark–recapture of nesting females. Together, these results indicate that the application of the refined analytical approach described in the current study may offer opportunities to increase understanding of leatherback age and growth. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Temperatures at local scales were best able to predict turtle presence. • Temperatures at intermediate and broad spatial scales had lower efficacy. • Capturing the persistence of temperatures was important to predicting turtle presence. • Warm water events independent to El Nino (e.g. "the Blob") can affect turtle presence. • The indicator successfully balanced fishery opportunity costs and bycatch avoidance. Abstract Extreme climatic events are expected to become more frequent under current conditions of increasing global temperatures and climate variability. A key challenge of fisheries management is understanding and planning for the effect of anomalous oceanic conditions on the distributions of protected species and their interactions with fishing gear. Atypical marine states can cause non-target species to shift outside of their normal distribution patterns, leading to unwanted bycatch events that threaten fisheries sustainability. Environmental indicators can serve as early warning signals that allow for proactive management responses before significant bycatch occurs. Marine heatwaves in the Pacific have caused shifts in the distributions of endangered loggerhead turtles (Caretta caretta) , increasing overlap with California's Drift Gillnet fishery and thereby the risk of turtle bycatch events. To reduce bycatch, a fishery closure offshore of Southern California – The Loggerhead Conservation Area – Is enacted when an El Niño event has been declared and local sea surface temperatures (SSTs) are warmer than normal. However, this regulation was based on qualitative assessment of bycatch that occurred during past El Niño events, and no explicit threshold for SST anomalies was defined. Additionally, closures enacted under the current regulation rely on structured expert decision-making. Providing a quantitative indicator could help to refine future decisions. We developed and evaluated potential new indicators to guide the Loggerhead Conservation Area closure timing based on thermal indices in three different regions: the equatorial Pacific, regional areas offshore of Southern California, and temperate pelagic areas off the US west coast. Our objectives were to: 1) quantify thermal indicators and their respective thresholds to guide closure timing, and 2) hindcast closure scenarios based on these indicator thresholds to evaluate efficacy in terms of opportunity costs to fishers and ability to avoid turtle interactions. The best indicator in terms of avoiding historical turtle interactions while minimizing opportunity cost to fishers was a six-month average local SST anomaly indicator with closures enacted above a threshold of 0.77 °C. This result can improve upon the current closure guidelines by providing a quantified and spatially-explicit indicator and threshold to supplement the structured decision-making process. Our analysis demonstrates a novel approach to developing fisheries management strategies for species with a paucity of data. Issues with data comprehensiveness are frequently present in fisheries management exercises, and precautionary approaches are needed to allow adherence with legislation while considering the best available science. [ABSTRACT FROM AUTHOR]