NOAA National Marine Fisheries Service Southeast Fisheries Science Center

BackgroundJuvenile loggerhead sea turtles represent a crucial but understudied stage of the species life cycle. Most studies have been conducted at regional scales and there remains a need for a broader scale synthesis. In the North Atlantic, loggerheads encounter numerous threats such as fishing during their transoceanic journey, so it is important to get a broad view of their distribution, movement and habitat preferences.MethodsFor this study, we gathered tracking data from 124 juvenile loggerheads tagged along the Azores, Canary Islands, Madeira and in the western North Atlantic to develop a habitat model for the entire basin. We used a SSM to interpolate tracks to daily positions, simulated pseudo-absences with a correlated random walk for background data, and explored 17 environmental variables using boosted regression trees to select the best model in terms of biological realism and predictive power. The best model obtained (AUC = 0.988) was then used to predict habitat suitability for the North Atlantic for the period 1998–2022. Stranding records of loggerheads in France, UK and Ireland were used to discuss the predictions.ResultsAfter filtering, tracks of 105 individuals, covering most of the basin, were used in the model. Our predictions of habitat suitability show the importance of the Gulf Stream and the Azorean Current. Habitat suitability is predicted to be higher in the area between 30° and 45°N all year round, while open waters below 30°N, including Cape Verde, are not predicted to be a suitable habitat. In northern and eastern areas, like the Bay of Biscay and UK and Irish waters, habitat suitability varied seasonally, with colder seasons showing lower values. Accordingly, strandings in those areas occurred mostly during winter (December-February; 45.1%) and spring (March-May; 34.1%).ConclusionsThe model offers a first basin-scale prediction of the seasonal distribution of juvenile loggerheads in the North-Atlantic, which shows consistency with stranding and bycatch data in the basin. This study represents a first step towards a broader scale understanding of juveniles’ habitat preferences that can be used to quantify the magnitude and extent of the threats that they face.Supplementary InformationThe online version contains supplementary material available at 10.1186/s40462-026-00640-2.

We evaluated 13 years of fishery-independent small juvenile (< 1.86 m stretch total length) endangered smalltooth sawfish sampling data from southwest Florida’s Charlotte Harbor estuarine system. From 2010 through 2022, within the sampling domain, estimated abundance declined, with an annual average across all seasons of 34 ± 11 individuals (range: 15–69). High-use areas were spatiotemporally stable and associated with well-oxygenated (dissolved oxygen > 7 mg/L), warm (25–33 °C), and brackish (salinity 5–27) waters between 5 and 15 km upriver along natural shorelines with concentrations of mangroves in both riverine nurseries. Adult female abundance, back-calculated from expected brood size (48 ± 16, range: 26–144) and stable age distribution (87 ± 30, range: 39–211), was low. Our findings of a significant declining trend in relative abundance of small juveniles and limited numbers of adult females are concerning considering ongoing threats from commercial shrimp trawl bycatch, destruction of nursery habitats, and major recent mortality events. Our model facilitates estimation of the number of individuals potentially exposed to harmful anthropogenic activities and identifies perennial high-use areas as priorities for permanent protection from habitat alterations and loss to promote recovery of the endangered smalltooth sawfish population in this unique estuarine system.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-025-14430-0.

The design of experiments to investigate the combined effects of multiple stressors requires exposing target organisms to multiple combinations of stressor doses. Concurrent manipulation of stressors is often infeasible with wildlife, but long-lasting health effects allow individual health to be used as an integrator of prior stressor exposure. The population of bottlenose dolphins in Barataria Bay, Louisiana, experienced long-lasting health effects after exposure to oil from the Deepwater Horizon spill. We investigated whether compromised health status affects dolphins' ability to respond to other stressors, specifically vessel traffic, potentially leadingto increased collision risk. We used this case study to develop a hypothesis-driven experimental approach to assess the combined effects of multiple stressors in a large, long-lived vertebrate species. We conducted controlled vessel approaches to test whether the health status of targeted dolphins affected their behavioral responses. Our results highlighted some effects of health, suggesting that oil spills may exacerbate the effects of other stressors in coastal populations. For example, lung disease was associated with a delayed dive response, which could affect the ability to vertically avoid vessels and lead to increased collision risk. However, health effects on response probability were overall smaller than anticipated, and other contextual variables (e.g., sex, age, calf presence, prior experience, and exposure context) contributed to response variability. Our work demonstrated the value of formalizing stressor interactions as multidimensional dose-response functions and showed the feasibility of an experimental, multiple-stressor study in a wild system in which individual health status can be used as an integrator of prior stressor exposure. This approach has broad implications for other species that are difficult to handle experimentally. The quantification and management of the cumulative risk from multiple stressors on wildlife will require a combination of empirical and mechanistic approaches to inform long-term, population consequences.

ABSTRACT Cetacean skin microbiome samples are traditionally collected by swabbing the skin of captured animals or using skin tissue from remote biopsies. The effects of different sampling methods are not well understood, and factors such as swab type and storage methods may affect the microbiome. The objective of this study was to determine if samples collected by swabbing biopsied skin from bottlenose dolphins yield sufficient microbial DNA for gene sequencing, while testing if commonly used sampling and storage methods affect the skin microbiome. Skin swab samples were collected during remote biopsy surveys with either a nylon flocked swab and flash frozen with liquid nitrogen or with a cotton swab and stored in RNAlater. Sequencing of the V3–V4 region of the 16S rRNA gene revealed swabs from dolphin skin biopsies yielded sufficient DNA to characterize the microbiome. We found no significant difference between the two sampling and storage methods tested, suggesting that studies using different techniques may be comparable. This work also demonstrates a novel technique to collect samples for interpretation of the skin microbiome of free‐ranging animals. Benefits of this method are that it can be done without capture and preserves valuable and typically scarce biopsy skin samples for other analyses.

Abstract In an era of increasing disturbances, understanding the capacity for coral reefs to recover and the drivers that underpin resilience is critical for predicting the health of future coral reefs. Traditional resilience paradigms for Western Atlantic reefs suggest that high herbivore biomass and low macroalgal cover are tenets of resilient systems. Yet, it is clear that some locations, such as Florida’s reefs, and potentially other locations, are not well explained by this paradigm. Here, we suggest that the proliferation and increased dominance of long-sediment-laden algal turfs (LSATs) create an additional negative feedback process that helps explain the compromised resilience of Florida’s reefs and further extends the existing Western Atlantic model. Collectively, coral mortality, reef flattening, and intense grazing appear to have created a series of negative feedback processes that reinforce a flat, sediment-laden benthos that impedes the recovery of already diminished coral populations. Importantly, feedbacks associated with LSATs could be strengthened in the presence of high herbivore biomass, thereby undermining foundational expectations of resilience based on grazing pressure alone. Here, we outline this destructive cycle and provide support for the mechanisms that drive these feedbacks. Although we focus on the ecological context of Florida’s reefs, our expansion of the conceptual framework will likely apply to other reef systems in the Caribbean with similar ecological attributes. Mounting evidence suggests that LSAT dominance represents a novel ecosystem state for Western Atlantic reefs.

Abstract The stable isotope ratio of oxygen (δ 18 O) stored in otoliths is a common and reliable tool for studying life history events including natal origin and migratory behavior of marine fish species. This approach is useful particularly in cases where traditional tagging is impossible, such as in early larval stages. However, small amounts of available otolith material have historically precluded analysis of δ 18 O in individual larval otoliths by traditional isotope ratio mass spectrometer (IRMS). The use of secondary ion mass spectrometer (SIMS) resolves this challenge, allowing users to obtain δ 18 O signatures in otoliths at the scale of tens of microns. This paper presents a method for the preparation of larval fish otoliths compatible with SIMS δ 18 O analysis through placement of larval otoliths (~ 20 to ~ 150 μ m diameter) on a single epoxy mount and use of a Cesium ion beam, 133 Cs + , of 12 μ m in diameter with 1 μ m penetration depth to excite source larval otolith material. In this pilot study, otoliths from Atlantic bluefin tuna ( Thunnus thynnus ) larvae were used to assess the efficacy of generating quality δ 18 O data using the newly developed preparation method for establishing spawning site baselines. The applied methods led to usable δ 18 O signatures in &gt; 90% of the otoliths selected for analysis. Challenges and unanticipated considerations that became apparent during the use of this method include the inverse relationship between 16 OH − / 16 O − , an indicator of hydrogen content, and δ 18 O, resulting in a limitation of using otoliths from preflexion larvae, as well as a statistically significant difference in δ 18 O (−0.17‰) after storage in Type B immersion oil.

ABSTRACT Objective Alewives Alosa pseudoharengus are a culturally, ecologically, and economically important anadromous fish in the northwest Atlantic, yet their movement ecology remains poorly understood. This study was designed to examine mortality events and movement patterns of Alewives, including diel vertical migrations. Methods Using acoustic telemetry, we tagged 32 Alewives during their postspawning migrations through Passamaquoddy Bay (New Brunswick, Canada, and Maine, USA) toward the Bay of Fundy. Generalized additive models (GAMs) were used to examine the spatial distribution and timing of Alewife migrations through the bay. We also used GAMs to investigate occurrences of diel vertical migration in relation to tidal levels. Results Six of the tagged Alewives died during the study, with most mortalities occurring earlier in their migration within the river and estuary habitats, including four cases of endothermic predation: three in the estuary and one in the inner bay. Alewives were predicted to occupy three distinct spatial hot spots over time: the river and estuary during weeks 25–27, the inner bay during weeks 28–30, and the outer bay during weeks 31–32. Regardless of tidal height, the GAMs predicted that Alewives were deeper in the water column during the day (1200–2000 hours) and shallower at night (0200–0700 hours), with intermediate periods used to transition between these depths, indicating that Alewives undertook diel vertical migrations in the marine environment. Conclusions As Alewife populations continue to decline, this research highlights critical aspects of their postspawning movement ecology and underscores the importance of binational and multijurisdictional cooperation in the effective management of this species.

Climate change will continue to alter key physical and biological oceanographic processes throughout the global ocean, modifying environmental conditions for U.S. highly migratory fish species found in the Atlantic Ocean. The Atlantic Highly Migratory Species Climate Vulnerability Assessment evaluated the vulnerability of 58 species and stocks to projected ocean conditions, using a combined qualitative and quantitative analysis of species sensitivity (physiological, ecological, and behavioral attributes) and estimated exposure to possible future ocean stressors. Key modeled environmental variables included bottom and sea surface temperature, sea surface oxygen, and ocean acidification (pH), whereas the most influential biological attributes considered were population growth rate, stock size, and stock status. We produced vulnerability rankings (i.e., low, moderate, high, and very high) based on biological attribute sensitivity and exposure to the environmental variables, and separate analyses including estimated ability of distributional shifts, predicted directional effects of climate change, certainty, and data quality scores for the species and stocks assessed, with exceptions for species with undetermined geographic distributions. Of the 58 species and stocks assessed, 4 had very high vulnerability to climate change, 14 had high vulnerability, 22 had moderate vulnerability, 6 had low vulnerability, and 12 could not be assigned a rank. The majority (n = 45) of species and stocks had high ability for distributional shifts in response to projected changes in climate. Further, directional effect results suggest that climate change impacts on the majority of species and stocks will be neutral, implying that these species have life history or behavioral traits that impart some level of resilience and adaptability to the impacts of climate change. These results provide information for use in ecosystem-based fisheries management, particularly for prioritization of vulnerable species and stocks in conservation activities and research endeavors.