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Copyright of Coral Reefs is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Global Change Biology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Body condition is an important proxy for the overall health and energetic status of fishes. The classically used Fulton's condition factor requires length and mass measurements, but mass can be difficult to obtain in large species. Girth measurements can replace mass for wild pelagic sharks. However, girth‐calculated condition has not been validated against Fulton's condition factor intraspecifically, across ontogeny or reproduction, or in a controlled setting. We used the epaulette shark (Hemiscyllium ocellatum), because they are amenable to captive reproduction, to track fine‐scale body condition changes across life stages, oviparous reproduction and between condition indices. We measured four girths, total length and mass of 16 captive epaulette sharks across 1 year and tracked female reproduction daily. We also collected length and mass data from an additional 72 wild‐caught sharks and 155 sharks from five previous studies and two public aquaria to examine the relationship between length and mass for this species. Even though data were derived from a variety of sources, a predictable length–mass relationship (R2 = 0.990) was achievable, indicating that combining data from a variety of sources could help overcome knowledge gaps regarding basic life history characteristics. We also found that condition factor decreased during early life stages, then increased again into adulthood, with predictable changes across the female reproductive cycle. Finally, we determined that both Fulton's and girth condition analyses were comparable. Outcomes from this study uniquely provide body condition changes across the complete life history, including fine‐scale female reproductive stages, and validate the use of girths as a nonlethal whole‐organism energetic assessment for fishes. [ABSTRACT FROM AUTHOR]

Biological rhythms that are mediated by exogenous factors, such as light and temperature, drive the physiology of organisms and affect processes ranging from cellular to population levels. For elasmobranchs (i.e. sharks, rays, and skates), studies documenting diel activity and movement patterns indicate that many species are crepuscular or nocturnal in nature. However, few studies have investigated the rhythmicity of elasmobranch physiology to understand the mechanisms underpinning these distinct patterns. Here, we assess diel patterns of metabolic rates in a small meso-predator, the epaulette shark (Hemiscyllium ocellatum), across ecologically relevant temperatures and upon acutely removing photoperiod cues. This species possibly demonstrates behavioral sleep during daytime hours, which is supported herein by low metabolic rates during the day and a 1.7-fold increase in metabolic rates at night. From spring to summer seasons, where average average water temperature temperatures for this species range 24.5 to 28.5 °C, time of day, and not temperature, had the strongest influence on metabolic rate. These results indicate that this species, and perhaps other similar species from tropical and coastal environments, may have physiological mechanisms in place to maintain metabolic rate on a seasonal time scale regardless of temperature fluctuations that are relevant to their native habitats. [ABSTRACT FROM AUTHOR]

Owing to climate change, most notably the increasing frequency of marine heatwaves and long-term ocean warming, better elucidating the upper thermal limits of marine fishes is important for predicting the future of species and populations. The critical thermal maximum (CTmax), or the highest temperature a species can tolerate, is a physiological metric that is used to establish upper thermal limits. Among marine organisms, this metric is commonly assessed in bony fishes but less so in other taxonomic groups, such as elasmobranchs (subclass of sharks, rays and skates), where only thermal acclimation effects on CTmax have been assessed. Herein, we tested whether three life history stages, sex and body size affected CTmax in a tropical elasmobranch, the epaulette shark (Hemiscyllium ocellatum), collected from the reef flats surrounding Heron Island, Australia. Overall, we found no difference in CTmax between life history stages, sexes or across a range of body sizes. Findings from this research suggest that the energetically costly processes (i.e. growth, maturation and reproduction) associated with the life history stages occupying these tropical reef flats do not change overall acute thermal tolerance. However, it is important to note that neither embryos developing in ovo , neonates, nor females actively encapsulating egg cases were observed in or collected from the reef flats. Overall, our findings provide the first evidence in an elasmobranch that upper thermal tolerance is not impacted by life history stage or size. This information will help to improve our understanding of how anthropogenic climate change may (or may not) disproportionally affect particular life stages and, as such, where additional conservation and management actions may be required. [ABSTRACT FROM AUTHOR]

Many species with broad distributions are exposed to different thermal regimes which often select for varied phenotypes. This intraspecific variation is often overlooked but may be critical in dictating the vulnerability of different populations to environmental change. We reared Port Jackson shark (Heterodontus portusjacksoni) eggs from two thermally discrete populations (i.e. Jervis Bay and Adelaide) under each location's present‐day mean temperatures, predicted end‐of‐century temperatures and under reciprocal‐cross conditions to establish intraspecific thermal sensitivity. Rearing temperatures strongly influenced ṀO2Max and critical thermal limits, regardless of population, indicative of acclimation processes. However, there were significant population‐level effects, such that Jervis Bay sharks, regardless of rearing temperature, did not exhibit differences in ṀO2Rest, but under elevated temperatures exhibited reduced maximum swimming activity with step‐wise increases in temperature. In contrast, Adelaide sharks reared under elevated temperatures doubled their ṀO2Rest, relative to their present‐day temperature counterparts; however, maximum swimming activity was not influenced. With respect to reciprocal‐cross comparisons, few differences were detected between Jervis Bay and Adelaide sharks reared under ambient Jervis Bay temperatures. Similarly, juveniles (from both populations) reared under Adelaide conditions had similar thermal limits and swimming activity (maximum volitional velocity and distance) to each other, indicative of conserved acclimation capacity. However, under Adelaide temperatures, the ṀO2Rest of Jervis Bay sharks was greater than that of Adelaide sharks. This indicates that the energetics of cooler water population (Adelaide) is likely more thermally sensitive than that of the warmer population (Jervis Bay). While unique to elasmobranchs, these data provide further support that by treating species as static, homogeneous populations, we ignore the impacts of thermal history and intraspecific variation on thermal sensitivity. With climate change, intraspecific variation will manifest as populations move, demographics change or extirpations occur, starting with the most sensitive populations. [ABSTRACT FROM AUTHOR]

In teleost fishes, catecholamine-induced increases in the activity of cation exchangers compensate for decreases in hemoglobin oxygen affinity and maximum blood oxygen carrying capacity caused by decreases in plasma pH (i.e., metabolic acidosis). The resultant red blood cell (RBC) swelling has been documented in sandbar (Carcharhinus plumbeus) and epaulette (Hemiscyllium ocellatum) sharks following capture by rod-and-reel or after a 1.5 h exposure to anoxia (respectively), although the underlying mechanisms remain unknown. To determine if RBC swelling could be documented in other elasmobranch fishes, we collected blood samples from clearnose skate (Rostroraja eglanteria), blacktip reef shark (Carcharhinus melanopterus), and sicklefin lemon shark (Negaprion acutidens) subjected to exhaustive exercise or air exposure (or both) and measured hematocrit, hemoglobin concentration, RBC count, RBC volume, and mean corpuscular hemoglobin content. We did likewise with sandbar and epaulette sharks to further explore the mechanisms driving swelling when present. We could not document RBC swelling in any species; although hematocrit increased in all species (presumably due to RBC ejection from the spleen or fluid shifts out of the vascular compartment) except epaulette shark. Our results indicate RBC swelling and associated ion shifts in elasmobranch fishes is not inducible by exercise or hypoxia, thus implying this response maybe of lesser importance for maintaining oxygen delivery during acute acidosis than in teleost fishes. [Display omitted] • Restoration of intracellular pH ameliorates hemoglobin-oxygen affinity impairments. • Red blood cell swelling occurs in two elasmobranch species following extreme stress. • The five species studied here did not exhibit red blood cell swelling following stress. • Four of five species did exhibit increased hematocrit. • Red blood cell swelling in elasmobranch fishes is not ubiquitous following stress. [ABSTRACT FROM AUTHOR]

Tropical coral reef flats can be 3-4 °C warmer than surrounding deeper reef slopes, and some experience daily temperature fluctuations of up to 12 °C, which will be exacerbated as global temperatures continue to rise. Epaulette sharks (Hemiscyllium ocellatum), predominantly found on reef flats, may have evolved behavioural and/or physiological strategies to mitigate the effects of these dramatic temperature fluctuations. Here, juvenile sharks were acclimated, for at least 6 weeks, to average summer temperatures (28 °C) or predicted end-of-century summer temperatures (32 °C) to investigate the effects of elevated temperatures on growth, survival, and the use of movement to thermoregulate. In addition, sharks experience seasonal temperature changes; therefore, the upper critical thermal limits were determined for adult, wild sharks during both summer and winter months. We found that regardless of acclimation temperature, juveniles maintained the same food consumption rates (~ 5% body mass every other day), but for those living at 32 °C, this resulted in significantly decreased growth rates (body mass and total length). During winter months, maximum habitat temperatures (~ 24 °C) are far below adult sharks’ critical thermal limits (35.92 ± 0.21 °C). During summer months, maximum habitat temperatures (~ 35 °C) are closer to adult critical thermal limits (38.85 ± 0.31 °C). When estimating thermoregulatory behaviour of juvenile sharks maintained at 28 °C, those sharks examined in winter exhibited no thermoregulatory behaviour, while those examined in summer actively sought to control their thermal exposure, preferring 30.7 ± 1.04 °C (day) and 28.54 ± 0.75 °C (night). Furthermore, after acclimation to predicted end-of-century conditions, these same sharks behaviourally sought out 32.94 ± 0.46 °C (day) and 30.74 ± 0.68 °C (night); despite the cost of decreased growth and/or survival. Sharks maintained in control conditions had a mortality rate of 33% during the initial 90-day period of exposure, while mortality was 100% in those sharks exposed to elevated conditions. Ultimately, as ocean temperatures continue to rise, the distribution and abundance patterns for epaulette sharks and many other coral reef species are likely to change if trade-offs associated with acclimation outweigh the benefits of moving to more favourable habitats. [ABSTRACT FROM AUTHOR]