1. Ocean sunfish (Mola mola) were believed to be inactive jellyfish feeders because they are often observed lying motionless at the sea surface. Recent tracking studies revealed that they are ...actually deep divers, but there has been no evidence of foraging in deep water. Furthermore, the surfacing behaviour of ocean sunfish was thought to be related to behavioural thermoregulation, but there was no record of sunfish body temperature. 2. Evidence of ocean sunfish feeding in deep water was obtained using a combination of an animal-borne accelerometer and camera with a light source. Siphonophores were the most abundant prey items captured by ocean sunfish and were typically located at a depth of 50–200 m where the water temperature was <12 °C. Ocean sunfish were diurnally active, made frequently deep excursions and foraged mainly at 100–200 m depths during the day. 3. Ocean sunfish body temperatures were measured under natural conditions. The body temperatures decreased during deep excursions and recovered during subsequent surfacing periods. Heat-budget models indicated that the whole-body heat-transfer coefficient between sunfish and the surrounding water during warming was 3–7 times greater than that during cooling. These results suggest that the main function of surfacing is the recovery of body temperature, and the fish might be able to increase heat gain from the warm surface water by physiological regulation. 4. The thermal environment of ocean sunfish foraging depths was lower than their thermal preference (c. 16–17 °C). The behavioural and physiological thermoregulation enables the fish to increase foraging time in deep, cold water. 5. Feeding rate during deep excursions was not related to duration or depth of the deep excursions. Cycles of deep foraging and surface warming were explained by a foraging strategy, to maximize foraging time with maintaining body temperature by vertical temperature environment.
Large pelagic fishes often dive and surface repeatedly as if they were airbreathers, raising a question about the functions of these movements. Some species (e.g., bigeye tuna, ocean sunfish) ...apparently alternate foraging in deep cold waters and rewarming in shallow warm waters. However, it is unclear how prevalent this pattern is among species. Blue sharks are the widest-ranging pelagic shark with expanded vertical niches, providing a model for studying foraging–thermoregulation associations. We used electronic tags, including video cameras, to record the diving behaviour, muscle temperature, and foraging events of two blue sharks. During repeated deep dives (max. 422 m), muscle temperature changed more slowly than ambient water temperature. Sharks shifted between descents and ascents before muscle temperature reached ambient temperature, leading to a narrower range (8 °C) of muscle temperature than ambient temperature (20 °C). 2.5-h video footage showed a shark catching a squid, during which a burst swimming event was recorded. Similar swimming events, detected from the entire tag data (20 − 22 h), occurred over a wide depth range (5 − 293 m). We conclude that, instead of alternating foraging and rewarming, blue sharks at our study site forage and thermoregulate continuously in the water column. Furthermore, our comparative analyses showed that the heat exchange rates of blue sharks during the warming and cooling process were not exceptional among fishes for their body size. Thus, behavioural thermoregulation linked to foraging, rather than enhanced abilities to control heat exchange rates, is likely key to the expanded thermal niches of this ectothermic species.
The ocean sunfish (Mola mola) is typically considered to feed on gelatinous zooplankton, but reports in the literature describe various benthic organisms being found in their stomachs. This might ...reflect ontogenetic dietary shift, as little was known about the foraging habit of this species. We examined their foraging habits using dietary analyses in combination with a behavioral study in Iwate, Japan (39°22′N, 141°58′E) from 2009 to 2010. Our stomach content analyses (n = 17, 31–250 cm total length) suggested that small sunfish (<50 cm) feed on benthic crustaceans, but large sunfish (>200 cm) feed on jellyfish. Larger sunfish showed higher values of both carbon and nitrogen stable isotope ratios. Deployment of accelerometers and animal-borne cameras on small sunfish in July (49–58 cm, n = 5) suggested their possibility of feeding, while they stayed near the seabed. This indicates that small sunfish might feed on benthic preys. Deployment of accelero-magnetometers on large sunfish in July (84–164 cm, n = 4) clarified that the large sunfish in July swam back and forth between the surface and deep water (>100 m). Temporary decelerations, which were considered to be associated with feeding of planktonic prey, were observed in deep water. Whereas deployment of accelero-magnetometers on large sunfish in November (105 cm, n = 3) showed several bursts, they swam within the mixed layer (0–100 m), which might be associated with chasing of rapid prey. These results suggest that ocean sunfish have heterogeneous diets depending on their body size and possibly season.
The redistribution of species has emerged as one of the most pervasive impacts of anthropogenic climate warming, and presents many societal challenges. Understanding how temperature regulates species ...distributions is particularly important for mobile marine fauna such as sharks given their seemingly rapid responses to warming, and the socio‐political implications of human encounters with some dangerous species. The predictability of species distributions can potentially be improved by accounting for temperature's influence on performance, an elusive relationship for most large animals. We combined multi‐decadal catch data and bio‐logging to show that coastal abundance and swimming performance of tiger sharks Galeocerdo cuvier are both highest at ~22°C, suggesting thermal constraints on performance may regulate this species' distribution. Tiger sharks are responsible for a large proportion of shark bites on humans, and a focus of controversial control measures in several countries. The combination of distribution and performance data moves towards a mechanistic understanding of tiger shark's thermal niche, and delivers a simple yet powerful indicator for predicting the location and timing of their occurrences throughout coastlines. For example, tiger sharks are mostly caught at Australia's popular New South Wales beaches (i.e. near Sydney) in the warmest months, but our data suggest similar abundances will occur in winter and summer if annual sea surface temperatures increase by a further 1–2°C.
Being able to predict how temperature regulates species distributions is particularly important for mobile marine animals such as sharks given their seemingly rapid responses to warming, and implications of human encounters with some dangerous species. We combined catch data and accelerometry tagging to show that coastal abundance and swimming activity of tiger sharks Galeocerdo cuvier are both highest at ~22°C. Our combination of distribution and performance data takes a step towards a mechanistic understanding of tiger shark's thermal niche, and delivers a simple indicator that may be useful for predicting coastal occurrences of this potentially dangerous species.
We do not expect non air-breathing aquatic animals to exhibit positive buoyancy. Sharks, for example, rely on oil-filled livers instead of gas-filled swim bladders to increase their buoyancy, but are ...nonetheless ubiquitously regarded as either negatively or neutrally buoyant. Deep-sea sharks have particularly large, oil-filled livers, and are believed to be neutrally buoyant in their natural habitat, but this has never been confirmed. To empirically determine the buoyancy status of two species of deep-sea sharks (bluntnose sixgill sharks, Hexanchus griseus, and a prickly shark, Echinorhinus cookei) in their natural habitat, we used accelerometer-magnetometer data loggers to measure their swimming performance. Both species of deep-sea sharks showed similar diel vertical migrations: they swam at depths of 200-300 m at night and deeper than 500 m during the day. Ambient water temperature was around 15°C at 200-300 m but below 7°C at depths greater than 500 m. During vertical movements, all deep-sea sharks showed higher swimming efforts during descent than ascent to maintain a given swimming speed, and were able to glide uphill for extended periods (several minutes), indicating that these deep-sea sharks are in fact positively buoyant in their natural habitats. This positive buoyancy may adaptive for stealthy hunting (i.e. upward gliding to surprise prey from underneath) or may facilitate evening upward migrations when muscle temperatures are coolest, and swimming most sluggish, after spending the day in deep, cold water. Positive buoyancy could potentially be widespread in fish conducting daily vertical migration in deep-sea habitats.
Greater amberjack (Seriola dumerili) is an important fishery resource with a circumglobal distribution from tropical to temperate waters. Here, we investigated the spawning migration and habitat ...utilization of S. dumerili in the East China Sea (ECS). Archival tags were attached to 22 adult fish to examine their horizontal and vertical movements and estimate the spawning ground. S. dumerili were captured and released in the coastal waters of eastern Taiwan on November of 2016 and 2017. Information from seven pop‐up satellite archival tags and seven depth–temperature recorders was recovered. Almost all of the fish stayed in the Taiwanese exclusive economic zone. Most individuals moved from released site to the southern edge of the ECS and showed behavior associated with the topographic features in winter (November to December). These phenomena may be related to foraging and be driven by oceanographic features such as the seasonal monsoon and the Kuroshio. The fish then migrated to the south offshore area of Taiwan in January and February. During their southward migration, the fish experienced a slowly elevated water temperature regime (SETR), which is one of the environmental factors that induce final oocyte maturation. In the spawning season (February to April), tagged females exhibited continuous diel vertical movements (DVMs) after experiencing the SETR. These continuous DVMs were observed over a wide geographic range from north to south in the Kuroshio off eastern Taiwan. Our study demonstrated that the putative spawning ground of S. dumerili must extend further in a north–south direction than predicted in a previous study.
During behavioural thermoregulation, it has been demonstrated that fish alter their heat exchange rates between warming and cooling. In the case of the ocean sunfish (Mola mola), there is a ...several-fold difference in the rate of heat exchange between foraging in the deep, cooler water and recovering body temperature at the warmer surface. Increased heat gain during warming has been suggested, but there is also the possibility of preventing heat loss during cooling. To examine this, we measured the vertical movement and muscle temperature of three captive sunfish that were released into the field under warmer conditions and compared them with previously reported sunfish that foraged in cooler deep water. The released sunfish vertically moved from near the surface, where the water temperature was 21–25 °C, to depths of 150–200 m, where the water temperature was 15–17 °C. All sunfish occasionally appeared on the sea surface and sometimes remained at the surface for <41 min. However, they reduced their muscle temperature by diving before their muscle temperature exceeded 21–22 °C, suggesting behavioural thermoregulation using the cooler water temperature at depth. In addition, the feeding events detected by video were limited to depths shallower than 60 m. This is in contrast from previously observed sunfish behaviour, in which fish were reported as recovering their body temperature using warmer temperatures at the surface after foraging in deep, cooler water. The heat-budget models indicated that the whole-body heat-transfer coefficients during warming in this study were similar to those of previously reported sunfish that had recovered their body temperature at the sea surface after foraging in deep, cooler water. In contrast, the heat-transfer coefficients at cooling in this study were higher than those of sunfish foraging in deep, cooler water. This suggests that ocean sunfish may have the ability to prevent heat loss in the physiological regulation of heat exchange rate during thermoregulation, while also indicating that sunfish have the ability to respond to changes in the temperature environment by altering their behaviour and heat exchange rate.
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•Ocean sunfish change their behaviour in response to the temperature environment.•Ocean sunfish alter heat exchange rate during behavioural thermoregulation.•Their cooling rate was very smaller when foraging in deep cooler water.•Ocean sunfish may have the ability to prevent heat loss during deep foraging dives.
We investigated movement pattern of commercial important fish around Offshore Wind Turbine (OWT) and neighboring habitats in Goto Islands. We tagged 55 individuals of 2 fish species and released ...around the OWT in 2017. (27 Pagrus major from 1st Feb 2017 to 16th Mar 2017 (winter), 8 P. major and 20 Seriola quinqueradiata from 13th July 2017 to 13th Oct 2017 (summer)). Acoustic receivers were deployed at OWT, south artificial reef (AS), trapnet (TN), north FAD (F1) and south FAD (F2) in winter and two more receivers were deployed at north artificial reef (AN) and natural reef (NR) in summer. We observed 12 P. major at OWT for a day after released in winter, majority of fish (13 individuals) were detected at TN. In summer, 7 P. major were observed at OWT, 1 visited TN within the day, but others disappeared. Ten S. quinqueradiata stayed at OWT longer than P. major after released and disappeared within 2 days. They mostly moved around AS, AN, NR. Residence time from K-M curve was 10 days for P. major in winter, a day in summer and 3 days for S. quinqueradiata. Both species showed low affinity for OWT as recorded low residency index despite the season.
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