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Chugey A Sepulveda - One of the best experts on this subject based on the ideXlab platform.
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Temperature effects on the blood oxygen affinity in Sharks.
Fish Physiology and Biochemistry, 2018Co-Authors: Diego Bernal, Joseph P. Reid, Julie M. Roessig, Shinsyu Matsumoto, Joseph J Cech, Chugey A Sepulveda, Jeffrey B. GrahamAbstract:In fish, regional endothermy (i.e., the capacity to significantly elevate tissue temperatures above ambient via vascular heat exchangers) in the red swimming muscles (RM) has evolved only in a few marine groups (e.g., Sharks: Lamnidae, Alopiidae, and teleosts Scombridae). Within these taxa, several species have also been shown to share similar physiological adaptations to enhance oxygen delivery to the working tissues. Although the hemoglobin (Hb) of most fish has a decreased affinity for oxygen with an increase in temperature, some regionally endothermic teleosts (e.g., tunas) have evolved Hbs that have a very low or even an increased affinity for oxygen with an increase in temperature. For Sharks, however, blood oxygen affinities remain largely unknown. We examined the effects of temperature on the blood oxygen affinity in two pelagic species (the regionally endothermic Shortfin Mako Shark and the ectothermic blue Shark) at 15, 20, and 25 °C, and two coastal ectothermic species (the leopard Shark and brown smooth-hound Shark) at 10, 15, and 20 °C. Relative to the effects of temperature on the blood oxygen affinity of ectothermic Sharks (e.g., blue Shark), Shortfin Mako Shark blood was less affected by an increase in temperature, a scenario similar to that documented in some of the tunas. In the Shortfin Mako Shark, this may act to prevent premature oxygen dissociation from Hb as the blood is warmed during its passage through vascular heat exchangers. Even though the Shortfin Mako Shark and blue Shark occupy a similar niche, the effects of temperature on blood oxygen affinity in the latter more closely resembled that of the blood in the two coastal Shark species examined in this study. The only exception was a small, reverse temperature effect (an increase in blood oxygen affinity with temperature) observed during the warming of the leopard Shark blood under simulated arterial conditions, a finding that is likely related to the estuarine ecology of this species. Taken together, we found species-specific differences in how temperature affects blood oxygen affinity in Sharks, with some similarities between the regionally endothermic Sharks and several regionally endothermic teleost fishes.
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thermal dependence of contractile properties of the aerobic locomotor muscle in the leopard Shark and Shortfin Mako Shark
The Journal of Experimental Biology, 2007Co-Authors: Jeanine M Donley, Chugey A Sepulveda, Robert E Shadwick, Douglas A SymeAbstract:The work loop technique was used to examine contractile properties of the red aerobic locomotor muscle (RM) in the ectothermic leopard Shark Triakis semifasciata and endothermic Shortfin Mako Shark Isurus oxyrinchus . The effects of axial position and temperature on the twitch kinetics, and the stimulus duration and phase producing maximum net positive work and power output were investigated. Contractile performance was measured over the temperature range of 15 to 25°C for Triakis and 15 to 28°C for Isurus at cycle frequencies (analogous to tailbeat frequencies) ranging from 0.25 to 3 Hz using muscle bundles isolated from anterior (0.4 L where L is total body length) and posterior (0.6–0.65 L ) axial positions. Pairwise comparisons of twitch times for anterior and posterior muscle samples indicated that there were no significant differences related to body position, except in Mako Sharks at unphysiologically cool temperatures (<20°C). We found no significant differences in optimal stimulus duration, phase, net work or power output between anterior and posterior bundles in each species. With increasing cycle frequency the stimulus duration yielding maximum power decreased while optimal phase occurred earlier. The cycle frequency at which peak power was generated in leopard Shark RM was only affected slightly by temperature, increasing from about 0.6 to 1.0 Hz between 15 and 25°C. In contrast, Mako RM showed a much more dramatic temperature sensitivity, with the peak power frequency rising from <0.25 to 2.25 Hz between 15 and 28°C. These data support the hypothesis that the contractile properties of RM are functionally similar along the body in both species. In addition, our data identify a significant difference in the effect of temperature on net work and power output between these two Shark species; at 15°C muscle from the ectothermic leopard Shark performs relatively well in comparison with Mako, while at higher temperatures, which reflect those normally experienced by the Mako, the optimal cycle frequency for power is nearly double that of the leopard Shark, suggesting that the Mako may be able to maintain greater aerobic swimming speeds.
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Thermal dependence of contractile properties of the aerobic locomotor muscle in the leopard Shark and Shortfin Mako Shark
The Journal of Experimental Biology, 2007Co-Authors: Jeanine M Donley, Chugey A Sepulveda, Robert E Shadwick, Douglas A SymeAbstract:The work loop technique was used to examine contractile properties of the red aerobic locomotor muscle (RM) in the ectothermic leopard Shark Triakis semifasciata and endothermic Shortfin Mako Shark Isurus oxyrinchus . The effects of axial position and temperature on the twitch kinetics, and the stimulus duration and phase producing maximum net positive work and power output were investigated. Contractile performance was measured over the temperature range of 15 to 25°C for Triakis and 15 to 28°C for Isurus at cycle frequencies (analogous to tailbeat frequencies) ranging from 0.25 to 3 Hz using muscle bundles isolated from anterior (0.4 L where L is total body length) and posterior (0.6–0.65 L ) axial positions. Pairwise comparisons of twitch times for anterior and posterior muscle samples indicated that there were no significant differences related to body position, except in Mako Sharks at unphysiologically cool temperatures (
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Thermal dependence of contractile properties of the aerobic locomotor muscle in the leopard Shark and Shortfin Mako Shark.
Journal of Experimental Biology, 2007Co-Authors: Jeanine M Donley, Chugey A Sepulveda, Robert E Shadwick, Douglas A SymeAbstract:The work loop technique was used to examine contractile properties of the red aerobic locomotor muscle (RM) in the ectothermic leopard Shark Triakis semifasciata and endothermic Shortfin Mako Shark Isurus oxyrinchus. The effects of axial position and temperature on the twitch kinetics, and the stimulus duration and phase producing maximum net positive work and power output were investigated. Contractile performance was measured over the temperature range of 15 to 25 degrees C for Triakis and 15 to 28 degrees C for Isurus at cycle frequencies (analogous to tailbeat frequencies) ranging from 0.25 to 3 Hz using muscle bundles isolated from anterior (0.4 L where L is total body length) and posterior (0.6-0.65 L) axial positions. Pairwise comparisons of twitch times for anterior and posterior muscle samples indicated that there were no significant differences related to body position, except in Mako Sharks at unphysiologically cool temperatures (
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thermal dependence of contractile properties of the aerobic locomotor muscle in the leopard Shark and Shortfin Mako Shark
The Journal of Experimental Biology, 2007Co-Authors: Jeanine M Donley, Chugey A Sepulveda, Robert E Shadwick, Douglas A SymeAbstract:The work loop technique was used to examine contractile properties of the red aerobic locomotor muscle (RM) in the ectothermic leopard Shark Triakis semifasciata and endothermic Shortfin Mako Shark Isurus oxyrinchus. The effects of axial position and temperature on the twitch kinetics, and the stimulus duration and phase producing maximum net positive work and power output were investigated. Contractile performance was measured over the temperature range of 15 to 25 degrees C for Triakis and 15 to 28 degrees C for Isurus at cycle frequencies (analogous to tailbeat frequencies) ranging from 0.25 to 3 Hz using muscle bundles isolated from anterior (0.4 L where L is total body length) and posterior (0.6-0.65 L) axial positions. Pairwise comparisons of twitch times for anterior and posterior muscle samples indicated that there were no significant differences related to body position, except in Mako Sharks at unphysiologically cool temperatures (<20 degrees C). We found no significant differences in optimal stimulus duration, phase, net work or power output between anterior and posterior bundles in each species. With increasing cycle frequency the stimulus duration yielding maximum power decreased while optimal phase occurred earlier. The cycle frequency at which peak power was generated in leopard Shark RM was only affected slightly by temperature, increasing from about 0.6 to 1.0 Hz between 15 and 25 degrees C. In contrast, Mako RM showed a much more dramatic temperature sensitivity, with the peak power frequency rising from <0.25 to 2.25 Hz between 15 and 28 degrees C. These data support the hypothesis that the contractile properties of RM are functionally similar along the body in both species. In addition, our data identify a significant difference in the effect of temperature on net work and power output between these two Shark species; at 15 degrees C muscle from the ectothermic leopard Shark performs relatively well in comparison with Mako, while at higher temperatures, which reflect those normally experienced by the Mako, the optimal cycle frequency for power is nearly double that of the leopard Shark, suggesting that the Mako may be able to maintain greater aerobic swimming speeds.
Mahmood Shivji - One of the best experts on this subject based on the ideXlab platform.
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the complete mitochondrial genome of an atlantic ocean Shortfin Mako Shark isurus oxyrinchus
Mitochondrial DNA Part B, 2019Co-Authors: Jonathan Gorman, Mahmood Shivji, Nicholas J Marra, Michael J StanhopeAbstract:We report the first complete mitochondrial genome of a Shortfin Mako Shark from the Atlantic Ocean. The genome had 16,700 base pairs and contained 13 protein-coding genes, 2 rRNA genes, 22 tRNA gen...
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Oceanic nomad or coastal resident? Behavioural switching in the Shortfin Mako Shark (Isurus oxyrinchus)
Marine Biology, 2018Co-Authors: Malcolm P. Francis, Mahmood Shivji, Clinton A. J. Duffy, Paul J. Rogers, Michael E. Byrne, Scott C. Tindale, Warrick S. Lyon, Bradley M Wetherbee, Megan M. MeyersAbstract:Pelagic Sharks are vulnerable to overfishing because of their low reproductive rates, generally low growth rates, and high catch rates in tuna and billfish fisheries worldwide. Pelagic Sharks often migrate long distances, but they may also occur close to shore, making it difficult to classify their behaviour on the continuum from oceanic nomad to coastal resident. This has important implications for fishery management, which must be targeted at an appropriate spatial scale. Conventional tagging indicates that Shortfin Mako Sharks move widely around the southwest Pacific Ocean, but there is little information on their habitat use or mobility in the region. This study deployed electronic tags on 14 mostly juvenile New Zealand Mako Sharks to investigate their habitat use, and the spatial and temporal scale of their movements. Movement behaviour was classified as Resident or Travel, with the former focused in New Zealand coastal waters, and the latter in oceanic waters around New Zealand and along oceanic ridges running north towards the tropical islands of Fiji, Vanuatu and New Caledonia. Sharks regularly switched between Resident and Travel behavioural states, but their residency periods sometimes lasted for several months. Sharks spent most of their time in the New Zealand Exclusive Economic Zone (median 77%, five Sharks > 90%), presumably because of the high coastal productivity and access to abundant prey. These results challenge the conventional view that Mako Sharks are nomadic wanderers, and suggest that fishing mortality should be managed at a local as well as a regional scale.
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Oceanic nomad or coastal resident? Behavioural switching in the Shortfin Mako Shark (Isurus oxyrinchus)
Marine Biology, 2018Co-Authors: Malcolm P. Francis, Mahmood Shivji, Clinton A. J. Duffy, Paul J. Rogers, Michael E. Byrne, Scott C. Tindale, Warrick S. Lyon, Bradley M Wetherbee, Megan M. MeyersAbstract:Pelagic Sharks are vulnerable to overfishing because of their low reproductive rates, generally low growth rates, and high catch rates in tuna and billfish fisheries worldwide. Pelagic Sharks often migrate long distances, but they may also occur close to shore, making it difficult to classify their behaviour on the continuum from oceanic nomad to coastal resident. This has important implications for fishery management, which must be targeted at an appropriate spatial scale. Conventional tagging indicates that Shortfin Mako Sharks move widely around the southwest Pacific Ocean, but there is little information on their habitat use or mobility in the region. This study deployed electronic tags on 14 mostly juvenile New Zealand Mako Sharks to investigate their habitat use, and the spatial and temporal scale of their movements. Movement behaviour was classified as Resident or Travel, with the former focused in New Zealand coastal waters, and the latter in oceanic waters around New Zealand and along oceanic ridges running north towards the tropical islands of Fiji, Vanuatu and New Caledonia. Sharks regularly switched between Resident and Travel behavioural states, but their residency periods sometimes lasted for several months. Sharks spent most of their time in the New Zealand Exclusive Economic Zone (median 77%, five Sharks > 90%), presumably because of the high coastal productivity and access to abundant prey. These results challenge the conventional view that Mako Sharks are nomadic wanderers, and suggest that fishing mortality should be managed at a local as well as a regional scale.
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Satellite telemetry reveals higher fishing mortality rates than previously estimated, suggesting overfishing of an apex marine predator
Proceedings of the Royal Society B: Biological Sciences, 2017Co-Authors: Michael E. Byrne, Jeremy J. Vaudo, Guy C.mc N. Harvey, Mark Sampson, Enric Cortes, Bradley M Wetherbee, Mahmood ShivjiAbstract:Overfishing is a primary cause of population declines for many Shark species of conservation concern. However, means of obtaining information on fishery interactions and mortality, necessary for the development of successful conservation strategies, are often fisheries-dependent and of questionable quality for many species of commercially exploited pelagic Sharks. We used satellite telemetry as a fisheries-independent tool to document fisheries interactions, and quantify fishing mortality of the highly migratory Shortfin Mako Shark (Isurus oxyrinchus) in the western North Atlantic Ocean. Forty satellite-tagged Shortfin Mako Sharks tracked over 3 years entered the Exclusive Economic Zones of 19 countries and were harvested in fisheries of five countries, with 30% of tagged Sharks harvested. Our tagging-derived estimates of instantaneous fishing mortality rates (F= 0.19-0.56) were 10-fold higher than previous estimates from fisheries-dependent data (approx. 0.015-0.024), suggesting data used in stock assessments may considerably underestimate fishing mortality. Additionally, our estimates ofFwere greater than those associated with maximum sustainable yield, suggesting a state of overfishing. This information has direct application to evaluations of stock status and for effective management of populations, and thus satellite tagging studies have potential to provide more accurate estimates of fishing mortality and survival than traditional fisheries-dependent methodology.
Jayson M Semmens - One of the best experts on this subject based on the ideXlab platform.
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High survivorship after catch-and-release fishing suggests physiological resilience in the endothermic Shortfin Mako Shark (Isurus oxyrinchus)
Conservation physiology, 2015Co-Authors: Robert P French, J M Lyle, Suzanne Currie, Sean R. Tracey, Jayson M SemmensAbstract:The Shortfin Mako Shark ( Isurus oxyrinchus) is a species commonly targeted by commercial and recreational anglers in many parts of the developed world. In Australia, the species is targeted by recreational anglers only, under the assumption that most of the Sharks are released and populations remain minimally impacted. If released Sharks do not survive, the current management strategy will need to be revised. Shortfin Mako Sharks are commonly subjected to lengthy angling events; how ever, their endothermic physiology may provide an advantage over ectothermic fishes when recovering from exercise. This study assessed the post-release survival of recreationally caught Shortfin Mako Sharks using Survivorship Pop-up Archival Transmitting (sPAT) tags and examined physiological indicators of capture stress from blood samples as well as any injuries that may be caused by hook selection. Survival estimates were based on 30 Shortfin Mako Sharks captured off the southeastern coast of Australia. Three mortalities were observed over the duration of the study, yielding an overall survival rate of 90%. All mortalities occurred in Sharks angled for
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high survivorship after catch and release fishing suggests physiological resilience in the endothermic Shortfin Mako Shark isurus oxyrinchus
Conservation Physiology, 2015Co-Authors: Robert P French, J M Lyle, S Tracey, Suzanne Currie, Jayson M SemmensAbstract:The Shortfin Mako Shark (Isurus oxyrinchus) is a species commonly targeted by commercial and recreational anglers in many parts of the developed world. In Australia, the species is targeted by recreational anglers only, under the assumption that most of the Sharks are released and populations remain minimally impacted. If released Sharks do not survive, the current management strategy will need to be revised. Shortfin Mako Sharks are commonly subjected to lengthy angling events; however, their endothermic physiology may provide an advantage over ectothermic fishes when recovering from exercise. This study assessed the post-release survival of recreationally caught Shortfin Mako Sharks using Survivorship Pop-up Archival Transmitting (sPAT) tags and examined physiological indicators of capture stress from blood samples as well as any injuries that may be caused by hook selection. Survival estimates were based on 30 Shortfin Mako Sharks captured off the south-eastern coast of Australia. Three mortalities were observed over the duration of the study, yielding an overall survival rate of 90%. All mortalities occurred in Sharks angled for <30 min. Sharks experienced increasing plasma lactate with longer fight times and higher sea surface temperatures (SSTs), increased plasma glucose at higher SSTs and depressed expression of heat shock protein 70 and β-hydroxybutyrate at higher SSTs. Long fight times did not impact survival. Circle hooks significantly reduced foul hooking when compared with J hooks. Under the conditions of this study, we found that physical injury associated with hook choice is likely to have contributed to an increased likelihood of mortality, whereas the high aerobic scope associated with the species' endothermy probably enabled it to cope with long fight times and the associated physiological responses to capture.
Kathryn A Dickson - One of the best experts on this subject based on the ideXlab platform.
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Digestive enzyme activities are higher in the Shortfin Mako Shark, Isurus oxyrinchus, than in ectothermic Sharks as a result of visceral endothermy
Fish Physiology and Biochemistry, 2015Co-Authors: Kyle C. Newton, James Wraith, Kathryn A DicksonAbstract:Lamnid Sharks are regionally endothermic fishes that maintain visceral temperatures elevated above the ambient water temperature. Visceral endothermy is thought to increase rates of digestion and food processing and allow thermal niche expansion. We tested the hypothesis that, at in vivo temperatures, the endothermic Shortfin Mako Shark, Isurus oxyrinchus , has higher specific activities of three digestive enzymes—gastric pepsin and pancreatic trypsin and lipase—than the thresher Shark, Alopias vulpinus , and the blue Shark, Prionace glauca , neither of which can maintain elevated visceral temperatures. Homogenized stomach or pancreas tissue obtained from Sharks collected by pelagic longline was incubated at both 15 and 25 °C, at saturating substrate concentrations, to quantify tissue enzymatic activity. The Mako had significantly higher enzyme activities at 25 °C than did the thresher and blue Sharks at 15 °C. This difference was not a simple temperature effect, because at 25 °C the Mako had higher trypsin activity than the blue Shark and higher activities for all enzymes than the thresher Shark. We also hypothesized that the thermal coefficient, or Q _10 value, would be higher for the Mako Shark than for the thresher and blue Sharks because of its more stable visceral temperature. However, the Mako and thresher Sharks had similar Q _10 values for all enzymes, perhaps because of their closer phylogenetic relationship. The higher in vivo digestive enzyme activities in the Mako Shark should result in higher rates of food processing and may represent a selective advantage of regional visceral endothermy.
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mitochondrial proton leak rates in the slow oxidative myotomal muscle and liver of the endothermic Shortfin Mako Shark isurus oxyrinchus and the ectothermic blue Shark prionace glauca and leopard Shark triakis semifasciata
The Journal of Experimental Biology, 2006Co-Authors: Cindy A Duong, Jeffrey B. Graham, Chugey A Sepulveda, Kathryn A DicksonAbstract:Mitochondrial proton leak was assessed as a potential heat source in the slow, oxidative (red) locomotor muscle and liver of the Shortfin Mako Shark ( Isurus oxyrinchus ), a regional endotherm that maintains the temperature of both tissues elevated above ambient seawater temperature. We hypothesized that basal proton leak rates in red muscle and liver mitochondria of the endothermic Shortfin Mako Shark would be greater than those of the ectothermic blue Shark ( Prionace glauca ) and leopard Shark ( Triakis semifasciata ). Respiration rate and membrane potential in isolated mitochondria were measured simultaneously at 20°C using a Clark-type oxygen electrode and a lipophilic probe (triphenylmethylphosphonium, TPMP+). Succinate-stimulated respiration was titrated with inhibitors of the electron transport chain, and the non-linear relationship between respiration rate and membrane potential was quantified. Mitochondrial densities of both tissues were measured by applying the point-contact method to electron micrographs so that proton leak activity of the entire tissue could be assessed. In all three Shark species, proton leak occurred at a higher rate in red muscle mitochondria than in liver mitochondria. For each tissue, the proton leak curves of the three species overlapped and, at a membrane potential of 160 mV, mitochondrial proton leak rate (nmol H+ min-1 mg-1 protein) did not differ significantly between the endothermic and ectothermic Sharks. This finding indicates that red muscle and liver mitochondria of the Shortfin Mako Shark are not specialized for thermogenesis by having a higher proton conductance. However, Mako mitochondria did have higher succinate-stimulated respiration rates and membrane potentials than those of the two ectothermic Sharks. This means that under in vivo conditions mitochondrial proton leak rates may be higher in the Mako than in the ectothermic species, due to greater electron transport activity and a larger proton gradient driving proton leak. We also estimated each tissue's total proton leak by combining mitochondrial proton leak rates at 160 mV and tissue mitochondrial density data with published values of relative liver or red muscle mass for each of the three species. In red muscle, total proton leak was not elevated in the Mako Shark relative to the two ectothermic species. In the liver, total proton leak would be higher in the Mako Shark than in both ectothermic species, due to a lower proton conductance in the blue Shark and a lower liver mitochondrial content in the leopard Shark, and thus may contribute to endothermy.
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Mitochondrial proton leak rates in the slow, oxidative myotomal muscle and liver of the endothermic Shortfin Mako Shark (Isurus oxyrinchus) and the ectothermic blue Shark (Prionace glauca) and leopard Shark (Triakis semifasciata).
Journal of Experimental Biology, 2006Co-Authors: Cindy A Duong, Jeffrey B. Graham, Chugey A Sepulveda, Kathryn A DicksonAbstract:Mitochondrial proton leak was assessed as a potential heat source in the slow, oxidative (red) locomotor muscle and liver of the Shortfin Mako Shark (Isurus oxyrinchus), a regional endotherm that maintains the temperature of both tissues elevated above ambient seawater temperature. We hypothesized that basal proton leak rates in red muscle and liver mitochondria of the endothermic Shortfin Mako Shark would be greater than those of the ectothermic blue Shark (Prionace glauca) and leopard Shark (Triakis semifasciata). Respiration rate and membrane potential in isolated mitochondria were measured simultaneously at 20 degrees C using a Clark-type oxygen electrode and a lipophilic probe (triphenylmethylphosphonium, TPMP(+)). Succinate-stimulated respiration was titrated with inhibitors of the electron transport chain, and the non-linear relationship between respiration rate and membrane potential was quantified. Mitochondrial densities of both tissues were measured by applying the point-contact method to electron micrographs so that proton leak activity of the entire tissue could be assessed. In all three Shark species, proton leak occurred at a higher rate in red muscle mitochondria than in liver mitochondria. For each tissue, the proton leak curves of the three species overlapped and, at a membrane potential of 160 mV, mitochondrial proton leak rate (nmol H(+) min(-1) mg(-1) protein) did not differ significantly between the endothermic and ectothermic Sharks. This finding indicates that red muscle and liver mitochondria of the Shortfin Mako Shark are not specialized for thermogenesis by having a higher proton conductance. However, Mako mitochondria did have higher succinate-stimulated respiration rates and membrane potentials than those of the two ectothermic Sharks. This means that under in vivo conditions mitochondrial proton leak rates may be higher in the Mako than in the ectothermic species, due to greater electron transport activity and a larger proton gradient driving proton leak. We also estimated each tissue's total proton leak by combining mitochondrial proton leak rates at 160 mV and tissue mitochondrial density data with published values of relative liver or red muscle mass for each of the three species. In red muscle, total proton leak was not elevated in the Mako Shark relative to the two ectothermic species. In the liver, total proton leak would be higher in the Mako Shark than in both ectothermic species, due to a lower proton conductance in the blue Shark and a lower liver mitochondrial content in the leopard Shark, and thus may contribute to endothermy.
Michael E. Byrne - One of the best experts on this subject based on the ideXlab platform.
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Oceanic nomad or coastal resident? Behavioural switching in the Shortfin Mako Shark (Isurus oxyrinchus)
Marine Biology, 2018Co-Authors: Malcolm P. Francis, Mahmood Shivji, Clinton A. J. Duffy, Paul J. Rogers, Michael E. Byrne, Scott C. Tindale, Warrick S. Lyon, Bradley M Wetherbee, Megan M. MeyersAbstract:Pelagic Sharks are vulnerable to overfishing because of their low reproductive rates, generally low growth rates, and high catch rates in tuna and billfish fisheries worldwide. Pelagic Sharks often migrate long distances, but they may also occur close to shore, making it difficult to classify their behaviour on the continuum from oceanic nomad to coastal resident. This has important implications for fishery management, which must be targeted at an appropriate spatial scale. Conventional tagging indicates that Shortfin Mako Sharks move widely around the southwest Pacific Ocean, but there is little information on their habitat use or mobility in the region. This study deployed electronic tags on 14 mostly juvenile New Zealand Mako Sharks to investigate their habitat use, and the spatial and temporal scale of their movements. Movement behaviour was classified as Resident or Travel, with the former focused in New Zealand coastal waters, and the latter in oceanic waters around New Zealand and along oceanic ridges running north towards the tropical islands of Fiji, Vanuatu and New Caledonia. Sharks regularly switched between Resident and Travel behavioural states, but their residency periods sometimes lasted for several months. Sharks spent most of their time in the New Zealand Exclusive Economic Zone (median 77%, five Sharks > 90%), presumably because of the high coastal productivity and access to abundant prey. These results challenge the conventional view that Mako Sharks are nomadic wanderers, and suggest that fishing mortality should be managed at a local as well as a regional scale.
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Oceanic nomad or coastal resident? Behavioural switching in the Shortfin Mako Shark (Isurus oxyrinchus)
Marine Biology, 2018Co-Authors: Malcolm P. Francis, Mahmood Shivji, Clinton A. J. Duffy, Paul J. Rogers, Michael E. Byrne, Scott C. Tindale, Warrick S. Lyon, Bradley M Wetherbee, Megan M. MeyersAbstract:Pelagic Sharks are vulnerable to overfishing because of their low reproductive rates, generally low growth rates, and high catch rates in tuna and billfish fisheries worldwide. Pelagic Sharks often migrate long distances, but they may also occur close to shore, making it difficult to classify their behaviour on the continuum from oceanic nomad to coastal resident. This has important implications for fishery management, which must be targeted at an appropriate spatial scale. Conventional tagging indicates that Shortfin Mako Sharks move widely around the southwest Pacific Ocean, but there is little information on their habitat use or mobility in the region. This study deployed electronic tags on 14 mostly juvenile New Zealand Mako Sharks to investigate their habitat use, and the spatial and temporal scale of their movements. Movement behaviour was classified as Resident or Travel, with the former focused in New Zealand coastal waters, and the latter in oceanic waters around New Zealand and along oceanic ridges running north towards the tropical islands of Fiji, Vanuatu and New Caledonia. Sharks regularly switched between Resident and Travel behavioural states, but their residency periods sometimes lasted for several months. Sharks spent most of their time in the New Zealand Exclusive Economic Zone (median 77%, five Sharks > 90%), presumably because of the high coastal productivity and access to abundant prey. These results challenge the conventional view that Mako Sharks are nomadic wanderers, and suggest that fishing mortality should be managed at a local as well as a regional scale.
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Satellite telemetry reveals higher fishing mortality rates than previously estimated, suggesting overfishing of an apex marine predator
Proceedings of the Royal Society B: Biological Sciences, 2017Co-Authors: Michael E. Byrne, Jeremy J. Vaudo, Guy C.mc N. Harvey, Mark Sampson, Enric Cortes, Bradley M Wetherbee, Mahmood ShivjiAbstract:Overfishing is a primary cause of population declines for many Shark species of conservation concern. However, means of obtaining information on fishery interactions and mortality, necessary for the development of successful conservation strategies, are often fisheries-dependent and of questionable quality for many species of commercially exploited pelagic Sharks. We used satellite telemetry as a fisheries-independent tool to document fisheries interactions, and quantify fishing mortality of the highly migratory Shortfin Mako Shark (Isurus oxyrinchus) in the western North Atlantic Ocean. Forty satellite-tagged Shortfin Mako Sharks tracked over 3 years entered the Exclusive Economic Zones of 19 countries and were harvested in fisheries of five countries, with 30% of tagged Sharks harvested. Our tagging-derived estimates of instantaneous fishing mortality rates (F= 0.19-0.56) were 10-fold higher than previous estimates from fisheries-dependent data (approx. 0.015-0.024), suggesting data used in stock assessments may considerably underestimate fishing mortality. Additionally, our estimates ofFwere greater than those associated with maximum sustainable yield, suggesting a state of overfishing. This information has direct application to evaluations of stock status and for effective management of populations, and thus satellite tagging studies have potential to provide more accurate estimates of fishing mortality and survival than traditional fisheries-dependent methodology.
