Natural History of Sharks, Skates, and Rays Metabolism & Energy MARE 394 Dr. Turner Summer 2009

1. Natural History of Sharks, Skates, and Rays Metabolism & Energy MARE 394 Dr. Turner Summer 2009

2. Metabolism Elasmobranchs are top-level predators in marine systems however – information on energetics & metabolism is lacking Metabolism – important component of daily energy budget – greatest/most variable portion

3. Metabolism Variability in metabolism is linked to variability in buccal pumping – O2 delivery Heterodontiformes & Rajiiformes – less active, demersal, O2 via buccal pumping Myliobatiformes & Carcharhiniformes – more active, pelagic, O2 via Ram Ventilation

4. Metabolism 1) methods of estimation 2) compare/contract requirements 3) discuss future research techniques

5. Metabolism Respirometry - O2 needed for conversion of food to energy O2 consumption rate = indirect calorimetry Standard for determining aerobic metabolism in postabsorptive elasmobranchs Oxygen consumption (VO2) - measured

6. Metabolism Oxygen consumption (VO2) - measured using an O2 electrode to quantify reduction in DO as animal respires Amount of O2 consumed over time – used to calculate metabolic rate Use respirometers

7. Respirometers Closed – common and simple; single electrode to measure O2 decrease in as water is continuously circulated Open – more sophisticated; require 2 O2 probes to measure difference b/w water entering chamber and exiting chamber

8. Respirometry Annular/Circular – permit fish to swim freely in a circular pattern or rest on the bottom; open or closed; allows for both RMR & SMR Swim tunnel -

9. Respirometry Swim tunnel – water treadmills; water moved through holding-chamber and fish swim in place against current; closed O2 rates more precise – water speed controlled Better in Ram vent. species – but no “rest”

10. Respirometry Biotelemetry – ability to measure physiological variables on free-swimming animals List of physiological parameters of metabolic rate: muscle temp, heart rate, swimming speed, tailbeat frequency

11. Telemetry Muscle Temperature Telemetry – rigid thermistor deep within internal epaxial red muscle; measuring ∆ in temp as pulse rate ∆ Determined endothermic properties of sharks

12. Telemetry Heart Rate Telemetry – 1st tested on leopard & lemon sharks EKG acoustic transmitters observed in respirometers to determine relationship b/w heart rate & VO2

13. Telemetry Swimming Speed Telemetry – speed-sensing transmitters to measure swimming speed & energy consumption in the field; size of transmitted limited use in small animals

14. Telemetry Tailbeat Frequency Telemetry – tailbeat frequency (TBF) has been used as a correlate of energy consumption Most fishes ↑ TBF in proportion to ↑ in SS TBF provides a reliable indicator of: activity & exertion

15. Metabolic Rate Standard Metabolic Rate (SMR) – metabolic rate of a postabsorptive fish completely at rest Directly measured in animals at rest Indirectly for obligate Ram ventilators

16. Metabolic Rate Ectothermic tropical & subtropical sharks have SMR similar to ectothermic teleosts SMR of skates & rays are similar to those of colder water, less-active sharks

17. Metabolic Rate Modified table 7.1

18. Metabolic Rate Maximum Metabolic Rate (MMR) – more active sharks have higher MMR when contrasted with less-active sharks Spiny Dogfish 2.0kg 250mg O2 kg-1 h-1 Lemon Shark 1.6kg 620mg O2 kg-1 h-1

19. Metabolic Rate Specific Dynamic Action (SDA) – energetic costs associated w/ digestion & assimilation 15-20% of ingested energy in teleosts; measured by ↑MR after feeding Few estimates in elasmobranchs; similar to teleosts

20. Metabolic Rate Anaerobic Metabolism – powered by white muscle; majority of muscle in ectothermic elasmobranchs Blue sharks & makos – short bursts Blacktip, Spinner, White – leaping ability

21. Energetic Costs Of Swimming Swimming Efficiency – relationship b/w relative SS & MR is similar among comparable sized ectothermic sharks

22. Energetic Costs Of Swimming Cost of Transport – overall impact of swimming and energy costs (SDA, maint., & locomotion); use of all available energy Demonstrates U-shaped relationship when plotted against SS

23. Endothermy Vs. Ectothermy Ectotherm – body temp.of most fishes is similar to ambient water temp. due to linkage b/w aerobic heat production & heat loss via gills & body surface Endotherm - have capability to conserve metabolic heat via countercurrent heat exchangers (retia mirabilia) – maintain temp > ambient water temp.

24. Endothermy Vs. Ectothermy Endotherms should have ↑SMR than endothermic sharks – endothermy ↑ the total aerobic capacity of an organism Direct evidence – lamnid sharks have retia & endothermy

25. Endothermy Vs. Ectothermy Indirect evidence for ↑aerobic & anaerobic capabilities in lamnids: Higher MR than ectothermic sharks Red muscle is internalized w/ separation b/w red & white muscle ↑ Gill surface area – ↑O2 to red muscle Large heart Blood hemoglobin & hematocrit - like birds & mammals

26. Environmental Effects Ectothermic - ambient temp. plays a major role in controlling metabolic rate Endothermic – affects of ambient temp. have reduced or no impact

27. Thermal Conformers Ectothermic fishes generally inhabit an optimal temperature between upper & lower lethal temperatures Optimal range – where physiological rates (metabolism, growth, digestion) would be optimized to enhance fitness

28. Physiological Ecology: how to cope w/ temperature change Conformer:Physiological state = environment Regulator: Physiological state different from environment Conformer Body Temp Regulator 0 10 20 30 Ambient Temp

29. Zones of Resistance & Compatibility Encounters stressful condition: 1) migrate 2) adapt, adjust, survive 3) die Zone of resistance 100 50 0 Zone of resistance Zone of compatibility Percent survival Lower Upper Incipient lethal points Environmental gradient

30. Physiology of Temp Control Endothermy:internal metabolic production of heat Ectothermy:depends on environmental heat sources Homeothermy:stable internal body temperature Poikilothermy:variable internal body temperature Ectothermy & Endothermy - Mechanisms Homeothermy & Poikilothermy – Body Temp Profiles

31. Physiology of Temp Control Homeotherms: Poikilotherms: Heterotherms: Heliotherms: Endothermy Ectothermy Endo + Ectothermy Depend on solar radiation for thermoregulation

33. Endothermy in Fishes Brain heaters in billfish ‘eye & brain’ have Thermogenic (heat producing) Cells Still NOT Homeotherms Are Heterotherms (ecto + endo)

34. Water = 19.3°C Tunas, billfish & some mackerel & sharks have thermogenic (heat producing) cells which aids in maintaining elevated body temps while moving through environments w/ variable temps Tuna Core = 31.4°C Why Important?

35. Advantages to Endothermy Higher Metabolic Rate More efficient prey capture Swim faster Better visual capabilities More efficient digestion More efficient utilization of food

36. High & constant body temp can be maintained at rest over a fluctuation of temperatures of 5-10 C w/ little extra metabolic workthis is the TNZ. Lower lethal temp. Thermo neutral zone (TNZ) Upper lethal temp. Metabolic Rate BMR Lower critical temp. Upper critical temp. Ambient Temperature

37. Behavioral Thermoregulation Telemetry suggests that elasmobranchs found in heterogeneous environments feed in warmer waters; rest in cooler waters WHY? Elevated metabolism in warmer water – feeding Lower metabolism while digesting; ↑ AE

38. So you’ve decided to live in the ocean: Practical tips for coping with your new life under the sea Coping with Salinity “Marge? Kids? Everything's going to be just fine. Now go upstairs, and pack your bags...we're going to start a new life...under the sea.” – Homer Simpson

39. Coping with Salinity May be some costs associated; will cover when we examine osmoregulation I hate the sea and everything in it: Practical tips from a salty dog “Yaahr, It’s a good read says I”

40. D.O. O2 levels throughout the marine environment vary in relation to depth, productivity, time of day, and other factors Activity level ↓ in areas of ↓ DO WHY? Thought to reduce energy expenditure; energy saved can be redirected to respiratory needs Will cover more when we examine respiration…

41. Night Moves… Elasmo exhibit changes in diurnal activity patterns; higher metabolic levels, swimming speed at night Likely influenced by pineal gland