natural history of sharks, skates, and rays metabolism & energy mare 394 dr. turner summer 2009
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Natural History of Sharks, Skates, and Rays Metabolism & Energy MARE 394 Dr. Turner Summer 2009. Metabolism. Elasmobranchs are top-level predators in marine systems however – information on energetics & metabolism is lacking - PowerPoint PPT PresentationTRANSCRIPT
Natural History of Sharks, Skates, and Rays
Metabolism & EnergyMARE 394Dr. Turner
Summer 2009
MetabolismElasmobranchs 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
MetabolismVariability 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
Metabolism1) methods of estimation
2) compare/contract requirements
3) discuss future research techniques
MetabolismRespirometry - O2 needed for conversion of food to energy
O2 consumption rate = indirect calorimetryStandard for determining aerobic metabolism in postabsorptive elasmobranchs
Oxygen consumption (VO2) - measured
MetabolismOxygen 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
RespirometersClosed – 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
RespirometryAnnular/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 -
RespirometrySwim tunnel – water treadmills; water moved through holding-chamber and fish swim in place against current; closedO2 rates more precise – water speed controlledBetter in Ram vent. species – but no “rest”
RespirometryBiotelemetry – ability to measure physiological variables on free-swimming animals
List of physiological parameters of metabolic rate: muscle temp, heart rate, swimming speed, tailbeat frequency
TelemetryMuscle Temperature Telemetry – rigid thermistor deep within internal epaxial red muscle; measuring ∆ in temp as pulse rate ∆
Determined endothermic properties of sharks
TelemetryHeart Rate Telemetry – 1st tested on leopard & lemon sharks
EKG acoustic transmitters observed in respirometers to determine relationship b/w heart rate & VO2
TelemetrySwimming Speed Telemetry – speed-sensing transmitters to measure swimming speed & energy consumption in the field; size of transmitted limited use in small animals
TelemetryTailbeat 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
Metabolic RateStandard Metabolic Rate (SMR) – metabolic rate of a postabsorptive fish completely at rest
Directly measured in animals at rest
Indirectly for obligate Ram ventilators
Metabolic RateEctothermic tropical & subtropical sharks have SMR similar to ectothermic teleosts
SMR of skates & rays are similar to those of colder water, less-active sharks
Metabolic RateModified table 7.1
Metabolic RateMaximum 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
Metabolic RateSpecific 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
Metabolic RateAnaerobic Metabolism – powered by white muscle; majority of muscle in ectothermic elasmobranchs
Blue sharks & makos – short burstsBlacktip, Spinner, White – leaping ability
Energetic Costs Of SwimmingSwimming Efficiency – relationship b/w relative SS & MR is similar among comparable sized ectothermic sharks
Energetic Costs Of SwimmingCost 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
Endothermy Vs. EctothermyEctotherm – 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.
Endothermy Vs. EctothermyEndotherms should have ↑SMR than endothermic sharks – endothermy ↑ the total aerobic capacity of an organism
Direct evidence – lamnid sharks have retia & endothermy
Endothermy Vs. EctothermyIndirect evidence for ↑aerobic & anaerobic capabilities in lamnids:
Higher MR than ectothermic sharksRed muscle is internalized w/ separation b/w red & white muscle↑ Gill surface area – ↑O2 to red muscleLarge heartBlood hemoglobin & hematocrit - like birds & mammals
Environmental EffectsEctothermic - ambient temp. plays a major role in controlling metabolic rate
Endothermic – affects of ambient temp. have reduced or no impact
Thermal ConformersEctothermic 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
Physiological Ecology: how to cope w/ temperature change
Bo
dy
Tem
p
Ambient Temp
0 10 20 30
Conformer
Regulator
Conformer: Physiological state = environment
Regulator: Physiological state different from environment
Zones of Resistance & CompatibilityEncounters stressful condition:
1) migrate
2) adapt, adjust, survive
3) die
Pe
rce
nt
su
rviv
al
100
50
0
Environmental gradient
Zone of
resistanceZone of
resistanceZone of
compatibility
Lower Upper
Incipient lethal points
Physiology of Temp ControlEndothermy: internal metabolic production of heat
Ectothermy: depends on environmental heat sources
Homeothermy: stable internal body temperature
Poikilothermy: variable internal body temperature
Ectothermy & Endothermy - MechanismsHomeothermy & Poikilothermy – Body Temp Profiles
Physiology of Temp ControlHomeotherms:
Poikilotherms:
Heterotherms:
Heliotherms:
Endothermy
Ectothermy
Endo + Ectothermy
Depend on solar radiation for thermoregulation
Endothermy in Fishes
Still NOT HomeothermsAre Heterotherms (ecto + endo)
Brain heaters in billfish ‘eye & brain’ have Thermogenic (heat producing) Cells
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
Advantages to EndothermyHigher Metabolic Rate
More efficient prey captureSwim fasterBetter visual capabilities
More efficient digestionMore efficient utilization of food
Ambient Temperature
Met
abo
lic
Rat
e
Lower lethal temp.
Lower critical temp.
Upper lethal temp.
Upper critical temp.
Thermo neutral zone (TNZ)
BMR
High & constant body tempcan be maintained at rest over a fluctuationof temperatures of 5-10 C w/ littleextra metabolic workthis is the TNZ.
Behavioral ThermoregulationTelemetry suggests that elasmobranchs found in heterogeneous environments feed in warmer waters; rest in cooler waters
Elevated metabolism in warmer water – feeding
Lower metabolism while digesting; ↑ AE
Coping with Salinity
So you’ve decided to live in the ocean:
Practical tips for coping with your new life under the sea
“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
I hate the sea and everything in it:
Practical tips from a salty dog
“Yaahr, It’s a good read
says I”
Coping with SalinityMay be some costs associated; will cover when we examine osmoregulation
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
Thought to reduce energy expenditure; energy saved can be redirected to respiratory needs
Will cover more when we examine respiration…
Night Moves…Elasmo exhibit changes in diurnal activity patterns; higher metabolic levels, swimming speed at night
Likely influenced by pineal gland