Natural History of Sharks, Skates, and Rays

Metabolism & EnergyMARE 394Dr. Turner

Summer 2008

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