Natural History of Sharks, Skates, and Rays

Sensory BiologyMARE 380Dr. Turner

Sensory BiologyLegendary sensory abilities

Often exaggerated; some deserved

Not just sense of “smell” but an array of senses working in conjunction

Wired to relative large fish brain

Sensory PerformanceOften characterized in two ways:

Sensitivity – minimum stimulus detected by the system

Acuity – the ability of the system to discriminate stimulus characteristics

- location, type, etc.

Sensory PerformanceVision

Hearing

Mechanosenses

Electrosenses

Olfaction & other Chemosenses

VisionEyes located laterally (Selachians), dorsally (batoids & benthic sharks)

Small related to body size (except Bigeye Thresher)

Nearly 360° visual field

Blind areas in front of snout; behind head

Binocular overlap small

VisionNearly 360° visual field

Blind areas in front of snout; behind head

Binocular overlap small

VisionSome species (carcharhinids & sphrynids) have a 3rd eyelid (nictitating membrane)

Extends from lower nasal corner to protect eye from abrasion during feeding or contact

VisionSome sharks w/out membrane can roll eye into orbit to protect (e.g. – white, whale shark)

VisionUnlike Teleosts – have dynamic iris – increase size of pupil in dim; decrease in bright

VisionUnlike Teleosts – have dynamic iris – increase size of pupil in dim; decrease in bright

VisionUnlike Teleosts – have dynamic iris – increase size of pupil in dim; decrease in bright

VisionUnlike Teleosts – have dynamic iris – increase size of pupil in dim; decrease in bright

VisionPossess yellowish pigments in eye similar to some teleosts & diurnal terrestrial animals

Also tapetum lucidum – reflective back retina

Color vision hypothesized…not known

Visiona) tapetum lucidum – reflective plates behind retina (b); intensifies light that strikes itWhen light increases a black melanin makes them opaque (c)

HearingDo not make noise; hearing shaped by ambient

Shark hearing lower than teleosts, especially those with air-bladder connected to ear

Unknown as to whether attracted to soundUpper portion – balance3 semicircular canals (a,b,c)& utricle (d)

Lower portion – hearingsaccule (sacculus) (e) which receives sounds along endolymphatic duct (f)

HearingCan localize on sound which shows directional hearing – to 10°

MechanosensesDetection of water movements (large & small scale) critical

Lateral line system is stimulated by different movement between the body & surrounding water – used to detect dipole sources (prey) and uniform fields (currents)

Used for rheotaxis, predator avoidance, hydrodynamic imaging, prey detection, social communication & mating in bony fishes

MechanosensesMechanosensory Neuromast – group of sensory hair cells surrounded by support cells and covered by gelatinous cupula

Functional unit of all lateral line end organs

MechanosensesDistributed on skin surface in grooves on raised papillae (skates, ray, some sharks) or b/w modified placoid scales (sharks)

bc

A – poreB – mucus-lined inner canalC – sensory ciliaD – sensory nerves

Mechanosenses

MechanosensesAlthough used for rheotaxis, predator avoidance, hydrodynamic imaging, prey detection, social communication & mating in bony fishes

Limited to prey detection & rheotaxis (Movement of an organism in response to a current of water or air)

ElectrosensesAll elasmobranchs possess an elaborate ampullary electroreceptor system that is exquisitely sensitive to low-frequency electric stimuli

ElectrosensesConsists of subdermal groups of electroreceptive units – Ampullae of Lorenzini

Originally thought to be mechanoreceptors

Ampullae of Lorenzini Marine elasmobranchs – many individual ampullae are grouped into discrete, bilateral cephalic clusters from which project the subdermal canals that radiate in many directions and terminate at individual skin pores on the head of sharks and the head and pectoral fins of skates & rays

Is This Them?“Is this them? Are these they? Who talks like that?!?” - Henchman 21 & 24

A – poreB – canalC – ampullaeD – nerves

Consists of (ampulla) & a subdermal canal about 1mm wide that projects to the surface

Olfaction & ChemosenseOriginally thought to be most important mechanisms for finding food

Lateral olfactory epithelium (sacs)

Olfaction & ChemosenseEach nares is blind slit divided in 2 by foldWater forced into specific olfactory cells as moves through nostril – flow-thru

Make Sense?

a - Acoustic-lateralis system

b - smell

c - sight

d – Ampullae of Lorenzini