Natural History of Sharks, Skates, and Rays Sensory Biology MARE 380 Dr. Turner

Sensory Biology Legendary 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 Performance Often 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 Performance Vision Hearing Mechanosenses Electrosenses Olfaction & other Chemosenses

Vision Eyes 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

Vision Nearly 360° visual field Blind areas in front of snout; behind head Binocular overlap small

Vision Some species (carcharhinids & sphrynids) have a 3 rd eyelid (nictitating membrane) Extends from lower nasal corner to protect eye from abrasion during feeding or contact

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

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

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

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

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

Vision Possess yellowish pigments in eye similar to some teleosts & diurnal terrestrial animals Also tapetum lucidum – reflective back retina Color vision hypothesized…not known

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

Hearing Do 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 sound Upper portion – balance 3 semicircular canals (a,b,c) & utricle (d) Lower portion – hearing saccule (sacculus) (e) which receives sounds along endolymphatic duct (f)

Hearing Can localize on sound which shows directional hearing – to 10°

Mechanosenses Detection 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

Mechanosenses Mechanosensory Neuromast – group of sensory hair cells surrounded by support cells and covered by gelatinous cupula Functional unit of all lateral line end organs

Mechanosenses Distributed on skin surface in grooves on raised papillae (skates, ray, some sharks) or b/w modified placoid scales (sharks) b c A – pore B – mucus-lined inner canal C – sensory cilia D – sensory nerves

Mechanosenses

Although 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)

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

Electrosenses Consists 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 – pore B – canal C – ampullae D – nerves Consists of (ampulla) & a subdermal canal about 1mm wide that projects to the surface

Olfaction & Chemosense Originally thought to be most important mechanisms for finding food Lateral olfactory epithelium (sacs)

Olfaction & Chemosense Each nares is blind slit divided in 2 by fold Water 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