Sea Turtle Physical Examination Part 1: Eyes-Ears-Nose-Throat

Introduction

When presented with a sick or injured sea turtle, the basic principles of patient evaluation are similar to that for other chelonians. Nevertheless sea turtles possess unique anatomic and physiologic features that reflect their adaptions to a marine lifestyle. These features influence not only physical examination but also components of clinical care including manual restraint and housing (Fig 1).

Perform exams upon entry and regularly during the rehabilitation process

Figure 1. Physical examination is an often-underutilized tool in sea turtle management. Perform exams upon entry and regularly during the rehabilitation process. Photo credit: Dr. Terry Norton. Click image to enlarge.

Perform a thorough, systematic physical examination of the turtle upon presentation and then regularly during the rehabilitation process. Use an examination form that includes a turtle diagram to record biological data and note external abnormalities such as shell fractures, missing flippers, and lacerations. Digital images can also be used to document specific lesions or injuries for long-term case monitoring.

Species identification

All sea turtle species except the leatherback turtle (Dermochelys coriacea) belong to family Cheloniidae. The leatherback is the only extant member of family Dermochelyidae (Box 1).

Box 1. There are seven extant sea turtle species
SpeciesScientific name
FlatbackNatator depressus
GreenChelonia mydas
HawksbillEretmochelys imbricata
Kemp's ridleyLepidochelys kempi
LeatherbackDermochelys coriacea
LoggerheadCaretta caretta
Olive ridleyLepidochelys olivacea

The leatherback (Dermochelys coriacea) is the only sea turtle that lacks a hard shell; instead it bears a mosaic of bony plates beneath its leathery skin (Fig 2). Additional distinguishing characteristics used for species identification include the prefrontal scales, the number and shape of scutes on the carapace, and the type of inframarginal scutes on the plastron.

The carapace of the adult leatherback turtle consists of a thin layer of tough, rubbery skin strengthened by tiny bone plates

Figure 2. The carapace of the adult leatherback turtle (Dermochelys coriacea) lacks scales, and instead consists of a thin layer of tough, rubbery skin strengthened by thousands of tiny bone plates. Shown here, individuals surrounding the turtle are performing venipuncture (A) and restraint (C), while keeping the animal cool (B). Photo credit: Connie Merigo. Click image to enlarge.

Visit Wyneken’s The Anatomy of Sea Turtles, the Sea Turtle Conservancy, or reef.org/reef_files/TurtleID.pdf for useful pictorial keys and identification information.

Visual examination

Upon arrival, carefully observe the turtle out of water. An in-water visual exam can occur during subsequent evaluations once the turtle is more stable. Turtle activity level and attitude usually improve dramatically when the animal is evaluated in the water.

Head

For a routine physical examination, begin with the head and work caudally. Look down on the turtle from above, note the symmetry of the head, eyes, tympani, nostrils, and rhamphothecae or beak (Fig 3).

Look at the turtle from above, assessing the head for evidence of asymmetry or abnormalities

Figure 3. Look at the turtle from above, assessing the head for evidence of asymmetry or abnormalities. Shown left, a normal green sea turtle (Chelonia mydas). Right: a loggerhead turtle (Caretta caretta) with a skull fracture. Photo credit: Dr. Terry Norton. Click image to enlarge.

Note evidence of injury or trauma, as well as head position and mentation. Also palpate the occipital protuberance as crepitus and movement in this region may be the only sign of skull fracture (Fig 4).

Creptitus or movement upon palpation of the occipital protuberance may be the only physical sign of a skull fracture in the sea turtle

Figure 4. Crepitus or movement upon palpation of the occipital protuberance may be the only physical sign of a skull fracture in the sea turtle. Photo credit: Dr. Terry Norton. Click image to enlarge.

The skull is organized into an inner braincase, the neurocranium, which encloses the brain, and an outer facial skeleton or splanchnocranium, which forms the supporting structure of the jaws (Fig 5, Fig 6). Some components of the skull are cartilaginous in hatchlings, however the skull is primarily bony in juveniles and adults. The neurocranium is protected by the jaw muscles and other surrounding structures. The jaw muscles attach in the space between the splanchnocranium and neurocranium rather than just under the skin, as is the case in mammals (Fig 7).

Gross appearance of the splanchnocranium and neurocranium

Figure 5. Gross appearance of the splanchnocranium and neurocranium. The braincase or neurocranium is found along the midline, internal to the skull roof, snout, and jawbones of the splanchnocranium. Photo credit: Dr. Terry Norton. Click image to enlarge.

The lateral facial and jawbones identified on this cheloniid skull vary in form with species.

Figure 6. The lateral facial and jawbones identified on this cheloniid skull vary in form with species. The auditory canal occupies the notch posterior to the quadratojugal bone. Photo credit: Dr. Jeanette Wyneken. Click image to enlarge.

Cross-section of the sea turtle skull

Figure 7. Cross-section of the sea turtle skull. Note the deep position of the muscles of mastication. Photo credit: Dr. Terry Norton. Click image to enlarge.

The hyoid arch components (part of the splanchnocranium) form a bony plate between the base of the tongue and the throat muscles and paired boney processes wrap around the lower jaw to join the back of the skull (Fig 8, Fig 9).

Hyoid arch components

Figure 8. The hyoid arch components form a bony plate between the base of the tongue and the throat muscles. Cartilaginous components also occur but are lost in skeletal preparation. The throat muscles and paired bony processes wrap posteriorly around the lower jaw to join the back of the skull. Photo credit: Dr. Jeanette Wyneken. Click image to enlarge.

Parasagittal section of the sea turtle head

Figure 9. Parasagittal section of the sea turtle head. Note parts of the hyoid apparatus are located posterior and ventral to the tongue. Also note the salt gland (arrow), which is ventral and rostral to the brain. In head trauma cases, it is often confused with brain tissue. Fortunately prognosis is much better with salt gland involvement as opposed to brain. Photo credit: Dr. Jeanette Wyneken (The Anatomy of Sea Turtles, 2001). Click image to enlarge.

Eyes

Housed in bony orbits, the sea turtle eyes are round and located dorsally and anterolaterally (Fig 10). Overlapping fields of view allow for limited binocular vision in some species. Evaluation of vision is best accomplished with an in-water examination and reaction to stimulus such as avoidance behavior and tracking of food placed in the water column on either side of the animal.

Examine the eyelids and nictitans carefully

Figure 10. Examine the eyelids and nictitans carefully. Shown here, normal green turtle (Chelonia mydas). Photo credit: Dr. Terry Norton. Click image to enlarge.

Corneal ulceration is relatively common in stranded turtles, and fluorescein staining of the cornea should be a routine part of the initial exam. Assess pupillary light response in a dark room with a very bright light source (Fig 11). The normal response may be fairly subtle. The palpebral reflex, menace response, and corneal reflex should also be part of the routine exam. Menace can diminish rapidly after the first attempt or it can be overridden behaviorally.

 Assess pupillary light response in a dark room using a very bright light source

Figure 11. Assess pupillary light response in a dark room using a very bright light source. Photo credit: Dr. Terry Norton. Click image to enlarge.

Variable amounts of striated muscle within the iris means that mydriasis, for the purpose of fundic examination, is as challenging in sea turtles as in other reptiles and birds.

Adnexa

Blepharospasm can make it challenging to open the eye (Fig 12). The eye is protected by dorsal and ventral lids in cheloniids, which are keratinized and mobile. These lids are oriented almost nasally and caudally in Dermochelys (Fig 13).

 It can be extremely challenging to open a sea turtle’s eyes

Figure 12. It can be extremely challenging to open a sea turtle’s eyes. Photo credit: Dr. Terry Norton. Click image to enlarge.

Closeup of a loggerhead turtle face

Figure 13. Closeup of a loggerhead turtle (Caretta caretta) face. Photo credit: Scott R. Benson, NMFS Southwest Fisheries Science Center via Wikimedia Commons. Click image to enlarge.

There is also a secondary lid at the lateral canthus that is keratinized but does not move (Fig 14). The ventral eyelid is continuous with the conjunctiva, which forms its inner surface. The nictitating membrane, which lies at the medial canthus, is also continuous with the conjunctiva. The conjunctiva and nictitans should not be easily seen in the normal turtle and easy visualization usually indicates illness or pathology. Palpebral scales are found in the margins of the ventral lid in chelonids, but not in Dermochelys.

Eye and eyelids of a loggerhead turtle

Figure 14. Eye and eyelids of a loggerhead sea turtle (Caretta caretta). Photo credit: Dr. Jeanette Wyneken. Click image to enlarge.

Fibropapillomatosis, discussed in more detail in Sea Turtle Physical Examination Part 2, is a common problem in green turtles (Chelonia mydas) and frequently involves the lids, conjunctiva, and cornea. A “Horner’s like” syndrome, including partial ptosis or drooping of the upper eyelid, small or miotic pupils, and enophthalmos has been noted in several sea turtles with anterior carapacial and cervical vertebral injury. Enophthalmia is more commonly associated with emaciation or severe dehydration.

Salt glands

Sea turtles possess extremely large salt glands that are located dorsomedial to the globe and are associated with the nasolacrimal duct system (Fig 15). The function of the salt gland is to remove excess salt. When turtles are out of the water for examination or when female turtles come out to nest, excess clear fluid or tearing may be noted. This is actually excess salt discharge from the salt glands. White, salt-like material may also be noted in the corner of the eye when turtles are out of the water.

The salt glands remove excess salt

Figure 15. The salt glands (arrow), located dorsomedial to the globe, serve to remove excess salt. Discharge can be observed as clear fluid or dry, white material. Photo credit: Dr. Jeanette Wyneken. Click image to enlarge.

Ears

The sea turtle possesses a middle ear and inner ear but no outer ear or pinna. The middle ear is involved in sound wave transmission while the inner ear functions in sound transduction. Each ear consists of an external tympanum covered by a tympanic scale that stretches across the otic notch or auditory canal, which is formed by the quadrate, quadratojugal, and squamosal bones. A single middle ear bone, the stapes (or columella) extends from the subcutaneous layer covering the middle ear cavity to the inner ear structures.

Tympanic swelling caused by air or fluid can be noted in sea turtles secondary to head trauma. Aural abscesses have not been documented in sea turtles but have been found in several other chelonian species and could potentially occur.

Nares

Note any asymmetry of the nares, nasal discharge, or traumatic wounds (Fig 16). The tissue lining the anterior portion of the nares is soft, highly vascular, and erectile in sea turtles. This allows the turtle to seal the nostrils when submerged, however this is not an automatic occurrence as this vascular tissue also closes when the turtle is at rest (Schwenk 2008).

Observe the nares for discharge, asymmetry, or evidence of trauma

Figure 16. Observe the nares for discharge, asymmetry, or evidence of trauma. Photo credit: Dr. Terry Norton. Click image to enlarge.

Beak

The rhamphothecae are the keratinous beaks that cover the maxillary, premaxillary, and vomer bones of the upper jaw and the dentary bone of the lower jaw in cheloniids (Fig 17).

The lower jaw is a composite of the dentary, angular, surangular, prearticular, splenial (not shown), and articular bones

Figure 17. The lower jaw is a composite of the dentary, angular, surangular, prearticular, splenial (not shown), and articular bones. Photo credit: Dr. Jeanette Wyneken. Click image to enlarge.

Beak shape varies with diet and can be used for species identification. The hawksbill turtle (Eretmochelys imbricata) has a relatively long, narrow beak that allows it to feed on sponges in narrow crevices found in coral reef. The green turtle (Chelonia mydas) has a serrated beak for feeding on sea grass and algae, and the loggerhead (Caretta caretta) has a relatively large, strong beak and jaw for crushing shelled invertebrates (Fig 18). The keratinized portion of the beak grows continuously and may become overgrown in a rehabilitation or captive setting (Fig 19). Traumatic injuries as well as bacterial and fungal infections are common problems. Palpation of the maxilla may demonstrate “softness” or elicit a pain response that could be indicative of infection and/or abscess. Misalignment or an asymmetrical appearance can also indicate mandibular fractures and should be evaluated radiographically.

The keratinous beak or rhamphothecae of the loggerhead sea turtle

Figure 18. The keratinous beak or rhamphothecae of the loggerhead sea turtle (Caretta caretta). Photo credit: Dr. Jeanette Wyneken. Click image to enlarge.

The beak can overgrown in captive or rehabilitated sea turtles

Figure 19. The beak can overgrow in long-term captive or rehabilitated sea turtles. Shown here, trimming the beak with a rotary power tool. Despite severe ocular injury, this turtle was released with a satellite transmitter. She did quite well for several months before being lost to follow-up due to transmitter failure. Photo credit: Dr. Terry Norton. Click image to enlarge.

Oral examination

Some sea turtles will open their mouth in an attempt to bite and a quick evaluation of the oral cavity can be made at that time. For a more detailed evaluation, open the mouth by applying constant pressure to the lower jaw (Fig 20). A Nylabone® wrapped with elastic bandage material or a rope padded with garden hosing can also be used as a mouth speculum (Fig 21). Juvenile turtles will need a padded speculum appropriate for their size. Use caution with rigid materials as it is easy to fracture or chip the keratin covering the jaws.

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Open the beak by applying steady pressure to the lower jaw

Figure 20. Open the beak by applying steady pressure to the lower jaw. Note the serrated appearance of the tomium or the cutting edge of the beak in this green sea turtle (Chelonia mydas). Photo credit: Dr. Terry Norton. Click image to enlarge.

Mouth specula use in sea turtles

Figure 21. A Nylabone® wrapped with elastic bandage material (left) or a rope padded with garden hose can be used as mouth specula in sea turtles. Shown left, loggerhead sea turtle (Caretta caretta) missing a significant portion of the upper beak. Right: An adult female unable to open her beak that required physical therapy using a rope and hose as well as yard sticks covered with duct tape.  Photo credit: Dr. Terry Norton. Click image to enlarge.

Evaluate mucous membrane color, and note any abnormalities such as oral plaques, ulcerations, abnormal odor, and fishhooks or line. Barnacles are commonly found within the oral cavity of loggerhead sea turtles from the US Eastern seaboard.

The external nares communicate with the internal nares through the choanal slit, which are visible on the roof of the mouth (Fig 22). A series of small, spike-like papillae line the lateral margin of the internal choanae in green turtles. These papillae are absent or poorly developed in other sea turtle species. Cheloniids have a partial secondary palate that separates the nasal and oral cavities. The choanal slits are oval and extremely short in leatherbacks as they lack a secondary palate.

The internal nares can be visualized through the turtle’s choanae, visible on the roof of the mouth

Figure 22. The internal nares can be visualized through the turtle’s choanae, visible on the roof of the mouth. Photo credit: Dr. Terry Norton. Click image to enlarge.

The glottis is found at the base of the tongue and should be free of discharge. The openings to the Eustachian tube can be visualized near the jaw joint in the caudolateral region of the mouth (Fig 23).

Gross necropsy photo showing the entrance to the Eustachian tube (probe)

Figure 23. Gross necropsy photo showing the entrance to the Eustachian tube (probe). The floor of the mouth and tongue are cut away and reflected caudally. Photo credit: Dr. Jeanette Wyneken. Click image to enlarge.

The proximal esophagus is sometimes visible during the oral examination. Sea turtles possess very prominent, sharp conical projections that line the esophageal surface. These esophageal papillae retain prey items while salt water is expelled during feeding. In cases with fishing interactions, the esophagus and its papillae is a common place for fishing hooks and the associated line to become to lodged (Fig 24, Fig 25).

The prominent esophageal papillae of the proximal esophagus can sometimes be visualized during oral examination of the sea turtle

Figure 24. Dissection showing the prominent esophageal papillae (right side of image), which are directed towards the stomach (left). The proximal aspect of the esophagus can sometimes be visualized during oral examination of the sea turtle. Photo credit: Dr. Terry Norton. Click image to enlarge.

Close-up of the esophageal papillae in the proximal esophagus of a leatherback sea turtle

Figure 25. Close-up of the esophageal papillae in the proximal esophagus of a leatherback sea turtle (Dermochelys coriacea). The leatherback esophagus is exceptionally long extending nearly to the pelvis before turning to the left and traveling cranially to enter the stomach. Photo credit: Dr. Terry Norton. Click image to enlarge.

Neck and cervical vertebrae

Like all turtles, sea turtles possess seven mobile cervical vertebrae. The eighth cervical vertebra (C8) is a transition point that forms part of the carapace. This nuchal region (C8) is predisposed to fractures, often in association with anterior carapacial fractures. A Horner’s-like syndrome has been observed in sea turtles with injury involving the anterior carapace and cervical vertebrae.

Summary

There are a number of normal physical examination findings that reflect the sea turtle’s adaptations to a marine lifestyle. Copious, viscous tearing or even dry, white, salt-like material at the medial or lateral canthus are normal findings. The anterior nares are lined with soft, highly vascular, erectile tissue that allows the turtle to seal its nostrils when submerged. Finally, prominent esophageal papillae may also be visible during the oral examination. These sharp projections serve to hold prey items while salt water is expelled during feeding.

For more information on the sea turtle exam, visit Sea Turtle Physical Examination Part 2 and Body Condition Scoring the Sea Turtle.

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