Bottlenose dolphin (Tursiops truncatus) Unusual Stranding Event of 21 October

2015 in San Diego, CA

Kerri Danil1, Nicky Beaulieu1, Sophie Dennison2, David Rotstein3, Teri Rowles4, Sarah Wilkin4

1

Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA, La Jolla, CA

Marine Mammalogy Radiology, Oakton, Virginia

3
Marine Mammal Pathology Services, Olney, Maryland

4
National Marine Fisheries Service, Office of Protected Resources, Silver Spring, Maryland

2

Background

Two bottlenose dolphin (Tursiops truncatus) stocks are recognized along the west coast of the United

States: a coastal population of approximately 450-500 individuals that are found within 1 kilometer of

shore, and an offshore population of roughly 1000 individuals that are typically found in waters greater

than a few kilometers from shore (Defran et al. 1999, Carretta et al. 2015, Lowther-Thieleking et al.
2015). The coastal population is known to move back and forth along the west coast, primarily from

Point Conception to San Quintin, Mexico, with little site fidelity (Feinholz 1996, Defran & Weller 1999,

Defran et al. 1999). In southern California, they are generally within 500 m of shore (Hanson & Defran

1993) and travel in schools of approximately 20 individuals (Defran & Weller 1999). Disease outbreaks

and anthropogenic threats such as pollution, fisheries, military training activities, and ship strikes put

both populations at risk due to their small size. For the coastal and offshore populations, the potential

biological removal (PBR) level is 2.9 and 5.5 dolphins per year, respectively. PBR is defined as the

maximum number of animals that can be removed from a stock (not including natural mortalities) that

allows the population to reach or maintain its optimal sustainable population.

Over the last 35 years, on average, 3.3 T. truncatus strand per year in San Diego County. Ninety nine

percent of stranded T. truncatus tested (n=104) have been genetically identified as the coastal ecotype.

No large scale disease outbreaks or impacts from military training exercises have been recorded for the

coastal stock. However, a small proportion of these dolphins (n=114) have been impacted by

anthropogenic activities: 2 entanglements, 1 gunshot, and 1 boat strike. One of the entanglements was

attributed to a fishery using 3.5 inch mesh gillnet, likely a set or drift gillnet targeting yellowtail, white

seabass, or barracuda (Carretta et al. 2015). Prior to the event described in this document there has

only been one other group stranding event for this species in San Diego. In 1963, two adult female T.

truncatus stranded alive and subsequently died for unknown reasons (Danil et al. 2010). The 3 T.

truncatus that stranded with spatial and temporal similarities during the event to be described here

truly represent an unusual occurrence for this region.

All three strandings described in this report were found within the Silver Strand Training Complex (SSTC),

which is used by the U.S. Navy for amphibious, special warfare, and mine countermeasure training

activities. The SSTC is located on and adjacent to the Silver Strand, a narrow isthmus separating San

Diego Bay from the Pacific Ocean (U.S Department of the Navy 2011). In 2011, a school of long-beaked

common dolphins (Delphinus capensis) were inadvertently exposed to an underwater detonation in this

1


 area during mine countermeasure training activities, which resulted in the death of at least three

dolphins (Danil & St.Leger 2011).

Overview of Event

A dead adult male bottlenose dolphin (T. truncatus) (NEB0075) was reported in Coronado (Figure 1) on

October 21, 2015 at 10:20 am by the Navy Region Southwest. The animal appeared to be in fresh

condition from the photos that were sent by the reporting party. However, upon arrival at the lab, the

genital slit had begun to swell, indicating a transition into an early decomposition code 3 (moderate).

The dolphin was placed in a refrigerator at 1300 until the necropsy on the following day.

At 1300 on the same day, Imperial Beach lifeguards reported a dead adult female T. truncatus
(KXD0280) 1 mile away from the stranding location of NEB0075 (Figure 1). When it was first reported, it

was thought that this was a duplicate report of NEB0075 due to spatial and temporal similarities, which

delayed initial response by the stranding team. Specimen KXD0280 was picked up at 1800 and placed in

a refrigerator at 1900 until necropsy the following day. Although the animal appeared to be in fresh

condition in photos taken by the Imperial Lifeguards at 1240 (Figure 2), it was a decomposition code 3

(moderate) at the time it was taken off the beach.

Ten days later, on October 31, 2015, a dead adult male T. truncatus (KXD0281) in advanced

decomposition was reported in Coronado (Figure 1) by Naval Amphibious Base personnel. A partial

necropsy was performed at the stranding site.


Figure 1. Map indicating the stranding locations of dolphins (NEB0075, KXD0280, and KXD0281) along Silver Strand Beach.


2


 Figure 2. Initial photograph of specimen KXD0280 taken by lifeguards.


Overview of Known Anthropogenic Activities in the Area

US Navy Activities

On October 22, 2015 the US Navy notified National Marine Fisheries Service (NMFS) that a Military

Training Exercise (MTE) began on October 21, 2015. In response to NMFS’s USE notification, the US

Navy queried explosive and sonar activities within 72 hours and 80 nm of the strandings. No explosives

were used in the SSTC area. Two ships used mid-frequency active (MFA) sonar within 80 nm during unit

level training for four periods of time: 35 minutes on October 19 th and 31 minutes, 22 minutes, and 9

minutes on October 20th.

Fishing Activities

Both squid and bait purse seine fisheries are known to operate in nearshore southern California waters

and both have had minimal observed marine mammal interactions. The squid purse seine fishery

typically operates from October to March, primarily at night, on average using 1.2 inch mesh, 27.5

fathoms deep, with a soak time just over an hour. A pilot observer program from July 2004 to January

2006 documented one unidentified common dolphin death in 135 squid fishery sets (Carretta et al.

2015). No squid fishery vessels were operating offshore San Diego County from October 19-21, 2015 (K.

Lynn, personal communication, February 26, 2016).

The bait fishery operates year round, using 11/16 inch to ¾ inch mesh size for capturing northern

anchovy (Engraulis mordax) (Knaggs 1972). The pilot observer program documented one California sea

lion (Zalophus californianus) death in 93 observed bait fishery sets. Only one bait company operates

fishing vessels along San Diego and they were fishing in the nearshore waters of the Coronado and

Imperial Beach areas October 19th and 21st, 2015. However, the owner of the company reports that no

3


 dolphin interactions occurred during these seining events (B. Everingham, personal communication,

February 16, 2016). A coastal pot fishery for California spiny lobster (Panuliris interruptus) operates off

San Diego but it would be highly unlikely to ensnare multiple marine mammals at one time in this type

of fishery. All other U.S. fisheries operate 3 miles or more offshore, outside of the range of coastal T.

truncatus. It is possible that coastal Mexican fisheries operate along the U.S/Mexico border.


Post-Mortem Examinations

NEB0075

The necropsy examination of a 295 cm long, 271.5 Kg adult male T. truncatus commenced at

approximately 0830 on 22 October 2015. The dolphin was robust and the body coloration was dark

grey, with no obvious cape (Figure 3). The skin has begun to wrinkle, creating fine linear creases in

various areas. Numerous healed and unhealed rake marks are present across the body. Transverse

linear creases in the throat region are present, common in many T. truncatus. Lingual papillae are

present but much reduced. A 2 cm wide bruise is present at the dorsal insertion point of the left

pectoral fin and upon incision hemorrhage in the blubber is apparent. The distal portion of the left

pectoral fin is absent and completely healed. The genital slit is swollen with the tip of the penis

protruding. There are three 1 –2 cm healed notches in the dorsal peduncle. Healed notch and rake

marks are present on the flukes.


Figure 3. Lateral view of NEB0075


Severe hemorrhage in the blubber extends circumferentially (both dorsal and ventral aspects) from the

rostrum to the cervical region, dissipating caudally and ending in the mid-thoracic region (Figure 4).

There is severe diffuse hematoma in the muscle surrounding the skull, concentrated along the muscles

of the lower jaws (Figure 5). Extensive subcutaneous emphysema (0.2 cm thick) is present in the dorsal

superficial fascia just posterior to head (Figure 5), extending laterally to deep fascia underneath the left

scapula (Figure 6). A 6 cm x 0.75 cm stingray barb is embedded in the left dorsal lateral muscle anterior

to the dorsal fin, lying longitudinally with the barb apex directed caudally. There is associated

hemorrhage in the surrounding muscle (12 cmx 24 cm area) and there is no associated scar in the

dermis or perforation of organs found (Figure 6).


4


 (a)

(b)

Figure 4. Subcutaneous hemorrhage in the dorsal (a) and ventral (b) aspects of blubber.

(a)

(b)

Figure 5. Severe diffuse hematoma along the muscles of the lower jaw (a) and subcutaneous emphysema in the dorsal

superficial fascia.

(a)

(b)

Figure 6. Subcutaneous emphysema in the deep fascia underneath the scapula (a) and an embedded stingray barb (b).


There are thin hair-like worms present in the trachea. Light raised areas are diffusely spread across

lungs and hard nodules 0.4 cm in diameter are diffusely scattered across right lung. A 2 cm mass is

present on a lymph node associated with the right lung. There is 140 ml of blood present in the

pericardial sac. The apex of the heart is dark red and this coloration continues a couple of centimeters

into the tissue upon incision. The epicardium in this area is gelatinous in texture (Figure 7). There are

two centrally located 0.5 cm focal circular areas of dark red tissue in the spleen (Figure 8).

5


 (a)

(b)

(a)

(b)

Figure 7. Dark discoloration at apex of heart with associated gelatinous texture, dorsal (a) and ventral (b) aspects.


Figure 8. Focal round dark areas in spleen.


Nematodes, likely Anisakis spp., are present in the esophagus. One liter of blood is present in the

abdominal cavity. The forestomach contains digested prey items and a low nematode load. Three gastric

ulcers, approximately 4 cm in diameter, are present. No perforations of the stomach are observed.

There are a few bubbles with small discontinuities of blood flow in the mesenteric vasculature (bubble

score 2). Feces are watery and red-tinged. Brain is dark pink with gas bubbles within the cerebral

vasculature that create large discontinuities in blood flow within some veins, filling some sections

completely with gas (bubble score 4) (Figure 9).


6


 (a)

(b)

Figure 9. Brain is dark pink (a) with gas bubbles (arrow) within the vasculature (b).


Summary

Significant gross findings from this adult male T. truncatus included hemoabdomen, hemopericardium,

subcutaneous hemorrhage and emphysema in the head region. The embedded stingray barb is likely

incidental.


KXD0280

The post-mortem examination of a robust 269.4 cm, 193 Kg female T. truncatus commenced at

approximately 1200 on October 22, 2015 (Figure 10). Signs of scavenging are apparent on the ventrum

and overall the skin is beginning to slough and wrinkle. The distal tip (1 cm) of the pectoral fin is

exposed. The urogenital openings are swollen.


Figure 10. Lateral view of specimen KXD0280.


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 There is 1 – 1.5 milliliters of blood within the globe of the eye (Figure 11). Upon incision of the left

pinna, ecchymoses of the blubber was apparent. Petechiae and echymoses in the cervical and melon

blubber are present with underlying low to moderate subcutaneous emphysema (Figure 12). There is

diffuse severe hematoma in the subcutaneous space, circumferentially extending from the rostrum to

the cervical region, concentrated along the muscles and blubber associated with both lower jaws (Figure

13).


Figure 11. Free blood within the globe of the eye.

(a)

(b)

Figure 12. Echymoses of the blubber at the left pinna (a) and hemorrhage in the cervical blubber with associated subcutaneous

emphysema (b).


(a)

(b)

Figure 13. Echymoses and petechiae in the melon fat (a) and hematoma in the lower jaw muscles (b).


8


 Froth and bloody fluid is present in the trachea. There are calcareous hard nodules throughout both

lumpy, dense, dark, and pink lungs. Two otoliths observed in the anterior region of the right bronchus.

Congestion or hemorrhage is concentrated on the ride side of the heart where the tissue throughout is

saturated with blood (Figure 14).


Figure 14. Right ventricle of heart is saturated with blood.


There is 1.5 L of blood in the abdominal cavity. A focal darkened region with the parenchyma of the

spleen is apparent. The left adrenal is enlarged (24.1 g vs. 9.3 g) and a focal dark area on the tip is

present. Areas of congestion or hemorrhage are present on both tips of the right adrenal (Figure 15).

(a)

(b)

Figure 15. Left (a) and right adrenal (b)


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 The forestomach contains 305 g of digested stomach contents and 4 ulcers. A red viscous fluid is

present in the main stomach. Intestinal fluid is watery and pink in color. Feces are mustard yellow in

color. The right liver lobe is almost twice the size of the left side and is very firm. The left liver lobe is

lumpy and dimpled. Liver parenchyma appears normal. Dark discoloration along the edges of the

pancreas that extend into the parenchyma are observed and overall the tissue is friable. There is a 2 cm

region of dark black viscous material lining the left kidney, which is slightly friable overall. The right

kidney is friable with a dark discoloration on the outer renal capsule and there is pooled dark viscous

material, possibly blood, in the capsule (Figure 16). The bladder is empty. A moderate amount of

superficial hemorrhage is present in the caudal medial aspect of both hemispheres of the brain. There

are gas bubbles within the cerebral vasculature that create large discontinuities in blood flow within

some veins, filling some sections completely with gas (bubble score 4) (Figure 17). There is a mucus plug

in the cervix and 2 corpora albicantia are present on the left ovary, indicating that this dolphin is sexually

mature.


Figure 16. Dark viscous material lining kidney.


Figure 17. Superficial hemorrhage in the medial aspect of both hemispheres of the brain and gas bubbles within the vasculature

(arrow).


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 Summary

Significant gross findings from this adult female T. truncatus included hemoabdomen, subcutaneous

hemorrhage and emphysema in the head region, unilateral (left) adrenal enlargement, and

petechiae/ecchymoses in the melon blubber.


KXD0281
This robust male T. truncatus, 307.2 cm in length, was examined on the beach on 31 October 2015.

Approximately 75% of the skin is missing and the carcass is very oily. The body is bloated, with the penis

and eyes protruding. The phalanges of the right pectoral fin are exposed and the teeth are loose in the

jaw from decomposition (Figure 18).


Figure 18. Lateral view of specimen KXD0281.


Patchy circumferential hemorrhage in the cervical blubber is apparent, focused bilaterally and ventrally,

with associated hemorrhage in the underlying muscles (Figure 19). Hemorrhage in the muscles and

blubber associated with the lower jaws is also present. All organs are intact but extremely friable. The

liver is discolored with black splotches that extend superficially into the parenchyma. A diffuse dark red

discoloration is observed on the serosal surface of both emphysematous kidneys (Figure 20). Brown

liquid digesta is present inside the forestomach. The right testis is approximately 200 g and 215mm

long.


11


 (a)

(b)

Figure 19. Circumferential hemorrhage in the cervical blubber.


(a)

(b)

(c)

(d)

Figure 20. Gross observations of the muscles and blubber associated with the lower jaw (a, b), liver (c), and kidney (d).


12


 Summary

Significant gross findings from this adult male T. truncatus include subcutaneous hemorrhage in the

head region.


Computed Tomography (CT)

The available CT scanner could not accommodate the carcasses due to weight limits. The heads of the

freshest animals, NEB0075 and KXD0280 were submitted.

NEB0075

Imaging Findings

Multifocal and extensive gas accumulation is present, consistent with the decapitated status of the head

being scanned. Several mandibular teeth are absent with lucent sockets suggesting recent (possibly post

mortem) loss. No evidence of skull fractures are identified. The tympanoperiotic complexes are intact.

There is mildly increased soft tissue within the peribullous sinuses bilaterally. Some fluid/soft tissue

attenuating material is present bilaterally within the pterygoid sinuses with greater volume on the left

than the right. The pterygoid bones are normal in appearance. There is soft tissue swelling ventral to the

tongue/mandible observe with altered attenuation of the ventral blubber layer at this level on midline.

Both eyes are in situ and are within normal limits. A large dorsal to dorsolateral cutaneous laceration is

present over the calvarium without changes to the underlying bone. The laceration is very linear and is

most likely post mortem.

Diagnostic Interpretation

Cause of death has not been determined. Ventral oral cavity/rostrum swelling Ddx: bruising, edema,

cellulitis. Mild peribullous and pterygoid sinusitis, likely within normal limits for the free-ranging status

of the patient.

Conclusions and Comments

A specific cause of death has not been determined from the study. The significance of the swelling

observed ventral to the tongue and mandible is of uncertain significance and determination of its

occurrence pre or peri stranding is challenging from imaging alone. Correlation with the full necropsy is

needed.

KXD0280

Imaging Findings

The head has been removed from the body and multifocal and extensive gas accumulations consistent

with this are present. Several teeth are absent from the mandible with lucent sockets, suggestive of

recent presumed post mortem extraction. There is no evidence of skull fracture observed. There is

increased soft tissue/fluid accumulation within the pterygoid sinuses bilaterally and within the


13


 peribullous sinuses that is mild. The pterygoid bones are normal in appearance. The tympanoperiotic

complexes are normal.

Diagnostic Interpretation

No cause of death identified. Mild bilateral pterygoid and peribullous sinusitis, likely within normal

limits for the free-ranging status.

Conclusions and Comments

Mild bilateral pterygoid and peribullous sinusitis has been found but is considered very mild and well

within normal limits for free-ranging dolphins, based on personal experience. Correlation with the full

necropsy examination is needed.
Histopathology

NEB0075

In the lung there is multifocal alveolar flooding with flocculent eosinophilic proteinaceous substances

(Figure 21). There is multifocal mild to occasionally moderate interstitial fibrosis and occasional alveolar

hyperinflation. In the lung, there are small deposits of Oil Red O-positive staining that correspond to the

flocculent fluid within the alveoli and within macrophages within alveolar lumina. The lipid is attributed

to cellular product (cholesterols) from pneumocytes that is freely within alveoli and within

macrophages.

(a)

(b)

Figure 21. Occasional clusters of alveoli are flooded with foamy proteinaceous substance (a) and Oil Red O-positive stain (lipid)

is found in a few alveoli and within alveolar lumina (b).


There is moderate congestion in the spleen. Splenic periarteriolar lymphoid sheaths are moderately

cellular. Lymphocytes in the lymph node are present in moderate numbers. Lymphoid follicles are wellformed.

There is regionally extensive moderate mucosal epithelial hyperplasia of the forestomach. There is focal

umbilication of the mucosal epithelium. The submucosa is mutlifocally infiltrated by lymphocytes,

plasma cells, and macrophages forming nodular aggregates (Figure 22).


14


 (a)

(b)

Figure 22. Hyperplasia in the gastric mucosa (a) and lymphoplasmacytic and histiocytic nodular aggregates in the submucosa

(b).


Epididymal ducts are filled with abundant spermatazoa within a lightly eosinophilic proteinaceous

substance. Testicular seminiferous tubules are lined by plump germ cells. There are few to occasionally

moderate spermatagonia and few spermatazoa. The interstitum is prominent.

Fourteen sections of spinal cord and brain are examined. There is distention of myelin sheaths primarily

within the ventral tracts (artifact, presumptive). In the brain, there is multifocal perivascular clearing

with no deposition of protein or inflammatory cells. Occasionally, there is infrequent disruption of the

neuropil by clear spaces without associated hemorrhage or inflammation (Figure 23). Scant lacey

proteinaceous substance is present within occasional spaces.


Figure 23. Rarely in the brain, there are clear spaces which expand the neuropil.


There is accumulation of proteinaceous fluid within the chamber of the eye. In the masseter muscle,

there is separation of myofibers by eosinophilic granular substance (edema) (Figure 24). Eosinophilic

proteinaceous fluid is present within the blubber. Oil Red O stains were applied to brain and lymph

node; there is no evidence of lipid within blood vessels or within the parenchyma of these tissues.


15


 Figure 24. In the masseter muscle, there is expansion of myofibers by lightly eosinophilic granular substance.


Tissues with No Significant Histological Findings: Skin, intestine, penis, trachea, tongue, urinary bladder,

skeletal muscle, adrenal gland, pancreas, heart, pituitary gland, main stomach, kidney, diaphragm, and

liver.

Conclusions

The cause of stranding of this cetacean was not determined with histopathological evaluation. Lesions in

the respiratory, digestive, and musculoskeletal system were incidental to mild. Pulmonary fibrosis was

mild and non-specific as this is a chronic change. Prior endoparasitism, bacterial, fungal, or viral infection

could have previously occurred resulting in the fibrosis (scarring). No infectious agents were observed.

Gastritis was parasite associated and was not beyond levels observed in other cetaceans finding.


KXD0280

There is multifocal flooding of alveoli with lightly eosinophilic proteinaceous fluid. There is multifocal

interstitial fibrosis. There are occasional foci of bronchiolar collapse and fibrosis leaving small islands of

cartilage (Figure 25). The bone marrow is 70% cellular. Megakaryocytes are present at 2 to 4 per 100X

field. Myeloid and erythroid cells exhibit eosinophilic pallor with diminished morphologic features.

Myeloid cells are present in all stages of storage and maturation. Erythroid cells are present in all stages.

The M:E ratio is 3:1. Tonsillar lymphoid tissue is moderately cellular. There is a single gland that is

moderately dilated and contains a concretion of clumped to lamellar basophilic mineral. Lymph node is

moderately cellular with loosely formed follicles. Splenic periarteriolar lymphoid sheaths are moderately

cellular. Within the capsule, there are multifocal accumulations of golden-brown amorphous pigment

(hematodin) surrounded by fibrous connective tissue, lymphocytes, plasma cells, macrophages, and few

multinucleated giant cells (Figure 26). Periarteriolar lymphoid sheaths are moderately cellular.


16


 Figure 25. In the lung, there is focal bronchiolar effacement by mature collagen. Islands of cartilage are present within the

collagen


Figure 26. Within the capsule, there is deposition of golden pigment (hematoidin). The pigment is surrounded by mixed

inflammatory cells including multinucleated giant cells (arrow).


Hepatocytes exhibit multifocal, mild cytoplasmic vacuolation. In the ventricle there are small

accumulations of eosinophilic proteinaceous fluid. The capsule of the kidney has deposits of basophilic

granular substance. Twelve sections of brain and spinal cord are examined. In the brain, there is

random, mild extravasation of erythrocytes in the meninges. Homogenous and granular eosinophilic

fluid is present within the anterior and posterior chamber of the eye.

There is a focally extensive periadrenal accumulation of lymphocytes and plasma cells. In the adrenal

gland, there is expansion of the periadrenal soft tissue by fibrin, necrotic cellular debris, neutrophils, and

macrophages. There are scattered colonies of bacterial cocci (Figure 27).Vessels exhibit

hypereosinophilia with a loss of nuclei. Occasional vessels contain clumped eosinophilic substance

(fibrin, suspect). Within the adrenal gland, there are abundant colonies of bacterial cocci. Occasional

foci have surrounding neutrophils and macrophages. Large bacilli are present within scattered vessels

17


 without an associated inflammatory response (Figure 28). Masseter myofibers are separated by an

eosinophilic proteinaceous substance.


(a)

(b)

Figure 27. In the peri-adrenal stroma, there are mixed inflammatory cells and fibrin (a); bacterial colonies are present within

the fibrinous exudate and inflammatory cells within the peri-adrenal soft tissue (b).


(a)

(b)

Figure 28. In the adrenal gland (a), there are numerous bacterial colonies. Some colonies are surrounded by mixed

inflammatory cells. Inset (b) demonstrates the same at higher magnification.


Oil Red O stains were applied to brain, lymph node, and lung. There are adipocytes which contain Oil

Red O-positive staining lipid (internal control); these are the adipocytes between bundles of muscle.

There is no evidence of lipid within blood vessels or within the parenchyma of non-adipose tissue.

Tissues with No Significant Histological Findings: Skin, fore stomach, trachea, cervix, aorta, tongue,

uterine horn, pituitary gland, main stomach, pancreas, mammary gland, kidney


18


 Conclusions

Histopathological findings were observed in the respiratory, urogenital, musculoskeletal, and endocrine

system. Of these, the bacterial adrenalitis was a significant finding. Bacteria were observed in large

numbers with no response to a histiocytic and neutrophilic response. Bacterial invasion would have

been embolic, but the primary source was not determined. No vegetations (bacterial vegetative

endocarditis) was not observed and there were no external skin wounds. Special stains for bacteria as

well as immunohistochemistry for Toxoplasma gondii (though no cysts were observed) could be done to

better define and rule out pathogens. It is possible that this cetacean was septicemic which could have

led to stranding. Petechiations and ecchymoses could be associated with the vasculitis, and while this

would be the differential for the hemorrhage observed in the cranial region, disseminated hemorrhage

would be expected with septicemia.

Fibrosis in the lung may have occurred from prior parasitic or other infection in the lung. No infectious

agents were observed and the impact on this animal was minimal. Disruption of the bronchioles with

consolidation of cartilage within a fibrous stroma likely accounted for the grossly palpable nodules.

Edema and serum exudation of the masseter muscle coincides with the grossly observed hemorrhage in

the head region.

Splenic siderotic plaques are an incidental finding. This indicates a site of prior hemorrhage with

degradation of senescent erythrocytes resulting in deposited hematoidin, an erythrocyte breakdown

pigment.


Ancillary Tests

Morbillivirus: PCR results indicate that the lung and brain of specimens NEB0075 and KXD0280 were

negative.

Biotoxins: ELISA tests indicate that the feces samples from both NEB0075 and KXD0280 were below the

detection limit for both domoic acid and saxitoxin.

Genetics: Based on the best information available, NEB0075, KXD0280, and KXD0281 have been

genetically assigned to the California Coastal Stock. This is further corroborated by the dorsal fin match

of KXD0280 to the coastal Southern California Bight (SCB) catalog (SCB dolphin no. 12054).

Discussion

All three T. truncatus had findings in common that included: coastal stock designation, robust body

condition, no external signs of fishery interaction, subcutaneous hemorrhage in the head region

concentrated along the lower jaws, subcutaneous emphysema associated with areas of cervical blubber

hemorrhage, and gas bubbles within the mesenteric and cerebral vasculature. In addition, the two

dolphins that were examined in more detail both had partially digested food in the stomach,

hemoabdomen, and were negative for morbillivirus, domoic acid, and saxitoxin.

19


 Two possible explanations for the observed findings in common with all three specimens are peracute

underwater entrapment (PUE) or exposure to mid-frequency active (MFA) sonar. Perimandibular

hemorrhage has been reported in cetacean mortalities associated with PUE (Jepson et al. 2013) while

mandibular hemorrhage in the “acoustic” fats has been associated with beaked whale mass stranding

events associated with MFA sonar (England et al. 2001, Fernandez et al. 2005, Ketten 2005). In addition,

the robust body condition of all three dolphins and recent feeding observed in the 2 stomachs

examined, indicate death was acute, which also supports both hypotheses. Gas emboli have been

reported for both MFA sonar and PUE cases (Fernandez et al. 2005, Moore et al. 2009), but it is possible

that the observed mesenteric and cerebral gas was present due to putrefaction. Hemorrhage in the

brain of one specimen (KXD0280) was found and scant lipids in the lungs of another (NEB0075); these

conditions have been observed in beaked whales associated with MFA sonar, albeit more severe and

extensive (England et al. 2001, Fernandez et al. 2005). Both hypotheses are plausible explanations

considering nearshore fishing activity occurs in this area and MFA sonar occurred in the area in the days

preceding the strandings of the two carcasses that were in fresh to moderate decomposition (NEB0075

and KXD0280). However, a lack of squid fishing effort and no bait fishing activity the day preceding the

strandings combined with no dolphin interactions reported gives less support for the PUE hypothesis. A

U. S. fishery operating illegally in nearshore waters or a Mexican nearshore fishery would be a more

likely source of PUE but there is no data to support or refute these as possible sources.

There are other observations or lack thereof that are not congruent with either PUE or MFA sonar. If

one is to consider PUE as the cause of death, the lack of external signs of PUE such as net/line/rope

marks, severed appendages, or sliced abdomen are perplexing. One would think that the force of a

struggle required to cause some of the observed traumatic lesions would leave external signs of that

struggle in the form of impressions, abrasions, or lacerations. If MFA sonar is considered as the cause of

death, hemorrhage around the ears might be expected as this has been noted in mass strandings of

beaked whales associated with MFA sonar (Fernandez et al. 2005, Ketten 2005), and this was not

observed. However, it is important to note that pathologies observed in relation to MFA sonar have

only been noted in beaked whales and could present differently in small delphinids such as T. truncatus
whose behavior and habitat differ.

Other conditions such as hemoabdomen that were observed in both fresh carcasses and

hemopericardium that was noted in one specimen, have not been reported in relation to PUE or MFA

sonar. Hemoabdomen is normally associated with either bleeding masses from major organs or

significant trauma to the abdomen. No masses or trauma to any of the organs was observed.

Hemopericardium can be caused by thoracic trauma or myocardial infarction. Subcutaneous

emphysema associated with areas of hemorrhage was also observed in both fresh dolphins, but this has

not been reported in association with either PUE or MFA sonar. It is likely that the hemoabdomen,

hemopericardium, and subcutaneous emphysema are a result of trauma, although it is not clear

whether that trauma was from PUE, MFA sonar, or some other unidentified source. Although the

bacterial adrenalitis noted in specimen KXD0280 was significant, it was likely an underlying condition,

considering the trauma that was common among all three strandings.


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 The tight correlations in time, space, and gross necropsy observations for all three T. truncatus discussed

here, suggest that they were all impacted by the same acute event. Although KXD0281 stranded 10

days after the first two dolphins, the advanced decomposition state of this dolphin suggests that it died

long before it was first observed on the beach and likely around the time the first two were observed.

All three dolphins clearly suffered severe trauma, likely anthropogenic in nature, although the exact

cause is unclear. PUE or MFA sonar are suspected etiologies.


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Division. January.


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