Aquatic Mammals 2012, 38(4), 423-427, DOI 10.1578/AM.38.4.2012.423
Low Prevalence of Visual Impairment in a Coastal Population of
Gray Seals (Halichoerus grypus) in the Gulf of St. Lawrence, Canada
Brian W. Kot,1, 2 Tadamichi Morisaka,3 Richard Sears,2
Don Samuelson,4 and Christopher D. Marshall1, 5
1Department of Marine Biology, Texas A&M University, Galveston, TX 77553, USA
2Mingan Island Cetacean Study, Inc., Longue-Pointe-de-Mingan, Québec G0G 1V0, Canada
3Wildlife Research Center, Kyoto University, Kyoto 606-8203, Japan
4Department of Small Animal Clinical Sciences, University of Florida, Gainesville, FL 32610, USA
5Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX 77843, USA
Visual impairment is common in captive pin-
nipeds (Sweeney, 1974; Ridgway et al., 1975;
Stoskopf et al., 1983; Greenwood, 1985; Colitz
et al., 2010a, 2010b), but its prevalence in the wild
is currently unclear due to the limited number of
published studies and inconsistent information in
the relevant literature (e.g., Griner, 1983; Filer
et al., 2003). Visual impairment is a broad cat-
egory that includes pathological, parasitological,
traumatic, or congenital conditions (e.g., Aguirre,
2004; Dailey et al., 2005). Although the preva-
lence of specific conditions affecting pinniped
vision (e.g., Leptospira pomona infection) may
be under-reported, partly due to the difficulties
of field diagnosis methods, general conditions
(e.g., opacities, lesions, etc.) are reported most
often (Stoskopf et al., 1985; Gerber et al., 1993;
Aguirre, 2004). What is clear is that visual impair-
ment reported in wild pinnipeds is usually associ-
ated with the cornea, anterior chamber, iris, and
lens (e.g., Smith et al., 1977; Stoskopf et al., 1985;
Schoon & Schoon, 1992; Baker et al., 1998).
However, this prevalence is likely because these
are the most conspicuous structures to observers.
Herein, we present results from a series of in-
water marine mammal surveys that included an
investigation of the prevalence of visual impair-
ment in a coastal population of western North
Atlantic gray seals (Halichoerus grypus). We
included behavioral information from individuals
with discernible eye problems and then showed
results from a literature survey to compare the
prevalence in our study area to those in published
studies of pinniped species, including gray seals,
around the world. A total of 23 surveys were con-
ducted from 21 June to 9 August 2011, and they
all were in the Mingan Archipelago of the Gulf
of St. Lawrence, Canada. Depending on weather
and sea conditions, most surveys consisted of four
12-km boat transects that were intermittent with
focal follows when one or more gray seals were
encountered. Observations were conducted with
the naked eye, 7 × 50 binoculars, and digital SLR
cameras (12.1-megapixel) with telephoto lenses
(300 and 600 mm). The total survey effort was
202.1 h with a mean of 8.8 h/d.
Survey results estimated 200 to 300 individ-
ual gray seals in the archipelago throughout the
summer, with highest abundances per survey effort
in three areas near identified haul-out locations
(Figure 1A-C). However, difficulties with identi-
fying and marking individuals likely resulted in
some repeated observations. Throughout our sur-
veys, only one gray seal with a conspicuous visual
impairment was observed, indicating a conserva-
tive prevalence of 1 of 200 (0.5%) gray seals in
The impaired gray seal was a bull that was
encountered on 22 July 2011 near 50° 09' 46.7" N,
63° 53' 49.2" W in approximately 35 m of water
(Figure 1). Its left eye exhibited a condition resem-
bling endophthalmitis (inflammation of the inter-
nal coats of the eye; Figure 2). The principal cause
of endophthalmitis is penetration of the eye, usu-
ally the cornea, by a sharp foreign body that can
introduce bacteria into the anterior chamber, lens,
and vitreous as well as the cornea. Other causes
include various endogenous systemic infections.
Typically, the entire eye becomes affected, often
filled with pus, and the cornea turns completely
opaque (Samuelson & Brooks, 2011) such as seen
in the impaired gray seal we observed.
424 Kot et al.
A second adult male without a visual impair-
ment was within 100 to 300 m of the first gray seal
throughout our 46-min observation period. Both
bulls were likely part of the herd of approximately
50 gray seals that were 2.3 km away within the
shallow Baie aux Loups Marins (Gray Seal Bay)
along the south shore of Grande Île (Big Island;
Figure 1). Approximately 25 gray seals were
hauled out at La Chaîne de Roches (Chain of
Rocks; H2 in Figure 1) within the bay, and the
other 25 were in adjacent shallow water (< 10 m).
Both gray seals were vigilant at the surface and
watched us for 10 to 30 s at least once before each
dive. The visually impaired gray seal initially
remained beyond 250 m of our 4.3-m boat, but
eventually he approached to within 75 m.
Published information on the prevalence of
visual impairment in the three taxonomic fami-
lies of pinnipeds in the wild is limited. The exist-
ing literature currently encompasses nine spe-
cies that collectively show 185 of 4,244 (4.3%)
individuals with any type of visual impairment
Figure 1. Map of study area (see open rectangle on inset map for a geographic reference) in Quebec, Canada (modified from
Google Earth, Version 6.1). H1: gray seal haul-out areas on Île de la Maison (House Island; left) and Île du Wreck (Wreck
Island; right); H2: La Chaîne de Roches (Chain of Rocks) haul-out area on Grande Île (Big Island; GI), the location near
where the impaired animal was encountered. A through C indicate locations of highest gray seal abundance throughout the
summer of 2011. Parenthetical values indicate estimated number of gray seals encountered per hour of effort in areas A
through C. Dashed lines indicate the four 12-km transect lines used for the surveys.
Figure 2. Photograph of a bull gray seal with visual impairment of its left eye from a condition resembling endophthalmitis
(A), including a close-up (B)
425 Visual Impairment in Gray Seals
(Table 1), although this differs widely among
specific reports. Among otariids, 4 of 765 (0.5%)
California sea lions (Zalophus californianus) had
some form of visual impairment (Gerber et al.,
1993). Likewise, 79 of 1,716 (4.6%) Northern
fur seals (Callorhinus ursinus) were reported
with eye lesions (Stoskopf et al., 1985). An ear-
lier account of northern fur seals showed 3 of 150
(2%) pups with a bacterial infection (Leptospira
pomona), causing dilated and congested vessels of
the iris, and hemorrhaging in the anterior chamber
of the eye (Smith et al., 1977). A report of subant-
arctic fur seals (Arctocephalus tropicalis) showed
1 of 12 (8%) individuals with protruding eyes
and an infected conjunctiva (Velozo et al., 2009).
Finally, a study of juvenile Galapagos sea lions
(Zalophus wollebaeki) showed individuals with
conjunctivae that held up to 47 parasitic eye flukes
(Philophthalmus zalophi; Dailey et al., 2005).
Among phocids, multiple reports of Weddell
seals (Leptonychotes weddellii) showed 14 of
295 (4.7%) seals and 28 of 498 (5.6%) seals with
leukomas (corneal opacities), punctured globes,
mucopurulent discharges, and purulent conjuncti-
vitis (McFarlane, 2009; Yochem et al., 2009). One
study of gray seals showed no visual impairment
in 36 individuals (Baker, 1987). Another showed
none in 33 young pups (< 16 wks) and 20 juve-
niles, but 2 of 50 (4%) older pups (> 16 wks)
with panophthalmitis (inflammation of the entire
eye) and 1 of 38 (2.6%) adults with corneal ulcer-
ations (Baker et al., 1998). Hawaiian monk seals
(Monachus schauinslandi) have been reported
with 21 of 158 (13%) individuals with ocular dis-
charge, “puffy eyes,” diffuse maculae and nebulas,
and leukomas (Aguirre, 2004).
Other reports of phocid visual impairment
include anecdotes of successfully foraging blind
ring seals (Phoca hispida saimensis; Hyvärinen,
1989), a harp seal with bilateral cataracts (Erlacher-
Reid et al., 2011), and a female Northern elephant
seal (Mirounga angustirostris) with a punctured
eye likely caused by male mating aggression
(Le Boeuf & Mesnick, 1991). A similar account of
aggression in Southern elephant seals (M. leonina)
reported 3 of 170 (1.7%) individuals with white
opacities, lacerated corneas, and inflamed nic-
titating membranes (Tierney, 1977). One report
showed 7 of 59 (11.8%) leopard seals (Hydrurga
leptonyx) with discharges and conjunctivitis (Gray
et al., 2009). An unusual case of Lake Baikal seals
(Pusa sibirica) with ophthalmitis was reported in
individuals with a morbillivirus infection similar
to canine distemper virus (CDV) (Grachev et al.,
1989). The highest reported prevalence of visual
impairment in any pinniped species in our lit-
erature survey was 21 of 44 (48%) harbor seals
(Phoca vitulina); bilateral lenticular lesions, len-
ticular malformations, and cataracts were identi-
fied, yet final conclusions about their causes could
not be determined (Schoon & Schoon, 1992).
Reliable estimates of the prevalence of visual
impairment in wild walruses (Odobenus rosmarus)
are not currently possible due to a paucity of pub-
lished reports. However, one investigation of 17
carcasses noted some individuals with prolapsed
Table 1. Low prevalence of visual impairment (% VI = [sum NVI / sum N] × 100 = 4.3%) reported from 16 studies of nine
different species of pinnipeds in the wild; studies with small sample sizes (N < 5) were not included. When considered
independently, the gray seal % VI was 1.6%, which is relatively similar to the 0.5% prevalence in our study area.
Species N NVI References
Stoskopf et al., 1985
Smith et al., 1977
Gerber et al., 1993
Velozo et al., 2009
Gray et al., 2009
Yochem et al., 2009
Schoon & Schoon, 1992
Baker et al., 1998
Baker et al., 1998
Baker et al., 1998
Baker et al., 1998
Kot et al., this study
Sum 4,244 185
% VI 4.3
426 Kot et al.
eyes (Garlich-Miller et al., 2011), although post-
mortem changes cannot be ruled out. Another
report generalized that walrus eye loss can develop
from dento-alveolar abscesses resulting from
advanced tusk wear (Cornell & Antrim, 1987).
In summary, our study provides evidence that
gray seals in the Mingan Archipelago within the
Gulf of St. Lawrence, Canada, have a low preva-
lence of visual impairment. This is consistent with
results from our literature survey that showed a
similarly low prevalence in nine other pinniped
species from around the world. When considered
independently, the gray seal literature indicated
a low prevalence of 1.6%, which is relatively
similar to the low prevalence in our study area.
Collectively, this study adds to the few published
records of North Atlantic gray seals with ocular
problems and provides information supporting
a low prevalence of visual impairment in wild
This study was funded as part of a collaborative
program between the National Fish and Wildlife
Foundation and the U.S. Marine Mammal
Commission, and the Department of Marine
Biology at Texas A&M University. Additional
support was provided by Bio-Logging Science,
The University of Tokyo (UTBLS; Investigator:
Katsufumi Sato). We thank Marie-Pierre Maillet
and the Mingan Island Cetacean Study, Inc. for
their logistical support of this work.
Aguirre, A. A. (2004, May). An ocular disease of
unknown etiology in Hawaiian monk seals (Monachus
schauinslandi). Abstracts of the European Association of
Zoo- and Wildlife Veterinarians 5th Scientific Meeting,
Baker, J. R. (1987). Causes of mortality and morbidity in
wild juvenile and adult grey seals (Halichoerus grypus).
British Veterinary Journal, 143, 203-220. http://dx.doi.
Baker, J. R., Jepson, P. D., Simpson, V. R., & Kuiken,
T. (1998). Causes of mortality and non-fatal condi-
tions among grey seals (Halichoerus grypus) found
dead on the coasts of England, Wales and the Isle of
Man. Veterinary Record, 142, 595-601. http://dx.doi.
Colitz, C. M. H., Renner, M. S., Manire, C. A., Doescher, B.,
Schmitt, T. L., Osborn, S. D., . . . Rudnick, J. C. (2010a).
Characterization of progressive keratitis in Otariids.
Veterinary Ophthalmology, 13(Supp. 1), 47-53. http://
Colitz, C. M. H., Saville, W. J. A., Renner, M. S., McBain,
J. F., Reidarson, T. H., Schmitt, T. L., . . . Terrell, K.
(2010b). Risk factors associated with cataracts and
lens luxations in captive pinnipeds in the United States
and the Bahamas. Journal of the American Veterinary
Medical Association, 237, 429-436. http://dx.doi.
Cornell, L. H., & Antrim, J. E. (1987). Anesthesia and tusk
extraction in walrus. Journal of Zoo Animal Medicine,
18, 3-6. http://dx.doi.org/10.2307/20094816
Dailey, M., Ellin, R., & Parás, A. (2005). First report of para-
sites from pinnipeds in the Galapagos Islands, Ecuador,
with a description of a new species of Philophthalmus
(Digenea: Philophthalmidae). The Journal of Parasitology,
91, 614-617. http://dx.doi.org/10.1645/GE-3425
Erlacher-Reid, C., Colitz, C. M. H., Abrams, K., Smith, A.,
& Tuttle, A. D. (2011). Bilateral ocular abnormalities in
a wild stranded harp seal (Phoca groenlandica) sugges-
tive of anterior segment dysgenesis and persistent hyper-
plastic primary vitreous. Journal of Zoo and Wildlife
Medicine, 42, 300-303. http://dx.doi.org/10.1638/2009-
Filer, R., Haulena, M., Fauquier, D., & Gulland, F. M. D.
(2003, May). Clear corneal cataract extraction in
a northern elephant seal (Mirounga angustirostris).
Proceedings of the 34th Annual Meeting of the
International Association for Aquatic Animal Medicine,
Kohala Coast, HI.
Garlich-Miller, J., Neakok, W., & Stimmelmayr, R. (2011).
Field report: Walrus carcass survey, Point Lay Alaska,
September 11-15, 2011 (Report of the U.S. Fish and
Wildlife Service). Washington, DC: U.S. Fish and
Gerber, J. A., Roletto, J., Morgan, L. E., Smith, D. M., &
Gage, L. J. (1993). Findings in pinnipeds stranded along
the central and northern California coast, 1984-1990.
Journal of Wildlife Diseases, 29, 423-433.
Grachev, M. A., Kumarev, V. P., Mamaev, V. L., Zorin, L. V.,
& Baranova, L. V. (1989). Distemper virus in Baikal seals.
Nature, 338, 209. http://dx.doi.org/10.1038/338209b0;
Gray, R. B., Rogers, T. L., & Canfield, P. J. (2009). Health
assessment of the leopard seal, Hydrurga leptonyx, in
Prydz Bay, eastern Antarctica and NSW, Australia. In R.
Kerry & M. J. Riddle (Eds.), Health of Antarctic wild-
life: A challenge for science and policy (pp. 167-192).
Berlin: Springer-Verlag. http://dx.doi.org/10.1007/978-
Greenwood, A. G. (1985). Prevalence of ocular anterior
segment disease in captive pinnipeds. Aquatic Mammals,
Griner, L. A. (1983). Pathology of zoo animals. San Diego:
Zoological Society of San Diego.
Hyvärinen, H. (1989). Diving in darkness: Whiskers
as sense organs of the ringed seal (Phoca hispida).
Journal of Zoology, 218, 663-678. http://dx.doi.
Le Boeuf, B. J., & Mesnick, S. (1991). Sexual behavior
of male northern elephant seals: I. Lethal injuries to
Visual Impairment in Gray Seals 427
adult females. Behaviour, 116, 143-162. http://dx.doi.
McFarlane, R. A. (2009). Health assessment and diseases of
the Weddell seal, Leptonychotes weddellii, in Vestfold Hills,
east Antarctica. In R. Kerry & M. J. Riddle (Eds.), Health of
Antarctic wildlife: A challenge for science and policy (pp.
139-166). Berlin: Springer-Verlag. http://dx.doi.org/10.1007/
Ridgway, S. H., Geraci, J. R., & Medway, W. (1975).
Diseases of pinnipeds. Rapport et Proces-Verbaux des
Réunions Conseil International pour l’Exploration de la
Mer, 169, 327-337.
Samuelson, D. A., & Brooks, D. E. (2011). Small animal
ophthalmology: Self-assessment color review. London:
Schoon, H-A., & Schoon, D. (1992). Lenticular lesions in
harbor seals (Phoca vitulina). Journal of Comparative
Pathology, 107, 379-388. http://dx.doi.org/10.1016/0021-
Smith, A. W., Brown, R. J., Skilling, D. E., Bray, H. L., &
Keyes, M. C. (1977). Naturally-occurring Leptospirosis
in northern fur seals (Callorhinus ursinus). Journal of
Wildlife Diseases, 13, 144-148.
Stoskopf, M. K., Hirst, L. W., & Graham, D. (1983). Ocular
anterior segment disease in captive pinnipeds. Aquatic
Mammals, 10(2), 34-44.
Stoskopf, M. K., Zimmerman, S., Hirst, L. W., & Green,
R. (1985). Ocular anterior segment disease in northern
fur seals. Journal of the American Veterinary Medical
Association, 187, 1141-1144.
Sweeney, J. C. (1974). Common diseases of pinnipeds.
Journal of the American Veterinary Medical Association,
Tierney, T. J. (1977). Disease and injury in the southern
elephant seal. Australian Veterinary Journal, 53, 91-92.
Velozo, R. S., Schiavetti, A., & Dórea-Reis, L. W. (2009).
Analysis of subantarctic fur seal (Arctocephalus
tropicalis) records in Bahia and Sergipe, north-eastern
Brazil. Marine Biodiversity Records, e117, 1-5.
Yochem, P. K., Stewart, B. S., Gelatt, T. S., & Siniff,
D. B. (2009). Health assessment of Weddell seals,
Leptonychotes weddellii, in McMurdo Sound,
Antarctica. In R. Kerry & M. J. Riddle (Eds.), Health
of Antarctic wildlife: A challenge for science and policy
(pp. 123-138). Berlin: Springer-Verlag. http://dx.doi.