Review
Shifting Baselines and The Extinction of The
Caribbean Monk Seal
JULIO A. BAISRE
Acuario Nacional de Cuba, Ave.1ra y Calle 60, Miramar, Playa, La Habana,email juliob@acuarionacional.cu
Abstract: The recent extnction of the Caribbean monk seal Monachus tropicalis has been considered an
example of a human-caused extinction in the marine environment, and this species was considered a driver
of the changes that have occurred in the structure of Caribbean coral reef ecosystems since colonial times. I
searched archaeological records, historical data, and geographic names (used as a proxy of the presence of
seals) and evaluated the use and quality of these data to conclude that since prehistoric times the Caribbean
monk seal was always rare and vulnerable to human predation. This finding supports the hypothesis that in
AD 1500, the Caribbean monk seal persisted as a small fragmented population in which individuals were
confined to small keys, banks, or isolated islands in the Gulf of Mexico and the Caribbean Sea. This hypothesis
is contrary to the assumption that the species was widespread and abundant historically. The theory that
the main driver of monk seal extinction was harvesting for its oil for use in the sugar cane industry of
Jamaica during the 18th century is based primarily on anecdotal information and is overemphasized in
the literature. An analysis of reported human encounters with this species indicates monk seal harvest was
an occasional activity, rather than an ongoing enterprise. Nevertheless, given the rarity of this species and
its restricted distribution, even small levels of hunting or specimen collecting must have contributed to its
extinction, which was confirmed in the mid-20th century. Some sources had been overlooked or only partially
reviewed, others misinterpreted, and a considerable amount of anecdotal information had been uncritically
used. Critical examination of archaeological and historical records is required to infer accurate estimations
of the historical abundance of a species. In reconstructing the past to address the shifting baseline syndrome,
it is important to avoid selecting evidence to confirm modern prejudices.
Keywords: historical data, historical ecology, marine mammals, Monachus tropicalis, rarity, shifting baseline
syndrome, species extinction, vulnerability
Puntos de Referencia Cambiantes y la Extinción de la Foca Monje Caribeña
Resumen: La reciente extinción de la foca monje caribeña Monachus tropicalis se ha considerado un
ejemplo de extinción causada por humanos en el ambiente marino. Esta especie fue considerada un conductor
de cambios en la estructura de los ecosistemas de arrecife de coral caribeños desde tiempos coloniales. Busqué
registros arqueológicos, datos históricos y nombres geográficos (usados como representación de la presencia
de focas) y evalué el uso y calidad de estos datos para concluir que desde tiempos prehistóricos la foca monje
del Caribe siempre fue rara y vulnerable a la depredación humana. Este hallazgo apoya la hipótesis de que
en 1500 DC, la foca monje del Caribe persistı́a como una pequeña población fragmentada en la que los
individuos estaban confinados a cayos pequeños, bancos o islas aisladas en el Golfo de México y el Mar
Caribe. Esta hipótesis es contraria a la suposición de que la especie históricamente tenı́a una distribución
amplia y era abundante. La teorı́a de que el principal conductor de la extinción de la foca monje era su
captura para obtener aceite que se usaba en la industria de la caña de azúcar en Jamaica durante el s. XVIII
se basa principalmente en información anecdótica y se sobreenfatiza en la literatura. Un análisis de reportes
de encuentros humanos con esta especie indica que la caza de focas monje era una actividad ocasional en
lugar de un operativo continuo. Sin embargo, dada la rareza de la especie y su distribución restringida, hasta
los niveles mı́nimos de caza o recolección de especı́menes debieron haber contribuido a su extinción, que fue
confirmada a mediados del s. XX. Algunas fuentes han sido pasadas por alto o solamente han sido revisadas
Paper submitted October 24, 2012; revised manuscript accepted March 24, 2013.
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Conservation Biology, Volume 27, No. 5, 927–935
C 2013 Society for Conservation Biology
DOI: 10.1111/cobi.12107
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Shifting Baselines and Caribbean Monk Seal Extinction
parcialmente, otras han sido malinterpretadas, y una cantidad considerable de información anecdótica ha
sido usada sin cuestionar. La examinación crı́tica de registros arqueológicos e históricos se requiere para
inferir las estimaciones precisas de la abundancia histórica de las especies. En la reconstrucción del pasado
para enfocarse al sı́ndrome de puntos de referencia cambiantes es importante evitar escoger evidencia que
confirme prejuicios modernos.
Palabras Clave: datos históricos, ecologı́a histórica, extinción de especies, mamı́feros marinos, Monachus
tropicalis, rareza, sı́ndrome de puntos de referencia cambiantes, vulnerabilidad
Introduction
Pauly (1995) coined the term “shifting baseline syndrome.” He pointed out to fishery scientists the need
to avoid the risk associated with erroneous perceptions
about the status of fish populations and emphasized the
use of past evidence to reconstruct the history of fisheries. This paper immediately gained wide acceptance
and marine ecologists have since turned to the past to answer scientific questions and to model the size of historical populations (e.g., Jackson 1997; Bjorndal & Jackson
2003; McClenachan et al. 2006; McClenachan & Cooper
2008).
The Caribbean monk seal (Monachus tropicalis) has
been used as an example of the shifting baseline syndrome. Advocates of the syndrome assumed the monk
seal played an important role in Caribbean coral reef
ecosystems (Jackson 1997, 2001; Jackson et al. 2001;
Pandolfi et al. 2003). Modeling the size of the unexploited population reinforced this view, and a simulation
model also showed that productivity of coral reef fishes
decreased by several orders of magnitude after the monk
seal was extirpated (McClenachan & Cooper 2008).
The Caribbean monk seal occurred in the Gulf of Mexico and in the Caribbean Sea. By the time the scientific
community started to learn about it, the species was
practically extinct (Allen 1887). The last individuals were
observed on the Serranilla Bank in 1952 (Rice 1973).
Extensive aerial surveillance in Yucatán and Central
America (Kenyon 1977) and maritime surveys between
the Bahamas and Santo Domingo (Sergeant et al. 1980)
and off the Yucatan Penninsula (LeBoeuf et al. 1986)
failed to detect a single individual. In 1996, the International Union for Conservation of Nature declared the
Caribbean monk seal extinct (IUCN 1996).
Understanding the causes and consequences of the extinction of species, particularly those associated with human presence, is a priority for conservation science. The
current mainstream view is that the Caribbean monk seal
was a widely distributed and relatively abundant species
in the region when Columbus first arrived in the Americas
(Allen 1887; Timm et al. 1997; Adam 2000). Its extinction
is blamed on intensive hunting for oil extraction during
early colonial times (Adam 2000; Adam & Garcı́a 2003;
McClenachan & Cooper 2008). The capture and killing
of seals for scientific collections (Allen 1887; Ward 1887;
Allen 1942) also contributed to their extincton.
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Volume 27, No. 5, 2013
Some believe there is not enough evidence to conclude
that the Caribbean monk seal was an abundant species
or that it was potentially resilient to human exploitation
(Baisre 2010). Why is this large and conspicuous vertebrate so scarce in the archaeological record? Why was
this supposedly widely distributed and abundant species
seen only during the second voyage of Columbus? Why
didn’t other European explorers, colonizers, and pirates
mention sighting monk seals? Why does the first scientific
description of the monk seal come more than 350 years
after they were seen for the first time?
We sought to provide a more objective interpretation of the evidence surrounding the extinction of the
Caribbean monk seal. I sought to provide new insights
into the need for rigor in interpreting historical information when establishing baselines to inform the design of
conservation measures for critically endangered species.
Methods
I critically examined all archaeological records, historical
observations and data on geographic names that have
been included and quoted in previous syntheses about
the Caribbean monk seal (Allen 1880; King 1956; Rice
1973; Timm et al. 1997; Adam 2000; Adam & Garcia 2003;
McClenachan & Cooper 2008) and added 3 archaeological and 2 historical records.
Overall, I included 115 observations: 21 paleontological and archaeological records, 67 historical observations, and 27 localities named after seals (Table 1). I
mapped all records in a geographical information system
Table 1. Number of observations and sources of data on the Caribbean
monk seal used in this paper in comparison with previous reviews.
Reference
Allen 1887
King 1956
Rice 1973
Timm et al. 1997
Adams & Garcia
2003
McClenachan &
Cooper 2008
Baisre, this paper
∗ Number
thors.
Archaeological
data
Historical
data
Geographic
names
Total
–
–
–
–
22
9
19
30
17
71
1
6
–
9
27
10
25
30
26
120
approximately
20∗
21
approximately
100∗
67
approximately
20∗
27
140
115
of observations estimated from the figures given by au-
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Baisre
Table 2. Pleistocene (1–4) and Holocene (5–21) records of the occurrence of monk seals in the Caribbean Sea and the Gulf of Mexico with
information about the material found in archaeological sites.
Paleontological and archaeological site∗
Melbourne (Brevard County, Florida)
Lake Hellen Blazes (Brevard County, Florida)
Leisey (Hillsborough County, Florida)
Rigby Shell Pits (Hillsborough County, Florida)
Long Bayou (Saint Petersburg, Pinellas County, Florida)
South Indian Field (Brevard County, Florida)
Wightman Site (Sanibel Island, Lee County, Florida)
Marco Island (Collier County, Florida)
Granada (Miami, Dade County, Florida)
Miami Circle (Miami, Florida)
Cumberland Island (Camden County, Georgia)
Caracoles Midden in Ponce, Puerto Rico
Cinnamon Bay (Saint John, U.S. Virgin Islands)
Sint Eustatius (Netherlands Antilles)
Hichman’s Site (Nevis)
Hichman’s Shell Heap (Nevis)
Santa Barbara (Curacao)
Sint Michiel (Curacao)
Manatı́, north coast of Cuba
Matanzas, north coast of Cuba
Xcambó, coast of Yucatan
Fossil records (years ago)
0.7–0.01 million
0.7–0.01 million
1.77–1.07 million
1.77–1.07 million
approximately 4500–2800
approximately 4000
approximately 2300–1900
2000–1500
2000–500
2500–1250
2600–1300
700–510
1000–510
1400–1100
1660
2550
1500–400
3820–3790
not dated
not dated
700–250
Materials
proximal phalanx
right mandible
left maxilla
bones of 3 individuals
bones of 3 individuals
lower premolar
mandible
2 foot bones
phalanx
incisor without decoration
rib fragment
cranial and leg bones of 9
specimens some perforated
dental pieces
Reference
Ray (1961)
Ray (1961)
Berta (1995)
Berta (1995)
Ray (1961), Cumbaa (1980)
Cumbaa (1980)
Wing (1992)
Cumbaa (1980)
Wing & Loucks (1984)
Adam (2000)
Milanich (1971)
Wing (1992)
Adam (2000)
Debrot (2000)
Wing (1992, 2001)
Wing (1992, 2001)
Debrot (2000)
Debrot (2000)
Arredondo (1996)
Vento Franco (2001)
Götz & Sierra Sosa (2011)
∗ Canines
of Caribbean monk seals have been found in 2 undated sites in Texas, but they may represent trade items of North American
indigenous people or colonial Spaniards (Raun 1964; Adam 2000).
database. But in contrast with previous authors (Timm
et al. 1997; Adam 2000; Adam & Garcia 2003; McClenachan & Cooper 2008), I did not combine data from the
different sources. Archaeological records and historical
observations are presented separately, in chronological
order, to avoid confusing temporal and spatial scales. I
classified human encounters with the Caribbean monk
seal into 4 groups: no interaction, hunting for food,
hunting for oil, and collection for research, including
capture of live animals for aquariums. The time elapsed
between historical observations was calculated for 2 periods, before and after the first published description of
the species in 1843.
Difficulties I faced in this review included lack of data
and observations and reliability and use of data. Many of
the observations available are anecdotal and do not meet
the basic requirements of ordinary zoological samples;
that is, they do not indicate species locality, number of
specimens, or date of collection.
Prehistoric Record
Paleontological and archaeological records with remains
of the Caribbean monk seal are rare and limited to very
few localities (Table 2). Records before the Holocene are
only known from Florida (Adam & Garcia 2003), and
there are only 4 records of Pleistocene fossils of this
species in Florida sites (Adam 2000). Archaeological remains from the Holocene are also scarce (Cumbaa 1980;
Adam 2000; Debrot 2000; Newson & Wing 2004), and
seals are notably absent from most archaeological sites in
the Lesser Antilles (Pregill et al. 1994). Most of the records
are from Florida, whereas Caribbean fossils are known
with certainty only from a few localities (Adam 2000;
Debrot 2000). Although I included 2 additional records
from Cuba and another from Yucatan in this review, the
scarcity of archaeological records is still remarkable. Even
more striking than the low number of archaeological sites
is the low number of specimens (Cumbaa 1980; Adam
2000). Most records consist of only a single specimen
and, in some cases, a few dental fragments, which may
have been used as trade items among prehistoric peoples
in the Caribbean region (Raun 1964).
The low number of archaeological records of individual
West Indian monk seals suggests the species was never
used as a major source of subsistence (Adam 2000).
Despite that, some archaeologists have interpreted the
limited record of monk seal remains as a sampling bias,
arguing that only the meat would have been brought to
the prehistoric settlements and that the skull and bones
were left at the butchering sites due to their weight and
limited use (Newson & Wing 2004). This argument does
not apply to other large animals in the Caribbean (e.g.,
manatees and sea turtles), for which there are clear indications of their consumption by prehistoric peoples.
It is probable that seals were exposed to hunting only
while hauled out on isolated islands and banks and were
never an important human food source. An early account
claimed monk seals did not seem to be eaten by the
indigenous people of Florida and were consumed only
by the upper classes (Fontaneda 1575). This account provides indirect evidence that the species was uncommon
at that time.
Absence of evidence is not evidence of absence. However, the rarity of monk seal remains in the archaeological
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Volume 27, No. 5, 2013
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Shifting Baselines and Caribbean Monk Seal Extinction
0
2
4
6
8
10
12
14
16
18
Triangle
Bahamas
DryTortugas
Pedro´s Bank
Alacranes Islands
Florida Keys
Alto Vela
Klein Curacao
Off Cape Florida
Off Campeche
Chinchorro Reef
Serranilla Bank
Rosalinda Bank
Guyana
Veracruz
Guadaloupe
Anina Islands
Isle of Pines
Off Yucatan
Havana
Barbareta Island
Morat Island
Guanaja Island
Key West
Savana-la-mar
Uvita
Providence Island
Key Salt Bank
Figure 1. Number of historical observations of monk seals from each locality.
Historical Records
There are 67 historical accounts that mention the presence of the Caribbean monk seal. Although these data
included first- and second-hand accounts and a few imprecise or inaccurate descriptions, it is noteworthy that
in the Triangle Islands in the Gulf of Mexico the presence of seals was not only well documented, but also
represented 25% of all the observations of this species.
Overall, presence of Caribbean monk seal was recorded
at 28 different localities; however, at 16 of these localities, seals were recorded only once (Fig. 1). The elapsed
time from the first report in 1494 (Kerr & Edin 1811)
to the last observation in Serranilla Bank in 1952 (Rice
1973) was 458 years, with an average time between observations of 7.4 years (SE 1.72). However, there was
a significant difference (p < 0.001) in the average time
between records before (20.1 years [SE 5.03]) and after
(2.5 years [SE 0.47]) the first description of the species
in 1843. As a species becomes rare, the proportion of
false positives increases (McKelvey et al. 2008), and this
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30
25
No. of observaons
record seems to be real and should not be interpreted as
being caused by sampling bias only. Therefore, I took this
scarcity of records as the starting point for a working hypothesis: Caribbean monk seals were rare when humans
first arrived in the islands and probably played a minor
ecological role. My analysis of the historical evidence is a
means to test this hypothesis.
20
15
10
5
0
16th
17th
18th
19th
20th
Century
Figure 2. Number of observations of monk seals
reported in different centuries. Number in the 16th
century includes a data point from the 15th century.
factor may explain the higher number of records after the
species was described for the first time. The temporal
grouping of all the historical accounts (Fig. 2) showed
there were 16 records during the first 3 centuries. Five
of these records are first-hand accounts. Considering the
large range of the species and the long time frame of the
historical record, the scarcity of records of the presence
of monk seals is surprising (e.g., Allen 1887; Rice 1973).
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Baisre
Until 1880, the only specimen of the Caribbean monk
seal extant in any museum was an imperfect skin in
the British Museum (Allen 1880). The lack of mention
of monk seals in several books dealing with the natural
history of the region during the 18th and 19th centuries
indicates monk seals escaped the naturalists’ eyes (e.g.,
Sloane 1707, 1725; Catesby 1731, 1754; Parra 1787; Poey
1851). The materials available in museum collections provide further indirect evidence of this seal’s abundance.
In England there are 2 specimens from Pedro’s Bank in
the collections of the British Museum and 1 specimen in
the Cambridge Zoological Museum (King 1956). There
is 1 skull at the Museum of La Plata, Buenos Aires, obtained from an expedition to the Triangle Islands in 1886
(Daneri & De Santis 2002). The largest collections are at
the American Museum of Natural History, where there are
14 specimens, 5 from Yucatán, Mexico, and the others
from unknown localities, and the U.S. National Museum
of Natural History, where there are 44 specimens, 40 from
Mexico, 1 from Cuba, and 3 from unknown localities.
The reports from the 4 long voyages of Columbus,
from 1492 to 1504, which were wide-scale exploratory
surveys of the whole region, and later the writings and
voyages of Dampier also provide indications of the historical rarity of Caribbean monk seals. Dampier’s writings
have been cited frequently as a credible and valuable
source of historical data on marine resources (Jackson
1997, 2001; Jackson et al. 2001; McClenachan & Cooper
2008). Nonetheless, Dampier’s reports seem to have been
misinterpreted in this case. He was the first to note the
scarcity of seals in the Caribbean region and wrote (emphasis added): “Seals are frequent in the northern parts of
Europe and America, and in the southern parts of Africa,
as about the Cape of Good Hope and at the Straits of
Magellan. I never saw any in the West Indies but in the
Bay of Campeche, at certain islands called the Alacranes,
and at others called the Desarts” (Dampier 1699: 90).
Geographic Names
Allen (1887) was the first to use a geographic name as a
proxy to indicate the presence of Caribbean monk seals.
Several authors subsequently produced maps outlining
the historical distribution of the species (e.g., Timm
et al. 1997; Adam 2000; Adam & Garcia 2003; McClenachan & Cooper 2008). However, information on geographic names should only be considered a complement
to actual sightings. Animal place names do not necessarialy indicate that an animal was present in high numbers
at a particular place; rather, they may reflect similarites
between features of the landscape and the animal. For
example, places have been named because they are reminiscent of turtles (e.g., Baisre 2010), and this practice may
also have occurrred with other large and conspicuous animals such as seals. Adam and Garcia (2003) identified 27
Acvity
Hunng for oil
Hunng for research
Hunng for food
No interacons
0
5
10
15
20
25
30
No. of encounters
Figure 3. Number of human encounters with the
Caribbean monk seal grouped by type of human
activity.
localities supposedly inhabited by Caribbean monk seals.
Most of these localities are so small and isolated, that it
is very difficult to conclude that dense concentrations of
seals could have been recorded there on historical nautical charts of the West Indies (McClenachan & Cooper
2008). Furthermore, the significance of 27 place names
must be considered in the context of the size of the
Caribbean Sea, which is over 2.5 million km2 (Richards &
Bohnsack 1990) and contains thousands of small islands,
keys, and oceanic banks.
Overhunting
I classified historical observations describing human encounters with the Caribbean monk seal into 4 groups to
assess the relative importance of these groupings. Contrary to expectation, encounters with no interactions and
collection of seals for research purposes comprised the
largest number of records (Fig. 3). Accounts of seals being hunted for food, including by shipwrecked persons,
were also relatively large; hunting for oil extraction had
the fewest records. I made a detailed analysis of the references dealing with the hunting of the Caribbean monk
seal for oil extraction (Table 3) to evaluate this practice. Contrary to the conclusions of Adam (2000) and
McClenachan and Cooper (2008), an unknown author
(Anonymous 1722) provided the only definite mention of
the use of the oil of the Caribbean monk seal for the sugar
cane industry. The records contain a notable lack of details (dates, localities, number of animals) and unrealistic
(e.g., seals killed by night) or fantastic claims (e.g., giant
seals). These data do not support the conclusion that seals
were the main source of oil in the Caribbean or that they
provided the oil for the sugar cane industry of Jamaica
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Shifting Baselines and Caribbean Monk Seal Extinction
Table 3. Historical accounts of Caribbean monk seal hunting for oil extraction, arranged in chronological order.
Locality
Alacranes Islands
Bahamas
Bahamas
Bahamas
Dry Tortugas
Bahamas
Triangle Islands
Off Honduras
Triangle Islands
∗ Italics
Observation
Reference
“Seals were especially common in the Alacranes Islands. The Spaniards do often
come hither to make oil of their fat. I never saw any [seal] in the West Indies.”
“The Bahamas Islands are filled with seals; sometimes fishers will catch 100 in a
night. They try or melt them, and bring off their oil for lamps to the Islands.”
“Yearly about winter the seals come up the shores of these Islands to breed and
are caught. Each of which affords about 20 gallons of oil which is exported to
Jamaica and other plantations for the use of their mills.”
“They make plenty of oil from the nurses, seals, etc. and a beneficial whale
fishery might be established here, as that fish comes in great numbers to wean
their young among the islands, and several have been thrown ashore, full of
the spermaceti; there is likewise found in the shore much ambergris.”
“At the north of Dry Tortugas there is a great plenty of seals, the fat of which the
Spaniards pay the bottom of their ships at Havana. The Indians of Ratones and
the fourth parts of Florida cure great quantities of this fish, which . . . they
exchange in traffic with the Spaniards, who come here from Havana with
European goods for the use of natives.”
“At the seal banks, they are to be seen, as far as the eye can discern, upward of
500 in number. They are usually from 15 to 18 feet long and about four feet
broad. The young seal are commonly born in pairs and are suckled for about
a fortnight at the place of their birth, when they are taken out to the sea by
their parents who instruct them in swimming and seeking for food, which
consists chiefly of seaweed. When taken very young, these animals may be
domesticated, will follow their master like a dog and come to him when
called by name.”
“In the spring, I was with Captain Lucas at the Triangle for a load of Mexican
guano. I only saw two seals there, which left the island in a hurry, so I can give
you no information from personal knowledge, although must have been great
numbers there, by the skeletons poor hides, etc.; and someone must have
carried on an extensive business in that line, for we made a grand bonfire of
perhaps hundred barrels of the remains.”
“By 1885, fishers from Bonacca (in Guanaja Island) were fishing them for meat
and oil.”
“the fishermen tell me that at one time there was a tremendous colony of
seals . . . but it is their belief that the Mexicans have killed a great many,
possibly all of them, for their oil . . . I know of no seals which have been taken
from the island in recent years.”
Dampier (1699, 1700)
Sloane (1707)
Anonymous (1722)
Bruce (1782)
Roberts (1763)
Nesbitt (1836)
Ward (1887)
Gaumer (1917)
Allen (1942)
highlight unrealistic observations (for further details see text).
(McClenachan & Cooper 2008). The lack of any trace
of oil-extraction practices, which needed large amounts
of firewood and would have left substantial quantities of
bones and skins on beaches, is further evidence against
the existince of monk seal oil industry in the Caribbean.
This evidence is noted in a report from the National Marine Fisheries Service (NMFS 2008) that recognizesthat
“documentation of harvest levels and practices that led
to this species’ population decline is nearly absent.”
Discussion
Two well-established facts in this extinction history of
the Caribbean monk seal require no further discussion:
the species is extinct (Kenyon 1977; LeBoeuf et al. 1986;
IUCN 1996; NMFS 2008) and human exploitation accelerated this process (Allen 1887; Gaumer 1917). The most
accepted view is that the Caribbean monk seal, albeit
vulnerable, was a relatively abundant species, widely dis-
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Volume 27, No. 5, 2013
tributed in the region, and massively hunted during the
early colonial period until its final extinction (Allen 1887;
Gaumer 1917; Timms et al. 1997; Adam 2000). Therefore,
the extinction of this large predator substantially affected
the Caribbean coral reef ecosystem (Jackson 1997, 2001;
Jackson et al. 2001; Pandolfi et al. 2003), which now
seems to be several times less productive than before the
extinction (McClenachan & Cooper 2008).
I found that most of the information about monk
seal distribution and abundance is anectodal. The historical existence of 13 breeding colonies (McClenachan
& Cooper 2008) (Table 1), for example, is poorly supported because the existence of several of the colonies
was inferred from the existence of 1 (Guadalupe, Guyana,
Veracruz, Serranilla Bank), or 2 (Alto Vela, Klein Curacao)
historical descriptions. Evidence of breeding colonies in
Anina Island (a locality impossible to chart) and on the
Cuban southern coast (from an erroneous historical account of a shipwreck) is even more difficult to accept.
Some of the evidence included no less than 14 repetitions
Baisre
of the same report (observations in the same locality and
with the same date). Despite the scarcity and inaccuracy
of these historical data, it has been concluded that hunting for oil extraction was the driver of the extinction of
the Caribbean monk seal, the historical population size of
which was alleged to be on the order of 233,000–338,000
individuals on the basis of mathematical modeling (McClenachan & Cooper 2008).
It seems obvious that more data and better models will
not address the problem of depleted resources, even if
the models include additional and more accurate historical data (Bolster 2006). It is hard to see how adding
more data to shift the model baseline is going to solve a
problem that modeling has been deeply complicit in creating (Van Sittert 2005). Good history begins with good
sources, and any analyses of the past should be based on
verifiable sources and recognizable historical methods
(Bolster 2006). Despite impressive analytical techniques,
poor input data may provide unreliable results (Jennings
et al. 2001).
An alternative hypothesis that I outlined previously
(Baisre 2010), considers that monk seals were a rare
species before European colonization. In The Origin of
Species, Darwin (1859) insisted that rarity is the attribute
of a vast number of species of all classes, in all countries, and both theory and empirical evidence suggest
that some species are extremely vulnerable because they
have a combination of traits that promote extinction.
There is a long and well-known list of biological and
ecological attributes associated with rare species, which
can be grouped into categories of rarity for regulatory or
conservation-planning purposes (Flather & Sieg 2007).
Rarity is often defined on the basis of a framework
(Rabinowitz et al. 1986) that considers the 3 axes of
habitat specialization, local abundance, and range size
(Harrison et al. 2008), all of which apply to the Caribbean
monk seal. This species was a habitat specialist, confirmed only from small islands and isolated banks in the
Gulf of Mexico and in the Caribbean Sea, and there is
no evidence that it lived on the mainland. Most of the
specimens found in Florida can be attributed to trade.
Such extreme habitat fragmentation not only makes encounters with humans difficult, but also does not support
the hypothesis of a high abundance. The low number of
historical records and the prolonged time between observations are additional evidence of low local abundance.
The most credible hypothesis that explains the lack of
archaeological and historical records of monk seals, their
limited geographic distribution, and the anecdotal information about hunting levels, hunting localities, and oil
trade is that the monk seal was a rare species when it
was first reported in the 15th century. This is the most
parsimonious explanation of why naturalists overlooked
a large mammal, obliged to haul out on sandy or rocky
beaches, for 350 years.
933
Extinction is a natural process that can occur without humans being present, but it is often accelerated or
driven by human activities. The rarity of the Caribbean
monk seal, the intrinsic vulnerability of this large and
slow-reproducing mammal, and its largely fragmented
distribution all contributed to its rapid extinction. The
question is “how naturally rare species have persisted
through evolutionary time, and whether particular characteristics have enabled them to avoid extinction despite
their small ranges, low abundances, and narrow habitat
requirements” (Harrison et al. 2008). What seems most
surprising in the case of the monk seal is how slowly
the process of extinction progressed. The most plausible
explanation is the restriction of this species to small, isolated islands and oceanic banks, which made contact with
humans more difficult. In areas with complex geography
it is more difficult to locate and kill every individual of
a larger organism than it is along more accesible coastlines or on individual islands (Carlton et al. 1999). When
European colonizers were shipwrecked on isolated islands of the Caribbean Sea and the Gulf of Mexico, they
rapidly exterminated the few individuals of the small
population. Unfortunately, the scientific interest in this
poorly known species also contributed to organized expeditions that completed the extinction processs (Allen
1887; Ward 1887).
In conservation biology, bad news (e.g., large decreases in populations, extirpations, and extinctions) is
often given priority in the highest ranked scientific journals (Hays 2004), and current views about monk seal
extinction may have been affected by this bias. Unfortunately, scientific evidence is too often poorly distinguished from the perpsective of the scientist in studies
of the effects of fishing (Jennings 2007). This prejudice
may raise public awareness about the effects of human
predation on extenction risk, but as I have demonstrated
here and as has been pointed out by Hilborn (2006),
this approach does not seem to provide a critical analysis of evidence. Although the value of data on historical distributions is widely recognized for improving our
understanding the structure, function, and processes of
ecosystems (Boshoff & Kerley 2010), historical population records for most species are fragmentary and of questionable quality if they exist at all (Balmford & Bond 2005;
Bonebrake et al. 2010). In adition, the use of anecdotal
data to establish the presence or geographic range of
rare or ellusive species is inherently unreliable (McKelvey
et al. 2008). Researchers should reexamine pre- and early
scientific evidence through modern prisms. However,
they must appreciate that the data may not be firm and
that testimonies may not be reliable (Taylor 2013). I hope
my review provides new insights into the rigorous process required to establish baselines aimed at informing
the design and implementation conservation measures
for critically endangered species.
Conservation Biology
Volume 27, No. 5, 2013
934
Acknowledgments
I am very grateful to W.F. Keegan, Florida Museum of
Natural History, for his encouragement and valuable suggestions, which improved very much the first draft of
this paper. I also thank the 4 anonymous reviewers,
who helped to correct some mistakes and improved the
manuscript, and H. Marsh, handling editor, who also provided appreciable help.
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