Vol. 11 (1): June 2008

So many seals, so little time:
The rapid extinction of the Caribbean monk seal

Kyle Baker, Fishery Biologist

National Oceanic and Atmospheric Administration, National Marine Fisheries Service
Southeast Regional Office, Protected Resources Division
St. Petersburg, Florida, U.S.A

Introduction

The U.S. National Oceanic and Atmospheric Administration’s National Marine Fisheries Service (NMFS) recently completed a review of the status of the Caribbean monk seal (Monachus tropicalis). The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and the World Conservation Union (IUCN) have set 50 years with no sightings as the cut-off for species extinction (World Conservation Union 1982). The last authoritative sighting of Caribbean monk seals was reported by C.B. Lewis in 1952 (Rice 1973), despite multiple survey efforts to locate the species. A sufficient period of time has elapsed since the last confirmed sighting of this once commonly observed species in the Caribbean, to support the conclusion that the species is now extinct. The IUCN Seal Specialist Group listed the Caribbean monk seal as extinct on its Red List of threatened and endangered species in 1996 (Seal Specialist Group 1996). However, interviews with coastal residents and fishermen, and reports of unidentified sightings of pinnipeds in the greater Caribbean region since 1996, resulted in speculation that a small population may have remained on some isolated reefs and atolls in the Caribbean Sea; thus, it has remained listed under the U.S. Endangered Species Act until its proposed removal due to extinction can be reviewed, and the public is provided an opportunity to comment on this finding, published in the species’ recent status review [see Further Information, below].

Upon review of the natural history and population decline of Caribbean monk seals, it is remarkable how a large population of an estimated few hundred thousand seals in the Caribbean region was so rapidly extirpated, and how little was actually known of the species prior to extinction. Caribbean monk seals were within the extinction vortex by the time any conservation actions could be implemented. The U.S. recently initiated status reviews on four species of pinnipeds: ribbon seals (Histriophoca fasciata), bearded seals (Erignathus barbatus), ringed (Phoca fasciata), and spotted seals (Phoca largha) to assess these species’ populations and evaluate their threats. Considering the threats to the remaining species of monk seals and other pinnipeds today, evaluation of rapid extinction of Caribbean monk seals and the conservation of extant species may be put into perspective. The following discussion evaluates some of the major events leading to the decline of Caribbean monk seals, most recent efforts to locate the species, and what can be learned from the first species of pinniped to be driven to extinction in modern times due directly to human activities.

Until recently, the genus Monachus included 3 allopatric species: M. tropicalis (Caribbean monk seals), M. schauinslandi (Hawaiian monk seals), and M. monachus (Mediterranean monk seals), of which the two surviving species are currently in danger of extinction. It is believed that Caribbean monk seals were more closely related to Mediterranean monk seals than to Hawaiian monk seals (Wyss 1988). However, the phylogenetic relationship among species of monk seals remains in dispute (Lavigne 1998), and no genetic studies of Caribbean monk seals have been conducted. Caribbean monk seals were the only pinniped commonly found in the southeastern United States and wider Caribbean region, including the Gulf of Mexico. The historic distribution of Caribbean monk seals (Figure 1) has been interpolated from historical sightings, archaeological records, fossil evidence, and geographical features bearing names suggestive of their presence (Timm et al. 1997, Debrot 2000, Adam and Garcia 2003).

Figure 1.  Historical distribution of Caribbean monk seals based on data summarized in Timm et al. (1997) and Adam and Garcia (2003) from historical sightings (), archeological records (), and geographical features bearing names suggestive of their presence (). There is evidence that Caribbean monk seals used mainland beaches of North and Central America as haul-out sites in great numbers prior to intense hunting for their blubber. Most sighting records were from isolated islands, cays, and reefs in the eastern Gulf of Mexico (Ray 1961) and western Caribbean Sea. The only evidence of Caribbean monk seals in the Lesser Antilles is from archaeological remains in the northern end of the chain (Wing 1992) and a single sighting record (Timm et al. 1997).

The Extinction Clock

Caribbean monk seals were first reported during the second voyage of Columbus in 1494 (Kerr 1824), when at least 8 animals were killed for their meat. This event in history marks the arrival of Europeans to the Caribbean, and the point in time at which the “extinction clock” was set in motion for this species (Table 1). Accounts of Caribbean monk seals were usually from isolated islands, keys, and atolls surrounded by shallow, reef-protected waters (Gaumer 1917 and Hill 1843, as summarized in Adam 2004, Kerr 1824, Ward 1887); nearshore rocks; and only occasionally from mainland beaches and inlets (Allen 1880). Prior to depletion, the species was reported to have hauled out in groups of up to 500 individuals (Nesbitt 1836).

Table 1. Timeline to extinction for Caribbean monk seals.

Due to their hauling out behaviour, Caribbean monk seals were readily and intensively exploited as a source of oil by Europeans colonizing the region, and to a lesser extent for food, scientific study, and zoological collection. Seals were presumably hunted in smaller numbers during the 1500s and 1600s, with intense exploitation beginning in the latter 1600s. Adam (2004) provides an excellent review on the historical exploitation of Caribbean monk seals. Blubber was processed and used for lubrication of machinery, caulking of boats, and as lamp and cooking oil. Large numbers of seals persisted in some areas as late as the early 1800s and were also hunted for food by sailors and fishermen for meat until about 1885. In at least one instance, two monk seals were killed simply ‘‘for fun’’ (Allen 1880).

Documentation of harvest levels and other impacts that led to this species’ population decline is nearly absent; however, reconstruction of the species’ decline and geographic pattern of extinction has been modelled using historical accounts of the species (McClenachan and Cooper 2008). The intense level of exploitation that occurred during the relatively brief period of time humans hunted the seals resulted in the rapid decline of the population throughout its range over a short period of time. Due to the heavy hunting pressure on the population following the arrival of Europeans in the wider Caribbean region, the species had changed its status from being considered common to rare by the mid-1800s (Allen 1887a, Elliot 1884, Gratacap 1900).

During the 1800s, Caribbean monk seal distribution became increasingly fragmented and their range drastically reduced by the time the species was first taxonomically described (Gray 1886). Consequently, little information on the species was available by the time scientific expeditions were organized to study the species. As accounts of the now rare species in the wild were reported, expeditions were organized to capture live specimens for zoological gardens (Townsend 1909), and dead specimens for scientific study (Allen 1887b, 1887c, Ward 1887). It is believed that expeditions to the Triangle Keys region of the Yucatan peninsula (Gaumer 1917, Ward 1887) led to the extirpation of what may have been one of the last remaining large colonies of Caribbean monk seals in the wild. Notably, few reports of seals exist following expeditions to the Triangle Keys region in the early 1900s.

Attempts to Locate a Vanishing Species

In 1949, the International Conference on the Protection of Nature (United Nations Scientific Conference on the Conservation and Utilization of Resources) included the Caribbean monk seal in a list of 14 mammals whose survival was considered to be a matter of international concern requiring immediate protection (Westermann 1953). However, the last confirmed sighting occurred in 1952 at Seranilla Banks in the western Caribbean (Rice 1973), thus limiting any conservation efforts for the species. Unconfirmed sightings of pinnipeds since that time resulted in speculation that the Caribbean monk seal still existed in a few, isolated colonies. Several efforts were made to investigate unconfirmed reports of the species in or near the Caribbean Sea, Gulf of Mexico, the Southern Bahamas, and Atlantic coast of the Greater Antilles from the 1970s through the 1990s (Table 1).

Following a review of the species’ status in 1984, the U.S. Marine Mammal Commission contracted a study to interview local fishermen, residents, and sailors along the north coast of Haiti. Although two reported seal sightings were obtained during the survey, there was no tangible evidence to confirm whether those sightings involved Caribbean monk seals or some other species. However, based upon a credible account of a sighting, it was believed that some isolated animals potentially remained in remote regions off the northern coast of Haiti (Woods and Hermanson 1987). A subsequent survey of fishermen in waters off Haiti and Jamaica also generated a few oral accounts of seal sightings, but again, there was no corroborating proof that these sightings involved seals, much less Caribbean monk seals (Boyd and Stanfield 1998).

Since the time of these surveys, a review of sightings and stranding data provided evidence of several positively identified arctic phocids in tropical and sub-tropical waters of the Western North Atlantic from 1917 through 1996 (Mignucci-Giannoni and Odell, 2001). Recently, analysis of NMFS stranding data from 1997 through 2007 resulted in 22 sightings of hooded seals in the southeast U.S. and Caribbean region (Table 2). Nine of these reports occurred in Florida or the Caribbean region (NMFS Southeast U.S. Marine Mammal Stranding Database 2008). All confirmed sightings have been of extralimital occurrences of arctic species in the Caribbean region.

Hooded seals, usually juveniles, have been documented wandering over large ranges. The wide ranging movement of hooded seals (Cystophora cristata) was recently supported by DNA research showing genetic exchange between four main breeding areas. Coltman et al. (2007) reported that mtDNA and microsatellite analyses indicate that the world’s population of hooded seals could be considered a panmictic breeding population. Many accounts of hooded seal sightings and strandings have been reported in the southeastern United States and Caribbean region (Mignucci-Giannoni and Odell 2001, Mignucci-Giannoni 1989, Mignucci-Giannoni and Haddow 2001, NMFS 2008), and hooded seals have also been recently reported in the Mediterranean Sea around the Straits of Gibraltar (Bellido et al 2007). Although some seal sightings in the Caribbean were not identified as a particular species, all those that have been confirmed in recent decades within the known range of the Caribbean monk seal have proven to be of other species, namely feral California sea lions (Zalophus californianus) (Rice 1973), misidentified manatees (Trichechus manatus), or hooded seals (Mignucci-Giannoni and Haddow 2002, Mignucci-Giannoni and Odell 2001, NMFS 2008).

Table 2. All reported hooded seal sightings and strandings in the southeast U.S and Caribbean, as well as other pinniped species in the former range of Caribbean monk seals, include sightings from Florida and the Caribbean from 1997 through 2007.

^*These data have not been validated and may contain errors or possibly missing records. These data are from the NOAA National Marine Mammal Health and Stranding Response Database and the NOAA SER Marine Mammal Stranding Database. All hooded seal sightings in the southeast U.S. and Caribbean region are included; however, only those sightings of other species of pinniped occurring in the former range of Caribbean monk seals (Florida and the Caribbean) are included since these species strand relatively more frequently in the mid-Atlantic region of the U.S. and include more numerous records.

Retrospective Analysis of Extinction

The unbridled hunting of Caribbean monk seals as a source of oil and meat by early mariners and European colonizers of the Caribbean region was the primary factor leading to extinction of the species. An analysis of the reef productivity in the Caribbean required to support a pre-exploited monk sea population was recently modelled using historical accounts on the spatial distribution and abundance of Caribbean monk seals. The historical population size for the entire Caribbean was estimated to have been approximately 233,000–338,000 individuals (McClenachan and Cooper 2008). Using an estimated annual consumption rate for juvenile and adult Caribbean monk seals, the historical biomass required to support the seal population was estimated to have been four to six times greater than those found on most Caribbean reefs today (McClenachan and Cooper 2008). Although this estimate of the pristine animal biomass supported by Caribbean reefs exceeds the productivity found on any Caribbean reef today, it is comparable to that supported by pristine Pacific reef communities, indicating that this is a reasonably accurate estimate.

Declines in reef productivity are not believed to have contributed to the decline of monk seal numbers; however, it is likely the extirpation of Caribbean monk seals as a major predator in the reef ecosystems had an ecological effect in the Caribbean region. In addition, although declines in prey from fishing activities are not believed to have contributed to the population decline, it is likely that entanglement and drowning in fishing nets or slaughter by fishermen viewing the seals as competitors for fish also contributed to their decline. Once the population was depleted and human encroachment increased, Caribbean monk seals were reported to have been sensitive to human disturbance (Allen 1880, Gaumer 1917, Ward 1887), including hunting, fishing, and other activities. As with both Hawaiian and Mediterranean monk seals, Caribbean monk seals apparently became sensitized to human presence after exposure to hunting or other negative interactions. Thus, although many recent descriptions of monk seals state that they are highly sensitive to human disturbance, some accounts, including early accounts of the species (e.g., E.W. Nelson, as cited in Adam and Garcia 2003), describe them as being very approachable when hauled out on beaches. As human settlements expanded in areas inhabited by this species and persistent hunting reinforced evasive seal behaviours, avoidance of human presence near populated shorelines and areas frequented by fishermen likely caused seals to abandon historic haul-out sites. Human encroachment also likely exacerbated natural stresses on a rapidly declining seal population.

By the time the alarm was sounded by the International Conference on the Protection of Nature (United Nations Scientific Conference on the Conservation and Utilization of Resources) on the dire need for immediate protection of Caribbean monk seals in 1949, remaining colonies of the species were unknown. It is possible that the Caribbean monk seal persisted for a short period in the years following their last confirmed sighting in 1952 at Seranilla Bank. Caribbean monk seals are estimated to have had a lifespan of 20-30 years. Although long-term studies of the species in the wild did not confirm such longevity, this estimate is consistent with that of other monk seals. Assuming its accuracy, adults and any newborn individuals may have possibly persisted in the wild between the 1950s and early 1980s. If any remnant population did survive, it seems likely they consisted of scattered individuals, with no remaining colonies large enough to be viable in the wild.

In retrospect, the Caribbean monk seal population was already severely depleted, and likely extirpated throughout most, and possibly all, of its range prior to the passage of protective legislation under the U.S. Endangered Species Act and Marine Mammal Protection Act. In a span of approximately 300 years (from the latter 1600s through the latter half of the 1900s), uncontrolled hunting and human exploitation of Caribbean monk seals resulted in the extinction of a species that is estimated to have numbered a few hundred thousand. Caribbean monk seals killed for scientific collections in the late 1800s and early 1900s may have been the last major human impacts on the population, sealing the fate of this species several decades later.

Discussion

Due to their status, little information is known about the life history, habitats, and ecology of species currently considered endangered, threatened, or rare. In the case of Caribbean monk seals, very little was known of the species (see Figure 2) until it was extirpated throughout much of its range. We will never know whether some of the unconfirmed seal sightings in the Caribbean region during the latter half of the 20^th century were among the last remaining individuals of the Caribbean monk seal or some other species. The call to protect Caribbean monk seals regrettably came too late and afforded little protection for a species that was already within the vortex of extinction before any meaningful conservation and recovery efforts could be undertaken.

Figure 2. Studies of monk seals are limited to retrospective analyses based on very limited information on the species and data from the Caribbean reef ecosystems that once supported a thriving population of seals. Caribbean monk seal bones and pelts remain in scientific collections and it is recommended genetic samples be isolated from them for future reference and analysis. Genetic characterization of the species should occur while genetically useful samples of the species remain available for analysis. (Caribbean monk seal replica skull and mandibles photograph courtesy of Skulls Unlimited International Inc., Oklahoma City, Oklahoma.)

Species’ extinction due to human causes can occur quite rapidly. After only about fifty years of commercial hunting for their blubber in the early 1800s to 1860, the northern elephant seal (Mirounga angustirostris) nearly became extinct (Townsend 1885). Fortunately, the northern elephant seal population has recovered remarkably well following a ban on hunting. It is unfortunate that Caribbean monk seals were not afforded diligent protection in due time, and have become the first pinniped to become extinct in modern times as a direct result of human activities. The swiftness with which human activities can extirpate a species from the wild should serve as a reminder of the need for continued support of research, proactive conservation efforts, and international cooperation to implement conservation and recovery actions for threatened and endangered species.

The decline of Caribbean monk seals demonstrates the importance of taking immediate conservation actions when a species shows signs of decline, regardless of the available information on the species. Immediate conservation actions should be implemented while coordinated research and monitoring plans are developed to better understand the threats to a population, and how it would be expected to respond to conservation actions through adaptive management. Research should not only focus on the behaviour and life history of a species, but also its ecological context so as to manage effectively its long-term recovery. Based on modelling of the historical productivity of the Caribbean reef system required to support the Caribbean monk seal population (McClenachan and Cooper 2008), the biomass supported by Caribbean reefs today would support perhaps one-fourth to one-sixth of the historical monk seal population. If seals still persisted in the region today, the implications of restoring reef productivity and protecting haul out sites would be integral to the recovery of seals as part of healthy reef ecosystems. Current conservation strategies must consider the direct impacts on a species, understanding both the natural processes affecting ecosystems, and human activities impacting them. Incorporating adaptive strategies into conservation and recovery plans is needed to respond to new information and meet the challenges of ecosystem management to maintain stable populations and manage the long-term recovery of threatened and endangered species. The success of conservation and recovery strategies in keeping the imperilled Hawaiian and Mediterranean monk seal populations from the brink of extinction will depend on the success of continued study and monitoring of the populations, adaptive management strategies, and effective cooperation among stakeholders to implement needed conservation actions to recover these remaining species of Monachus to sustainable levels as part of a healthy ecosystem. The extinction of the Caribbean monk seal is regrettable, but should serve as a beacon for the conservation of species and their habitat, and as a reminder that species can, and do, quickly go extinct on our watch.

Acknowledgements

Many thanks and gratitude to the following individuals who reviewed and commented on drafts of the status review from which much of this information was summarized: Jason Baker, Gordon Waring, and Larry Hansen of the National Marine Fisheries Service; David Laist, U.S. Marine Mammal Commission; Ian Boyd, University of St. Andrews; William Johnson, the Monachus Guardian; thanks to the Southeast US Marine Mammal Stranding Network for the collection of stranding data; and thanks to Amanda Frick of NMFS for her assistance with GIS.

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Further information

NMFS. 2008. Endangered Species Act 5-Year Review for the Caribbean Monk Seal (Monachus tropicalis). National Marine Fisheries Service Southeast Regional Office, St. Petersburg, Florida, March 7, 2008: 1-20. [PDF  255KB]