Socorro Island

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Coordinates: 18°42′N, 110°57′W

Socorro Island, from satellite image
Socorro Island, from satellite image

Socorro Island (Spanish: Isla Socorro) is a volcanic island in the Revillagigedo Islands, a Mexican possession lying some 600 kilometers off that country's western coast at 18°48'N, 110°59'W. The size is 16.5 by 11.5 km, with an area of 132 km².

Contents

The island rises abruptly from the sea to 1050 meters (3,445 ft) in elevation at its summit. Isla Socorro is a shield volcano. It most recently erupted in 1993, which was a submarine flank eruption off the coast from Punta Tosca. Some of its earlier eruptions have been around 1848[verification needed] and 1896, and in 1905 and 1951. Mount Evermann (Spanish: Cerro Evermann) is the name give to the summit dome complex. The island's surface is broken by furrows, small craters, and numerous ravines, and covered in lava domes, lava flows and cinder cones.[1]

There is a naval station 18°43′41″N 110°57′07″W / 18.728, -110.952, established in 1957, with a population of 250 (staff and families), living in a village with a church, that stands on the western side of Bahia Vargas Lozano, a small cove with a rocky beach, about 800 meters east of Cabo Regla, the southernmost point of the island. The station is served by a dock, a local helipad and a 1200 meter long airstrip located six kilometers to the north, at 18°46′23″N 110°55′52″W / 18.773, -110.931.

There is a freshwater spring about 5 km northwest of Cabo Regla, at the shoreline of Ensenada Grayson (or Caleta Grayson), an inlet. This is brackish or even covered by the sea at high tide. Apart from some temporary pools and maybe[verification needed] one that is more permanent, a small freshwater seep exists most of the time[verification needed] some 45 meters (50 yard) inland at Bahia Lucio Gallardo Pavon (Binner's Cove), 800 meters NW of the naval station.[2]

[edit] History

Offshore Socorro Island
Offshore Socorro Island

No evidence of human habitation on Socorro exists before its discovery by Spanish explorers. Hernando de Grijalva and his crew discovered an uninhabited island on December 25, 1533 and named it Inocentes[verification needed]. In 1542, Ruy González de Villalobos, while exploring new routes across the Pacific, rediscovered Inocentes and changed its name to Isla Anublada ("Cloudy Island") due to the clouds frequently forming on the northern slopes of Mount Evermann. In 1608, Martín Yañez de Armida, in charge of another expedition, visited Santo Tomé[verification needed] and changed its name to Isla Socorro ("Island of [Our Lady of Perpetual][verification needed] Rescue").

At the beginning of the twentieth century, Barton Warren Evermann, director of the California Academy of Sciences in San Francisco promoted the scientific exploration of the island. The most comprehensive biological collections were obtained at this time. The volcano on Socorro was renamed in his honor.

In September 1997, the island was struck by Hurricane Linda, one of the strongest hurricanes ever recorded.

[edit] Ecology

Map of Socorro Island
Map of Socorro Island

The lowlands of Socorro - except on the northern, more humid side - are covered with thick shrubland, consisting mainly of endemic Croton masonii and a cactus, probably Engelmann's Prickly Pear (Opuntia engelmannii). Above 650 m (2000 ft) and on the northern side, a richer vegetation occurs. This includes small trees such as Ficus cotinifolia, Black Cherry (Prunus serotina[3]), and the endemic Guettarda insularis, which bear epiphytic orchids (Epidendrum nitens, Epidendrum rigidum and the endemic Pleurothallis unguicallosa).[2]

The native land fauna is depauperate, with birds predominating and mammals absent. There is one endemic speces of iguanid lizard and the land crab Gecarcinus planatus which occurs on islands throughout the region.[2]

Sheep, cats and rodents were introduced to the island by human activity; more recently, the locust Schistocerca piceifrons has also established itself on the island[4]. Unlike the mammals on Guadalupe Island or Clarión, their impact on the local flora was minor, but cat predation had a drastic effect since the mid-1970s due to the fauna's island tameness[5] and the locusts swarm twice a year and seriously damage vegetation during that time. There have been no recorded extinctions of plants on Socorro; several birds have been drastically affected by cat predation however and one taxon appears to have gone extinct.

Socorro is an important breeding location for several seabirds, many of which have here one of their most north(east)ernmost breeding colonies. The present status of these birds is not well-known, and they presumably have suffered from cat predation. In 1953, the following taxa were present:

  • Wedge-tailed Shearwater, Puffinus pacificus (or Ardenna pacifica)
  • Western Red-billed Tropicbird, Phaethon aethereus mesonauta - breeding suspected but not verified
  • Nazca Booby, Sula granti - breeding suspected but not verified
  • Northeast Pacific Brown Booby, Sula leucogaster brewsteri - breeding suspected but not verified
  • East Pacific Great Frigatebird, Fregata minor ridgwayi - breeding suspected but not verified; a doubtfully distinct subspecies
  • East Pacific Sooty Tern, Onychoprion fuscatus crissalis - a doubtfully distinct subspecies
  • East Pacific Brown Noddy, Anous stolidus ridgwayi

Non-endemic landbirds and shorebirds occur mostly as vagrants or use the island as a stopover during migration; the Northern Mockingbird has become established in the late 20th century[4]. Among those that are recorded not infrequently are Great Blue Heron, Hudsonian Curlew, Spotted Sandpiper and Wandering Tattler. Opposed to the situation on smaller and more isolated Clarión, wind-blown or vagrant birds seem to consititute the bulk of the records, including species such as Brown Pelican, Osprey, Peregrine Falcon, Semipalmated Plover, Willet, Sanderling, Belted Kingfisher and Buff-bellied Pipit. It may be that this puzzling observation is due to the presence of the Red-tailed Hawks and cats, which has at least made the local Urosaurus more wary than its relative on Clarión, and might deter passing birds from stopping on Socorro.[2]

[edit] Endemism

Being the largest of the Revillagigedo Islands and closer to land than Clarion, Socorro sports a rich array of endemic taxa, mainly plants and landbirds.

Animals

The Socorro Dove (Zenaida graysoni) only survives in captivity at present
The Socorro Dove (Zenaida graysoni) only survives in captivity at present

Plants[6]

  • Acalypha umbrosa
  • Aegopogon solisii
  • Aristida vaginata
  • Aristolochia socorroensis
  • Bidens socorrensis
  • Botrychium socorrense
  • Castilleja socorrensis
  • Cestrum pacificum
  • Coreocarpus insularis
  • Croton masonii
  • Erigeron socorrensis
  • Eupatorium pacificum
  • Guettarda insularis
  • Hypericum eastwoodianum
  • Ilex socorroensis
  • Lantana involucrata var. socorrensis
  • Lepechinia hastata ssp. socorrensis
  • Meliosma nesites
  • Paspalum longum
  • Peperomia socorronis
  • Physalis mimulus
  • Pleurothallis unguicallosa
  • Salvia pseudomisella
  • Sida nesogena
  • Sideroxylon socorrense (Vulnerable)
  • Verbena sphaerocarpa
  • Vernonia littoralis

Brickellia peninsularis var. amphithalassa[verification needed], Cheilanthes peninsularis var. insularis, Nicotiana stocktonii, Spermacoce nesiotica and Zapoteca formosa ssp. rosei are near-endemics, being restricted to Socorro and Clarión. Whether Teucrium townsendii ssp. affine is the same plant as those on San Benedicto is not conclusively determined.[6]

[edit] Visiting information

Socorro Island is a popular scuba diving destination known for underwater encounters with dolphins, sharks, manta rays and other pelagic animals. Since there is no public airport on the island, divers visit here on live-aboard dive vessels such as the 112' Solmar V out of Cabo San Lucas, Mexico. The most popular months are between November and May when the weather and seas are calmer.

[edit] Footnotes

  1. ^ GVP (2007)
  2. ^ a b c d Brattstrom & Howell (1956)
  3. ^ Probably ssp. capuli according to biogeography, Brattstrom & Howell (1956) contra CMICD (2007)
  4. ^ a b BLI (2007a)
  5. ^ Brattstrom & Howell (1956), BLI (2007b)
  6. ^ a b CMICD (2007

[edit] References

[edit] External links

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