Redalyc.FERAL SHEEP ERADICATION at SOCORRO

Interciencia ISSN: 0378-1844 [email protected] Asociación Interciencia Venezuela

Ortiz-Alcaraz, Antonio; Aguirre-Muñoz, Alfonso; Méndez-Sánchez, Federico; Ortega- Rubio, Alfredo FERAL SHEEP ERADICATION AT SOCORRO ISLAND, MEXICO: A MANDATORY STEP TO ENSURE ECOLOGICAL RESTORATION Interciencia, vol. 41, núm. 3, marzo, 2016, pp. 184-189 Asociación Interciencia Caracas, Venezuela

Available in: http://www.redalyc.org/articulo.oa?id=33944256007

How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative FERAL SHEEP ERADICATION AT SOCORRO ISLAND, MEXICO: A MANDATORY STEP TO ENSURE ECOLOGICAL RESTORATION Antonio Ortiz-Alcaraz, Alfonso Aguirre-Muñoz, Federico Méndez-Sánchez and Alfredo Ortega-Rubio

SUMMARY

Domestic sheep have been introduced to numerous islands were captured and equipped with radio-collars (Judas sheep). worldwide; they became feral and caused indiscriminate im- From March 2010 to April 2012 eradication continued using pacts on ecosystems. On Socorro, a tropical Mexican island terrestrial hunting; 505 sheep were dispatched at this stage. in the Pacific Ocean, feral sheep caused soil compaction and The use of Judas sheep and detection dogs were critical in lo- erosion, loss of vegetation, habitat destruction, landscape al- cating the last remaining sheep. A systematic monitoring pro- terations, and species extinction. In response to these biodiver- gram conducted during two years confirmed eradication suc- sity threats, feral sheep were removed from Socorro Island. In cess. In June 2014, Socorro Island was declared free of feral 2009, 1257 sheep were dispatched using aerial hunting over 35 sheep. To date (November 2015), a remarkable ecosystem re- hours of flight time. To locate remaining herds, twelve sheep covery has been recorded.

Introduction even the primary cause of ex- environment with Psidium so- erosive processes caused by tinctions (Baillie et al., 2004; corrense and Guettarda insu- feral sheep (Ortega-Rubio Insular ecosystems have un- Reaser et al., 2007). In partic- laris, both endemic species, et al., 1992). This degradation usually high rates of endemic ular, the settlement of herbi- was severely disturbed. problem was alarming since species present in their envi- vores like feral sheep (Ovis Constant overgrazing resulted the erosion rate for deforested ronments. Islands are import- aries) has caused important in the abundance of paths areas on Socorro Island was ant breeding grounds for a ecological impacts on insular formed by the trampling of estimated at 20 to 90 tons/ha/ variety of birds and marine ecosystems. In 1869, 100 sheep on the soil, which trig- year (Arnaud et al., 1993; mammals. Mexican islands are sheep were introduced to gered different erosive pro- Maya-Delgado et al., 1994; known for their high biodiver- Socorro Island for ranching cesses and put native flora and Ochoa-López et al., 1998). sity richness (Aguirre-Muñoz (they supplied food to boaters fauna at risk (Figure 1). Similarly, areas covered by et al., 2005, 2011). Despite and fishermen); over time, Among the most significant introduced vegetation have a their ecological significance, without humane care, sheep changes on the original floral negative effect on local natu- many islands around the world became feral, successfully composition has been an in- ral processes, since native receive serious impacts derived adapting to island conditions crease in the presence of fauna species depend on na- from human activity (Johnson (Levin and Moran, 1989; graminacea species and scrub tive plants for food, shelter or and Stattersfield, 1990). Álvarez-Cárdenas et al., 1994; species as well as a reduction nesting. Arthropods are rare Approximately 75% of all ani- Brattstrom, 2015). Since its of the area covered by the na- on disturbed areas (Jimenez mal extinctions have occurred introduction, feral sheep has tive flora. Sheep are particu- et al., 1994). Vertebrates were on islands, the majority being caused great modification to larly efficient in the propaga- negatively affected due caused by introduced species the natural habitat. Erosion tion of introduced plant spe- to habitat loss; for example, (Diamond, 1989; Groombridge, rates and loss of vegetation cies (they carry seeds in coat the Socorro Blue Lizard 1992). Feral species are among coverage derived from the and excret). The change in (Urosaurus auriculatus) and the main causes of biodiversity sheep presence were docu- native vegetation has been ob- the endemic birds Socorro loss and ecological disequilib- mented along the south- served in every habitat that Mockingbird (Mimus gray- rium in many environments ern-central region of the island sheep occupied (SEMARNAT, soni) and Socorro Wren (Courchamp et al., 2003; (León de la Luz et al., 1994; 2004). Nearly 30% of the orig- (Troglodytes sissonii) were Blackburn et al., 2004, Maya-Delgado et al., 1994). inal soil and vegetation on less abundant in eroded Aguirre-Muñoz et al., 2008), Particularly, a shrub land Socorro Island was lost due to areas (Martínez-Gómez et al.,

KEYWORDS / Environmental Restoration / Eradication / Exotic Fauna / Feral Sheep / Ovis aries / Socorro Island / Received: 11/24/15. Modified: 02/08/2016. Accepted: 02/09/2016.

Antonio Ortiz-Alcaraz. Biologist, Islands Project, Grupo de Federico Méndez-Sánchez. B.Sc. Mexico. Researcher, CIBNOR, Universidad Autónoma de Baja Ecología y Conservación de in Oceanography, UABC, Mexico. Address: CIBNOR. California (UABC), Mexico. Islas, (GECI), Mexico. Mexico). M.Sc. in Environmental Av. Instituto Politécnico Masters in Use, Management Alfonso Aguirre-Muñoz. B.Sc. Management, University of Nacional 195, Playa Palo de and Conservation of Natural in Oceanography, UABC, Auckland, New Zealand. Direc- Santa Rita Sur, La Paz, Baja Resources, and Ph.D. candidate Mexico. Ph.D. in Sustainable tor for Development, GECI, California Sur, C.P. 23096, in Ecology, Centro de Development and Regional Mexico. México e-mail: aortega@cib- Investigaciones Biológicas del Studies, El Colegio de la Fron- Alfredo Ortega-Rubio. Doctor nor.mx Noroeste (CIBNOR), Mexico. tera Norte, Mexico. Executive of Science in Ecology, Director, Gulf of California Director, GECI, Mexico. Instituto Politécnico Nacional,

184 0378-1844/14/07/468-08 $ 3.00/0 MARCH 2016, VOL. 41 Nº 3 ERRADICACIÓN DE BORREGO FERAL EN ISLA SOCORRO, MÉXICO: ACCIÓN REQUERIDA PARA LOGRAR SU RESTAURACIÓN ECOLÓGICA Antonio Ortiz-Alcaraz, Alfonso Aguirre-Muñoz, Federico Méndez-Sánchez y Alfredo Ortega-Rubio RESUMEN Borregos domésticos han sido introducidos en numerosas equipados con radio-collares (borregos Judas); una vez libe- islas alrededor del mundo; éstos se vuelven ferales y pro- rados sirvieron para localizar las manadas remanentes. De vocan impactos indiscriminados en los ecosistemas. En Isla marzo 2010 a abril 2012 se continuó con la erradicación me- Socorro, una isla tropical mexicana en el Océano Pacífico, diante cacería terrestre; 505 borregos fueron sacrificados en los borregos ferales causaron la erosión y compactación del esta etapa. El uso de borregos Judas y perros de muestra en- suelo, pérdida de vegetación y destrucción de hábitat, alte- trenados fue fundamental para la localización de los últimos raciones del paisaje, y la extinción de especies. En respues- borregos. Con el fin de confirmar la erradicación se llevó a ta a estas amenazas a la biodiversidad, los borregos fueron cabo por dos años un programa de monitoreo sistemático. En erradicados de Isla Socorro. En 2009, 1257 borregos ferales junio 2014, Isla Socorro fue declarada libre de borregos fera- fueron sacrificados durante la fase de cacería aérea, con 35 les. A la fecha (noviembre 2015) se ha registrado una mejoría horas de vuelo. Un total de 12 borregos fueron capturados y notable del ecosistema.

ERRADICAÇÃO DE CARNEIROS FERAIS NA ILHA SOCORRO, MÉXICO: UM PASSO OBRIGATÓRIO PARA GARANTIR A RESTAURAÇÃO ECOLÓGICA Antonio Ortiz-Alcaraz, Alfonso Aguirre-Muñoz, Federico Méndez-Sánchez e Alfredo Ortega-Rubio RESUMO Carneiros domésticos foram introduzidos em numerosas leiras (carneiros Judas) para localizar os rebanhos restantes. ilhas em todo o mundo; tornaram-se ferais e tiveram impactos Entre março 2010 a abril 2012, continuo a erradicação com amplamente indiscriminados sobre os ecossistemas. Em Socor- caça terrestre e 505 carneiros foram sacrificados nesta fase. ro, uma ilha tropical mexicana no Oceano Pacífico, os carnei- O uso de “carneiros Judas” e cães de detecção foram funda- ros ferais causaram a compactação e erosão do solo, perda de mentais para localizar os últimos carneiros. Para confirmar o vegetação e habitat, mudança da paisagem, e extinção de es- sucesso da erradicação um programa de monitoração sistemá- pécies. Em resposta a estas ameaças à biodiversidade os car- tica foi realizado nos dois anos seguintes. Em junho 2014, Ilha neiros ferais foram retirados da Ilha Socorro. Em 2009, 1257 Socorro foi declarada livre de carneiros selvagens. Até a pre- ovinos foram sacrificados durante 35 horas de vôo de caça aé- sente data (novembro 2015) se registra uma recuperação notá- rea. Doze ovinos foram capturados e equipados com rádio co- vel do ecossistema.

Armada de México), the Mexican civil society organi- zation Grupo de Ecología y Conservación de Islas, A.C. (GECI) completed the feral sheep eradication on Socorro Island by 2012. In this paper we report the methods used to achieve this significant restoration project.

Methods

Study site

Figure 1. Loss of vegetation (left) and soil (right). Socorro Island (13,200ha; 1,040masl) is located in the 2001; Martínez-Gómez and graysoni), with the last re- (CONANP, CONABIO and Revillagigedo Archipelago Jacobsen, 2004), but highly maining specimens now kept INECC) and USA (USFWS) (Figure 2), 460km west from abundant in areas where the only at zoos in Mexico, USA governments, and national Los Cabos, Baja California Sur floral composition remained and Germany. (Alianza WWF-Fundación and 694km west from unaltered (Galina et al., 1994; The removal of feral spe- Carlos Slim) and international Manzanillo, Colima (18º47´N, Rodríguez-Estrella et al., cies has showed to be an (American Bird Conser- 110º58´W). It harbors 118 na- 1994). Feral sheep contribut- achievable task in many is- vancy, Packard and Marisla tive vascular plants, 30 of ed, along with feral cats lands of the world (e.g., Foundation) donors, and with which are endemic (León de la (Felis catus), to the extinction Veitch and Clout, 2002; the invaluable logistic support Luz et al., 1994). Socorro’s from the wild of the endemic Veitch et al., 2011). With from the Mexican Navy fauna includes 103 bird species Socorro Dove (Zenaida funds from both Mexican (Secretaría de Marina; (terrestrial, marine, wading and

MARCH 2016, VOL. 41 Nº 3 185 their sterilization. The latter was done by GECI’s personnel, previously trained on Guada- lupe Island by experts from the Galápagos Islands National Park. Sheep were kept for ob- servation three days prior to their liberation. The animals were equipped with radio-telemetry collars (Telenax Mexico), with frequencies between 164 and 168Mhz. These Judas sheep were deployed back to the sites where they were captured.

Terrestrial hunting and trapping

From February 2010 to April 2012, 4 to 7 experienced hunters (with gun permits) carried out this stage of the project. Every hunter had a handheld GPS to record their hunting tracks. Rifles with telescopic sights (Leupold VX- I), caliber .222, .243 and .308, Figure 2. Location of Socorro Island. as well as 12 gauge shotgun with cartridges 00 buck were used. Periodically, Judas sheep migratory); eight of the terrestri- possible and that aerial hunting behind the pilot and another were located to locate herds. al birds are endemic to the is- was the best method. During next to the pilot. Manual Simultaneously, leg hold traps land. Also, two terrestrial rep- October 2005, several flights counting devices were used to (Oneida Victor Soft Catch # 3) tiles are present, one being en- aboard a Beechcraft Bonanza register the number shot. Also, and snare traps were used on demic (SEMARNAT, 2004). aircraft were made over the is- a GPS was used in order to identified trails; both types of The island is permanently in- land. This allowed to identify record the flight trajectories traps were checked daily. habited by military personnel the main areas where sheep and the areas where the high- Traps were used to capture (40-50 people) stationed at a were distributed. At the same est numbers of sheep were remaining sheep in places Naval Base located in the south- time, land surveys were con- found. All flights were done where previously hunted; thus, ernmost part of the island. ducted by foot and in motorized between 07:00 and 11:00, and hunting efforts focused on new Based on the experienced vehicles (ATV´s). Mexican Navy between 16:00 and 19:00, areas of the island. gained around the world (e.g., officers guided these surveys. when sheep have a higher ac- Campbell and Donlan, 2005) The locations of the sheep herds tivity. During the first two Hunting dogs and in Mexico (Aguirre-Muñoz were recorded into a GIS. flights we covered the whole et al., 2011) in the eradication island in order to identify the As the last stage of the erad- of ungulates (mainly goats and Aerial hunting main herds of sheep. For the ication, we used two hunting sheep), we selected aerial hunt- subsequent 25 flights, hunting dogs (Beagle and Foxhound) to ing aided with global position- The aerial hunting cam- efforts were concentrated in track down the last sheep ing systems, geographic infor- paign, using a single turbine areas with the higher densities herds. Dogs were fitted with mation systems (GIS), terrestri- helicopter (model MD369D), of sheep (east zone of the is- GPS collars to record their lo- al hunting and trapping as took place between April 20 land). Flights were done at an cations and movements. The main eradication methods. and 29, 2009. Twelve gauge average speed of 42km/h and dogs were rented; they were Judas animals and specialized semi-automatic shotguns average height of 35m. trained for localizing of sheep hunting dogs were also used (Winchester SX3) equipped and goat. Two dogs worked si- for localizing remaining sheep. with near-range scopes Judas sheep multaneously during 2h periods (Sightmark SM13003), and with 30min rest. Feral sheep monitoring semi-automatic .308 rifles During the hunting flights 12 (Benelli R1) were used. Guns live animals were captured, to Results and Discussion In 2002, GECI began with a permits from the Secretariat of be used as Judas sheep (Taylor feral sheep monitoring program National Defense were ob- and Katahira, 1988). These an- Feral sheep monitoring on Socorro Island to assess tained and hunting was super- imals were neutered and fitted eradication feasibility; herbs lo- vised by Mexican Navy per- with radio-telemetry collars. Both aerial and ground sur- cation and major distribution sonnel on the island. Two The captured animals were veys confirmed the description areas were determined. It was hunters were hunting simulta- taken to Socorro’s Naval Base made in 1992 by Álvarez- concluded that eradication was neously during the flights, one and kept in a barn prior to Cárdenas et al. (1994) that

186 MARCH 2016, VOL. 41 Nº 3 sheep were present in the east Aerial hunting few animals were dispatched convinced of the ecological zone of the island (in an area in an hour of flight. Aerial impacts caused by sheep and of ~6000ha). Patches of A total of 35 hours of hunting is a highly effective cooperated with this project. Bumelia, Ficus, Psidium and flight were done in one week method to use in invasive The tropical climate of the Guettarda are abundant in this for the aerial hunting stage, in species eradications (Campbell island allowed the carcasses area. However, due to the re- which the majority of the is- and Donlan, 2005). The tech- to decompose rapidly. Land building of the island’s airstrip land was covered (Figure 3). nique allows hunters to access invertebrates, aided by the and to ground hunting done by During this period, 1,257 in- animals that otherwise would microbial array present in the the Mexican Navy for local dividuals were dispatched. have been completely inacces- soil, were capable of fully human consumption, sheep The total amount of flight sible by foot, considering that decomposing one adult sheep were congregating in higher hours and the sheep dis- their location was confined to in two weeks. The high irra- areas of the island. The areas patched are detailed in cliffs or canyons. The effec- diance rates of the tropical frequented by sheep were wide Figure 4. The average flight tiveness of this technique is sun avoid for the carcasses to open spaces, with scarce vege- time was 1h 20min. We backed up by the results, become a source of infection tation, but further away from stopped hunting when sheep since it only took 35h of fly- on the island. Furthermore, human presence. were difficult to localize, and ing time to dispatch a large the decays enrich the soil of part (~70%) of the sheep the area. GECI personnel car- population. ried out an on-foot survey, the Sheep were mainly present day after the last hunting ef- at least 1km away from the fort, in order to verify the main trails and the airstrip. state of the carcasses; they The rest of the hunting sites were beginning to dry out. were located >2km away from the Navy Base. The distance Ground hunting and trapping from the trails made it very difficult to carry back the Ground hunting was concen- hunted sheep for human con- trated on sites identified by air sumption. Nevertheless, certain with the greatest abundance of areas with little or no vegeta- sheep traces (Figure 5). A tion allowed the use of the summary of hunting and trap- helicopter to carry back some ping efforts is shown in sheep. Approximately 75 sheep Table I; 505 sheep were dis- were recovered and given to patched through ground hunt- the Mexican Navy personnel. ing, in 9 months over a period The Mexican Navy carries of two years (March 2010 to food to Socorro Island every April 2012). Judas sheep were two weeks for its personnel, so most effective when there was sheep did not represent their a greater amount of remaining source of meat. They were sheep, because it increases

Figure 3. Helicopter flight trajectories on Socorro Island.

Figure 4. Amount of sheep dispatched by hours of flight (total Figure 5. Hunting tracks (black line) and use of dogs (white line), from accumulated). 2010 to 2012.

MARCH 2016, VOL. 41 Nº 3 187 TABLE I GROUND HUNTING EFFORT Sheep Captured Dispatched Year Months Personnel Hours/hunter Distance (km) with Judas Traps/Night sheep Hours/dogs sheep 2010 Mar-Apr 7 1323 815 53 900 41 - 355 Jul 6 588 460 18 - - - 48 2011 Apr 5 512 433 11 650 8 - 67 Ago-Sep 4 728 644 4 - - - 25 Nov-Dec 4 420 385 - - - 49 8 2012 Apr 4 240 216 - - - - 2 Total 3811 2953 86 1550 49 49 505 possibility of aggregation. methods used reduced project transportation of staff and Survival Commission Nº 42. Hunting dogs were only used cost, which was of US$ 38/ha, equipment from the Manza- IUCN-CBB. Gland, Switzerland. to locate the last ten remaining while other projects of sheep nillo Harbor in Colima to the pp. 250-258. animals, which were difficult eradication, such as that on island, accommodation and use Aguirre-Muñoz A, Samaniego- to locate for hunters. Santa Cruz Island, California, of the heliport and other facil- Herrera A, García-Gutiérrez C, A total of 1762 sheep were had a cost of US$ 80/ha, due ities. The support of the Luna-Mendoza L, Rodríguez- dispatched from Socorro Island to capture and transport of Mexican federal government Malagón M, Casillas-Figueroa F (2005) El Control y la erradica- in a 3-year eradication cam- sheep to the continent agencies SEMARNAT, DGVS, ción de Fauna Introducida como paign (April 2009 to April (Faulkner and Kessler, 2001). CONANP, SEGOB, SEDENA Instrumento de Restauración 2012). After aerial hunting, it Since the sheep eradication and the granting of all needed Ambiental: Historia, Retos y took two years to dispatch project was concluded vegeta- permits were key for the suc- Avances en México. Temas so- 30% of the sheep population tion began to recover passive- cess of the program. Donors bre Restauración Ecológica. by terrestrial hunting, due to ly. Comparison of satellite im- were: Mexican (CONANP, Instituto Nacional de Ecología. difficult logistics because of ages from 2008 and 2013 show CONABIO, INECC) and México. 254 pp. the distances, topography and that vegetation has recovered United States (USFWS) gov- Álvarez-Cárdenas S, Castellanos- size of the island. During the in 1450ha. Results from a field ernments, Alianza WWF- Vera A, Galina-Tessaro P, following two years (May assessment of vegetation Fundación Carlos Slim, Arnaud G (1994) Aspectos de 2012 to December 2014), a to- showed an average of 21% of American Bird Conservancy, la población y el hábitat del tal of 14 expeditions of 21 vegetation cover in 2009, at Packard and Marisla Foun- borrego doméstico (Ovis aries). days each were carried out to the most impacted sites by dation. We thank support from In Ortega-Rubio A, Castellanos V (Eds.) La Isla Socorro, find traces of sheep (footprints sheep, while in 2014 average CONACYT Natural Protected Reserva de la Biosfera and feces) on the island; no vegetation cover reached 79%. Areas Network (RENANP). Archipiélago de Revillagigedo, traces of sheep were recorded. México. Centro de Investi- Conventionally, islands are Conclusions REFERENCES gaciones Biológicas del declared free of invasive spe- Noroeste. México. pp. 301-317. cies after two or three years The aerial hunting method Aguirre-Muñoz A, Croll D, Donlan Arnaud G, Rodríguez A, Ortega- without evidence of exotics showed to be an ideal tech- J, Henry RW, Hermosillo MA, Rubio A, Álvarez CS (1993) (Rejmanek and Pitcairn, 2002; nique for the eradication of Howald G, Keitt B, Luna- Predation by cats on the unique Regan et al., 2006). Socorro sheep from Socorro Island. It Mendoza L, Rodríguez-Malagón endemic lizard of Socorro Island was declared free of enabled the eradication team M, Salas-Flores LM, Sama- Island (Urosaurus auriculatus), feral sheep in June 2014. This to dispatch a high number of niego-Herrera A, Sánchez- Revillagigedo, México. Ohio J. Pacheco JA, Sheppard J, Tershy Sci. 93(4): 101-104. project had an approximate animals in few days of work, B, Toro-Benito J, Wolf S, Wood cost of US$ 500,000. This while allowing the hunters to Baillie JEM, Hilton-Taylor C, Stuart B (2008) High-impact conserva- SN, Eds. (2004) IUCN Red List amount does not include the complete difficult access ar- tion action: A case study from contribution in-kind from the eas. The use of Judas sheep of Threatened Species. A Global the islands of Western Mexico. Species Assessment. IUCN. Mexican Navy: maritime and hunting dogs were cru- Ambio 37:101-107. Gland, Switzerland. 191 pp. transportation, accommodation, cial for concluding eradica- Aguirre-Muñoz A, Samaniego- use of heliport and vehicles; tion. There-fore, these tech- Blackburn TM, Cassey P, Duncan Herrera A, Luna-Mendoza L, RP, Evans KL, Gaston KJ and the costs of the two con- niques can be used on other Ortiz-Alcaraz A, Rodríguez- (2004) Avian extinction and secutive years for confirmation islands in Mexico and other Malagón M, Méndez-Sánchez F, mammalian introductions on of the absence of sheep (US$ countries. Félix-Lizárraga M, Hernández- oceanic islands. Science ~200,000). Compared with oth- Montoya JC, González-Gómez 305: 1955-1958. R, Torres-García F, Barredo- er islands where goat or sheep ACKNOWLEDGMENTS Brattstrom B (2015) Food Webs and Barberena JM, Latofski-Robles have been eradicated (Van Feeding Habits on the M (2011) Island restoration in Vuren, 1992), feral sheep erad- This work would have not Revillagigedo Islands, Mexico. 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