IS THE NORTHERN-CENTRAL COAST OF VERACRUZ, DOLPHINS (Tursiops truncatus Montagu, 1821)?

Transcripción

1 Thalassas, 30(2) June 2014: An International Journal of Marine Sciences IS THE NORTHERN-CENTRAL COAST OF VERACRUZ, MEXICO AN IMPORTANT AREA FOR BOTTLENOSE DOLPHINS (Tursiops truncatus Montagu, 1821)? LAURA VÁZQUEZ-CASTÁN (1), ARTURO SERRANO (1 * ), MARISELA LÓPEZ-ORTEGA (2), JOSÉ A. GALINDO (1), MIGUEL A. DÍAZ-ARREDONDO (3) & ASENCIÓN CAPISTRÁN-BARRADAS (1) (1)Laboratorio de Mamíferos Marinos, Universidad Veracruzana, Tuxpan, Veracruz, México,CP 92850, Km 7.5 Carretera Tuxpan-Tampico, Col. Universitaria. (2)Laboratorio de Análisis de Agua, Universidad Veracruzana, Tuxpan, Veracruz, México, CP 92850, Km 7.5 Carretera Tuxpan-Tampico, Col. Universitaria. (3)Instituto Oceanográfico del Golfo y Mar Caribe, Secretaría de Marina, Alvarado, Veracruz, México, CP 95263, Int. HESCNAV s/n, Antón Lizardo. 1*Corresponding author: Arturo Serrano ( arserrano@uv.mx) ABSTRACT The northern and central coasts of the state of Veracruz are inhabited by a great variety of organisms due to its high primary productivity. The bottlenose dolphin (Tursiops truncatus Montagu, 1821) is one of the most charismatic species of this area. The purpose of this study was to determine the density and abundance of bottlenose dolphins on the northern and central coasts of Veracruz. The study area was subdivided into three zones, each housing a bottlenose dolphin population: Tamiahua, Tuxpan and Nautla. Distance sampling methodology was used to estimate dolphin density and abundance. In total, 89 surveys were conducted, totalizing h of survey effort and an area sampled of 7,430 km 2. Dolphins were sighted during 59 surveys, and of the 950 animals observed, 532 were determined to be unique individuals based on photo-identification. The abundance estimated for the entire study area is 2,632 dolphins (CV= 10.37%), with a density of 0.35 dolphin/km 2 (CV= 10.37%), and density group of 0.35 group/km 2 (CV= 10.37%). The results indicate that even though the study area is small it supports a larger density of bottlenose dolphins than the surrounding waters and may represent an important bottlenose dolphin conservation area in the Gulf of Mexico. Key words: Abundance, bottlenose dolphin, density, distance sampling, Gulf of Mexico, marine and coastal ecosystems, Mexico, Tursiops truncatus. RESUMEN Las costas del norte y centro del estado de Veracruz son habitadas por una gran variedad de organismos debido a su alta productividad primaria. El delfín nariz de botella (Tursiops truncatus Montagu, 1821) es una de las especies más carismáticas del área. El propósito de este estudio fue determinar la densidad y la abundancia de delfines nariz de botella en las costas norte y centro de Veracruz. El área de estudio se subdividió en tres zonas, cada una albergando una población de delfines nariz de botella: Tamiahua, Tuxpan y Nautla. La metodología de muestreo a distancia fue utilizada para estimar la densidad y abundancia de delfines. En total se hicieron 89 censos, teniendo un total h de esfuerzo y se muestreó un área de 7,430 km 2. Los delfines fueron observados en 59 censos y se observaron 950 animales de los cuales se determinó por medio de la foto identificación que 532 animales eran individuos únicos. La abundancia de delfines estimada para toda el área de estudio es de 2,632 delfines (CV= 10.37%), con una densidad de 0.35 delfines/km 2 (CV= 10.37%) y una densidad de grupo de 0.35 grupos/km 2 (CV= 10.37%). Los resultados muestran que a pesar de ser un área pequeña, soporta una alta densidad de delfines nariz de botella y por lo tanto la zona puede representar un área importante para la conservación de delfines nariz de botella en el Golfo de México. Palabras clave: Abundancia, delfín nariz de botella, densidad, ecosistemas marinos y costeros, Golfo de México, México, muestreo a distancia, Tursiops truncatus. Thalassas, 30(2) June

2 LAURA VÁZQUEZ-CASTÁN, ARTURO SERRANO, MARISELA LÓPEZ-ORTEGA, JOSÉ A. GALINDO, MIGUEL A. DÍAZ-ARREDONDO & ASENCIÓN CAPISTRÁN-BARRADAS Figure 1: Geographical position of the three study zones: A) Tamiahua; B) Tuxpan; and C) Nautla. Mapping prepared by the Laboratory of Tropical Geomatics. INTRODUCTION The Gulf of Mexico has a great variety of marine mammals, and one of the most common coastal species is the bottlenose dolphin (Tursiops truncatus Montagu, 1821) (Würsig et al., 2000). Bottlenose dolphins are distributed along most of the tropical and temperate oceans of the world (Leatherwood & Reeves 1982), and are an integral part of marine and coastal waters of the Caribbean Sea and Gulf of Mexico (Ward & Moscrop, 1999). Cetacean abundance estimates in the southern Gulf of Mexico come mostly from photo-identification studies, unlike minimum abundance studies, which use the line transect method and distance sampling (Buckland et al., 1993; Buckland & York, 2002). Dolphin abundance estimation is mainly calculated using photo-identification studies and capture-recapture analyses (Hammond et al., 1990; Ortega-Ortiz, 2002; Buckland & York, 2002). In Mexico, all marine mammal species are protected under Mexican laws (SEMARNAT, 2010), but there are few accurate abundance data for any cetacean species, even though this information is essential to make management and conservation decisions. Northern Veracruz has been suggested as an area of importance for these dolphins 58 Thalassas, 30(2) June 2014

3 IS THE NORTHERN-CENTRAL COAST OF VERACRUZ, MEXICO AN IMPORTANT AREA FOR BOTTLENOSE DOLPHINS (Tursiops truncatus Montagu, 1821)? Figure 2: Plot showing how the curve adjusted to the data; the model used was a Half-Normal/Polynomial. (Valdes-Arellanes et al., 2011; Galindo et al., 2009). Thus, the purpose of this study was to determine the density and abundance of bottlenose dolphins on the northern and central coasts of Veracruz, Mexico. MATERIALS AND METHODS The study area is located along the northern and central coasts of Veracruz, from Tamiahua to Nautla (Fig. 1), and represents approximately 7,430 km 2. The study area was subdivided into three zones because dolphin populations appear to be divided accordingly. This assumption is based on photo-identification studies for Tamiahua (Martínez-Serrano et al., 2011; Heckel, 1992; Schramm, 1993), Nautla (Martínez-Serrano et al., 2011; Ramírez et al., 2005) and Tuxpan (Martínez-Serrano et al., 2011; Valdes-Arellanes et al., 2011). Data Collection Random line transects were carried out covering the entire study area. Transects were done biweekly using a 12-m boat, equipped with two 150 HP outboard engines. The surveys were carried out at 15 km/hr and the following data were noted: date, time, general climate conditions such as visibility, glare and sea state, and general comments. During dolphin sightings, the following data were taken: sighting time, number of animals sighted, location (taken with a Garmin GPS model 76CSx precision + 3m), movement of animals with regard to the boat, the distance to the boat and the angle (relative to the boat) at which they were sighted. The distance and angle to the boat were taken with a range finder Bushnell model Legend 1200 ARC Laser (range: 4.5 m to 914 m). When the animals were sighted, they were approached slowly in order to take photographs for photo-identification using a Canon digital SLR camera model EOS Rebel 6.3 MP, with a Canon mm zoom lens. Data Analysis Photo-Identification Photos were named and catalogued as the methodology recommended by Mazzoil et al. (2004). Density and Abundance To estimate the density and the abundance of bottlenose dolphins Distance Sampling methodology was employed (Buckland et al., 2001). Systematic line transects were carried out covering the entire study area. Transects were done biweekly, and during dolphin sightings the number of animals sighted was written, animals movement with regard to the boat, the distance to the boat and the angle (relative to the boat) in which they were sighted. The distance and angle to the boat were taken with a range finder Bushnell model Scout 1000 ARC Laser (range: 4.5 m to 914 m). The model considers that the greater the distance, fewer animals are detected. So to have a more accurate data about the size of the study population, it must estimate how many animals were not Thalassas, 30(2) June

4 LAURA VÁZQUEZ-CASTÁN, ARTURO SERRANO, MARISELA LÓPEZ-ORTEGA, JOSÉ A. GALINDO, MIGUEL A. DÍAZ-ARREDONDO & ASENCIÓN CAPISTRÁN-BARRADAS Figure 3: Map of the study area showing the geographic location of the transects covered by boat by year. observed when carrying out the transect. To do this, an estimate detection function, and a density estimate of organisms in the study area must be done (Begon, 1989; Buckland et al., 2001). This information allows us to calculate a coefficient of variation for the population studied (Buckland et al., 2001). The abundance was calculated using the Distance Sampling Software, Version 5.0, Release 2 (Thomas et al. 2006). A Half- Normal Polynomial Model for the analysis of the data was used (Fig. 2). A comparison of relative abundance and group size between the zones studied was done using a Kruskal- Wallis test. RESULTS Photo-Identification From 2005 to 2008, a total of 89 surveys were conducted, totaling a search effort of h and 1,890 km; covering an area of 7,430 km 2 approximately (Fig. 3). The entire study area was fully covered each year. Dolphins were sighted in 59 of the 89 surveys. A total of 96 dolphin groups were observed during the study. A total of 950 animals were observed, 532 were determined to be unique individuals based on photo-identification. A total of 187, 265 and 80 dolphins were identified in the Tamiahua, Tuxpan and Nautla zones, respectively. The 60 Thalassas, 30(2) June 2014

5 IS THE NORTHERN-CENTRAL COAST OF VERACRUZ, MEXICO AN IMPORTANT AREA FOR BOTTLENOSE DOLPHINS (Tursiops truncatus Montagu, 1821)? Figure 4: Map showing the geographical sightings of dolphins in the study area: triangles indicate dolphins sighted in the Tuxpan zone, squares indicate dolphins sighted in the Tamiahua zone, and the cross indicates dolphins sighted in the Nautla zone. total number of dolphin sighting hours was hr. Dolphin sightings per year and by zone were: 2005 Tamiahua 4 sightings, Tuxpan 12 sightings, Nautla 2 sightings; 2006 Tamiahua 15 sightings, Tuxpan 15 sightings, Nautla 4 sightings; 2007 Tamiahua 7 sightings, Tuxpan 18 sightings, Nautla 3 sightings; and 2008 Tamiahua 1 sightings, Tuxpan 12 sightings, NA 3 sightings (Fig. 4). Pulling the three zones together, by year, the number of dolphins photo-identified were 43 in 2005, 169 in 2006, 157 in 2007 and 163 in Tamiahua presented the highest average group size with 8.9 animals per group, followed by Nautla with 8.8 animals per group and Tuxpan with 8.2 animals per group. A Kruskal-Wallis test showed that there are not significant differences in group size between zones (p= 0.822; d.f.= 3; H= 0.361). The average bottlenose dolphin group size by year was 7.1 animals in 2005, 10.5 animals in 2006, 6.8 animals in 2007, and 10.5 animals in Abundance Bottlenose dolphin abundance for the entire study area and for the entire period of time of the study was 2,632 animals (CV= 10.37%). The estimated bottlenose density was 0.35 animal/km 2 (CV= 10.37%) (Table 1). Thalassas, 30(2) June

6 LAURA VÁZQUEZ-CASTÁN, ARTURO SERRANO, MARISELA LÓPEZ-ORTEGA, JOSÉ A. GALINDO, MIGUEL A. DÍAZ-ARREDONDO & ASENCIÓN CAPISTRÁN-BARRADAS Table 1:. Dolphins density and abundance estimation summary; a Half-Normal/Polynomial Model was used. Description Estimate %CV* gl* 95% Confidence interval Cluster density Density Abundance 2, ,148 3,227 *Note: %CV: Coefficient of variation; gl: degress of freedom. There is an estimated abundance of 1,639 bottlenose dolphins (CV = 26.9%) in Tamiahua, with a density of 0.9 animal/km 2 (CV = 26.9%). The bottlenose dolphins abundance in Tuxpan is 1,032 (CV = 17.6%), with a density of 0.39 animal/km 2 (CV = 17.6%). The estimated bottlenose dolphin abundance for Nautla is 835 animals (CV = 33.8%), with a density of 0.29 animal/km 2 (CV = 33.8%) (Table 2). DISCUSSION Photo-Identification Heckel (1992) photo-identified 58 bottlenose dolphins in the Tamiahua zone. Schramm (1993) photo-identified 41 animals for the same zone. In both studies, the photo-identification techniques and the Darling-Morowitz model (1986) were used to estimate dolphin abundance. In this study, a total of 187 dolphins were identified for Tamiahua. The difference is due to the bigger sampling effort done in this study, and because Heckel (1992) and Schramm (1993) only worked inside the lagoon and made only a couple of surveys on coastal waters. Comparing the photo-identification catalogs of Heckel (1992) and Schramm (1993) with ours, there were four dolphins that have been in the area since That means that at least some of the dolphins are residents in the study area (over 20 years). Valdes-Arellanes et al. (2011) studied bottlenose dolphins in Tamiahua and Tuxpan, identifying 202 bottlenose dolphins: 118 dolphins from Tamiahua population and 84 dolphins from Tuxpan. A total of 532 bottlenose dolphins were photo-identified in this study for the entire study area (Tamiahua, Tuxpan and Nautla). Of the 532 dolphins, 265 belonged to Tuxpan, 187 animals to Tamiahua and 80 dolphins to Nautla. Once again, the difference between the two studies originates from the difference in sampling effort. Table 2: Dolphins density and abundance estimation summary for the Tamiahua, Tuxpan and Nautla zones; a Half-Normal/Polynomial Model was used. Description Estimate %CV* gl* 95% Confidence interval Zone Tamiahua Cluster density Tuxpan Nautla Tamiahua Density Tuxpan Nautla 1, ,789 Tamiahua Abundance 1, ,458 Tuxpan ,631 Nautla *Note: %CV: Coefficient of variation; gl: degress of freedom. 62 Thalassas, 30(2) June 2014

7 IS THE NORTHERN-CENTRAL COAST OF VERACRUZ, MEXICO AN IMPORTANT AREA FOR BOTTLENOSE DOLPHINS (Tursiops truncatus Montagu, 1821)? Abundance The only previous bottlenose dolphin abundance study in Mexico was the one made by Valdes-Arellanes et al. (2011). Valdes-Arellanes et al. (2011) used Jolly-Seber capture-recapture technique (1965) to estimate dolphin abundance. They estimated for Tamiahua and Tuxpan 302 dolphins ± 113 dolphins (which is a variation greater than 30%). This variation is really high, and it is explained by the fact that they had few recaptures. The Jolly-Seber (1965) model requires at least three recaptures per animal (Begon, 1989). This results in an unreliable model for abundance of dolphins in open areas, because they are extremely mobile, and do not always have visible marks on their dorsal fin. Distance sampling methodology is more precise and effective when working with marine mammals (Buckland et al., 2001). A difference in dolphin densities between the subzones was observed. Martínez-Serrano et al. (2011) reported for these three subzones an exchange of dolphins according to the season (a dry season from March to June, a rainy season from July to October, and a cold-front season from November to February). These authors also reported a change in home range size according to the season. These variations in the behavior of the dolphins, and considering that dolphins form fission-fusion groups may explain the differences in densities observed in this study. Fulling et al. (2003) reported an abundance of 25,320 dolphins (CV = 0.26%) for the North American Gulf of Mexico continental shelf, from the Mexican border all the way up to Key West, Florida (a total of 245,800 km 2 ). A similar study carried out in Mexico, estimated 2,897 bottlenose dolphins ± animals in Sonora-Sinaloa (a total of 150,000 km 2 ) (Patiño et al., 2008). Our study area represents 3% of the Fulling et al. (2003) study area, and 5% Patiño et al. (2008), and we estimated 2,632 dolphins. The dolphin population of northern-central Veracruz represents 10% of the population studied by Fulling et al. (1993), and 90% of the population studied by Patiño et al. (2008). Thus, the northern-central coast of Veracruz is a highly important site for bottlenose dolphins. Therefore, should be considered a conservation area for marine mammals. ACKNOWLEDGMENTS Funding was provided by the Cetacean Society International through a grant to A. Serrano. Raya- Cruz and Alanís-Méndez from the Tropical Geomatics Laboratory for their help on the making of the maps for the manuscript. Valuable comments on earlier versions of the manuscript were made by E. Keith and P. Abgrall. Also, we would like to thank two reviewers who provided comments that improved the manuscript. REFERENCES Begon M (1989). Ecología animal: modelos de cuantificación de poblaciones. Editorial Trillas. México, 136 pp. Buckland S T, Anderson D, Burnham K, Laake J, Borchers D & Thomas L (2001). Introduction to distance and sampling: estimating abundance of biological populations. Oxford University Press. Oxford, UK. Buckland S T, Anderson D R, Burnham K P & Laake J L (1993). Distance sampling: Estimating abundance of biological populations. Chapman and Hall, London, U.K. Buckland S T & York A E (2002). Abundance estimation. En: Perrin W F, Würsig B & Thewissen J G M (eds.) Encyclopedia of marine mammals. Academic Press. San Diego, CA, EE. UU. p.1-6. Darling J & Morowitz H (1986). Census of Hawaiian humpback whales (Megaptera novaeangliae) by individual identification. Canadian Journal of Zoology, 64 (1): Fulling G L, Mullin K D & Hubard C W (2003). Abundance and distribution of cetaceans in outer continental shelf waters of the U.S. Gulf of Mexico. Fishery Bulletin, 101 (4): Galindo J A, Serrano Solís A, Vázquez Castán L, González Gándara C & López Ortega M (2009). Cetacean Diversity, Distribution, and Abundance in Northern Veracruz, Mexico. Revista Aquatic Mammals, 35 (1): González Gándara C, Trinidad Martínez S & Chávez Morales V (2006). Peces ligados a Thalassia testudinum en el arrecife Lobos, Veracruz, México: diversidad y abundancia. Revista de Biología Tropical, 54 (1): Hammond S P, Mizroch S A & Donovan G P (1990). Individual recognition of cetaceans: use of photo-identification and other technique to estimate population parameters. Reports of the International Whaling Commission, Special Issue 12. International Whaling Commission, Cambridge, Gran Bretaña. Heckel G (1992). Foto-identificación de tursiones Tursiops truncatus (Montagu, 1821) en la Boca de Corazones de la Laguna de Tamiahua, Veracruz, México (Cetácea: Delphinidae). Tesis de Licenciatura, Facultad de Ciencias, Universidad Nacional Autónoma de México, México, D.F. Jefferson T A & Schiro A J (1997). Distribution of cetaceans in the offshore Gulf of Mexico. Mammal Review, 27 (1): Jolly G M (1965). Explicit estimates from capture-recapture data with both death and immigration - Stochastic model. Biometrika, 52 (1): Kaschner K, Tittensor D P, Ready J, Gerrodette T & Worm B (2011). Current and future patterns of global marine mammal biodiversity. PLoS ONE, 6 (5): e doi: / journal.pone Leatherwood S & Reeves R R (1982). Bottlenose dolphins, Tursiops truncatus, and other toothed cetaceans. In: Thalassas, 30(2) June

8 LAURA VÁZQUEZ-CASTÁN, ARTURO SERRANO, MARISELA LÓPEZ-ORTEGA, JOSÉ A. GALINDO, MIGUEL A. DÍAZ-ARREDONDO & ASENCIÓN CAPISTRÁN-BARRADAS Wild mammals of North America: Biology, management, economics (J.A. Chapman y G. A. Feldhamer, eds). John Hopkins University Press, Baltimore, MD, Mazzoil M, McCulloch S D, Defran R H & Murdoch E (2004). The use of digital photography and analysis for dorsal fin photo-identification of bottlenose dolphins. Aquatic Mammals, 30 (2): Martínez Serrano I, Serrano A, Heckel G & Schramm Y (2011). Distribution and home range of bottlenose dolphins (Tursiops truncatus) off Veracruz, Mexico. Marine Sciences. Ciencias Marinas, 37(4A): Ortega Ortiz J G (2002). Multiscale analysis of cetacean distribution in the Gulf of Mexico. Ph. D. Dissertation, Texas A & M University, College Station, TX, 170 pp. Patiño V J L, Vargas M A G & Díaz AC (2008). Estimación poblacional de toninas Tursiops truncatus, en la Bahía de Agiabampo Sonora-Sinaloa, México en Verano y Otoño de 1995 al Revista de Zoología, 19: Ramírez T, Morteo E & Portilla-Ochoa E (2005). Basic Aspecto on the Biology of the Bottlenose Dolphin, Tursiops truncatus, in the Coast of Nautla, Veracruz, Mexico. Resume 16 th Biennal Conference on the Biology of Marine Mammals. San Diego, California, U.S.A. Schramm Y (1993). Distribución, movimientos, abundancia e identificación del delfín Tursiops truncatus (Montagu 1821) en el Sur de la Laguna de Tamiahua, Veracruz y aguas adyacentes (Cetácea: Delphinidae.) Tesis de Licenciatura, Universidad Autónoma de Guadalajara, México. D.F. SEMARNAT Secretaría de Medio Ambiente y Recursos Naturales (2010). NORMA Oficial Mexicana NOM-059- ECOL-2001, Protección ambiental-especies nativas de México de flora y fauna silvestres-categorías de riesgo y especificaciones para su inclusión, exclusión o cambio-lista de especies en riesgo. Diario Oficial. México, D.F., 153 pp. Thomas L, Laake J L, Strindberg S, Marques F F C, Buckland S T, Borchers D L, Anderson D R, Burnham K P, Hedley S L, Pollard J H, Bishop J R B & Marques TA (2006). Distance 5.0. Release 2. Research Unit for Wildlife Population Assessment, University of St. Andrews, UK. Available from [accessed 3 June 2007]. Valdes Arellanes M P, Serrano A, Heckel G, Schramm Y & Serrano I M (2011). Abundancia de dos poblaciones de toninas (Tursiops truncatus) en el norte de Veracruz, México. Revista Mexicana de Biodiversidad, 82: Ward N & Moscrop A (1999). Mamíferos del Gran Caribe: Un resumen preliminar de su estatus de conservación. Programa de las naciones Unidas para el Medio Ambiente. Cuarta Reunión del Comité Asesor Científico y Técnico Interino (ISTAC) del Protocolo Relativo a las Áreas de Flora y Fauna Silvestres, especialmente protegidas (SPAW) en la región del Gran Caribe. La Habana, Cuba, 20 pp. Würsig B, Jefferson T A & Schmidly D J The Marine Mammals of the Gulf of Mexico. (W. L. Moody Jr. Natural History Series) (Ed.). Texas A and M University Press, College Station. (Received: November, 29, Accepted: February, 28, 2014) 64 Thalassas, 30(2) June 2014