Biological observations and first stranding record of Mesoplodon peruvianus from the central Pacific coast of Oaxaca, Mexico

THERYA, 2017, Vol. 8 (2): 179-184 DOI: 10.12933/therya-17-451 ISSN 2007-3364 Biological observations and first stranding record of Mesoplodon peruvianus from the central Pacific coast of Oaxaca, Mexico Jesús García-Grajales1*, Alejandra Buenrostro Silva2, Eunice Rodríguez-Rafael3, and Juan Meraz1 Instituto de Recursos, Universidad del Mar campus Puerto Escondido. Km 2.5, Carretera Federal Puerto Escondido – Sola de Vega, Puerto Escondido, CP. 71980, Oaxaca. Oaxaca, México. E-mail: (JGG), (JM) 2 Instituto de Industrias, Universidad del Mar campus Puerto Escondido. Km 2.5, Carretera Federal Puerto Escondido – Sola de Vega, Puerto Escondido, CP. 71980, Oaxaca. Oaxaca, México. E-mail: (ABS). 3 Licenciatura en Biología Marina, Universidad del Mar. Ciudad Universitaria, Puerto Ángel, Distrito de San Pedro Pochutla, CP. 70902. Oaxaca, México. E-mail: (ER-R). *Corresponding author 1 The knowledge of Mesoplodon peruvianus species about its distribution and ecology is limited, because the range of the species is unknown. Mainly due to their inconspicuous behaviour. A survey was conducted from November 2014 to January 2015 along a near 80 km long transect in the central coast of Oaxaca. Additionally, based on an stranded individual at Zicatela beach, we measured it and performed a necropsy to report the probable cause of stranding. Two individuals of M. peruvianus species were observed on December 5, 2014 at about 9.3 km from the coast at 12:45 local time. The identification was clearly positive because of the black and white large individual, with an estimated size of 4 m. This is the first record of M. peruvianus in the area. On March second 2016, a carcass of a male of M. peruvianus was found stranded at Zicatela beach; was classified as scale 2 stranded individual (freshly dead). Our main pathological findings were related with the respiratory and the digestive systems. The thoracic cavity arose out of air suggesting a pneumothorax; lungs were collapsed and to the touch showed a consistency of atelectasis. In total, 18 marine mammal species have been recorded for the state of Oaxaca, this study adds a new record, confirming the presence of M. peruvianus and its distribution in the region. The collapsed lungs of the stranded individual, probably resulted from an apnea state, were related with dysbarism. In Mexico no exist the practice of necropsies in wild marine mammals, therefore, our work contributes to gather relevant information on the health of marine mammals and the threats they face. El conocimiento acerca de la distribución y ecología de Mesoplodon peruvianus es limitada debido a que su comportamiento enigmático limita el conocimiento acerca de su ámbito hogareño. Se realizaron muestreos en transectos lineales paralelos a la costa de Oaxaca de noviembre de 2014 a enero de 2015 con el fin de obtener registros de mamíferos marinos. Adicionalmente, con base en un ejemplar varado en la playa Zicatela en 2016, realizamos su medición y necropsia para indagar las posibles causas del varamiento. Dos individuos de M. peruvianus fueron avistados el 5 de diciembre de 2014 a 9.3 km de la costa alrededor de las 12:45 horas del día. La identificación se realizó por la típica coloración y se le estimó una longitud de 4 m. Estos avistamientos son el primer registro de M. peruvianus en la zona, contribuyendo al conocimiento de la especie. El 2 de marzo de 2016, se encontró el cadáver de un ejemplar macho de M. peruvianus varado en la playa Zicatela. Se le clasificó en la escala 2 (recién muerto). Nuestros principales hallazgos patológicos se relacionaron con el sistema respiratorio y el digestivo. La cavidad toracica presentó evidencia de aire sugiriendo un pneumotorax y los pulmones estuvieron colapsados y al tacto presentaron una consistencia elástica atribuida a una posible atelectasia. En total, 18 especies de mamíferos marinos han sido registrados para el estado de Oaxaca y nuestro trabajo adiciona un nuevo registro con distribución en esta region y confirma la presencia de M. peruvianus. Respecto al ejemplar varado, los pulmones colapsados encontrados en el cadaver, probablemente sean resultado de una condición de apnea, relacionada con disbarismo. En México, no existe la práctica de las necropsias en animales de vida silvestre, por tanto, nuestro trabajo contribuye a reunir información acerca del conocimiento de la salud de los mamíferos marinos y sus amenazas. Keywords: Cetaceans; necropsy; sightings; Zicatela; Ziphiidae. © 2017 Asociación Mexicana de Mastozoología, www.mastozoologiamexicana.org Introduction The Ziphiidae family is one of the most wide-ranging families of cetaceans, occurring from the ice edge at both poles, to the equator in all the world´s oceans (McLeod et al. 2006). However, knowledge of individual species range varies greatly, in some cases the species range is fairly well known (V. gr. Mesoplodon bidens, McLeod 2000) and some species are regularly sighted at sea (V. gr. Ziphius cavirostris, McLeod et al. 2006), while other species are almost completely unknown (V. gr. M. traversii van Helden et al. 2002; M. peruvianus McLeod et al. 2006). There is a number of reasons for this knowledge variation. First, in some species there are many distribution records obtained by trained observers during marine mammal survey cruises and by tuna purse seiners during their fishing activities (Pitman et al. 1988) or by stranding records (V. gr. M. bowdoini McLeod et al. 2006; Ziphius cavirostris Gallo-Reynoso and HoyosPadilla 2015), for other species their range is unknown due to their unknown behaviour (McLeod et al. 2006). The pygmy beaked whale (Mesoplodon peruvianus) is one of the 14 Mesoplodon species that are present in the North Pacific Ocean (Leatherwood et al. 1982; Mead 1989; Dalebout et al. 2008), the specie was described by Reyes et al. (1991) based in the cranial characteristics, and those characteristics related to teeth (Reyes et al. 1991). Due the lack of intact specimens (only two reported then) external appearance, in terms of coloration, was limited to deep grey (biggest individual) or brown (from a calf ), both with a MESOPLODON PERUVIANUS IN OAXACA grey belly (Reyes et al. 1991). Because of this relatively small body size (up to 3.7 m according with Reyes et al. 1991) the species has been known as the pigmy beaked whale. A year later of the species first description, M. peruvianus was sighted in the North Pacific, at Bahia de La Paz, Mexico (Urbán-Ramírez and Aurioles-Gamboa 1992). These authors showed two important points: 1) M. peruvianus might be distributed from Peru, to Northern Mexico, possibly including all the Eastern Tropical Pacific, and 2) at that time, both Mesoplodon sp. A. and M. peruvianus were considered as two possibly species, however, this assumption continued for several years with some literature and field guides including both as separate species (Carwardine 1995; Jefferson and Leatherwood 1995; Ceballos et al (...truncated)