A method to measure captive giant otters ( Pteronura brasiliensis ) without sedation

The giant otter, Pteronura brasiliensis, is one of the largest carnivores of South America (Duplaix, 1980). Its historical distribution extended from the northern part of the South American continent to the north-central portion of Argentina (Carter and Rosas, 1997). Because of the destruction of its habitat and intense hunting pressure due to the demand of the international “haute couture” for giant otter skins, P. brasiliensis numbers had decreased significantly by the early 1970s. The species is classified as endangered by The World Conservation Union (IUCN, 2006). Currently, it is believed that P. brasiliensis is extinct in the southern portion of its historical distribution; however stable populations can still be found in the Pantanal and Amazon (Rosas et al., 1991; Carter and Rosas, 1997; Rosas, 2004). Although the species is threatened, much information regarding its basic biology and morphometrics still remains scarce. According to Duplaix (1980) the morphometric data, such as maximum length and weight, mentioned in the literature for P. brasiliensis are tentative at best. The genus Pteronura is monospecific. Although it has not been scientifically proven, two subspecies are mentioned in the literature: P. brasiliensis brasiliensis distributed in the Amazon Basin; and P. brasiliensis paranensis which occurs in the Paraguay and Paraná river basins, including the Pantanal wetland area (Harris, 1968; Duplaix, 1980). Genetic studies are necessary to confirm the existence of species division. According to Harris (1968) the total length of P. b. paranensis is shorter than that of P. brasiliensis brasiliensis. One difficulty in assessing captive giant otters involves the ability to adequately follow-up the animals’ morphometrics. Giant otters are very active carnivores with high metabolic rates (Carter et al., 1999), requiring special handling procedures in captivity. As a rule of thumb, the body measurements of cubs and juveniles can be obtained by the physical restraint of the animal. However, adult animal morphometrics can only be obtained using sedatives. It is important to stress that in addition to the costs, chemical contention involves a preliminary physical restrain in order to apply the anesthetics, and requires further care procedures because side effect reactions can occur (Marsicano et al., 1986). Additionally, anesthetic procedures, in general, are not justifiable for only obtaining morphometric data. Although giant otters can be weighed at a low cost using special cages in which the animals are contained and weighed, obtaining the total length of captive giant otters has always been a challenge for institutions. The aim of this study was to obtain reliable total length estimates of captive giant otters without the use of anesthetics. Knowing that giant otters rest during the day on top of trunks or other objects in the enclosure, we tested the use of previously calibrated plywood boards strategically placed inside the enclosures at the National Institute of Amazonian Research (INPA). The boards, which were 400cm long, 26.5cm wide, and 4.5cm thick, were painted yellow and marked every 5cm with alternating black and red paint (Figure 1). The calibrated plywood boards were placed in such a way that allowed the animals to lay on them. The animals were observed systematically by two independent observers at different times of the day, especially around 12:00pm and the end of the afternoon before entering their dens for the night. Good weather was taken into consideration as well. Each time the otters laid on the board in a specific position, where the entire body of the animal is stretched, from the snout to the tip of the tail, on top of the plywood board (Figure 1), the total length was estimated using the 5cm marks that were painted on the board. An adaptation period was necessary in order for the giant otters to become accustomed to the boards and the presence of the observer.