Marsh deer Blastocerus dichotomus population estimate in the Paraná River, Brazil

This paper reports the results of an aerial survey of a marsh deer Blastocerus dichotomus population occupying an ara to be flooded by the construction of a hydroelectric power plant (Pôrto Primavera) in the Paraná River, Brazil. Forty transects totalling 143 km were flown during the dry and flood seasons. Population size was estimated using the modified Petersen estimator, the line transect method, and two variations of the strip transect method. The results revealed mean densities of 0·50–0·54 deer/km 2 and a population of approximately 950 individuals, the second largest population reported for this vulnerable species in Brazil. Individuals were most commonly alone, but group sizes of up to five deer were observed. Newborn fawns were observed from September to November. The effectiveness of a rescue operation is discussed relative to the possible benefits for the species' conservation. Deer translocations have a high failure rate. Public pressure to translocate marsh deer is not likely to aid in their conservation but may actually assist to precipitate their decline locally. Instead, acquisition of suitable marsh habitat in which the deer already reside could be much more successful and less costly.