Can local ecological knowledge be used to assess status and extinction drivers in a threatened freshwater cetacean?

Abstract

Local ecological knowledge constitutes a potentially useful source of information for conservation, but the quality, limitations and biases of this body of knowledge remain largely untested. The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is a highly threatened freshwater cetacean found in one of the world’s most densely populated human environments. The dynamics of porpoise decline remain poorly understood, and local ecological knowledge from fishing communities across its range may represent an important conservation tool for monitoring porpoise population status and quantifying levels of human-caused mortality. We used interview data from an extensive survey of fishing communities across the middle-lower Yangtze drainage to investigate spatial and temporal patterns of porpoise abundance, mortality and population change. Interview data on porpoise relative abundance and decline, especially weekly sighting frequencies, show congruent spatial patterns with data collected from boat-based Yangtze cetacean surveys, demonstrating that informant data can provide accurate quantitative information on these two key parameters of species conservation status. Interview-based collection of local ecological knowledge therefore represents a useful monitoring method for assessing population trends in freshwater cetaceans and other charismatic or distinctive aquatic species, and may be particularly appropriate in regions where resources for regular boat-based surveys are limited. Using local ecological knowledge to identify primary threats to the porpoise population is less straightforward due to probable biases in interview data on porpoise mortality. However, interview data are able to demonstrate that the number of porpoises killed annually in the Yangtze mainstem may have doubled and that the annual mortality rate may have quadrupled over the past two decades, with mortality due to vessel strikes and other factors having increased more in recent years than by-catch mortality. It seems unlikely that fisheries mortality has been the dominant driver of porpoise decline in the Yangtze mainstem, suggesting that regulating regional fisheries may not be sufficient for porpoise conservation.