Precautionary Principle or Evidence-Based Conservation? Assessing the Information Content of Threat Data for the Yangtze Finless Porpoise

Abstract

Conservation management requires evidence, but robust data on key parameters such as threats are often unavailable. Conservation-relevant insights might be available within datasets collected for other reasons, making it important to determine the information content of available data for threatened species and identify remaining data-gaps before investing time and resources in novel data collection. The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) has declined severely across the middle-lower Yangtze, but multiple threats exist in this system and the relative impact of different anthropogenic activities is unclear, preventing identification of appropriate mitigation strategies. Several datasets containing information on porpoises or potential threats are available from past boat-based and fishing community surveys, which might provide novel insights into causes of porpoise mortality and decline. We employed multiple analytical approaches to investigate spatial relationships between live and dead porpoises and different threats, reproductive trends over time, and sustainable offtake levels, to assess whether evidence-based conservation is feasible under current data availability. Our combined analyses provide new evidence that mortality is spatially associated with increased cargo traffic; observed mortality levels (probably a substantial underestimate of true levels) are unsustainable; and population recruitment is decreasing, although multiple factors could be responsible (pollutants, declining fish stocks, anthropogenic noise, reduced genetic diversity). Available data show little correlation between patterns of mortality and fishing activity even when analyzed across multiple spatial scales; however, interview data can be affected by multiple biases that potentially complicate attempts to reconstruct levels of bycatch, and new data are required to understand dynamics and sustainability of porpoise-fisheries interactions. This critical assessment of existing data thus suggests that in situ porpoise conservation management must target multiple co-occurring threats. Even limited available datasets can provide new insights for understanding declines, and we demonstrate the importance of an integrative approach for investigating complex conservation problems and maximizing evidence in conservation planning for poorly known taxa.

Spatiotemporal relationships of threatened cetaceans and anthropogenic threats in the lower Yangtze system

“…Analysis of porpoise mortality data obtained through interviews with artisanal fishers by Turvey et al (2013) suggested that bycatch mortality has decreased over time, and might therefore merely be tracking rather than driving population decline. Mogensen et al (2022) also found limited spatial correlation between observed porpoise deaths and fishing activity patterns at multiple spatial scales, but population modeling suggested that reported bycatch mortality might exceed sustainable levels. The dynamics of how bycatch and other potential threats act and interact across the different multi-threat landscapes of the Yangtze system, their specific relationships with porpoises (e.g., levels and patterns of spatial overlap), and how these might vary at different scales across time and space, remain poorly understood.…”

“…Furthermore, our data cannot in themselves indicate whether bycatch is a more serious or significant threat than sand-mining or other uninvestigated anthropogenic pressures, necessitating further research into the dynamics of humanenvironmental relationships within this system. In particular, additional research is required into individual-level and population-level effects on porpoises of other vessel traffic, other sources of anthropogenic noise and habitat alteration, and pollutants known to affect cetacean reproductive success and survivorship, all of which remain poorly understood in the Yangtze (Mei et al, 2021;Mogensen et al, 2022). We encourage future investigation to determine multi-scale relationships between porpoises, threats, and biotic and abiotic environmental variables that might regulate porpoise habitat use, along with investigation of additional anthropogenic activities, to work towards establishing a more nuanced understanding of the sustainability of different threats to porpoises.…”

Understanding the Interactions between Small-Scale Fisheries and the Mediterranean Monk Seal Using Fishermen’s Ecological Knowledge

“…An example is the Yangtze River dolphin ( Lipotes vexillifer ) which was brought to extinction as a result of incidental capture in fisheries [ 28 ]. Currently, the vaquita ( Phocoena sinus ) [ 29 ] and the Yangtze finless porpoise ( Neophocaena asiaeorientalis asiaeorientalis ) [ 30 ] are in the same fate if no immediate conservation measures are taken. Accidental entanglement of the Mediterranean monk seal on fishing gear due to depredation has been reported in Greek fisheries and has been identified to be among the main causes of the species’ mortality [ 31 , 32 , 33 ].…”

Integrating biodiversity conservation and local community perspectives in China through human dimensions research

“…However, the main cause(s) of unsustainable porpoise mortality are unclear. Robust evidence remains lacking to suggest a primary role of fisheries interactions in driving porpoise decline, and Yangtze fisheries restrictions represent a precautionary conservation approach for porpoises (Mogensen et al, 2022). Indeed, other factors (e.g.…”