Effects of bycatch on the population viability of the narrow-ridged finless porpoises in Ariake Sound and Tachibana Bay, Japan

K Shirakihara,M Shirakihara,M Hashimoto

doi:10.3354/esr00658

Abstract

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 27:87-94 (2015) - DOI: https://doi.org/10.3354/esr00658 Effects of bycatch on the population viability of the narrow-ridged finless porpoises in Ariake Sound and Tachibana Bay, Japan Midori Hashimoto1,*, Kunio Shirakihara1, Miki Shirakihara2 1Graduate School of Frontier Sciences/Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan 2Faculty of Science, Toho University, 2-2-1 Miyama, Funabashi, Chiba 274-8510, Japan *Corresponding author: midori_84-10a@nenv.k.u-tokyo.ac.jp ABSTRACT: The narrow-ridged finless porpoise Neophocaena asiaeorientalis is a coastal cetacean that is threatened by various human activities. Bycatch mortality is a particular danger to the porpoise population in Ariake Sound and Tachibana Bay, Japan. To evaluate the impact of bycatch mortality on the viability of this population, we simulated changes in population size over the next 100 yr, using a Leslie matrix model. The simulation trials were repeated for 3 scenarios of possible bycatch mortality rates. If bycatch mortality remains at the reported level, the estimated annual rate of decrease is 0.671 to 3.87%, and the estimated population size reduction over 3 generations is 29.6 to 86.3%. A population size reduction of ≥30% was predicted in almost half the simulation trials, even in the most optimistic scenario. The reported bycatch mortalities would pose a serious threat to the viability of this porpoise population; therefore, the population should be classified at least as ‘Vulnerable’ according to Criterion A4, as defined in the IUCN Red List. Our predictions were sensitive to annual bycatch mortality rate estimates. Hence, the collection of current abundance and bycatch data should be promoted in order to minimize uncertainty in risk assessments. KEY WORDS: Bycatch · Extinction risk · Leslie matrix model · Narrow-ridged finless porpoise Full text in pdf format PreviousCite this article as: Hashimoto M, Shirakihara K, Shirakihara M (2015) Effects of bycatch on the population viability of the narrow-ridged finless porpoises in Ariake Sound and Tachibana Bay, Japan. Endang Species Res 27:87-94. https://doi.org/10.3354/esr00658 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 27, No. 1. Online publication date: February 11, 2015 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2015 Inter-Research.

Highlights

Narrow-ridged finless porpoises Neophocaena asiaeorientalis inhabit coastal waters and rivers in East Asia
If bycatch mortality remained at the reported level, the medians ofλwould be
Bycatch mortality poses a serious threat to the viability of the narrow-ridged finless porpoise population in Ariake Sound and Tachibana Bay

Summary

Introduction

Narrow-ridged finless porpoises Neophocaena asiaeorientalis inhabit coastal waters and rivers in East Asia. The species is critically affected by a wide variety of human activities, such as bycatch (i.e. incidental capture during fishing), ship strikes, and the degradation and reduction of habitats due to dredging and pollution (Kasuya et al 2002, IWC 2006). Bycatch in particular can have a serious impact on porpoise populations because it is lethal and, can threaten the viability of the populations (Reeves et al 1997, IWC 2006). A rapid decline caused by humaninduced mortality has been noted in some populations (Kasuya et al 2002, Zhao et al 2008, Mei et al.2012, Hashimoto et al 2013). Because of a suspected past decline in population size, this species is classified worldwide as ‘Vulnerable’ (VU) according to Criterion A2 of the IUCN Red List of Threatened Species (Wang & Reeves 2012). Little work has been conducted on classification at the population level

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