Electrofishing as a potential threat to freshwater cetaceans(e.g. dredging, noise, boat strikes),...

REVIEW

Electrofishing as a potential threatto freshwater cetaceans

Peter O. Thomas1,*, Frances M. D. Gulland1, Randall R. Reeves2, Danielle Kreb3, Wang Ding4, Brian Smith5, Muhammad Imran Malik6, Gerard E. Ryan7, Somany Phay8

1Marine Mammal Commission, 4340 East-West Highway, Bethesda, Maryland 20814, USA2Okapi Wildlife Associates, 27 Chandler Lane, Hudson, Quebec J0P1H0, Canada

3Yayasan Konservasi Rasi, Komplek Pandan Harum Indah, Samarinda, 75124 Kalimantan Timur, Indonesia4Institute of Hydrobiology, The Chinese Academy of Sciences, Wuhan, Hubei 430072, PR China

5Wildlife Conservation Society, Asian Coastal Cetacean Program, IUCN SSC Cetacean Specialist Group, Arcata, California 95518, USA

6Indus River Dolphin Conservation Project (IRDCP), WWF-Pakistan, Sukkur 65310, Pakistan7School of BioSciences, University of Melbourne, Melbourne, Victoria 3052, Australia

8WWFund Cambodia, #21, St. 322, Boeung Keng Kang I, Chamkar Morn, Phnom Penh 12300, Cambodia

ENDANGERED SPECIES RESEARCHEndang Species Res

Vol. 39: 207–220, 2019https://doi.org/10.3354/esr00962

Published July 11

1. INTRODUCTION

Several species of cetaceans occur solely or partly infreshwater systems of South America (Amazon,Orinoco, Tocantins/Araguaia, Madeira), southern Asia(Indus, Ganges, Brahmaputra, Karnaphuli), South east

Asia (Ayeyarwady, Mekong, Mahakam), and EastAsia (Yangtze), and many of these populations are en -dangered. The Amazon River dolphin Inia geoffrensis isendemic to the 4 aforementioned South American riversystems and was recently Red-Listed by the IUCN asEndangered (da Silva et al. 2018a). The tucuxi Sotalia

*Corresponding author: [email protected]

ABSTRACT: Electrofishing is an accepted practice for legal fish sampling and surveying, but its usefor subsistence food and market fishing has long been illegal in most countries. Illegal use affectsfreshwater fish populations in many parts of the world, and has been cited as a cause of mortality forendangered freshwater cetaceans in China (Yangtze dolphins and finless porpoises) and SoutheastAsia (Ayeyarwady, Mekong, and Mahakam dolphins in Myanmar, Cambodia, and Indo nesia, respec-tively), although the extent of this threat to cetaceans is unclear. Given their threatened status, thesepopulations can ill afford such mortality in addition to the other threats they face (e.g. entanglementin gillnets, habitat deterioration and loss, declines in prey). Here, we review the evidence that elec-trofishing is a serious threat to freshwater cetaceans. It may alter the behavior of dolphins and por-poises, and contact with electrical currents may even directly kill or injure these animals, althoughquestions remain unanswered concerning the exact nature and scale of the impacts. While otherthreats may appear more certain and urgent, electrofishing could be playing a significant role in driv-ing the declines of some critically endangered freshwater cetaceans in Asia. Due to ethical and logis-tical challenges to improving our understanding of the impacts of electrical currents on cetaceans,clear descriptions of lesions in dead animals found stranded are needed to characterize the damagecaused by electrofishing, to be more certain about cause and effect beyond spatiotemporal associa-tions, and to determine the extent of this threat. Mortality from electrofishing seems to be uncommon,but in face of the uncertainties and the numerous other threats to these small populations, highpriority should be given to enforcing electrofishing bans in the freshwater habitat of dolphins and fin-less porpoises.

KEY WORDS: Freshwater cetaceans · River dolphins · Finless porpoises · Electrofishing · Cetaceanconservation

OPENPEN ACCESSCCESS

Contribution to the Special ‘Marine vertebrate bycatch: problems and solutions’

© The authors 2019. Open Access under Creative Commons byAttribution Licence. Use, distribution and reproduction are un -restricted. Authors and original publication must be credited.

Publisher: Inter-Research · www.int-res.com

Endang Species Res 39: 207–220, 2019

fluviatilis, which is endemic to the Amazon system, iscurrently listed as Data Deficient (Secchi 2012) but ur-gently needs reassessment as its conservation statushas deteriorated rapidly in recent years, at least in Brazil(da Silva et al. 2018b). The South Asian river dolphinPlatanista gangetica is Endangered (Braulik & Smith2017), with 2 subspecies (both Endangered): the bhulanP. g. minor in the Indus system (Braulik et al. 2012)and the susu P. g. gangetica in the Ganges, Brahmapu-tra, and Karnaphuli systems (Smith et al. 2012). TheIrra waddy dolphin Orcaella brevirostris, an Endangeredand primarily coastal marine species (Minton et al.2017), has 3 entirely freshwater subpopulations, all ofthem Red-Listed as Critically Endangered — one in theAyeyarwady of Myanmar (Smith 2004), one in theMekong of Cambodia and Laos (Smith & Beasley2004), and one in the Mahakam of Indonesia (Jeffer-son et al. 2008). Finally, 2 fresh water cetaceans histori-cally inhabited the Yangtze River and adjoiningDongting and Poyang lakes. The Yangtze River dol-phin, or baiji Lipotes vexillifer, continues to be Red-Listed as Critically Endangered (possibly Extinct), butit has been at least functionally extinct since the early21st century (Smith et al. 2017). The Yangtze finlessporpoise, a subspecies of the En dan gered narrow-ridged finless porpoise Neophocaena asiaeorientalis(Wang & Reeves 2017), is Red-Listed as Critically En-dangered (Wang et al. 2013).

All freshwater cetaceans face numerous types anddegrees of anthropogenic threats, and their threatenedstate is, in every case, due to multiple factors — thevast majority of which are being driven by human ac-tion, whether deliberate or incidental. The primaryfactors threatening their survival are direct injury andmortality in legal and illegal fisheries (e.g. entangle-ment in gear, deliberate retaliation to protect gear andcatch from depredation); deliberate hunting to obtainfish bait (particularly for the Amazon River dolphin),and loss and fragmentation of cetacean and prey habi-tat due to water development projects (e.g. dams andbarrages, embankments, conversion of wetlands). Ad-ditional threats in some areas include vessel traffic(e.g. dredging, noise, boat strikes), harbor construction(e.g. noise, land reclamation for infrastructure), andexposure to contaminants (e.g. from industrial efflu-ent, urban and agricultural runoff, gold mining).

The focus of this paper is on a specific form of fish-ing — electrofishing — that has been characterized,but not well-documented or well-described, as a seri-ous threat to some freshwater cetacean populationsin Asia. Electrofishing has not (yet) been identified asa threat to freshwater cetaceans in South America(Secchi 2012, da Silva et al. 2018a).

Our objectives were four-fold: (1) to explain whatelectrofishing is and how it might be expected to affectcetaceans; (2) to summarize available evidence con-cerning mortality as well as responses of the animalsto exposure; (3) to critically evaluate such evidence;and (4) to identify gaps in our understanding of howelectrofishing threatens freshwater cetaceans.

2. INFORMATION SOURCES AND METHODS

Information on the mechanics and physics of electro - fishing was obtained by requesting advice from ex -perts on the subject who work (or worked) with theUS Fish and Wildlife Service (Alan Temple and JanDean) and by reviewing manuals and publications onits use and the potential hazard it poses to mammals,including humans.

All the authors of this paper have field experience withfreshwater cetaceans and have participated in con feren -ces, workshops, and informal discussions with fisher -men, fishery managers, and government officials inthe range countries. Some of us have ob served electro -fishing in the vicinity of dolphins or porpoises, somehave examined dead cetaceans that were thought tohave died of electrocution, and some have seen electro -fishing equipment deployed in areas inhabited bycetaceans. As a result, much of the information in thispaper, as well as many of the ideas discussed and theconclusions reached, come from direct experience.

In addition, we canvassed colleagues in the variousrange countries to determine where electrofishingdoes and does not occur and to obtain as much detailas possible regarding spatial and temporal overlapwith dolphins and porpoises. This included an initialinformal questionnaire to researchers in Cambodia,Myanmar, Indonesia, and China to identify concerns,equipment used, and perspectives on the nature ofeffects of electrofishing on freshwater cetaceans.Wherever we found reference to mortality of cetaceansattributed to electrofishing in the literature or mediaoutlets, we made an effort to follow this up with theoriginal source or sources to learn more about the cir-cumstances and how causation was diagnosed.

3. RESULTS

3.1. Electrofishing

3.1.1. What it means

Electrofishing is an important and commonly usedtool that allows fish biologists to collect a variety of

208

Thomas et al.: Electrofishing and freshwater cetaceans

data in the field, e.g. to assess species composition,estimate populations and growth rates, and collectindividual fish for analysis (Bohlin et al. 1989, Snyder2003). Generally, legal electrofishing for scientificpurposes is not intended to kill fish but to stun themso that they can be counted or so that individuals orsamples can be collected. When used for fish sam-pling, the type, power, and form of the electrical cur-rent are adjusted, and the size and shape of anodesare designed to reduce or eliminate the likelihood offish being injured or killed by the electrical current(Kolz 1989).

3.1.2. How it works

A basic manual (www.efish-solutions.com/ support/library- intro/) describes electrofishing as:

the process of using electricity to catch fish by creatingan electrical-field through water, around an anode (usu-ally on a hand-held pole or hanging from a boat) andcathode (trailing in the water behind the operator or boat).The electric-field between the 2 electrodes develops avoltage along the length of fish exposed to it, such thatgalvanotaxis stimulates their nervous system, and theyswim ‘up current’ towards the anode (the source of thefield). At a point approaching the source of the field, thefish enter a zone where the field is then of sufficientstrength to temporarily immobilize them and thus aidin their capture.

Elec trofishing manuals define 3 primary zones ofinfluence around the electrodes based on fish be -havior and physiological/muscular response to electri-cal fields, the dimensions of which depend upon thevoltage used and the conductivity of the environ-ment. The ‘zone of detection’ (or ‘perception’) is theportion of the electrical field where the fish is awareof it but can move away; the ‘effective zone’ (for fishcapture) is where fish may be forced to swim towardthe electrode and become immobilized but are notharmed; and the ‘injury zone’ is where fish experi-ence such high voltage gradients and power (andcurrent) densities that they are injured or killed (J.Dean pers. comm.). Understanding these zones andthe equipment and electrical currents used to createthem provides the operational basis for capturingfish. For boat-mounted equipment, the effective zonetypically has a radius of 2−3 m.

The voltages required to immobilize fish of differentsizes and types have been carefully studied, althoughmany details of the effects on fish are still uncertain.In general, larger fish (in terms of total body surfacearea) are more likely to be paralyzed or injured(spinal injuries from sudden muscular contractions),

and thus are more easily captured than smaller ones,because larger size allows a larger voltage differenceto develop across the body (Emery 1984, Mahoney etal. 1993, Dalbey et al. 1996, Dolan & Miranda 2003,Snyder 2003). Thin-scaled and unscaled fishes, in-cluding large catfishes, are less resistant to electricalcurrents than are thick-scaled fishes (Green 2011).

Electrofishing gear is generally powered by DCbatteries (carried in backpack units) or small genera-tors on boats. The need for mobility usually limits thesize of the power supply and the amount of powerthat can be applied in the water (Mahoney et al.1993, Reynolds & Harlan 2011).

3.1.3. How it could affect cetaceans

Cetaceans could be injured or killed directly byelectrofishing when they come into (1) direct contactwith the electrodes, thus becoming part of the electri-cal circuit or (2) contact with the electrical fields pro-duced in the water by electrofishing devices. Theimpact of a given electrical field depends on the dis-tance of an animal from the source and the nature ofthe field itself.

There is no question that direct contact with elec-trodes in water is potentially fatal for mammals ofall sizes. For example, when an animal makesphysical contact with a metal electrode, whetheraccidentally or deliberately (e.g. out of curiosity), itbecomes ‘directly “wired” to the power source and issubject to possible electrocution’ (Kolz & Johnson1995, p. 211). Large-scale experiments with electricharpoons in the 1930s proved this in a dramatic man-ner with blue whales Balaenoptera musculus (Mitchell1986). The prototypes used in field trials under theauspices of the Norwegian Association of WhalingCompanies proved extremely effective, paralyzingthe whales and causing them to roll over onto theirsides with flippers and flukes above water. It report-edly did not matter where the whale was hit — theresult was usually a rapid death. Although the ‘killingcurrent’ was 220 V 50 Hz AC, resistance was so lowthat on average a potential of 20 V passing throughthe body was claimed to be sufficient for killing theselarge creatures.

Electrocution, cardio-respiratory failure, and drown-ing can also be the fate of fishermen who make mis-takes when using electrofishing equipment (DiNunno et al. 2003). In descriptions of potential humaninjury from electrofishing it is often difficult to discernwhether authors are referring to direct physical con-tact with electrical circuits or with electrical fields,

209


but the vulnerability is clear, regardless. Reynolds &Kolz (2013, p. 337), for example, confirmed that thebatteries and generators used in electrofishing aspracticed for scientific fish monitoring deliver ‘morethan enough energy to electrocute a person.’ Theynote that grasping a wire carrying as little as 0.01 Acan cause muscular tetany and inability to releaseone’s grip, leading to death from respiratory arrest,asphyxia, or ventricular fibrillation. Primavesi (2009)emphasized that in human electrical injuries, skinthickness and moisture are crucial factors because skinresistance impedes current flow and protects againstelectrocution.

There is greater uncertainty about the harm thatcould come to freshwater cetaceans when they comeinto contact with the electrical fields in the water pro-duced by electrofishing devices. Fish behavior andsize, water conductivity and temperature, substrate,and current strength are among the well-studied vari-ables that influence the effectiveness of electro fishing(Emery 1984, Mahoney et al. 1993), but we have littleknowledge of the be havioral, physiological, and neu-rological responses of cetaceans as they enter an elec-trically charged zone, or of the distances or voltagesat which they would begin to detect it. Experiencedelectrofishing personnel reported that geese, ducks,beavers, muskrats, and nutrias did not appear to be‘inadvertently shocked at the power levels normallyused for fish’ (Kolz & Johnson 1995, p. 208).

Pictures and descriptions of electrofishing equip-ment used by artisanal fishermen in the rivers andlakes of East and Southeast Asia do not suggest thatthe electrical outputs or effective distances producedwould be of signi ficantly greater magnitude thanthose produced by standard devices used for legal fishsampling elsewhere. There is no evidence of tech no - logical difference, other than the power of the electri-cal source, that would significantly increase the powerand range of influence of such basic equipment orchange the basic behavior of electrical fields. Thisleads electrofishing experts to discount general state-ments such as ‘the lethal electric charge was able to killanything within a range of 20 meters…’ (Turvey 2008,p. 39), but the larger apparatus described as being usedin the Yangtze River may have greater reach (A. Tem-ple pers. comm.).

3.1.4. Sensitivity and response of freshwatercetaceans and other mammals to electrical fields

There are few descriptions of the behavior of smallcetaceans or other aquatic mammals reacting to elec-

trical fields. Research on dolphin electro-receptivityand pinniped deterrence indicates that some marinemammals can detect low-level electrical fields. Guianadolphins Sotalia guianensis can easily detect low-level electrical fields produced by electric fish andhave specialized sensory anatomy (‘vibrissal crypts’)for doing so (Czech-Damal et al. 2012). Deterrenceexperiments on California sea lions Zalophus califor-nianus (Burger 2008) and harbor seals Phoca vitulina(Forrest et al. 2009) showed that pinnipeds detect andare actively deterred from weak electrical fields infreshwater environments. An expert in electrofishing(A. Temple pers. comm.) suggested that if free-swim-ming dolphins have the ability to detect extremelylow electrical field strengths, they should be able toavoid entering the ‘effective’ and ‘injury’ zones. Thisassumes that they recognize the low electrical fieldstrengths as a danger, and that they are as resistant aspinnipeds to them. Cetacean skin, however, is less ker-atinized and hairless, potentially increasing the electri-cal conductance of this external barrier in comparisonwith other mammals (Harrison & Thurley 1974).

3.1.5. Legal status of electrofishing

Electrofishing is banned or restricted in most of therivers and lakes where freshwater cetaceans occur inAsia (Table 1), but the economic incentives for its useare strong. In Cambodia, for example, legal fishingwith a cast net (cost: USD $10−12) yielded a fisher-man 6−7 kg of small fish, or $3−4 d−1 (Kurien 2007),whereas with a $30−40 investment in illegal electro -fishing equipment, an unskilled and untrained per-son could catch 20−30 kg of large fish worth $10−13d−1 and a skilled electro-fisherman could catch 30−40 kg in a single haul (Kurien 2007). The equipmentfor electro fishing is relatively inexpensive (and thebattery can be used in the home for other purposes),little maintenance is required (unlike for nets, long-lines, bamboo traps, and fishing fences which requireconstant repair), and relatively large catches can bemade with little effort (Smith & Tun 2007).

3.1.6. Illegal electrofishing gear

We have not found detailed technical descriptionsof apparatus used for illegal electrofishing in therivers of Asia, nor have we had the opportunity toexamine such equipment, except through photos.Table 1 summarizes descriptions of electrofishingoperations and apparatus that we found in fisheries

210


reports and news accounts or obtained from theinformal responses of researchers to our simplequestion naire.

3.2. Impacts of electrofishing

3.2.1. Impacts on prey species and the ecosystemsof freshwater cetaceans

Like dynamite and poison fishing, electrofishing, ifused without controls, is a potentially destructive andindiscriminate fishing method with lethal or sub-lethal impacts on both target and non-target spe-cies. The entire ‘ecological footprint’ of freshwaterelectro fishing falls outside established managementregimes, catch limits, and other restrictions thatmight apply to legal fishing activity (Garcia et al.2003, Kreb et al. 2007, Phen & Nam 2011, FAO 2016).

In China, Zhou et al. (1998) reported that electro -fishing, though ‘strictly banned by the fishery agency,’was pursued at night, in small boats that hid duringthe day in small channels adjacent to the YangtzeRiver. In Myanmar, electrofishing is used illegally forcommercial fishing on the Ayeyarwady River, reportedlywith wide-ranging impacts on fish stocks and bio di -versity, including riverine fish and turtles (https:// www.mmtimes. com/ news/ working- save- symbol- human-animal- cooperation. html).

The presence of multiple illegal operators, some-times working in organized gangs to avoid detec-tion and intimidate enforcement officers, as occurson the Ayeyarwady River, greatly increases the over-all impact on fishery resources and aquatic biodi-versity (Smith 2004, Smith & Tun 2007, Holland 2015,http:// news. nationalgeographic. com/ news/ 2015/ 02/150217- irrawaddy- dolphins- myanmar- electro- fishing-mandalay/).

3.2.2. Behavioral impacts on freshwater cetaceans

Interactions between fishermen and dolphins arelikely because freshwater cetaceans generally feedin relatively confined and specific areas (e.g. deeppools, eddies, confluences) that are also prime fishinggrounds exploited by fishermen using nets and linesas well as electricity.

In addition to prey depletion, reports from theAyeyarwady River suggest that electrofishing and as -sociated activities by gangs of fishermen in motorizedvessels have disrupted the traditional mutualistic fish-ing relationship between humans and Irrawaddy

dolphins (Smith et al. 2009). In this relationship, thedolphins, upon receiving an acoustic signal from net-fishermen in non-motorized boats, approachedthe boats and assisted the fishing operation by herd-ing fish toward the nets (Smith & Tun 2007). Alreadyby the mid-2000s, the dolphins reportedly had begunto stay away from certain areas to avoid beingshocked (Smith & Tun 2007), and more recent obser-vations (in 2012 and 2014) indicate that they rarelyapproach oar-powered boats to engage in ‘coopera-tive’ fishing (Holland 2015, https://www.marine-mammalscience.org/letters/letter-to-myanmar-offi-cials-regarding-irrawaddy-dolphins/).

Anecdotal evidence suggests that electro-fishermenhave taken advantage of the normal fish-herdingbehavior of dolphins in the Ayeyarwady by signalingto the dolphins using acoustic means, similar to thecooperative cast-net fishermen (see Smith et al.2009), so that they can deploy their electrical gearnear the dolphins to catch more fish (A. M. Chit pers.comm.). Exploiting what used to function as mutuallybeneficial interspecies signaling, the electro-fishermenmight switch off the electrical current as dolphinsmove into an area (generally an indication of fishpresence) and then turn it back on to stun the fishthat try to escape ahead of the approaching dolphins.This situation could put dolphins in close proximity toelectrodes as the electrical current is activated, a sit-uation that could lead to injury or even death of thedolphins (Myanmar Times 6−12 August 2012 https://www. mmtimes. com/ national- news/ mandalay- upper-myanmar/ 239- battery- fishing- rise- threatens- unique-dolphin- cooperation. html).

In some circumstances, Mahakam river dolphinsappear to co-exist with electrofishing operationsand approach the boats and gear without apparentharm. On several occasions, one of the authors (D.Kreb) observed dolphins as close as 15 m to a boatthat was actively electrofishing. The dolphins showedno obvious reaction but appeared to be eating fishthat had been stunned or escaped from the elec-trical field.

3.2.3. Pathology and diagnosis of electrofishing ascause of death of freshwater cetaceans

It is widely assumed, implied, or asserted in the lit-erature that exposure to electrofishing can electro-cute or stun freshwater cetaceans. In the river-by-riverreview below, we consider scientific and popular ac -counts that cite electrofishing as a possible or knowncause of death of cetaceans.

211


Riv

er b

asin

Cet

acea

n s

pec

ies

Leg

al s

tatu

s: c

oun

try

Det

ails

Ref

eren

ce

Aye

ryaw

ady

Orc

aell

a b

revi

rost

ris

Ille

gal

: Mya

nm

ar(w

ith

in 7

4 k

m r

iver

dol

ph

in p

rote

cted

area

)

A n

ews

arti

cle

on t

he

thre

at o

f ‘b

atte

ry f

ish

ing

’ to

th

e u

niq

ue

coop

erat

ion

bet

wee

nfi

sher

men

an

d d

olp

hin

s in

Mya

nm

ar i

ncl

ud

es t

he

foll

owin

g d

escr

ipti

on:

‘Ele

ctri

cfi

shin

g s

tart

ed w

ith

peo

ple

usi

ng

a b

icyc

le d

ynam

o …

th

en c

ar b

atte

ries

wer

e u

sed

and

now

we

hea

r so

me

use

gen

erat

ors.

’

Bat

tery

fis

hin

g r

ise

thre

aten

s u

niq

ue

dol

ph

in c

oop

erat

ion

: Mya

nm

ar T

imes

6−12

A

ug

ust

20

12

htt

ps:

// w

ww

.m

mti

mes

. com

/ na t

ion

al-n

ews/

man

dal

ay- u

pp

er- m

yan

mar

/ 239

-b

atte

ry- f

ish

ing

- ris

e- th

reat

ens-

un

iqu

e- d

olp

hin

- coo

per

atio

n. h

tml

‘…el

ectr

ic s

hoc

k f

ish

ing

is

wh

ere

the

fish

erm

en t

ake

a ca

r b

atte

ry a

nd

tw

o el

ec-

trod

es,

stic

k t

hem

in

th

e w

ater

an

d e

lect

rocu

te t

he

fish

, st

un

th

em o

r k

ill

them

an

dth

en s

coop

th

em u

p,’

said

Ale

x D

imen

t, a

sen

ior

tech

nic

al a

dvi

ser

at W

ild

life

Con

ser-

vati

on S

ocie

ty (

WC

S).

Mya

nm

ar’s

riv

er d

olp

hin

s an

d f

ish

er -

men

dou

ble

dow

n o

n u

niq

ue

re la

-ti

on sh

ip, a

s fi

sh s

tock

s d

win

dle

ww

w.a

bc.

net

.au

/ new

s/ 20

18-0

3-12

/th

e- m

yan

mar

- riv

er- w

her

e- m

an-

and

- dol

ph

in- c

atch

- fis

h- t

oget

her

/95

2844

0

‘Du

rin

g t

he

pas

t 3

year

s, v

iole

nt

gan

gs

of f

ish

erm

en h

ave

bee

n s

talk

ing

th

e Ir

raw

add

y.T

hei

r m

ore

sop

his

tica

ted

tech

niq

ue

is to

thre

ad c

opp

er w

ires

thro

ug

h tr

awlin

g n

ets,

an

dth

en c

onn

ect

the

wir

es t

o b

ank

s of

car

bat

teri

es a

nd

hig

h-v

olta

ge

tran

sfor

mer

s. T

he

hea

vy d

oses

of

elec

tric

ity

sen

t in

to t

he

rive

r b

y th

is m

eth

od s

tun

a w

hol

e lo

t m

ore

fish

.‘

Hol

lan

d (

2015

)

Mah

akam

Orc

aell

a b

revi

rost

ris

Ille

gal

: In

don

esia

Th

e m

etal

pol

e an

d n

et f

ixed

to

it h

ave

a ca

ble

att

ach

ed t

o a

bat

tery

(or

bat

teri

es)

org

ener

ator

. Th

ese

are

atta

ched

to

a w

ood

en p

ole

that

is h

and

-hel

d o

ff t

he

fron

t of

th

eb

oat

and

use

d t

o sc

oop

ele

ctro

cute

d f

ish

ou

t of

th

e w

ater

. S

imp

le b

atte

ry o

per

ated

gea

r u

ses

a p

ole

wit

h a

n a

nod

e in

on

e h

and

wit

h t

he

fish

ing

net

dep

loye

d w

ith

th

eot

her

han

d t

o sc

oop

ou

t fi

sh. A

rec

ent

gea

r in

nov

atio

n i

s to

att

ach

a s

coop

ing

net

on

2 w

ood

en p

oles

sti

ckin

g o

ut

in f

ron

t of

th

e b

oat

that

has

an

ele

ctri

c cu

rren

t g

oin

gth

rou

gh

th

e n

et i

tsel

f. T

he

woo

den

pol

es a

re m

anu

ally

low

ered

in

to t

he

wat

er a

nd

pu

lled

up

ag

ain

th

ereb

y ef

fect

ivel

y sc

oop

ing

sm

all

rive

r fi

sh a

lon

g t

he

rive

r b

ank

s.T

he

targ

et fi

sh s

pec

ies

is a

lso

kn

own

pre

y fo

r th

e d

olp

hin

s. B

atte

ries

(D

C-b

atte

ry w

ith

bet

wee

n 1

2−60

A, 1

2−24

V)

and

gen

erat

ors

(AC

400−

900

W, 2

20 V

, an

d D

C 1

2 V

8.3

Am

p)

are

use

d a

s p

ower

sou

rces

. T

he

equ

ipm

ent

is u

sed

to

stu

n f

ish

in

th

e op

enw

ater

of

the

rive

r, s

wam

p o

r la

ke

and

is

rep

orte

d t

o b

e ef

fect

ive

from

1.5−

3 m

wit

hb

atte

ry p

ower

an

d, d

epen

din

g o

n t

he

dep

th, u

p t

o 10−

15 m

wit

h a

gen

erat

or (

wit

h a

smal

ler

ran

ge

in d

eep

er w

ater

s).

Kre

b e

t al

. (20

07, 2

010)

,D

. Kre

b p

ers.

ob

s.

Mek

ong

Orc

aell

a b

revi

rost

ris

Ille

gal

: Cam

bod

ia,

Lao

s‘T

wo

typ

es o

f el

ectr

o fi

shin

g [

gea

r] u

sed

:(1

) co

nsi

der

ed a

s sm

all

scal

e, c

ond

uct

ed b

y 1−

2 p

eop

le p

er o

utf

it,

wit

h o

r w

ith

out

ab

oat.

Fis

her

men

pu

t th

e el

ectr

ic s

hoc

ker

in t

he

wat

er m

anu

ally

(lo

cal

peo

ple

cal

l th

ism

eth

od ‘h

ot e

lect

rofi

shin

g’)

,(2

) co

nd

uct

ed b

y 2−

3 p

eop

le w

ith

1−

2 b

oats

, th

e el

ectr

ic s

hoc

ker

cab

les

are

low

ered

in th

e w

ater

col

um

n fr

om o

ne

boa

t wh

ich

mov

es o

n g

rad

ual

ly a

nd

th

e el

ectr

ic s

hoc

ker

is a

ctiv

e co

nti

nu

ousl

y. T

he

oth

er b

oat

foll

ows

beh

ind

col

lect

ing

th

e fi

sh (

loca

l peo

ple

call

th

is m

eth

od ‘c

ool

elec

tro f

ish

ing

’). C

ool

elec

trof

ish

ing

cou

ld k

ill

dol

ph

ins.

’

Ph

en &

Nam

(20

11, p

. 34)

Fis

her

men

use

d D

C c

urr

ent f

rom

a b

oat t

hat

‘was

eff

ecti

ve fo

r fi

sh c

aptu

re f

or 2

5−30

m’

and

wh

en c

arri

ed o

n t

he

bac

k w

as e

ffec

tive

for

2−

3 m

.M

ekon

g R

iver

Gu

ard

s (i

nfo

rmal

inte

rvie

w)

Bat

teri

es f

or e

lect

rofi

shin

g d

evic

es a

re o

ften

‘d

ual

-pu

rpos

ed’

to l

igh

t h

omes

an

dp

ower

tel

evis

ion

s in

a r

egio

n w

her

e th

ere

is n

o ru

ral

elec

trif

icat

ion

.

Com

mu

nit

y an

d lo

cal o

ffic

ial a

ttri

bu

tion

s of

ele

ctro

fish

ing

as

the

sou

rce

of d

olp

hin

mor

-ta

lity

du

e to

lack

of

evid

ence

for

oth

er c

ause

s an

d s

igh

tin

gs

of e

lect

rofi

shin

g in

are

asu

sed

by

dol

ph

ins.

Ku

rien

(20

07)

G. R

yan

an

d S

. Ph

ay p

ers.

com

m.

Tab

le 1

. Riv

er b

y ri

ver

acco

un

ts o

f el

ectr

ofis

hin

g in

th

e vi

cin

ity

of f

resh

wat

er c

etac

ean

sTable continued on next page

Thomas et al.: Electrofishing and freshwater cetaceans 213Y

ang

tze

Neo

ph

ocae

na

asia

e -or

ien

tali

sas

iaeo

rien

tali

s,L

ipot

esve

xill

ifer

Ille

gal

: Ch

ina

‘In

rec

ent

year

s th

e u

se o

f el

ectr

ic f

ish

ing

gea

r h

as b

een

in

crea

sin

g.

Su

ch g

ear

isco

mp

osed

of

a st

orag

e b

atte

ry a

nd

tra

nsf

orm

er w

hic

h a

re c

arri

ed b

y a

smal

l b

oat.

Ah

igh

vol

tag

e is

pro

du

ced

bet

wee

n a

n e

lect

rod

e lo

wer

ed f

rom

th

e b

oat

and

an

oth

eron

e se

t in

th

e ri

ver

du

rin

g o

per

atio

n.

Ele

ctri

c fi

shin

g g

ear

ind

iscr

imin

atel

y d

estr

oys

fish

erie

s re

sou

rces

an

d i

s th

eref

ore

stri

ctly

ban

ned

by

the

fish

ery

agen

cy. H

owev

er,

the

smal

l b

oats

th

at c

arry

th

is t

ype

of g

ear

hid

e d

uri

ng

th

e d

ay i

n s

mal

l ch

ann

els

alon

g t

he

Yan

gtz

e R

iver

, an

d o

per

ate

at n

igh

t.’

Zh

ou e

t al

. (19

98, p

. 128

)

‘Th

e p

rim

ary

fact

or r

esp

onsi

ble

for

th

e b

aiji’

s ex

tin

ctio

n w

as p

rob

ably

un

sust

ain

able

inci

den

tal

by-

catc

h i

n l

ocal

fish

erie

s, p

rim

arily

fro

m i

lleg

al m

eth

ods

such

as

‘rol

ling

-h

ook

’ lo

ng

-lin

es a

nd

pos

sib

ly e

lect

ro-fi

shin

g (

Zh

ou &

Wan

g 1

994;

Zh

ang

et

al.

2003

),w

hic

h in

volv

es to

win

g a

n e

lect

rifi

ed (>

300

volt

) met

al-f

ram

ed n

et b

ehin

d a

fish

ing

boa

tat

nig

ht

in t

he

mai

n r

iver

ch

ann

el a

nd

oth

er m

ajor

wat

er b

odie

s.’

Tu

rvey

et

al. (

2013

, p. 3

53)

‘Th

ere

are

not

on

ly b

ig g

ang

s of

ele

ctro

fish

ing

, in

div

idu

al f

ish

erm

an a

lso

use

th

ism

eth

od t

o ca

tch

fis

h.

Th

ey w

ill

firs

t u

se a

pu

mp

to

low

er t

he

wat

er l

evel

an

d c

has

efi

shes

in

to s

mal

ler

area

; th

en p

ut

elec

tric

ch

arg

es i

nto

th

e ri

ver;

fin

ally

col

lect

th

efl

oate

d b

ig f

ish

es t

o sh

ip t

o th

e m

ark

et a

nd

lef

t th

e ot

her

s on

th

e g

rou

nd

.’

htt

p:/

/yan

gtz

efin

less

por

poi

se.

wee

bly

. com

/ in

dex

.htm

A w

eb a

rtic

lere

por

ted

that

12

dea

d fi

nle

ss p

orp

oise

s fo

un

d d

uri

ng

an

ext

rem

ely

low

-w

ater

per

iod

fro

m 3

Mar

ch−

15 A

pri

l 20

12 a

t or

nea

r D

ong

tin

g L

ake,

th

e se

con

dla

rges

t la

ke

in C

hin

a, a

t le

ast

one

of w

hic

h h

ad f

ish

in it

s m

outh

at

the

tim

e of

dea

th,

had

‘d

ied

fro

m e

lect

rofi

shin

g.’

Th

e ar

ticl

e st

ated

th

at s

ome

of t

he

por

poi

ses

die

dd

irec

tly

from

ele

ctri

cal

shoc

k w

hil

e ot

her

s ‘f

ain

ted

’ fr

om t

he

shoc

k a

nd

th

en d

ied

‘fro

m d

row

nin

g’.

htt

p:/

/yan

gtz

efin

less

por

poi

se.

wee

bly

. com

/

Ind

us

Pla

tan

ista

gan

get

ica

min

orIl

leg

al: P

akis

tan

Ele

ctro

fish

ing

is

an e

mer

gin

g t

hre

at t

o th

e In

du

s d

olp

hin

s as

we

coll

ecte

d 6

car

-ca

sses

of

the

dol

ph

ins

last

yea

r (2

017)

fro

m t

he

up

stre

am G

ud

du

Bar

rag

e. W

hen

we

inve

stig

ated

th

e m

orta

lity

an

d i

nte

rvie

wed

nea

rby

inh

abit

ants

th

ey s

aid

th

e ca

r-ca

sses

wer

e b

elie

ved

to

hav

e d

ied

fro

m e

lect

ric

shoc

k.

Th

e lo

cal

fish

erm

en a

lso

said

th

at t

he

elec

trof

ish

ers

wer

e n

ot t

he

fish

erm

en,

they

wer

e th

e cr

imin

als,

wh

o h

ad b

een

hid

den

in t

he

thic

k r

iver

ine

fore

st s

ince

mor

e th

ana

year

an

d u

sed

12

V 1

60 A

bat

teri

es o

r el

ectr

ic g

ener

ator

s to

cat

ch th

e m

axim

um

fish

in n

o ti

me.

Mor

e re

cen

t fi

eld

in

vest

igat

ion

s in

201

8 re

veal

ed t

hat

loc

al f

ish

erm

en a

re a

lso

invo

lved

in e

lect

rofi

shin

g, w

ork

ing

in g

rou

ps

in s

hal

low

poo

ls a

nd

lak

es u

pst

ream

of

the

Gu

dd

u &

Su

kk

ur

Bar

rag

es. T

he

dol

ph

ins

ente

r th

ese

lak

es d

ue

to t

he

abu

nd

ance

of f

ish

, b

ut

in l

ow f

low

mos

t of

th

e la

kes

an

d w

ater

bod

ies

bec

ome

cut

off

from

th

em

ain

stre

am a

nd

the

dol

ph

ins

bec

ome

trap

ped

. Th

e sh

allo

w w

ater

an

d a

bu

nd

ant f

ish

also

att

ract

th

e fi

sher

men

wh

o u

se t

he

pow

erfu

l AC

gen

erat

ors

to f

ish

in t

hes

e la

kes

.

M. I

. Mal

ik p

ers.

ob

s.

Gan

ges

-B

rah

map

utr

aP

lata

nis

ta g

ang

etic

ag

ang

etic

aIl

leg

al: N

epal

, In

dia

Nor

thea

ster

n I

nd

ia:

'Usi

ng

som

e cr

ud

e d

evic

es,

an e

lect

ric

fiel

d i

s cr

eate

d i

n w

ater

to i

mm

obil

ize

and

col

lect

ed f

ish

. C

urr

ent

is p

asse

d t

hro

ug

h a

nak

ed w

ire/

pla

te a

nd

the

fish

es a

re c

olle

cted

wit

h h

and

s or

net

s. T

his

met

hod

is

pop

ula

r in

mos

t p

arts

of

Man

ipu

r.'

Gu

rum

ay

am

& C

ho

ud

hu

ry (

20

09

,p

. 239

), D

. Su

tari

a p

ers.

com

m.,

N.

Kel

kar

per

s. c

omm

., R

. K. S

inh

ap

ers.

com

m.

Ku

lsi R

iver

: 'C

hem

ical

poi

son

ing

, dyn

amit

ing

, ele

ctro

-fis

hin

g, e

tc.,

bec

ome

very

pop

u-

lar

bu

t d

estr

uct

ive

for

aqu

atic

eco

syst

em i

ncl

ud

ing

fis

hes

ag

ain

st t

he

dis

cuss

ed t

rad

i-ti

onal

met

hod

s.'

Isla

m e

t al

. (20

13, p

. 291

)

Up

per

Gan

ga

Riv

er s

yste

m o

f C

entr

al H

imal

aya,

In

dia

: 'e

lect

ric

wir

e is

con

nec

ted

to

the

mai

n p

ower

on

an

ele

ctri

c p

ole

or s

omet

imes

con

nec

ted

to

the

por

tab

le g

ener

a-to

r. W

ire

is t

hen

pas

sed

alo

ng

th

e ri

ver

ban

k a

nd

is

con

nec

ted

wit

h n

aked

wir

ed

ipp

ed i

n t

he

stre

am w

ater

. A

s th

e cu

rren

t is

pas

sed

to

the

stre

am,

elec

tric

fie

ld i

sd

evel

oped

up

to

cert

ain

dis

tan

ce i

n t

he

stre

am.

In t

he

reg

ion

of

elec

tric

fie

ld a

ll t

he

fish

es (

fry,

fin

ger

lin

gs,

ju

ven

ile

and

bro

oder

) ei

ther

get

kil

led

or

par

alyz

ed;

floa

tin

gto

the

wat

er s

urf

ace

and

eas

y to

cat

ch w

ith

han

ds.

Fis

hes

wh

ich

nor

mal

ly e

scap

e n

et-

tin

g b

y h

idin

g u

nd

er t

he

rock

s ar

e ca

ug

ht

easi

ly u

sin

g e

lect

ric

curr

ent.

Man

y p

re-

cau

tion

s ar

e n

eed

ed f

or a

pp

lyin

g t

he

elec

tric

cu

rren

t.'

Sin

gh

& A

gar

wal

(20

14, p

. 201

)

Nep

al:

‘We

can

usu

ally

see

use

of

‘tra

dit

ion

al’

typ

e of

ele

ctri

c fi

shin

g i

n N

epal

. W

eh

ave

seen

it

ofte

n i

n t

he

fiel

d d

uri

ng

ou

r su

rvey

tim

es.

It i

s m

ore

com

mon

in

th

eS

apta

Kos

hi

and

Kar

nal

i ri

vers

th

an i

n N

aray

ani

rive

r sy

stem

s. A

ll th

ese

rive

r sy

stem

scu

rren

tly

hav

e ri

ver

dol

ph

in p

opu

lati

ons.

I d

on’t

th

ink

th

ere

are

reco

rd o

f in

cid

ents

du

e to

ele

ctri

c fi

shin

g. W

e h

ave

only

fis

her

ies

byc

atch

.’

S. P

aud

el p

ers.

com

m.

Table 1 continued


As with most cetacean deaths other than thosecaused by deliberate hunting or fishery bycatch (atleast when the animal is found in the gear), the causeof death of freshwater cetaceans usually has to bedetermined from examining tissues obtained fromcarcasses. Death by electricity is often invoked as thecause when carcasses are unmarked or bear littleexternal or internal evidence of fishery interaction,disease, or trauma (Zhou et al. 1998). Cause of deathhas been attributed to electrofishing for Yangtze fin-less porpoises, baijis, Indus River dolphins (bhulans),and Irrawaddy dolphins in the Mahakam, Mekong,and Ayeyarwady rivers (Table 1).

Conclusively identifying electric shock as a causeof death is difficult, and the absence of signs causedby other factors such as net entanglements or propellerwounds does not necessarily imply electric shock asthe cause of death. In humans, electrocution is iden-tified by histological detection of damage to cardiacmuscle and, in cases of severe electric shock (e.g.lightning strike), burning of surface tissue (Wright &Davis 1980, Fineschi et al. 2006). Ideally, a sample offresh cardiac muscle tissue is available that can befixed in formalin and examined histologically to detectcharacteristic lesions of cardiomyopathy. However, itis rare to recover carcasses of freshwater cetaceans,and even more rare for someone to recover sampleswithin 24 h of death and fix them in formalin for his-tological examination.

3.3. River-by-river reports

Table 1 provides the details of reports of electro -fishing and operational interactions with freshwatercetaceans in the rivers of Asia.

3.3.1. Yangtze River

Yangtze River finless porpoises. Reports of electro -fishing as the possible cause of death of cetaceanscome most frequently from China and involve Yangtzefinless porpoises and baijis in the Yangtze River. Themost commonly reported sources of mortality of fin-less porpoises in the Yangtze are boat strikes andentanglement in fishing gear.

The most recent reports of finless porpoise mortalityfrom electrofishing and other illegal fishing activitiescome from the 2 large lakes (Poyang and Dongtinglakes) adjoining the Yangtze River (Fig. 1). Mei et.al. (2019) reported that of the 29 out of 60 dead por-poises collected from 2008 to 2013 from Poyang

Lake (the largest lake in China) for which cause ofdeath could be determined, 11 (37.9%) were killeddirectly by illegal fishing (1 by rolling hooks, 3 byset nets, and 7 by electrofishing gear) and only 1was killed by a propeller strike. In 2009 during alow-water period at Poyang Lake, several porpoiseswere found that had been injured or killed byentanglement in fixed stake nets (http:// english. ihb.cas. cn/ rh/ rp/ 201003/ t20100319_51725. html).

The cause of death was determined for 7 out of 22dead porpoises collected from 2008 to 2012 in Dong -ting Lake: 4 were killed by illegal fishing (2 by elec-trofishing, 1 by rolling hooks, and 1 by set nets) and 3were killed by propeller strikes. In addition to risksposed by illegal fishing gear and methods, the finlessporpoises in the lakes adjoining the Yangtze Riverare exposed to other threats, including toxic pollutionand disturbance from sand mining and dredgingactivities (Wang & Reeves 2017). There was concernthat the increasing use of both stake nets and elec-trofishing during times of low water would increasethe risk of injury to the porpoises.

In a personal communication to F. M. D. Gulland(10 July 2017), Dr. Zheng Jinsong of the Institute ofHydrobiology, Chinese Academy of Sciences, notedthat electrofishing was inferred to be the cause ofdeath for Yangtze finless porpoises by ruling outother possible causes, such as boat impact or pro-peller wounds, entanglement in fishing gear, disease,or starvation, and on the basis of the presence of elec-trofishing in the area. Usually, the carcasses forwhich electrocution was assigned as the cause ofdeath were intact without any obvious trauma orwounds, although sometimes there were lesions suchas blood spots in the blubber, signs of ‘sclerosis’ ofthe heart (distended blood vessels), symptoms ofasphyxiation in the lungs, and intact prey fish in theforestomach, all supportive of a diagnosis of suddendeath due to electrocution. For example, investiga-tors concluded that an adult female finless porpoisethat stranded with no obvious evidence of external orinternal trauma, appeared to be in good health, andhad fed just prior to death, was most likely killedby electrofishing (Turvey 2009, https:// www. edge ofexistence. org/ blog/ what- is- killing- finless- porpoises-in- the- yangtze/).

Baijis. Electrofishing has been widely cited as acontributing factor in the decline and extinction ofthe baiji (Chen & Liu 1992, Turvey et al. 2007, Smithet al. 2017), although mortality caused by rollinghook longlines, gillnets, fish traps, boat propellers,and explosives was more conclusively documented(Perrin & Brownell 1989, Zhou & Zhang 1991). Death

214


from electrofishing was usually inferred from a lackof external marks or internal injuries on carcasses —when animals were found dead with no observedlesions, electrofishing was often judged to be themost probable cause of death. The most direct state-ment related to the baiji comes from the 1980s, whenChen & Hua (1989, p. 84) stated, ‘In some cases, theelectro fishing teams are formed by several electrofish-ing vessels cooperating with small boats. One dolphinwas killed in February 1981 near Paizhou in this way.’

The limited information on causes of baiji deaths,summarized below, suggests that the overall con -tribution of electrofishing to the species’ demise isless certain than is sometimes implied or stated in theliterature.

In the middle reaches of the Yangtze, 15 of 28 recor -ded baiji deaths from 1973 to 1983 were caused byrolling hook longlines (Zhou & Wang 1994). Of 31baiji carcasses from the lower Yangtze examined todetermine cause of death between 1978 and 1985, 13were entangled in rolling hook longlines or caught innets, 6 were killed by illegal fishing with explosives,10 were struck by propellers, 1 was trapped in asluice gate, and 1 was simply reported as stranded(Zhou & Li 1989). Of 13 carcasses from the lowerYangtze examined between 1989 and 1996, 3 werefound entangled with hooks, 1 bore propeller wounds,and 4 had no evidence of entanglement in nets orrolling hook longlines (Zhou et al. 1998, p. 128). Inthe absence of an obvious cause, Zhou et al. (1998)

concluded that these last 4 were ‘pos-sibly killed by shocks of electric fish-ing,’ which reportedly was increasingon the river at the time. In a sample of12 baiji carcasses examined between1990 and 1999 (apparently distinctfrom those reported by Zhou et al.1998), a cause of death was given for10, of which 4 were said to have diedfrom electrocution (Zhang et al. 2003).This appears to be the source of thecon clusion that electrofishing ac -counted for 40% of baiji deaths in the1990s and was ‘apparently the biggestthreat to baiji survival’ (Turvey 2008,p. 39). While the possibility of deathsfrom electrofishing cannot be dis-counted, little or no direct evidencewas provided to substantiate thesecause-of-death determinations (Wanget al. 2006, Smith et al. 2017).

The reports on the 2 species (baijiand finless porpoise) from the Yangtze

River suggest 2 possible scenarios in which electro-cution of cetaceans could occur: (1) the animals areentrapped by declining water levels in segments of alake or side-channel of the river, and (2) the dolphinsor porpoises are corralled, intentionally or un in ten -tion ally, by multiple electro fishing boats workingtogether. The entrapped or encircled animals mightthen be ex po sed to electric shock at close proximityas the fishermen seek to stun the fish near them (Linet al. 1985, Chen & Hua 1989, Zhou & Li 1989, Zhou& Wang 1994, Zhou et al. 1998, Zhang et al. 2003).

3.3.2. Indus River dolphins

Electrofishing is regarded as an emerging threatin Pakistan. Six dolphin carcasses (4 males, 2 fe -males) were collected between 10 October and 12December 2017 from an area 5−10 km upstream ofthe Guddu Barrage (M. I. Malik unpubl. data).Nearby villagers who were interviewed said theybelieved that the animals had died from electricshock in the vicinity of electrofishing conducted bycriminals operating out of the thick riparian forest.More recent field investigations in 2018 revealedthat local fishermen are also involved in electro -fishing, working in groups in shallow pools andlakes upstream of the Guddu and Sukkur barrageswhere they might encounter dolphins (M. I. Malikunpubl. data).

215

Fig. 1. Yangtze River finless porpoise (foreground) near large electrofishing boatwith an electrified trawl in Poyang Lake, China, December 2017. Electric currentfrom the wires on the net stuns or kills fish, which are then collected by thenet. Despite the presence of electrofishing, entanglement in fishing gear-remains the greatest threat to freshwater cetaceans. Photo credit: Dr. X. Yijie


3.3.3. Ganges River dolphins

Electrofishing is practiced in various forms in theGanges River (see Table 1) but we have found noreports of Ganges River dolphins being affected.

3.3.4. Irrawaddy dolphins in the Mahakam River

Fishermen in the Mahakam River reported 2deaths of Irrawaddy dolphins suspected to haveresulted from electric shock, one in 2003 (Kreb etal. 2007) and one in 2008 (Kreb et al. 2010). Onthe first occasion, a dead juvenile dolphin wasseen floating with a blue bruise on its head afterit came in contact with an electrofishing boat. Onthe second occasion, some people were observedfishing with high-voltage AC generators in smallpools and channels of the upstream section of theMahakam. They were deliberately chasing andharassing dolphins, and not long afterward, a fish-erman observed a dead calf floating downstream.According to his statement, the dead calf’s bellywas blue.

In the first instance, the dolphin apparently camein direct contact with the electrodes of the electro -fishing apparatus and was electrocuted. The secondof these reports suggests that in the small pools andchannels of the upper Mahakam it is more difficultfor dolphins to avoid the fishing activity than it is inbroader downstream reaches. D. Kreb has also ob -served dolphins approaching and then moving awayfrom electrofishing operations without harm, indica-ting that proximity alone does not necessarily leadto death or injury (Fig. 2).

3.3.5. Irrawaddy dolphins in the Ayeyarwady River

Electrofishing has been mentioned repeatedly as acause of dolphin mortality in the Ayeyarwady River,and some recent observations were mentioned above.Smith & Tun (2007) cited electrocution as a directthreat, but provided few details. On 4 December 2014,2 dead young dolphins (male and female) were foundon the same day in a protected stretch of the rivernorth of Mandalay with no sign of entanglement and‘no sign of toxics.’ According to a journalist (Holland2015), sources he interviewed stated that necropsiesshowed the dolphins to have been victims of elec-trofishing. This report, like so many that cite electro-cution as the cause of death of freshwater cetaceans,has proven impossible to validate.

3.3.6. Irrawaddy dolphins in the Mekong River

Electrofishing has been reported and considered asa possible cause of death for Irrawaddy dolphins inthe Mekong River. It is reported as a widespread andcommon practice within and around dolphin habitat(Phen & Nam 2011) and has been the subject of sig-nificant enforcement efforts. From October 2013 toMay 2017, river guards aggressively enforced the banon electrofishing, with 53 cases of interdiction andconfiscation of electroshock units (including in -verters, batteries, and wires) (S. Keo pers. comm.).This enforcement effort was centered on what arecalled core dolphin areas and buffer zones. The riverguards encountered electrofishing during day andnight, but mostly at night. Electro-fishermen weresaid to fish from motorboats in mid-stream, not alongthe shore.

Carcass recovery and investigations of the causesof dolphin mortality have been carried out in theMekong in southern Laos and Cambodia since theearly to mid 1990s (Baird & Mounsouphom 1994, 1997,Gilbert & Beasley 2005, WWF & FiA 2014, 2017). Thepresence of external net marks with no internal lesionsand full stomachs is almost always interpreted toindicate gillnet entanglement as the cause of death.Although electrofishing has never been demon-strated as having a role in the death of dolphins in theMekong River, the appearance of un marked car-casses (often neonates or very young calves) that lackevidence of net entanglement or other wounding hasled to speculation that electrofishing is a source ofmortality (G. Ryan and S. Phay pers. obs.). Since 2012there has been an effort (led by WWF-Cambodia) tosecure and perform necropsies on the carcasses ofthese young dolphins. Roughly 20% ex hibit internalevidence of blunt trauma that, while still poorly doc-umented, may be the result of intra specific interac-tions in which adult dolphins rush at and hit calves,sometimes throwing them out of the water; at leastsome of these interactions occur at or near the time ofbirth (WWF & FiA 2017). Until other possible causessuch as infectious diseases and toxicosis have notbeen ruled out, death from electrofishing interactionis not indicated for these young animals.

4. CONCLUSIONS

While we do not have any information on the elec-trical power required to injure or kill a dolphin orporpoise, or how closely an animal would have toapproach an electrical field to be injured or killed,

216


the general factors of increasing impact of electricityon organisms of larger body size, mammalian sus-ceptibility to respiratory and cardiac impacts fromelectrical currents, and decreased electrical resist-ance of the hairless, poorly keratinized cetacean skinin water, all suggest that freshwater cetaceans are atrisk of injury or death if they come in close enoughcontact with electrical fields. The reporting of illegalelectrofishing, confiscation of gear, and anecdotalreports of carcasses with no external evidence oftrauma from nets or lines or vessel strike all supportthe concern that electrofishing poses a threat toendangered cetacean populations.

Unlike electric whaling, electrofishing techniquesare usually designed to stun fish as they encounterelectrical fields, not to electrocute the fish by directcontact with electrodes. We have found no evidenceof intentional electrocution of dolphins or porpoisesby fishermen in the rivers of Asia and are unaware ofany incentive for such a practice to evolve (but seeRobards & Reeves [2011] for discussion of how theconsumption of marine mammals, and in turn theirdeliberate capture, has arisen out of other types ofbycatch mortality).

Whether, and under what conditions, free-swim-ming dolphins or porpoises would move into thevicinity of electrofishing operations that could harmor kill them and how close they would have to cometo be harmed remain open questions. The evidencecited above, that cetaceans can detect low-level elec-

trical fields and that pinnipeds andother aquatic mammals are deterredby them, suggests that free-swimmingfreshwater cetaceans could detect andavoid such fields as long as they recog-nize the danger. This capability ofdetection and avoidance would dependon how the electrofishing equipment isdeployed in the vicinity of cetaceans:whether the electric current is on con-tinuously, turned on and off to con-serve energy, or deployed in a mannerto optimize the number of fish killed orstunned. It also may depend on theearlier experiences of the cetaceansswimming close to electrical fields — anovel experience could arouse curios-ity, particularly in young animals,inducing them to swim closer to inves-tigate. The few observations that wehave to go on suggest the followingscenarios where cetaceans might beput at risk: (1) entrapment in shallow

water or restricted river or lake areas (resulting fromdrought, or the intentional draining or enclosure ofwater bodies to entrap fish) and subsequent inabilityto move away from electrofishing activities (e.g.Yangtze finless porpoises); (2) encounters betweencetaceans and electrofishing activities in naturallyrestricted river reaches such as shallow upstreamareas and narrow tributaries where it is difficult tomove away from the electrical charges in the water(e.g. Mahakam and Indus dolphins); (3) incidentalor deliberate corralling of cetaceans into the prox-imity of electrofishing apparatus by multiple fishingboats working together (e.g. baijis and Ayeyarwadyand Mahakham dolphins); (4) appropriation by electro-fishermen of the mutualistic behavioral cues usedby dolphins and throw-net fishermen (‘cooperative fishing’) to get near fish concentrations (e.g.Ayeyarwady dolphins); (5) intentionally leaving elec-trofishing gear switched off and allowing cetaceansto approach an area while chasing fish, then turningthe current back on when the cetaceans are insidethe ‘effective’ danger zone to stun the fish herded inby the dolphins (e.g. Ayeyarwady dolphins); and (6)attraction of cetaceans to fish that have been immo-bilized by electrofishing activities (e.g. Mahakamdolphins).

Except possibly in the case of Ayeyarwady throw-net fishermen exploiting the mutualistic relationshipbetween them and dolphins, and the single reportedcase of harassment in the Mahakam, we found no

217

Fig. 2. Small boat fishing with electrofishing gear powered by a portable electricgenerator in the vicinity of an Irrawaddy dolphin mother and calf pair, MahakamRiver, Indonesia. Areas of abundant fish such as deep pools, confluences, andeddies may draw freshwater cetaceans and fishermen into close proximity.

Photo credit: D. Kreb,Yayasan Rasi


evidence of people intentionally drawing cetaceansinto the proximity of electrofishing operations inorder to capture, kill, or harass them.

Mortality of cetaceans from exposure to electrofish-ing appears to be uncommon, but this must be con-sidered in the context of populations with fewer than100 individuals in several river systems (Irrawaddydolphins in the Mahakam, Mekong, and Ayeyarwadyrivers) or that are surrounded by human activityand subject to numerous threats (finless porpoises inthe Yangtze River). Diagnosis of cause of death forstranded cetaceans is generally difficult, but particu-larly so for determining death by electrocution (orelectrically induced paralysis and subsequent drown-ing). Fresh carcasses suitable for histological exami-nation of tissues, and collection and formalin fixationof heart and lung tissue are needed, but in most cir-cumstances, there is little or no local expertise in fieldnecropsy techniques.

This review indicates a need for further assessmentof electrofishing practices and of when and how suchfishing might threaten freshwater cetaceans. Knowingmore about the nature of interactions between theanimals and the operations, the ability of cetaceans todetect and respond to electrical currents, the impacton immersed mammals of the electrical fields pro-duced by electrofishing, and diagnostic histology ontissues from dead animals would enable improvedassessment of the implications for conservation. Weacknowledge, however, that pursuing research onthe effects of electrical currents on cetaceans and theirability to detect currents is ethically and logisticallychallenging, and thus not a recommended avenue topursue. Rather, efforts should focus on obtaining freshcarcasses to determine cause of death through histo-logical examination of fresh tissues fixed in formalin,as this will also enhance detection of other threats.

Acknowledgements. The authors thank Jan Dean and AlanTemple, who teach legal electrofishing sampling techniquesat the US Fish and Wildlife Service, for sharing their ex -pertise. We thank Ravindra K. Sinha, Dipani Sutaria, andNatchiket Kelkar for information from India and ShambhuPaudel for information from Nepal. F. M.D.G. thanks the Mar-ine Mammal Center where she was employed during thedevelopment of this paper. R.R.R. thanks the Marine Mam-mal Commission for covering part of his time while workingon this paper.

LITERATURE CITED

Baird IG, Mounsouphom B (1994) Irrawaddy dolphins(Orcaella brevirostris) in southern Lao PDR & northeast-ern Cambodia. Nat Hist Bull Siam Soc 42: 159−175

Baird IG, Mounsouphom B (1997) Distribution, mortality,

diet and conservation of Irrawaddy dolphins (Orcaellabrevirostris Gray) in Lao PDR. Asian Mar Biol 14: 41−48

Bohlin T, Hamrin S, Heggberget TG, Rasmussen G, SaltveitSJ (1989) Electrofishing—theory and practice with spe-cial emphasis on salmonids. Hydrobiologia 173: 9−43

Braulik GT, Smith BD (2017) Platanista gangetica. The IUCNRed List of Threatened Species 2017: e.T41758A50383612.https:// www. iucnredlist.org/ species/ 41758/ 50383612(accessed 2 July 2019)

Braulik, GT, Smith BD, Sinha R (2012) Platanista gan geticassp. gangetica. The IUCN Red List of Threatened Spe-cies 2012: e.T41757A17628296. http:// dx. doi. org/10. 2305/IUCN. UK. 2012. RLTS. T41757A17628296. en (accessed 16August 2018)

Burger C (2008) Behavioral deterrence responses of captiveCalifornia sea lions exposed to a mild, electric voltage gra-dient at Moss Landing Marine Labs, CA. Report submittedto Bonneville Power Administration as part of Project2007-524-00, Contract 43248. https: // www. mediate. com/DSConsulting/ docs/ Smoth-Root% 202010% 20Report. pdf(accessed 12 January 2019)

Chen P, Hua Y (1989) Distribution, population size and pro-tection of Lipotes vexillifer. In: Perrin W, Brownell R, ZhouK, Liu J (eds) Biology and conservation of the river dol-phins. Occasional Papers, IUCN Species Survival Com -mission 3. World Conservation Union, Gland, p 81−85

Chen P, Liu R (1992) Baiji: a rare treasure. Institute of Hydro -biology, Wuhan (in Chinese and English, with notes byT. Kasuya)

Czech-Damal NU, Liebschner A, Miersch L, Klauer G andothers (2012) Electroreception in the Guiana dolphin(Sotalia guianensis). Proc R Soc B 279: 663−668

da Silva VMF, Trujillo F, Martin A, Zerbini AN and others(2018a) Inia geoffrensis. The IUCN Red List of ThreatenedSpecies 2018: e. T10831A50358152. http:// dx. doi. org/ 10.2305/ IUCN. UK. 2018-2. RLTS. T10831A50358152. en

da Silva VMF, Freitas CEC, Dias RL, Martin AR (2018b) Bothcetaceans in the Brazilian Amazon show sustained, pro-found population declines over two decades. PLOS ONE13: e0191304

Dalbey SR, McMahon TE, Fredenberg W (1996) Effect ofelectrofishing pulse shape and electrofishing-inducedspinal injury on long-term growth and survival of wildrainbow trout. N Am J Fish Manage 16: 560−569

Di Nunno N, Vimercati L, Viola L, Vimercati F (2003) A case ofelectrocution during illegal fishing activities. Am J Foren-sic Med Pathol 24: 164−167

Dolan CR, Miranda LE (2003) Immobilization thresholds ofelectrofishing relative to fish size. Trans Am Fish Soc 132: 969−976

Emery L (1984) The physiological effects of electrofishing.Cal-NEA Wildlife Transactions, p 59−72

FAO (2016) The state of world fisheries and aquaculture2016. Contributing to food security and nutrition for all.FAO, Rome

Fineschi V, Karch SB, D’Errico S, Pomara C, Riezzo I, TurillazziE (2006) Cardiac pathology in death from electrocution. IntJ Legal Med 120: 79−82

Forrest KW, Cave JD, Michielsens CGJ, Haulena M, SmithDV (2009) Evaluation of an electric gradient to deter sealpredation on salmon caught in gill-net test fisheries.N Am J Fish Manage 29: 885−894

Garcia SM, Zerbi A, Aliaume C, Do Chi T, Lasserre G (2003)The ecosystem approach to fisheries. FAO Fish Tech Pap443: 1−71

218

https://doi.org/10.1007/BF00008596https://www.iucnredlist.org/species/41758/50383612https://doi.org/10.2305/IUCN.UK.2012.RLTS.T41757A17628296.enhttps://www.mediate.com/DSConsulting/docs/Smoth-Root 2010 Report.pdfhttps://doi.org/10.1098/rspb.2011.1127https://doi.org/10.1577/M08-083.1https://doi.org/10.1007/s00414-005-0011-8https://doi.org/10.1577/T02-055https://doi.org/10.1577/1548-8675(1996)016%3C0560%3AEOEPSA%3E2.3.CO%3B2https://doi.org/10.1371/journal.pone.0191304https://doi.org/10.2305/IUCN.UK.2018-2.RLTS.T10831A50358152.en


Gilbert M, Beasley I (2005) Mekong River Irrawaddy dolphinstranding and mortality summary, January 2001−Decem-ber 2005. Wildlife Conservation Society Tech Rep,Phnom Penh

Green EK (2011) Telephoning fish: an examination of thecreative deviance used by wildlife violators in the UnitedStates. Int J Rural Criminol 1: 23−39

Gurumayam SD, Choudhury M (2009) Fishing methods in therivers of Northeast India. Indian J Trad Knowl 8:237-241

Harrison RJ, Thurley KW (1974) Structure of the epidermisin Tursiops, Delphinus, Orcinus and Phocoena. In: Harri-son RJ (ed) Functional anatomy of marine mammals, Vol2. Academic Press, London, p 45−73

Holland H (2015) Rogue ‘electro-fishing’ puts river dolphins atrisk in Myanmar. http: // news. nationalgeographic. com/news/ 2015/ 02/ 150217- irrawaddy- dolphins- myanmar-electrofishing- mandalay (accessed 16 August 2018)

Islam MR, Das B, Baruah D, Biswas SP, Gupta A (2013) Fishdiversity and fishing gears used in the Kulsi River ofAssam, India. Ann Biol Res 4: 289−293

Jefferson TA, Karczmarski L, Kreb D, Laidre K and others(2008) Orcaella brevirostris (Mahakam River subpopula-tion). The IUCN Red List of Threatened Species 2008: e.T39428A98842174. http:// dx. doi. org/10. 2305/ IUCN. UK.2008. RLTS. T39428A10237530. en (accessed 16 August2018)

Kolz AL (1989) Electrofishing, a power related phenomenon.U.S. Department of Interior, Fish and Wildlife Service,Fish and Wildlife Tech Rep 22

Kolz AL, Johnson RE (1995) In-water electroshock tech-niques to repel aquatic mammals and birds. In: Mason JR(ed) Repellents in wildlife management symposium pro-ceedings. National Wildlife Research Center RepellentsConference, 8−10 August 1995, Denver, CO. NationalWild life Research Center, Fort Collins, CO, p 203−215.http: // digitalcommons. unl. edu/ cgi/ viewcontent.cgi? article= 1022&context =nwrcrepellants

Kreb D, Budiono, Syachraini (2007) Review of status andconservation of Irrawaddy dolphins Orcaella brevirostrisin the Mahakam River of East Kalimantan, Indonesia. In: Smith BD, Shore RG, Lopez A (eds) Status and conserva-tion of freshwater populations of Irrawaddy dolphins.Working Paper No. 31. Wildlife Conservation Society,New York, NY, p 53−66

Kreb D, Reeves RR, Thomas PO, Braulik G, Smith BD (eds)(2010) Establishing protected areas for Asian freshwatercetaceans as flagship species for integrated river con -servation management, 19−24 October 2009, Samarinda.Final workshop report. www.mmc.gov/wp-content/uploads/ asian_fw_dolphin_ws.pdf (accessed 2 July 2019)

Kurien J (2007) Shocking reality: Cambodia electrofishing.SAMUDRA Rep 48: 35−36

Lin KJ, Chen PX, Hua YY (1985) Population size and conser-vation of Lipotes vexillifer. Acta Ecol Sin 5: 77−85 (in Chi-nese with English summary)

Mahoney BD, Iverson TK, Mathews SB (1993) Synopsis andannotated bibliography on electrofishing with specialreference to Columbia River squawfish control. FisheriesResearch Institute, Seattle, WA

Mei Z, Han Y, Dong L, Turvey ST and others (2019) Theimpact of fisheries management practices on the survivalof the Yangtze finless porpoise in China. Aquat Conserv29:639–646

Minton G, Smith BD, Braulik GT, Kreb D and others (2017)Orcaella brevirostris (errata version published in 2018).

The IUCN Red List of Threatened Species 2017: e.T15419A123790805. http:// dx. doi. org/10.2305/ IUCN.UK. 2017-3. RLTS. T15419A50367860. en (accessed 16 Au -gust 2018)

Mitchell E (1986) Aspects of pre-World War II Germanelectrical whaling. Rep Int Whal Comm Spec Issue 7: 115−139

Perrin WF, Brownell, RL Jr (eds) (1989) Report of the work-shop. In: Perrin WF, Brownell RL Jr, Zhou K, Lin J (eds)Biology and conservation of the river dolphins. Occa-sional Papers of the IUCN Species Survival CommissionNo. 3, p 1–22

Phen C, Nam S (2011) Assessment of gillnets and other fish-ing gear used in the Mekong River between Kratie andthe Lao PDR border. Inland Fisheries Research andDevelopment Institute (IFReDI) Fisheries Administration.http: // ifredi- cambodia. org/ wp-content/ uploads/ 2014/ 08/Chheng_Phen__So_Nam_2011_Assessment-of-gillnets-andother-fishing-gears.pdf

Primavesi R (2009) A shocking episode. Can Fam Physician55: 707−709

Reynolds J, Harlan L (2011) Quick-start guide to electrofish-ing. Smith-Root, Vancouver, WA

Reynolds J, Kolz AL (2013) Electrofishing. In: Zale AV,Parrish DL, Sutton TM (eds) Fisheries techniques,3rd edn. American Fisheries Society, Bethesda, MD,p 305−361

Robards MD, Reeves RR (2011) The global extent and char-acter of marine mammal consumption by humans: 1970−2009. Biol Conserv 144: 2770−2786

Secchi E (2012) Sotalia fluviatilis. The IUCN Red List ofThreat ened Species 2012: e.T190871A17583369. https://www. iucnredlist. org/ species/ 190871/ 17583369 (accessed2 July 2019)

Singh G, Agarwal NK (2014) Fishing methods in upper GangaRiver system of Central Himalaya, India. J Fish 2: 195−202

Smith BD (2004) Orcaella brevirostris (Ayeyarwady Riversubpopulation). The IUCN Red List of Threatened Spe-cies 2004: e. T44556A10919593. http:// dx. doi. org/10. 2305/IUCN. UK. 2004. RLTS. T44556A10919593. en (accessed 16August 2018)

Smith BD, Beasley I (2004) Orcaella brevirostris (MekongRiver subpopulation). The IUCN Red List of ThreatenedSpecies 2004: e. T44555A10919444. http:// dx. doi. org/ 10.2305/ IUCN. UK. 2004. RLTS. T44555A10919444. en (ac cessed10 November 2018)

Smith BD, Tun MT (2007) Review of the status and conserva-tion of Irrawaddy dolphins Orcaella brevirostris in theAyeyarwady River of Myanmar. In: Smith BD, Shore RG,Lopez A (eds) Status and conservation of freshwater pop-ulations of Irrawaddy dolphins. Working Paper No. 31.Wildlife Conservation Society, New York, NY, p 21−39

Smith BD, Tun MT, Chit AM, Win H, Moe T (2009) Catch com -position and conservation management of a human−dol-phin cooperative cast-net fishery in the Ayeyarwady River,Myanmar. Biol Conserv 142: 1042−1049

Smith BD, Braulik GT, Sinha R (2012) Platanista gan getica ssp.gangetica. The IUCN Red List of Threatened Species 2012:e. T41756A17627639. https:// www. iucnredlist. org/ species/41756/ 17627639 (accessed 2 July 2019)

Smith BD, Wang D, Braulik GT, Reeves R and others (2017)Lipotes vexillifer. The IUCN Red List of Threatened Species 2017: e.T12119A50362206. http:// dx. doi. org/10.2305/ IUCN. UK. 2017-3. RLTS. T12119A50362206. en (ac -cessed 29 March 2019)

219

https://doi.org/10.18061/1811/51128http://news.nationalgeographic.com/news/2015/02/150217-irrawaddy-dolphins-myanmar-electro-fishing-mandalayhttps://doi.org/10.2305/IUCN.UK.2008.RLTS.T39428A10237530.enhttp://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1022&context=nwrcrepellantshttp://www.mmc.gov/wp-content/uploads/asian_fw_dolphin_ws.pdfhttps://doi.org/10.1002/aqc.3078https://doi.org/10.2305/IUCN.UK.2017-3.RLTS.T15419A50367860.enhttps://doi.org/10.2305/IUCN.UK.2017-3.RLTS.T12119A50362206.enhttps://www.iucnredlist.org/species/41756/17627639https://doi.org/10.1016/j.biocon.2009.01.015https://doi.org/10.2305/IUCN.UK.2004.RLTS.T44555A10919444.enhttps://doi.org/10.2305/IUCN.UK.2004.RLTS.T44556A10919593.enhttps://doi.org/10.17017/jfish.v2i3.2014.43https://doi.org/10.1016/j.biocon.2011.07.034http://ifredi-cambodia.org/wp-content/uploads/2014/08/Chheng_Phen__So_Nam_2011_Assessment-of-gillnets-and-other-fishing-gears.pdf


Snyder DE (2003) Invited overview: conclusions from areview of electrofishing and its harmful effects on fish.Rev Fish Biol Fish 13: 445−453

Turvey ST (2008) Witness to extinction: how we failed to savethe Yangtze River dolphin. Oxford University Press, Oxford

Turvey ST, Pitman RL, Taylor BL, Barlow J and others (2007)First human-caused extinction of a cetacean species?Biol Lett 3: 537−540

Turvey ST, Risley CT, Moore JE, Barrett LA and others(2013) Can local ecological knowledge be used to assessstatus and extinction drivers in a threatened freshwatercetacean? Biol Conserv 157: 352−360

Wang JY, Reeves R (2017) Neophocaena asiaeorientalis. The IUCN Red List of Threatened Species 2017: e.T41754A50381766. http:// dx. doi. org/ 10. 2305/ IUCN. UK.2017-3. RLTS. T41754A50381766. en (accessed 8 January2019)

Wang K, Wang D, Zhang X, Pfluger A, Barrett L (2006) Range-wide Yangtze freshwater dolphin expedition: The lastchance to see baiji? Environ Sci Pollut Res Int 13: 418−424

Wang D, Turvey ST, Zhao X, Mei Z (2013) Neophocaenaasiaeorientalis ssp. asiaeorientalis. The IUCN Red Listof Threatened Species 2013: e.T43205774A45893487.http:// dx. doi. org/10. 2305/ IUCN. UK. 2013-1. RLTS.T43205774A45893487. en (accessed 10 November 2018)

Wright RK, Davis JH (1980) The investigation of electricaldeaths: a report of 220 fatalities. J Forensic Sci 25: 514−521

WWF & FiA (Fisheries Administration of the Ministry of

Agriculture, Forestry, and Fisheries) (2014) Workshopon the conservation of Irrawaddy dolphins in theMekong River. www.iucn-csg.org/wp-content/ uploads/2010/ 03/ Report-of-the-2017-International- Workshop- on-the- Conservation- of- Irrawaddy- Dolphins- in- the- Mekong-River. pdf

WWF & FiA (2017) Report of the International workshop on theconservation of Irrawaddy dolphins in the Mekong River,Kratie, Cambodia. www.iucn-csg.org/wp-content/ uploads/2010/ 03/ Report-of-the-2017-International-Workshop-on-the-Conservation-of-Irrawaddy-Dolphins-in-the-Mekong-River.pdf

Zhang X, Wang D, Liu R, Wei Z, Hua Y and others (2003)The Yangtze River dolphin or baiji (Lipotes vexillifer): population status and conservation issues in the YangtzeRiver, China. Aquat Conserv 13: 51−64

Zhou K, Li Y (1989) Status and aspects of the ecology andbehavior of the baiji, Lipotes vexillifer, in the lowerYangtze River. In: Perrin W, Brownell R, Zhou K, Liu J(eds) Biology and conservation of the river dolphins.World Conservation Union, Gland, p 86−91

Zhou K, Wang X (1994) Brief review of passive fishing gearand incidental catches of small cetaceans in Chinesewaters. Rep Int Whal Comm Spec Issue 15: 347−354

Zhou K, Zhang X (1991) Baiji: the Yangtze River dolphin andother endangered animals in China. Yilin Press, Nanjing

Zhou K, Sun J, Gao A, Würsig B (1998) Baiji (Lipotes vexillifer)in the lower Yangtze River: movements, numbers, threatsand conservation needs. Aquat Mamm 24: 123−132

Editorial responsibility: Jeff Mangel (Guest Editor),Lima, Peru

Submitted: January 15, 2019; Accepted: April 17, 2019Proofs received from author(s): July 4, 2019

https://doi.org/10.1007/s11160-004-1095-9https://doi.org/10.1098/rsbl.2007.0292https://doi.org/10.1016/j.biocon.2012.07.016https://doi.org/10.2305/IUCN.UK.2017-3.RLTS.T41754A50381766.enhttps://doi.org/10.1002/aqc.547www.iucn-csg.org/wp-content/uploads/2010/03/Report-of-the-2017-International-Workshop-on-the-Conservation-of-Irrawaddy-Dolphins-in-the-Mekong-River.pdfhttps://doi.org/10.1520/JFS11252Jhttps://doi.org/10.2305/IUCN.UK.2013-1.RLTS.T43205774A45893487.enhttps://doi.org/10.1065/espr2006.10.350

Electrofishing as a potential threat to freshwater cetaceans(e.g. dredging, noise, boat strikes),...

Documents

Transcript of Electrofishing as a potential threat to freshwater cetaceans(e.g. dredging, noise, boat strikes),...