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ocP/vcu/HYBro/ 85 .3 ORIGINAI FRENCII

Page 1

EVALUATION OF THE MEDIUM-TERM EFFECT OT WEEKLY

CARBOSULFAN LARVICIDING ON AQUATIC INVERTEBRATES

1.

^{Upstrean Bema}

L.

^Yam6ogo,

B. Coulibaly, B.

Dolbezarr.ga,

L.

Bakon6

1.

Since

the

appeareance

ln

L980

of reslstance to

Abate and then

to

chlorphoxlm

in certain forest

cytotypes

of

West

Africa, the

screening maln

dlrectlons of

research Basin Area (OCP).

Slmulium damnosum

s.1.; the vector of

hunan onchocerctasis

in of

nen

larvlcldes and/or fornulatlons

has become one

of

the

of the

Onchocerciasis

Control

Progranme

in the Volta

Rlver

I

2.

The research

ls currently dlrected

towards chemlcal

fanilles different fron that

of

the

above-mentloned

larvlcldes, in order to

equlp

the

Prograrnme

wlth effectl.ve

means

to

check any problem

of

resLstance and thereby safeguard

the results

obtained.

3. Bactllus thurlnglensls

serotype

II-I-4,

an

insectlclde of blologLcal

orLgLn, was

[email protected]

against the vector

as

well

as

lts relative great

harmlessness

to the non-target

fauna.

Unfortunately, thls

product Ls

not operatlonal all the

year round

for fornulatlon

and cost

reasons.

Research

is

belng contlnued

to select a formulatlon

which would

quite

satl.sfac-

toril-y

meet t,he

constralnts of

^OCP

control

methods.

4. Different

ehenlcal molecules were aLso

tested (pyrethrotds,

carbamates, lnsect growth

regulators).

Carbosulfan

or

Marshall rras one

of the

carbamates which underwent

these sel-ectLon

trLals. It

was

the subject of spot rlver trials

(yaneogo

et al

¹⁹³⁵⁾

followlng

whlch

it

was

retained for

high-water

operational trlals,

during whlch

perlod it

could be

utlllzed ln

case

of

absolute necessity should

the

medlun-term

trial-s

^be

conclusLve.

5. This

document

glves the results

obtained

at

upstream Bema

during the

1l- weeks of weekly

larvicldlng of the

White Bandama

ln the Ivory

Coast as

part of the

large-scale

trlal of thls

carbamate.

TECHNIQUES OF TIIE STUDY AI.ID CITAMCTERISTICS OF TIIE PRODUCT

6.

Carbosul-fan

or

Marshall

ls

an Lnsectl.cide

of the

carbamate

family.

The formulation

tested, called

PL83-237

or

^{OMS 3022,} was produced by

the

company

F.M.C. It Is a

^257"

emulslflable

concentrate (Yameogo

et aL.1986).

The

formulation

concerned

ls stable ln tts containers,

even

at hlgh temperatures.

The remanence

of the

product

ls fron 1 to

¹⁴

days

wlth a

mean

of

about

7 Llz

days dependlng on

the pH.

Froo

a

molecuLe

of

carbosulfan, 582

of

carbofuran

is

obtained which decomposes

qulckly in

alkaLlne environment, by

microblologlcal actlon.

Carbofuran

ls

used

ln

rLce

fields

because

lt ls

consldered

to

^be

very safe

envlronmentally

(Phytagrt,

Geneva, personal

comnunlcatlon).

The carbosulfan

larvlciding

Iras

carrled out

by heLlcopter

at a

dose

of

O.O5 ppm/I-O mlnutes.

7.

The

nonltoring

protocoL _used was

that

approved

by the Ecologlcal

Group

durlng lts sixth

sesslon

ln Aprtl

1985 (see Annex

1).

Three monltoring

statlons,

one

of

^{whlch was a}

control,

were selected on

the

While Banadama.

Drift

and

ltght trap

colLections were ^made

there.

The

collectlon of artiflclal

substrates and saxl.coLous fauna

wlth the

Surber sampl-er was made when

the

hydrological" condttLons permltted

it.

The

faunlstic

densitles were evaluated before

the

beglnning

of the trlals.

) ^{oo . tz4C7 vcu} ftx. ^\'

^E

ocP/vcu/HYBro/86.3 Page 2

8. Thls report

anaLyses

the results

obtalned

at

^Beua

^(Figure 1)

where

the l-arvicldlng

was

carrled out at

about 5OO

netres

upstream from

the

sarnpling

zone. It

must be noted

that the first

carbosulfan

larvLctdlng took

place on 22 August 1985,

after

two weekrs suspensLon

of

any

larvlcldlng of the tlhlte

Bandama. The

larviclding

was then contl.nued every Wednesday

for

11

weeks.

Considering

the high

dlscharge

of the rlver at

the

beglnnlng

of the

experiment,

only the

breedLng

sltes with

fol-lage could be

positlve ln

^the

section concerned.

Our

stations

were sprayed

nainly to

evaluate

the effect of the

product on

the non-target

fauna.

RESULTS AND DISCUSSIONS

Short-term

effect (first

week)

9.

The mean number

of individuals

caught

with drift net ls ^glven in

^Annex

2.

^The

drift

^was almost

ninlnal

before

the Larviciding.

The same

applled to the control

^(Figure

2)

where

the

mean

daytlne

and

night-time drtft indices

were 1.75 and 2.89

respectively.

However,

there

rras

a dlffference

betrreen

the

mean nLght-tLme

drlft lndlces of the control (2.89)

_{and those}

of the pre-larvicldlng period at

upstream Bema

(10.2).

The nean

nlght-

ttne/daytLne

drlft ratlo

^(ND/DD) was equal

to

2.89

at

Badikaha

while Lt

was

6.8

at

upstream Bema. The

greater thls ratlo the better the blologieal

balance (ORSTOI'i Annual

Report,

L977)

ln the

absence

of

any

external Lnterventlon.

The

lntenslty of the drift

^at

Bema was lnfLuenced malnly by

the

Chirononldae-ChironomLnl,

but also

by young stages

of

Caenldae (Epheneroptera).

10.

A few mLnutes

after the larvlctding, carried out at

about 1OhOO,

the lntenslty

of

the drift

lncreased (Flgures

3ar 3br

3c and

3d) but there ls

no

possible

comparlson between

thls

lncrease and

that

recorded

during the spot trlal

undertaken

durlng the

low-

water perlod (3 _n3/sec)

on

the

^Wawa

at the

same dose (Yam6ogo

et aL.

1985).

11.

The

ratlo of

^maxLmun

drift

lncrease

(ratlo of

^maxLmum

value attained after

larviciding to the

mlninum recorded

just after the

passage

of the toxin)

was around 16O, a

value which

is close to that generally

obtalned

with

chlorphoxim.

L2.

The

difference ln effect

^which vas observed between

this first larvlclding of

the I.Ihlte Bandaua and

the spot trial carrled out

on

the

I'Iawa could be

attributed to

several

phenomena:

(a) the

Wawa

is a rlver in a

mountalnous zone whose

qulte part.icular

fauna

is

not subjected

to

weekly

larvlcidlng. Thls

fauna could

therefore

be more

susceptlble

to insectLcldes:

(b) the

discharges

of the

two lratercourses were

not

comparable

at the tlme

the

trLals

lrere

carried out. It ls well

^known

that the effect of larvlcldes

on aquatLc

lnvertebrates ls

severer

durlng the

low-water

period

than

the

htgh-water one;

(e) whlle the dtfference

observed

for

carbosulfan could be due

to a

comblnatlon

of the

above

factors, it

must be polnted

out,

however,

that

permethrin

trlals carried out

under dlscharge

condltlons sinllar to

those

of

carbosulfan gave comparable

results for the

low-water and spate

perlods. This

suggests

that there are

other explanatlons

for the difference ln effect observed. In fact, a

comparison between

the gutter

fauna

of the

tlawa and

the pre-larvlcidlng

saxicolous one

of

the

l{hite

Bandana made

it possible to note that the Trlcoptera

represented almost 50%

of

the fauna

of

Bema as

against only

6%

at DJodji.

Since

thl,s

taxonomic group

is

relatively not very susceptible, Lt

could

not influence

beyond measure the

intenslty of the drift at

Bema where

it

constl,tuted

half of the

rock-slab

lnvertebrdtes.

ocP/vcu/HYBro/86.3 Page 3

13. Flnally,

carbosulfan

ls certalnly a

product whose

effects

on

the non-target

fauna

I : ^{are greatly}

tnfluenced by

river discharge.

The

next

chapter w111

offer

an

opportunlty

to

return to thls

observatlon.

-

Mediun-term

effect

L4. In order to verLfy the results

recorded

durlng the flrst larvlciding, the

protocol was

sllghtl-y nodifled

by naklng

durlng the third

week

of larvlcldlng the

same observations as

during the first

^week.

15.

The

trend of the drlft intenslty of the third larvlcidlng cycle

showed

ltttle

dlfference

1n comparison

with the first one.

The appearance

of the

^graphs

did not

change

fundauentally and

the

Chlronomidae

stt11 constituted the greater part of the

organlsms

collected

(Figures _{3a and}

3b,

4a and

4b).

Contrary

to

^what could have been

belleved,

the low detachment

of the aquatic invertebrates

rf,as

not

due

to a larvtciding faiLure.

16.

The observatlons

of the flrst

week were repeated

durlng the

41st week,

i.€. in

the

8th larvicidlng cycle.

The discharge

of the l{hite

^Bandama was around L67 m3/sec at upatream Bena (Table

I).

The

trend of the drift of the

organLms (Flgures 5a and 5b) reveal"s

a

marked lncrease

ln the effect of the larvicide.

The maximum

drift intensity

recorded

after the

spraylng was around L105 whereas

it

^was about 314

during the first larvlciding, i.eo

8o increase

of 3.5 tlmes. At the

same

tlme, the

discharge feLL by

Station

Week

Badlkaha Downstream Niaba

34 35 36 37 38 39 40 4L 42 43 44

229.5 310.8 319.0 259.O L90.2 23L.5 L49.2

7 2.9

33.2

27 .o 8.7

525.O 550.O 544.O 458.O 289.O 358.3 245.8 L66.9 92.7 59.6 40.4

Table

I:

Discharges

(n3/sec.) of the

White Bandama

at

Badikaha and

iffiffiean

Niaka

durlng the period of

carbosulfan

rrials.

N.B.3 The Souloumougou-Bou reach, hence

the statlons of

^{Bema and}

Souroukoudougou, rras sprayed by usl-ng

the

dlscharges

of

down-

stream Nlaka.

ocP /vcu lHYBro/86.3 Page 4

almost 358

n3/sec. It

was

therefore 3.15 tines

lower than

that

^recorded

durlng the flrst larvlclding.

The

intenslty of the drift of the lnvertebrates therefore

lncreased

wlth

the

fall ln

dlscharge

(Figure 6), in

almost comparable

proportlons.

The

post-larvicldlng

mean

day-tlne drlft

lndex was

four tlues higher

than

that calculated for the first

^week of sparying (Table

II),

whl1e

the

mean

night-tlme drlft

^Lndex

multlplled

by

alnost

9.

34th week

lst

cycle

36th week

3rd

cycle

38th week

5th

cycle

41st

week

8th

cycle

44rh week

Llth

cycle

DI B.L. A.L. B.L. A.L. B.L. A.L. B.L . A.L. B.L.

DD

iil

ND/DD

L.92

LO.2

s.3

60 9

4 5

o.07

4.36

14.2

3.26

24.A5

9.39

0.39

8.29

L2.8

L5.L7

L.2

266.r2

36.79

0.14

9.48

29.4

3.1

Table

II:

Mean daytlme and

nlght-tlme drlft

indices

calculated

before and

after

carbosulfan

larvLcidlng at the

upstream Bema

station.

B.L. ₌

Before

larvlcldlng A.L. ₌ After larviclding DI

= ^mean

Drlft

Index

DD

= ^mean

Day-tlne drift

lndex

ND

= ^mean

Ntght-tlne drift

index

ND/DD

=

^RatLo

of

ND

ro

^DD

L7.

On

the

whole,

the

mean

daytlne drift lndices, calculated

24 hours before

larvlcidlng,

present an upward

trend

week

after

^{week. The}

pre-larvlcldlng ntght-time

ones

also

show

the

same

trend (Flgure 7).

As regards

the

^mean

night-tine/day-tine

ratLos, although

a fa1l ln

vaLue was noted

durlng the thlrd larvlciding cycle, a slight

^Lncrease

rras recorded

before the llth

cycle.

18.

The

trend of the

mean

drift lndices of the control

was

unfortunately

lnfluenced by temephos

larvlclding

(Table

III).

Table

III:

Mean

daytine

and

nlght-tlme drlft lndlces calculated at

Badikaha

(control _treated wlth

Abate

(R)).

The sanpling

of the

26th week was

carried out

48 hours

after the larvlcLding, that of the

34th week

during a perlod of larviclding

suspension

but

those

of the

38th

and 44th weeks

unfortunately

colnclded

with

temephos spraying.

larviciding

J-st cycle

5th

cycle

l1th

cycle 32.8 52.O4

1.59

ocP/vcu/HYBro/86 .3 Page 5

L9. At

Bema,

the

upstream

trend

observed

as

regards

the pre-larvicldlng

mean

drlft ' lndlces

rras due mainly

to the

Epheneroptera and

the

Chironomldae

(Dlptera). It

should be

noted

also that the

Trlchoptera whlch were almost absent from

the collectlons

made during

the perlod of larvlciding

suspension were encountered

regularly ln

those nade

six

^days

. after the

carbosulfan

spraylng.

Changes

therefore

occurred

ln the

behavlour

of the

main

taxonomlc

groups.

The

effect of the larvicide

on

the aquatic lnvertebrates

was

stilL

being

felt six

days

after the larvlcidlng.

20. If after the first larvlciding the lntenslty of the drift

rras

greatly influenced

by

the

Chlronomldae (rnainly

the Chlrononlni.), thls

phenomenon recurred

during the thlrd

and

elghth larvlclding cycles.

The

inposslblltty of

knowlng

the

composltlon

of the

fauna present durLng

the high-lrater period

does

not permlt the susceptlbtllty of this

taxonomlc group

to

be compared

wlth

those

of the other

groups.

21.

The

fact that the

ChlrononLdae seemed

to

be

less susceptible

than

the

Ephemeroptera

during the spot river trial carried out

on

the

^Wawa, Ln Togo, suggests

that the

^great

influence of the

Chironomidae on

the totaL drtft

was due

to a greater

representatlon of

lndlvlduaLs of thls fanily tn the

environment.

22.

While

the

Chlronomini seemed

to

be

the

leasE

susceptible of the

Chironomidae to Talcord permethrin (Elouard

et al.

I-984, Paugy

et al.

1984), carbosulfan seems

to

be more

toxtc for the lndividuals of this tribe.

23. Finally, desplte the effect of the larvtclding

on

the

main taxonomlc groups, Eost

of

them remained

ln the

environment throughout

the trlals.

The surveys

carried out

on 9

and,29 October 1985

at

^Bena

lndlcated the

presence

of

Baetidae, Caenldae (Epheneroptera),

Chirononlni, TanytarsLni, Orthocladiinae,

Hydropsychldae, Philopotanidae

(Trtchoptera)

and

other organisms. It

should be pointed

out,

^however,

that

Amphlpsyche senegalensls (Trichoptera-Hydropsychldae) were absent

in the last collecLions-

.

CONCLUSION

24. A

few remarks can be made as

a resuLt of the

study

of the

medlum-term

effect

of

-

carbosul-fan on

the aquatlc

lnvertebrates:

. (a) the modlfications

whlch were made

in the protocol by taking the first field

observations

lnto

account gave us

a better idea of the effect of the

product on the

non-target

fauna;

(b)

an

evaluation of the

mean daytime

drlft

lndex on

the

day before

the larvlcidlng

can provlde

useful

Lnformatl.on, complement.ary

to that

obtalned by means

of

the

night-tlme drift one. Collections

made every

hour, fron

l4hOO

to

22hOO, are important;

(c) it

Ls necessary

to

undertake coxnplete

drlft cycles three tlmes (at

Least on the

statlon directly treated) during the

htgh-water

trials;

(d)

when

the

controL

ls treated with

temephos,

the

sampling should be made on the eve

of the larvlcidlng. In the

case

of the

Whlte Bandama,

that

woul-d have

necessitated

either the setting

up

of a thlrd

^team

or the carrylng out of

the

coll-ectlons

a week before

or after

^those

of the stations treated.

The use

of B.t.

II-14 wouLd have, however, created

addltional logistlc

problems

for the aerial

.

operatlons.

-

ocP/vcu/HYBro/86 .3 Page 6

25.

The

effect of the

carbosulfan

larvicldlng of the

White Bandama on

the

aquatic

invertebrates

lncreased

wlth the fal1 ln rrater level-.

While

the

maximum lncrease

ln

the

lntenslty of the drlft (at

525 m3/sec) was

close to that generally

recorded

for

chlorphoxim,

the

maximum

drift lndex (at

L67 n3/sec) rras comparable

to that of

Talcord

pernethrln (at

6OO

n3/sec)

on

the

Sassandra.

26.

The

short-term trend of the drift lntensity

lras

greatly

lnfluenced

by

the

Chirononidae

(mainly the Chlrononlni) but the other

taxonomic groups whlch were

rare in the pre-larvlciding drtft

seemed

to

have undergone behavioural changes

wlth the

repeated

l-arvlciding.

They became quLte

frequent ln the drift collected

24 hours before each

spraying.

Nevertheless, most

of the

^maln taxonomLc groups were

stl1l in the drlft

up to

the

cessatLon

of the larviclding.

The

effects of

carbosulfan were reduced

by

the existence

of trlbutaries l-lke the Laflgue

and

the

Souloumougou as welL

as the

hlgh discharges

of the lrlhite

Bandama whose upstream reach was

treated with

temephos.

27.

The

faunistic densltles

were reduced and

a thlck

I-ayer

of

algae covered

the

rocks.

28. With the continuation of the monitorlng, the trend of the faunlstlc sltuatlon wil-l

be assessed

in a report

which

will take into

account

also the

resul-ts recorded at

Souroukoudougou,

a station

estabLlshed

for the

study

of the effect of

carbosulfan on the

non-target

invertebrates.

29. It

can be

sald already that

carbosulfan

(PL.83-237) is a pestlcide

which, when

used

durlng the

hlgh-water

period,

has

a relatlvely

acceptable

effect

on

the

aquatlc

invertebrdtes.

The

spot trial carrled out

on

the

Wawa (Togo)

at

3 m3/sec,

that of

^Grechan

on

the

Leraba

(Ivory

_Coast)

at

13 n3/sec as

well as the last larvlcidlng at

^Bema

lndicate that a

mtnimum discharge according

to the configuratlon of the

watercourse (hemed

in

by

steep banks

or not) wlLl

have

to

^be

establlshed ln order to avold serious effects

on the

aquatlc

fauna.

BIBLIOGRAPIIY

-

^Elouard

^{(J.M.), Illdeux} (P.), 1984.

Test

I

^moyen terme de

la toxlclt6

de 1a perm6thrlne 6pandue

sur le

Sassandra dans 1e cadre du Programme de

Lutte contre ltOnchocercose. I.

Quatre premiEres seoaines de

traltement.

Rapport ORSTOM Hydroblologie Bamako No.3 dec.

1984.

-

^Paugy

(D.),

Yan6ogo

(L.),

Bihoun

(M.),

Cou1lba1y

(B.), L984. Short

Lerm lmpact

of

permethrim on

the non-target aquatlc fauna.

^Rapport OCP/VCU/HYBIO/84.L4.

-

^Yau6ogo

(L.),

Coul-ibaly

(B.), Zida (A.), 1986.

Impact

sur les lnvert6br6s

aquatiques dr6pandages hebdomadaires de pern6thrine Talcord

- ^r6sultats enregistr6s

E Guessabo

sur le

Sassandra (C6te

drlvolre).

^Rapport OCP/VCU/HYBIO/86.1.

-

^Yan6ogo

(L.), Coulibaly (B.), 1985.

Essais ponctuels en

rlviEres

de nouveaux

larvicldes

antisirnulldiens. I. Effets sur

l-a faune

non-clble

du carbosulfan ou

Marshall.

Rapport ocP/vcu/HYBro _{/ 86} .2.

ocP lvcu/HYBro/86.3

ANNEX

I

PROTOCOL FOR TESTING THE },IEDIUM-TERM EFFECTS OF

CARBOSULFAN ON TIIE NON-TARGET FAUNA OF ^TIIE

SASSANDRA

RMR (MRY

COAST)

Insectl.cide:

Carbosulfan (carbamate)

at

^{O.O5 pprn}

Perlodlcity of

treatment

:

^Once

per

week

Planned

duratton :

Three months (beginntng

in

mld-August L985)

River :

Sassandra,

fron the

confluence

with the

Bagbe down

to the lake of

Buyo (see nap).

Monltorlng

sites :

^{(see map)}

Site 1 :

Vialadougou

(control)

upstrean from

the treated

reach.

Stte 2 :

Semlen

ferry, slte dlrectly treated wlth the larvicide

^(about

a

hundred metres downstream from

a

treatment

polnt).

Site 3 : ^Vtllage of

SemLen,

sLte not treated directly, sltuated 7

km downstream from the previous one,

at the

end

of the theoretical carry of the insecticlde tested. It

should make

it posslble to

study

the carry

and

the resldual action of

the

lnsectlclde

wave on

the non-target

fauna.

A.

Entomologlcal monitoring

Two types

of drift

monLtorlng have been planned.

Type

1 (Tl-) ls for the

study

of klnetlcs of

detachment and

the quantity _of .. drlftlng

^fauna

slx

days

after

each treaLment.

Type

2 (T2) is

sole1y

for the evaluatlon of the drifttng

fauna under

the

^same

.

conditLons as Type 1.

A.L

^{Sampling methods}

Type

1 (T1)

(week

of flrst

treatment and

8th

week)

+ Drlfr

-

^O7h0O

to

^22h00

: 1

col-Lection every hour (eve

of treatnent) - (t - hr) to (t ^{+ 3} hr) : 1 collection

every 3O minutes (on the

day

of

treatment)

- (t ^{+ 3} hr) to

22h00

: 1 collectlon

every hour.

t ₊

Surber and broom samples

to

be taken

the

day before treatment and when

the

seasonal drop

in

water

tevel

^permits.

. 1. t = time of

^treatment

ocP/vcu/HYBro/86 .3 Annex

I

Page 2

Type

2 (T2)

(see tlmetable)

* Drifr

-

^18h00

to

^21hOO

:

every 3O ml-nutes (eve

of treatnent)

*

Surber and ^broom sauples

to

^be taken

the

day

before

treatment and when

the

seasonal drop

in

water 1evel ^permits.

A.2

Timetable

WeekNo. L 2 3 4 5 6 7 I 9 10 1L L2

¹³

L4 15 16 Slte

No.

T1 T2

^T2

T2 T2

^T1

T1

^T2

A.3

LeveL

of identlficatlon of

^organlsms

Level adopted

for the

whole monltoring programme

(famlly, tribe).

B. Flsh nonltoring . 8.1

Sanpllng methods

.. 8.1.1 TrLals in

cages

(c)

(see

table ln

paragraph B.2)

Scaled

flsh wtLl, as far

as

posstble,

be caught

wlth traps to avoid injurtes.

.

Furthermore, each cage (dimenslon: 50

x

5O

x

50 cm)

wl1l contaln five to

1O

flsh

(dependlng on

thelr size).

Not

only

w111

the

scaled

fish

be separated from

the

others,

but also

those

wlth

spines

wlll not

be mixed

with the

harmless

specles. Flsh

have

to

^be

caught

in the river

and

put lnto

cages

three to four

days

ln order to select the

most

viable ones. In additlon to

observing

thelr

behavlour

just after treatment,

these

flsh will

be monitored

frequently (every three hours, for example).

Some

of the

cages have to be placed

at a

distance

of

about 1O

n

away from

the

treatment

point

and

the rest at

about

3

kn downstream.

8.L.2 Fishing wlth gtLl net

^(GN)

See

table in

paragraph B.2.

During

the trial-s wlth

permethrln

the

cage

test

^showed

that the flsh try to flee .

from

the larvlclde

wave,

but the

catches

ln ^{gl11 nets}

^rrere

not affected. Drlfts

caused by

the insectlcide

cannot,

therefore,

be considered as

of ^great

Lmportance.

- '

_lmmediate The

effect larvlcides

^on

the

subjected

ftsh fauna. to operatlonal

^To

that

must be

trlals

added

are

knolrn

the difficulty to

have no

wlth the significant

present techniques

ln

showing mlnor

short-term effects. It is, therefore, not

lndlspensable to

- ^{carry out frequent}

^sanpllng.

T1 T1 T2 1

2 3

T2 T2

T2 T2 T2

ocP lvcv /HYBro/86 .3 Annex

I

Page 3

A few weeks

before treatment, a control

sanpllng

of the

selected

statlons

should be

undertaken.

During

the trlal ^perlod, the

_91L1

nets wlll-

always be place and

retrleved the

day before treatment.

In addition to

species

ldentlflcation,

welghts and l-engths

will

have

to

^be

measured

ln order to calculate the coefflclents of conditlon before, during

and

after

the

perlod of treatment.

The

gut

contents w111

also

have

to

be examined.

8.2

TirnetabLe

The

table

below gl.ves

the

^periods

for the

monltorLng

of the flsh

^fauna

at

the

dlfferent sltes.

As

far

as

posslble

observatlons w111 be made on macrocrustaceans ^Ln cages.

Week No.

L 2 3 4 5 6 7 8 9 L0 LL L2 13 L4 15

^L6

Slte

No.

CGN CGN

GN

C. Analysls of

resldus

It is

proposed

to carry out

an

analysls of

carbosulfan resldues

in

mud samples

from

the lake of

Buyo,

at the

end

of the trlal-.

1 2 3

CGN CGN GN

CGN CGN GN

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Longo

5;nhoho In, ⁿ d,ir,

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