hydroaccoustic survey lake kariba-web-33

8/20/2019 Hydroaccoustic Survey Lake Kariba-web-33

1/30

FAO SmartFish

Publication

PRELIMINARY RESULTS OF THE

HYDROACOUSTIC SURVEY CONDUCTED

ON LAKE KARIBASeptember 2014

33


2/30

Cover photograph courtesy FAO SmartFish


3/30

REPORT/RAPPORT: SF-FAO/2014/33

Preliminary Results of theHydroacoustic Survey conducted

on Lake Kariba

September 2014

GCP/RAF/466/EC SmartFish Project


4/30


5/30

3

Executive Summary

As a continuation of a hydroacoustic training in 2013 supported by SmartFish FAO, and in

accordance with recommendations of the Fifth Technical Consultation on Development

and Management of the Fisheries of Lake Kariba, SmartFish FAO supported a

hydroacoustic survey in August 2014.

The preliminary results of the survey that was undertaken to determine the standing

biomass of Kapenta in Lake Kariba show that by adding the estimated biomasses of the

basins and stratum, the estimated average standing biomass was 16,277 i.e. ± 9,730

tonnes.

In order to ascertain any changes over time and to draw substantial conclusions,

comparisons across time is necessary. A regular hydroacoustic survey programme will

have to be established and the relationship between densities and environmentalparameters should be assessed.


6/30

4

Résumé exécutif

Suite à la formation en hydroacoustique qui a été organisée en 2013 grâce au support de

SmartFish FAO, et conformément aux recommandations de la Cinquième Consultation

sur le Développement et la Gestion du Lac Kariba, SmartFish FAO a supporté laréalisation d’un relevé hydroacoustique en aout 2014.

Ce relevé a été réalisé pour déterminer la biomasse du kapenta dans le Lac Kariba.

Les résultats préliminaires montrent qu’en additionnant les relevés des biomasses des

bassins et couches, la moyenne estimée de biomasse est de 16 277 c’est-à-dire +/- 9

730 tonnes.

Pour vérifier les changements dans le temps et tirer des conclusions fiables, il est

nécessaire d’effectuer des comparaisons dans le temps. Un programme de relevés

hydroacoustiques réguliers devra être établi et les relations entre les densités et les

paramètres environnementaux devront être établies.


7/30

5

Contents

Executive Summary ______________________________________________________________ 3

Résumé exécutif _________________________________________________________________ 4

Contents ________________________________________________________________________ 5

List of Tables _____________________________________________________________________ 6

List of Figures ____________________________________________________________________ 6

List of Photos ____________________________________________________________________ 6

1. Background___________________________________________________________________ 7

2. Material and methods _________________________________________________________ 7

2.1 Description of the study area _______________________________________________ 7

2.2 Methods __________________________________________________________________ 82.3 Data analysis ____________________________________________________________ 11

3. Results _______________________________________________________________________ 11

3.1 Average length and weight of Kapenta along the lake ____________________ 11

3.2 Fish densities _____________________________________________________________ 11

3.2.1 Zimbabwean side of Lake Kariba _______________________________________ 11

3.2.2 Zambian side of Lake Kariba ____________________________________________ 13

3.3 Fish biomass _____________________________________________________________ 13

4. Conclusion and recommendations ____________________________________________ 15

Annex 1. List of participants and survey agenda __________________________________ 16

Annex 2. Pictures from the hydroacoustic survey __________________________________ 17

Annex 3. Data used to derive densities ___________________________________________ 24


8/30

6

List of Tables

Table 1: Average length and weight of Kapenta along Lake Kariba ______________ 12

List of Figures

Figure 1: Location of Lake Kariba in Africa ________________________________________ 8

Figure 2: Research vessel, Namazambwe ________________________________________ 9

Figure 3: The pre-defined sampling transects and basin boundaries _______________ 10

Figure 4: Trip track log __________________________________________________________ 10

Figure 5: Average Kapenta densities on the Zimbabwean side of Lake Kariba _____ 12

Figure 6: Correlation between Kapenta density and sampled depth in

Leisure Bay (un-fished area) ____________________________________________________ 12Figure 7: Average Kapenta densities on the Zambia side of Lake Kariba __________ 13

Figure 8: Average standing biomass per basin on the Zimbabwean

side of Lake Kariba. ____________________________________________________________ 14

Figure 9: Average standing biomass per basin on the Zambian side of Lake Kariba 14

List of Photos

Photo 1: Team photo taken during the official launch of the

hydroacoustic survey held in the Sinasongwe District Council Hall ------------------------- 17

Photo 2: The team members during preparations for the survey ---------------------------- 17

Photo 3: Some members of the team monitoring the screen during calibration ------- 18

Photo 4: Team members setting the sphere and the transducer during calibration -- 18

Photo 5: View of the screen during calibration ---------------------------------------------------- 19

Photo 6: Preparing the transducer --------------------------------------------------------------------- 19

Photo 7: Team photo prior to departure from Sinazongwe for the survey ---------------- 20

Photo 8: Launching CTD during the survey ---------------------------------------------------------- 20

Photo 9: Kapenta fish sample taken from a Kapenta rig during the survey -------------- 21

Photo 10: The biggest Kapenta collected during the survey ---------------------------------- 21

Photo 11: Measuring and weighing Kapenta samples ------------------------------------------ 22

Photo 12: The survey team just before disembarking “Namazambwe”

at Siavonga, after the hydroacoustic survey ------------------------------------------------------- 22

Photo 13: Data analysis being carried out by the survey team ------------------------------ 23


9/30

Preliminary results of the hydroacoustic survey conducted on Lake Kariba 7

1. Background

Lake Kariba is jointly owned by the governments of Zambia in the north and Zimbabwe in

the south. It lies between latitudes 16°28´ and 18°06´ south and longitude 26°40´ and

29°03´ east. The full operation of the reservoir was reached in 1963. Although the lakewas created as a hydroelectric reservoir, there are accounts of a considerable number of

activities taking place both in the lake and along its shores, including capture fisheries and

aquaculture.

In order to implement one of the recommendations of the Fifth Technical Consultation on

Development and Management of the Fisheries of Lake Kariba, a hydroacoustic survey was

conducted in Lake Kariba from 14 to 24 August 2014. The survey was conducted as a

continuation of the training conducted in Songo in 2013 and, for this reason, involved all

the personnel that attended this course, i.e: two officers from Zambia; two from

Zimbabwe; two from Malawi and two from Mozambique. The survey was co-funded by FAOand SmartFish. The survey agenda and the list of those involved is given in Annex 1.

The main objective of the hydroacoustic survey was to determine the standing biomass of

Kapenta in Lake Kariba, given that the last hydroacoustic survey on Lake Kariba was

carried out in 1997. Determination of the current biomass is thought to provide useful data

for the management of the Kapenta fishery.

In order to fulfill the aforementioned objective, the following activities were implemented:

♥ Calibration of the EK-60 split beam echo-sounder;

♥ Sampling with EK-60 along pre-established zigzag transects;

♥ Sampling of Kapenta from Kapenta fishing rigs;

♥ Sampling with CTD along the transects and;

♥ Data analysis.

2. Material and methods

2.1 Description of the study area

Lake Kariba is a man-made lake which lies between latitudes 16°28´ and 18°06´ south

and longitude 26°40´ and 29°03´ east. Figure 1 below, shows the geographic location of

the lake.


10/30

Material and methods8

Figure 1: Location of Lake Kariba in Africa

Overlaid on NDVI by Henry Ndaimani

The principal physical characteristic of the lake at the normal operating level of 485m

above mean sea level can be summarized as follows:

Catchment area 409,600 km²

Surface area 5,364 km²

Maximum length 320 km

Maximum depth 120 m

Maximum width 40 km

For management purposes, the lake is divided into five basins (Mlibizi, Binga, Sengwa,

Bumi/Chalala and Sanyati) on the Zimbabwean side and four strata numbered from 1 to 4,

west-easterly, on the Zambian side (Figure 3).

2.2 Methods

The survey was conducted at night, on board the Department of Fisheries of Zambia ’s

research vessel, “Namazambwe” (Figure 2). During sampling with EK-60, the transducer

was towed alongside the vessel, which moved at an average speed of 7 knots.


11/30


Figure 2: Research vessel, Namazambwe

Calibration was done at the bay, close to the harbour. The actual sampling began where

the first transect starts, close to the town of Binga. Figures 3 and 4 show the pre-definedtransects and the trip log.


12/30


Figure 3: The pre-defined sampling transects and basin boundaries

Figure 4: Trip track log


13/30


CTD casts and fish samples were taken along the transects. CTD provides profile readings

of environmental parameters such as temperature, conductivity and depth, as well as

dissolved oxygen and chlorophyll. Fish samples were taken to derive the average weight of

fish in order to determine the biomass.

2.3 Data analysis

Sampled data from EK-60 were converted and analyzed using data analysis software

“SONAR 4”. Converted samples were analyzed for fish densities per transect and late

average densities per basin were calculated using Excel. The results of data sampled in the

different transects are presented in Annex 3.

In order to derive the average length and weight, weighted length and weight were

calculated per basin.

3. Results

3.1 Average length and weight of Kapenta along the lake

Both the average length and weight of Kapenta differ across basins and across stratum

(Table 1). Bigger individuals are found at the Sanyati basin, probably (possibly) as a result

of a spillover from the Leisure Bay, which is an un-fished area.

Table 1: Average length and weight of Kapenta along Lake Kariba

Basin/Stratum Average fishweight (g) Average fishlength (mm)

Mlibizi

Binga 1.06 52.23

Sengwa 1.01 50.76

Bumi-Chalala 0.85 49.79

Sanyati 1.14 50.72

Stratum 1 1.06 52.23

Stratum 2 1 49.77

Stratum 3 0.97 51.44

Stratum 4 1.14 50.72

3.2 Fish densities

3.2.1 Zimbabwean side of Lake Kariba

Fish densities for the Zimbabwean side of Lake Kariba are presented in Figure 5. The

highest densities were observed in Leisure Bay at an average of 50,000 fish/ha. However,

it should be noted that there was a significant variation of Kapenta fish densities at

different sampled points along the transects, which is consistent with an uneven

distribution of Kapenta along the lake.


14/30


In fact, it was observed that, for the un-fished area, there was a strong correlation

between fish density and sampled depth (Figure 6). This scenario was not observed in

fished areas, which would suggest that other factors such as fishing are affecting fish

densities.

Figure 5: Average Kapenta densities on the Zimbabwean side of Lake Kariba

Figure 6: Correlation between Kapenta density and sampled depth in Leisure Bay

(un-fished area)

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

M l i b i z i

B i n g a

S e n g w a

B u m

i - C h a l a l a

S a n y a t i

L a i s u r e b a y

K a p e n t a d e n s i

t y ( f / h a )

Basin

Kapenta fish density on the Zimbabwe side of Lake

Kariba

y = -1109.8x + 111644R² = 0.9252

0

20,000

40,000

60,000

80,000

100,000

120,000

0 20 40 60 80 100 120

K a p e n t a d e n s i t y ( f / h a )

Sampled depth (m)

Correlation between depth and fish density at Leisure

bay


15/30


3.2.2 Zambian side of Lake Kariba

On the Zambian side of Lake Kariba, the Kapenta densities seemed highest on the first

stratum and lowest on the third. These results are somehow comparable with those of the

Zimbabwean side of the lake, with the exception of the 4 th stratum, which presents

relatively lower densities than its closest counterpart, the Sanyati basin.

Figure 7: Average Kapenta densities on the Zambia side of Lake Kariba

3.3 Fish biomass

The average Kapenta biomasses for the different basins on both sides of Lake Kariba are

presented in Figure 8 and Figure 9. Just as for the fish densities, the standing biomasses

vary across the basins and are highest in the Sanyati basin on the Zimbabwean side of the

lake.

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

Stratum 1 Stratum 2 Stratum 3 Stratum 4

K a p e n t a d e n s i t y ( f /

h a )

Stratum

Kapenta densities on the Zambia side of lake Kariba


16/30

Results14

Figure 8: Average standing biomass per basin on the Zimbabwean side of Lake

Kariba.

Figure 9: Average standing biomass per basin on the Zambian side of Lake Kariba

0

1000

2000

3000

4000

5000

6000

7000

K a p e n t a s t a

n d i n g b i o m a s s ( t o n n e s )

Basin

Kapenta standing biomass on the Zimbabwe side oflake kariba

0

500

1000

1500

2000

2500

3000

3500

4000

4500

Stratum 1 Stratum 2 Stratum 3 Stratum 4

K a p e n t a s t a n d i n g B i o m a s s ( t o n n e s )

Stratum

Kapenta standing biomass on the Zambia side of Lake

Kariba


17/30


Total standing biomass

By adding the estimated biomasses of the basins and stratum, the estimated average

standing biomass was 16,277 i.e. ± 9,730 tonnes.

4. Conclusion and recommendations

Comparisons between the results reported in this study and those from previous surveys

are necessary in order to ascertain any changes over time.

Further analysis on the samples collated is required in order to assess densities/depth

variation along the transects.

The relationship between densities and environmental parameters should be assessed.

Fish densities versus distribution of Kapenta fishing efforts should be determined andmapped.

A regular hydroacoustic survey programme will have to be established.


18/30

Annexes16

Annex 1. List of participants and survey agenda

List of participants

Name Country

Jorge Mafuca Mozambique

Antonia Manica da Costa Mozambique

Daniel Mueleque Mozambique

Emmanuel Silwimba Zambia

Taylor Banda Zambia

Mebelo Wamulume Zambia

Itai Tendaupenyu Zimbabwe

Michael Tiki Zimbabwe

Stanley Mvula Malawi Innocent Gumurila Malawi

Nobuhle Ndhlovu FAO

Drivers (2) FAO

Boat crew (3) Zambia

Survey agenda

Day Date Activity

1 10/08/2014 Arrival of participants in Harare

2 14/08/2014 Departure to Sinazongwe, Zambia via Kariba (to pick

up Kariba and Siavonga participants)

3 15/08/2014 Official opening

Recap. for participants

4 16/08/2014 Calibration of equipment

5 17/08/2014 Calibration of equipment

6 18/08/2014 Night survey



21/08/2014 Night survey

22/08/2014 Night survey

23/08/2014 Arrival in Siavonga, disembarcation from boat and

departure for Kariba, Zimbabwe.

9 24/08/2014 Data analysis at Lake Kariba Fisheries Research

Institute

10 25/08/2014 Departure for Harare and participants from Zambia

travel back to Zambia

11 26/08/2014 Participants travel back to respective countries


19/30


Annex 2. Pictures from the hydroacoustic survey

Photo 1: Team photo taken during the official launch of the hydroacoustic survey

held in the Sinasongwe District Council Hall

Photo 2: The team members during preparations for the survey


20/30

Annexes18

Photo 3: Some members of the team monitoring the screen during calibration

Photo 4: Team members setting the sphere and the transducer during calibration


21/30


Photo 5: View of the screen during calibration

Photo 6: Preparing the transducer


22/30

Annexes20

Photo 7: Team photo prior to departure from Sinazongwe for the survey

Photo 8: Launching CTD during the survey


23/30


Photo 9: Kapenta fish sample taken from a Kapenta rig during the survey

Photo 10: The biggest Kapenta collected during the survey


24/30

Annexes22

Photo 11: Measuring and weighing Kapenta samples

Photo 12: The survey team just before disembarking “Namazambwe” at

Siavonga, after the hydroacoustic survey


25/30


Photo 13: Data analysis being carried out by the survey team


26/30

Annexes24

Annex 3. Data used to derive densities

Transect Basin StratumSample

NumberDepth Total f/ha

1 Binga 1 1 37.95 62,911

1 Binga 1 2 27.7 63,165

1 Binga 1 3 17.17 2,589

1 Binga 1 4 12.74 8,523

2 Binga 1 1 31.86 6,410

2 Binga 1 2 44.6 70,144

2 Binga 1 3 36.84 15,534

2 Binga 1 4 40.17 58,346

2 Binga 1 5 55.68 80,577

2 Binga 1 6 42.94 49,058

2 Binga 1 7 38.78 26,685

2 Binga 1 8 32.41 45,652

3 Binga 1 1 32.69 32,396

3 Binga 1 2 45.43 29,552

3 Binga 1 3 42.94 39,131

3 Binga 1 4 40.17 48,515

3 Binga 1 5 31.30 11,560

3 Binga 1 6 28.53 32,602

3 Binga 1 7 26.59 19,7073 Binga 1 8 18.00 22,351

3 Binga 1 9 24.65 31,071

3 Binga 1 10 21.61 48,450

4 Binga 2 1 22.44 35,981

4 Binga 2 2 19.94 28,229

4 Binga 2 3 19.11 11,079

4 Binga 2 5 23.55 11,232

4 Binga 2 6 18.56 2,662

4 Binga 2 7 27.15 19,327

4 Binga 2 8 23.55 10,406

5 Sengwa 2 1 26.04 253

5 Sengwa 2 2 24.1 7,408

5 Sengwa 2 3 32.69 31,087

5 Sengwa 2 4 40.72 12,889

5 Sengwa 2 5 37.95 8,003

5 Sengwa 2 6 31.58 43,511

5 Sengwa 2 7 23.27 26,204

6 Sengwa 2 1 23.55 14,794

6 Sengwa 2 2 40.04 79,8776 Sengwa 2 3 51.25 42,046


27/30




6 Sengwa 2 4 65.93 2,691

6 Sengwa 2 5 36.46 21,652

7 Sengwa 2 1 56.01 7,177

7 Sengwa 2 2 43.69 9,092

7 Sengwa 2 3 49.31 22,747

7 Sengwa 2 4 50.69 34,911

7 Sengwa 2 5 67.31 17,411

7 Sengwa 2 6 27.98 1,274

8 Sengwa 2 1 31.03 49,374

8 Sengwa 2 2 60.39 46,636

8 Sengwa 2 3 53.74 35,055

8 Sengwa 2 4 31.3 27,250

8 Sengwa 2 1 19.94 27,9449 Sengwa 2 2 31.86 40,508

9 Sengwa 2 3 42.11 10,522

9 Sengwa 2 4 39.61 83,331

9 Sengwa 2 5 50.97 92,396

9 Sengwa 2 6 57.34 10,320

9 Sengwa 2 7 53.14 24,202

9 Sengwa 2 8 22.99 10,626

9 Sengwa 2 9 24.93 6,225

10 Sengwa 3 1 38.5 52,541

10 Sengwa 3 2 48.75 58,574

10 Sengwa 3 3 46.81 88,998

10 Sengwa 3 4 59.83 33,237

11 Sengwa 3 1 39.61 6,967

11 Sengwa 3 2 46.26 10,623

11 Sengwa 3 3 52.35 25,863

11 Sengwa 3 4 31.58 7,863

11 Sengwa 3 5 32.69 6,284

11 Sengwa 3 6 56.23 31,636

11 Sengwa 3 7 20.78 9,54211 Sengwa 3 8 25.76 37,385

11 Sengwa 3 9 21.88 14,166

12 Bumi-Chalala 3 1 24.38 12,831

12 Bumi-Chalala 3 2 42.66 10,284

12 Bumi-Chalala 3 4 60.94 13,836

12 Bumi-Chalala 3 5 62.88 19,907

12 Bumi-Chalala 3 6 53.35 22,767

12 Bumi-Chalala 3 7 40.17 13,713

12 Bumi-Chalala 3 8 32.96 8,475

12 Bumi-Chalala 3 9 39.9 6,486

12 Bumi-Chalala 3 10 21.88 12,840


28/30

Annexes26



12 Bumi-Chalala 3 11 17.17 12,540

12 Bumi-Chalala 3 12 15.79 9,000

12 Bumi-Chalala 3 13 13.85 41,560

12 Bumi-Chalala 3 14 30.47 18,000

12 Bumi-Chalala 3 15 41.27 8,013

12 Bumi-Chalala 3 16 26.87 8,146

12 Bumi-Chalala 3 17 65.37 21,562

12 Bumi-Chalala 3 18 39.34 26,136

13Tashinga/SambaKaluma 4 1 41.27 21,146


13

Tashinga/Samba

Kaluma 4 3 85.04 27,428




14 Sanyati 1 65.10 38,900

14 Sanyati 2 55.12 45,048

14 Sanyati 3 27.42 43,301

14 Sanyati 4 30.75 48,811

14 Sanyati 5 51.25 64,80314 Sanyati 6 46.54 60,275

14 Sanyati 7 52.63 38,168

14 Sanyati 8 23.55 68,756

14 Sanyati 9 23.82 56,231

15 Sanyati 1 26.04 60,050

15 Sanyati 2 33.52 34,891

15 Sanyati 3 34.09 58,704

15 Sanyati 4 37.95 32,025

15 Sanyati 5 61.50 31,964

15 Sanyati 6 66.48 35,280

15 Sanyati 7 66.48 36,247

15 Sanyati 8 32.13 69,106

15 Sanyati 9 71.47 60,538

16 Sanyati 1 60.66 41,794

16 Sanyati 2 54.45 42,988

16 Sanyati 3 50.14 40,477

16 Sanyati 4 52.08 53,436

16 Sanyati 5 25.21 64,130

16 Sanyati 6 36.01 51,29317 Leisure Bay 1 15.51 87,234


29/30




17 Leisure Bay 2 19.39 98,747

17 Leisure Bay 3 23.27 98,468

17 Leisure Bay 4 35.73 68,499

17 Leisure Bay 5 57.06 39,552

17 Leisure Bay 6 63.16 34,746

17 Leisure Bay 7 71.47 27,211

17 Leisure Bay 8 81.44 19,940

17 Leisure Bay 9 77.84 20,413

17 Leisure Bay 10 95.57 21,859


30/30

SmartFish is a regional fisheries project managed by the Indian Ocean

Commission, funded by the European Union and co-implemented by theFood and Agriculture Organization of the United Nations. SmartFish, which

operates in 20 countries throughout the East and Southern Africa - Indian

Ocean region, focuses on fisheries governance, management, monitoring,

control and surveillance, trade, and food security.

As a continuation of a hydroacoustic training in 2013 and in accordance

with recommendations of the Fifth Technical Consultation on Development

and Management of the Fisheries of Lake Kariba, SmartFish supported a

hydroacoustic survey in August 2014. This report documents the

preliminary results of the survey that was undertaken to determine the

standing biomass of Kapenta in Lake Kariba.

hydroaccoustic survey lake kariba-web-33

Documents