The effectiveness of 2 mark and recapture techniques was evaluated using tiger fish, Hydrocynus vittatus. The 2 techniques used were: tagging with a plastic tag and fluorescent spray marking. While the tagging method resulted as the logical method to use within the constraints of the tiger fish study, it cannot be considered completely reliable for the estimation of population size in Lake Kariba

Langerman, J.D.

English

Aquatic Commons

AN EVALUATION OF MARK AIJ]) RECAPTURE TECHNIQUES
FOR ESTIMATING TIGERFL3H BIOMASS IN LANE KARIBA.
LAKE KARIBA FISHERIES RESEARCH INSTITUTE'
PROJECT REPORT NO. 38
by
J.D. LANGERMAN
DECEMBER 1980
DEPARTMENT OF NATIONAL PARKS AND VJ.LDLIFE MANAGEMENT
ZIMBABWE

Part 1 The Technicues,
Introduction.
Ways of marking fish have been used widely in studies of stock
assessment, growth, distribution and movement of fish populatìons. Most
marking techniques fall within three categories, (i) Excision of body
parts, (2) tagging and (3) biological staining (Phinney et al, 1967).
Tagging methods have been used in estimation of tigerfish biomass in Lake
Kariba (Junor, pers. Comm.) and while succoasful, limitations in sampling
of the fish led to dubious results. In 1977 the relatively ne\7 method of
fluorescent spray marking was introduced to the tigerfish programme in
Kariba. It was applied again in 1978, nd again in conjunction with a
tagging programme in 1979.
Fluorescent spray marking was developed by Jackson (1959) and has
been used on Salmon by a number of workers (Phinney et al, 1967 White
1976 : Hennick & Tyler, 1970). The technique basically involves the use
of dry, finely-ground fluorescent pigments which are sprayed onto the
dermis and epidermis of fish with compressed air. Most of the pigment
only penetrates the mucous layer which is sloughed off, but the remaining
pigment is embedded in the epidermal and dermal layers covering the scales.
The mark is therefore soon invisible to the naked eye, but fluoresces
when activated by ultra-violet light.
Tagging has been used successfully on tigerfish in Lake Kariba
(L.K..F.R.I., unpublished data). A plastic tag, comnionly used in the
clothing industry, is introduced into the musculative adjacent to the
dorsal fin of the fish by means of a tag gun and provides a clearly
visible mark which causes no apparent distress to the fish.
MaterIal and Methods.
2.1 Fluorescent Spray Markin.
2.1.1 Materials.
The pigments used in the exercise consisted of a solid solution of
-2-
fluorescent dyes in a resin of melamino-sulphonamide-formaldehyde. Because
of their insolubility in water, these pigments are non-toxic to fish.
(Phinney et al, 1967). The compounds consisted of powders with a particle
size of less than 20u in diameter and came in four colours red, green,
blue and yellow. This material was imported from the U.S.A. but remaining
equipment was obtained in this country.
The markihg equipment consisted of a spray-gun with a 2-litre
carmister, of the type commonly used by garages for cleaning engines. This
type 0± gun uses the tyonturit principle to lift material from the canriister
and blast it through a nozzle. The spray-gun was connected, by high
pressure hosing, to a 100kg compressed air cylinder through a regulator
capable of delivering 1000 kpa.
Detection equipment consisted of ultra-violet lamps, with 125 watt
bulbs, connected to a 220 volt A.C. power source. The scanning procedure
normally had to be oarried out in a darkened room.
2.1.2 Preliminy tests.
The fluorescent spray marking technique was tested on captive
tigerfish in the laboratory prior to its application in the field. The
tests wore designed to determine mark retention and to assess post-marking
mortality in tigerfish. The procedures for testing are summaries in Table 1.
Table 1 Fluorescent 3pray Marking - Preliminary Tests.
1Ar(ING
PRAY GUN PREbSURE 400 kpa to 650 pica
jDIST. NOZZLE TO FISH 10 to 35 cm
DATE NO. FISH IvLAcED SIZE FISH M0RTLITY SIÎPLE COD
21. 9. 77
7.9.7
3. i . 78
18-22mm NIL i
6-8cm NIL
}
2
19-25cm! 20 3
11
5
10
DATE
5.12.1977
1.12.1979
bTATION
2
3
TOTAL
i
2
TOTAL
NO. MARKEDj
299
183
183
703
548
2.2 Tagging
2.2.1 Materials
The equipment required for tagging is very simple and light,.
consisting primarily of a tag-fastener and clips of plastic tags. The tag
fastener or 'tag gun', in conjunction with the tags are designed for use in
the clothing industry, but the system lends itself to the marking of fish,
The instrument used in our programme was a "Mark II Swiftacher" tg
fastener with a detachable 2cm needle. The plastic tags, coloured red and
white, were 5cm in length and arranged in clips of 25.
2.2.2 Tagin
A tagging programme was begun in 1977 but the uipment failed and the
attempt abandoned. However, in 1979 an extensive tagging exercise was
carried out with new equipment in the Sanyati Gorge with very gratifying
results, At each of the stations fish were either spray-marked or tagged,
3
2.1.3 ADpljcation in the Field.
The spray technique was used to estimate standing crop of tigerfish
in the Sanyati Gorge in 1977, 1978 and 1979. The exercise was aborted in
1978 because of adverso weather conditions, but sorne measure of success was
achieved i the application of the technique in the other two years. The
numbers of fish marked are shown in Table 2.
Table 2 Fluorescent spray marking in the Sanyati Gorge.
1548
2096
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arid, until the tage were exhausted, this system kept pace with the spray
iarking. A total of 984 fish were tagged, 535 at Station i (with 548
sprayed) and 449 at Station 2.
3. Results.
3.1 Fluorescent Spray Marking
The results of the preliminary tests on spray marking were variable,
and were very much a function of the distance and pressure of dye
application, The results are shown in Table 3.
Fluorescent
In samples i and 2 mark retention was low after only two months and
this was attributed to insuíficient pressure from the spray gun. In sample
3, mark retention was fairly good, but at the cost of a 20% mortality rate
in the marked population. It was noticed that at pressures approaching
100 p.s.i. and distances below 10cm there was a loss ofscales during
application. This could have lead to fungal infection and subsequent death.
Of 700 tigerfish marked in the gorge in 1977, 19 were recovered. In
all cases the marks were clearly visible to the naked eye and indications
were that mark retention was good. However, in 1979, only 4 marked
tigerfish were recovered even though more than 2000 were marked. The
recapture exercise that year involved returning the fish to a factory in
Kariba where they were examined the following day. On the night ol'
pray Marking - Preliminary Tests,
DATE 0F NUMEER
DETECTION MARKED RETAINING MARK
NUMEER TIME ELAPSED SAMPLE CODE
6. 10. 77
25.11.77
11 4 (36%)
4
15 days
65 days
6.10.77
25,11,77
5 1 (2o%)
i
9days 2
59 days
9.8.78
4.41.79
10 (62.5%)
i
219 days
457 days
3
recapture several fish with clearly visible dye marks were seen as they
were landed, but these had disappeared b the time the fish reached the
factory. Features contributing to the f ai.lure of the spraying exei'oise in
1979 probably included:
Deterioration of the skin of the fish through bruising, rough
handling and rotting. Many of the t±gerfish inspected at the factory had
lost a large number of scales, and the skin had become dìscoloured and
soft. The majority of marks were probably lost for this reason.
Spraying technique and spray gun failure; often very little dye
was lifted by the 'venturi' and so consequently only compressed air was
blown onto the fish. This was often shown by a shower of scales being
blown off the fish.
3.2 Tagging
Tag recoveries in the 1979 marking exercise were encouraging. On the
night of recapture 68 tagged fish viere recovered, and an interesting feature
was that none of these showed any adverse effects from the tagging trauma.
During the subsequent week asmall tagged tigerfish was recovered from a
gill-net some 3km from the point of release. Later during the saine month,
an angler caught a male tigerfish which carried a tag from the 1976
programme (Junor, pers. comm.). The 1980 International Tigerfish Tournament
produced a tigerfish that had been taggod in 1979 and a further report of
a tagged tigerfish came in from the angling census in the Sanyati Gorge.
4. Discussion,
The use of both spray marking and tagging in the 1979 mark and
recapture exercise afforded the opportunity to evaluate and compare the two
techniques. Obviously there are limitations to both methods and at present
there is a puacity of data on such aspects as post marking mortality and
mark retention under Kariba conditions. However, this pertains
particularly to stock assessment studies and, as will be discussed in Part
2, these limitations may well be overshadowed by far greater sources of
-6-
error in population estimates. There is, therefore, adequate potential for
the utilization of these techniques in other studies such as growth,
distribution and movement of fish populations.
An evaluation of the two techniques, within the constraints of the
tigerfish study, must favour tagging as the logical method to use, The
reasons may be summarised as f ollos:
a) Tagging is the simpler method, requiring only a small, light
tag gun and tags. Conversely the spray-marking technique requires hea
bulky equipment subject to the caprioiousnes of faulty regulators and
leaking valves.
'o) It was found that the nozzle o± the spray gun tended to clog-up
periodically under the damp conditions in which the work was conducted, Ne
such fault lay with the tag gun.
The argument that the spraying is a much quicker technique proved
unfounded in our exercise.
A severe shortcoming of the spray marking technique was the very
rapiddeterioration of the mark when fish were handled roughly. Under
similar conditions tags were found to remain securely in place.
Detection of tagged fish is far easier than sprayed fish. Scanning
each individual fish with U.V. lights proved to be a laborious arid time
consuming job. Further, in tagging there is far more potential for
recaptures to be recorded through anglers and commercial fishermen.
r) In terms of capital outlay, maintenance and operation1 tagging is
more cost-effective than spray-marking.
5. Conclusions.
Marking techniques have numerous applications to fish biology in Lake
Kariba arid will remain an important ecological tool. The advantages of
simplicity, flexibility and cost effectiveness has made tagging the
preferred marking technique for local conditions.
-7-
Part 2 Estimatipns of Tigerfish Biomass based on mark end recapture
methods (Petersen Method).
Introduction:
The marking and recapture of fish is one of the principal techniques
employed in the estimation of fresh water fish populations (Robson & Reiger,
1968). Petersen developed the practice of using marked fish to estimate
populations in closed bodies of water towards the end of the last century
(Ricker, 1975).
The method involves marking fish from a population, releasing them,
and then taking a subsequent sample and examining it for marked fish. The
population size, N, is then estimated by the formula:
N= M.C.
R
Where, N size of population,
M number of fish marked,
C = sample taken for census,
R = number of recaptured marks in sample.
The formula was slightly modified by Chapman (1951) to give ari
unbiased estimate of population size and now becomes:
= CM + i)(c + i)
R+ i
This method was used In 1977, 1978 and 1979 in an attempt to estimate
the standing crop of tigerfish in the Sanyati Gorge, Lake Kariba.
Materials and Methods:
The spray-marking arid tagging techniques have been described in Part
i of this report.
The tigerfish were generally captured with a purse-seiner using
light-attraction in the Sanyati Gorge. In each case a commercial fishing
company was asked to undertake the capture exercises. The Sanyati Gorge
was considered the most suitable locality or the mark and recapture
programme because of the congregation of mature fish there prior to their
spawning run Generally the exercises were completed in late November
eaQh year, just before the start oí' the main rains.
2,1 First mark and recapture exercise
- 1977.
The first exercise was carried out on the night of 5th December 1977,
using a ohircmila net and three light boats, Two hauls were made at each
light boat and a total of 703 tigerfish marked. Recaptures were done with
the same fishing unit on the nights of the 9th, 13th, 14th and 15th
December,
2.2 Second mark and recapture -
This exercise was abandoned because of very poox weather,
2,3 Third mark and recapture - 1979.
Two sampling stations were chosen, one at the first crossroads and
the other about 1,5km nearer the mouth of the gorge. The captures were
made with a purse-seine net measuring 100m x 20m and the fish were
attracted by means of a light boat at each station. The recaptures were
made on the following night, 24 hours after the marking exercise, The
same stations were chosen and it was considered that 24 hours between
marking and recapture was sufficient to allow the marked fish to mingle
with the population without migrating too far from the experimental area,
All the reepatured fish were returned to the factory at Kariba for mark
detection.
3, Results and Discussion.
The results for the 1977 and 1979 mark and recapture exercises are
summarised in Table 1.
L1 : lieSult3 of Lk and Rea pure exeres.
ïz'A NO. 1AXED NO. REOàPTtJR iO. .LHKD FIH /T.
IN bMPJ.i RCATURD FIbH (kg.)
An adjusted Petersen estimate vtas applied to this data to obtain ai
estimation of biomass and the results are shown in Table 2. lso included
in the table are the biomass estimates f o:r 1976 (L..K.F.R,I., unpublished
data) for comparison.
* The Petersen estimate of 45 401 tigerfish in 1979 related to a very
small sampling area, and was therefore adjusted to inoludo the entire gorgo,
assuming a uniform distribution of tigerfish throughout the gorge. The two
sampling stations were assumed to be representative of only a third of the
Table Estimates of Tigerfish populations.
YEAR NO. FISH BIOMASS IN TONNES kg. /ha
1976 1 1 936 968 1976 564, 6
2 1385942 1414 404,0
3 237 328 76 21,7
4 292 218 140 40,0
5 549 108 417 119,1
1977 1 30096 31,3 89,0
2 306 62e 300,5 85,9
3 594 920 392,6 112,2
4 521 249 302,3 86,3
1979 1 45481 71,4 20,4
* 140 000 210 59,5
1979 2RAYED TAGGED RÁYD TiGUED
2096 984 3253 4 68 1,57
1977 703 341 7 1 04
2631 5 0,i4
4279 4 0,66
3012 3 0,56
- lo -
gorge area, and so the adjusted estimate was 140 000 fish,
The Petersen estimates of tigerfish biomass show a great deal of
inconsistency. The 1976 estimates are very variable and rango extremely
high, A figure of 564kg per ha., or two million fish for th Sanyati
Gorge, is without doubt an overestimation. The estimates were again
variable in 1977 and high compared to the 1979 figure. One reason for
this could be poor tag recovery in 1976 and 1977. In 1976 a total of 20
tags were recovered during the course of five reoapture exercises, while in
1977 the total was 19 during four recaptures. In 1979, 68 tags were
recovered from a single recapture exercise and there is no doubt that the
larger percentage tag recovery, the more accurate the final estimate wì]l
be. Another reason could have been the time interval betweGn the work and
reoapture phases of the exercise. During the 1976 and 1977 programmes, at
least a week elapsed between the marking and recapture. This may well have
resulted In marked fish migrating out of the area, resulting in fewer tag
recoveries and exaggerated estimates of biomass. The 1979 exercise lasted
48 hours, which allowed sufficient time for the marked fish to be absorbed
into the unmarked population while not enough time for large scale
movement of marked fish out of the area. Consequently, the 1979 mark and
recapture programme was considered more successful than previous attempts,
although the final estimate of biomass may not be realistic. However,
data from commercial catches and angling have suggested that the tigerfish
population has decreased over the last two years, and the results of the
mark and recapture programmes do reflect this trend.
4. Conclusions,
Mark and recapture techniques for the estimation of population size
of tigerfish cannot be considered completely reliable for Lake Kariba.
The method has a number of limitations, some of which are particularly
applicable to Kariba. Conditions which must be met include (Ricker,
1975):
- 11 '
Marked fish must auff er the same fiaftral mortality as unmarked
fish, i.e. mortality due to marking should be neglible.
Marked fish must be equally vulnerable to fishing as unmarked
fish.
e) Marks should not be lost.
Marked fish must become randomly mixed with unmarked fish upon
release,
There should be no emj.gration of marked fish during the exercise.
There should be only a negligible amount of recruitment to the
eatchable population during the exercise, i.e. no immigration.
Our work has shown that there is low mortality amongst marked
tigerfish and that mark retention is good; at least during the mark and
recapture exercise. However, the question of emigration and immigration
of fish from and to the gorge during the mark and recapture exercises
could well invalidate our estimates. In addition, we may not have marked
sufficient tigerfish in our programmes to give meaningful estimates.
Although the method cannot be used for estimates of absolute biomass, it
has reflected the general downward trend in the tigerfish population in
Basin 5.
However, while the method may have limited use in poilation
etimato, marking does have application in other fields in tigorfish
biology in Kariba and i being used in studies of its growth, movement
and distribution,
ACKNOWLEDGETENTS
Mr. R. Cameron gave valuable advice on all technical aspects of the
study. Sgt. Chris Gahamadze assisted in sampling and rnvId.ng.
12 -
REFERENCES
Hennick, D.F. & Tyler, R.W. (1970) Eperimental marking of emergent pink
salmon (Oncorhyncus gorbusoha) fry with sprayed fluorescent pigment.
Trans. rn. Fish Soc. 99 (2) 397-400.
Phinney, E., et al. (1967) Mass-marking young balmonids with fluorescent
pigment. Trans. Am. Fish Soc. 96 (2) 156-162.
Ri.cker, W.E. (1975) Computation and interpretation of biological
statistics of fish populations. Bull. Fish. Res. Boaid Can. 191
38 2p.
Robson, D.S. & Regier, H.A. (1968) Estimation of population nunther and
mortality rates : In Rickor, W.E. (Ed.) Methods for Assessment of Fish
production in fresh waters. I.B.P. Handbook No. 3.
White, L.E. (1976) Fluorescent pigment retention by pink salmon miked
as soriess fry. The Frog. Fish Cult. 38 (4) 184-185.




An evaluation of mark and recapture techniques for estimating tigerfish biomass in Lake Kariba

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