Departmental Reports


Title:

Catch Assessment Survey Design for Monitoring
the Upper Meta River Fishery, Colombia, South America



Author(s):

Malvestuto, S., R. Scully and F. Garzon



Date: 1980



Funding Agency: USAID



Keywords: colombia, fisheries, meta river, catch assessment, international, development



Category: International Funded Research Report



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Summary/Recommendations/Objectives:

Catch and fishing
effort in the Upper Meta River System for

the hydrological
year April 10, 1978 - April 9, 1979, were

estimated using a
statistically designed catch assessment survey

(CAS). The design
was based on CAS methods used at Auburn

University and
incorporated results from a frame survey

conducted during
the 1977 hydrological year on the Upper Meta

River.

Total catch in 1978
was 1,071,366 kilograms from 126,334

Fishing Economic Unit
(FEU)-days where 1 FEU-day was

equivalent to 1.8
fisherman-days. Average catch per FEU-day

was 8.1 kilograms.
Ninety-one percent of the catch came from the

main river and
upper tributaries (70 percent and 21 percent,

respectively). Similarly,
88 percent of fishing effort (FEU -days)

was expended in the
main river and upper tributaries (70 percent

and 18 percent,
respectively). Catch and fishing effort in lower

tributaries,
especially those on the southern side of the Meta

River, were
relatively insignificant.

The annual harvest
was evenly distributed between the high

and low water
seasons. However, because the low water season

was 71 percent as
long as the high water season, daily catch was

actually higher
during low water. This was due primarily to

increased daily
fishing effort within the main river stratum

during the low
water period. Catch per unit effort changed only

slightly from the
high water season (7.9 kilograms per FEU-day)

to the low water
season (8.4 kilograms per FEU-day).

The relative standard
error (RSE) for fishing effort (9.9

percent) indicated
that samples were providing relatively

precise estimate of
this variable on an annual basis. Variation in

fishing effort was
inherently low because artisanal fishermen

live near the river
and their frequency of fishing changes little

within seasons.
Catch estimates were more variable, however,

giving a 1\SE of
25.1 percent for the year; greatest variation was

encountered in the
low water season (RSE = 44.4 percent).

further seasonal
stratification is recommended to reduce

variation in catch
estimates.

Future catch
assessment surveys on the Upper Meta River are

outlined and
sampling schedules within time strata are defined.

The number of time
strata will be increased from two to four

with the addition
of one stratum for the rising and one stratum

for the falling
water season. It is recommended that six samples

be taken within each
time stratum; due to the logistics of

sampling, two or
three samples will be taken during a single field

trip and trips will
be systematically scheduled. The Upper Meta

River will be divided
into two geographical strata, one

composed of all tributaries
and the other composed of the main

river only. Sample
sections will be chosen with nonuniform

probability, with
twice as many samples coming from the main

river stratum as
from the tributary stratum (four samples and

two samples,
respectively).

Application of
nonuniform probability sampling is

recommended for
initial surveys of all river fisheries within

Colombia's Orinoco
System. A pre-survey overflight will

provide initial
sampling probabilities based on number of

canoes counted per
section, and initial time strata will be the

same as defined for
the Upper Meta River. Strata definition and

sampling
probabilities for later surveys can be amended based

on information
gathered during the initial survey.

A 10-year CAS
sampling program for Colombia's Orinoco

System is proposed.
Sampling will be conducted on the Upper

Meta River in
alternate years (from 1978). Six other Orinocian

rivers will be
sampled, one each year, during successive

alternate years
beginning in 1979. These other rivers have much

less potential for
immediate fisheries development than does the

Upper Meta River
and thus merit less sampling effort. After

1989, consolidation
of sampling to include two or more river

fisheries in 1 year
may be feasible, thereby allowing completion

of data collection
necessary for a Schaefer surplus field

model in all
fisheries of the Colombian Orinoco System

within 15-20 years
from 1978. Methods for obtaining estimates of

maximum sustainable
yield and optimum fishing effort at the

community level
based on the Schaefer surplus yield model are

discussed.

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