Cpue

 Fishery-dependent data collection is one of the
most valuable tools available to fishery managers.
 The management plans put into effect based on
this type of sampling will only be as good as the
data collected. It is critical that managers
determine what is the most important data to be
collected and implement some system of data
recording before signs of overfishing occur.
 One of the biggest mistakes fishery managers
make is waiting until the populations are in peril
before initiating some type of management plan.

 Catch estimates are used to illustrate the species
composition of individual fisheries and utilization
rates, monitor quotas, estimate fishing mortality,
and to calculate Catch Per Unit Effort (CPUE).
 Includes both the target and non-target species.
 These estimates include not only what is sold at
port, but also that which is discarded or utilized as
bait at sea and that which is retained for personal
consumption or transferral by the vessel’s crew.

 Catch disposition is the manner how certain
species of catch are disposed (e.g., saved for
market, used for bait, discarded live, discarded
dead, discarded after removing fins, etc.).
 It also refers to the final fate of the catch how
fishermen disposed them.
 Disposition data taken by at-sea observers allow
fishery managers to acknowledge the cryptic
mortality incurred by all species caught and can
help detect declines in abundance

 Catch per unit effort - the number of fish caught by
an amount of effort.
 Typically, effort is a combination of gear type, gear
size, and length of time the gear is used.
 Catch per unit of effort is often used as a
measurement of relative abundance for a particular
fish; the total catch divided by the total amount of
effort used to harvest the catch.
 CPUE is an indirect measure of the abundance of a
target species. Changes in the catch per unit effort are
inferred to signify changes to the target species' true
abundance.
 A decreasing CPUE indicates overexploitation while
an unchanging CPUE indicates sustainable
harvesting.

 Catch per unit effort (CPUE) is a ratio commonly used to
eliminate temporal and regional trends in fish stock
abundance.
 The “catch” portion of the measure may be expressed as
the number or weight of the entire catch, a selected subset
of the catch, or a particular species in the catch.
 The “unit effort” portion of the rate usually refers to the time
a uniformly designed and employed piece of fishing gear is
deployed in the water. In the absence of uniform gear use,
CPUE can be applied on a coarser scale utilizing whatever
effort data is available.
 Units of effort are dependent on the type of fishing gear
used and can use (in increasing levels of fine scale
reliability) such measures as the numbers of vessels,
vessel-days, gillnet or longline sets or number of hook
hours, and trawl or gillnet hours.

 Advantages of CPUE as index of abundance
1. It does not interfere with routine harvesting operations,
and data area easily collected.
2. The data are also easy to analyze, even for non-
specialists, in contrast to methods based on transects.
 To yield meaningful result, the effort should always be
standardized (e.g. number of traps or duration of
searching),

 Although CPUE is a relative measure of abundance, it can
be used to estimate absolute abundances. The main
difficulty when using measures of CPUE is to define the
unit of effort.

 Catch (total)
 refers to all species taken together and is usually computed
within the logical context of a) a limited geographical area
or stratum, b) a given reference period (i.e. a calendar
month) and c) a specific boat/gear category.

 Effort (estimated from sample) is expressed uniformly in
total number of boat-days within the same logical context
used for total catch and overall CPUE.
 CPUE (sample, overall Catch-Per-Unit-Effort)

 is an overall average deriving from sampling and
expressing how much fish (all species) is caught by a unit
effort. Sampling context is the same as that for the
estimated catch.


 Fishing Effort. The amount of fishing gear of a
specific type used on the fishing grounds over a given
unit of time e.g. hours trawled per day, number of
hooks set per day or number of hauls of a beach seine
per day.
 When two or more kinds of gear are used, the
respective efforts must be adjusted to some standard
type before being added or the total fishing gear in
use for a specified period of time.
 When two or more kinds of gear are used, they must
be adjusted to some standard type. Sometimes
referred to as Effective fishing effort.

 Fishing effort measures
 Three levels of precision of fishing effort are identified in reporting
forms. Data should be provided for all three levels indicated as
categories.
Category A. refers to a detailed unit of measure, e.g. hours fished or
number of sets, etc. These units of measure will vary with the gear
used.
Category B. refers to "number of days fished", i.e., the number of days
on which fishing took place. For those fisheries in which searching is a
substantial part of the fishing operation, days in which searching but no
fishing took place should be included in "days fished" data.
Category C. refers to "number of days on ground" in addition to days
fishing and searching also all other days while the vessel was on the
ground should be indicated.

 The unit of effort is expressed in different ways depending
on the type of gear and operation
 No. of sets: Number of times the gear has been set or shot,
whether or not a catch was made. This measure is appropriate
when school size and packing density is related to stock
abundance or sets are made in a random manner. (Surrounding
nets, purse seine, beach seine)
 Searching time: This represents time on the grounds less time
spent shooting net and retrieving the catch as well as time hove
to. This measure is complicated by the use of aircraft spotting as
well as by the dissemination of information from vessel to vessel.
The measure is appropriate when school size and packing
density is unrelated to stock abundance and a set is only made
when a school has been located.(Surrounding nets, purse seine,
beach seine)

 No. of hours fished: Number of hours during which
the gear was in the water and fishing. (Boat seines,
dansih seines, trawls, dredges).
 No. of effort units: Length of nets expressed in 100-
metre units multiplied by the number of sets made (=
accumulated total length in metres of nets used in a
given time period divided by 100). (set or drift gill nets)
 No. of effort units: Length of net expressed in 100-
metre multiplied by the number of times the net was
cleared.(fixed gill net)

 No. of effort units: Number of days fished times the number of
units hauled. (traps, uncovered pound nets)
 No. of effort unit: Number of lifts times the number of units (=
total number of units fished units in a given time period.
(Covered pots, fyke nets)
 No. of hooks: Number of hooks used in a given time period.
(longlines, set or drift).
 Thousand of hooks: Number of hooks fished in a given time
period divided by 1000. (longlines, set or drift)
 No. of line-days: Total number of lines used in the given time
period. (handlines, pole and line, troll line, jigger etc)

 No. of days fished: The number of days (24-hour
periods, reckoned from midnight to midnight) on which
any fishing took place. For those fisheries in which
searching is a substantial part of the fishing operation,
days in which searching but no fishing took place
should be included in "days fished" data. (All gears)
 No. of days on grounds: The number of days (24-
hour periods, reckoned from midnight to midnight) in
which the vessel was on the fishing ground, and
includes in addition to the days fishing and searching
also all the other days while the vessel was on the
ground. (All gears)

 No. of days absent from port: The number of days
absent from port on any one trip should include the day the
fishing craft sailed but not the day of landing. Where it is
known that fishing took place on each day of the trip the
number of "days absent from port” should include not only
the day of departure but also the day of arrival back in port.
Where on any trip a fishing craft visits more than one
"fishing area" (as defined for statistical purposes) and
appropriate fraction of the total number of days absent from
port should be allocated to each "fishing area" in proportion
to the number of days spent in each, so that the total
number of days absent on the trip will be the sum of the
number of days allocated to all of the different "fishing
areas“ visited. (All gears)

 No. of trips: Any voyage during which fishing took
place in only on "fishing area" is to be counted as one
trip.When in a single trip a craft visits more than one
"fishing area" an appropriate fraction of the trip should
be apportioned to each "fishing area“ in proportion to
the number of days spent fishing in each, so that the
total number of trips for the Major Fishing Area as a
whole will be the same as the sum of trips to each
“fishing area". (All gears)
 No. of fishermen: the number of fishermen operating
the gear over the time spent in fishing. Usually
express in manhours. (gill nets, handlines etc.)
 Vessel’s engine Horsepower. Refers to the fishing
boat engine’s horsepower. (Trawl)

 Gill net
 Determine the panel size, soaking time and catch.
 Example:
 Consider a situation in which the total fishing hours
was 300, the total panels fished was 5, and total
number of female sharks caught was 10.
 Unit effort is calculated by multiplying the total hours
(300) by the total number of panels (5), resulting in
1500 panel-hours of effort. The female catch (10
sharks) then is divided by the panel-hours (1500),
resulting in a CPUE of 0.0067 females per panel-hour.

 If a CPUE measure is a small number, as in this
case, the CPUE’s numerator and denominator
often are multiplied by an exponent of 10 (e.g., 10,
100, 1000) to produce a larger and more easily
expressed CPUE numerator.
 For example, if our CPUE of 0.0067 female sharks
caught per panel-hour is multiplied by 1000, the
result is a more readily understood catch rate of
6.7 sharks caught per 1000 panel-hours.

 Longline
 To calculate the catch rate of sharks per hookhour,
one must know the total number of sharks captured
while fishing in depths of known depth, the total
number of hooks used while fishing in this depth
range, and the total time the gear was in the water in
this depth range.
 Example:
 Assume 12 sharks were caught on 100 hooks fishing
for 12 hours. The fishing effort, then, is 1200 hook-
hours (100 hooks x 12 hours) and the CPUE is 0.01
sharks per hook-hour (12/1200), which also can be
expressed (after multiplying by 100/100) as 1.0 shark
per 100 hook-hours fishing at depths of 25-50 m.

 Raising Factor- is the factor by which the numbers in the
sample have to be multiplied to give the total numbers in
the population sampled.
 Raising Factor = No. of days in month
 No. of sampling days
 Raising factor is used for production estimates
 Production Estimates
 Estimated production per boat of the different gears per site
can be computed from the monthly total catch of each gear
per site divided by the total number of boat landings.
 The result will be multiplied by the raising factor to
determine the raised catch per boat per month.

Example:
Determine days in a month and samplings days(January – 31/7)
RF = 4.43, Feb (28/6), 4.67, March (31/5), 6.2, Apr (30/4) 7.5
January February March April
1 20 23 27 35
2 15 30 30
3 25 21
4 30 25 22 18
5 35 26 15 16
6 18 30
7 20 18 23
Total (kg) 163 143 117 99

 The raised catch per boat per month can be computed
by the formula:
 Raised catch = Total Catch x raising factor ;
 No. of boat landed
 If there are 3 boats then RC = (163/3) * 4.43= 240.7 kg for January
1 20 23 27 35
2 15 30 30
3 25 21
4 30 25 22 18
5 35 26 15 16
6 18 30
7 20 18 23
Total (kg) 163 143 117 99
240.70

 The raised catch per boat per month can be computed by the
formula:
 Raised catch = Total Catch x raising factor ;
 No. of boat landed
 If there are 5 boats then RC = (143/5) * 4.67= 133.56 kg for February
1 20 23 27 35
2 15 30 30
3 25 21
4 30 25 22 18
5 35 26 15 16
6 18 30
7 20 18 23
Total (kg) 163 143 117 99
240.70

 The length frequencies can be raised to the
corresponding raise in weight with the following
formula:
 Raised length = Frequency x raising factor;
 Raising factor = Total weight
 sampled weight

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