Transcript Unit 8 (Fisheries Assessment)

UNIT 8:
Fisheries assessments
Fisheries data
Why do we need fisheries data?
FAO (2005): “Information is critical to EAF. It underpins the formulation of
national policies, the development of management plans and the
evaluation of management progress.”
Fisheries information can be biological, ecological, economic, social
or cultural. It can be documented or oral history.
Fisheries information tells us about
- Current fishery status
- Fishery trends through time
- Management effectiveness
All information types should be used where possible (scientific data
– traditional knowledge). But remember, we will always be lacking
information!
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Data in the Pacific
Govan (2011): “To date the financial costs of scientific research
and monitoring appear to have far exceeded investments in
actual management of coastal areas. Using locally available
information with simple approaches to community monitoring
is a cost effective solution, and collaboration with government
or regional technical agencies for generating highly technical
and specific information such as stock assessment, is another.”
In the Pacific:
• Simple data collection approaches will generally be warranted.
• Need to identify approaches in consultation with stakeholders.
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Data types
Traditional knowledge/anecdotes
- simplest form of data
- needs stakeholder/community consultation
- collect using interviews with community members, especially
elders or through community meetings
- need wider community involvement
- issues and management needs can be determined by
consensus
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Data types
Catch and effort data
Catch = how much is caught (weight or numbers)
Effort = how long fishing; how many fishers; how many nets;
length of nets
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Data types
Catch and effort data
• Use these to calculate Catch per Unit Effort (CPUE) = a
measure of relative abundance
Examples:
- number of sea cucmbers collected for every hour spent
collecting them for each collector;
- weight of a target species caught per hour of line fishing for
each collector and each fishing line used
For example:
Catch (C) = 36 kg; Effort (E) = 6 hours; Fishers (F) = 2
CPUE = (C/E)/F = (36/6)/2 = 3 kg/fisher/hour
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Data types
Size data
• Measure weight and/or size of all fish caught (sub-sample)
• Can be done by fishers themselves, landing sites or at markets
• Calculate average size:
Totals
Fish #
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2
3
4
5
6
7
7
Fish length (cm)
32
34
36
29
44
35
43
253
Average fish length = 253/7 = 36.14 cm
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Data types
Underwater Visual Surveys (UVS)
• In-water (SCUBA or snorkel) surveys of fish/invertebrate numbers
and/or habitats
• Can collect:
• Species numbers per area (density = relative abundance) and sizes
• Species diversity
• Habitat types and characteristics
This approach requires training and is more resource intensive
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UVC sample data sheet
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Data types
Biological samples
• Includes gonads and otoliths
• Determine sex, maturity,
reproductive status, age & longevity
• Derive:
• Sex ratios
• Size/age at maturity
• Collecting data of this type
• Spawning seasonality
requires resources and
• Age structure
training.
• Growth rates
• Mortality rates
• Careful consideration of
• Longevity
resources and management
needs is required.
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Data types
Social/economic data
• Why fisheries benefit communities
• Can help ensure these benefits continue
• Data collected by interviews with community members
• Data types include:
• # of fishers, dependence on fisheries
• income derived from fishing
• % of total income derived from fishing
• profitability
• use of harvested fish
• fishers’ involvement in decision-making
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Data type
How collected
Traditional
knowledge/anecdotes
Community meetings;
individual surveys with elders
Catch and effort
Record fisher catch (numbers
per species) and how long
fished, either by surveys or
logbooks; regular fishing
‘surveys’ by fisheries officers
Size
Fishers or fisheries officers
record length and/or weight
of fish caught; fish measured
in the marketplace
What used for
Important fishery sites;
indication of historical
fishery health (species,
sizes, locations); species
life history
Catch-per-unit effort
(CPUE) used as an
indicator of relative
abundance; used to
determine population
trends
Average size (length or
weight) can be calculated
and monitored across:
species, years, areas, etc
Numbers/transect give an
estimate of relative
Cost
effectivenes
High
Medium
Medium
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Catch and effort
Size
Data type
Traditional
knowledge/anecdotes
Underwater Visual
Surveys
Catch and effort
Biological
Size
Social/Economic
per species) and how long
fished, either by surveys or
logbooks; regular fishing
‘surveys’ by fisheries officers
Fishers or fisheries officers
record length and/or weight
of fish caught; fish measured
How collected
in the marketplace
Community meetings;
SCUBA or snorkel transects to
individual
surveys with elders
record species number, size,
habitat type, etc
Record fisher catch (numbers
per species) and how long
Samples
can by
besurveys
collected
fished,
either
or
directly
independently
of
logbooks; regular fishing
fishers; samples can be
‘surveys’ by fisheries officers
indicator of relative
Medium
abundance; used to
determine population
trends
Average size (length or
weight) can be calculated
Medium
and monitored across:
Cost
What used for
species, years, areas, etc effectivenes
Numbers/transect
give an
Important fishery sites;
estimateof
ofhistorical
relative
indication
abundance;
species
fishery
health (species,
High
diversity; habitat
sizes, locations); species
Low
changes. These can be
life history
monitored through time
effort
toCatch-per-unit
determine population
(CPUE)trends
used as an
indicator of relative
Used
to determine
sex
abundance;
used to
and age to derive: growth
determine population
rates, age/size at
collected from fisher catches
trends
maturity, sex ratios, sex
and/or
Samples
Fishersmarketplaces.
or fisheries officers
Average
sizefecundity
(length or
change,
includelength
gonads
and otoliths
record
and/or
weight
weight) can be calculated
Determine
how across:
fisheries
of fish caught; fish measured
and monitored
Survey
with
benefityears,
communities;
in theinterviews
marketplace
species,
areas, etc
community individuals
derive strategies to
Numbers/transect give an
ensure benefits continue
Medium
Low
Medium
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High
Activity
DVD: Second half of Module 1
Activity 8.1: Identify examples of different fisheries data, how
collected and how used in fisheries management?
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Use of CPUE
Russ et al (2003)
Apo Island,Philippines
use of CPUE data
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Use of size data
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A 35 cm minimum
size limit was
introduced in 2005
after community
concerns of fewer
and smaller fish.
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Average size (cm)
Average fish size
from local catches
of grouper over an
11 year period.
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35
30
25
20
15
10
5
0
2000
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2002
2004
2006
Year
2008
2010
201
Use of UVS data
Russ et al (2003) Apo Island, Philippines: use of UVS data
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Indicators
Indicators & reference points
• Many data types can be used as an Indicator
• An indicator will inform us about changes in the resource
we are managing
• It will also inform how well particular objectives are being
met
• Based on the objective the desirable level of the indicator
should be identified. This is called the target reference level.
• Also, a level below which the indicator goes is undesirable
should be identified. This is called the limit reference level.
• How well the indicator is perfomring against reference levels is
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called the performance measure
Indicators
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Use of indicators
An example of the use of UVS data at SPC workshop (see Box
13, SPC, 2010):
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Other analyses
There are many other more complex analyses that use fishery
data to describe populations dynamics including:
• Growth
• Mortality
• Yield per recruit
• Biomass dynamic models
• Age structured models
These methods require robust data on size, age and catch
• Should be used only in data- and resource-rich situations
Photo:
Dave
Welch
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Unit review
Fisheries data are important to inform about:
- Current fishery status
- Fishery trends through time
- Management effectiveness
Collection of data should be dictated by resource capability
- Simple approaches are often needed
Indicators are the data we use to measure fisheries status and
management perfromance
There are many different data types:
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Data type
Traditional
knowledge/anecdotes
How collected
Community meetings;
individual surveys with elders
What used for
Important fishery sites;
indication of historical
fishery health (species,
sizes, locations); species
life history
Catch-per-unit effort
(CPUE) used as an
indicator of relative
abundance; used to
determine population
trends
Average size (length or
weight) can be calculated
and monitored across:
species, years, areas, etc
Numbers/transect give an
estimate of relative
abundance; species
diversity; habitat
changes. These can be
monitored through time
to determine population
trends
High
Unit review
Catch and effort
Record fisher catch (numbers
per species) and how long
fished, either by surveys or
logbooks; regular fishing
‘surveys’ by fisheries officers
Size
Fishers or fisheries officers
record length and/or weight
of fish caught; fish measured
in the marketplace
Underwater Visual
Surveys
SCUBA or snorkel transects to
record species number, size,
habitat type, etc
Biological
Samples can be collected
directly independently of
fishers; samples can be
collected from fisher catches
and/or marketplaces. Samples
include gonads and otoliths
Used to determine sex
and age to derive: growth
rates, age/size at
maturity, sex ratios, sex
change, fecundity
Survey interviews with
community individuals
Determine how fisheries
benefit communities;
derive strategies to
ensure benefits continue
Social/Economic
Cost
effectiveness
Medium
Medium
Low
Low
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High
Assessments
Activity 8.3: In two teams use simulated data to calculate some
basic fisheries statistics. Report back on methods, results, and
the relevance to management.
DVD: Fish and People Module 5: Fish and people: today and
tomorrow
15 minute personal review: unit review, students to review main
concepts of unit in the course notes, contribute any new words
(new to them) to their own personal glossary in the back of
their notebook (local language equivalent terms should also be
recorded where possible)
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Homework
Answer one of the following:
1. Describe a method that is used to assess a fishery that you
are familiar with and explain how the information is used
in management. Do you think it is effective, or do you think
that there is a better way to do things?
2. If you had an unlimited amount of money, design a plan to
collect data on a fishery you are familiar with. Once you
have your plan, imagine that after a few years you lost the
funding to collect all but one piece of the data-what one
thing would you keep collecting and why?
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