Standards, Protocols and Guidelines: Salmon Escapement Estimation
Introduction:
All salmon stock management systems rely on estimates of annual and seasonal variations in
total abundance determined at each of several life history stages by a variety of different
methods. Because of the history and focus on adult salmon as a harvestable resource, the most
basic fisheries management system depends on annual assessments of total returns of adults.
Total returns are comprised of all fish of a given species and “stock” accounted for in catch plus
the remainder that manage to escape harvest in fisheries to return as spawners to their freshwater
locations of origin. Consequently, the number of spawners that succeed in returning to a given
lake or stream is also commonly known as the “escapement”. Thus, annual assessments of
salmon escapement and associated variables are critical activities required to satisfy federal, First
Nations/treaty tribal, provincial, and state fisheries agency mandates in several areas including:
(1) stock conservation, (2) compliance with fiduciary obligations to aboriginal fisheries groups,
(3) harvest management, (4) habitat conservation and management, (5) indexing and
maintenance of ecosystem integrity, and (6) stock and habitat research.
The collection of salmon escapement information involves a diverse set of activities including
specification of stream survey enumeration plans, training of field surveyors, data gathering and
documentation, data review and upload, data analysis or synthesis of summary estimates, and
release of the data to both internal (i.e. fisheries agency personnel) and external clients. In
Canada the coordination of these activities is performed by federal (Stock Assessment Division
of Fisheries and Ocean’s Science Branch) or provincial stock assessment groups. In the U.S.
these activities typically are coordinated by the state and tribal fishery managers.
Standards
Standards are intended to provide information of a specific quality, in terms of accuracy,
precision, and reliability, to attain specific objectives, and so the standards for salmon
escapement programs vary depending according to scientific objectives. Ultimately the choice
of standards rests with the principal investigator and balance between program objectives,
resources, and characteristics of the species and environment.
The accuracy, precision and reliability of escapement estimates are affected by characteristics
such as the assessment method, species behaviour, hydrological and other environmental
conditions (as seen in Table 1 below). It is often highly demanding on resources to gain
information about the accuracy (i.e., the amount by which the average of repeated estimates
exceeds or falls below the true value of the indicator in nature) of a specific assessment method
under certain conditions, so such studies are typically rare. However from the limited
information available, there are several types of assessment methods with common aspects of
accuracy, precision, and reliability, while recognizing that exceptions occur (Table 1).
Protocols and Guidelines
Escapement assessment methods are well described in the scientific fisheries literature (see
example references below), including peer-reviewed papers, published manuscript reports, and
text books. However, study designs can vary among locations and species to best achieve a
balance between objectives, resources, species behaviour and environmental conditions which
has contributed to a high diversity among the methods used to estimate salmon spawner
numbers. Typically assessment methods are described in manuscript reports, stream narratives,
or stock assessment reports to communicate the quality of the annual escapement estimate or
assessment program. The following field survey methods have been commonly used to
enumerate salmon spawners:
Fixed Site Surveys
Fences
Fishways
Fixed Location Acoustics
Electronic Gates
Optical Gates
Fishwheels
Traps or Nets
Towers
Mobile Surveys
Aerial Surveys
Fixed Wing Overflight
Helicopter Overflight
Remote Surveys
Ground Surveys
Streamwalk
Streamfloat – Above Surface Observer
Streamfloat – Below Surface Observer
Mobile Acoustics
Mark-Recapture Surveys
Interval Counts
Catch per Unit Effort Surveys
Surveys of other life stages
Redd Surveys
Egg Surveys
Juvenile Surveys (fry, smolts)
Table 1. Characterization of escapement estimates based on associations between survey method, reliability, accuracy and
precision.
Estimate
Type
Type-1, True
Abundance,
high quality
Type-2, True
Abundance,
high quality
Type-3, True
Abundance,
medium
quality
Type-4,
Relative
Abundance,
medium
quality
Survey Method(s)
total, seasonal counts
through fence or
fishway; virtually no
bypass
High effort (8 or more
annual trips), standard
methods (e.g. markrecapture, serial counts
for area under curve
with direct2 survey life,
etc...)
low effort (2-3 trips) of a
standard method (e.g.
peak count method)
expanded by a factor to
estimate true
abundance
high effort (5 or more
trips), standard methods
(e.g. equal effort
surveys executed by
walk, swim, overflight,
indirect2 survey life etc.)
Type-5,
Relative
Abundance,
low quality
low to moderate effort
(1-4 trips), known
survey method but no
expansion factor
Type-6,
Relative
Abundance,
poor quality
low effort (e.g. 1 trip),
use of vaguely defined,
inconsistent or poorly
executed methods
Analytical
Method(s)
simple, often single
step
Reliability (within
stock comparisons)
reliable resolution of
between year
differences >5% (in
absolute units)
Units
Accuracy
Precision
Documentation1
absolute
abundance
actual,
very high
infinite
i.e.+ or zero%
detailed SIL(s), SEN, field
notes or diaries,
published report on
methods
absolute
abundance
actual or
assigned
estimate
and high
actual
estimate,
high to
moderate
detailed SIL(s), SEN, field
notes or diaries,
published report on
methods
actual
estimate,
moderate
detailed SIL(s), SEN, field
notes or diaries,
published report on
methods examining bias
and precision of applied
factors in retrospect
simple to complex
multi-step, but
always rigorous
reliable resolution of
between year
differences >10% (in
absolute units)
simple multi-step
index surveys, but
rigorously calibrated
to estimates of true
abundance (Type-1
or Type-2)
reliable resolution of
between year
differences >25% (in
absolute units))
absolute
abundance
actual or
assigned
estimate
and
moderate
simple to complex
multi-step, but
always rigorous
reliable resolution of
between year
differences >25% (in
absolute units)
relative
abundance
linked to
method
assigned
range and
medium to
high
assigned
estimate,
medium to
high
detailed SIL(s), SEN, field
notes or diaries,
published report on
methods
simple analysis by
known methods, not
calibrated
reliable resolution of
between year
differences >200%
(in relative units)
relative
abundance
linked to
method
unknown
assumed
fairly
constant
unknown
assumed
fairly
constant
complete SEN or
equivalent with sufficient
detail to verify both
survey and analytical
procedures
unknown to poorly
defined; inconsistent
or poorly executed
uncertain numeric
comparisons, but
high reliability for
presence or absence
relative
abundance,
but vague or
no ID on
assessment
method
unknown
assumed
highly
variable
unknown
assumed
highly
variable
incomplete SEN, only
reliable to confirm
estimate is from an actual
survey
Type-7,
moderate to high
any of above sufficient to
medium to
Presence or
any of above
not required
reliability for
(+) or (-)
unknown
confirm survey and
high
Absence
presence or absence
reliable species ID
1. SIL is Stream Inspection Log and SEN is Salmon Escapement Number.
2. Direct or indirect survey life here indicate whether direct observations/estimates are made in monitoring, or indirect extrapolation is used from other studies.
GENERAL REFERENCES (methods for estimating spawning escapement)
Atkinson, C. E. 1944. The problem of enumeration of spawning populations of sockeye salmon.
Int. Pac. Salmon Fish. Comm. Annu. Rep. 1943: 37-44.
Canada Department of Fisheries and Oceans, Pac. Reg., Field Serv. Br. 1986. Fishery officer's
guide to consistency in the collection, recording, and use of sub-district salmon management
data. CDFO Unpubl. manual: 22p.
Canada Department of Fisheries and Oceans, Pac. Reg., Field Serv. Br. 1986. Corroboration
exercises in field counting techniques for the enumeration of spawning salmon. CDFO
Unpubl. manual: 50p.
Fredd, L. C. 1966. Review and analysis of fish counts, counting techniques and related data at
Corps of Engineers dams on the Columbia and Snake Rivers. U. S. Army Corps of
Engineers, Fish. Eng. Res. Program Prog. Rep. 3: 91-95.
Hillborn, R. 1983. Design of the B.C. salmon escapement monitoring system: notes from a
workshop. Misc. Coop. Fish. Res. Unit Rep. 6: 25 p.
Ricker, W. E. 1975. Computation and interpretation of biological statistics of fish populations.
Bull. Fish. Res. Board. Can. 191: 382 p.
Ricker, W. E. (Ed.). 1968. Methods for assessment of fish production in fresh waters. Int. Biol.
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Russell, L. R. 1975. An annotated bibliography on salmonid marking, enumeration and trapping
techniques. B. C. Fish and Wildlife Branch Fish. Tech. Circ. 18: 194 p. Ref #: 1-75
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Griffin & Co. Ltd., London: xvii + 654 p.
Smith, C. J. and P. Castle. 1994. Puget Sound chinook salmon (Oncorhynchus tshawytscha)
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COMPARISON OF METHODS
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