Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 83
4
Data Requirements for Population Assessment
Three kinds of data are required in developing population assessment
models: (1) total catch (or total removals if including bycatch); (2)
demographic information on the size, age, and taxonomic composition of
the fish removed; and (3) indices of relative abundance. Total removals
by size and age are used to measure the level of mortality incurred by
different components of the population. Abundance indices serve to
denote relative change in the fish population over time. These indices can
be based on data collected directly from the fishery (i.e., fishery-
dependent indices, such as catch rate indices from fishery logbooks) or
data collected independent of the fishery (i.e., fishery-independent
indices, such as research surveys). Information on these three kinds of
data ideally should be obtained from all fisheries and gear types involved
in removals from the population.
Commercial fisheries have been the main source of fishery-
dependent data used in developing quantitative population assessments;
however, more and more often, data from recreational fisheries are relied
on to complement data collected from other sources or as the sole source
of information for some assessments. This increased demand on recre-
ational fisheries data necessitates a discussion of the survey methods
used in recreational fisheries and whether these methods provide data
adequate for assessment purposes.
Certainly the survey design and data collection recommendations
outlined in earlier chapters are likely to improve the information used for
population assessments. In particular, the establishment of mandatory
logbooks to monitor catch for all vessels in the for-hire sector would
provide more in-depth data--the kind of data that would be ideal for use
in population assessments. Logbooks could provide fishing location, time
of day, and weather conditions, all of which could be helpful in inter-
83
OCR for page 84
84 REVIEW OF RECREATIONAL FISHERIES SURVEY METHODS
preting catch rate estimates. Onboard observers also could be used for
one-time studies into catch rate, such as investigations into the influence
of the kind of bait used or the depth being fished, or they could assist in
the collection of specific oceanographic and meteorological data during
the fishing trip.
In addition to identifying reliable data sources, data quality must be
assessed and accounted for appropriately. Modern statistical population
assessment models are capable of dealing with data characterized by
different variance structures, or even unknown variance. Not surpris-
ingly, what goes into the model influences what comes out, and the
accuracy of population estimates is influenced by the accuracy of the
data used. Statistical fitting procedures used in these models often
assume variance structure for data inputs that are not likely to be met by
most recreational fisheries sampling programs. Assessment models can
be modified to accommodate such data characteristics, but these
characteristics first must be identified and quantified at the source level
of the surveys.
Inconsistencies in how dockside samples are collected can be
particularly aggravating when conducting population assessments. For
example, the lack of a common knowledge base among anglers, data
collectors, and data users with regard to taxonomic identification will
bias mortality estimates for all species concerned. Population assessment
scientists must have confidence that species designations are accurate
and applied consistently in the sampling process. Therefore, biological
data obtained from intercept surveys must be consistent with categories
used in assessments.
Two additional issues complicate the usefulness of recreational
fisheries data for population assessment. One concern is the challenge
faced by population scientists in interpreting catch and effort data
recorded from recreational fisheries surveys in ways that are analogous
to commercial and scientific indices to measure changes in relative
abundance. Obtaining a measure of catch per unit effort (CPUE) that is a
true measure of relative abundance is challenging since the measures for
these different data sources are compiled with different purposes in
mind. For commercial fisheries, catch and effort are obtained simul-
taneously from individuals in association with an area fished and species
targeted; thus, CPUE can be seen as a direct measure of relative
abundance for a given area and species, as long as fishing efficiency and
catchability do not change. In recreational fisheries surveys, such as the
Marine Recreational Fisheries Statistics Survey (MRFSS), CPUE is
obtained from individuals and is expanded by an estimate of effort across
OCR for page 85
DATA REQUIREMENTS FOR POPULATION ASSESSMENT 85
all individuals to develop an estimate of total catch. For these surveys,
recreational CPUE typically is not associated with specific areas or even
with specific target species; thus its applicability as a relative abundance
measure is clouded by its design as a means to obtain total catch in the
survey. To better address these issues, a closer look needs to be taken at
effort and CPUE calculations as they are carried out in a recreational
fisheries context.
The other complicating issue is how catch and release influences the
accuracy of total removals reported and the subsequent underestimation
of fishing mortality. Underreported removals occur when fish are
released but subsequently die from capture and handling. If catch-and-
release survivorship rates are not known, the proportion of releases that
die is not known. This is further complicated by the fact that the number
of releases (by species) probably is not estimated accurately either. The
numbers of released fish are obtained from the intercept survey, and the
accuracy of this information may be dependent upon the memorableness
of the release event. Most anglers would remember releasing a marlin but
may be uncertain as to how many of a more common species, such as
striped bass or mackerel, were released.
EFFORT AND CATCH PER UNIT EFFORT CALCULATIONS
Stock assessment scientists often use the reported CPUE from
commercial logbooks as a fishery-dependent index of abundance. The
basic assumption is that catch (C) is a function of fishing effort (E), and
catchability of the fish to the fishing gear used (q) is constant over time,
such that:
C = f(E,q,N)
where N is the population size. Effort is usually a function of time spent
actively fishing (trawling) or the time a specific amount of passive gear
(e.g., traps, pots, longlines) was in the water. The simplest form for this
function is a proportional relationship:
C = E × q× N
and as a result:
OCR for page 86
86 REVIEW OF RECREATIONAL FISHERIES SURVEY METHODS
CPUE = C = q × N
E
Assuming a constant catchability, CPUE should track changes in
population size over time.
In the MRFSS, the catch per trip from the onsite interview survey is
often referred to as a catch rate or CPUE, but this estimate is rarely the
one used in stock assessments when defining a recreational CPUE index
of abundance. The definition of fishing effort, and hence, fishery catch
rate as an index of abundance needs to take into account what species the
effort was directed for and not just the total catch over a set amount of
time.
Holiman (1996) defines three types of effort that can be calculated
from the MRFSS data: target effort, catch effort, and directed effort.
Population assessment scientists must be aware of the presence of these
three different types of effort in the database and understand how they
relate to the problem of estimating relative abundance. Those in charge
of data collection and monitoring also must be aware of these effort types
in order to document them properly but also to insure that the right type
of information can be made available to those in need of it.
Target effort is based on the anglers' identification of their primary
or secondary target species to the intercept interviewer, whether or not
they were successful in catching any of that species. Interviews occur
after the fishing trip is completed; therefore, accepting the angler's
designation of target species after the fact may result in biased estimates,
as some people may report only what they caught as being what they
targeted. This is often referred to as "prestige" bias since it is a result of
anglers not wanting to admit that they were unsuccessful in catching
what they were targeting.
In cases where there are multiple anglers (e.g., head boats) and catch
cannot be separated by angler, total catch is attributed to one angler
(termed "leader" in the MRFSS) who represents the other anglers on the
trip (designated as "followers"). Generally, it is assumed that all
followers fish when the leader fishes for the target species (Holiman,
1996). If followers do not fish when the leader does, the amount of target
effort will be overestimated. However, if the leader does not report a
target species but one of the followers does, it is not assumed that all
followers also targeted that species. This assumption may result in an
underestimate of target effort. The most recent Atlantic bluefish stock
assessment used target effort to define catch rate indices (Lee, 2003) and
OCR for page 87
DATA REQUIREMENTS FOR POPULATION ASSESSMENT 87
therefore might suffer from the difficulties mentioned above. In addition,
for schooling fish species (such as bluefish), there is an increased
probability that if a follower reports targeting that species, the other
anglers did as well.
Catch effort is the effort associated with the successful catch of a
species, whether or not it was targeted. In addition to the issues raised
above for target effort, assumptions have to be made when calculating
the total effort for groups of anglers. Again, all catch, either kept for
interviewer inspection or not available (i.e., filleted, released dead or
alive, given away), is attributed to the leader. However, the number of
angler trips associated with catching these fish is not recorded. That is,
assuming that bag limits exceed one fish per angler, one person may
have caught more than one of these fish. For example, Holiman's code
assumes that if the number of fish is less than the number of anglers, then
the number of trips equals the number of fish because the focus here is
the successful catch of a specific species; otherwise, the number of trips
equals the number of anglers. Effort calculations for the red grouper
assessment simply use all of the anglers when dealing with multiple
angler intercepts (Southeast Fisheries Science Center, 2002).
Directed effort is the effort associated with all catch of a particular
species whether targeted (including unsuccessful catch) or not. The
difference between target effort and catch effort is referred to as effort
associated with incidental catch.
All of the above deal with effort estimates obtained from anglers
interviewed during intercept surveys. However, there is no information
available in the MRFSS on target or other kinds of effort for anglers who
have private access. At present, it must be assumed that this portion of
the angler effort is represented adequately by the sampled portion from
intercepts.
Most stock assessments try to use some form of target effort, and the
main issue is how to calculate the "target but no catch" portion of the
effort in a way that does not rely on the anglers' identification of target
species. Ralston and Dick (2003) use location data from the California
commercial passenger fishing vessel (CPFV) data to restrict black
rockfish data to only those locations where black rockfish had been
caught in at least five separate locations. The latest assessment for red
snapper (Gulf of Mexico Fishery Management Council, 2005a) uses only
trips where at least one snapper was caught or where a catch of species
typically associated with snapper was caught in the past. No-catch reef
trips for hogfish are defined as reef trips using hook and line or spear in
counties where hogfish were not caught in the current trip but had been
OCR for page 88
88 REVIEW OF RECREATIONAL FISHERIES SURVEY METHODS
caught at least once in the period 19822001 (Ault et al., 2003). As
another approach, Stephens and MacCall (2004) describe a logistic
regression approach based on multispecies presenceabsence information
that predicts the probability that the target species would be present
based on other species caught, even if no catch of the target species was
recorded. Methods that depend upon species-complex indices to
determine targeted non-catch trips may be confounded by differential
targeting of the fishery from year-to-year (or season-to-season) on more
desirable species or by changes in the complex arising from different
dynamics of the component species. Also, regulation changes for associ-
ated species may complicate interpretation of species-complex catch
information. While all of these methods are genuine attempts to measure
target effort, confidence in their use in stock assessments will require
more research with respect to multi-species associations and the impact
of species-specific catch regulations.
In recent west coast Stock Assessment Review Panel (STAR Panel)
reports (Pacific Fishery Management Council, 2006), the use of
recreational catch rate data from CPFV logs or Recreational Fisheries
Information Network (RecFIN) data for rockfish and similar species has
come under close scrutiny. The usual assumption of proportionality
between catch rate and abundance used for commercial indices has not
been tested for recreational fisheries. These reports note that recreational
fishing, especially when conducted by the for-hire sector, focuses on
giving the angler a successful fishing experience with respect to the
desirability of and the challenge of landing the species being sought. This
behavior may lead to the targeting of fish in high density areas, resulting
in catch rate indices exhibiting a slower decline than what the actual
population is experiencing (i.e., hyperstability). There are many other
factors also at play in determining what makes a successful fishing
experience (Holland and Ditton, 1992) that may further complicate the
link between recreational catch rate and population size. Technological
improvements (e.g., Global Positioning System [GPS]) are not usually
taken into account when using recreational catch rates as indices of
abundance. In addition, changes in fisheries regulations for the targeted
or associated species may change the relationship between catch rate and
population size. As fisheries become more restrictive with respect to bag
and size limits, the increasing number of releases may result in CPUE
being prone to recapture bias (e.g., lingcod) (King and Haggarty, 2004).
For many fisheries where there, currently, is a small or no com-
mercial component (e.g., rockfish on the U.S. west coast), recreational
catch rates are usually the only abundance indices available for the recent
OCR for page 89
DATA REQUIREMENTS FOR POPULATION ASSESSMENT 89
years. Despite the problems that have been identified with using recre-
ational effort data, assessment scientists need to have access to the best
effort data possible either to determine whether these kinds of data can
be used to monitor abundance or to make the necessary modifications so
the data are useful.
CATCH AND RELEASE
For stock assessment purposes, the total number of fish removed
from the population by the fishery is of more interest than just the
number of fish landed. Total removals are calculated as the sum of those
fish caught and landed or known to be dead upon capture and those fish
that were released (or discarded) but did not survive. There are two types
of catch records in the MRFSS database: type A and B. Type A records
account for fish that were caught, landed whole, and available for
identification by the intercept interviewers. These fish are available for
weight and length measurements, although these measurements may not
always be taken. For type B records, the fish were caught but were either
not kept or were unavailable for identification. These records are further
identified as either type B1 or B2. The former type refers to fish that
were filleted, released dead, given away, or disposed of in some way
other than for types A or B2. Those fish that were caught and released
alive are coded as B2. Total landings from the recreational fishery are
calculated as A+B1 for stock assessments where there are recreational
components. For example, in 2003, recreational landings (A+B1) in the
striped bass fishery were estimated at 2.4 million fish or 11,486 metric
tons (25.3 million pounds) from the MRFSS. These landings constituted
74 percent of the total landings of striped bass by the recreational and
commercial fishery (Atlantic States Marine Fisheries Commission,
2004).
Some fish released alive, as recorded in the B2 records, are expected
to die after being released. This subsequent mortality is often referred to
as a hooking or release mortality and can arise for a number of reasons,
including swim bladders expanding too quickly as a result of fish being
brought up from significant depths. There is also the possibility that fish
exhausted from fighting the angler are more susceptible to predation. In
2003, for striped bass, the B2 catch was estimated at 14.6 million fish.
Assuming an 8 percent hooking mortality rate, catch and release resulted
in an estimated removal of 1.2 million additional fish.
OCR for page 90
90 REVIEW OF RECREATIONAL FISHERIES SURVEY METHODS
The issue of hooking or release mortalities has been the subject of a
number of studies (e.g., Lucy and Studholme, 2002; Policansky, 2002),
but these mortalities have not been estimated for all recreational species.
Specific studies have often limited their attention to particular
combinations of factors, such as hook type, depth range, and temper-
atures, that can be manipulated in an experimental setting. Not all factor
combinations that could be significant may have been studied, but more
to the point, there may not be enough detail on the released fish from the
intercept surveys to determine which, if any, of these factors are
operating at any one time. Although some hooking mortality studies
appear to be reliable for the restricted conditions they apply to, not all are
reliable, and for many species, the hooking mortality associated with
particular gear types under a variety of conditions simply is not well
known. In addition to providing information for stock assessment
scientists, hooking mortality studies also have the potential to improve
management by advising anglers on how to handle and release hooked
fish to increase their chances of survival.
The lack of accurate information for estimating release (or discard)
mortality has been identified as problematic for the red snapper
assessment in the Gulf of Mexico. For red snapper, recreational data
were obtained from three sources:
· The MRFSS (19811998) with some exceptions: (1) no wave 1
data in 1981, (2) no Texas boat mode in 19821984, (3) no
Texas data after 1986, and (4) no head boat sampling after 1985
· The National Marine Fisheries Service's Beaufort Laboratory
head boat survey for all states after 1985
· The Texas Parks and Wildlife Department's coastal sport fishing
survey
Recreational discards data are collected by the MRFSS in the Gulf of
Mexico but are not available for Texas landings or for landings from
head boats. Mortality rates used for discarded live red snapper differ
according to depth and area and therefore depend upon accurate location
information of where the discards occur across the whole range of the
fishery (see Appendix C).
Many stock assessments convert numbers caught to weight caught.
Weight conversions are based on the length and weight information
obtained from the type A catch; the size compositions of the type B1 and
B2 catch are assumed to be similar to the type A catch--a potentially
OCR for page 91
DATA REQUIREMENTS FOR POPULATION ASSESSMENT 91
strongly biased approach given that one of the main reasons for releasing
fish is that they are below the size limit. At present, there are some
limited programs to capture length, weight, or age data from the
recreational discards (e.g., striped bass lengths are available from vol-
unteer angler logbooks and American Littoral Society data), and, starting
in 2003, California Recreational Fisheries Survey (CRFS) samplers have
measured length and weight of discarded fish from CPFVs and from
onshore anglers. (See Appendix B for more detail on CRFS.)
Another problem is the comparability of discard data between
different recreational surveys that may be combined into a stock
assessment. As an example, recreational catch data for lingcod on the
Pacific coast come from a variety of sources, but not all sources provide
the same level of detail with respect to the condition of the fish caught or
released. For California, the RecFIN database (including the MRFSS)
was used for 19801989 and 19932003. Beginning in 2004, CRFS has
been used in place of the MRFSS in California. Oregon recreational
catch data are provided by the Oregon Department of Fish and Wildlife,
and Washington catch data are obtained from the Washington
Department of Fish and Wildlife (WDFW) Ocean Sampling Program
(see Appendix B). Discard information on numbers and disposition
(released alive or dead) is available from CRFS. On the other hand, only
the number released is available from the Oregon Recreational Boat
Survey data (see Appendix B). The WDFW has collected discard
information from the recreational fishery since 2002 but does not collect
information on the portion of the catch discarded live or dead. In
Washington, 57 percent of the lingcod catch is estimated to be discarded,
but it is unknown how many of the live releases survive. Various
adjustments are made to the catch and projections in the assessment to
account for discard mortality. Yet, recent stock assessments for lingcod
identified the need for better coastwide enumeration of at-sea discards
and mortality of released recreational fish to account for total removals
from the population more accurately.
CONCLUSIONS AND RECOMMENDATIONS
Documentation of the source of the effort available in the
MRFSS, as to whether it falls into the category of target effort, catch
effort, or directed effort, would go a long way in helping population
scientists use this data in an appropriate manner. Population
scientists should work in collaboration with those involved with data
OCR for page 92
92 REVIEW OF RECREATIONAL FISHERIES SURVEY METHODS
collection and monitoring to design data collection protocols and sum-
mary statistics that are appropriate for use in population assessment.
Information on target species and area fished also would make catch and
effort data collected from recreational fisheries more amenable for use in
the development of assessment indicators.
The establishment of mandatory logbooks to monitor catch for
all vessels in the for-hire sector also would be appropriate for the
collection of target effort data. Basic data recorded by the vessel
captain on the number of anglers, actual hours spent fishing, and target
species would get around the complications of the leaderfollower
designations currently being used in the MRFSS. The logbooks also
could record position, time of day, and weather conditions, all of which
could be helpful in interpreting catch rate estimates.
These logbooks would not be considered the sole source of
information, and similar to the commercial fishery, onboard observers
should be used on a sample of the vessels to validate the information,
especially in the case of numbers, species, condition, and size
composition of the released fish. Recall bias of released fish has been
identified as an issue in recreational fisheries (Pollock et al., 1994) and
shown to be significant for salmon fisheries in the Strait of Georgia
(Diewert et al., 2005). These observers also could be used for one-time
studies into catch rate, such as investigations into the influence of the
kind of bait used, depth being fished, and discard mortality, or perhaps
they could assist in the collection of specific oceanographic and meteoro-
logical data during the fishing trip.
Information on targeted effort, such as discussed for the for-hire
sector, could be obtained for private access anglers as part of a panel
survey. Panel surveys could be used to collect a wide range of detailed
data from the previously unsampled private access mode. Participants
could be contacted by telephone or as part of an internet survey. It may
be possible to design these panel surveys in a way that detailed infor-
mation on catch rate and targeted species can be related back to the
larger telephone survey of private sector anglers providing fisherywide
or regional estimates of catch rate for stock assessments. These surveys
also can be used to collect information on the sizes of kept or released
fish. This may require significant training to ensure accurate species data,
but since data will be collected from each participant over a long period
time, this investment in training may be worthwhile.
Representative terms from entire chapter:
marine recreational
