West Coast Groundfish Stocks
In this appendix, we summarize the information available regarding
fishery stock status for each California species. We focus on
estimates of the fraction of lifetime egg production (FLEP, the
lifetime reproductive effort realized on average by a successful
recruit, relative to the unfished value) and the critical replacement
threshold (CRT, the slope at the origin of the stock-recruit curve),
which is the value of FLEP below which a population does not
persist. The amount of data varies by species, and for some only
rough estimates of current FLEP and the CRT are possible. For
some species there has not been a stock assessment to determine
the status, and even for species that have been assessed, the status is
not known with certainty. For some assessed species, assessment
conclusions rest upon speculative assumptions about the CRT. For
all of the species, there are several plausible estimates for both FLEP
and CRT. Here we explain the values chosen for analysis in our
model and the weighting scheme applied to the various combinations of
FLEP and CRT in order to represent the optimistic and pessimistic
future fishery management scenarios. The distribution of
probabilities associated with each scenario for each species is
summarized in Table 2 in the main text. Since the actual values
of FLEP and CRT are poorly known, the process of assigning weights is
subjective and the values chosen here are for illustrative purposes
only. For the optimistic scenario, we generally assigned high
weights to low values of CRT and high values of FLEP. For the
pessimistic scenario, we based probabilities on the contemporary
management success for each species; we made this scenario more
precautionary by assuming higher values for CRT and lower values for
FLEP, especially when less empirical information on those values was
available (Smith et al. 2007).
The information available for each species varies in part because each
is managed by one or both of two different management
authorities. Red abalone and red sea urchin are managed by the
State of California, and black rockfish, cabezon, canary rockfish and
lingcod are also managed under the U.S. federal regional council
process through the Pacific Fisheries Management Council. Because the
definition of overfished (and "overfishing", which typically refers to
the condition of continuing to harvest an overfished stock) differs
between regulatory agencies, we do not use that term to classify
fisheries in our analysis. Rather we focus on whether FLEP of new
recruits is below the CRT, a state that leads to population collapse at
The history of management of abalone fisheries in California is an
example of serial depletion (Karpov et al. 2000), and one species,
white abalone Haliotis sorenseni,
is listed under the Endangered Species Act. Red abalone harvest
is permitted only in northern California (north of San Francisco Bay),
where they are taken in a recreational free-diving fishery only (SCUBA
is prohibited). Because of that the northern California stock was
believed to be protected from overfishing by the presence of a spatial
refuge consisting of the area occupied by abalone that is deeper than
the limits of free diving. In recent years that has not been
viewed as reliable protection, but red abalone densities have been
nonetheless stable over the past decade (CDFG 2005).
There have been some analyses of population dynamics of red abalone
(Tegner et al. 1989), but there has been no stock assessment.
There is some concern over the understanding of population parameters
since recently estimated natural mortality rates (Leaf et al. 2007).
are so high that very few individuals would survive to fishable age
(see Appendix B).
Because no stock assessment has been conducted and there is no estimate
of the CRT or FLEP for this species, we chose a value of CRT = 0.35 and
used FLEP = 0.4, 0.3, and 0.2 in the model, spanning a range of
potential fishery conditions. For the optimistic scenario, we
assigned 100% probability to FLEP = 0.4, indicating a sustainably
fished stock. For the pessimistic scenario, we assumed there was
a 50:50 chance of FLEP exceeding the CRT, and chose weights of 0.5,
0.25, and 0.25 for FLEP = 0.4, 0.3, and 0.2, respectively. This
weighting reflects the data suggesting that population densities have
been stable for several years, indicating that the stock is sustainably
fished, discounted by the observation of long term recruitment failure
in other California abalones (CDFG 2005) and the fact that the
management plan presumes MPAs will be present.
|Red sea urchin
There has also been no official stock assessment of the red sea
urchin. Nonetheless, growth and mortality rates estimated from
size distribution data in the 1990s provide the necessary information
(Morgan, et al. 2000). Those estimates were used to calculate
both YPR (yield per recruit) and EPR (eggs per recruit) (Morgan, et al.
1999, Botsford, et al. 2004). Those calculations indicated FLEP
(EPR) was less than 20 percent of the unfished value. Since that
time, catches have remained steady but currently most individuals are
harvested immediately after reaching legal size (CDFG 2003), so it is
possible that FLEP is actually lower. Nonetheless, we used a
value of FLEP = 0.2 in the model. Lacking an estimate of the CRT,
we used values of 0.35 (conservative) and 0.15
For the optimistic scenario, we placed the full weight on CRT = 0.15,
so that FLEP > CRT. For the pessimistic scenario, we assumed a
50:50 chance that FLEP < CRT, so we assigned a weight of 0.5 to each
value of the CRT, holding FLEP = 0.2.
|West Coast Groundfish
The groundfish species included here all have
stock assessments based on single interbreeding populations over a
spatial scale of hundreds of kilometers. In addition to that
simplifying assumption, they also do not account for ontogenetic
movement of younger rockfish from nearshore to offshore waters.
Nonetheless, these assessments represent the best available information
on the status of these species in most cases.
|Black rockfish (Sebastes melanops)
The most recent stock assessment of black rockfish
(Sampson 2007) assumed a threshold steepness value of 0.6, which
corresponds to CRT = 16% (steepness, h,
is alternative parameter used to describe the slope of the stock
recruit curve; CRT = (1-h)/4h, Martell et al. 2008).
Alternatively, Dorn (2002) analyzed the stock-recruit curves for
several west coast rockfish species using a hierarchical Bayesian
approach. There were insufficient data to estimate steepness for
black rockfish alone, but the overall estimate for all species was h = 0.7, corresponding to CRT =
0.11. A third estimate of CRT derives from the observation that
managing rockfish stocks with a target SPR (= FLEP) of 0.35 in the
1990s produced undesirably low population abundances (Ralston 1998), so
CRT may be in the vicinity of 0.35 for those species (Clark 2002,
As for estimates of FLEP, the stock assessment's model projections of
biomass ages 2 and greater shows a decline to low values in the 1990s
followed by an increase in the late 1990s to a peak near 2005 (third
figure in Executive Summary of Sampson 2007). The coastwide value
of biomass depletion dipped below 40% in the 1990s before
returning to a value of 70% in the mid 2000s (Fig. 31 in Sampson
2007). These values would roughly correspond to FLEP = 0.4 and
FLEP = 0.7. Strictly speaking, biomass depletion does not
necessarily predict FLEP, but if the biomass depletion has not yet led
to decreased recruitment then the two valeus should be similar.
There is one trend in the data in the opposite direction from these
projections: the CPUE in the recreational fishery in California
shows a declining trend since 2000 (Fig. 14 in Sampson 2007).
Another assessment of the status of black rockfish is more closely
focused on local California populations and is based on size
distributions from the California recreational fishery.
Comparison of size distributions in the early 1980s with those in more
recent years indicates the current value of FLEP = 0.13 (O'Farrell and
Botsford 2006). This estimate assumes the size distribution in
1980 is near the unfished state. To the extent that it is not
(i.e., that the size structure had already been substantially altered
by fishing by 1980), this estimate of FLEP is optimistic (i.e., biased
Based on these results, we considered three different estimates of the
CRT for black rockfish (0.11, 0.16, and 0.35) and two estimates of
FLEP: 0.7, based on the depletion estimate from the latest stock
assessment, and 0.13, drawn from O'Farrell and Botsford's (2006)
results. For the optimistic future fishery scenario, we used FLEP
= 0.7 and assigned equal probabilities to the three values of
CRT. For the pessimistic scenario we used FLEP = 0.13 with equal
weighting among the CRT values.
|Cabezon (Scorpaenichthys marmorata)
The most recent stock assessment of cabezon divides the stock into
northern and southern California substocks (Cope and Punt 2005). The
stock assessment focuses on the depletion reference point, i.e.,
the fraction to which spawning stock biomass (SSB) has been depleted,
rather than the replacement reference point (i.e., SPR or FLEP and
The current spawning biomass in northern California is 40% of the
unfished value, which places it in the precautionary zone under both
federal and state regulations. The previous stock assessment made
projections of the probability distribution of depletion 12 years in
the future, over a range of assumptions involving natural mortality,
steepness and possible management. The mode of this distribution
was just below 40 percent, still in the precautionary zone. Their
base model used a steepness value of 0.7, which correspond to CRT
values of 11%, although the likelihood profile for steepness actually
suggests the biologically implausible value of unity, which tends to
indicate the available data were not informative regarding steepness.
Several declining trends in cabezon data are cause for concern.
The three estimates of CPUE for California all exhibit long term
declines (Figs. 6 and 8 in Cope et al. 2004), albeit with a slight
increase in the most recent data year (Fig. 34 in Cope and Punt
2005). The estimated spawning output is declining both in the
long term, as well as in the short-term (i.e., since the late 1990s)
decline (Cope et al. 2004; Fig. 49 in Cope and Punt 2005).
Based on these results we used the value FLEP = 0.4, corresponding to
the recent estimates of depletion, as well as the lower value FLEP =
0.3 as a conservative alternative. Once again, we are assuming
that recruitment has been relatively constant so that depletion and
FLEP are similar. For the CRT, we used values of CRT = 0.11
(based on the value used in the stock assessment) as well as the more
conservative estimate of CRT = 0.35 based on the poor quality of the
data. For the optimistic fishery scenario, we used CRT = 0.11 and
assigned equal weight to the two FLEP values; for the pessimistic
scnenario we used CRT = 0.35 and assigned weights 0.75 and 0.25 to FLEP
= 0.3 and FLEP = 0.4, respectively. This choice reflects the
unknown nature of the CRT and the evidence for declining CPUE under the
current management regime.
|Canary rockfish (Sebastes pinniger)
The canary rockfish was declared overfished in the
year 2000, and the most recent stock assessment contains a summary of
information from the rebuilding plan, as well as an estimate of the
current status (Stewart 2007). SPR (i.e., FLEP) declined
approximately linearly from a value near 60 percent in 1970 to less
than 10 percent in the 1990s. However, in response to reductions
in trip limits and spatial closures, it is projected to have increased
to > 90% recently. The values of the CRT used in models in the
stock assessment were 51% (i.e., steepness = 0.329) and 31% (i.e.,
steepness = 0.449). The former value was derived from Dorn's
(2002) analysis, and is well-supported because data are actually
available at low stock abundances. Abundance reached its lowest
level in the mid 1990s, and has increased since then to between 1 and 7
percent of the estimated unfished spawning biomass.
Based on these results we used CRT = 0.51, a
well-supported value, and FLEP = 0.9 (representing the current estimate
of SPR) and FLEP = 0.1 (representing the current estimate of total
spawning biomass). For the optimistic scenario we assigned 100%
of the weight to the FLEP = 0.9 case; for the pessimistic scenario we
assigned weights of 0.75 and 0.25 to FLEP = 0.9 and FLEP = 0.1,
respectively. These weights reflect the strong evidence that the
stock is well managed and rebuilding but the non-negligible possibility
that future management will again be unsuccessful. For example,
one cause of concern is that the nature of the fishery is changing,
with the fraction of catch in the recreational fishery increasing from
an average of 6 percent of the catch to 60 percent.
|Lingcod (Ophiodon elongatus)
The most recent stock assessment for lingcod divides the
population into two separate populations, with the southern one
(Eureka, California to Monterey, California) being the one of interest here (Jagielo
and Wallace 2005). The depletion level of the southern stock is a
spawning biomass that is 24% of the unfished state, which is a level
considered overfished under both state and federal guidelines (i.e.,
less than 30% and 25%, respectively). The stock assessment
indicates abundance reached a low in the mid-1990s, and has increased
slightly since then (Fig. ES-1 in Jaglielo and Wallace 2005). The
stock assessment assumed a CRT of 3% (i.e., steepness = 0.9).
Sensitivity analyses explored the range from CRT = 0% (steepness = 1.0)
to CRT = 6% (steepness = 0.8).
The trawl logbook CPUE for the years used in the assessment showed a
decline from 1978 to 1997, with a possible leveling off in the
mid-1990s (Fig. 9 in Jaglielo and Wallace 2005). The most recent
value of CPUE from the National Marine Fisheries Service trawl survey
has the highest value observed since the survey began in the late 1970s
(Fig. 2, App II in Jaglielo and Wallace 2005). The estimated
exploitation rate has declined from values near 0.2 in the early 1990s
to values near 0.1 since 2000.
Based on these results we used values of CRT = 0.03 (the value assumed
by the stock assessment) and CRT = 0.35 (a more conservative value,
given the lack of empirical data), along with the value FLEP = 0.24,
based on the current level of depletion for the California stock.
In the optimistic scenario we assigned the full weight to CRT = 0.03;
in the pessimistic scenario we assigned 75% weight to CRT = 0.35 and
25% to CRT = 0.03, reflecting the lack of empirical support for the
lower CRT value and the recent steep declines in CPUE in this
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