Proposal

An evaluation of the significance of climate forcing on time-varying growth and fecundity of
rockfish in the California Current
Susan Sogard, 1 John Field, 1 and Chris Harvey 2
1 Southwest Fisheries Science Center, National Marine Fisheries Service, Santa Cruz, CA.
2 Northwest Fisheries Science Center, National Marine Fisheries Service, Seattle, WA.
Summary
Climate effects on ecosystem productivity are well established for the California Current,
and climate variability is reflected in bottom-up effects on fish growth and productivity. Stock
assessments have increasingly begun to include these important effects in estimating abundance
and production. In turn, critical metrics used in stock assessments (spawning biomass, spawning
output and recruitment) vary as a function of current environmental conditions. Our working
hypothesis for this study is that poor feeding conditions during warm oceanographic regimes
result in trade-offs affecting bioenergetic allocation patterns by females, resulting in reduced
growth and reduced fecundity. We will rigorously address this hypothesis in three ways: (1) by
expanding on process studies relating environmental conditions to growth and fecundity; (2) by
using these results to modify existing bioenergetics models, investigating mechanisms by which
climate may drive changes in energy budgets; and (3) by incorporating findings from these
efforts into existing stock assessment models of West Coast groundfish for which time-varying
growth (and potentially fecundity) have been identified as key factors. These refinements should
improve future assessments by increasing precision and decreasing uncertainty.
Background
Examples of climate effects on fish condition, growth and fecundity are evident for
rockfishes (Sebastes spp.). Growth rates of yelloweye rockfish are correlated with climate
indices such as upwelling, the Northern Oscillation Index (NOI), Pacific Decadal Oscillation
(PDO) and sea surface temperature (Black et al. 2008). Comparable to patterns observed in
salmonids, growth of yelloweye rockfish was negatively correlated with 'warm' oceanographic
regimes in California but positively correlated in British Columbia. Strong El Niño conditions
have been associated with reduced growth in widow and yellowtail rockfish (Woodbury 1999)
and poor condition in chilipepper, yellowtail, and blue rockfish (Lenarz et al. 1995, VenTresca et
al. 1995). Poor feeding conditions during warm regimes likely also result in trade-offs affecting
reproductive allocation patterns by females. VenTresca et al. (1995) demonstrate a clear decline
in condition of adult female blue rockfish during both the strong 1982-83 and weaker 1992-93 El
Niño periods. Interannual variability in fecundity of yellowtail rockfish was evident for young
females (15) for fish in California, south of the species’ main
areas of concentration (Eldridge and Jarvis 1994). Populations in Washington, in contrast, did
not exhibit interannual differences. Weight-specific fecundities (eggs g -1 ) of California fish were
significantly lower than those of Washington fish, indicating a latitudinal effect. Washington
fish generally had higher lipid reserves and fewer incidences of parasitism than California fish,
suggesting an overall higher level of condition.
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In blue rockfish, gonadal indices for females were negatively correlated with sea surface
temperatures during the fall (VenTresca et al. 1995), suggesting a possible reduction in
fecundity. Yellowtail rockfish likewise had lower lipid reserves and smaller ovaries during an El
Niño (Lenarz and Wyllie Echeverria 1986). Bioenergetic models derived by Harvey (2005)
suggest that enduring multiple El Niño events dramatically decreases the lifetime fecundity of
blue rockfish. In an analysis of the severely overfished boccacio, Tolimieri and Levin (2005)
found that recruits per spawning output increased when oceanographic conditions supported
enhanced production during the preceding summer and fall, suggesting a potential linkage with
female foraging success and energy storage. These examples clearly indicate the potential for
climate effects to impact growth and reproductive capacity in rockfishes.
The intent of this proposal is to enhance rockfish stock assessments by improving the
rationale, the available data (age and length, reproductive effort, and climate indices) and the
implementation of time-varying growth. Evaluating environmentally induced changes in energy
allocation between growth and reproduction is clearly key to better understanding the cumulative
effects of climate on productivity, as any impacts of poor female condition on their fecundity, the
quality of larvae they produce, or the timing of parturition will reduce their expected contribution
to recruitment. Investigating the consequences of extended periods of either exceptional or
unfavorable environmental conditions to assumptions regarding stock status and productivity is
key to avoid over- (or under-) estimating reproductive output in assessment models and
subsequent status determinations.
Approach
Growth analyses: Time varying growth has been shown to be an important factor in several
stock assessments on the west coast, and has been incorporated into models of Pacific hake,
English sole and chilipepper rockfish (Helser et al. 2008; Stewart 2008; Field 2008), all of which
highlighted a need for additional work on both the modeling approach and the mechanisms
behind such variability. Our analyses of interannual differences in growth will focus on
chilipepper rockfish (Sebastes goodei), a mid-size, semi-pelagic rockfish found primarily in shelf
and shelf-break waters off California, where they have been among the most important
commercial and recreational rockfish species in both historical and contemporary fisheries. As
past stock assessments had identified variable growth rates as a key source of uncertainty, the
most recent assessment using the model Stock Synthesis II (SS2) estimated time-varying growth
internally (Field 2008). This was done by allowing the von Bertalanffy growth coefficients (K)
to vary over time. Several approaches were evaluated to find the appropriate level of parsimony
between model complexity and data availability. The final model utilized freely estimated
growth offset parameters, based on time period blocks that were informed by major shifts in the
signal for the PDO (Figure 1). Thus, while climate was not directly incorporated into the
assessment, it was critical for the rationale behind the modeling approach that was ultimately
adopted. Using this approach improved the model fit to the data by nearly one hundred
likelihood units at the “cost” of five parameters, with most of the improvement accounted for in
fits to length frequency data (Figure 2).
Although both the assessment team and the review panel found this approach to be
reasonable in the near term, there was a recognized need for ageing fishery-independent otoliths
from historical surveys to better inform growth curves and offsets, to model ages using
conditional age-at-length compositions rather than traditional age-compositions, and to undertake
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a greater exploration of methods for modeling time-varying growth as influenced by
environmental factors. Our project will address these needs by focusing additional ageing effort
on archived chilipepper otoliths from historical fishery-independent surveys. These data are
necessary to better predict growth rates of smaller individuals. This in turn will facilitate a reevaluation
of the model developed in the last stock assessment by including fishery-independent
age and size information, which together with the fishery-dependent age and size data will be
modeled using conditional age-at-length information. Concurrently, we will evaluate the likely
or potential mechanisms driving time-varying growth by simulating climate and growth
interactions using an existing bioenergetics model of rockfish (Harvey 2005, Harvey et al. 2006).
This model estimates rockfish energy budgets, allocating energy to somatic growth, gonadal
production, and metabolic costs as a function of variables such as body size, temperature,
feeding rate and prey quality. The model has been used, for example, to evaluate the influence
of El Niño conditions on rockfish growth and fecundity (Harvey 2005), and can be reconfigured
to evaluate factors that relate to the observed changes in growth suggested in the size-at-age data
and the assessment model. This model framework thus provides a direct, mechanistic linkage
between climate variability and rockfish growth, and supports improved assessment and better
predictions by anticipating varying patterns of chilipepper rockfish growth and reproductive
capacity under alternate climate scenarios.
Fecundity analyses: We expect climate effects on reproductive capacity, fish condition and fish
health to be primarily driven by large scale oceanographic parameters such as the PDO. As a
consequence, rockfish responses will likely be similar among a diverse suite of species. There is
substantial evidence that rockfish recruitment within California follows coherent temporal
patterns despite interspecies differences in life histories (Field and Ralston 2005, Laidig et al.
2007). Thus, we expect reproductive capacities of different species to be similarly affected by
large scale changes in oceanographic conditions. Several studies have documented a decline in
female health or growth during warm ocean periods, but how this effect translates into changes
in reproductive capacity is not known.
We will make use of available data acquired from a wide array of studies for a
retrospective analysis of fecundity relationships during contrasting oceanographic conditions.
All fecundity estimates will be examined for relationships with maternal age, length, and weight
to derive appropriate adjustments accounting for maternal effects (Boehlert et al. 1982, Bobko
and Berkeley 2004, Sogard et al. 2008, Dick in prep). Our analysis of fecundity will include all
species of California rockfish for which sufficient data are available: EJ Dick, here at the FED,
has compiled a comprehensive database of published and unpublished fecundity estimates in a
broad suite of Sebastes species for a phylogenetic analysis of maternal effects. He has not
examined interannual differences in fecundity previously and has agreed to collaborate with us
on this effort. We also have available an extensive dataset of fecundities for yellowtail rockfish
captured on Cordell Bank in the 1980s (1985-1991), much of which is published (i.e., Eldridge et
al. 1991, Eldridge and Jarvis 1994). For comparison, we have recently collected large numbers
of yellowtail, chilipepper, and widow rockfish from Cordell Bank over a 3 year time period
(2005-2008). These two datasets will allow a detailed comparison from the same location over
two contrasting time periods.
In addition to deriving a time series of fecundities for evaluation of correlations with
oceanographic factors, we will examine the relationship of fish health with fecundity. We expect
any reduction in annual fecundities to be associated with decreased female condition. Fulton's K
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(somatic weight * length -3 ) provides a simple index of fish condition. Where data are available
on fish length, somatic weight, and fecundity, we will be able to determine any relationships and
potentially how they vary with fish size or age. For example, relative fecundity may decrease
with condition in young females but not for older females that have more absolute levels of
energy reserves. Such an age effect could account for Eldridge and Jarvis's (1994) finding of
interannual variation in fecundity of young but not old yellowtail rockfish. If Fulton's K is
correlated with fecundity (after adjusting for fish size and age), it may provide a useful indirect
proxy for fecundity.
Ongoing laboratory experiments at FED are examining the reproductive allocation
strategies of rockfish. Experiments will test the responses of female rockfish of several species
to low food availability in the fall prior to parturition. Females held with low rations will be
compared to females receiving unlimited food, with metrics of fecundity, larval size and quality
(lipid reserves), and timing of parturition. These experiments will provide direct tests of any
shifts in allocation associated with poor foraging success and will be valuable in establishing the
relationships of fish health/condition with reproductive performance. All fecundity estimates
will be standardized by fish size or age to examine the interactive role of maternal effects on
reproductive capacity. We expect that environmental factors will have a greater influence on
reproduction in small, young females than in large, old females. If this is true, then climaterelated
biases in fecundity estimates used in stock assessments would be exacerbated for heavily
fished stocks that have few older fish remaining compared to lightly fished stocks that have a
relatively diverse size and age structure.
Furthermore, questions related to tradeoffs between growth and fecundity are inextricably
linked in stock assessment models, which typically assume length-based maturity functions.
Many approaches for incorporating time-varying growth in an assessment model assume that
maturity is a function of length rather than age, inferring that during periods of poor growth the
age at maturity is extended (although Stewart (2008) modeled both time-varying growth and
time-varying maturity independently in a stock assessment model of English sole). There has
been no concerted effort to test the validity of this assumption. Consequently, we will revisit the
existing size, maturity and fecundity data described earlier to investigate this issue.
Deliverables
Reproductive capacity and growth are critical components of stock assessments, and
improved understanding of how these factors vary with ocean conditions will be of great utility
in incorporating environmental variability into stock assessments and management. As the
significance of these factors can easily be evaluated in the existing assessment model of
chilipepper rockfish, and potentially in models of widow or yellowtail rockfish currently being
developed, methods to incorporate and evaluate the sensitivity of assessment models to these
factors are the primary deliverables of this effort. These methods will be presented in a
comprehensive report defining the application of our results to current stock assessments. In
addition, we anticipate one to two manuscripts submitted to peer-reviewed journals describing
empirical and modeled interactions between environmental conditions and growth, fecundity and
condition, based on experimental analysis and bioenergetics modeling. We will also develop a
peer-reviewed manuscript that reviews the approach and sensitivity of assessment models to time
varying growth and fecundity, including an evaluation of the significance of these factors in
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estimating reference points. Finally, we anticipate presenting the results of these efforts at the
annual FATE meetings as well as high profile national meetings (e.g., AFS, AGU, etc).
Benefits
This proposal capitalizes on a species with clearly recognized variation in growth over
time (chilipepper), and for which a recent, relatively data-rich assessment model is available.
Existing bioenergetics models can be evaluated simultaneously to explore the potential role of
climate-related mechanisms behind this growth. Additionally, reproductive capacity is a critical
component of stock assessment, and improved understanding of how fecundity varies with the
environment will be of great utility in incorporating oceanographic factors into stock assessments
and management advice. Furthermore, we intend to evaluate whether insights gained from such
(relatively) data-rich species could translate into insights for more data-poor species, such as blue
or bocaccio rockfish (Key et al. 2008; MacCall 2003), as both of these assessments (and
associated reviews) identify time-varying growth as a factor in urgent need of additional
analysis. The bocaccio stock assessment will be conducted by Field in 2009, providing an
opportunity to apply results from this project in the very near term to a model that lacks adequate
age composition information (Ralston and Iannelli 1998; MacCall 2003). Our results can also
provide a base model from which time-varying growth and fecundity can be explored in other
species. Additional insights into the consequences of variable reproductive capacity will also
address another key uncertainty in stock assessments, regarding the utility of larval abundance
data (primarily from the CalCOFI sampling program).
Statement of work
Year 1
The technician will divide time between analysis of annual increment widths in archived
chilipepper rockfish otoliths and analysis of fecundity in archived ovary samples of chilipepper,
yellowtail, and widow rockfish. D. Pearson (here at the FED) will supervise and assist with the
otolith analysis. S. Sogard will supervise and assist with the fecundity analysis. J. Field will
develop appropriate environmental indices for comparison with growth and fecundity data in the
chilipepper model and will explore possible benefits and impacts of inclusion of climate indices
in other models (including the anticipated 2009 bocaccio model). C. Harvey will initiate
bioenergetic modeling. The P.I.s will have regular meetings to discuss data analysis.
Year 2
The technician will continue growth and fecundity analyses, with an anticipated
completion by mid-year. The full team will then collaborate in data analysis, modeling, and
preparation of final reports and manuscripts for submission to peer-reviewed fisheries journals.
In addition, the results will be directly applied to a revised chilipepper assessment by Field, using
the information obtained on time-varying growth and time-varying fecundity. Field will also
have completed a bocaccio rockfish assessment model by this stage, and will explore the
applicability of incorporating time-varying growth and/or fecundity into this assessment, as well
as an existing assessment of blue rockfish.
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References
Black, B. A., G. W. Boehlert, and M. M. Yoklavich. 2008. Establishing climate-growth
relationships for yelloweye rockfish (Sebastes ruberrimus) in the northeast Pacific using a
dendrochronological approach. Fisheries Oceanography 17:368-379.
Bobko, S. J., and S. A. Berkeley. 2004. Maturity, ovarian cycle, fecundity, and age-specific
parturition of black rockfish, (Sebastes melanops). Fishery Bulletin, U.S. 102:418-429.
Boehlert, G. W., W. H. Barss, and P. B. Lamberson. 1982. Fecundity of the widow rockfish,
Sebastes entomelas, off the coast of Oregon. Fishery Bulletin, U.S. 80:881-884.
Eldridge, M. B., J. A. Whipple, M. J. Bowers, B. M. Jarvis, and J. Gold. 1991. Reproductive
performance of yellowtail rockfish, Sebastes flavidus. Environmental biology of fishes
30:91-102.
Eldridge, M. B., and B. M. Jarvis. 1994. Temporal and spatial variation in fecundity of yellowtail
rockfish. Transactions of the American Fisheries Society 124(1):16-25.
Field, J. C., and S. Ralston. 2005. Spatial variability in rockfish (Sebastes spp.) recruitment
events in the California Current System. Canadian Journal of Fisheries and Aquatic
Sciences 62:2199-2210.
Field, J.C. 2008. Status of the Chilipepper rockfish, Sebastes goodei, in 2007. In: Status of the
Pacific Coast Groundfish Fishery Through 2007, Stock Assessment and Fishery
Evaluation: Stock Assessments and Rebuilding Analyses Portland, OR: Pacific Fishery
Management Council.
Harvey, C. J. 2005. Effects of El Nino events on energy demand and egg production of rockfish
(Scorpaenidae: Sebastes): A bioenergetics approach. Fishery Bulletin, 103: 71-83.
Harvey, C.J., N. Tolimieri and P.S. Levin. 2006. Changes in body size, abundance, and energy
allocation in rockfish assemblages of the Northeast Pacific. Ecological Applications 16:
1502-1515.
Helser, T.E., I.J. Stewart and O.S. Hamel. 2008. Stock Assessment of Pacific Hake, Merluccius
productus, (a.k.a Whiting) in U.S. and Canadian Waters in 2008. Stock Assessment and
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Assessment of Blue Rockfish (Sebastes mystinus) in California. In: Status of the Pacific
Coast Groundfish Fishery Through 2007, Stock Assessment and Fishery Evaluation:
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Laidig, T. E., J. R. Chess, and D. F. Howard. 2007. Relationship between abundance of juvenile
rockfishes (Sebastes spp.) and environmental variables documented off northern
California and potential mechanisms for the covariation. Fishery Bulletin, U.S. 105:39-
48.
Lenarz, W. H., and T. Wyllie Echeverria. 1986. Comparison of visceral fat and gonadal fat
volumes of yellowtail rockfish, Sebastes flavidus, during a normal year and a year of El
Nino conditions. Fishery Bulletin, U.S. 84:743-745.
Lenarz, W. H., D. A. Ventresca, W. M. Graham, F. B. Schwing, and F. Chavez. 1995.
Explorations of El Nino events and associated biological population dynamics off central
California. California Cooperative Oceanic Fisheries Investigations Reports 36:106-119.
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MacCall, A. 2003. Status of bocaccio off California in 2003. In: Status of the Pacific Coast
Groundfish Fishery Through 2002, Stock Assessment and Fishery Evaluation: Portland,
OR: Pacific Fishery Management Council.
Ralston, S. and J. N. Ianelli. 1998. When lengths are better than ages: The complex case of
bocaccio. Pp. 451-468 In: F. Funk, T. J. Quinn II, J. Heifetz, J. N. Ianelli, J. E. Powers, J.
F. Schweigert, P. J. Sullivan, and C.-I. Zhang (eds.), Fishery Stock Assessment Models.
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a comparison among species. Marine Ecology Progress Series 360:227-236.
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Portland, OR: Pacific Fishery Management Council.
Tolimieri, N., and P. S. Levin. 2005. The roles of fishing and climate in the population dynamics
of bocaccio rockfish. Ecological Applications 15:458-468.
VenTresca, D. A., R. H. Parrish, J. L. Houk, M. L. Gingras, S. D. Short, and N. L. Crane. 1995.
El Nino effects on the somatic and reproductive condition of blue rockfish, Sebastes
mystinus. California Cooperative Oceanic Fisheries Investigations Reports 36:167-174.
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entomelas and S. flavidus) during the 1983 El Nino. Fishery Bulletin, U.S. 97:680-689.
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4
0.45
Mean Winter Anomaly Pacific Decadal Oscillation
3
0.4
2
0.35
1
0.3
0
0.25
-1
0.2
-2
0.15
-3
-4
0.1
1960 1970 1980 1990 2000 2010
Estimated value for K
Figure 1: Estimates of time-varying growth coefficient (K) for the most recent stock assessment
of chilipepper rockfish, with mean annual winter PDO and a running three year mean of the
winter PDO.
Observed and predicted female chilipepper mean size at age
470
430
Fork Length (mm)
390
350
310
270
230
1975 19 80 1985 1990 1995 2000 2005
3 6 9 pred3 pred6 pred9
Figure 2: Observed mean and predicted (with time-varying k parameter) size at age for female
chilipepper rockfish from the 2008 stock assessment.
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