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Status of the Yelloweye Rockfish Resource in 2001 for Northern California and Oregon Waters

Category: Fish/Shellfish Research and Management - Management and Conservation

Date Published: August 30, 2001

Number of Pages: 86

Author(s): Farron R. Wallace

DESCRIPTION:
Appendix to: Status of the Pacific Coast Groundfish Fishery Through 2001 and Recommended Acceptable Catches for 2002

EXECUTIVE SUMMARY:

Stock
This assessment incorporates two separate assessments corresponding to yelloweye rockfish (Sebastes ruberrimus) found in waters off the northern California coast (PMFC areas 1B and 1C) and from waters off the Oregon coast. An assessment model was not developed for Washington due to limited length and age composition time series. Because of differing sport CPUE trends, aggregating Washington and Oregon data into a single model was not justified.

Catches

Northern California
Trawl landings of yelloweye rockfish declined from an average of 42 mt in the 1980s to less than 11 mt in the 1990s. A commercial line fishery developed in the late 1980s peaked at 100 mt in 1991 and declined to less than 10 mt by 1999. Sport catches of yelloweye rockfish averaged 60 mt during the 1980s and precipitously declined to less than 18 mt in the 1990s averaging only 5 mt 1998-2000.

Oregon
Trawl landings of yelloweye rockfish averaged over 70 mt since 1980 declining abruptly to less than 16 mt in 1998. A commercial line fishery developed in the early 1990s and has averaged 35 mt until management restrictions in 2000 reduced catches to less than 5 mt. Sport catches of yelloweye rockfish averaged 34 mt during the 1980s and declined to 20 mt in the 1990s.


Data and assessment
This is the first time yelloweye rockfish have been formally assessed in Pacific Council managed waters. Rogers et al. (1996) estimated a yelloweye rockfish ABC of 39 mt for the Northern area (Columbia and Vancouver) based on biomass estimates from the triennial trawl survey and assumptions about natural mortality (M) and catchability (Q).

Two length-based Stock Synthesis models were used to derive population trends for northern California and Oregon. Auxiliary indices of abundance from the NMFS triennial trawl survey and halibut longline survey (Halibut Commission) were examined but rejected. The northern California assessment includes two sport CPUE indices constructed from Marine Recreational Fishery Statistical Survey (MRFSS) sample data and CDFG data collected on-board Commercial Passenger Fishing Vessels (CPFV). The Oregon assessment model includes a sport CPUE index derived from ODFW estimated bottomfish effort and yelloweye catch. Both assessment models are for combined sexes, include two fisheries, sport and commercial spanning 1970-2000. Length composition data are available beginning 1978 and 1980 for the northern California and Oregon assessment, respectively.

Unresolved problems and major uncertainties
There are a number of uncertainties that contribute to interpretation of results presented in this assessment. Some were explored through sensitivity analysis including natural mortality, selectivity and level of historical catch. Data on growth, maturity, movement and age were very limited precluding formal analysis. Length composition data have been collected for two decades, but sample sizes are small. Yelloweye can live over 100 years and information derived from length composition data is limited beyond age 25-30 as yelloweye approach asymptotic length.

There are also concerns that fisheries dependent indices of abundance may introduce bias resulting from annual variability in fishery catchability. No indication of bias was found, but data are likely imprecise. The Oregon recreational CPUE data provided by ODFW did not allow for complete review due to the aggregate nature of the data. For this reason, there is some uncertainty associated with these data.

Little is known about yelloweye stock structure. The specific habitat requirement for yelloweye rockfish support hypothesis for site fidelity, and little mixing may occur after settlement. It is likely that discrete sub-populations corresponding to high-relief rocky areas form a much larger meta-population.

Reference points
The proxy target fishing mortality rate for rockfish allowable catch is F50%. This represents a SPR rate that would reduce the spawning biomass 50% from its unfished level. The rate can be further reduced by a precautionary "40-10 default OY" such that the further the stock is below B40% the greater the reduction in harvest until at B10% all harvest is prohibited. A formal rebuilding plan is required in the stock falls below B25%.

Stock biomass

Northern California
Results from the Stock Synthesis model indicate that stock biomass has significantly declined throughout the time series. Current spawning biomass is estimated to be approximately 7% of the unfished spawning biomass.

Year Biomass (mt)
Begin Year Spawning
90
760
280
91
678
245
92
558
199
93
458
164
94
420
151
95
380
137
96
346
123
97
280
99
98
214
79
99
198
74
00
194
73

Oregon
Results from the Stock Synthesis model indicate that stock biomass has significantly declined throughout the time series. Current spawning biomass is estimated to be approximately 13% of the unfished spawning biomass.

Year Biomass (mt)
Begin Year Spawning
90
1626
593
91
1600
569
92
1508
520
93
1357
454
94
1193
397
95
1110
362
96
903
296
97
778
255
98
603
207
99
562
198
00
500
182

Recruitment

Northern California
Recruitment is variable across the time series and parallels a decreasing trend in population biomass. The last above average recruitment was 1987 (age 3 recruits) and recruitment failure is apparent during the last decade.

1,000's of Age 3 Recruits
Year Recruitment
86
15.1
87
91.5
88
18.1
89
26.3
90
15.4
91
8.8
92
13.8
93
13.6
94
5.2
95
3.4
96
3.8


Oregon
Recruitment estimates are quite variable and imprecise across the time series. Above average recruitment (age 3 recruits) occurred during 1986 and 1987, but recruitment failure is evident during the last decade.

1,000's of Age 3 Recruits
Year Recruitment
86
174.6
87
53.9
88
32.9
89
23.8
90
21.3
91
17.5
92
12.2
93
8.8
94
8.2
95
8.3
96
9.5

Exploitation status

Northern California
Commercial exploitation rate peaked at over 25% in 1997 decreasing to less that 1% in 2000. Exploitation rate in the sport fishery peaked at over 10% in 1985 decreasing to less than 5% in recent years.

Exploitation Rate
Year Sport Commercial
90
0.071
0.099
91
0.057
0.204
92
0.044
0.225
93
0.021
0.131
94
0.039
0.130
95
0.037
0.125
96
0.044
0.237
97
0.066
0.265
98
0.033
0.106
99
0.041
0.071
00
0.012
0.005

Oregon
Commercial exploitation rate peaked at over 30% in 1997 decreasing to less that 2% in 2000. Exploitation rate in the sport fishery has been at or below 3% across the time series.

Exploitation Rate
Year Sport Commercial
90
0.015
0.039
91
0.016
0.092
92
0.023
0.144
93
0.020
0.179
94
0.017
0.115
95
0.017
0.274
96
0.010
0.221
97
0.021
0.322
98
0.030
0.098
99
0.030
0.170
00
0.017
0.011

Management performance
Base run estimates indicate harvest levels well above natural mortality since 1980. This coupled with recent poor recruitment may have led to population decline and over-exploitation. This is of concern because, like many other species of rockfish, yelloweye have been managed as part of a complex with little attention given to individual species. Yelloweye rockfish can be characterized as relatively small population(s) of fish that are long-lived, late maturing, slow growing, and susceptible to overfishing. Recent management decisions have greatly restricted "shelf" rockfish catch, which is reflected in recent low level of yelloweye landings by commercial fisheries.

Decision Table and Forecasts

Northern California
Forming the basis for a decision table, five-year yield projections (F50%) are provided representing three assumed levels of recruitment including mean recruitment across the time series, mean recruitment in the most recent 10 years and recruitment estimated from a Beverton-Holt stock recruitment relationship.

Oregon
Decision table for the Oregon yelloweye assessment also provides five-year yield projections (F50%) representing three assumed levels of recruitment including mean recruitment across the time series, mean recruitment in the most recent ten years and recruitment estimated from a Beverton-Holt S-R relationship.

Recommendations: research and data needs
Additional effort to collect age and maturity data is essential for improved population assessment. Collection of these data may be necessary by onboard observers if this species becomes prohibited. Increased effort toward habitat mapping will provide information on essential habitat and distribution for this species. Development of fishery independent indices will be necessary as allowable catch becomes restricted. A study of the role of MPAs in harvest management will be beneficial for yelloweye rockfish and other sedentary species. Genetic study is required as a first step in delimiting stock boundaries for this species.

Sources of additional information
STAR panel report

Rogers, J.B., M. Wilkins, D. Kamakawa, F. Wallace, T. Builder, M. Zimmerman, M. Kander and B. Culver. 1996. Status of the Remaining Rockfish in the Sebastes Complex in 1996 and recommendations for management in 1997. Pacific Fishery Management Council 2130 SW fifth Ave. Suite 224, Portland, Ore. 97210.