Slide 1: Objectives of a Stock Assessment
Estimate Current Stock Status:
- How many exploitable fish? How much biomass? How many incoming recruits?
Determine Target Fishing Rate:
- What fraction of the stock can be safely harvested? Balance short-run catches against possible changes in long-run productivity.
Analogous to a bank statement: stock size is the balance; harvest rate is the interest rate.
Slide 2: (chart) A Fishery Regulated using Catch Quotas
Slide 3: (chart) Fishing at FMSY to Catch the MSY
Slide 4: Reconstructing a Stock’s Demographic History
Population dynamics equations to predict:
- year-to year changes in age and size composition in the population and the catch;
- new recruits to the population and annual spawning potential.
Parameters estimated from observations of:
- fishery removals (including mortal discards);
- age and/or size composition of the catch;
- tuning indices - abundance or biomass trends;
- biological traits – growth, fecundity, maturity.
Slide 5: Reconstructing a Stock’s Demographic History (continued)
Excel worksheet demonstration:
- annual random recruitment sets the year-class strength;
- year- and age-specific survival for each cohort determine the annual changes in numbers of fish.
Slide 6: Status of Black Rockfish off Oregon and California
Slide 7: Black Rockfish Biology
- Found from the Gulf of Alaska to Baja California, but rare south of Point Conception.
- Internal fertilization, winter extrusion of larvae.
- Juveniles are pelagic, for months to a year.
- Settlement in estuaries and nearshore, gradual movement to deeper water.
- Found as adults near and over hard bottom structure, at depths < 40 fathoms.
- Tagging studies indicate limited, small-scale movement for most adults.
Slide 8: Black Rockfish Biology (cont.)
- Feed on zooplankton, krill, mysids, sandlance.
- Females slightly larger than males.
- 50% maturity for females: ~ 40 cm, ~ age-7-yr.
- High fecundity: a 6-yr-old female produces ~300,000 embryos, a 16-yr-old produces ~950,000 embryos.
- Max age: 50-yr-old reported in Alaska; 29-yr-old in Oregon.
- Apparent deficit of females compared to males, starting at about age-10-yr, modeled by a “ramp” in natural mortality for females.
Slide 9: (chart)Black Rockfish Biology (cont.) The older females are missing
Slide 10: Stock Structure
- The assessment for northern black rockfish (Wallace et al. 2007) claims genetic evidence for stock separation at Cape Falcon, OR
- Additional samples from Oregon indicate little evidence for a stock boundary at Cape Falcon.
- Ralston & Dick (2003), the last assessment for southern black rockfish, assumed a unit stock south of the Columbia River.
- Current assessment has Cape Falcon as its northern boundary, to avoid overlap with the WA assessment and to simplify data compilation.
Slide 11: (maps) The Assessment Area
Slide 12: The Assessment Structure
- Similar to the 2003 assessment.
- Three types of fishery (trawl, non-trawl, recreational) in each of Oregon and California.
- Recreational CPUE data provide abundance indices, from RecFIN and from state programs.
- Age composition data are from Oregon only, and more limited than in the last assessment.
- Length composition data are available for all fisheries and are the dominant data type.
Slide 13: (chart) Historic Landings
Slide 14: Historic Landings (cont.)
In Oregon during the 1940s:
"The rockfish are caught by otter trawl and long-line gear. The principal species caught by the otter trawl are the black rockfish (Sebastodes melanops); green or yellow-tail rockfish (S. flavidus); red or orange rockfish (S. pinniger); and rosefish (S. alutus). … The landings of rockfish (all species) rose rapidly during the war from 1,301,400 pounds in 1941 to a peak of over 17,000,000 in 1945. Subsequently the landings fell rapidly because of decreased demand and leveled off at about 4,000,000 per year in 1949."
From: Cleaver (1951). Fisheries statistics of Oregon. Oregon Fish Commission.
Slide 15: Catch Reconstruction
The approach:
- apply assumed values for the percent black rockfish to reported commercial landings of rockfish by gear group and area.
- PacFIN 1981-2006 (black rockfish and unspeciated rockfish).
- PMFC series 1956-80.
- US Fishery Statistics 1927-1955.
- Linear interpolation to zero catch in 1915.
Slide 16:(charts) %Black from PacFIN
Slide 17: (chart) Assumed %Black Values
Slide 18: (chart) Base-Run Historic Landings (mt)
Slide 19: Abundance Indices
- Standardized CPUE indices (one for each state) developed from raw angler interview data (RecFIN/ MRFSS).
- Standardized CPUE index from the ODFW Ocean Recreational Boat Survey (ORBS).
- Standardized CPUE index from the California Commercial Passenger Fishing Vessel (CPFV) Observer Program (CDFG).
- ODFW Tag abundance index for Newport, OR.
- Pre-recruit abundance index from the juvenile fish survey (SWFSC/PWCC).
Slide 20: (charts) RecFIN CPUE Indices
Slide 21: (chart) Oregon ORBS CPUE Index
Slide 22: (chart) California CPFV Index
Slide 23: (chart) Bag-Limit Changes
Oregon: 15 rockfish until 1994, then 10 black rockfish sub-limit. 10 rockfish (all species) in 2000. 10 marine fish in 2003. 5 marine fish in July 2005. 6 marine fish in 2006.
Slide 24: (chart) ODFW PIT-Tag Abundance Index
Slide 25: (chart) ODFW PIT-Tag Index “Q”
Slide 26: (chart) Pre-recruit Abundance Index
Slide 27: Age Composition Data
- Age composition data are available from the three type of fisheries in Oregon, but not for any of the fisheries in California.
- The 2003 assessment included Oregon age composition data from 1990-2001.
- The current assessment excludes some age composition data because of concerns about age-reading bias.
- The age composition data do not show clear evidence of strong year-classes moving through the population.
Slide 28: (chart) Age Reading Drift
Slide 29: (chart) Selecting a Standard Set of Age-Readers
Slide 30: (chart) Age Composition Data (cont.)
The data show little evidence of strong year-classes
Slide 31: Length Composition Data
- Length composition data are available from the three types of fisheries in both states.
- There are more length composition data than any other type of data.
- If age and length composition data were both available for a given year & fishery, the length data were excluded from the SS2 model fitting to avoid double-use of the same data.
- The length composition data show little clear evidence of strong year-classes moving through the population.
Slide 32: (charts) Length Composition Data (cont.)
The data show little evidence of strong year-classes.
Slide 33: Base-Run Model
- Stock Synthesis 2 model with 6 fisheries, 6 indices and 24 non-zero likelihood components.
- Fisheries begin from an unfished state in 1915.
- Deviations in recruitment begin in 1970 and extend through 2006.
- Natural mortality is fixed for males at 0.16 and is constant with age.
- Natural mortality for females is 0.16 for females less than age-10, ramps to 0.24 over the ages 10 to 15, then remains constant at 0.24.
- Selection is by length (not age) and does not differ by gender.
Slide 34: (chart) Example Base-Run Fits ORBS Survey CPUE Index
Slide 35: (chart) Example Base-Run Fits (cont.) OR Sport Fishery Length Compositions
Slide 36: (chart) Example Base-Run Fits (cont.) ORBS Survey Age Compositions - Females
Slide 37: (chart) Base-Run Model Profile – R0 Tension among the data sources
Slide 38: (chart) Base-Model Results Selection Curves
Slide 39: (chart) Base-Model Results (cont.) Selection Curves (cont.)
Slide 40: (chart) Base-Model Results (cont.) Relative Spawning Output
Slide 41: (chart) Base-Model Results (cont.) Recruitment
Slide 42: (chart) Base-Model Results (cont.) Exploitation Status
Slide 43: (chart) Base-Model Results (cont.) Historical Analysis
Slide 44: (chart) Base-Model Results (cont.) Historical Analysis (cont.)
For more information about this presentation, contact:
david.sampson@oregonstate.edu