2023 Pre-assessment workshop for black rockfish in off Oregon
Jason M. Cope, Northwest Fisheries Science Center
Alison Whitman, Oregon Department of Fish and Wildlife
Aaron M. Berger, Northwest Fisheries Science Center
Leif Rasmuson, Oregon Department of Fish and Wildlife
2023-02-01
Disclaimer: All data summaries and exploration presented here are preliminary and may not be indicative of the final data that will be incorporated in the 2023 assessment models
Overview
Description of data and model specification being considered for use in the 2023 assessments for black rockfish off Oregon.
Summary of the 2015 Assessment
The last assessment of black rockfish rockfish in waters off of Oregon was conducted in 2015 and estimated stock status for that year at 60.4%, and never showed a decline below the target biomass. This assessment was highly constrained by the choice to treat the catchability of the tagging index as known, thus the uncertainty in the assessment is very low. The complete assessment document can be found here.
Bridging the assessment model from Stock Synthesis 3.24 to 3.30
Since several years have passed from the last assessment model, the Stock Synthesis (SS) modelling framework has undergone many changes. While the specific changes in the model can be found in the model change log, here we simply update the model from the older 3.24V version to the newer 3.30.20 version. The point here is to present any differences in the model outputs when using the same information. This was first done by migrating the data and parameter specifications from the former files to the newer files. This migration was assisted using the SS-DL tool. Once the old data was transferred to the SS 3.30.20 file, two versions of the model were run.
- fixing all parameter values to the values found in the 2015 model.
- Allowing the same parameters estimation specification as in the 2015 model
Results are similar between models when all parameters are fixed from the 2015 model in the updated SS files, while there are slight scale differences, but little relative stock status differences, when the new SS version is allowed to estimate the same parameters as estimated in the 2015 version. Theses model comparisons are adequate to move ahead using the newest version of SS 3.30.20 without expecting large differences in reference models being due to versions of SS.
Unresolved Questions and Issues from the 2015 Assessments
- Investigation the lack of older (> age 10) females in data. This affects the definition of natural mortality and selectivity values for females.
- Improved historical catch reconstructions. The trawl fishery catches in particular need attention.
- Identifying stanzas or periods of uncertainty in the historical catch series will aid in the exploration of catch uncertainty in future assessment sensitivity runs.
- Treatment of the ODFW tagging study, mainly, the prior value on catchability.
- Evaluate a nearshore survey.
- Stock structure for black rockfish.
Stock Structure
The stock structure of black rockfish continues to be based on state-specific boundaries. Stocks definitions are based on a variety of factors that include genetics, biology, ecology, habitat availability and fishing mortality history. Black rockfish range from southern California up to Alaska. Their ecology as a nearshore (i.e., commonly an area of restricted gene flow) rockfish with semi-pelagic behavior (e.g., can demonstrate rare, but substantial adult movements) under strong and differential fishing pressure by state provides an interesting assortment of considerations. A recent genetics study done by Hess et al. (2022) found that Alaskan and west coast populations showed significant genetic difference. The population from Washington to California showed a variety of interesting genetic signatures, with decreased genetic diversity north of Cape Mendocino and North of the Columbia River, but increasing in waters off of Oregon. There were also pockets of isolation by distance and odd signatures off Brookings, Oregon. These variable genetic signatures combined with the lack of consistent black rockfish habitat in southern Washington, and the different exploitation histories in each of the states made state-level designations to support management decisions the most logical. This does not suggest there is no exchange of individuals among California, Oregon and Washington, but instead acknowledges that the exchange is likely low enough not to homogenize the populations, and that different population trends can be expected in each state. This was supported in the results of the last assessment, where important differences in stock status were observed.
Fleet Structure
Currently, the following fleet structure is being considered for modeling commercial and recreational fisheries in both area models:
- Commercial fixed-gear Fleet (dead and live fisheries combined)
- Commercial trawl (mostly a historical fishery)
- Recreational boat-based
- Recreational shore-based
Defining fleets is largely based on whether a fishing approach differs in the selectivity (i.e., the capture of fish by length and/or age). Selectivity translates how the removals are taken via length and/or age out of the population. The above four fishery types are distinguished by different fishing activities that result in different selectivities. While in the past the commercial fixed-gear fisheries had been separated by the condition of the landed fish (dead and live), it has been determined that the designation of how the fish will be delivered is a processing issue, not a capture/selectivity issue (Figure \(\ref{fig:comm_dead_live}\)). Thus the gear selectivity is considered the same in these gears. This similarity in selectivity is also apparent when looking at the 2015 assessment selectivity estimates for each fishery and is consistent with other recent nearshore assessments. The fixed-gear and trawl fisheries do present different selectivities (Figure \(\ref{fig:com-length-dist}\)) justifying different fleets.
For the recreational fishery, the private and charter ocean boat-based fisheries show similar aggregate length compositions and are treated as one fleet (Figure \(\ref{fig:private_charter_lts}\)). The ocean boat- and shore-based fleets show distinct aggregate compositions that demonstrate the well known characteristic of shore-based landings catching smaller fish (Figure \(\ref{fig:boat_shore_lts}\)). Fish caught by recreational boats within Oregon’s estuaries are included in the shore-based fleet. These recreational fleets are the same treatments as in the 2015 assessment.
Removal Data
Commercial Landings & Discards
Black rockfish are not considered a major commercial species, but historical reconstructions have shown prominent trawl catches in the past that have subsequently waned over the last 40 years. Historical catch reconstruction were done for the 2015 assessment, and are heavily based on applying highly variable catch compositions to years that do not have those composition, but rather just report total or “unknown” rockfish catches.
When providing data to the 2015 Black rockfish assessment, ODFW staff noted that trawl landings from the 1940s to the 1980s had high year to year variability and an unreasonable magnitude of landings in some years. These data were from the then newly completed Karnowski et al (2014) catch reconstruction. ODFW provided an alternative time series that was eventually used in the 2015 assessment (P. Mirick (ODFW) was the main source of this reconstruction). Additionally, the Karnowski et al. (2014) reconstruction did not account for fish taken off of Washington but landed into Oregon, specifically Astoria port landings. The Mirick reconstruction substantially reduced the magnitude of historic trawl catches and stabilized interannual variation in landings compared to the Karnowski et al. (2014) reconstruction. Total rockfish 3A landings were of similar magnitude between the two reconstructions, though different data sources were used in each approach. Species compositions, though, were from the same dataset (Douglas report), but differentially applied. The annual Douglas compositions were used for the Karnowski reconstruction, but these annual compositions were pooled for the Mirick reconstruction. Comparisons of 3A black rockfish from the Douglas report are different than in the Mirick reconstruction but of similar magnitude.
As a part of the 2015 assessment, trawl landings from 3A were also split between OR and WA by using the pooled Douglas compositions and other ODFW sources of information. Static average percentages of black rockfish were applied over multiple decades to allocate fish to WA. The STAT team is still considering the best magnitude of black rockfish in area 3A (dependent on the assumption of black rockfish composition within the unknown rockfish category) to apply to this OR-WA split. The STAT is also considering further information that may confirm the level of black rockfish in 3A that are landed in Astoria but should be assigned to the Washington state history.
Items for Discussion
- Absolute magnitude of historical black rockfish catches in Oregon as a percentage unknown rockfish Landings, In particular, trawl catches in the 3A area.
- The allocation of catches in 3A between Oregon and Washington (currently 1.4% and 98.6%, respectively, for years 1940 - 1993; thereafter, varies annually based on trawl logbook data)
Recreational Landings & Discards
Black rockfish are one of the most important recreational fisheries in Oregon, especially in the ocean boat-based fleets. Boat-based landings were reconstructed in 2015, and only moderate changes were made to the catch history from 2015, based on the most recent comprehensive ODFW sport reconstruction (Whitman in review). A ramp in catch from 1973 to 1979 will complete the series.
For Shore/estuary landings, a more current reconstruction is proposed that uses the filtered weights from MRFSS to reconstruct biomass. A 10 year average of landings from 1996 - 2005 is used to estimate recent landings (2006 - 2022) rather than the 2015 assessment assumption of a linear relationship with fish licenses. There is also a ramp from 1892 - 1979 to account for landings prior to the availability of MRFSS data.
For the final landings time series, estimate of discarded fish will be added to the shore-based landings time series. A review of the available data from RecFIN (2001 - 2022) shows an average % discarded of 0.92%. This low amount of discard is consistent with both expectations from management measures and the desirability of black rockfish in the recreational fishery. Discards for the ocean-boat fleet are available from 2001 - 2022 from RecFIN.
Items for Discussion
There are no major items for discussion regarding the recreational fishery, though there are notable unknowns as far as the historical recreational catches and unsampled shore-based catches. These are not believed to be of a magnitude that should influence assessment output.
Indices of Abundance
Fishery-Independent
There are four fishery-independent surveys that will be explored and considered:
- Adult tagging index (2002-2013, excluded 2002 - 2004 based on ODFW recommendation) - central Oregon pit tagging project
- Adult acoustic survey (2021) - Oregon coastwide hydroacoustic survey developed for mid-water rockfish
- OR marine reserves hook and line survey (2013 - 2022) - standardized hook and line survey in Oregon’s marine reserve network (surveys similar to CA reserve H&L survey)
- SMURFS juvenile index (tentatively, 2011-2022) - YOY rockfish survey in two locations in Oregon’s marine reserves
Only the first was included in the 2015 assessment. Selectivity for this survey was mirrored to the ocean-boat fleet in the 2015 assessment. The first two are potential measures of absolute abundance, the third of relative abundance, and the final could be used as an indicator of recruitment.
Fishery-Dependent
There are four fishery-dependent surveys that will be developed for consideration:
- MRFSS dockside index (1980 - 2000) - MRFSS dockside interviews of ocean boat trips
- ORBS dockside index (2001 - 2022) - ORBS dockside interviews of ocean boat trips
- Oregon on-board observer index (2001, 2003 - 2022) - state observed charter boat trips
- Oregon nearshore logbook index (2003 - 2022) - commercial nearshore fixed gear trips
All four of these were included in the 2015 assessment.
Composition Data
Commercial length compositions
Samples sizes reflect the fact that the fixed-gear fishery is more prominent than the trawl fishery. The trawl fishery is an amalgam of several contemporary gear types that do not necessarily have similar selectivities, but the removals are so small that parsimony argues for a “trawl” gear of other commercial gears taking black rockfish.
Recreational length compositions
The recreational length composition data summarized below represent data pulled from RecFIN collected by either the MRFSS (1980 - 2003) or ORBS (2001 - 2022). MRFSS data has both shore/estuary boat samples and ocean boat samples. ORBS samples ocean boat trips exclusively. Where the two datasets overlap (2001 - 2003), ocean boat samples are combined.
Biology
Maturity and Fecundity
The 2015 assessment was one of the first assessments to use functional maturity to express maturity. Functional maturity takes into consideration skipped spawning, atresia and other factors that may delay a reproductive event as opposed to biological (sexual) maturity that only considers whether the reproductive organs are potentially functioning. Functional maturity often produces a right-shifted curve and/or non-asymptotic behavior. The length at 50% functional maturity is 41.57 cm vs 34.12 cm for 50% biological maturity. The figures below show the difference in the full maturity relationship. Melissa Head and Claire Rosemond, the biologists who have provided this information, have also documented the presence of parasites in about 10% of mature female black rockfish. We plan on using the spline model for functional maturity as the maturity relationship.
Fecundity-at-length is based on Dick et al. (2017) as was assumed in the last assessment and is shared among all black rockfish assessments.
Length-Weight
The length-weight relationship from Oregon in 2015 was based on around 4000 unsexed samples. This relationship will be revisited with additional samples.
Length-at-Age
Black rockfish samples are currently being aged. These are available from both the commercial and recreational fleets, with most samples having been sexed. A comparison from the past assessment of age and length data show clearly the pattern of missing the older, but not larger, females in the samples. This age and length data will be used to estimate growth parameters outside and inside (as conditional age at length data) the model, with the hope that we can rely on growth estimates within the model.
Natural Mortality
Natural mortality is not directly measured, but has been estimated in past black rockfish assessments. We will again attempt to estimate natural mortality for both males and females separately. Females demonstrate a lower frequency of occurrence than expected once they get past age 20-25. This issue is seen from California to Alaska, and has been extensively explored in the “kill ’em or hide ’em” hypotheses. These suggest either females are dying off quicker one they reach maturity (i.e., use an elevated natural mortality to kill them in the model) or have age-specific fishing avoidance behavior causing age-based dome-shaped gear selectivity (i.e., hide them from the fishery and create cryptic biomass). These hypotheses were extensively explore in the last assessment. The last assessment fixed a slight natural mortality ramp (from 0.17 to 0.2). We will likely estimate a constant natural mortality for females that is expected to be higher than males, but explore the sensitivity of results to the former assessment treatment. We will use the Natural Mortality Tool to develop a prior for black rockfish.