/harvest/Jul2notes.pdf

At the last full committee meeting (May 26) Troy reported that the PSC Chinook Model shaker algorithm appeared to be incompatible with the new model framework. This turned out to be the case, and the problem was discussed by the work group. The main difficulty is that the current algorithm uses the somewhat arbitrary "Preterminal" and "Terminal" designation of a stock/fishery combination to compute some intermediate variables. For example, during the preterminal time step, age 2 and age 3 cohorts from Fraser River stocks are considered unavailable to the Fraser Net fishery (because they are designated "terminal" for that fishery), but are considered available for all other fisheries. This creates the unusual situation where the Fraser River net fishery is allowed to occur during the preterminal timestep and to harvest age 2 and age 3 fish from non-Fraser River stocks, but is prevented from harvesting age 2 and age 3 fish from Fraser River stocks.

Jim showed a table illustrating how the new model structure could be configured to represent the above ocean net fishery situation (see notes at: /harvest/Jul2notes.pdf). The ocean would be divided into several subareas. At the start of each year, all age 4 and age 5 cohorts from all stocks would reside in an open ocean region. The age 2 and age 3 cohorts would occupy appropriate near-coastal subareas. For example, these cohorts from the Fraser River stocks would occupy a Fraser River preterm area, and the Puget Sound stocks would occupy a Puget Sound preterm area. During the preterm timestep, all troll fisheries would operate in all preterminal areas (open ocean plus all subareas). The net fisheries would not operate in the open ocean area, and would be assigned to operate in all preterm subareas except the area associated with stocks from their river system. For example, the Fraser River net fishery would be assumed to operate in the WCVI, Puget Sound, and all other age 2 and age 3 preterm areas except the Fraser River preterm area (in which the age 2 and age 3 Fraser River cohorts are located, but which they are not allowed to harvest during the preterm timestep). Similar subarea designations would be required for terminal areas.

Jim noted that another option for the new model was to assign "Preterm" and "Term" flags to each cohort/fishery combination and write a special shaker algorithm. Jim Scott suggested that this option not be selected, and that the new model be configured as above to implement the PSC chinook model shaker algorithm. Jim Norris agreed to reconfigure the new model, rather than use the flag system.

Another algorithm discussed by the work group was the FRAM South Puget Sound allocation/escapement goal algorithm. Jim passed out a narrative description of that algorithm (available for viewing at: : /harvest/Jul2notes.pdf).

Jim reiterated that the current code design includes (1) Harvest Process that describes the relationship between fishing mortalities (legal and incidental), fishing effort, and fish abundance at the year, timestep, region, fishery, cohort level, and (2) Fishing Process that determines the fishing effort required at the year, timestep, region, and fishery level to meet some objective. Thus, the output from a Fishing Process is an amount of fishing effort which is input to a collection of Harvest Processes, each of which returns fishing mortalities. One conclusion from the work group meeting was that it appears that higher level processes should output constraints (e.g., fixed harvest rates, a quota, escapement goal) to Fishing Processes. The next higher level process would be a "Region Process" that controlled constraints on fisheries at the year, timestep, and region level. Jim noted that under this configuration interactions between fisheries operating within the same timestep and region would be handled by a Region Process, not individual Fishery Processes.

Jim Scott asked whether the above framework was consistent with the type of harvest rates that would be estimated by the SSM. His general concern was that the new model framework should be consistent with the SSM model estimates, and that these estimates might have inherit assumptions about interactions between fisheries operating within the same region. Jim Norris said he would look into this subject and report back.


4. Update on model comparisons program (Jim Norris).

Jim reported that computing parameters for the SSM and the Proportional Migration (PM) model required storing life history data for each school in the Base Model (e.g., timestep, location, abundance, fishery index, and region index). When he attempted to do this by creating a list of life history records for each school, the number of objects became too large for the Visual Basic development environment. Thus, he stored the life history data into MS Access database tables. This worked fine, and was faster. The program now plots the abundance and location of each school in the Base Model. The code to do the SSM and PM model parameter estimates has not been implemented yet.


5. Experimental design recommendations for model comparisons (Jim Norris).

Jim showed his planned BaseModel configuration for doing model comparisons. His goal is to approximate the passage of Voights Creek stock through several regions and fisheries. The configuration included the following:

Five regions: ocean, Juan de Fuca Strait, Area 6B9, South Sound, and River (spawning area).

Seven fisheries: ocean troll, Juan de Fuca sport and net, Area 6B9 sport and net, and South Sound sport and net.

One stock: Voights Creek surrogate with two cohorts--marked and unmarked.

Jim noted that in the existing FRAM model the sport fisheries are treated as "preterminal" for all stocks, even though they actually occur in the same geographic regions as the net fisheries, which are considered "terminal." After a lengthy discussion of the difficulties in duplicating this arrangement (the problem is similar to that of simulating the PSC Chinook Model Shaker Algorithm discussed earlier in the meeting), it was decided that for the purposes of the model comparisons, the sport fisheries should be considered as "terminal" in the FRAM model.

Jim presented some preliminary ideas about how the model comparisons program could be used to determine the inherent biases of each model (FRAM, PM, SSM). The discussion made clear that these ideas were not fully thought out yet, and he promised to provide a written description of the proposed methods.

Ken Newman presented some ideas for the experimental design. He noted the following six factors (or "treatments") that may be included in the analysis:

-- Fishery types (commercial troll, sport, gillnet, etc);
-- Harvest plan (effort by time and region);
-- Stock (e.g. may have up to 50 stocks);
-- Natural survival;
-- Initial distribution;
-- Migration (rates and pattern).

Jim Scott and Gary Morishima suggested two additional factors:

-- Growth;
-- Measurement errors.

Even with only two levels per factor that would create 256 possible combinations. Ken recommended reducing this to 32 (or 16, if possible) combinations with the following factor levels:

-- 1 set of fisheries;
-- 2 harvest plans;
-- 2 stocks;
-- 2 natural survival rates;
-- 2 initial distributions;
-- 2 migration patterns.

Once the treatment combinations are determined the evaluation analysis proceeds in three steps.

Step 1. Generate baseline data. Generate 6 baseline years of data by running 6 simulations of the survival, fishing, and migration processes. The data from these six simulations would be used by the different models to estimate parameters and calibrate the model. One approach (per simulation) is to fix the stock and release number and then:

 -- randomly select survival rates according to a uniform distribution between the low and high values from the above survival factor;
-- randomly generate a fishing plan (e.g., take the 2 plans in the fishing plan factor, randomly pick a plan, then use a Poisson distribution to randomly perturb the effort in each time-area cell;
-- randomly distribute the initial survivors in space (uniform, truncated normal, etc);
-- simulate "some" migration process.

Step 2. Generate the "truth." For each treatment combination simulate 100 random sets of data (catches, abundances) at finest space-time resolution. These 100 simulations will represent the pre-season uncertainty even if one knew the parameters. You could then calculate the average catches, abundances, escapement to arrive at a single number. If one wants a single number for the "truth", running the true model in deterministic mode is not going to give the same result as the expected value for runs made in a stochastic mode. For each stock/fishery/time/region cell compute the distribution parameters of the 100 simulated catches.

Step 3. Simulate each treatment. The modelers have the 6 base years for calibration--but these are independent of step 2 above. For the model evaluations, the modelers would only get the stock, release number, catch (??) and effort by time and area used in step 2. They would not see any of the 100 simulations. The modelers run their models to predict what the catch and escapement will be under each treatment combination in step 2.

Step 4. Evaluate performance. The qualities of the models would be measured by distance between their predicted catches by time and area (and escapement) and the "true" catches. There's several ways to define distance:

 -- Method a.

    Sum_{time} Sum_{area}

    Catch-bar_{time, area}*(percentile_{time, area}(model) - 0.5)^2

where Catch-bar is the average of the 100 simulations and percentile_{time, area)(model) is the percentile the modeler's forecasted catch falls into amongst the 100 simulations.

 -- Method b.

    Sum_{time} Sum_{area}

   (Catch_{time, area}(model) - Catch-bar_{time, area})^2
    ------------------------------------------------------
                Catch-bar_{time, area}

where Catch_{time, area}(model) is the modeler's forecast. This measure is just like a Chi-square goodness of fit.

-- Method c.

   Sum_{time} Sum_{area}

  (Catch_{time,area}(model) - Catch-bar_{time,area})^2

 Ken recommended Method a because it gives higher weights to larger catches. There was a general discussion of these suggestions, but no specific analysis plan was adopted.


6. Report on June PFMC meeting (Robert Kope).

Robert reported that the June PFMC meeting dealt mostly with non-salmon issues, and had no salmon issues of significant concern to this committee.


7. Next Meeting.

The next meeting will be held on July 30, 1998 at 9:00 am at NMFS Montlake.