Preliminary Staff Regulatory Proposals: 1998

CATCH LIMIT RECOMMENDATIONS

The presentation of staff recommendations for 1998 departs from that of previous years. Staff catch limit recommendations in recent years have been accompanied by only a single estimate of yield from the assessment. Such a presentation reflects neither the breadth of examinations contained in the stock assessment, nor the range of potential biomass associated with key assumptions of the assessment. For 1998, we present potential setline yields estimated using two different assumptions about the selectivity for fish in the standardized setline surveys. We use the surveys as a fishery-independent index of relative abundance in the stock assessment model. The first assumption is that the selectivity of the survey is based primarily on the size of the fish, because fish of different sizes are not equally vulnerable to the survey gear. For example, the fish might have to be of a certain minimum size to bite the size of hooks used in the fishery. Under this assumption, selectivity at length is held constant throughout the period of the assessment, even when growth rates change. The second assumption is that selectivity of fish by the survey gear is based primarily on the age of the fish and reflects primarily the availability of fish of different ages on the grounds. For example, if recruitment were governed by the time it took to migrate to the fishing grounds, irrespective of size, then selectivity would be determined by age, rather than size. Under this assumption, it is the selectivity at age that is held constant over time. Both of these assumptions are plausible although neither may fully reflect the true underlying relationships. The yields associated with these two assumptions are listed under the headings of LEN SEL 1998 and AGE SEL 1998 in the accompanying tables and figures.

In addition to the setline yield estimates based on these two selectivity assumptions, we also present the yields estimated from the 1997 assessment and the quota adopted by the Commission in 1997, for reference.

A new assessment model was introduced in 1997 and the staff was cautious in accepting its results, due both to the number and magnitude of the changes from the previous assessment which were based on known changes in the growth of halibut in recent years. It was also noted that we lacked a comprehensive fishery-independent index of relative abundance with which to calibrate the model. Accordingly, the Staff 1997 catch limit recommendations were lower than the assessment estimates and the Commission adopted quotas that reflected Staff’s caution. A comprehensive, five-year, setline survey program was initiated in 1997 to begin providing the fishery-independent data that have been missing for some areas.

For this year's assessment, we have continued development of the assessment model. During 1997, we commissioned a review of our entire assessment by a panel of external international experts. The panel noted several areas of the assessment that might require greater scrutiny. We have implemented some of these suggestions for this year's assessment. Estimates from the model continue to indicate a substantial biomass of halibut. Biomass estimates using the length-based selectivity assumption are only slightly higher than those using the age-based assumption, except for Area 3A where the length-based assumption estimates a much higher biomass. Commercial CPUE increased in 1997 for all areas (+10-22%) except Areas 3A and 4, which experienced modest declines (-1.4 and -5.4%, respectively). In addition, survey CPUE estimates remained near existing levels or increased over 1996 values where comparisons are possible (notably in Areas 2C and 3A). The model has also benefited from the data obtained during the first year of the comprehensive survey program, which has broader areal coverage than the fishery.

In summary, the analytic assessment, the standardized surveys, and the commercial fishery all indicate that the exploitable biomass of halibut is at a high level. In developing catch limit recommendations based on these findings, the staff was also guided by consideration of other issues about the dynamics of the halibut stock and the need for a precautionary approach to management. Six items are of particular concern.

1. The estimated yields from the assessment are, in aggregate, higher than any catches in the history of the halibut stock. The historic yield from the halibut fishery occurred in 1962 when total removals, including bycatch and directed foreign catches, were approximately 100 Mlb. This level was also approached in 1988, when total removals were approximately 99 Mlb.

2. We continue to develop the assessment model and have but a single year of data from the comprehensive survey program. We need to have additional years of data from the survey program and to proceed with the resolution of some outstanding issues within the analytic assessment.

3. Any catches of halibut from present levels of biomass are not considered to be sustainable because the underlying biomass is expected to decline, as a result of natural fluctuations in recruitment. The time frame of such changes is not known and their prediction is an area of Commission research.

4. We believe our harvest policy is robust to those changes in stock dynamics that are generated through natural recruitment variation. The virtue of such policies is that they allow yields to follow the natural fluctuations of the stock biomass. However, the major increment in estimated biomass in recent years is not associated exclusively with natural changes, but also represent changes to our stock assessment methodology. These biomass changes are substantial and would result in abrupt changes in yields if quotas were based solely on the fixed harvest rate that we consider appropriate for sustainable management. Such yields are also substantially higher than the estimated long-term average yields that would be obtained under fixed harvest rates. We estimate this long-term average yield to be in the 55-65 Mlb range, for the stock as a whole. Therefore, we believe that caution should be exercised in increasing yields in consideration of maintaining stability in the fishery, a concern that has always been a component in the choice of harvesting strategy.

5. The distribution of fishing in some areas is highly localized relative to the distribution of assessed biomass and our standardized surveys. We are concerned that removal of yields from areas more restricted than that of the assessed biomass may lead to localized depletions. While tagging and fishery evidence suggest that halibut from unfished areas regularly re-populate such fished areas, we do not know the precise time frame for such replenishment. The precautionary management approach should therefore set yields to avoid the potential for serial depletion of successive areas if replenishment does not occur within one year.

6. Areas 4 and 3B have limited or no history of standardized surveys and/or market sampling sufficient for a detailed analytic assessment. A persistent anomaly of the analytic assessment is a lower estimated biomass in Area 3B relative to that in 3A than is estimated with the standardized surveys. The assessment indicates 3B contains about 27% of the 3A biomass while the surveys suggest it contains about 61% of the 3A biomass. The analytic assessment is also believed to produce poorly determined estimates for Area 4 because of the lack of historical survey information from the area, and the restricted area covered by the fishery. We therefore require a method to deal with these areas that combines sources of information for which we have higher confidence.

Staff catch limit recommendations do not approach the yield estimated using either the length or age-based selectivities, even though we have high confidence in the assessment methods. Indeed, we believe that the abundance of halibut is high. However, we also believe that a graduated approach to yield increases is prudent and adheres to the precautionary management principle. If biomass levels are as high as assessed levels indicate, then there will be some loss of yield with quotas set below the CEY level. However, this yield loss must be balanced against our caution concerning rapid quota increases while we continue to evaluate our analytic assessment and collect necessary fishery-independent information. Our framework for catch limit recommendations in Areas 2A-3A is therefore to step from 1997 quotas toward the age-based selectivity estimates of setline yield (the lower of the two model estimates), using equal increments over a three-year period. This results in recommended catch limits that increment the 1997 quotas by 33% of the difference between these quota levels and the age-based selectivity estimates of setline yield (Table 1, Fig. 1).

For Areas 3B and 4A/B, we use a procedure that scales the estimates of exploitable biomass and setline CEY in Areas 2A-3A (the reference area), by the relationship between estimated survey biomass in either Areas 3B or 4A/B to that in Areas 2A-3A, (Tables 2-4, Fig. 2). For example, this means that if the survey estimate of biomass in Area 3B was 40% of that in Areas 2A-3A combined, then the exploitable biomass (and setline CEY) in Area 3B would also be 40% of that estimated for Areas 2A-3A with the analytic model. These relationships can be seen in Tables 2-4. Following determination of the appropriate setline CEY estimates based on the model, we apply the same three-year incremental approach to catch limit recommendations. We note that the large differences in the age-based vs. length-based estimation in Area 3A is projected into this procedure because Area 3 represents a large component of the reference area.

It is important to recognize that we have also presented an age-based assessment for Area 3B and it results in lower estimates of biomass than this scaling procedure. The relationship of the two sets of estimates can be seen in Fig. 3. The precision of this age-structured estimation is much lower than that for other areas where we have adopted the age-structured results, largely due to the lack of a historical survey series for the area and the restricted distribution of the fishery. We have also considered the strong difference in the two years of survey estimates of biomass distribution between Areas 3A and 3B vs. that in the age-structured assessment. In summary, we believe that the survey-scaled procedure more appropriately reflects our perception of the true biomass. In future, the acquisition of a longer time series of survey estimates or different combinations of areas in the assessment may lead to age-structured estimates for Area 3B in which we place greater confidence.

Lastly, we required a specific procedure to provide a recommendation for Area 4C/D/E. We calculate two separate estimates of setline CEY for this area, using the foregoing procedure. One estimate is for all of the area and the other is for only the 4C/D continental shelf edge, where almost all of the fishery occurs. We provide these two estimates to show the impact of including the Eastern Bering Sea Flats, where substantial but low-density biomass exists, in our calculations. If this area were to be fully included in catch limits, then the recommendation would be about 6 Mlb. We believe that some of this biomass eventually mixes across the 'edge' and is not separately vulnerable to a fishery on the 'flats'. We therefore consider that the Area 4C/D/E quota should be increased slightly over the 2.07 Mlb that would be calculated solely from consideration of the 'edge' area, and present a recommendation of 3.0 Mlb.

Fishing Periods

Individual quota fisheries will be in effect for all areas except Area 2A. The staff is still in favour of a winter closure to reduce the interception of fish that move between regulatory areas during spawning migrations, but will not object to a March 15 to November 15 that was in place during 1997.

In Area 2A, the staff recommends fishing periods similar to those in effect in 1997: a series of 10-hour periods, with fishing period limits to be sure the catch limit is not exceeded. The size of the fishing period limit will be determined later when more information is available on fleet size.

Miscellaneous Recommendations

The staff recommends eliminating the requirement for sport charter licenses in British Columbia and Alaska in 1998. The present license system does not provide information of value to IPHC assessment or management, and therefore is an unnecessary requirement for industry. The staff recommends no change in the license system in Area 2A where licenses are used as part of the allocation regulations developed by the Pacific Fishery Management Council.

The staff recommends reviewing the need for the present Closed Area in the Bering Sea in 1998, and possibly opening the area to halibut fishing in 1999. The area was originally closed to protect juvenile halibut in 1967 . However, the area is presently open to fishing for other species and is a major area of halibut bycatch. Keeping the area closed to halibut fishing may have little benefit, and prevents harvesting large halibut that occupy the area in low densities.

The staff recommends that all vessels greater than 25 feet fishing for halibut complete an official logbook. This proposal primarily applies to U.S. vessels because Canadian regulations already require an official logbook for Canadian halibut vessels. An official logbook would be defined as the current IPHC logbook, the NMFS catcher vessel logbook, or other possible logbooks that are acceptable to IPHC, NMFS Enforcement, and U.S. Coast Guard. We welcome suggestions from the Industry on this issue.

Table 1. Halibut Setline Yield

* CEY scaled using survey estimates

Table 2. Standard Exploitable Biomass (millions of pounds) used for calculating biomass in Areas 3B and 4.

Table 3. Exploitable biomass (millions of pounds) in Areas 3B and 4, relative to exploitable biomass in Areas 2A-3A.

Table 4. Total CEY and Setline CEY (millions of pounds) for Areas 3B and 4, calculated from Table 3.

Figure 1. Comparison of Setline Yields - Areas 2 and 3

Figure 2. Comparison of Setline Yields - Area 4

Figure 3. Comparison of Setline Yields - Area 3B