If fisheries science is to be successful we must learn from and avoid the mistakes of the past. We must recognize that stock assessment involves understanding and making predictions about the response of fishery systems to alternative management actions. We must help managers make ''choices" about "dynamic" fishery systems in the face of "uncertainty."
Quantitative Fisheries Stock Assessment: Choice, Dynamics, and Uncertainty
R. Hilborn and C. Walters 1992
The matter in hand is not simply a scientific one. It is a complicated matter, and has its economic as well as its technical side.
An Enemy of the People
Stock assessment is only one component of the fishery management process. However, it is the primary scientific basis for management of the fishery. When reviewing any fishery management process, it is important to clarify which issues are in question. In some cases, stock assessments are challenged when the contentious issue is some other aspect of the management process. Recent research has demonstrated that the uncertainties inevitably associated with stock assessments create opportunities for strategic, self-interested behavior on the part of council members, the fishing industry, politicians, and interested parties (Healy and Hennessey, 1998a, 1998b). This seems to be the case with the Northeast fishery.
The committee met with interested parties at a public hearing in Gloucester, Massachusetts, on July 11, 1997 (see the section "Public Hearing" later in this chapter). It appeared to the committee that the main reasons for questioning the assessments were the strong management measures proposed as a result of the 1994 assessments, not the assessments themselves. Those at the hearing generally agreed with the results of the current assessments, which indicate substantially lower fishing mortality in 1995 and 1996, and increasing spawning stock biomass for four of the five stocks reviewed. For Gulf of Maine cod, where fishing mortality remains high and stock size low, interested parties at the public hearing did not appear to disagree with the current assessment, but some harvesters were concerned that new management measures might further restrict their fishing operations.
Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 69
4 SCIENCE AND MANAGEMENT If fisheries science is to be successful we must learn from and avoid the mistakes of the past. We must recognize that stock assessment involves understanding and making predictions about the response of fishery systems to alternative management actions. We must help managers make ''choices" about "dynamic" fishery systems in the face of "uncertainty." Quantitative Fisheries Stock Assessment: Choice, Dynamics, and Uncertainty R. Hilborn and C. Walters 1992 The matter in hand is not simply a scientific one. It is a complicated matter, and has its economic as well as its technical side. An Enemy of the People Henrik Ibsen ROLE OF STOCK ASSESSMENT IN THE FISHERY MANAGEMENT PROCESS Stock assessment is only one component of the fishery management process. However, it is the primary scientific basis for management of the fishery. When reviewing any fishery management process, it is important to clarify which issues are in question. In some cases, stock assessments are challenged when the contentious issue is some other aspect of the management process. Recent research has demonstrated that the uncertainties inevitably associated with stock assessments create opportunities for strategic, self-interested behavior on the part of council members, the fishing industry, politicians, and interested parties (Healy and Hennessey, 1998a, 1998b). This seems to be the case with the Northeast fishery. The committee met with interested parties at a public hearing in Gloucester, Massachusetts, on July 11, 1997 (see the section "Public Hearing" later in this chapter). It appeared to the committee that the main reasons for questioning the assessments were the strong management measures proposed as a result of the 1994 assessments, not the assessments themselves. Those at the hearing generally agreed with the results of the current assessments, which indicate substantially lower fishing mortality in 1995 and 1996, and increasing spawning stock biomass for four of the five stocks reviewed. For Gulf of Maine cod, where fishing mortality remains high and stock size low, interested parties at the public hearing did not appear to disagree with the current assessment, but some harvesters were concerned that new management measures might further restrict their fishing operations.
OCR for page 69
Given that the inherent uncertainty of stock assessments leads to concerns about their central role in the fishing management process, there are two conditions that must be met for stock assessments to be useful in management. First, managers must trust that the uncertainty is within acceptable bounds. Second, managers must act on this trust and use the information in a timely manner. Uncertainty in Stock Assessments Uncertainly in stock assessments can be introduced by a variety of factors, including limited survey information, lack of catch and discard data, and limited or incorrect size and age information, as described in Chapters 2 and 3. One method of describing the uncertainty is by showing the coefficients of variation for survivorship estimates. The coefficient of variation (CV) defines the level of variation in an estimated mean value: high CV indicates a high degree in variation; low CV indicates a low degree of variation. Coefficients of variation of the survivor estimates by age for each of the five stocks assessed are given in Table 4.1. These CVs are typical of age-based assessments calibrated with two to three survey-based stock size indices. As indicated in "Evaluating the Consequences of Alternative Management Actions" (Chapter 2), the uncertainties in stock projections can even be greater than suggested by the CVs in Table 4.1. The fishery management tools implemented for the Northeast groundfisheries do not now involve the setting of total allowable catches (TACs). Uncertainties of this magnitude might jeopardize the credibility of a TAC-based management system in which TAC is adjusted yearly in response to changes in stock size in an attempt to maintain a given exploitation rate or keep the biomass above a given threshold. The principal management measures used in Amendment 7, days at sea and closed areas, do not demand the amount of precision in assessments that TAC management systems do. However, the committee suspects that effort controls of the sort used here will lead to improvements in efficiency by harvesters, which will eventually negate the intended reductions in fishing effort. Therefore, mechanisms to monitor and assess fishing efficiency will be necessary. Furthermore, it is now not possible to predict what future levels of fishing mortality will be, based on current management regulations. Perhaps such predictions will be possible after the current regulations have been in place for a number of years. Regardless of the management system, the uncertainty in assessments can be reduced by estimating total removals more reliably; collecting more biological samples to characterize the catches; reducing the variance of survey-based stock size indices; and perhaps, deriving stock size indices from commercial or recreational fisheries. It is clearly impossible to implement a science-based decisionmaking process without collecting and analyzing information. The costs involve normal expenditures that must be borne in any kind of business that relies on analyses for decisionmaking. Data collection and analysis are particularly required when individual enterprises benefit from resources that collectively belong to the nation. Timely Use of Stock Assessment Information Stock assessments are irrelevant if the information provided is not used in a timely manner by fishery managers. In the case of Northeast groundfish, strong management measures appear to be justified by the stock assessments performed for a number of years. Estimates of fishing mortality were very high and increasing, estimates of spawning stock biomass were very low and decreasing, and some estimates of recruitment were at or near the lowest on record, indicating that the harvesting strategy was not sustainable. Management actions prior to 1995 had little effect on controlling fishing mortality, so that only the series of actions commencing with Amendments 5, 6, and 7 seem to have been able to reduce fishing mortality to levels that may be sustainable. The 1997 assessments show some positive
OCR for page 69
TABLE 4.1 Coefficient of Variation (percent) of Survivor Estimates by Age Age Gulf of Maine coda Georges Bank codb Georges Bank haddockc Georges Bank yellowtaild Southern New England yellowtaile 1 52 62 2 46 33 40 53 71 3 31 27 31 35 44 4 31 27 29 32 36 5 41 28 27 22 34 6 57 30 26 7 32 33 8 33 34 9 a Table 17; Mayo, 1997. b Table 20; O'Brien, 1997. c Page 15 (Appendix); Brown, 1997. d Table 19; Cadrin, et al., 1997. e Page 55; Overholtz, et al., 1997. signs of increases in spawning biomass and a widening age composition in the population and catch, although these estimates are uncertain and could change as new information becomes available. It is difficult to say which of the regulations (e.g., which closed areas, what reduction in days at sea) have contributed most to the estimated reduction in fishing mortality. Future stock assessments will have to address this question. In assessing the value of timely stock assessment information it is important to note that the failure of managers in Canada to incorporate scientific information appropriately played a central role in management decisions that helped precipitate the collapse of Atlantic cod in eastern Canada (Hutchings et al., 1997). STRATEGIC THINKING AND PROCESS In marine wild capture fisheries, such as the ones under review, fisheries management is often more about managing human activities than managing fish, because there are substantial ecological, economic, and technical constraints on marine fish enhancement. In an ideal fisheries management system, the management agency and interested parties specify social, economic, and biological management objectives to be reached. The scientific assessments then help scientists and managers evaluate the probabilities of reaching these management objectives under various scenarios. In the Northeast fishery, the specification of both long-term and short-term goals is the purview of the New England Fishery Management Council. Biological limit reference points and the definitions of overfishing and biomass thresholds are now used as de facto objectives. This interim strategy is designed to start the rebuilding process for fish stocks, but at some point, long-term management goals will have to be developed. It is quite possible that stringent management measures, such as those contained in Amendments 5, 6, and 7, would not have been necessary, had a long-term strategy been formulated and implemented in the 1980s. It is possible that implementation of alternative management measures also could result in stock rebuilding.
OCR for page 69
Science has a role to play in assisting management with the process of adopting clear social and economic objectives within biological constraints and developing a management plan designed to reach the objectives. The first role is the customary one of stock assessment science: to investigate the biological productivity of fish populations in a changing world and the effect of harvesting on that productivity. The second role is to identify the socioeconomic changes that might occur due to changes in biological productivity and management measures. Socioeconomic studies have been conducted in the Northeast (Aguirre International, 1997; Clay and Dolen, 1997; OECD, 1997) and have had an influence in the decisionmaking process. One challenge is how to incorporate socioeconomic considerations formally and explicitly into scientific advice and the decisionmaking process. Such a policymaking framework or process would include, to a much larger extent, the participation and concerns of stakeholders in the fishery. Giving stakeholders more say in formulating and implementing policy might mitigate some of the existing tensions between NMFS and harvesters, as well as transfer some of the responsibility for the consequences of policy to those involved directly with exploiting the fishery. The stock assessment group could undertake a number of analyses, probably in collaboration with a fisheries economist, that might greatly enhance the New England Fishery Management Council's ability to evaluate policy options and set more stable and socially acceptable management policies. Such policies would take a long-term view, with built-in adaptive components; provide interested parties with prior knowledge of what happens when a run of poor recruitment years reduces stocks to dangerously low levels; and enable them to make contingency plans for such events. Most of these additional analyses that could be undertaken come under the rubric of "scenario experimentation." To provide some idea of the types of risk analyses that might be useful to managers, for example, consider the issue of setting a policy to rebuild stocks. Additional analyses would provide an evaluation of how projections may be affected by both uncertainties in the true values of fishing mortality each year and the form of the stock-recruitment relationship (as mentioned earlier). Specific questions that might be addressed include the following: What if the real level of fishing during the past season is much higher (or lower) than estimated and current regulations are unchanged? What if actual recruitment potential over the next two to three years is much stronger (or weaker) than anticipated, yet current regulations cause a particular proportion of harvesters to abandon the industry during the next season? What if historically high levels of recruitment never return once the stocks are rebuilt, because of fundamental changes to the ecosystem (e.g., changes in food web structures, pollution, or gear damage to the environment)? For such additional risk analyses to be worthwhile, greater interaction and information exchange between assessment scientists and policymakers may be needed. Scientists can help policymakers develop long-term strategies for managing the fisheries, rather than merely short-term tactics to get the fisheries through their current difficulties. Similarly, policymakers can help scientists in their assessment activities by articulating clear policies that can then be investigated with careful scientific modeling of both assessment and management processes. PUBLIC HEARING The committee devoted one afternoon to a public hearing with harvesters and representatives of harvesters' associations, representatives of conservation and environmental organizations, and social scientists studying harvesters. Formal presentations were made by some participants and informal comments were provided by others. Several opportunities were provided during the afternoon for informal discussions between participants and committee members. Some of the salient points raised at this hearing are as follows:
OCR for page 69
Participants generally agreed that the current regulations designed to reduce fishing mortality are working. Environmental groups stressed the importance of continuing regulatory measures leading to the rebuilding of stocks. A number of harvesters and representatives of their associations, as well as sociologists working with them, stressed their concerns that environmental factors not included in stock assessment models may play an important role in determining stock sizes. Pollution and global climate changes were raised as two of the possible environmental factors. Harvesters and their representatives spent a good portion of the public hearing criticizing fisheries management measures, specifically their development and implementation. Although they reported having ample opportunities to speak at hearings and other meetings, they expressed feelings that no one was really listening to them. They reported difficulties in communicating effectively with National Marine Fisheries Service (NMFS) scientists in the past, although they mentioned an improving climate of interaction recently. Harvesters repeatedly stated that the way in which regulations were implemented, often one on top of another, made planning difficult. The harvesters expressed concern that they alone had to pay for the mistakes of the past—both their own and those of government. In particular, they pointed out that when foreign harvesters were excluded when the exclusive economic zone (EEZ) was introduced in the 1970s, various public plans were put in place to increase the capacity of the Northeast fishing fleet. The plans encouraged recruitment of harvesters and increased investments in the industry, evidently in excess of what the fishery could sustain. "Is it right," they ask, "that the harvesters now should bear the burden of the government's overoptimism then?" Committee Comments on the Public Hearing The committee's task is to review the scientific basis for stock assessment techniques, and its considerations are necessarily focused on scientific issues rather than social, economic, and management-associated concerns. Thus, although the major points raised at the public hearing have been reported here, the committee cannot directly address those that do not deal with scientific issues of stock assessment. All of the concerns raised at the public hearing, however, have served the useful purpose of reminding committee members of the impact of stock assessments on the community of harvesters. The committee has endeavored to make its scientific review with these human concerns always in mind. It was heartening to learn that there appears to be a general recognition that fishing mortality is decreasing and that stocks are increasing. No one seems to doubt that the current effort to restore depleted fish populations is succeeding. Likewise, the reports of improved communication between harvesters and NMFS scientists may help to reduce misunderstanding about the way stock assessments are produced and used in fisheries management. The committee learned that harvesters will begin to accompany NMFS personnel on scientific surveys; the committee commends this effort and encourages the continuation and extension of similar efforts. Because the regulation of fishing effort affects the livelihood of harvesters and because regulations flow directly from the stock assessments, it is inevitable that harvesters should be concerned about the stock assessment process. Mutual efforts at communication and education can only help reduce tension between harvesters and management.
OCR for page 69