TILLMAN and STADELMAN: SIMULATION MODEL OF ANCHOVY FISHERY 



meal and oil in the United States are established 

 primarily by the world market for these products. 

 Consequently we have assumed that northern 

 anchovy processors can only accept the prices of- 

 fered for their meal and oil, rather than being 

 able to affect the world market through their own 

 efforts. In this case, demand curves for their 

 products are nonexistent, and the fixed prices 

 given in Table 9 hold throughout a given simula- 

 tion experiment. 



APPLICATIONS OF THE MODEL 



Analytical Technique 



Nature of Results 



Due to the rough nature of many of the esti- 

 mates utilized by the model, little credence has 

 been attached to the absolute values of economic 

 return, catch in weight, or population size ob- 

 tained in the following simulation experiments. 

 These results are at best only informed extrapola- 

 tions, and, even though their values are of the 

 proper orders of magnitude, it is not the intent of 

 the following applications to accurately predict 

 future returns, yields, or sizes. Of greater impor- 

 tance are the relations between values obtained 

 in different experiments. Consequently, the re- 

 sults have been analyzed on a comparative rather 

 than an absolute basis. 



Criteria for Comparisons 



The primary results obtained from each exper- 

 iment include the net economic return (before in- 

 come tax) generated annually by the entire sys- 

 tem, the number of days fished each season, the 

 annual catch in weight, and population size in 

 terms of annual average biomass. In most exper- 

 iments, these four variables satisfactorily mea- 

 sure the economic and biological performance 

 achieved during an experiment. In preliminary 

 long run equilibrium experiments, values of 

 these variables stabilized within a 10-yr period. 

 Thus, 10 yr has been chosen as the length of all 

 experiments. 



Differences between various experiments are 

 measured primarily in terms of the differences 

 between respective net economic returns. Net 

 economic return is obtained by subtracting amal- 

 gamated harvester-processor costs from amalga- 

 mated gross revenues at the end of each year of 



simulation. Amalgamated costs include the an- 

 nual opportunity costs of labor and capital. 



Alternative Regulations and 

 Stock- Recruit Sensitivity 



Recalling the spectacular decline of the sar- 

 dine fishery during the 1950's and fearing a 

 similar debacle over another forage species, 

 sportsmen and bait fishermen have become 

 allied in sponsoring state legislation to limit com- 

 mercial development of the northern anchovy. As 

 a consequence of their efforts, the reduction 

 fishery has been plagued by low quotas and cur- 

 rently cannot fish during the summer (15 May- 

 15 September) nor within 3 miles (4.8 km) of 

 shore. These two specific exclusions define areas 

 wherein tradeoffs might be made to gain conces- 

 sions from the sport and bait fisheries. Decision 

 makers might retain the summer or inshore clo- 

 sures intact to placate the nonindustrial groups 

 and receive in trade the concession of larger 

 quotas for industrial use of anchovy. Some idea 

 of what is lost by such trades might be obtained 

 by contrasting these closures to others wherein 

 more lenient measures were enforced. 



Some evidence exists which indicates that con- 

 siderable gains in harvesting efficiency might be 

 achieved by lengthening the season to a year or 

 by opening the inshore area. In Figure 3, the 

 pattern of availability extrapolated for May- 

 September indicates that an improving trend is 

 expected during the summer. Also, Tillman's 

 (1972) analysis of age-specific catchability re- 

 vealed that age-groups and 1 tend to be more 

 available in the inshore area than in the offshore 

 commercial fishery area; he subsequently calcu- 

 lated catchability coefficients reflecting this ap- 

 parent areal difference (results given in our 

 Table 7). 



Using these catchability coefficients implicitly 

 assumes that older anchovies (ages 2-6) are 

 equally available in the inshore and offshore 

 areas. As indicated in Figure 3 we have, of course, 

 attempted to account for the seasonal availability 

 of older anchovies as related to their spawning 

 behavior, but the net result of spawning move- 

 ments might also tend to distribute older fish 

 farther offshore than younger ones. This cir- 

 cumstance would effectively reduce the inshore 

 catchability coefficient for older fish. 



Unfortunately, data on the areal distribution of 

 age-groups, such as the age compositions of 



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