These process-explicit ecosystem models with spatial representation are also 

 useful for investigating the impacts of various alternative management strategies. 

 Improved data gathering technologies (e.g., satellite remote sensing), combined 

 with improved computer capabilities will render these complex models more 

 credible, giving them wider acceptance, and they will probably become the 

 preferred management tool of the future. 



The fact remains that rational decisions must be made now, in the 1980s, 

 concerning relatively complicated and important resource management alterna- 

 tives. The indicator species, process-explicit modeling approach to environmental 

 impact assessment provides a workable compromise between the statistical and full 

 ecosystem approaches. Single species indicator models have seen extensive use 

 in assessing the impact of power plant location and operation in riverine, 

 estuarine, and coastal areas on commercial and sport fisheries (Lawler 1972; 

 Hess et al. 1975; Van Winkle 1977; Spaulding and Isaji 1979). Narrowing the 

 scope of an ecosystem model to address one important species, retains process- 

 explicit capabilities (e.g., physical transport, migration, or feeding), 

 increases validation potential through parameter identif lability (Gentil and 

 Blake 1981), and therefore model credibility, while reducing time, expense, 

 and data demands in development. In short, a single species modeling approach, 

 augmented by a judicious choice of processes for inclusion in the model, represents 

 a utilitarian compromise between the two other alternatives discussed above, and 

 provides a useful methodology for estimating environmental impacts and investigating 

 management alternatives. 



The single species modeling approach has been used to estimate the impact 

 of oil spills on the Georges Bank cod fishery (Reed 1980; Reed et al. 1981). 

 This impact assessment methodology is currently being extended to additional 

 species (Spaulding, Saila et al. 1981; 1982). A summary of some recent results 

 from this work follows. 



OVERVIEW OF OIL SPILL FISHERY IMPACT ASSESSMENT MODEL SYSTEM 



The oil spill fishery impact assessment model system addresses first order 

 direct impacts of oil on a commercial fishery through hydrocarbon-induced egg 

 and larval mortality. The model system components follow the approach given by 

 Reed (1980), Reed and Spaulding (1978, 1979), and Reed et al . 1981 for the 

 hydrodynamic, ichthyoplankton transport and fates, and oil spill fates components, 

 and the approach given by Lorda and Saila (1980) and Lorda et al. (1982) for 

 the fish population dynamics component. The simulated processes within an 

 relationships among these four models are shown in figure 1. 



In operation, the ichthyoplankton transport and fates model, using a 

 toxicity threshold assumption, output from the oil fates model on the distribu- 

 tion of spilled oil, and a definition of the spatial and temporal spawning 

 patterns of the species of interest, estimates the oil-induced mortality of eggs 

 and larvae. Surviving eggs and larvae undergo transport and mortality as usual, 

 except that density-independent mortality is increased in proportion to the 

 number lost due to the oil spill. An impact analysis is achieved by running the 

 fishery model to determine the perturbations caused by the spill event on the 

 baseline equilibrium catch. 



105 



