POWER PLANT IMPACT ASSESSMENT: 

 A SIMPLE FISHERY PRODUCTION MODEL APPROACH 



Alec D. MacCall, 1 Keith R. Parker, 2 Ronald Leithiser, 3 and Bill Jessee 3 



ABSTRACT 



The relative abundance of a cohort affected by power plant entrainment mortality as a fraction (R c ) of the 

 abundance of that cohort in the absence of power plant impact can be calculated by R c = exp (— E.-fc) where t- 

 is the duration of life stage i, and£, is the entrainment mortality rate at stage i. Rate E, can be estimated by the 

 ratio of nonsurviving entrained organisms during a given time interval to the mean standing crop of stage i 

 organisms in the source water during that interval. An estimate of adult abundance allows calculation of 

 equivalent adult losses. When insufficient information is available to determine the long-term effect on the 

 population, the fishery "potential yield" formula provides an interim estimate. Relative equilibrium abun- 

 dance of the affected population (R e ) is approximated by R e = 1 - (LE,f; + F p + F f )/2M, where F is adult 

 mortality rate due to power plant impingement, F f is adult mortality rate due to fisheries, and M is adult 

 natural mortality rate. As in the case of the "po'ential yield" formula, this approximation of long-term 

 equilibrium impact should be discarded when better estimates can be developed. 



In recent years considerable effort has been expended 

 in evaluating the impact of fish removals by intake 

 cooling water systems at power plants in the United 

 States. Methods of impact assessment are as diverse 

 as the power plant sites at which the studies have 

 been conducted, but may generally be classified into 

 those which, according to Hackney etal. (1980), 1) of- 

 fer an "expert" opinion as to the presence or absence 

 of impact, or 2) are fish population models in which 

 the sensitivity of the source water fish populations 

 are examined under varying impingement rates. 



The first category of assessments generally at- 

 tempts to compare losses of organisms owing to 

 power plant operation with sport and commercial 

 fishery harvests and/or estimates of standing stock 

 (DeMartini 1979). For adults, which are subject to 

 impingement, comparison is fairly straightforward. 

 However, for eggs and larvae, which are subject to en- 

 trainment, meaningful comparison is less direct. 

 Goodyear (1978) extended a method proposed by 

 Horst (1975) for treating entrained larvae in terms of 

 equivalent adult losses which may then be con- 

 sidered alongside losses because of impingement. 

 The second category of assessments includes more 

 complex models using Leslie matrices (Vaughan and 

 Saila 1976; Horst 1977; Vaughan 1981), differential 

 equations (Hackney et al. 1980), or stock-progeny- 

 recruit models (Christensen et al. 1977). 



' Southwest Fisheries Center La Jolla Laboratory, National Marine 

 Fisheries Service, NOAA, P.O. Box 271, La Jolla, CA 92038. 



2 KRP Inc., 1837 Puterbaugh, San Diego, CA 92103. 



'Lockheed Ocean Sciences Laboratory, 3929 Calle Fortunada, San 

 Diego, CA 92123. |"^-(.l*) 



Manuscript accepted December 1982. 

 FISHERY BULLETIN: VOL. 81, NO. 3, 1983. 



Several problems are inherent in many of these 

 methods. There is an absence of an impact "scale" 

 which enables the investigator to judge objectively 

 the significance or insignificance of fish removals 

 relative to the source water stock and to removals by 

 fisheries. Additionally, sophisticated methods such 

 as Leslie matrices and Goodyear's (1978) calculation 

 of equivalent adult losses require life history pa- 

 rameters (i.e., fecundity, survivorship), which are of- 

 ten unknown for the species in question, and require 

 substantial expenditures of time and money to ob- 

 tain. Finally, these models may be difficult to inter- 

 pret. While the investigator may understand the 

 subtleties of interpretation, agency reviewers often 

 lack the technical background to evaluate the results 

 of complicated models. 



The approach presented in this paper will alleviate 

 many of the above problems. The proposed methods 

 draw on techniques and models used in fishery 

 management in order to provide a criterion for signifi- 

 cance of impact. Indeed, the objectives of fishery 

 stock assessment are very similar to those of power 

 plant impact assessment. In both cases, we wish to 

 know the effect of removals relative to what the stock 

 can sustain through its density-dependent or other 

 compensatory mechanisms. The models we propose 

 do not require detailed life history information, 

 and are sufficiently simple that the assumptions are 

 apparent and results can be interpreted according- 



ly. 



The methods may be separated into two somewhat 

 independent analyses. The first is short-term assess- 

 ment, which estimates entrainment impact on a 



613 



