FISHERY BULLETIN: VOL. 71, NO. 2 



Table 9. — CV^ values and character means (^^+/) by size class of barred surfperch.i 



Includes specimens from Bahia Sebastian Vizcaino, Son Simeon, and Santa Rosa Island. 



5-1 



3- 



2- 



1969-70 



I •(4 4) 

 S 

 \ 

 \ 

 \ 



I970«(I5) 



1970-71^ 

 (44)* 



esv 



BSO 



BS 



C SRI 



4- 



ss 



400 300 200 100 100 200 



APPROXIMATE DISTANCE IN MILES TO POINT FERMIN 



Figure 3. — Geographic and historic CV^ trends in barred 

 surfperch. Connected points are more or less "contem- 

 porary" samples. Letter codes are as follows: BSV, Bahia 

 Sebastian Vizcaino; ESQ, Bahia San Quintin; BS, Belmont 

 Shore; C, Carpinteria; SRI, Santa Rosa Island; SS, 

 San Simeon. Dates of collection and sample sizes (N) for 

 each collection are as indicated. 



metry differences, and the second is the main- 

 tenance of these differences. We consider two 

 possible origins: genetic and environmental. 

 The parallel dichotomy with regard to main- 

 tenance is that the observed patterns are 

 maintained by natural selection differentials 

 in time and space, or the patterns are main- 

 tained by a geographically stable pattern in 

 the distribution of the relevant environmental 

 factor(s). (Other combinations of causative 

 categories exist, but are rejected for lack of 

 evidence and are ignored here.) 



The hypotheses explaining our results are 

 grouped into three categories: (A) hypotheses 



assuming a genetic origin, (B) hypotheses 

 assuming an environmental origin stemming 

 from natural causes, and (C) hypotheses assum- 

 ing an environmental origin stemming from 

 various pollutants. 



Arguments for 

 Category A Hypotheses 



All genetic explanations assume the relaxa- 

 tion of stabilizing selection, thus allowing the 

 accumulation of "abnormal" genotypes in the 

 population resulting in an increase in the 

 asymmetry variance of bilateral characters. 



Various changes that could bring about- such 

 a decrease in the intensity of stabilizing selection 

 in the populations studied are thought to have 

 occurred in the recent past. These changes are 

 of four types: (1) increased cropping of adults 

 by fishermen, (2) a fish population explosion, 



(3) a decrease in the predator-prey ratio, and 



(4) an increase in the carrying capacity of the 

 environment. A rapid increase in a population 

 (type 2) depends on a high juvenile recruitment 

 rate. In this respect, the effect of a population 

 explosion is similar to that of increased fishing 

 pressure on adults (type 1), although the former 

 change is usually more transient than fishing 

 pressure changes. 



Fishing pressure and the number of fish 

 being caught in southern California are increas- 

 ing (Frey, 1971). Given that the adult popula- 

 tions of the three species in question have 

 remained stable (there is no evidence to the 

 contrary), then at some stage the removal of 

 adults must be compensated for by increased 

 survival of recruits. One possible consequence 

 of this is an increase in the probability of survival 



364 



