AUSTIN and HICKEY: PREDICTING ABUNDANCE OF STRIPED BASS 



the New York harvest and the modal length at age 

 11+ via Model II correlation analysis. 



These analyses were performed in an effort to 

 describe a method for predicting the commercial 

 harvest (and therefore the apparent abundance) of 

 striped bass in New York waters. As each of the 

 several steps in the analyses were dependent on 

 the results of those previously calculated, they are 

 discussed in more detail along with the results 

 below. 



The reliability of the suggested technique for 

 predicting the abundance of striped bass in New 

 York waters is dependent on several assumptions: 



1 ) The Chesapeake Bay stock of fish is the major 

 contributor of striped bass to the New York 

 commercial fishery, as suggested by the several 

 authors noted above; 



2 ) The annual relative contribution of the several 

 Atlantic coastal breeding stocks to the coastal 

 stock of fish and, therefore, to the New York 

 fishery remains constant or that it fluctuates or 

 cycles in a consistent manner; 



3) The commercial fishery for striped bass in New 

 York effectively collects representative "sam- 

 ples" of the Chesapeake Bay stock of fish; this 

 assumption appears to be valid based upon the 

 relationships described by Schaefer (1972), 

 Texas Instruments, Inc. (see footnote 5) and 

 those described herein, and based upon our ob- 

 servations and those of Schaefer (1972) that 

 many size classes of fish are present in the 

 commercial catch — small age II prerecruits to 

 large mature fish >16 kg total weight; 



4) The forecast of commercial striped bass land- 

 ings is based upon past historical landings in 

 relation to past life history events of the species 

 (year class abundance and length at age 11+) 

 and does not reflect changes in commercial 

 fishing effort or any changes in the contribu- 

 tions to the reported landings by recreational 

 fishermen; we have assumed a constant fishing 

 effort, as did Schaefer (1972), and thus com- 

 pared our results with his; while we recognize 

 the weakness in this assumption, there is no 

 alternative as there is no estimate of effort. 



RESULTS AND DISCUSSION 



Year Class Strength and Modal Size 



The lengths of striped bass at age 11+ near Long 

 Island are probably related to ecological cir- 



cumstances encountered by the fish during their 

 first 2 yr of residence in the rivers of Chesapeake 

 Bay (density, competition, amount of available 

 food). Similarly, Cushing ( 1968) found a close rela- 

 tionship between the mean length of age III Atlan- 

 tic herring, Clupea harengus, and the density of 

 their food source in the sea, and Clark (1967) de- 

 scribed reduced growth rates for sunfish, Lepomis, 

 due to overcrowding, excessive competition, and 

 reduced food supply. It has also been demonstrated 

 by Anthony ( 1 97 1 ) that the growth of young ( age I 

 and II) Atlantic herring is inversely related to 

 their abundance, and Wagner (1969) has stated 

 that in most fishes the growth rate per individual 

 is inversely related to their density. 



If an inverse relationship exists between the 

 abundance of a year class of striped bass and the 

 cohort length at age II + , a similar relationship 

 should exist between the commercial harvest (as 

 an index of abundance) and the length at age II + , 

 assuming that fishing effort remains approxi- 

 mately constant. To test this hypothesis, age 11 + 

 modal length data for year classes 1970 and 1972 

 (Figure 2) were combined with other published 

 modal length data for year classes at age 11+ in 

 New York waters from Alperin (1966) and 

 Schaefer ( 1968 ) (Table 1 ), providing a total of eight 

 annual data points. A correlation analysis was 

 performed between these eight annual modal 

 lengths of age 11+ fish and their respective 

 Chesapeake Bay year class strengths 2 yr earlier 

 (Figure 3). The year class strength data (supplied 

 by the Maryland Department of Natural Re- 

 sources) are expressed as the annual mean 



Table l. — Comparison of observed and computed modal fork 

 lengths for age II striped bass in New York waters. 



'Courtesy Joseph Boone. Maryland Department of Natural Resources, An- 

 napolis, Md,, data expressed as annual mean number of ageO+ juveniles per 

 standard seme haul. 



^Based on the relationship y = 333 - 3X, where Vis the modal length of age 

 11+ fish and X is the strength of the year class (Figure 3). 



^Extrapolated from Schaefer (1968), 



■•Extrapolated from Alperin (1966). 



^Data from the present investigation. 



469 



