ULANOWICZ ET AL.: IDENTIFYING CLIMATIC FACTORS INFLUENCING MARYLAND LANDINGS 



the same causal mechanism is affecting the 

 catches of both fishes. 



Both species included in landings asalewives, 

 A. pseudoharengus and A. aestivalis, areanadro- 

 mous, tributary spawners in Maryland (Hilde- 

 brand and Schroeder 1927). Thus, poor spawn- 

 ing success could readily be related to low 

 freshwater runoff caused by low precipitation. 

 However, the age of first spawning of these spe- 

 cies is from 3 to 5 yr, with the majority spawning 

 at 4 or 5 ( Davis et al. 14 ). The regression (graphed 

 in Fig. 4) suggests the possibility that recruit- 

 ment in Maryland occurs at a younger age, but 

 data on the age distribution of the catch are un- 

 available to confirm or refute this suggestion. 

 The other variable entering the alewife regres- 

 sion (Table 2) is lagged by 2 yr. Since fish taken 

 in a given year would have been present in the 

 Atlantic Ocean 2 yr before being harvested, this 

 correlation is difficult to explain in a causal man- 

 ner. Ep3 is the major predictor in 50% of the 

 trials and is followed by Xt2 in 20% of those cases. 



The least significant of all the predictors 

 cited is the one for striped bass (see Fig. 5). Both 

 terms show a favorable correlation with cold air 

 temperatures over a season. Cold seasons are 



"Davis, J., J. V. Merriner, W. J. Hoagman, R. H. St. Pierre, 

 and W. L. Wilson. 1971. Annual Progress Report, Anadro- 

 mous Fish Project. Proj. No. Va. AFC7-1, 106 p. Virginia 

 Institute of Marine Science, Gloucester Point, Va. 



01 



a 



z 

 Q 



z 



1000 



— 2000 



Q 



Z 



I I I I 

 1940 



l " .. | ..  !  I 



1960 

 YEAR 



I I I | I 1 1 

 1970 



1980 



Figure 5.— Predicted (dotted line) and tabulated (solid line) 

 landings in metric tons of striped bass from 1944 to 1976, based 

 on the regression model in Table 2. Environmental factors 

 were high annual average air temperature (3-yr time lag) 

 (negative effect) and cumulative low air temperature (1-yr 

 time lag). 



conducive to greater amounts of ice formation 

 along river edges. The scouring from ice floes 

 contributes high quality detritus to the riverine 

 system to supplement the food source for zoo- 

 plankton, in turn providing the larvae with 

 abundant food (Heinle et al. 1976). Boynton et 

 al. 15 have previously remarked that year class 

 success correlates jointly with cold winters and 

 high runoff. The chosen variables did not domi- 

 nate the trials heavily. AT3 was the major pre- 

 dictor in only 33% of the trials, one-third of which 

 were accompanied by the variable Ctl. Xs4 ap- 

 peared as the major predictor almost as often 

 (25% of the time there was no major predictor), 

 but did not result in a significant correlation 

 with the full data. 



An examination of the power spectra of the 

 errors of the five models ( using subroutine POW- 

 DEN in Univac STAT-PAK) revealed no appre- 

 ciable differences from the spectral pattern of 

 random noise. 



CONCLUDING REMARKS 



Perhaps the most significant observations to 

 be made from this exercise involve the compari- 

 son of the results reported herein with those re- 

 ported previously from a conventional search for 



Figure 4.— Annual landings (solid line) in metric tons of ale- 

 wife, 1944-76, as compared with predicted values (dotted line), 

 based on the regression model in Table 2. Environmental fac- 

 tors were an episode of low daily precipitation (3-yr time lag) 

 (negative effect) and an extremum of low air temperature (2-yr 

 time lag). 



15 Boynton, W. R.. E. M. Setzler, K. V. Wood, H. H. Zion, M. 

 Homer, and J. A. Mihursky. 1976. Potomac River fisheries 

 program ichthyoplankton and juvenile investigations. Ref. 

 No. 77-169CBL, 328 p. Center for Environmental and Estua- 

 rine Studies, Solomons, Md. 



617 



