598 



Fishery Bulletin 91(4). 1993 



biological or environmental perturbation, to fishing 

 pressure or to some combination of these factors. Posi- 

 tive differences are taken as increased species abun- 

 dance in response to favorable conditions. Nonetheless, 

 significant differences of this sort alone do not establish 

 a direct causal association between change in popula- 

 tion abundance and sewage sludge dumping, or alter- 

 nately between fishing pressure, natural environmen- 

 tal perturbations, or any of combination of these. Any 

 such inference must come from further interpretation 

 of the data in respect to what is known about natural 

 ecology of the subject species, fishing pressure on these, 

 and any known sensitivities to sewage sludge. 



Abundance indices for the 11 species individually and 

 for all species combined for pre- and post-dumping 

 period surveys (Tables 4-7, pgs. 601-604) were com- 

 puted by using the groundfish survey analysis program 



-'"Kramer. W. P. 1985. Groundfish survey analysis program (SURVAN 

 version 5.2). program report. Prepared for U.S. Dep. of Commer., 

 NOAA,. Natl. Mar. Fish. Serv.. Northeast Fish. Cent., Input Output 

 Computer Service Inc., Waltham, MA. 137 p. 



(Kramer 2 "). Basic assumptions and methodology for es- 

 timation of abundance indices based on NEFSC bot- 

 tom trawl survey data are detailed by Pennington and 

 Brown (1981). Trends in indices and variabilities in 

 time and space may also be interpreted as suggesting 

 some general shift in species abundance attributable 

 to sludge dumping, even though there may be no di- 

 rect proof of an association between population abun- 

 dance change and sludge disposal. 



Results 



Temporal differences 



Test statistics based on species CPUE, and species 

 abundance indices, including estimates for both spring 

 and autumn cruises, are summarized in Tables 1 and 

 4-7. Combining the information from these two sources 

 reinforces the inferences of significant change in spe- 

 cies abundance over time. 



