DeMartini et al. Pressure effects on regurgitation of Pristipomoides filamentosus 



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Sampling date sequence 



Figure 1 



Mean prey volume for bagged (diagonal-line histograms! 

 and unbagged (open histograms) juvenile pink snapper, 

 Pristipomoides filamentosus, collected on each of nine dates 

 during February-August 1994. Number offish sampled is 

 noted above histograms. 



the smaller of the two sample sizes was nontrivial 

 (>3 fish, Table 1). Prey volumes bootstrapped with- 

 out fish size and date adjustments averaged 112% 

 (95% CI=72-152%) greater for bagged than for 

 unbagged fish. For unbagged fish, predicted prey 

 volumes (based on predicted values for bagged fish 

 of the same body size and date) averaged 0.64 mL 

 among dates, compared with observed prey volumes 

 that averaged <0.30 mL. Bootstrapped differences 

 of predicted minus observed prey volumes for 

 unbagged snapper averaged +116% (95% CI=70- 

 157% ) or were 116% greater for bagged fish. Adjusted 

 bootstrapped estimates thus were slightly larger than 

 the bootstrapped estimates from unadjusted data. 



Prey types 



Three prey types (crustaceans, benthos, and jellies) 

 were retained with greater relative frequency by 

 bagged versus unbagged samples ( 2x2 Contingency 

 X 2 tests, P<0.01 for each of the three types; Fig. 2). A 

 greater relative frequency of nekton for bagged (25% ) 

 versus unbagged ( 14% ) snapper was only suggestive 

 (P=0.06; Fig. 2). The proportion offish with uniden- 

 tifiable prey was similar in both bagged (49%) and 

 unbagged (43%) fish (2x2 Contingency X 2 ; P=0.47). 

 Bagged fish in general retained greater numbers of 

 major prey types (mean=2.9; median and mode=3) 

 than did unbagged fish (mean=2.2; median and 

 mode=2) (2-sample K-S test, P<0.001; Fig. 3). 





1 









Crust Benthos Nekton Jellies 



Figure 2 



Percentage presence ( 1 standard error noted) for 

 each of four major identifiable prey types (crus- 

 taceans, benthos, nekton, and jellies) for bagged 

 (diagonal-line histograms) and unbagged (open 

 histograms) juvenile pink snapper, Pristi- 

 mopoides filamentosus, collected on nine dates 

 during February-August 1994. 



Prey sizes 



On average, the maximum size of prey retained by 

 bagged samples was greater than the maximum prey 

 size for unbagged samples (2-sample K-S test, 

 P<0.001; Fig. 4). The minimum and median sizes of 

 prey retained were equivalent, however, for bagged 

 and unbagged ( 2-sample K-S tests, both P>0. 1 ). Maxi- 

 mum prey size increased with fish body size for both 

 bagged (i? 2 =0.94) and unbagged (P 2 =0.91) snapper. 



Discussion 



Fundamental influences of ingestion 



Two factors (fish body weight and date of collection) 

 appear naturally to influence the amounts of prey 

 consumed by juvenile snapper. The positive relation 

 between fish size and prey volume was associated 

 with snapper growth; juveniles averaged 50% greater 

 body weight at the end versus the beginning of the 

 7-month period of study. Our observation of a mono- 

 tonic temporal (date) effect in addition to the effect 



