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Fishery Bulletin 101(2) 



hepsetus) were combined into a single-prey category. In 

 addition, gizzard and threadfin shad (Dorosoma cepedia- 

 num and D. petenense), and blueback and alewife herring 

 (Alosa aestivalis and A. pseudoharengus) were treated as 

 single-prey categories. Unidentified prey consisted pri- 

 marily of unidentified fish remains and were recorded as 

 such. 



Striped bass were categorized by fish length and month 

 of capture. Fish were partitioned into two size classes cor- 

 responding to mixed resident and migratory fish (458-710 

 mm total length) and coastal migrant fish (711-1255 mm 

 total length) based on the Atlantic States Marine Fisher- 

 ies Service classification of fish 711 mm and above as 

 fully recruited to the coastal migratory stock. For spatial 

 analysis of feeding habits, each fish was placed into one of 

 two salinity regimes; tidal freshwater (0-5 ppt) or meso- 

 haline waters (6-28 ppt). Tidal freshwater- waters include 

 the upper reaches of the James, York, Rappahannock, and 

 Potomac rivers. Mesohaline waters include the open waters 

 of Chesapeake Bay and the lower reaches of most rivers. 

 No fish were collected in the fall from tidal freshwater For 

 both monthly and spatial analyses, diet was quantified by 

 weight only. 



To measure intensity of feeding, a stomach fullness index 

 (SFI) was calculated according to Hureau ( 1969); 



„^, Stomach coiuen! wt'iiilu 



Sri = X 10. 



Fish weight 



SFI values were calculated for all fish regardless of the 

 presence or absence of stomach contents. 



A regression of striped bass total length versus prey total 

 length was fitted by least-squares linear regression of the 

 untransformed values. Prey lengths were reconstructed 

 from partially digested backbones by using regressions of 

 backbone length on total length obtained from samples col- 

 lected in 1998 by the authors and those given by Hartman 

 and Brandt (1995a). 



Results 



Of the 1225 striped bass examined, 688 (56%) contained 

 items in the stomachs (Table 1). Thirty-four different spe- 

 cies offish and 18 species of invertebrates were observed in 

 the diet. Overall, clupeid fishes dominated the diet and men- 

 haden, in particular, accounted for 44';'( of the weight and 

 occurred in 18% of all stomachs (Table 2). Menhaden ranged 

 in length from 103 to 360 mm total length. A '/r IRI value of 

 58.3 for menhaden was higher than that for all other species 

 combined. Anchovies were numerically the most abundant 

 (229^ ) of all prey items and were equal to spot (Leiostomus 

 xanthiirus) in '7( IRI, both sharing a value of 12.3. Other prey 

 in order of decreasing '^r IRI were gizzard shad (genus Doro- 

 soma ) with a ''/i IRI of 6.7, and blue crab (C'a//(>iectes saptdus} 

 with %IRI values of 3.4. Atlantic croaker (Micropogonius 

 undulatus) and summer flounder iParaUchthys dentatus) 

 had '''( IRl values of 1.1 and 1.0, respectively. 



All other prey categories had 'MRI values <1 and ap- 

 peared relatively unimportant in the overall diet of striped 



bass, although some increased in relative importance at 

 certain times and locations. Invertebrates were relatively 

 minor constituents of the overall diet of large striped bass, 

 providing only 4.4% of the total IRI. In contrast, clupeid 

 fishes contributed 65% of the IRI and both sciaenid and 

 engraulid fishes combined contributed over 25% of the 

 total IRI. 



Clear seasonal and spatial patterns in diet corresponded 

 with the migratory behavior of large striped bass. Striped 

 bass in both sizes classes, 458-710 mm and 711 mm and 

 above, migrated into tidal freshwater to spawn in the 

 months of March, April, and May. Striped bass fed in the 

 tidal freshwater region, although at a reduced intensity 

 as evidenced by the lower stomach fullness values and 

 the lower percentages of nonempty stomachs compared 

 to those at other times and locations (Table 1). Gizzard 

 shad, white perch (Morone americana), and anadromous 

 herrings (Alosa pseudoharengus and Alosa aestivalis) were 

 the main constituents of the diet of both sizes of striped 

 bass in the tidal freshwater region (Table 3, Fig. 2). 



During spring, striped bass also pass through the meso- 

 haline waters of Chesapeake Bay prior to and after spawn- 

 ing, during which time they feed fairly heavily as indicated 

 by higher than average stomach fullness values and per- 

 centages of nonempty stomachs (Table 1). Approximately 

 83% of the striped bass sampled from mesohaline waters 

 during this time had food in the stomachs indicating active 

 feeding during the pre- and postspawning migration. Men- 

 haden dominated the diets by weight of both size classes of 

 striped bass from mesohaline waters in the spring. Striped 

 bass of both size classes also consumed croaker, blue crab, 

 and white perch (Table 3, Fig. 2); however, the size classes 

 differed in that smaller fish consumed bay anchovy and 

 juvenile spotted hake ( Urophycis regia ) and larger striped 

 bass consumed anadromous herrings. 



Large striped bass are generally absent from Chesapeake 

 Bay in significant numbers in the summer and return in 

 the fall to mesohaline waters of Chesapeake Bay and its 

 lower tributaries. The fall return is essentially a feeding 

 migration and the high stomach fullness values and high 

 percentages of nonempty stomachs (Table 1 ) indicate active 

 feeding. Striped bass of both size classes fed predominantly 

 upon menhaden, which had percent weight values between 

 53% and .58 Ve (Fig. 3). Sciaenid fishes, including spot, At- 

 lantic croaker, and weakfish iCynoscion regalis) combined 

 provided between 23"^^ and '3l"i of the diet by weight for 

 both size classes of fish. Notable differences occurred in 

 the high percentage of summer flounder (Paralichthys 

 dentatus) found in the diets of larger striped bass (\b% 

 by weight) and in the high percentage of both butterfish 

 (Peprilus triacanthus, 4%) and gizzard shad (11%) found 

 in the diets of smaller fish (Fig. 3). The only invertebrates 

 found in abundance in the diets during this time were blue 

 crabs, which contributed 70"^; of the diet by weight for the 

 smaller size class of striped bass in September (Table 3). 

 The greatest number of species occurred in the diet in fall 

 with forty-four different species of prey items observed, 

 although many were isolated occurrences of rare prey and 

 only a few species contributed to the overall diet at this 

 time. 



