Stillwell and Kohler. Food habits of Carcharhmus plumbeus off US. northeast coast 



139 



42°N 



40 



38 - 



36 - 



34 



A. US*^ 



CHINCOTEAGUE 

 BAY' 



7 8°W 



Figure 1 



Fishing area off the U.S. northeast coast where 415 sandbar shark Carcharhmus plumbeus 

 pups, juveniles, and adults were caught and examined for food habits studies, 1972-84. 

 The 100 m depth contour separates the nearshore and offshore sampling areas. 



offshore (>100m) (Fig. 1). The 

 Chincoteague sample was further 

 separated into two distinct age 

 classes: newborn pups (esti- 

 mated <3d-old) and small juve- 

 niles (>3 d-3+ yr). Newborn pups 

 were distinguished by pale, un- 

 pigmented edges on the fins, 

 unhealed or partially-healed um- 

 bilical openings, and the presence 

 of large cream-colored livers that 

 floated slightly above the surface 

 when placed in seawater. "Older" 

 pups and small juveniles had liv- 

 ers that were reduced in size, 

 varied in color from tan to gray- 

 green, and sank slowly or floated 

 just beneath the water surface. 

 In addition, their umbilical open- 

 ings were completely healed, vis- 

 ible only as white streaks 5- 

 6 mm long. Juveniles and adults 

 of both sexes were separated, 

 based on a minimum reproduc- 

 tive size of 150cmFL (Casey et 

 al. 1985). 



longline gear aboard research and commercial fishing 

 vessels from Cape Hatteras to Georges Bank, and 

 (3) during a 6d period of fishing at the end of June 

 1983 with rod-and-reel in Chincoteague Bay, Virginia 

 (Fig. 1). Collections and examinations of all stomachs 

 were made during March to September, with the ma- 

 jority being taken in June and July. Stomachs were 

 excised and the volume of the contents (liquid and 

 solids) measured as soon after capture as possible. Solid 

 remains were drained, sorted, and identified to the 

 lowest taxon possible, then enumerated and measured 

 volumetrically by water displacement in a graduated 

 beaker. A conversion of lmL=lg was used to convert 

 volume to weight for comparisons with shark body 

 weights. Major forage categories were expressed as per- 

 centages by number of particular prey items, as total 

 volume of the prey items, and as frequency of their 

 occurrence (number of stomachs). Maximum capacity 

 was estimated by filling the stomachs with water un- 

 der low pressure, then measuring the volume of water 

 in a graduated container. The maximum capacities of 

 stomachs from Chincoteague Bay sharks were not 

 determined because a pressurized water system was 

 not available. Analysis of the data for differences in 

 prey, food volumes by area, and daily ration was 

 accomplished by separating the samples into three 

 groups: Chincoteague Bay, nearshore (<100m), and 



Results and discussion 



Stomachs from 415 sandbar sharks were examined, 

 including 321 from nearshore (268) and offshore 

 (53) waters between Cape Hatteras, North Carolina 

 and Georges Bank, and 94 from Chincoteague Bay, 

 Virginia. 



Analysis of nearshore and offshore samples 



In the nearshore area, juvenile males and females and 

 adult females were represented by almost equal num- 

 bers, i.e., 81, 84, and 89, respectively, whereas only 12 

 adult males were sampled. Offshore, juvenile males 

 were most abundant (37), with adult males represented 

 by four individuals. Females were limited to four adults 

 and eight juveniles. Mean fork length (FL) and body 

 weight (BW) of sandbar sharks for the whole sample 

 were 138cm (range 69.0-212.0) and 34.0kg (3.0-145.0) 

 (Table 1). Offshore, only juvenile males were numer- 

 ous enough in the sample to derive reliable mean 

 values. 



Prey analysis Prey consumed by sandbar sharks in 

 the study area consists primarily of benthic and 

 demersal species, both vertebrate and invertebrate 

 (Table 2). Of the 40 different prey types observed in 



