FISHERY BULLETIN: VOL. 74, NO. 2 



laboratory. Gut contents included material in the 

 total digestive tract, from foregut to anus. 



Current Speed and Feeding Intensity 



Larval pinfish and spot were collected within 2 

 m of the shore (depth 0-2 m) where refuge from 

 current was available and in the center of the 

 adjacent channel (depth 5-7 m) approximately 25 

 m from shore where a current normally was pres- 

 ent. Three separate collections were made for 

 pinfish and two for spot. Twenty fish of each 

 species from each collection were measured, dis- 

 sected, and the mean number of copepods per fish 

 determined. Surface tows for zooplankton were 

 made at the same time and location using a 30 cm 

 in diameter, 0.158-mm mesh net with current 

 meter attached. Observations on copepods 

 throughout this investigation were restricted to 

 adult and copepodid stages. Copepod measure- 

 ments were made of carapace length. Current 

 velocities were measured with a Gurley current 

 meter. 



Feeding rates of pinfish and spot at varied cur- 

 rent speeds also were studied in the laboratory. 

 Fish were captured, placed in four donut-shaped, 

 11-liter tanks (46 cm in diameter, 10- by 10-cm 

 cross-sectional area), and allowed to acclimate 

 overnight in filtered, food-free seawater with no 

 current flow. Two tanks were used as controls 

 (zero current flow) and contained 50 and 100 fish, 

 respectively. The other two tanks, containing 50 

 fish each, were attached to pumps, providing cur- 

 rent velocities of 1.7 and 5.1 m/s, respectively. 

 Current speed was estimated by recording the 

 amount of time required for a minute innate par- 

 ticle to complete one revolution of the donut- 

 shaped tank. At the beginning of each experi- 

 ment, current flow was started in the two test 

 chambers and Artemia salina nauplii (1.0/ml) 

 were provided to each of the four tanks. Fish were 

 allowed to feed for 1 h with additional food pro- 

 vided after 30 min to assume a minimum density 

 of 1 Artemia/ml throughout the experiment. 

 Twenty fish were sampled from each tank to cal- 

 culate the mean number of Artemia consumed. 



Temporal Variation in 

 Midday Feeding 



Day-to-day variation in the feeding intensity of 

 larval pinfish and spot was studied at midday 

 (1100-1300 h) when larval digestive tracts con- 



424 



tained the greatest amounts of food. Fifl;een col- 

 lections were made from 21 January to 28 Feb- 

 ruary at one site within 2 m of the shore. Each 

 collection consisted of 20 fish of each species. 

 Total lengths of the fish were measured, the total 

 number of copepods in each gut counted, and a 

 geometric mean of the number of copepods per 

 fish calculated. Geometric means were used as a 

 measure of central tendency because frequency 

 distributions of the copepods or Artemia nauplii 

 per fish showed a positive skewness. In addition, 

 a geometric mean was used to limit the bias of a 

 few individuals feeding at a rate not representa- 

 tive of the population because variation increased 

 as the mean values increased. 



A zooplankton tow was taken at the time and 

 location of fish capture. The tows were made just 

 below the surface, against the current, and sam- 

 pled approximately 5 m^ of water. Estimates of 

 copepod density were made from three 10-ml sub- 

 samples of each tow. Twenty copepods per sample 

 were measured for length frequencies. 



Evacuation Rates 



To refine our information on larval evacuation 

 rates of copepods, two laboratory experiments 

 were performed using pinfish and spot that had 

 been fed an abundance of natural copepods. Four 

 to five hundred fish were starved for 8 to 12 h and 

 then they were allowed to feed for 1 h. Food densi- 

 ties averaged 2.5 copepods/ml for pinfish and 3.0 

 copepods/ml for spot. Larvae were acclimated and 

 experiments run at ambient estuarine tempera- 

 tures and salinities. Temperature was 12°C for 

 the pinfish evacuation and 17°C for spot; salinity 

 was 301.. Following feeding, 30 fish were re- 

 moved, anesthetized with MS-222 to prevent any 

 possible regurgitation, dissected, and counts 

 made of the numbers of copepods per fish. At the 

 same time, three groups of 100 fish were trans- 

 ferred to separate food-fi*ee tanks, and the de- 

 crease in their gut contents observed by sampling 

 10 fish from each tank at 2-h intervals until more 

 than one-half of the fish had empty tracts. Instan- 

 taneous evacuation rates were then calculated 

 according to the method of Peters and Kjelson 

 (1975). The amount of food remaining in the 

 stomach at any time can be predicted from the 

 following equation: 



log C = log A + Bt 



where C = content of gastrointestinal tract -i- 1 



