FISHERY BULLETIN: VOL. 79, NO. 2 



Figure 2. — Relationships between the 

 distance traveled by the center of mass 

 I the point about which propulsive forces 

 act) and elapsed time during fast starts of 

 Citharichthys stigmaeus. The motion of 

 the center of mass was resolved into the 

 distance traveled in the horizontal (A, B) 

 and vertical iC, D) planes. These data 

 were used to calculate the resultant dis- 

 tance traveled (E, F). Fast-start perfor- 

 m.ance is shown for fish accelerating in 

 the water column (A, C, E) and from the 

 grid iB, D, F). The dotted lines in B, D, 

 and F show the motions of the center of 

 mass offish accelerating in the water col- 

 umn from A, C, and E to facilitate com- 

 parison with fast starts from the grid. Ver- 

 tical bars shown ±2 SE. 



_ c 



_ D 



•>..^.— »**!^t I I I I I I I I II 



./' 



./ 



,/ 



,<♦ 



il 



#' 



# 



,# 



 



hydrodynamic ground effect influenced speckled 

 sanddab fast starts. All data for fish accelerating 

 from the grid were therefore combined for sub- 

 sequent analysis and for comparison with fish ac- 

 celerating in the water column. 



The performance of fish accelerating from the 

 grid differed from that offish accelerating in the 

 water column. The differences were seen in hori- 

 zontal and vertical motions and in the net (resul- 

 tant) motion. In the horizontal plane, fish ac- 

 celerating from the grid traveled 0.8 ±0.2 cm in 63 



ms at the end of stage 1, compared with 1.9±0.4 cm 

 in the same time for fish accelerating in the water 

 column. By the end of stage 2 fish starting from the 

 grid had moved forward 3.9±0.9 cm in 124 ms. 

 This was an improvement over stage 1, but still 

 less than that of fish in the water column which 

 moved forward 6.8 ±0.9 cm in the same time. The 

 small initial displacement offish in contact with 

 the grid was probably due to frictional interac- 

 tions between the fish and the grid (Arnold and 

 Weihs 1978). The normal force at the point of con- 



274 



