FISHERY BULLETIN: VOL. 75, NO. 2 



young scalloped hammerhead shark, Sphyrna 

 lewini (45-90 cm TL), caught by gill net at night in 

 the channels of Kaneohe Bay. 



Solitary barracuda and needlefish slowly 

 cruised along just under the surface of the water 

 when they were near schools of silversides. When 

 stalking, they usually remained relatively mo- 

 tionless as they drifted or used slow caudal fin 

 undulations to scull along the surface. The 

 barracuda attacked by quickly dashing, usually 

 horizontally, a short distance towards an indi- 

 vidual or school of silversides. 



Individuals or schools of jacks and leather- 

 jackets usually swam near the bottom in the 

 lagoon or at some midwater depth in the deeper 

 channels near Lilipuna Pier. Individuals of these 

 species slowly approached or rapidly attacked the 

 silversides, usually at an angle of about 45° to the 

 surface. They immediately retreated towards the 

 bottom after their approach or attack. 



Lizardfish are cryptically colored, solitary ben- 

 thic "sit and wait" predators. When a school of 

 silversides swam over a lizardfish, it usually 

 dashed at an angle nearly perpendicular to the 

 surface, or at an angle greater than about 45° to 

 the surface as it approached the silversides. 



Because the silversides were located just under 

 the surface of the water, the attacks by their 

 predators could usually be detected in one or both 

 of two ways. The momentum of a rapidly moving 

 predator often carried it clear out of the water 

 during an attack. This was particularly evident 

 during attacks made in a vertical direction. If the 

 predator turned as it approached the surface, its 

 body and/or caudal fin usually created a boil of 

 water at the surface, which often erupted with a 

 popping sound into a splash or spray of water. If it 

 was calm, a boil of water often left a small area of 

 residual foam bubbles as concentric circles moved 

 out across the water. When chases occurred along 

 or near the surface, the predators often left a wake 

 of disturbed water and froth to mark its path of 

 pursuit. 



In the Lilipuna Pier area an infrequent diurnal 

 aerial predator was also observed. One to four 

 common noddies, Anous stolidus pileatus, re- 

 mained near or on the pier and flew to the areas of 

 jumping silversides and attempted to catch them 

 while the fish were still at the surface. Noddies 

 were more successful at catching silversides when 

 predatory fish attacked and then chased the 

 silversides along the surface. 



BEHAVIOR OF 

 CAPTIVE SILVERSIDES 



Over 100 h of observations of captive silversides 

 in net enclosures (3mx3mx3m deep to 6. 1 m x 

 6.1 m x 2 m deep) in the lagoon in Kaneohe Bay 

 and in a circular cement tank ( 9 m in diameter and 

 3 m deep with an underwater viewing window) 

 were made during day and night periods. Within 

 several days after introduction into the enclosures 

 that lacked predators, the individuals in the 

 schools of silversides slowly increased their 

 interfish distances from less than one or two body 

 lengths (as seen in the field) up to distances of 5-10 

 body lengths or more. Although the individuals 

 were often randomly aligned with respect to each 

 other, they did not lose their polarity to one 

 another when a school moved. Individuals occa- 

 sionally fed during the day, much as they did 

 when free in the field. However, they did not dash 

 out towards an object and immediately return to a 

 school. When one or more predators, such as jacks 

 or barracuda, were introduced into an enclosure 

 the schools tightened as interfish distances be- 

 tween silversides decreased to less than one to two 

 body lengths. Individuals continued to dart out 

 from the relatively stationary and motionless 

 schools, much as they did in the field. If attacks or 

 approaches were not initiated by a predator, the 

 schools loosened as interfish distances increased 

 once again. These distances were not as great as 

 they had been prior to the introduction of the 

 predator(s). Feeding continued until approaches 

 or attacks occurred. When approached, schools 

 split and formed a halo around the predator as 

 they moved to the rear of the predator to reform a 

 school again. When attacked, individuals jumped 

 out of the water and across the surface, away from 

 the predator. The behavior of individuals and 

 schools of silversides in the enclosures was much 

 the same as that observed in the field, as described 

 above. 



During evening twilight periods, interfish dis- 

 tances increased as individuals in the schools 

 spread out across the surface. During the twilight 

 period, I could see the prey silhouetted against the 

 evening sky, but not the predators against the 

 bottom. As darkness increased, it rapidly became 

 impossible to see the silversides as well, although 

 the boils of water and splashes made by an 

 attacking predator and the return of jumping prey 

 into the water could be heard. During morning 



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