Table l. — Basic drop net design characteristics of previous studies and the current net system. 



A drop net design was needed which would not 

 significantly disturb the water surface and yet 

 take an adequate sample. Some previous portable 

 drop net designs sampled a larger area, but with 

 greater water surface contact (Moseley and Cope- 

 land 1969; Kjelson and Johnson 1973). This new 

 gear design allows less water surface disturbance 

 (i.e., noise and shading) than previous drop nets 

 and yet is capable of sampling 10 m^ without com- 

 promising portability. The sample area is rigidly 

 controlled and all fishes are collected from the 

 sample area. The design criteria and success of 

 this drop net system is comparable with, and in 

 some cases surpasses, previous drop net designs in 

 the literature with regard to sample area control 

 and the capture of certain small demersal fish 

 species. This study was conducted to compare this 

 new drop net system with a larger haul seine sys- 

 tem sampling 1,160 m^ used concurrently for shal- 

 low water estuarine fish studies. The duration of 

 this study was from April to December 1976. 



Drop Net Description and Operation 



The drop net apparatus consists of two primary 

 sections: the collapsible aluminum tripod with the 

 trigger mechanism and the drop net (Figure 1). 

 The 5.2-m tripod legs are held together by 

 aluminum hinges at the upper end and three 

 4.0-mm flexible steel support cables attached to 

 the legs below the upper hinges. Two sheaves are 

 mounted to the upper ends of two of the tripod legs, 

 one to carry the winch line (i.e., upper frame har- 

 ness line) to hoist the net and the other to carry the 

 drop frame harness line that is released as the net 

 is triggered. 



After the sample site is straddled by the tripod, 

 the drop net (3.16 x 3.16 m) is deployed using a 

 pontoon boat. The boat is floated under the open 



tripod legs to prevent disturbing the bottom 

 within the sample area. To lift the net, the drop 

 frame harness plate and the upper frame harness 

 plate are coupled together with a steel set pin 

 (Figure la). The net is then lifted from the boat 

 deck using the winch. After the net is in the set 

 position, the drop frame harness line is set on the 

 trip lever via a set ring (Figure lb), and the pon- 

 toon boat is pushed out from under the net. The 

 trip lever is held down with a notched trigger pin 

 attached to the remote trigger line. The remote 

 trigger line has a fluorescent floating jar attached 

 to the distal end 20 to 30 m from the net apparatus. 

 Once the net is set at the correct height, the steel 

 set pin is pulled, and the drop frame plate and 

 harness are free to fall when the trigger 

 mechanism is tripped. Within 15 min three people 

 can deploy a single net set to drop. 



The trigger mechanism and drop frame are re- 

 leased with one pull of the remote trigger line. 

 Once the net has fallen, the drop frame harness is 

 undipped from its harness plate and a drop net 

 seine, made of tubular aluminum and 3.2-mm 

 mesh netting, is used to seine the enclosure (Fig- 

 ure Ic). The seine fits closely against the inside 

 walls of the drop net, and it is pulled by three 

 people, two on either handle and one pulling a line 

 attached to the bottom, center of the seine. The 

 seine frame is kept firmly on the bottom and a 

 standard five hauls are made to collect the sample. 

 For night operations, an amber flashing light is 

 attached to one tripod leg. Once the net has drop- 

 ped, a lantern can be hung from the flexible steel 

 support cable. Although night operations may 

 take longer, V2 h is generally taken from the drop 

 to complete sample removal. 



To store and disassemble the drop net the pon- 

 toon boat is brought under the raised net. The net 

 and frame are lowered onto the deck. The harness 



286 



