WICKHAM and RUSSELL: EVALUATION OF MID-WATER ARTIFICIAL STRUCTURES 



that fish were being attracted to the structures 

 on a daily basis. 



Comparison of Day and Night Collections 



A series of day and night sets were conducted 

 to determine whether fish leave the structures at 

 night. Divers estimated the quantities of fish 

 at four selected structures which were then set 

 on during daylight hours. The quantity offish at 

 four other structures was estimated by divers 

 just before dark and fish around these structures 

 were collected after dark. Diver estimates, and 

 day and night catch results, are plotted in Figure 

 6. The diver estimates were conservative for 

 structures set on during the day, with estimates 

 for both days being less than the actual catch for 

 three of the four structures. The divers frequent- 

 ly estimated that concentrations of fish present 

 at the structures fished at night were larger 

 than at the structures fished in the daylight. 

 Nighttime collections however, consistently pro- 

 duced only 45.5 kg (100 lb) or less of mixed 

 species. These results provided further evidence 

 that bait fish leave the structures at night and 

 that new recruitment was occurring daily. The 

 nighttime sets were made during the new moon 

 and we lack data on whether bait fish also leave 

 the structures at night during the full moon. 



Size and Color Evaluation 



The success of bait fish attraction with arti- 

 ficial structures appeared to be dependent upon 

 the visibility of the structure. We evaluated two 

 sizes of structures to determine whether dou- 

 bling the structure size would increase the num- 

 ber of fish attracted. An analysis of variance for 

 purse seine capture data (F — 0.75< Fo.90(i,5) 

 = 4.06) and diver estimates revealed no sig- 

 nificant difference in attraction by structure 

 size. 



Structure attraction was also evaluated in 

 terms of color visibility. We compared a white 

 structure with ones painted fluorescent green, 

 blue, and yellow since Kinney (1970) reported 

 that fluorescent paints provide greater visibility 

 under water. Structure position was rotated 

 daily so that a structure of each color occupied 

 each of the four positions. An analysis of vari- 

 ance for catch data (F=0.026<Fo.90(3.9) = 2.8) 

 and diver estimates revealed no significant 



- 2800 



E 

 o 



I 2400 



o 2000 



uj 



S 



O^ OIVEB CSTIM4TE (TOTALl 



PU«Se 3CINE C4TCM (TOTALl 



*- STWUCTUBCS 1,2,7,9 

 B - STBUCTUBCS 3,4,9,6 





^ 



6000 s 



A B 



3 D4Y 



ACCUMULATIVE 



TOTAL 



Figure 5. — Total of daily average diver estimates and purse 

 seine catch weights, 17-19 August 1970. (A) Structures 

 estimated by divers and fished daily by purse seine. (B) 

 Structures estimated daily by divers but fished by purse 

 seine only on day three. 



difference in the number of fish attracted to the 

 structures on the basis of color. During these 

 color evaluation studies, the bait fish schools 

 were occasionally scattered by little tunny. 

 These predator attacks may have affected the 

 catch data; however our diver estimates were 

 not affected and also indicate no significant 

 color preference. 



Divers reported the experimental changes in 

 size and color extended the visible range of a 

 single structure less than 2.1 m (6 ft) which ap- 

 parently was not sufficient to significantly 

 improve the structures' attraction capabilities. 



Structure placement (Figure 3) in relation to 

 the distance offshore (water depth) or to the 

 along-shore current direction tended to have 

 some effect on the number of fish attracted, with 

 larger numbers of fish being attracted to struc- 

 tures positioned offshore than to those positioned 

 inshore. Structures positioned on the eastern 

 end of the experimental area also tended to 

 attract more fish than those on the western end. 

 These general patterns probably vary with 

 seasonal changes in water temperature and pre- 

 vailing current direction. Our experiment was 



187 



