FISHERY BULLETIN: VOL. 87, NO. 3, 1989 



E 

 O 

 O 



\ 



I 



u 

 h- 

 a: 

 u 



WINDOWPRNE FLOUNDER 



□ DRY 

  NIGHT 

 TWILIGHT 



E 

 o 

 o 



I 

 u 

 I— 

 cc 

 u 



Figure 4. — Conthmed. 



2 - 



the haddock. Both butterfish and B. glaciale 

 catches are about the same for night and day, 

 regardless of length. Three species show a trend 

 of decreasing ratios of night:day with increasing 

 length with night catches exceeding day catches 

 at the smaller lengths: witch flounder, Glypfo- 

 cephalus cynoglossus; fourspot flounder, Para- 

 lichthys oblongus; and fourbeard rockling, 

 Enchelyopus cunbrius. The last three species, 

 Atlantic cod, Gadus morhua; goosefish; and 

 American plaice, Hippoglossoides platessoides, 

 have day catches exceeding night catches at the 

 small lengths and as they grow the ratios of 

 night:day equal or exceed one. 



If net avoidance by fish larvae is visually cued, 

 the expected ratios of twilight-to-day catches 



nMERicnN PLnicE 



D DRY 



 NIGHT 



 TWILIGHT 



7 8 9 10 

 LENGTH (mm) 



12 13 



would exceed one and increase with increasing 

 fish length. Another expectation would be that 

 night catches would exceed, on average, twilight 

 catches. As shown in Table 3, 16 of 36 taxa con- 

 form to the ranking of night > twilight > day 

 catches. A total of 16 of the 26 taxa analyzed by 

 length (Fig. 4) shows increasing twilightiday 

 catch ratios, determined from expected values 

 from the regression analysis, with increasing 

 length. However, Figure 4 also shows twilight 

 catches often exceeding night catches at some 

 lengths for many taxa. Outstanding examples of 

 dominant twilight catches are offshore hake, 

 American plaice, butterfish, and windowpane 

 flounder, Scophthalmus aquosus. The catches of 

 offshore hake show that twilight catches domi- 



434 



