Steele et a\ Efficiency of bycatcfi reduction devices in small otter trawls in [he Florida shrimp fisfiery 



343 



effect between season and BRD type occurred in shrimp 

 CPUE for the 14-m, EMF-equipped net (P=0.027). 



Similarly, finfish CPUE differed seasonally for most 

 net sizes iFFE P range: 0.009-< 0.001; EMF P for all 

 tests: <0.001; exceptions; 14-m and 17-m, EMF-equipped 

 nets), and NPUE differed seasonally for all net sizes 

 (FFE P for all tests; <0.001; EMF P range: <0.001-0.000). 

 However, the season in which the largest catch was har- 

 vested differed between net sizes and between BRD types. 

 Both finfish CPUE and NPUE were significantly higher 

 during winter than during fall in the 14-m and 17-m FFE- 

 equipped nets but finfish CPUE and NPUE were signifi- 

 cantly lower during fall than during winter in the '20-m 

 FFE-equipped net. For the EMF-equipped nets, finfish 

 CPUE differed seasonally only in the 20-m nets: CPUE in 

 winter was higher than in fall. Finfish NPUE values for 

 the EMF-equipped nets were always significantly higher 

 in winter (P for all tests; <0.001). 



Percent reduction 



Differences in the percentage of shrimp in the BRD- 

 equipped versus the control nets varied with season, net 

 size, and BRD type. Although many of these differences 

 were not significant (Table 1), patterns in shrimp loss 

 or retention were apparent. Other than the 17-m, FFE- 

 equipped net in fall, the addition of a BRD to a 14-m or 17-m 

 net resulted in a reduction in shrimp CPUE and NPUE, 

 regardless of BRD type. Howe%'er, the reductions were sig- 

 nificant only for the 14-m nets in winter. In contrast, shrimp 



CPUE and NPUE usually were slightly higher in the 20-m 

 BRD-equipped nets than in the control nets. 



Finfish CPUE was always less in BRD-equipped nets 

 than in control nets (Table 1). The reduction in finfish 

 bycatch CPUE was nearly always significant in fall, and 

 most reductions were dramatic (20-60%). Reductions in 

 finfish NPUE also had a strong seasonal component. For 

 all net sizes, finfish bycatch NPUE in the BRD-equipped 

 nets was notably (and nearly always significantly) less 

 than that in the control nets in fall, whereas more (but 

 not significantly more) finfish were captured in the BRD- 

 equipped nets than in the control nets in winter. 



Catch composition 



Most of the biomass in both the BRD-equipped and the 

 control nets usually was composed of finfish (30-70%). 

 The remainder of the catch consisted of shrimp (1.5-20%), 

 horseshoe crabs (Limulus polyphemus) and blue crabs 

 (Callinectes sapidus) (15-58%), and miscellaneous inver- 

 tebrates such as ctenophores, portunid crabs, sponges, and 

 gastropods (<25'>). Wlien the catch of arthropods (princi- 

 pally horseshoe crabs) was large, the finfish catch was gen- 

 erally small. The shrimp catch was relatively stable even 

 when the bycatch composition fluctuated. 



Horseshoe crabs were the most abundant invertebrate 

 bycatch species. A total of 2867 horseshoe crabs were 

 caught during the two sampling seasons; largest catches 

 occurred during fall. Although the catch of horseshoe crabs 

 caught in the BRD-equipped nets was generally smaller 



