344 



Fishery Bulletin 100(2) 



than the catch in the corresponding control nets, only in 

 the 14-m FFE-equipped net and the 20-m EMF-equipped 

 net was the number of horseshoe crabs caught significant- 

 ly lower than the number of horseshoe crabs caught in 

 the corresponding control nets (P=0.001 and P=0.05. re- 

 spectively). Blue crabs were the second most abundant 

 invertebrate bycatch species. A total of 544 blue crabs 

 were caught during the two sampling seasons; the largest 

 catches occurred during winter Although fewer blue crabs 

 were caught in the BRD-equipped nets, only in the 14-m 

 EMF-equipped net was the number of blue crabs signifi- 

 cantly lower than that in the corresponding control net 

 (P=0.005 for both seasons). 



A total of 44 species of finfish were caught during our 

 study (Table 2). Numerically, ten finfish species composed 

 more than 92^( of the total finfish count, and a single spe- 

 cies, the leopard searobin iPrionotus scitiilus), composed 

 over 40'? . Abundance differed gi'eatly between seasons for 

 nearly all fishes (Table 2). The silver jenny {Eiicinnsto- 

 inus gula), hardhead catfish (Arius felis), gafftopsail cat- 

 fish (Bagre marinus), sand seatrout (Cynoscion arena/ius), 

 and silver perch (Bairdiella chryi^oura) predominated in 

 the catch during fall. These were replaced during winter 

 by the leopard searobin (Prionotus scitulus), blaekcheek 

 tonguefish iSyrriphurusplagiusa). southern kingfish (Men- 

 ticirrhus americanus), pinfish (Lagodon rhomboides). and 

 spadefish iChaetodipteriis faber). 



Ten of the finfish species that we captured are important 

 to the recreational or commercial fishing sectors. These are 

 the southern kingfish (Menticirrhus americanus), scaled 

 sardine (Harengula jaguana), striped anchovy (Anchoa 

 hepsetus). bay anchovy i Anchoa mitchelli), spot (Leiosto- 

 mus xantluunis). spotted seatrout iCynoscion nehulosus), 

 gulf menhaden tBrevoortia patronus), gidf flounder iPara- 

 lichthys albigutta), pompano (Trachinotus carolinus), and 

 permit (Ti-achinotus falcatiis). These species each account- 

 ed for less than Vi of the total finfish count, except for the 

 southern kingfish, which accounted for 4.6''( . 



For the species captured principally in fall, the overall 

 proportion of the bycatch excluded by the 14-m and 17-m 

 BRD-equipped nets was similar, and both sizes of nets 

 tended to exclude high percentages of these fishes (Fig. 4). 

 The 20-m BRD-equipped net was not as effective in reduc- 

 ing the numbers of these species. For the species captured 

 principally in winter, the efficiency with which the BRD- 

 equipped nets excluded these fishes varied among net sizes 

 and BRD types. For some species (e.g. the leopard searobin 

 and blaekcheek tonguefish), BRD-equipped nets retained 

 more individuals than did the corresponding control nets. 



Size distribution 



Shrimp size-frequency distributions for pooled trawls ( BRD- 

 equipped net and its corresponding control ) had significant 

 seasonal variation (P<0.001,?=16.1,df=2,416). In fall, mean 

 carapace length was 23.4 mm (SD=4.7 mm) and the range 

 was 11.2—40.4 mm, whereas in winter, the mean was 27.0 

 mm (SD=6.5 mm) and the range was 7.3—43.8 mm. 



Mean sizes of the 10 most abundant finfish species dif- 

 fered significantly between the BRD-equipped nets and 



their corresponding controls in approximately '257( of the 

 trawls with the FFE-equipped nets and in 30"r of the trawls 

 with the EMF-equipped nets (Table 3). The differences in 

 mean sizes of individuals were usually small regardless of 

 statistical significance. Nevertheless, the ratio of compari- 

 sons in which mean size of fish from BRD-equipped nets 

 was smaller than that of fish from control nets to compari- 

 sons in which the mean size offish from BRD-equipped nets 

 was larger than that offish from control nets was 2:1 for 

 the trawls with the FFE-equipped net and 3: 1 for the trawls 

 with the EMF-equipped net. The only net size and BRD- 

 type combination for which the mean size of individuals 

 from the BRD-equipped net was always smaller than that 

 from the control net was the 14-m FFE-equipped net. 



Discussion 



Shrimp catch 



Although most BRD-equipped nets retained less biomass 

 and fewer numbers of shrimp than did their corresponding 

 control nets, the difference in these measures between the 

 BRD-equipped nets and their controls was significant only 

 for the 14-m net in winter Indeed, shrimp biomass and 

 number in the 20-m BRD-equipped net slightly exceeded 

 biomass and number in the corresponding control net. In 

 previous studies, researchers evaluating the efficiency of 

 BRDs also found that the shrimp catch in BRD-equipped 

 nets tended to be higher than in control nets. They attrib- 

 uted the increase in shrimp catch in their BRD-equipped 

 net to a greater net spread caused by a reduction in the 

 amounts of bycatch and drag (Rogers et al., 1997; Coleman 

 and Koenig'") and to an increase in the volume of water 

 filtered through the net due to the position of the BRD 

 (Christian et al.'''). 



The numbers of shrunp retained in all BRD-equipped 

 nets and in nearly all control nets were greater in winter 

 than in fall. In the Tampa Bay region, adult female shrimp 

 migi'ate out of the bay to spawn during spring and fall and 

 juvenile shrimp are recruited into the bay during sum- 

 mer and winter lEldred et al., 1965). The increase in abun- 

 dance and the larger size range of shrimp that we caught 

 during winter support this finding. 



Finfish bycatch 



Overall, both BRDs proved to be highly effective in reduc- 

 ing finfish bycatch without greatly reducing shrimp catch. 

 The reduction in bycatch was usually significant in the 

 14-m and 17-m BRD-equipped nets. The mean ratio of fin- 

 fish biomass to shrimp biomass in our BRD-equipped nets 

 was within the range of ratios reported by others who 

 tested the BRD-equipped nets in the Gulf (Alverson et al., 

 1994; GSAFDF-). Branstetter (1997) and Watson et aV^ 



Watson.J.,A. Shah, and D.Foster. 1997. Report on the status 

 of bycatch reduction device (BRD) development. National 

 Marine Fisheries Sei-vice, Mississippi Laboratories, P.O. Drawer 

 1207, Pascagoula. MS, 39568. 



