Steele et a\ . Efficiency of bycatcfi reduction devices in small otter trawls in the Florida shnmp fishery 



349 



size combinations. Similar, comparatively high reduction 

 rate.s for nets equipped with an EMF have been reported 

 elf^ewhere (P'uls and McEachron"'). 



Both BRDs reduced (usually notably and significantly) 

 the biomass of finfish in all net sizes during both seasons. 

 However, the number of fish in the BRD-equipped nets 

 comparc>d with the control nets varied markedly between 

 seasons. In fall, the number of fish in the BRD-equipped 

 nets was nearly always much lower than the number in 

 the corresponding control nets; but in winter, the number 

 in the BRD-equipped nets was generally slightly higher 

 than the number in the corresponding control nets. This 

 increase was due to the sizable influx of juvenile leopard 

 searobins in the finfish catch in winter. The long pectoral- 

 fin rays on these fish became entangled in the nets (and in 

 the BRD) and prevented the fish from escaping. 



The detailed analysis of species-specific change in num- 

 bers of fish in the BRD-equipped nets compared with 

 their corresponding control nets revealed additional in- 

 teresting patterns. The number of silver Jennys was re- 

 duced in all BRD-equipped nets, except in the 17-m BRD- 

 equipped net during winter. The numbers of hardhead 

 catfish, sand seatrout, silver perch, and southern kingfish 

 were always reduced in the BRD-equipped nets except 

 in the 20-m FFE-equipped net during fall. The number 

 of leopard searobins and blackcheek tonguefish nearly al- 

 ways increased in the BRD-equipped nets, regardless of 

 season. With some exceptions, larger fish were more like- 

 ly to escape than smaller fish, probably because swim- 

 ming ability is positively associated with size in fishes 

 (Wardle, 1993). However, fish (particularly large individu- 

 als) of species with protruding bony scutes or long fin rays 

 (e.g. gafftopsail catfish, leopard searobin. southern king- 

 fish) became entangled in the nets and thus could not es- 

 cape. The potential for large individuals of these types of 

 fish to become entangled in the net may have increased 

 because of the restricted net circumference, caused by the 

 presence of the EMF. Thus, for these types of species, mean 

 size of individuals retained in the BRD-equipped nets was 

 frequently larger than mean size of individuals retained 

 in the corresponding control nets. 



A number of factors other than morphological features, 

 such as pointed, projecting body structures, influence the 

 ability of fish to escape from trawl nets equipped with 

 BRDs. The behavior of fish in response to trawls has been 

 described as a combination of optomotor response and 

 rheotactic reaction, both of which contribute to a fishes' 

 ability to escape capture in a trawl (Watson'"). When am- 

 bient light conditions and water clarity allow for sufficient 

 contrast between the trawl and the background, many, 

 but not all, fishes orient their heads toward the mouth of 

 trawl and maintain swimming speeds comparable to the 

 trawling speed. Thereby, a fish can align itself with the in- 

 trawl current. This optomotor response is usually associat- 



" Watson, J. W. 1988. Fish behavior and trawl design; poten- 

 tial for selective trawl development. In Proceedings of the 

 world symposium on fishing gear and fishing vessel design. (S. 

 G. Fox and J. Huntington, eds.). p. 2.5-29. Newfoundland and 

 Labrador Institute of Fisheries and Marine Technology. P.O. 

 Box 4920. St. Johns, Newfoundland AlC 5R3. 



ed with the well-developed lateral line system found in pe- 

 lagic schooling species and is usually absent in demersal 

 species (Pavlov, 1969). However, this response is consider- 

 ably diminished during nighttime and in turbid water, and 

 both of these conditions existed during our trawling. Thus, 

 fishes with well-developed optomotor responses probably 

 required additional stimuli to escape from our nets, even if 

 they were in close proximity to an escape opening. Most of 

 these fishes may have escaped the trawl through the BRD 

 when the trawl speed was reduced during trawl haul-back 

 (Watson'"). The rheotactic response allows demersal fish 

 to detect turbulent water flows and associated pressure 

 gradients through the lateral line even when substantial 

 visual cues are not available (Wardle, 1993). Areas of dis- 

 turbed water exist within a moving trawl, especially near 

 objects such as BRDs, which interrupt water flow. Demer- 

 sal fishes with well-developed rheotactic responses can 

 sense these areas of reduced velocity, align themselves be- 

 hind these areas, and eventually escape through the exit 

 provided by the BRD while the trawl is being towed. The 

 finfish species with the largest percentage reductions in 

 numbers in our BRD-equipped nets compared with the 

 corresponding control nets were demersal and most likely 

 used this response to assist in their escape. 



BRDs and Fishery management 



Both the FEE and EMF are standard bycatch reduction 

 devices recommended by NMFS and used by the shrimp 

 industry. The effectiveness of these two BRDs in reducing 

 finfish bycatch without greatly reducing shrimp catches 

 has been well documented for the Gulf and the South 

 Atlantic shrimp fisheries. (Captiva and Rivers, 1960; 

 Gutherz and Pellegrin, 1988; Murray et al., 1992; Watson 

 et al., 1993; Branstetter, 1997; Rogers et al., 1997; Cole- 

 man et al."; Christian et al.''^; McKenna and Monaghan'"'; 

 Watson et al.'^; our study). The FEE is now required in 

 all shrimp trawls used in the federal Exclusive Economic 

 Zone along the South Atlantic and in the Gulf 



The policy set forth by the EMEC in 1990 to reduce the 

 overall finfish bycatch in the Florida shrimp fishery has 

 been addressed in our study. In part as a result of this 

 study, Florida is the first state bordering on the Gulf of Mex- 

 ico to require the use of BRDs in state waters. BRDs not on- 

 ly serve to conserve natural marine resources, in the Flor- 

 ida shrimp fishery they provide additional benefits to the 

 shrimp fishermen. Reducing bycatch decreases drag during 

 tow times, which, in turn, lowers fuel consumption thereby 

 reducing fuel costs, diminishes wear and tear on the trawl 

 gear, decreases culling time by the deck crew, and produces 

 a better shrimp product. From a cost-benefit perspective, 

 BRDs clearly provide consei-vational, economic, and socio- 

 logical benefits that far outweigh their actual costs. 



Acknowledgments 



This paper is a publication of the Florida Fish and Wild- 

 life Conservation Commission and was funded in part by 

 Cooperative Agreement number NA67FI0118 from the 



