The efficiency of a bycatch reduction device used in skimmer trawls in the Florida shrimp fishery

Daniel A. Warner, Anne L. McMillen-Jackson, Theresa M. Bert, and Charles R. Crawford

SEDAR-PW6-RD49

23 June 2014 This article was downloaded by: [College Of Charleston] On: 24 June 2014, At: 05:47 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

North American Journal of Fisheries Management Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/ujfm20 The Efficiency of a Bycatch Reduction Device Used in Skimmer Trawls in the Florida Shrimp Fishery Daniel A. Warner a , Anne L. McMillen-Jackson a , Theresa M. Bert a & Charles R. Crawford a a Florida Fish and Wildlife Conservation Commission, Florida Fish and Wildlife Research Institute , 100 Eighth Avenue SE, St. Petersburg, Florida, 33701-5095, USA Published online: 08 Jan 2011.

To cite this article: Daniel A. Warner , Anne L. McMillen-Jackson , Theresa M. Bert & Charles R. Crawford (2004) The Efficiency of a Bycatch Reduction Device Used in Skimmer Trawls in the Florida Shrimp Fishery, North American Journal of Fisheries Management, 24:3, 853-864, DOI: 10.1577/M03-110.1 To link to this article: http://dx.doi.org/10.1577/M03-110.1

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The Ef®ciency of a Bycatch Reduction Device Used in Skimmer Trawls in the Florida Shrimp Fishery

DANIEL A. WARNER,1 ANNE L. MCMILLEN-JACKSON,THERESA M. BERT,* AND CHARLES R. CRAWFORD Florida Fish and Wildlife Conservation Commission, Florida Fish and Wildlife Research Institute, 100 Eighth Avenue SE, St. Petersburg, Florida 33701-5095, USA

Abstract.ÐOf principal concern to those who regulate shrimp harvesting gear are the quantity and composition of nontargeted species (bycatch) harvested by any allowable gear type. The use of skimmer trawls in the Florida shrimp ®shery is a contested issue, in part because little bycatch characterization data exist for this gear. We characterized skimmer trawl bycatch and evaluated the ef®ciency of the Florida Fisheye (FFE) bycatch reduction device in a skimmer trawl typically used by commercial ®shermen in Apalachicola Bay, Florida, an area with an active ®shery for white shrimp Litopenaeus setiferus (also known as Penaeus setiferus). In general, the ®n®sh bycatch in a 4.9-m-long ϫ 3-m-wide skimmer trawl net equipped with an FFE was signi®cantly lower than that in an identical net towed simultaneously but without the FFE; the two nets, however, did not differ in the quantity of shrimp retained. The magnitude of the reduction in bycatch in the FFE-equipped net varied between seasons (spring and fall) and among ®n®sh species and, in the case of silver seatrout Cynoscion nothus and Atlantic croaker Micropogonias undulatus, between size- (i.e., age-) groups. Preliminary tests of FFEs in skimmer trawls in North Carolina also show a reduction in bycatch; we provide further details on how bycatch reduction devices work in skimmer trawls. Overall, our results indicate that skimmer trawls equipped with FFEs should compare favorably with other allowable shrimping gear.

The penaeid shrimp ®shery often ranks higher 1997a, 1997b; Broadhurst 2000; Steele et al. in value than any other commercial ®shery in the 2002). southeastern United States (Klima 1989; NMFS The skimmer trawl is a type of shrimping gear 1997), but the greatest amounts of nontargeted or- that is commonly used in the North Carolina and ganisms (e.g., ®n®sh and miscellaneous inverte- Louisiana shrimp ®sheries (Hines et al. 1993; Es- brates) are also harvested in this ®shery because trada et al. 2000). This gear is similar to a wing shrimp trawls harvest nonselectively (Alverson et net in that the net is held open by a rigid frame al. 1994). The catches of these nontargeted organ- and deployed amidships of the towing vessel. The isms, also known as bycatch, often exceed those skimmer trawl is different from the commonly of the targeted species. For example, in the south- used otter trawl in that this shallow water gear eastern U.S. shrimp trawl ®sheries, the total weight ®shes the entire water column and is pushed of bycatch is frequently two to four times the total through the water instead of being pulled. The weight of the shrimp catch and can be as high as skimmer trawl has several advantages over other Downloaded by [College Of Charleston] at 05:47 24 June 2014 ten times the total weight (Alverson et al. 1994; types of shrimping gear. For example, the skimmer Wallace and Robinson 1994; GSAFDF 1997). trawl is more effective at reducing bycatch and Thus, the capture of bycatch in shrimp trawls is increasing shrimp catch than the otter trawl, and an important concern for ®shermen, ®shery man- captured ®n®sh bycatch species have higher sur- agers, and environmentalists (Alverson and vival probabilities after being released from the Hughes 1996). Recently, researchers have focused net (Hines et al. 1993; Coale et al. 1994). on various ways to reduce the amount of bycatch, The use of skimmer trawls in the Florida shrimp including the development and evaluation of var- ®shery is limited and relatively recent. Florida ®sh- ious bycatch reduction devices attached to shrimp ermen ®rst expressed an interest in using skimmer nets (McKenna and Monaghan 1993; Rogers et al. trawls to harvest white shrimp Litopenaeus setiferus (also known as Penaeus setiferus) in the Apalach- * Corresponding author: [email protected].¯.us icola region (Figure 1) in 1993. At that time, skim- 1 Present address: School of Biological Sciences, Uni- mer trawls were approved for use in Florida only versity of Sydney, New South Wales 2006, Australia. under a special activities license and within a re- Received June 20, 2003; accepted October 22, 2003 stricted ®shing zone in Apalachicola Bay. However,

853 854 WARNER ET AL.

FIGURE 1.ÐMap of Apalachicola Bay, Florida. The hatched region is the area where sampling was conducted, which was also the only area in Florida where the use of skimmer trawls was allowed until 2002.

in 2002, skimmer trawls were classi®ed as allow- uate the ef®ciency of the Florida Fisheye (FFE) able shrimp-harvesting gear throughout the North- bycatch reduction device (BRD) in reducing the west Florida Shrimping Region (Northwest Region capture of nontarget species and retaining shrimp. Food Shrimp Production Gear Speci®cations This information should assist ®shery managers 2002). when they consider the use of skimmer trawls and The principal concerns of those who regulate the FFE bycatch reduction device. shrimp-harvesting gear are the quantity and com- position of the bycatch species harvested by the Methods gear. To our knowledge, only three papers have Gear speci®cations.ÐWe conducted our sam-

Downloaded by [College Of Charleston] at 05:47 24 June 2014 been published on skimmer trawls in general pling on a commercial shrimp boat (12.5 m long (Hines et al. 1993; Coale et al. 1994; Hines et al. ϫ 4.9 m wide and powered by a General Motors 1999), and no detailed information has been pub- 8-71 engine) equipped with paired skimmer trawls lished on the ef®ciency of bycatch reduction de- identical to the type used in the Florida commercial vices in skimmer trawls. Furthermore, little by- shrimp ®shery (Figure 2). The skimmer trawls con- catch characterization data exist for the skimmer sisted of rigid aluminum frames (4.9 m wide ϫ trawl in Florida waters. In May 1994, Felicia Co- 3.0 m high) that were suspended off each side of leman (Florida State University, Tallahassee, un- the boat and hinged to the base of an A-frame published data) conducted an initial survey of located 60% of the way aft of the bow. This al- skimmer trawl bycatch. However, her shrimp catch lowed the trawls to be raised and lowered (Hines was small, and she was unable to determine catch et al. 1993). A ``shoe'' (30.5 cm ϫ 91.4 cm) at- rates of ®n®sh and shrimp from the data. Thus, a tached to the bottom of the vertical arm slid along more comprehensive characterization of skimmer the sea ¯oor when the trawls were ®shing. Com- trawl bycatch in Florida waters was needed. mercial food-shrimp nets (no. 9 twine) with a The goal of our study was to characterize the stretch-mesh size of 3.8 cm were attached to the bycatch captured by skimmer trawls and to eval- frames; accordingly, the mouths of the nets were A BYCATCH REDUCTION DEVICE IN SKIMMER TRAWLS 855

FIGURE 2.ÐDiagram showing (A) the skimmer trawl frame and (B) the components of the net. Both the Turtle Excluder Device (TED) and the Florida Fisheye Bycatch Reduction Device (BRD) were attached to the shrimp net.

Downloaded by [College Of Charleston] at 05:47 24 June 2014 the same dimensions as the frames. The tail bags cod end. The FFE was constructed of 13-mm- (3.35 m long) were made of no. 21 twine and had diameter stainless steel rods. It was 30 cm in length a stretch-mesh size of 3.5 cm. For each net, a 113- and had a 15-cm ϫ 15-cm opening to allow ®sh kg weight tied to an inboard line spread open the to escape. The FFE has been tested in other types bottom of the net, and a tickler chain was con- of shrimping gear (Whitaker et al. 1992; Rogers nected between the shoe and the weight. et al. 1997a; Steele et al. 2002) and is an approved Each net was equipped with a Super Shooter BRD for the Florida shrimp ®shery. Turtle Excluder Device (TED). The TED was at- Sampling protocol.ÐWe conducted our study in tached to the net according to federal regulations Apalachicola Bay, a 549-km2 estuary located in and consisted of a metal grid of seven aluminum northwestern Florida (Figure 1). An active ®shery bars with a 9-cm interbar distance; the grid was for penaeid shrimp, principally the white shrimp, set at a 45Њ angle to direct turtles downward toward is located in the bay. At the time of this study, the escape opening. Each net was also equipped shrimp ®shing with skimmer trawls in the bay was with an FFE. The FFE was mounted at the top restricted to a designated ®shing area (Figure 1) center of the tail bag approximately halfway be- that had an average water depth of about 3 m. We tween the tie-off rings and the beginning of the sampled only within this area. 856 WARNER ET AL.

During each sampling period (spring [May of trawling time. We report large weights as ki- 2001] and fall [September 2001]), we trawled at lograms for simplicity. All comparisons of NPUE night when commercial ®shermen were actively and CPUE were made between the BRD-equipped ®shing. The trawls were towed at a speed of 2.5 net and its corresponding control net for each sea- knots (1 knot ϭ 0.514 m/s), as determined by the son separately. We compared mean NPUE and global positioning system. We conducted a total CPUE values using the Mann±Whitney U-test. We of forty 30-min tows using paired trawls, one at- also calculated the percent difference in mean tached to each side of the boat. The ®rst 10 tows NPUE or CPUE between the BRD-equipped and were used as a preliminary study to determine control nets using the method of Rogers et al. whether the biomass catchability of the two trawls (1997a), namely, was equivalent; thus, they were conducted with the BRDs in both nets sewn shut. The subsequent Percent difference 30 experimental tows were conducted with the BRD value Ϫ control value ϭϫ100. BRD in one trawl sewn shut (control net) and the ΂΃control value BRD in the other trawl left open (BRD-equipped net). To reduce any bias associated with differ- Number per unit effort and CPUE comparisons ences in the catch related to the side of the boat were done separately for shrimp, total ®n®sh by- on which we placed the BRD-equipped net, we catch, total invertebrate bycatch (excluding spong- performed 15 experimental tows with the BRD- es and tunicates) as well as for each ®n®sh bycatch equipped net on the port side of the boat and then species in an ``abundant'' category, which we de- changed the position of the BRD-equipped net to ®ned as those that collectively composed 95% of the starboard side for the remaining 15 tows. the ®n®sh bycatch in terms of numbers or biomass. All samples were processed onboard the boat Although relatively small individuals of some spe- immediately after each tow. For the preliminary cies may have passed through our nets, we used study, only the total weights of shrimp plus by- all ®n®sh species in our analyses, including small catch were recorded for each tow. For each of the species such as anchovies Anchoa spp., scaled sar- experimental tows, the shrimp were separated from dine Harengula jaguana, and Atlantic silversides the bycatch and the bycatch was separated by spe- Menidia menidia, because they contributed rela- cies. The total shrimp catch was weighed and tively large proportions of the overall bycatch counted to determine the count per gram. Twenty NPUE and CPUE in both seasons (Tables 1, 2). randomly chosen shrimp (or all shrimp if n Ͻ 20) We used the KolmogorovϪSmirnov two-sample were measured (total length [TL]) to obtain a size test to determine whether there were shifts in the distribution. Similarly, for each bycatch species, size distributions of the shrimp captured in the the total catch was weighed and 20 randomly cho- BRD-equipped net and the control net. This test sen individuals (or all individuals if n Ͻ 20) were was also used to determine whether there were measured (TL). Miscellaneous debris and organ- signi®cant differences in the size distributions of isms (turtle grass Thalassia testudinum, manatee the ®n®sh bycatch species in the abundant cate- grass Syringodium ®liforme, rocks, shells, sponges, gory captured in the BRD-equipped net and those

Downloaded by [College Of Charleston] at 05:47 24 June 2014 tunicates, anthropogenic garbage, etc.) were sep- captured in the control net. However, the sizes of arated out of each tow. certain large species that were rarely captured (i.e., Statistical analyses.ÐStatistical analyses fol- longnose gar, cownose ray, and blacktip shark) lowed the methods of Sokal and Rohlf (1995) and were not evaluated because sample sizes were were performed using the STATISTICA software small. package (Statsoft, Inc. 1999). A signi®cance level of 0.05 was used for all tests. Most variables did Results not conform to parametric assumptions of nor- The shrimp catch consisted principally of white mality (ShapiroϪWilk test) or homogeneity of var- shrimp with occasional pink shrimp Farfantepen- iances (Levene's test), even after log transforma- aeus duorarum. For this study we did not separate tion. Thus, appropriate nonparametric tests were these two species during data collection. used for all analyses, as detailed below. The catchability rates of the net on the port side We calculated the number per unit effort of the boat and that on the starboard side were (NPUE) as the number of individuals caught per similar when no BRDs were used. The differences minute of trawling time and the catch per unit between the port and starboard nets in catchability effort (CPUE) as biomass (g) caught per minute rate (total biomass) were 0.8% in the spring (U ϭ A BYCATCH REDUCTION DEVICE IN SKIMMER TRAWLS 857

TABLE 1.ÐComposition (number) of ®n®sh bycatch species captured in a skimmer trawl net equipped with a bycatch reduction device (BRD) and skimmer trawl net without a BRD (control) in Apalachicola Bay, Florida, during the spring and fall of 2001. Only species that collectively contributed to 95% of the total catch are identi®ed in the table; the remaining species are listed in the footnotes. The acronym NPUE refers to the number of ®sh captured per minute of towing. Crosses denote species important to commercial or recreational ®sheries. Asterisks represent signi®cant differ- ences in catch between the BRD-equipped and control nets (P Ͻ 0.05*, P Ͻ 0.01**, P Ͻ 0.001***).

Total count NPUE in NPUE in Percent Species (%) control net BRD net difference Spring Striped anchovy² Anchoa hepsetus 6,964 (37.1) 3.55 4.43 24.8* Atlantic croaker Mircopogonias undulatus 3,913 (20.9) 2.16 2.31 7.0 Atlantic bumper² Chloroscombrus chrysurus 2,734 (14.6) 1.66 1.54 Ϫ7.4 Star drum Stellifer lanceolatus 1,165 (6.2) 0.70 0.64 Ϫ9.2 Gulf menhaden² Brevoortia patronus 977 (5.2) 0.78 0.34 Ϫ57.2* Atlantic silverside² Menidia menidia 885 (4.7) 0.54 0.49 Ϫ9.9 Harvest®sh² Peprilus alepidotus 608 (3.3) 0.34 0.37 8.4 Hardhead cat®sh² Arius felis 315 (1.7) 0.20 0.17 12.2 Scaled sardine² Harengula jaguana 254 (1.4) 0.19 0.10 Ϫ45.4** Caribbean pomfret Brama caribbaea 203 (1.1) 0.12 0.11 Ϫ9.3 Other ®nish combineda 717 (3.8) 0.41 0.41 0.4 Fall Gulf menhaden² 39,789 (68.3) 33.39 11.71 Ϫ64.9*** Scaled sardine² 7,166 (12.3) 4.95 3.37 Ϫ32.0 Silver perch² Bairdiella chrysoura 4,387 (7.5) 2.69 2.43 Ϫ9.7 Bay anchovy² Anchoa mitchilli 1,852 (3.2) 0.94 1.21 29.7 Spot² Leiostomus xanthurus 1,783 (3.1) 1.25 0.83 Ϫ33.9* Atlantic bumper² 1,323 (2.3) 0.31 1.14 267.6 Other ®n®sh combinedb 1,938 (3.3) 0.95 1.29 36.3 a Other ®nish bycatch species captured in spring 2001 (in order of relative abundance) are as follows: Atlantic thread herring² Opisthonema oglinum, pin®sh² Lagodon rhomboids, leatherjack Oligoplites saurus, Atlantic spade®sh² Chaetodipterus faber, Spanish mackerel² Scomberomorus maculates, bluestriped grunt² Haemulon sciurus, bon- nethead² Sphyrna tiburo, bighead searobin Prionotus tribulus, lady®sh² Elops saurus, sapphire eel Cynoponticus savanna, Atlantic needle®sh² Strongylura marina, blackcheek tongue®sh Symphurus plagiusa, spotted whiff Cith- arichthys macrops, hogchoker Trinectes maculates, spiny butter¯y ray Gymnura altavela, reef shark Carcharhinus perezi, southern ¯ounder² Paralichthys lethostigma, southern stingray² Dasyatis Americana, and stippled cling®sh Gobiesox punctulatus. b Other ®n®sh bycatch species captured in fall 2001 (in order of relative abundance) are as follows: striped anchovy², Atlantic silverside², silver seatrout² (Cynoscion nothus), Caribbean pomfret, Atlantic thread herring², banded rud- der®sh² Seriola zonata, pin®sh², spot®sh mojarra² Eucinostomus argenteus, spotted seatrout² Cynoscion nebulosus, leatherjack, lookdown² Selene vomer, bluntnose jack Hamicaranx amblyrhynchus, Atlantic spade®sh², Spanish mackerel², bluestriped grunt², Atlantic moon®sh² Selene setapinnis, bonnethead, inshore lizard®sh Synodus foetens, bighead searobin, lady®sh², cownose ray² Rhinoptera bonasus, gray snapper² Lutjanus griseus, Atlantic needle®sh², blackcheek tongue®sh, sand seatrout² Cynoscion arenarius, striped burr®sh Chilomycterus schoep®, bandtail puffer Sphoeroides spengleri, hogchoker, king mackeral² Scomberomorus cavalla, Atlantic stingray² Dasyatis Sabina, crevalle jack² Caranx hippos, gulf king®sh² Menticirrhus littoralis, remora Remora remora, sand perch² Diplectrum formosum, smalltail shark Carcharhinus porosus, southern puffer² Sphoeroides nephelus, and tripletail² Lobotes Downloaded by [College Of Charleston] at 05:47 24 June 2014 surinamensis.

49.0, df ϭ 18, P ϭ 0.940) and 0.9% in the fall (U the other side of the boat. The biomass of the in- ϭ 30.5, df ϭ 18, P ϭ 0.377). The shrimp biomass vertebrate bycatch was too small for reliable sta- captured in the two nets (spring: 13.0%; fall: 8.7%) tistical tests. differed to a greater degree than did the ®n®sh In the experimental study, the total biomass cap- bycatch biomass (spring: 0.6%; fall: 0.0%), but tured in the BRD-equipped net and the control net none of the differences were statistically signi®- (all data combined for each net type) in the spring cant (spring shrimp: U ϭ 33.5, df ϭ 18, P ϭ 0.212; consisted of 84.1% and 87.3% ®n®sh bycatch, re- fall shrimp: U ϭ 37.5, df ϭ 18, P ϭ 0.791; spring spectively, and 11.8% and 10.1% shrimp. The re- ®n®sh: U ϭ 46.5, df ϭ 18, P ϭ 0.791; fall ®n®sh: mainder of the catch consisted of invertebrate by- U ϭ 33.0, df ϭ 18, P ϭ 0.508). In addition, the catch (Ͻ2.0% of the total biomass in each net) and net on one side of the boat did not have a consis- miscellaneous debris (Ͻ2.5% of the total biomass tently higher or lower catch rate than the net on in each net). Of the total biomass captured in the 858 WARNER ET AL.

TABLE 2.ÐComposition (biomass) of ®n®sh bycatch species captured in a skimmer trawl net equipped with a bycatch reduction device (BRD) and a skimmer trawl net without a BRD (control) in Apalachicola Bay, Florida, during the spring and fall of 2001. Only species that collectively contributed to 95% of the total catch are identi®ed in the table; the remaining species are listed in the footnotes to Table 1. The acronym CPUE refers to the biomass of ®sh captured per minute of towing. Crosses denote species important to commercial or recreational ®sheries. Asterisks represent signi®cant differences in catch between the BRD-equipped and control nets (P Ͻ 0.05*, P Ͻ 0.01**, P Ͻ 0.001***).

Total biomass (g) CPUE in CPUE in Percent Species (% of catch) control net BRD net difference Spring Hardhead cat®sh² 93,650 (14.0) 59.69 51.26 Ϫ14.1 Gulf menhaden² 85,870 (12.9) 64.88 34.37 Ϫ47.0** Atlantic croaker 68,470 (10.3) 35.58 42.75 20.2 Striped anchovy² 65,400 (9.8) 36.69 39.20 6.9 Atlantic bumper² 51,770 (7.8) 29.91 30.55 2.1 Gafftopsail cat®sh² Bagre marinus 46,250 (6.9) 39.12 13.73 Ϫ64.9 Star drum 43,940 (6.6) 26.21 24.33 Ϫ7.2 Harvest®sh² 34,480 (5.2) 19.28 20.73 7.5 Atlantic silverside² 32,630 (4.9) 19.98 17.99 Ϫ10.0 Atlantic midshipman Porichthys plectrodon 22,440 (3.4) 13.25 12.71 Ϫ4.1 Silver perch² 17,270 (2.6) 10.59 9.65 Ϫ8.8 Banded rudder®sh² 16,280 (2.4) 10.85 8.14 Ϫ25.0 Blacktip shark² Carcharhinus limbatus 16,050 (2.4) 12.32 5.67 Ϫ54.0 Scaled sardine² 15,700 (2.4) 12.47 5.66 Ϫ54.6** Silver seatrout² 10,410 (1.6) 7.70 4.33 Ϫ43.8 Cownose ray² 8,100 (1.2) 9.70 0.00 Ϫ100.0 Spotted seatrout² 7,750 (1.2) 3.94 5.00 26.8 Other ®n®sh combined 30,380 (4.4) 17.49 17.27 Ϫ1.3 Fall Gulf menhaden² 435,300 (61.6) 365.10 131.12 Ϫ64.1*** Silver perch² 82,860 (11.7) 51.35 45.41 Ϫ11.6 Scaled sardine² 56,840 (8.0) 38.18 27.55 Ϫ27.8 Spot² 42,070 (6.0) 29.53 19.84 Ϫ32.8* Longnose gar Lepisosteus osseus 31,400 (4.4) 21.07 15.94 Ϫ24.4 Atlantic croaker 10,410 (1.5) 3.94 7.75 96.6 Gafftopsail cat®sh² 9,220 (1.3) 4.15 6.74 62.4 Hardhead cat®sh² 7,370 (1.0) 3.77 4.58 21.5 Other ®n®sh combined 32,230 (4.5) 19.80 16.54 Ϫ16.5

fall, the BRD-equipped net contained 91.6% ®n- the BRD-equipped net. The presence of only one ®sh bycatch and 8.0% shrimp; the control net con- or a few of these ®sh in a net strongly in¯uenced tained 95.0% ®n®sh bycatch and 4.4% shrimp. The the overall CPUE. Notable decreases in the number

Downloaded by [College Of Charleston] at 05:47 24 June 2014 invertebrate bycatch and debris was less than 1% or biomass of smaller ®sh, such as the gulf men- of the total biomass in each net. haden, scaled sardine, and silver seatrout, also con- tributed to the reduction in CPUE (Tables 1, 2). Effects of the BRD on NPUE and CPUE In the fall, both NPUE (U ϭ 210.0, df ϭ 58, P In the spring, the NPUE of the ®n®sh bycatch Ͻ 0.001) and CPUE (U ϭ 184.0, df ϭ 58, P Ͻ in the BRD-equipped net did not differ signi®- 0.001) of the ®n®sh bycatch were approximately cantly from that in the control net, but the CPUE 50% lower in the BRD-equipped net than in the did differ signi®cantly (U ϭ 278.0, df ϭ 58, P ϭ control net (Figure 3A, B). These differences were 0.011; Figure 3A, B). The ®n®sh bycatch CPUE due to the capture of fewer gulf menhaden in the in the BRD-equipped net (343.3 Ϯ 84.9 g/min BRD-equipped net than in the control net. The gulf [mean Ϯ SD]) was 20% lower than that in the menhaden composed 68% and 62% of the ®n®sh- control net (429.7 Ϯ 193.5 g/min). The discrep- bycatch NPUE and CPUE, respectively; these ancy between the NPUE and CPUE results was measures were 65% and 64% lower, respectively, partially due to the decrease in the catch of rela- in the BRD-equipped net than in the control net. tively small numbers of large ®sh such as the gaff- When gulf menhaden were omitted from the anal- topsail cat®sh, blacktip shark, and cownose ray in yses, neither NPUE nor CPUE differed signi®- A BYCATCH REDUCTION DEVICE IN SKIMMER TRAWLS 859

of shrimp harvested in the BRD-equipped and con- trol nets were not signi®cant in either season (Fig- ure 3E, F).

Bycatch Composition Overall, we captured 58 species of ®n®sh (Ta- bles 1, 2) and 6 species of invertebrates. Twenty- six of the ®n®sh species were common to both the spring and the fall sampling periods. In the spring, we captured a total of 37 ®n®sh bycatch species. Only 10 species composed 96.2% of the 18,735 ®n®sh caught (Table 1). The striped anchovy was the most common; the number of striped anchovy collected was nearly twice that of the second most common species, the Atlantic croaker. The Atlantic bumper was also relatively common. In biomass, no single species notably predominated (Table 2); total biomass was well distributed among the species captured. In total biomass, 29 species contributed small percentages (Ͻ5%). The invertebrate bycatch in the spring consisted of squid (family Loliginidae) and blue crabs. We caught 322 squid, which composed 76% of the FIGURE 3.ÐComparisons of the mean number cap- total number of bycatch invertebrates, and 99 blue tured per minute of towing (NPUE) and the mean bio- crabs. Due to their small size, we did not weigh mass captured per minute of towing (CPUE) of (A, B) ®n®sh bycatch, (C, D) invertebrate bycatch, and (E, F) the squid. The blue crabs had a total biomass of shrimp in a skimmer trawl net equipped with a bycatch about 10.0 kg. reduction device (BRD) and one without a BRD (con- The species composition of our ®n®sh bycatch trol) in Apalachicola Bay, Florida, during the spring and in the fall was highly diverse (47 species). Gulf fall of 2001. The numbers above the bars are the per- menhaden were predominant in both numbers and centage differences between the control and BRD- biomass (Tables 1, 2). Scaled sardine and silver equipped nets; P 0.01*, P 0.001**. The error bars Ͻ Ͻ perch were also relatively common. Together, represent standard deviations. these three species accounted for 88.1% of the count and 81.3% of the biomass of the ®n®sh by- cantly between the BRD-equipped and control catch. nets, despite relatively large percentage reductions The invertebrate bycatch was also speciose in of some of the less prevalent species (Tables 1, 2). the fall. Squid (600 individuals; 81% of total in-

Downloaded by [College Of Charleston] at 05:47 24 June 2014 Equipping the skimmer trawl net with the FFE vertebrate bycatch numbers) and comb jellies Mne- did not signi®cantly reduce either the NPUE or miopsis spp. (100 individuals; 14%) were the most CPUE of invertebrate bycatch during either season abundant species, followed by mantis shrimp (Figure 3C, D). The differences in NPUE between Squilla empusa (17 individuals; 2%), blue crab (12 the performances of the two nets were relatively individuals; 2%), and cannonball jelly (8 individ- small, but the differences in CPUE were large and uals; 1%). Cannonball jelly predominated in the were principally due to the occasional capture of invertebrate bycatch biomass (4.0 kg). a large blue crab Callinectes sapidus or cannonball A number of the ®n®sh species harvested are jelly®sh Stomolophus meleagris in either the BRD- commercially or recreationally important as bait- equipped or the control net during a particular ®sh, food ®sh, or sport ®sh (Tables 1, 2). The pres- trawl. As a result, the high variances precluded ence of a BRD in a net greatly reduced the harvest statistical signi®cance. of some of these species (e.g., the gulf menhaden, Except for NPUE in the fall, the shrimp harvest scaled sardine, spot, and to a lesser extent, Atlantic in the BRD-equipped net was slightly lower in silverside) but increased the harvest of others; both number and biomass than that in the control however, these increases were signi®cant for only net. However, differences in the NPUE and CPUE one case (the NPUE of striped anchovy in spring). 860 WARNER ET AL.

TABLE 3.ÐMean total lengths (mm) of the ®n®sh commonly captured in a skimmer trawl net equipped with a bycatch reduction device (BRD) and a skimmer trawl net without a BRD (control) during spring and fall 2001 in Apalachicola Bay, Florida; n ϭ the number of ®sh measured. Asterisks denote signi®cant differences between BRD-equipped and control nets (P Ͻ 0.05*, P Ͻ 0.01**). Comparisons of species with high biomass per minute of towing and low numbers per minute of towing were not made due to small sample sizes.

Spring Fall Control net BRD net Control net BRD net Species n Mean Ϯ SD n Mean Ϯ SD n Mean Ϯ SD n Mean Ϯ SD Striped anchovy 600 58.7 Ϯ 4.8 600 58.0 Ϯ 5.3** 180 81.2 Ϯ 12.1 241 81.5 Ϯ 11.4 Atlantic croaker 548 63.7 Ϯ 10.9 560 62.3 Ϯ 9.1** 59 128.8 Ϯ 30.2 66 113.5 Ϯ 31.0* Atlantic bumper 529 63.3 Ϯ 5.3 532 63.7 Ϯ 6.0 128 41.12 Ϯ 12.9 197 38.8 Ϯ 10.2 Star drum 434 84.1 Ϯ 14.6 422 84.4 Ϯ 14.3 0 0 Atlantic silverside 423 90.3 Ϯ 6.4 390 89.3 Ϯ 7.6 1 75.0 2 81.0 Ϯ 14.1 Gulf menhaden 546 122.9 Ϯ 52.0 266 119.3 Ϯ 55.0 584 85.6 Ϯ 14.6 604 85.3 Ϯ 16.3 Harvest®sh 295 74.6 Ϯ 8.1 287 75.0 Ϯ 9.5 0 0 Hardhead cat®sh 167 218.3 Ϯ 61.0 148 218.8 Ϯ 53.0 29 162.4 Ϯ 60.4 31 170.3 Ϯ 63.6 Scaled sardine 168 87.5 Ϯ 9.2 90 86.7 Ϯ 7.5 582 74.8 Ϯ 9.1 559 74.6 Ϯ 8.5 Caribbean pomfret 107 52.1 Ϯ 7.1 93 51.9 Ϯ 6.7 55 48.7 Ϯ 9.1 56 49.7 Ϯ 15.0 Silver seatrout 80 81.1 Ϯ 42.2 84 61.5 Ϯ 27.1** 148 103.4 Ϯ 25.7 154 104.3 Ϯ 54.5 Silver perch 67 109.6 Ϯ 12.3 61 111.46 Ϯ 10.9 571 94.6 Ϯ 29.0 557 93.9 Ϯ 12.6 Bay anchovy 0 0 531 52.0 Ϯ 4.5 549 52.4 Ϯ 4.7 Spot 0 0 529 94.1 Ϯ 14.5 446 93.1 Ϯ 10.4 Gafftopsail cat®sh 13 340.1 Ϯ 75.0 12 323.3 Ϯ 100.0 30 168.6 Ϯ 76.3 25 172.2 Ϯ 96.8 Atlantic midshipman 77 134.1 Ϯ 16.9 91 132.3 Ϯ 16.7 0 0 Banded rudder®sh 30 155.6 Ϯ 9.6 33 156.8 Ϯ 10.0 18 75.8 Ϯ 17.0 9 64.6 Ϯ 24.4 Spotted seatrout 9 208.0 Ϯ 22.4 10 209.2 Ϯ 21.6 8 199.9 Ϯ 27.4 25 110.6 Ϯ 45.3**

Size Distribution large-sized ®sh than did the control net for both We made 31 comparisons of the mean size of silver seatrout (P ϭ 0.008) and Atlantic croaker ®n®sh species caught in the BRD-equipped net (P ϭ 0.039). with that of those caught in the control net, and The shrimp size-frequency distributions did not only ®ve of those comparisons were statistically differ signi®cantly between the BRD-equipped and signi®cant (Table 3); in all ®ve of these cases, the control nets in either the spring or the fall. In the mean size of ®sh in the control net was signi®- spring (n ϭ 1,182), mean total length was 109.9 cantly larger than the mean size of ®sh in the BRD- mm (SD ϭ 24.3) in the BRD-equipped net and equipped net. However, only three of these were 111.5 mm (SD ϭ 23.0) in the control net. In the notableÐsilver seatrout in the spring and Atlantic fall (n ϭ 1,163), mean total length was 94.5 mm croaker and spotted seatrout in the fall (Table 3). (SD ϭ 20.3) in the BRD-equipped net and 94.3 Two size-classes of both the silver seatrout and the mm (SD ϭ 20.1) in the control net. Atlantic croaker were captured (Figure 4); in both Discussion Downloaded by [College Of Charleston] at 05:47 24 June 2014 cases, the BRD-equipped net retained more ®sh in smaller size-classes and fewer ®sh in larger size- Shrimp Catch classes than did the control net. In additional anal- Shrimp biomass was a small component of the yses, we grouped the size-classes of these species total biomass that we caught in our nets, and the into ``small individuals'' (silver seatrout: 30±99 presence of a BRD had no signi®cant effect on the mm TL; Atlantic croaker: 80±119 mm TL) and NPUE, CPUE, or mean size of shrimp harvested. ``large individuals'' (silver seatrout: 110±189 mm However, the NPUE of shrimp harvested in the TL; Atlantic croaker: 120±199 mm TL) and com- BRD-equipped net was 5% greater than that in the pared the NPUE between the BRD-equipped and control net during the fall season. Moreover, the control nets for these size groupings using the proportion of shrimp biomass relative to the total Mann±Whitney U-test. The NPUE of large-sized ®n®sh biomass was nearly twice as high in the silver seatrout was signi®cantly lower in the BRD- BRD-equipped net than in the control net during equipped net than it was in the control net (U ϭ the fall season. The higher proportion of shrimp 309.0, df ϭ 162, P ϭ 0.037). A Wilcoxon's signed- in the BRD-equipped net in the fall was due to the ranks test showed further support for this pattern; notably large (50%) decrease in ®n®sh bycatch in the BRD-equipped net captured signi®cantly fewer the BRD-equipped net. Other studies of the ef®- A BYCATCH REDUCTION DEVICE IN SKIMMER TRAWLS 861

FIGURE 4.ÐSize-frequency distributions of the two ®n®sh bycatch species that differed signi®cantly and notably in size between the net equipped with a bycatch reduction device (BRD) and the control net: (A) silver seatrout in the spring and (B) Atlantic croaker in the fall. Downloaded by [College Of Charleston] at 05:47 24 June 2014 ciency of bycatch-reduction devices have also tude of the reduction in bycatch varied between shown that BRD-equipped trawl nets retain more seasons and among ®n®sh species. The seasonal shrimp than do control nets (Steele et al. 2002). differences in BRD ef®ciency were most likely due The reduction in the amount of bycatch and, con- to seasonal differences in species composition and sequently, the drag in the BRD-equipped net may abundance. For example, in the fall, gulf menha- allow the net to spread and cover a proportionally den made up more than 60% of the total count and larger area than a net without a BRD. Thus, more biomass and were responsible for the large reduc- shrimp could be caught because an increased vol- tion (ϳ50%) in both bycatch NPUE and CPUE ume of water is ®ltered through the net (Christian between the BRD-equipped net and control net. In et al. 1993; Coleman and Koenig 1994; Rogers et Louisiana waters, the Authement-Ledet BRD also al. 1997a; Steele et al. 2002). effectively reduces bycatch when gulf menhaden are abundant (Rogers et al. 1997a). Rogers et al. Bycatch Reduction (1997a) note that the capability of a BRD to reduce In general, the FFE was successful in reducing ®n®sh bycatch depends on the species assemblage ®n®sh bycatch and retaining shrimp. The magni- present, which could vary among seasons and lo- 862 WARNER ET AL.

cations. In our study, the FFE performed well dur- were retained more frequently in the control net ing the fall when gulf menhaden were abundant, than in the BRD-equipped net, possibly because but its performance was reduced during the spring they are more likely to escape through the FFE when the species composition differed. than small individuals are. In ®sh, swimming abil- The lower number of ®n®sh in the BRD- ity and size are positively associated (Blaxter and equipped net was probably due to a combination Dickson 1958; Wardle 1993). Studies of other of behavioral and optomotor responses of ®sh to types of trawling gear (such as the otter trawl) and moving shrimp trawls (Watson 1988; Wardle BRDs also report higher capture rates of small ®sh 1993). The ability of ®sh to respond to and escape in BRD-equipped nets than in control nets (e.g., from shrimp nets can vary with species, size, Steele et al. 2002). Because of the potentially det- swimming ability, physiological condition, and en- rimental effects of harvesting ®n®sh in the early vironmental conditions (Watson 1988). Many ®sh- life stages, more research on the effect of BRDs es tend to swim at speeds similar to that of the on the size-speci®c capture of ®sh is warranted. trawling gear and to align themselves with the in- trawl currents by orienting their heads toward the Skimmer Trawls, BRDs, and Fishery Management mouth of the net. In dark conditions, like those The capture of commercially or recreationally present during our study, many ®shes sense the important ®n®sh species in shrimp trawl nets has netting via their lateral lines and maintain ®xed been a major concern of ®shermen and ®shery distances from the net while swimming with the managers (Hendrickson and Grif®n 1993). In our gear (Watson 1988; Wardle 1993). Fish may re- study, some of the species that were captured in spond to holes in the netting because these areas high quantities are important food ®sh, bait®sh, or contrast in color or structure with the rest of the sport ®sh. The harvest of some of these species net (Watson 1988). Thus, a hole or a BRD in the was greatly reduced by the presence of a BRD in net may stimulate the ®sh to escape. In addition, the net. The harvest of other such species was BRDs disturb the water currents within the trawl. somewhat higher in the BRD-equipped net. These Many species with well-developed rheotactic re- increases and decreases of ®n®sh species bycatch sponses sense these areas and eventually escape in the BRD-equipped net demonstrate that BRD through the BRD (Watson 1988). The variation in ef®ciency was species speci®c. However, almost bycatch reduction among the ®n®sh species that none of the increases in bycatch in the BRD- we observed probably can be attributed to a com- equipped net were statistically or biologically sig- bination of these factors. An additional concern, ni®cant; an increase in bycatch in the BRD- however, is the ability of ®n®sh to survive after equipped net was signi®cant for only one case they have escaped through the BRD (Rulifson et (striped anchovy in spring). Thus, the use of the al. 1992). Fish are sometimes injured when es- FFE in skimmer trawl nets is an effective way of caping through a BRD and therefore may become reducing the bycatch mortality of several econom- susceptible to disease or predation. Nevertheless, ically important ®n®sh species. it seems likely that ®sh that have escaped through The results of our study are consistent with those a BRD will still have a greater probability of sur- of preliminary tests of FFEs in skimmer trawls in

Downloaded by [College Of Charleston] at 05:47 24 June 2014 vival than ®sh that are captured in nets without North Carolina, which also reported a reduction of BRDs. Experimental studies of postescape surviv- bycatch (Hines et al. 1993). However, we found al of ®n®sh bycatch are needed to address this that the performance of the FFE varied seasonally concern. and depended on the composition of the ®n®sh In contrast to ®n®sh, penaeid shrimp are rela- bycatch. The shrimp catch, however, was not sig- tively weak swimmers and are unable to maintain ni®cantly in¯uenced by the presence of the FFE their orientation in the currents generated by the during either season. Thus, the FFE in a skimmer trawl (Watson 1988); thus, they probably rarely trawl not only serves to reduce bycatch but also escape through the BRD. provides other bene®ts to shrimp ®shermen. Re- The differences between the BRD-equipped net ducing bycatch decreases drag during tow times, and the control net in the harvested quantities of which, in turn, decreases fuel consumption, wear at least two species (silver seatrout and Atlantic on the trawl gear, and culling time by the deck croaker) were size-class speci®c. The two size- crew. Consequently, from the perspective of ®sh- classes of silver seatrout and Atlantic croaker ermen and ®shery managers, skimmer trawls probably represent two age-groups: age 0 and age equipped with FFEs should compare favorably 1 and above. Large individuals of these species with other allowable shrimping gear. A BYCATCH REDUCTION DEVICE IN SKIMMER TRAWLS 863

Acknowledgments mospheric Administration, contract NA57FF0285). National Oceanic and Atmospheric Administration, This study was funded in part by the U.S. De- Tampa, Florida. partment of Commerce National Oceanographic Hendrickson, H. M., and W. L. Grif®n. 1993. An anal- and Atmospheric Administration through Cooper- ysis of management policies for reducing shrimp ative Agreement number NA97FI0028 to the Flor- bycatch in the Gulf of Mexico. North American ida Fish and Wildlife Conservation Commission. Journal of Fisheries Management 13:686±697. Hines, B., J. S. Coale, R. Rulifson, and J. Murray. 1993. We thank L. Miller for allowing us to conduct our The skimmer trawl in North Carolina estuaries. Uni- research on his shrimp boat, the M&M; P. Steele versity of North Carolina, Sea Grant College Pro- for initiating the shrimp bycatch work and for com- gram, Publication UNC-SG-93-01, Raleigh. ments on an early draft of this paper; K. Burns and Hines, K. L., R. A. Rulifson, and J. D. Murray. 1999. K. Reynolds for their assistance in ®eld sampling; Performance of low-pro®le skimmer trawls in the the FWRI editorial staff for help with the Figures inshore shrimp ®shery of North Carolina. North and editorial assistance; and J. O'Hop for infor- American Journal of Fisheries Management 19: 569±580. mation on commercially important ®n®sh species. Klima, E. F. 1989. Approaches to research and man- agement of U.S. ®sheries for penaeid shrimp in the References Gulf of Mexico. Pages 87±111 in J. F.Caddy, editor. Marine invertebrate ®sheries: their assessment and Alverson, D. L., M. H. Freeberg, S. A. Murawski, and management. Wiley, New York. J. G. Pope. 1994. A global assessment of ®sheries bycatch and discards. FAO (Food and Agriculture McKenna, S. A., and J. P. Monaghan, Jr. 1993. Gear Organization of the United Nations) Fisheries Tech- development to reduce bycatch in the North Caro- nical Paper 339. lina trawl ®sheries. Completion report to Gulf and Alverson, D. L., and S. E. Hughes. 1996. Bycatch: from South Atlantic Fisheries Development Foundation emotion to effective natural resource management. (cooperative agreement NA90AA-H-SK052). Gulf Reviews in Fish Biology and Fisheries 6:443±462. and South Atlantic Fisheries Development Foun- Blaxter, J. H. S., and W. Dickson. 1958. Observations dation. on the swimming speeds of ®sh. Journal du Conseil Northwest Region Food Shrimp Production Gear Spec- International pour l'Exploration de la Mer 24:472± i®cations. 2002. Florida Administrative Code, Rule 479. 68B±31.010. Broadhurst, M. K. 2000. Modi®cations to reduce by- NMFS (National Marine Fisheries Service). 1997. By- catch in prawn trawls: a review and framework for catch in the southeast shrimp trawl ®shery: a data development. Reviews in Fish Biology and Fish- summary report. National Marine Fisheries Service, eries 10:27±60. Southeast Science Center, Miami. Christian, P. A., D. L. Harrington, D. R. Amos, R. G. Rogers, D. R., B. D. Rogers, J. A. de Silva, and V. L. Overman, L. G. Parker, and J. B. Rivers. 1993. Final Wright. 1997a. Effectiveness of four industry-de- report on the reduction of ®n®sh capture in south veloped bycatch reduction devices in Louisiana's Atlantic shrimp trawls. National Marine Fisheries inshore waters. Fishery Bulletin 95:552±565. Service, contract NA27FD0070±01, Brunswick, Rogers, D. R., B. D. Rogers, J. A. de Silva, V. L. Wright, Georgia. and J. W. Watson. 1997b. Evaluation of shrimp Coale, J. S., R. A. Rulifson, J. D. Murray, and R. Hines. trawls equipped with bycatch reduction devices in 1994. Comparisons of shrimp catch and bycatch inshore waters of Louisiana. Fisheries Research 33: between a skimmer trawl and an otter trawl in the 55±72. Downloaded by [College Of Charleston] at 05:47 24 June 2014 North Carolina inshore shrimp ®shery. North Amer- Rulifson, R. A., J. D. Murray, and J. J. Bahen. 1992. ican Journal of Fisheries Management 14:751±768. Fin®sh catch reduction in south Atlantic shrimp Coleman, F. C., and C. C. Koenig. 1994. Florida inshore trawls using three designs of bycatch reduction de- shrimping: experimental analysis of bycatch reduc- vices. Fisheries 17(1):9±20. tion. Institute for Fishery Resource Ecology, Florida Sokal, R. R., and F. J. Rohlf. 1995. Biometry: the prin- State University, Final report to the National Marine ciples and practice of statistics in biological re- Fisheries Service, MARFIN grant NA37FF0051, search, 3rd edition. Freeman, New York. Tallahassee. Statsoft, Inc. 1999. STATISTICA software. Statsoft, Estrada, J., A. Diagne, and D. Lavergne. 2002. The Inc., Tulsa, Oklahoma. Louisiana shrimp industry: a preliminary analysis Steele, P., T. M. Bert, K. H. Johnston, and S. Levett. of the industry's sectors. Louisiana Department of 2002. Ef®ciency of bycatch reduction devices in Wildlife and Fisheries, Socioeconomic Research small otter trawls used in the Florida shrimp ®shery. and Development Section, SRD Publication 6, Ba- Fishery Bulletin 100:338±350. ton Rouge. Wallace, R. K., and C. L. Robinson. 1994. Bycatch and GSAFDF (Gulf and South Atlantic Fisheries Develop- bycatch reduction in recreational shrimping. North- ment Foundation). 1997. Bycatch and its reduction east Gulf Science 13:139±144. in the Gulf of Mexico and South Atlantic shrimp Wardle, C. S. 1993. Fish behaviour and ®shing gear. ®shery. Final report to the National Oceanic and At- Pages 609±643 in T. J. Pitcher, editor. Behaviour of 864 WARNER ET AL.

teleost ®shes, 2nd edition. Chapman and Hall, Lon- rador Institute of Fisheries and Marine Technology, don. St. John's. Watson, J. W. 1988. Fish behaviour and trawl design: Whitaker, J. D., L. B. DeLancey, and J. E. Jenkins. 1992. potential for selective trawl development. Pages 25± A pilot study to examine the ef®ciency of ®n®sh 29 in S. G. Fox and J. Huntington, editors. Pro- excluder devices in a shrimp trawl. Final report, ceedings of the world symposium on ®shing gear project number F-47. South Carolina Wildlife and and ®shing vessel design. Newfoundland and Lab- Marine Resources Department. Charleston. Downloaded by [College Of Charleston] at 05:47 24 June 2014