Sttrth American Journal »t h'i\hene\ Management 14:131-136. 1994American Fisheries Society

Field Experiments on Survival Rates ofCaged and Released Red Snapper

GREGG R. GITSCHLAG AND MAURICE L. RENAUDNational Marine Fisheries Service

Southeast Fisheries Center, Galveston Laboratory4700 Avenue U. Galveston. Texas 77551. USA

Abstract.—Survival of red snapper Lutjanus campechanus captured by hook and line and thenreleased was evaluated by two methodologies: release into cages and surface release. Fish capturedat a depth of 50 m off the northeastern Texas coast were placed in cages, lowered to a depth of 35m. and monitored at irregular intervals by scuba divers for 10-15 d. Sixty-four percent of cagedred snapper survived. There was no significant difference in survival due to size (<30 cm versus>30 cm fork length; P = 0.59, N = 55) or to gas bladder eversion from the oral cavity (P =0.13,N = 45). No predation on red snapper released at the surface was observed. Survival rates were99%, 90%, and 56% for fish captured at depths of 21-24 m, 27-30 m, and 37^40 m, respectively.Survival rates varied significantly with depth (P = 0.00, N = 232), suggesting an inverse relationshipbetween survival and capture depth.

The red snapper Lutjanus campechanus is foundthroughout the Gulf of Mexico and along the eastcoast of the United States. It has been an importantcommercial species since the late 1800s (Bradleyand Bryan 1974), and it is considered a premiumtarget for sport and commercial fishers. Studies ofpopulation dynamics during the 1980s indicateddeclining red snapper stocks (Parrack and Mc-Clellan 1986:' Gulhcr/and Pcllcgrin 1988). Morerecently, increased commercial and recreationalfishing pressure, together with mortality of redsnapper taken as bycatch in shrimp trawls, resultedin severe overfishing (Goodyear 1988, 1991;Goodyear and Phares 1990; Muller 1990). In anattempt to increase stocks, federal regulations es-tablished size and catch limits for red snapper takenin the Federal Conservation Zone (FCZ) of theGulf of Mexico and Atlantic Ocean. Fishers havea bag limit of seven fish and are required to releasesnapper measuring less than 30 cm fork length(FL). The success of this management strategy de-pends on the survival of released fish.

Critics of regulations requiring the release of redsnapper predict high mortality after release andclaim that size limits may not be an effective man-agement tool for the fishery. Although few re-searchers have described direct observations ofsurvival of red snapper and other reef fish (Parker1985, 1991; Fable 1993; Collins, in press; Renderand Wilson, in press), several other investigators

1 This and other unpublished reports are listed sepa-rately in the appendix.

have addressed survival and related topics (Got-shall 1964; Tong 1978; Fable 1980; Harper et al.,in press). It is widely known that capture depthplays a critical role in survival of released fish(Gotshall 1964; Fable 1980), especially for phy-soclistic species.

The primary objective of our experiments wasto determine the survival rates of undersize andlegal size red snapper captured with hook and lineat 20-50-m water depths. A secondary objectivewas to investigate the effect on survival of man-ually venting gas bladders everted from the oralcavity.

MethodsDuring the fall of 1985, survival rates of red

snapper captured at several water depths off thenortheastern Texas coast were estimated with twotypes of experiments: a study of captured fish placedin cages and a surface release study. Because dis-tension of the gas bladder can prevent submer-gence of released fish and cause mortality, survivalof fish with and without vented gas bladders wascompared. The venting procedure is described inthe next section.

Survival in cages.— The cage study was con-ducted at an offshore gas production platform(Tenneco HI A 270B) approximately 140 kmsoutheast of Galveston, Texas. Fish were capturedon the sea bottom with rods and sport fish ing reelspowered by 12-V batteries. Each fish was broughtto the surface, dehooked, measured, and observedfor signs of stress including fish hook ingestion,bleeding, gas escapement beneath scales, intestinal

131

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132 GITSTHLACi AND RENAUD

TABLE I.—Numbers of red snapper given various gasbladder treatments in relation to depth of capture andsi/c-class.

Capturedepth and

fish si/c(fork length)

Gas bladder condition

Everted, Evened,Une verted vented un vented Total

Cage study50m

<30cm>30cm

1423

5a

5a08

1936

Surface release study2 1-24 m

<30cm>30cm

27-30 m<30cm> 30 cm

37-40 m<30cm>30cm

1362

140

223

00

3*0

00

20

104

25I I

1382

274

4714

a Three of five survived.h Two of three swam down.

protrusion from the anus, and distension of thegas bladder (which can cause the stomach to evertthrough the oral cavity). Except on a few occasionswhen several fish were captured simultaneously,fish were individually placed in numbered chick-en-wire cages (0.6 m * 0.6 m x 0.6 m) and de-ployed over the side of a platform. Cages remainedat 35 m for the duration of the experiment exceptwhen one descent line parted and sent 12 live,caged fish to 46 m. Survival of caged fish wasmonitored by scuba divers at irregular intervalsover a IO-15-d period. Gas bladders of five fishmeasuring less than 30 cm FL and five measuring30 cm FL or more were vented with a syringeneedle or fish hook before the fish were placed inthe cages (Table 1).

Surface release study. — Red snapper captured at21-40-m depths on rods and manually operatedreels during three, 1-d head boa I trips were mea-sured, observed for gas bladder aversion from theoral cavity, and released at the surface. Additionalred snapper captured by patrons aboard the head-boat were observed for bladder aversion, althoughthese fish were not available for release. Two-manscuba teams monitored fish behavior during de-scent and watched for predators and predation.Nine dives totalling 160 min were made to observered snapper and other species released on the sur-face. To conserve underwater time, divers did notdescend below 24 m. Shipboard observers notedthe number of red snapper floating at the surfacethat were unable to return to depth. Chi-squareand Fisher's exact tests were used to analy/c testvariables for cage and surface release studies.

ResultsSurvival in Cages

Caged fish ranged from 25 to 43 cm FL. Traumarelated to capture was common. Fifty-one percent(28 of 55) of red snapper displayed signs of cap-ture-related stress due cither to partially ingestedhooks or to hypcrbaric trauma, which includeddistension of the gas bladder with resulting stom-ach cvcrsion from the oral cavity, intestinal pro-trusion from the anus, bleeding, or gas escapementfrom beneath scales. Survival offish with externalstress symptoms was not significantly different fromsurvival offish without symptoms (Table 2). Theoccurrence of stress symptoms and the survival ofstressed fish were statistically unrelated to si/c (le-gal versus undersi/e; Table 2). Overexpansion ofgas bladders caused stomachs to evert from theoral cavities of 33% (18 of 55) of fish (Table 1).Because no significant differences in survival could

TABLE 2.—Summary of chi-square and Fisher's exact test (FET) results for red snapper survival. Asterisk denotessignificance at P < 0.05*.

Test usedTest com pan son or variable Ch i-square FET

CattstadyUn vented everted bladder versus vented everted bladder(Jnvenled everted bladder versus uncvcrtcd bladder xStressed" versus unstressed xUndcrsi/c versus legal si/e xFish with stress symptoms:' undcrsi/c versus legal si/c

x 18455555

x 28

0.230.130.650.590.38

Sorfacc release studyCapture depth 232 0.00*a Stress symptoms include fish hook ingestion, bleeding, gas escaping from beneath scales, intestinal protrusion from anus, and

eversion of gas bladder from oral cavity.

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SURVIVAL OF CAUGHT AND RELEASED RED SNAPPER 133

Surface Release

Depth (m)Cage

FIGURE 1.—Survival of caged and surface-released red snapper by size (fork length) and capture depth. Samplesi/e is shown at the top of each histogram.

be attributed either to bladder eversion or to vent-ing of everted bladders (Table 2), gas bladder con-dition was ignored in further analyses.

Survival of all caged red snapper was 64% (Fig-ure 1). Frequency of survival by si/e is shown inFigure 2. Survival of legal and undersi/e fish wasnot significantly different (Table 2). Ninety percentof all deaths occurred during the first day of theexperiments and 95% occurred by the end of thesecond day (Figure 3).

Surface Release StudyResults of surface release studies pertain pri-

marily to undersi/e red snapper, because 212 of

232 fish in the experiments were less than 30 cmFL. All fish observed actively swimming downfrom the surface were recorded as survivors. Sub-sequent mortality could not be measured, so thesesurvival data represent maximum values. Maxi-mum survival rales for red snapper captured atdepths of 21-24 m, 27-30 m, and 37-40 m were99%, 90%, and 56%, respectively (Figure 1). Depth-related differences in survival were highly signif-icant (Table 2), suggesting an inverse relationshipbetween survival and capture depth.

The occurrence of everted gas bladders was sig-nificantly lower at the shallowest capture depth (P= 0.00 for all three depths; P = 0.98 for the twodeepest depths). Everted gas bladders occurred in

CO

I&25 45 5030 35 40

Length (cm)FIGURE 2. —Length-frequency histogram of survival

and mortality for caged red snapper captured at 50-mdepths. Length is fork length.

5010-15

Time In Cages (Days)FIGURE 3. —Percentages of surviving red snapper by

time after release in cages.

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134 G1TSCHLAG AND RENAUD

1 % (2 of 149), 56% (18 of 32), and 56% (47 of 84)offish captured at 21-24 m, 27-30 m, and 37-40m, respectively (data include fish caught by head-boat patrons as well as those represented in Table1).

Of 90 red snapper released in the presence ofscuba divers, 32 live and 2 dead fish were observedunderwater. Limited visibility prevented diversfrom monitoring fish during their entire descent.Even though predators (i.e., sharks) were in thearea, as evidenced by landings aboard the head-boats, divers did not observe predation.

DiscussionRapid retrieval offish from depth may increase

mortality due to hyperbaric trauma (Gotshall 1964;Collins, in press; Harper et al., in press). Com-mercial snapper boats have large-diameter reelspowered by hand, electricity, or hydraulics, andthese reels can retrieve fish much faster than thebattery-powered, small-diameter sport reels weused in our cage study. In turn, our reels recoveredfish more rapidly than the manual reels commonlyused by recreational anglers and may have induceda somewhat higher mortality than recreational gearmight cause.

Deployment of fish in cages introduced certainartifacts into the study offish survival. Cages elim-inated predation as a source of mortality. Severalfish with everted gas bladders might have diedfloating at the surface had they not been forciblyreturned to depth in cages. For these reasons, sur-vival rates obtained from cage studies should betaken as an upper limit for survival of released redsnapper. Similarly, comparisons between cage andsurface release studies should be interpreted withcare due to the effects of forced submergence andpossible variations in retrieval speed on survival.

Internal trauma may not always be visible dur-ing external inspection offish. Mortality of healthy-looking fish was similar to that of fish displayingobvious signs of stress (P = 0.65). Several factorsmay have contributed to this finding. For example,some expanding gas bladders may have been vent-ed by fish hooks during ascent and consequentlymay not have been detected on arrival at the sur-face. Red snapper may have suffered internal hy-perbaric trauma that subsequently proved lethalbut was not evident to an observer immediatelyafter the fish surfaced.

Determining estimates of predation on redsnapper released in open water is extremely dif-ficult. Complicating factors include limited un-derwater visibility, which may affect a diver's ob-

servational abilities as well as those of predatorand prey; bottom time and depth restrictions ofdivers; difficulty in monitoring long-term survival;variability in the number of predators present whenfish are released; and potential effects of the pres-ence of divers on the behavior of predators andreleased fish. Although we did not observe pre-dation, the predation rate on released snapper isexpected to be higher than that for snapper notpreviously captured (Gotshall 1964). Fish thatsuccessfully return to the sea bottom may perishwithin hours or days because of injuries sustainedduring capture and handling or because of an im-paired ability to escape predators or capture prey.In our surface release study, two snapper appar-ently died underwater during descent. Some fishdisplayed no apparent fear of divers (one fish waseven touched by a diver's hand). Such abnormalbehavior for a species that generally keeps a safedistance from divers (our observations) is proba-bly related to stress.

Venting of everted bladders had little effect onsurvival of caged red snapper captured at 50-mdepths, although our sample size was small. Ren-der and Wilson (in press) also reported that gasbladder deflation had no significant effect on sur-vival of red snapper captured at 20-m depths. Inpreliminary work on vermilion snapper Rhom-boplites aurorubens. Fable (1993) found survivalrates of 79% for apparently normal fish and 60%for fish with vented, expanded, but not evertedbladders.

Our results combined with those from other cagestudies suggest an inverse relationship betweensurvival and capture depth (Table 3). Render andWilson (in press) found 80% (200 of 250) survivalfor red snapper captured at 20-m depths and re-leased at the surface into a 9-m-deep cage. Parker(1985) observed 79% (11 of 14) survival of redsnapper captured at 22-m depths in the AtlanticOcean oflT Daytona. Florida, and 89% (39 of 44)survival offish caught at 30-m depths in the Gulfof Mexico off the Texas coast. In summary, sur-vival rates of 79-89% were found for fish capturedat 20-30-m depths compared with 64% for fishcaptured at 50 m. Variables that may affect inter-pretation of these combined results include geo-graphic area, capture technique, and handling pro-cedures.

Data arc also available for other reef species. Of82 vermilion snapper captured at depths of 27-30 m, 67% survived in floating cages during a 15-29-d holding period (Fable 1993). Survival was71% for red grouper Epinephelus morio captured

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SURVIVAL OF CAUGHT AND RELEASED RED SNAPPER 135

TABLE 3.—Summary of pertinent studies on survival of surface-released and caged reef fish (after Parker 199la).

Species % survival Depth (m) Reference

Cage studiesRed snapperRed snapperRed snapperRed snapperVermilion snapper

28214445582

8079896467

20223050

27-30

Render and Wilson (in press)Parker (1985)"Parker (1985)*This studyFable (1993)*

Surface release studiesRed snapperRed snapperRed snapperRed snapperRed grouperMixedMixedMixedMixedMixed

14030316123

161248197109202

991009056659089758480

21-2430

27-3037-^0

442136

46-544646

This studyParker (1 99 l)a

This studyThis studyWilsonb

Collins (in press)Collins (in press)Collins (in press)Collins (in press)Collins (in press)

a Given in the appendix.h Personal communication in Parker (1991).

at 44 m on rod and reel and released at the surfaceofl'the west coast of Florida (R. Wilson, Universityof South Florida, personal communication in Par-ker 1991). In a scries of surface release studiesi n v o l v i n g a variety of reef species, survival was90% at 21-m capture depths, 89% at 36 m, and75% at 46-54 m (Collins, in press). In tag-and-release studies, fish first captured in shallowerdepths were recaptured in higher numbers, indi-cating higher survival relative to fish first caughtat greater depths (Schirripa et al. 1993). This resultis consistent with an inverse relationship betweensurvival and capture depth. Survival was 78.5%for 1,884 fish (representing 79 species) capturedin wire fish traps at depths of 31-82 m and releasedal the surface (Harper et al., in press).

The Gulf of Mexico Fishery Management Coun-cil's Reef Fish Fishery Management Plan estab-lished a goal of 20% spawning stock biomass perrecruit, to be attained by the year 2000 (Muller1990). Current red snapper bag limits can only besuccessful if survival of released fish is high. Ex-isting data do not indicate high survival of fishcaught from deep water. Recent yield-per-recruitand population dynamics estimates require ac-curate survival estimates for released red snapper(Waters and Huntsman 1986; Muller 1990). In-corporation of these values in the models will low-er overall estimates of recruitment, spawning po-tential ratio, and yield per recruit.

Accurate estimates of survival for released fishare critical to developing successful managementstrategies. These estimates must account for depthof capture, mortality of floating fish unable to re-

turn to depth, mortality associated with captureand handling, delayed mortality (several days orweeks after release), predation, and perhaps sea-son. Additional studies employing standard cap-ture and handling techniques should increase theaccuracy and repeatability of survival estimates.These studies should also address questions relat-ing to the value of venting expanded gas bladdersand to optimal field techniques for venting.

AcknowledgmentsWe acknowledge Gene Huntsman and Pete Par-

ker for their advice on field methodologies andtheir review of an early draft of the manuscript.

ReferencesBradley, E., and C. Bryan. 1974. Life history and fish-

ery of the red snapper (Luljanus campechanus) inthe northwestern Gulf of Mexico. Proceedings of theGulf and Caribbean Fisheries Institute 27:77-106.

Collins, M. R. In press. Survival estimates for demersalreef fishes released by anglers. Proceedings of theGulf and Caribbean Fisheries Institute 43.

Fable, W. A. 1980. Tagging studies of red snapper(Luljanus campechanus) and vermilion snapper(Rhomboplites aumrubens) off the south Texas coast.Contributions in Marine Science 23:115-121.

Gotshall. D. W. 1964. Increasing tagged rockfish (Ge-nus Sehastodes) survival by deflating the swim blad-der. California Fish and Game 50:253-260.

Gutherz, E. J., and G. J. Pellegrin. 1988. Estimate ofthe catch of red snapper. Lutjanus campechanus, byshrimp trawlers in the U.S. Gulf of Mexico. U.S.National Marine Fisheries Service Marine FisheriesReview 50(1): 17-25.

Harper. D. E., J. A. Bohnsack. and D. B. McClcllan. In

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136 GITSCHLAG AND RENAUD

press. Investigation of bycatch from the wire fish-trap fishery in federal waters off southern Florida.Proceedings of the Gulf and Caribbean Fishery In-stitute.

Render, J. H., and C. A. Wilson. In press. Hook-and-line mortality of caught and released red snapper(Lutjanus campechanus). Bulletin of Marine Sci-ence.

Tong, L. J. 1978. Tagging snapper (Chrysophrys au-ratus) by scuba divers. Journal of Marine and Fresh-water Research 12:73-76.

Waters, J. R., and G. R. Huntsman. 1986. Incorpo-rating mortality from catch and release into yield-per-recruit analyses of minimum size limits. NorthAmerican Journal of Fisheries Management 6:463-471.

Appendix: Unpublished References

Numerous unpublished references are of great importance for an understanding ofprevious studies on red snapper survival. Those referenced in this paper are given hereas a separate listing.

Fable. W. A. 1993. Reef fish release mortality progressreport. National Marine Fisheries Service, PanamaCity Laboratory, Panama City, Florida.

Goodyear, C. P. 1988. Recent trends in the red snapperfishery of the Gulf of Mexico. National Marine Fish-eries Service, Southeast Fisheries Center, MiamiLaboratory, Contribution CRD 87/88-16, Miami.

Goodyear, C. P. 1991. Sensitivity of shrimp-bycatchmortality estimates to natural mortality for redsnapper. National Marine Fisheries Service, South-east Fisheries Center, Miami Laboratory. Contri-bution MIA 90/91-28, Miami.

Goodyear, C. P., and P. Phares. 1990. Status of redsnapper stocks of the Gulf of Mexico, report for1990. National Marine Fisheries Service, SoutheastFisheries Center, Miami Laboratory, ContributionCRD 89/90-05, Miami.

Muller, R. 1990. Final report of the reef fish assessmentpanel, March, 1990. National Marine Fisheries Ser-vice, Southeast Fisheries Center. Miami Labora-tory.

Parker, R. O., Jr. 1985. Survival of released red snap-per. Unpublished progress report to South Atlanticand Gulf of Mexico Fisheries Management Coun-cils, Charleston, South Carolina, and Tampa, Flor-ida.

Parker, R. O., Jr. 1991. Survival of released reef fish—a summary of available data. Report to South At-lantic Fisheries Management Council. Charleston,South Carolina.

Parrack, N. C., and D. B. McClellan. 1986. Trends inGulf of Mexico red snapper population dynamics,1979-85. National Marine Fisheries Service, South-east Fisheries Center, Miami Laboratory, Contri-bution CRD-86/87-4, Miami.

Schirripa, M. J., K. Burns, and J. A. Bohnsack. 1993.Reef fish release survival based on tag and recoverydata. National Marine Fisheries Service, SoutheastFisheries Center, Miami Laboratory, ContributionMIA 92/93-34, Miami.

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