QUEEN CONCH STOCK RESTORATION

Transcription

1 QUEEN CONCH STOCK RESTORATION Robet Glaze Associate Reseach Scientist Floida Maine Reseach Institute South Floida Regional Laboatoy Maathon, Floida INTRODUCTION Queen conch ae found in pedominantly south Floida fom the Floida Keys to Key Biscayne. They once constituted significant commecial and eceational fisheies in Floida. In 1975, the commecial fishey was closed due to ovefishing. This ban was extended to the eceational fishey in 1985 in state wates (Floida Administative Code, Chapte 68b ) and 1986 in contiguous fedeal wates fo those aboad vessels egisteed in Floida (Floida Administative Code, Chapte 68b ). In 1986, the State of Floida began a eseach pogam designed to monito the ecovey of the conch stock and to detemine how best to ehabilitate the depleted population. The queen conch pogam has taken a community-based appoach; most of the laboatoy and field studies wee conducted unde patneships involving the State, the U.S. Fish and Wildlife Sevice, The Natue Consevancy, and an extensive base of community voluntees. RESEARCH RESULTS Stock Assessment/Monitoing In 1986, the State began a pogam to monito the ecovey of the conch stock afte the closue. Fom 1987 though 1993, we conducted suveys using towed-dives. These suveys showed that the population was not ecoveing on its own (Glaze and Beg, 1994; Beg and Glaze, 1995). In 1992, we began to shift ou focus towads the conch spawning stock and stock estoation. The spawning stock suveys wee conducted using belt-tansects at all spawning aggegations located on the eef tact. These suveys examined up to 27 aggegations fom Key Lago to Key West on a yealy basis. The suveys detemined densities (conch pe m 2 ) within the Numbe of Adult Conch 22,000 20,000 18,000 16,000 14,000 12,000 10,000 8,000 6,000 4, Yea Figue 1. Estimates of adult spawning stock of queen conch in offshoe aggegations fom suveys conducted fom 1992 though

2 aggegations and the aea encompassed by each aggegation. The numbe of conch in each aggegation was estimated by multiplying these two paametes. Though 1997, we obseved an oveall incease in the numbe of adult conch within the aggegations (Figue 1). The minimum numbe of adult conch we obseved was appoximately 5,750 in 1992 and the maximum was 20,650 in In 2000, we estimated that thee wee appoximately 18,200 adult conch within spawning aggegations in south Floida. We also obseved an incease in the aea encompassed by the aggegations. Laval Suveys Conch ecovey in south Floida has been slowe than we anticipated afte the closue of the fishey. Since ecovey is dependant on the supply of lavae, we initiated a seies of studies designed to detemine the oigin of conch lavae supplying south Floida s conch population. In 1990, we conducted expeiments that demonstated that the conch population in south Floida was not isolated fom othe populations in the Caibbean and that thee was a component of the Floida conch population that oiginated elsewhee (Campton et al., 1992). The next step was to detemine the extent of the contibution to the south Floida conch population fom upsteam souces in the Caibbean egion (e.g., Mexico, Cuba, Belize). In 1996, we began a study to examine the extent of the contibution fom to lavae ecuiting to south Floida. (Hawtoff et al., 1998). The esults fom this study showed that few lavae wee enteing the Floida Keys and that the contibution fom Caibbean souces was minimal. Thus, we detemined that inceasing the local spawning stock should esult in inceased laval availability. Two additional studies suppoted this conclusion. In 1992, we conducted a study in conjunction with a NOAA patne, the Caibbean Maine Reseach Cente, to detemine the laval supply to Looe Key in the Floida Keys and to compae it with a population in the Bahamas whee conch ae abundant. This study demonstated that laval conch abundance in Floida was an ode of magnitude lowe than in the Bahamas (Stone et al. 1996). In 1997, we epeated ou suveys at Looe Key. In this study, we demonstated that the lavae wee an ode of magnitude moe abundant than in the pevious suvey (Hawtoff et al., in pess). The incease in laval abundance occued simultaneously to the incease in the spawning stock (Figue 1). This led futhe suppot to ou conclusions which suggested that the local spawning population is a citical souce of lavae supplying south Floida. Thus, based on ou suveys of the spawning stock and on ou laval suveys, we believe that the slow ate of ecovey of the Floida conch population is due mainly to limited laval availability. We also believe that the ecovey of the local conch stock will not occu apidly until the local spawning stock inceases substantially beyond the cuent levels and that futhe enhancement of the spawning stock is citical to ehabilitating the south Floida conch population. 2

3 Stock Restoation We conducted a seies of field and laboatoy expeiments with the goal of evaluating the efficacy of using hatchey-eaed juvenile conch to supplement the wild spawning stock. Specifically, we examined the vaiables that limit post-elease suvival and examined how to maximize that suvival. All animals used in the expeiments wee poduced at ou eseach-scale conch hatchey on Long Key in the Floida Keys. Table 1 pesents the vaiables that wee examined and the esults fom those expeiments. Based on the esults of the expeiments, we detemined that we should elease 10-cm (appoximately 4 inches) conch in the fall on upcoming full moons. Additionally we detemined that the elease site should be distant fom aeas of high pedato density. We detemined that exposing a hatchey-eaed conch to a caged pedato pio to elease esulted in development of optimal behavioal and mophological chaacteistics that will esult in significantly geate suvival than those conch that ae not exposed. Afte these expeiments wee complete, we coupled the cost of seed poduction with post-elease suvival to detemine the cost pe 15-cm (appoximately 6 inches) suvivo. We detemined that a 10-cm conch eleased in the fall on upcoming full moons and suviving to 15-cm costs appoximately $9.00 pe individual. Table 1. Vaiables examined and the esults of expeiments in the queen conch stock estoation assessment. Refeences cited ae (1) Glaze and Jones, 1997; (2) Glaze and Delgado, 1999; (3) Delgado et al., 2000; and (4) Delgado et al., in pep. Vaiable Result Refeence Season Fall was optimal 1 Luna Phase Full Moon was optimal 1 Size 9-cm was optimal 2 Pedato Density Bette suvival distant fom optimal pedato habitat 1 Behavioal Deficits Conch can be tained to buy 3,4 Mophological Deficits Exposue to pedato esults in geate shell weight 3,4 Pedato Exposue Exposue to pedato esults in geate suvival 4 Cost to Seed a 10-cm conch eleased in fall and suviving to 15- cm costs appoximately $

4 ISSUES Issue 1. Repoductive Failue in Neashoe Conch Conch in the Floida Keys ae distibuted within two dispaate zones (Figue 2). In the offshoe zone, conch ae found in discete aggegations in coal Eveglades N National ubble and sand envionments Pak W E in the back eef. In the S neashoe zone, conch ae located in the hadbottom Gulf of Mexico Floida community adjacent to the Bay shoeline. Conch distibution within the neashoe zone is, fo Neashoe Aggegation the most pat, widespead. Hawk Channel Juvenile and adult conch do not Offshoe Aggegation migate between the two zones Atlantic Ocean because the silt which Kilometes chaacteizes the bottom of Hawk Channel is poo habitat Figue 2. Distibution of conch in south Floida. Conch ae located in fo conch and effectively seves 2 zones - neashoe and offshoe. Spawning only occus in as a baie (Beg and Glaze, aggegations in the offshoe zone. 1995). Theefoe, conch that ae tanspoted as lavae fom the offshoe zone and settle in the neashoe zone emain thee. Despite extensive suveys, we neve obseved conch epoducing o spawning in neashoe aggegations; all spawning was obseved offshoe (Glaze and Quinteo, 1998). Howeve, we have eceived seveal anecdotal epots indicating that conch once epoduced neashoe. In 1998, we conducted a study to compae conch epoductive behavio and gonadal OFFSHORE NEARSHORE Figue 3. Female gonadal tissue fom conch collected in offshoe and neashoe zones. The offshoe conch wee ipe with ove 75% gonadal mateial; the neashoe conch had no epoductive tissue. development between the two zones (McCathy et al., 2000). Ou studies showed that conch in the offshoe zone developed nomal gonads wheeas those located neashoe had distinct gonadal 4

5 deficits and wee unable to epoduce (Figue 3). Ou study also examined the epoductive development of conch tansplanted between the two zones. The esults indicated that conch tansplanted fom the neashoe zone to the offshoe zone developed fully functional gonads. Convesely, those conch tansplanted fom offshoe to neashoe showed apid loss of gonadal tissue. Issue 2. Chonic Effects of Poo Wate Quality on Laval Fitness The queen conch hatchey on Long Key was designed and constucted in When hatchey poduction was initiated, we quickly ealized that the maximum laval density we could achieve was one lava pe 2 lites of seawate. Additionally, the time to metamophosis in ou cultues was appoximately 45 days. This contasted with conditions at a commecial conch hatchey in the Tuks and Caicos whee they epoted densities of 20 conch pe lite and time to metamophosis of appoximately 20 days. Afte caeful analysis, we implemented an ozone system fo the teatment of incoming wate. Ozone, when applied to seawate, emoves dissolved oganic mateials. By adding ozone, we effectively made the neashoe wates moe closely esemble the wate associated with eef conditions. When the ozone system became functional, we wee able to cultue conch lavae at densities appoaching 10 lavae pe lite and the time to metamophosis dopped fom appoximately 45 days to appoximately 20 days. Since dissolved oganic mateials may esult fom eutophication, the esults fom this study suggest that declining wate quality associated with nutification may educe the oveall fitness of laval conch. This obsevation has widespead implications fo the effects of neashoe coastal development on Floida s conch stock. FUTURE DIRECTION Monitoing and Laval Suveys We will continue to monito the spawning stock in ode to assess the ecovey of the population. We will also expand the monitoing pogam to include neashoe populations. We intend to continue limited laval suveys to facilitate the evaluation of the impacts of ou estoation effots. Restoation Reseach Beginning in the sping of 2001, we began implementing a estoation pogam based on a two-pat appoach: 1) We began tansplanting conch as a method to incease the spawning stock. Juvenile and adult conch ae tansplanted fom neashoe, non-spawning aeas to offshoe spawning aggegations. We ae eceiving assistance in this effot fom The Natue Consevancy and ou lage base of community voluntees. We pefe this stategy to amping-up hatchey poduction because it is fa less costly (Glaze and Delgado, 1999). Additionally, the conch that ae used to enhance the population ae wild and, theefoe, have genetic, mophological, and behavioal advantages ove hatchey conch 5

6 (Stone and Glaze, 1998). Additionally, a tansplantation pogam fostes community involvement in the management of this esouce. Since this poject began in May 2001, we have tansplanted 920 adult and late-stage juvenile conch. This is equivalent to eleasing at least 10,000 hatchey-aised juveniles based on the expected motality afte elease. 2) Hatchey conch will be poduced fo elease by ou pivate patnes. We have developed stong public-pivate patneships with two not-fo-pofit oganizations (Keys Maine Consevancy and the Conch Reseach and Education Foundation) who have specific chates to poduce conch fo a queen conch estoation pogam. We have and will continue to povide technical assistance fo the cultue of hatchey-eaed conch and will define the potocols fo elease. Conch poduced by these oganizations will be eleased only unde the guidance and supevision of the FMRI at no cost to the State. These eleases will augment ou tansplantation effots. The effectiveness of these pogams will be evaluated by monitoing spawning aggegations fo density, aea encompassed by the aggegations, and abundance of conch. We also intend to continue monitoing laval supply as a mechanism fo evaluating the success of these initiatives. We will examine diffeences in esouce utilization and epoductive behavio between native conch and thei tansplanted and hatchey-eaed countepats. Additionally, we will examine the effects tansplanting has on the habitat fom which and into which they ae tansplanted. LITERATURE CITED Beg, C. J., J., and R. A. Glaze Stock assessment of a lage maine gastopod (Stombus gigas) using andomized and statified towed-dive censusing. - Rapp, P.-v. Réun. Cons. int. Explo. Me, 199: Campton, D. E., L. Robison, C. J. Beg, J, and R. A. Glaze Genetic patchiness among populations of queen conch Stombus gigas in the Floida Keys and Bimini. Fish. Bull., 90: Delgado, G., R. A. Glaze, N. J. Stewat, K. J. McCathy, and J. A. Kidney Modification of behavioal and mophological abnomalities in hatchey-eaed queen conch: implications fo a stock enhancement pogam (Stombus gigas, L.). Poc. Gulf Caibb. Fish. Inst. 51: Delgado, G., R. A. Glaze, N. J. Stewat, K. J. McCathy, and J. A. Kidney. In Pep. Pedato Induced Behavioual and Mophological Plasticity in the Topical Maine Gastopod, Stombus gigas L. Glaze, R. A. and C. J. Beg, J Queen conch eseach in Floida: an oveview. In: R. S. Appeldoon (ed.) pp Poc. 1st Latin Ameican Malacological Confeence. Special Wokshop on the Management and Cultue of Queen Conch. 6

7 Glaze, R. A. and G. Delgado Optimizing Size at Release of Hatchey-Raised Queen Conch Outplants: A Cost-Benefit Appoach. U.S. Fish and Wildlife Sevice Poject P p. Glaze, R. A. and R. Jones Tempoal factos influencing suvival of queen conch outplants. Final Repot. U.S. Fish and Wildlife Sevice Poject P p. Glaze, R. A. and I. Quinteo Obsevations on the sensitivity of queen conch to wate quality: implications fo coastal development. Poc. Gulf Caibb. Fish. Inst. 50: Hawtoff, D. B., K. J. McCathy, and R. A. Glaze Distibution and abundance of queen conch, Stombus gigas, in the Floida Cuent: implications fo ecuitment to the Floida Keys. Poc. Gulf Caibb. Fish. Inst. 50: Hawtoff, D. B., R. A. Glaze, and K. J. McCathy. In pess. Spatial and tempoal distibution of queen conch lavae in the offshoe wates of the Floida Keys. Poc. Gulf Caibb. Fish. Inst. 52. McCathy, K. J., C. T. Batels, M.C. Dacy, J. R. Stye and R. A. Glaze Habitat induced epoductive failue of queen conch, Stombus gigas, in the Floida Keys. U.S. Fish and Wildlife Sevice Poject P p. Stone, A. W., R. A. Glaze and P. J. Baile Laval supply to queen conch nuseies: elationships with ecuitment pocess and population size. Jou. Shellfish Res.15: Stone, A. W. and R. A. Glaze Vaiation in natual motality: implications fo queen conch maine stock enhancement. Bull. Ma. Sci. 62: