Synopsis. Site Characterization for Biscayne National Park: Assessment of Fisheries Resources and Habitats

Transcription

1 Synopsis Site Characterization for Biscayne National Park: Assessment of Fisheries Resources and Habitats Jerald S. Ault, Steven G. Smith, Geoffrey A. Meester, Jiangang Luo, and James A. Bohnsack* University of Miami Rosenstiel School of Marine and Atmospheric Science Center for Sustainable Fisheries 4600 Rickenbacker Causeway Miami, FL (305) ph (305) fax *NOAA Southeast Fisheries Science Center 75 Virginia Beach Drive Miami, FL (305) ph Final Report on Contract No. CA for Biscayne National Park United States Department of the Interior National Park Service Homestead, FL May 2002

2 Site Characterization for Biscayne National Park: Assessment of Fisheries Resources and Habitats Synopsis Introduction - Biscayne National Park (BNP) is a unique tropical marine environment of national significance, renown for its productive coral reef ecosystem, diverse natural resources, important fishing opportunities, and spectacular scenic beauty. BNP s coastal bay and coral reef habitats play a critical role in the function and dynamics of the larger Florida Keys coral reef ecosystem and contribute substantially to the multibillion dollar tourism and fishing industry of south Florida. Park waters provide critical nursery habitats and food web links for many important commercial and recreational fishery resources including: bonefish, snook, tarpon, permit, pink shrimp, spotted seatrout, spiny lobster, blue crabs and stone crabs, baitfishes; and, numerous coral reef fishes that include snappers, groupers, grunts, barracuda, spadefish, parrotfish, surgeonfish and triggerfish. The health of these valuable natural resources are closely linked to the impacts of fishing as well as the quality of the environment in which they occur. Because of the large increases in human population and coastal development within south Florida since the establishment of Biscayne National Park in 1968, the National Park Service is concerned about the condition of Biscayne s marine and fishery resources. However, any new management strategies proposed for BNP will require precise estimates of resource distribution and status prior to implementation. The data must provide a concise and unambiguous baseline estimation of the Park resource status, provide critical inputs for models used to forecast effects of any regulatory or policy changes, and enable design of an efficient sampling program to monitor future performance of any given management actions. In a proactive movement towards identifying actions and strategic plans necessary to insure adequate conservation of park resources, the park contracted with the University of Miami, Rosenstiel School of Marine and Atmospheric Sciences, to establish a quantitative characterization and assessment of fisheries resources and habitats within BNP. The study involved an extensive review of pertinent scientific and technical literature and an analysis of biological, fishery, and physical data relevant to the status and change of fishery resources in Biscayne National Park, Florida. Steps included database assimilation, identification and mapping of fish-habitat linkages, and fish population assessments for several reef fish species. The resultant estimated status of fish stocks was compared to Federal fishery management guidelines to determine whether management actions may be needed. The stock assessment research focused on 3 data sets containing more than 25 years of fishery-dependent and fisheryindependent data from BNP. Fishery dependent data consisted of recreational creel survey information (CREEL), and fishery independent data included both SCUBA diver visual fish census (RVC) and rollerframe trawl (TRAWL) samples collected between Commercial fisheries data were also acquired, but were deemed generally unreliable for the purposes of park specific assessments. Results of the study were submitted to the National Park Service in a report titled Site Characterization for Biscayne National Park: Assessment of Fisheries Resources and Habitats. 1

3 This Synopsis provides a brief overview of that report and provides additional discussion of possible interpretations of the data in light of comments received from a peer review panel convened by the National Park Service and the Florida Fish and Wildlife Conservation Commission to review the study. Methods - Digital maps were created for a variety of habitat features including water depth, benthic substrates, salinity and other water quality parameters that relate to fishery resource distributions and abundances. Biscayne Bay is known to be an important primary nursery area for many coastal bay and coral reef fishes and macroinvertebrates (i.e., gray, mutton, lane, schoolmaster and yellowtail snappers; bonefish, tarpon, permit, sharks, molluscs, sponges, snook, seatrout, and pink shrimp, blue crabs, and spiny lobsters). Therefore, the analysis was conducted with respect to the relevant life stages of each species assessed. Biological data were separated into 4 life-stage phases in terms of length for analysis: juvenile (from length of recruitment to size of sexual maturity); pre-exploited (recruitment length to minimum legal harvest size); mature (length of sexual maturity to maximum size); and, exploited (minimum legal to maximum size). Habitat data were co-plotted with species life-stage abundance and community diversity distributions to assess the spatial distribution and dynamics of fish and their dependence on habitats found in BNP. A computerized modeling approach, based on the observed length composition data, was used to conduct stock assessments on exploited fishery resources found in the Park. This analysis used both fishery-independent and fishery-dependent data for fish length, which, when combined with extensive biological and fishery information on population dynamics including age-growth relationships, age (size) class distribution, and natural mortality rates, allowed estimates of fishing mortality and spawning stock biomass for park populations. Estimates of stock status were developed for 35 exploited species for which reliable population dynamic parameters were available. However, the number of fish length observations for a number of these species was limited and the status of these stocks may need further investigation. A large amount of data was available for 17 of the species assessed and the resultant stock status of these species are considered reliable. Results - Thirty-five (35) species of fish (about 11% of the total BNP fishes) were found to be present in all three survey types (TRAWL, CREEL, RVC), suggesting that there is use of all park habitats amongst these species (Table 1). However, in most cases habitat use was connected to life stage phases. The diverse spatial pattern of many species distributions reflects specialized ontogenetic use of certain habitats across the park. This suggests that a critical mosaic of interconnected habitats may be essential for sustaining fishery resources and ecosystem productivity within the park. Fish diversity was lowest on the western fringe of Biscayne Bay, particularly at areas proximal to canal outfalls where freshwater influxes may affect habitat suitability for many species. Diversity increased moving seaward, and was highest in eastern BNP (areas on the barrier coral reef system open towards the Straits of Florida). Along with human population growth, the recreational boating fleet in South Florida has grown at a near exponential rate since There has been a 444% increase in registered recreational boats from 1964 to 1998 with no limits on the number of boats allowed to fish (Fig. 1). In addition, the effective fishing power of the recreational fleet is estimated to have quadrupled 2

4 due to depth indicators, fish finders, global positioning systems, improved vessel designs, larger motors, and two-way radio communications. With regards to fish stock conditions, the following points summarize the study findings: For all of the harvested species analyzed, the average sized fish within the exploited phase of their populations appears to have remained very close to minimum harvest size for the past 25 years, not natural historical unfished population size. For example, the average size of black grouper is now 40% of what it was in 1940 and the spawning stock appears to be less than 5% of its historical unfished maximum. The mean length of fish observed (compared to what is known about the growth characteristic and maximum size of the species observed) suggests that overall loss of individuals from park populations as growth occurs is very high for most of the species analyzed. Three fundamental hypotheses can be put forth to account for this loss of larger individuals within the populations. Two of these hypotheses suggest that serious overfishing is occurring within the park. One of the hypotheses might suggest that overfishing is not necessarily occurring, although supporting evidence for this hypothesis is lacking. The hypotheses are: 1. Overall mortality rates are very high within the Park, yet recruitment has remained fairly constant due either to the minimum harvest regulations protecting stocks from recruitment overfishing, or the recruitment source coming from areas unaffected by the overfishing. Given known natural mortality rates of the species analyzed, most of the observed loss (mortality) is likely to have come from fishery harvest, fish releases, and bycatch mortality. If so, fishing mortality is much greater than that which would occur at maximum sustainable harvest for most stocks analyzed. 2. Overall mortality rates are extremely high within the Park and may be affecting recruitment. If recruitment has been reduced, fishing mortality may be even higher than the estimates under hypothesis number 1. The lack of change in mean size of fish harvested may be an expected result if recruitment overfishing is occurring and somewhat supports this hypothesis. 3. Fishing mortality may not be as high as would be predicted under hypothesis numbers 1 or 2 if there has been either a long-term increase in annual recruitment or there is significant movement of individuals out of the Park as they get larger. It is highly unlikely recruitment has been increasing since catch per unit effort and overall landings have been declining. If there is significant movement of larger individuals out of the Park, then the loss of larger individuals from the Park s populations is due to migration not mortality. This could be happening with some of the grouper and snapper species, but there is little evidence to support the occurrence of large numbers of individuals of these species outside the Park. Most regional fishery investigations and data also suggest overharvest patterns similar to that found within the park with little support for a movement hypothesis to entirely account for Park observations. Overall, 71% of the 17 individual stocks with sufficient length observations to be confident in estimates of mortality (loss) appear to be overfished. An analysis of the Spawning Potential Ratios (SPR) of the exploited reef fish shows that 4 of 5 grouper species, 5 of 6 3

5 snapper species, barracuda, and 2 of 5 grunt species for which there are reliable mean length and population dynamics data are below the SPR that constitutes overfishing by Federal definitions as defined in the Magnuson-Stevens Fishery Management Conservation Act (Fig. 2). Furthermore, all but three of 18 additional stocks assessed (for which there were less reliable mean length observations) are likely to be overfished as well. Stock biomass appears critically low for most of the key targeted species within the recreational fishery. For example, the apparent current level of fishing mortality for grouper stocks range from 3 to 10 times the exploitation level that would achieve Maximum Sustainable Yield (MSY). Some stocks appear to have been chronically overfished since at least the late 1970's. Exceptionally high and sustained exploitation pressures appear to have precipitated serial overfishing of key fishery resources. Smaller and less desirable species have consistently increased in the catch as larger more vulnerable species have been eliminated. A substantial proportion of the fish in catches observed at the Biscayne NP boat ramps during creel surveys appeared to be smaller than the minimum size limit for legal harvest. However, fish at the ramp were measured by fork-length while state regulations are established for total length and conversion of these measurements may account for some of this discrepancy. Undersized fish appeared to be as high as 70% for yellowtail and mutton snapper at the Biscayne ramp! A preponderance of undersized illegal fish seen in creel catch size frequency distributions and the extremely poor status of reef fish resources may signal eminent resource collapses. Enforcement needs to be stronger to discourage poachers. For 14 of 35 species analyzed, minimum size of harvest is lower than the reported 50% minimum size of sexual maturity. For these species, it appears that most fish are being captured before they ever have a chance to spawn. The minimum harvest size for six of these 14 species is currently set by state regulations, whereas harvest size for the remaining 8 species is unregulated at present. Little data was found to be available on a number of highly prized species like bonefish, tarpon and permit, despite the fact that they are the focus of extremely important recreational fisheries. For example, bonefish have undoubtedly been under sampled, as only seven (7) fish have been reported in 23 years of BNP creel sampling, despite the fact that bonefish support an enormous regional recreational fishery. We believe this is largely because these are catch and release fisheries that do not have fish coming across the boat ramp. There is also no monitoring program in place for pink shrimp, which is thought to be under heavy exploitation pressures from commercial bait-shrimp and wing-net fisheries. In addition, economically important spiny lobsters, blue crabs and stone crabs lack monitoring in BNP. 4

6 Conclusions - The park provides important habitat for all ages of most of the exploited fish species analyzed and therefore some special management consideration may be needed to adequately protect those habitats critical to the juvenile stages of these species. The juveniles of most species are linked to specific habitat types that occur within the park. The fishery resources of Biscayne NP may be seriously overfished based on one or more interpretations of the study results. If these conclusions are correct, the fishery resources may not be sustainable in BNP under the present levels of exploitation and human population growth affecting stock status and habitat quality. Stocks will even be more at risk with expected future growth in the recreational fishery. The total harvest of fish from park waters must be permanently reduced if stocks are to be sustainable. Continued uncontrolled growth in recreational fishing effort may require that new approaches to managing fisheries within the park be taken. The history of fishery management actions for Biscayne NP waters clearly reflects the characteristics of trying to manage fisheries under increasing stress with conventional approaches. Actions have been taken only after declines have already occurred and were finally acknowledged. Actions are then usually only minimal and not at a level that ensures recovery will take place. (The history of increasingly more restrictive size limits placed on several grouper species until the fishery for some was eventually closed is a prime example of failure in conventional management approaches). Recommendations - The qualities that make BNP and the Florida Keys such valuable and desirable tourism and fishing destinations are eroding. Clearly, without some type of immediate proactive fishery management in BNP, collapse of many important fisheries resources appears imminent. A multistock recovery strategy to sustainable target levels is needed. This strategy must address the recreational and commercial fleet fishing capacity, continued growth in fishing activity, and develop strategies to buffer exploitation, reduce stress on key habitats, and reduce harvest on a permanent basis. The obvious links that BNP has with the rest of the Florida Keys coral reef ecosystem means that long-term planning efforts for BNP should also include close integration of efforts with the Florida Keys National Marine Sanctuary, Dry Tortugas National Park, and the State of Florida. No-take marine reserves and research natural areas are being implemented regionally and this may be a necessary step at Biscayne National Park to ensure sustainable fisheries in the future and to conserve marine biodiversity. In addition to the above management actions, we recommend that the park consider the following additional resource studies and data gathering efforts to fully understand and support its fishery management actions: Undertake additional time series and conventional stock assessment analyses of all available fish data to further determine, cross-check and verify fish population mortality levels. These analyses should be supplemented by tagging studies to help determine the degree to which fish movement may be affecting these calculations for those fish species known to move into deeper water as adults. A broader, more integrated strategy of monitoring, assessment and modeling is needed for effective fishery management in BNP. This comprehensive strategy must consider concurrent sampling of bay, mangrove, coral reef, and pelagic fishery environments, and some consideration of new or enhanced use of data and technologies (e.g., recreational creel 5

7 and commercial catches, visual census, trawls and other nets, acoustics, LIDAR, etc.). There are severe limitations to the use of a single survey gear-type to conduct a meaningful synoptic study of Park fish and shellfish. The current, somewhat piecemeal, monitoring program must be reconfigured to meet assessment data demands. Monitoring efforts need to be integrated into an overarching design to facilitate short and long-term fishery and habitat surveys. The analysis of a cost-effective design for key target species is needed. Special attention should be given to the barrier islands, mangrove fringe, and patch reef environments of the Park which have been sparsely sampled to date. Management endeavors must rely on a precise and cost-effective mechanism to understand and manage these valuable and essential fishery resources. Such a mechanism will likely involve modeling of population responses to past and proposed management actions. Advanced modeling efforts will require refined resolution and precision of existing base habitat maps, including directed efforts to fill in data gaps. An experimental design to assess water quality effects of Everglades restoration on fishes in the tide will be important to develop and integrate into overall fish population predictions and assessments. Monitoring activities should be designed at a time frequency dependent on key process rates, and integrated such that critical data for determining the efficacy of proposed management alternatives will be available Many of BNP s most important fishery resources have received little attention (e.g., shellfish, bonefish, tarpon, snook, etc.). There is great need to develop additional population dynamics models and conduct fishery-dependent and -independent surveys for these resources. This will require an improved capacity to monitor fishery resources across the breadth of environments. Little to no information was available for bonefish-tarpon, two mainstays of the highly valuable inshore recreational fishery, and broad knowledge gaps exist. There is an obvious need to protect flats environments from excessive use and degradation, and to develop a quantitative reef and coastal fish community index which includes these species. The full report has been published as NOAA Technical Memorandum NMFS-SEFSC-468, and can be found on the web at URL 6

8 Table 1.- Species captured or seen in all three fishery surveys (RVC, CREEL, TRAWL) during Common name Family Scientific Name Groupers: Black grouper Serranidae Mycteroperca bonaci Snappers: Mutton snapper Lutjanidae Lutjanus analis Schoolmaster Lutjanidae Lutjanus apodus Yellowtail snapper Lutjanidae Ocyurus chrysurus Gray snapper Lutjanidae Lutjanus griseus Dog snapper Lutjanidae Lutjanus jocu Lane snapper Lutjanidae Lutjanus synagris Hogfish Labridae Lachnolaimus maximus Grunts: Porkfish Haemulidae Anisotremus virginicus Tomtate Haemulidae Haemulon aurolineatum French Grunt Haemulidae Haemulon flavolineatum Sailors choice Haemulidae Haemulon parrai White grunt Haemulidae Haemulon plumieri Bluestriped grunt Haemulidae Haemulon sciurus Other Reef Fishes: Great barracuda Sphyraenidae Sphyraena barracuda Atlantic spadefish Ephippidae Chaetodipterus faber Ocean surgeonfish Acanthuridae Acanthurus bahianus Doctorfish Acanthuridae Acanthurus chirurgus Rainbow parrotfish Scaridae Scarus guacamaia Gray triggerfish Balistidae Balistes capriscus Ocean triggerfish Balistidae Cantherhines sufflamen Scrawled filefish Balistidae Aluterus scriptus Trunkfish Ostraciidae Lactophrys trigonus Sea bream Sparidae Archosargus rhomboidalis Littlehead porgy Sparidae Calamus proridens Sand perch Serranidae Diplectrum formosum Spotted moray eel Muraenidae Gymnothorax moringa Gray angelfish Pomacanthidae Pomacanthus arcuatus Coastal Inshore Ballyhoo Exocoetidae Hemiramphus brasiliensis baitfishes: Yellowfin mojarra Gerreidae Gerres cinereus Blue runner Carangidae Caranx crysos Macroinvertebrates: Spiny lobster Palinuridae Panulirus argus 7

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