Jonathan M. Shenker

Larval supply of shorefishes to nursery habitats around Lee Stocking Island, Bahamas. II: Lunar and oceanographic influences

Plankton nets were moored in tidal channels around Lee Stocking Island to monitor larval supply of fishes to nursery habitats that fringe Exuma Sound, Bahamas. Sampling was conducted continuously through two consecutive winters of 1990–1991 and 1991–1992. Meteorological and hydrographic data were also recorded during these periods. Three of the six most abundant taxa (leptocephali, Bothidae and Ophidiidae) showed strong lunar associations, with periodicities between 28 and 30 d. Labrids were the only family to show evidence of any semi-lunar activity. The time series for the families Clupeidae and Tetraodontidae appeared to be stochastic. Cross-correlation analyses were used to examine coupling of larval replenishment and physical processes. Four of six taxa examined showed significant relationships between larval supply and onshore winds at short time lags during 1990–1991. In 1991–1992, however, taxa showed stronger associations with the northwest, long-shore wind component than with onshore winds. Coherency in larval supply among several taxa was remarkably strong. This implies either that the magnitude of spawning is linked among taxa, or that planktonic processes are affecting a number of taxa in very similar ways. The similarities in the magnitude of supply events among taxa found here may be related to complex interactions between larval behavior and the physical environment.

The teratogenic effects of methylmercury on early development of the zebrafish, Danio rerio

Chronic bioassays were used to evaluate the concentration and exposure duration of methylmercury that resulted in specific teratogenic defects in Danio rerio embryos exposed at different developmental stages. Embryos in different stages of development (cleavage, blastula, gastrula, or segmentation) were exposed to 20 or 30 µg/l of methylmercuric chloride (CH(3)HgCl) for various exposure durations (8, 16, 32 h, or continuously to hatching). These exposures frequently caused two morphological defects, tissue abnormality in the median finfold and a flexure of the posterior tail region. The critical period of exposure for the production of both effects begins around 18-20 h after fertilization, with increased exposure resulting in more severe effects. These critical periods coincide with both tail and median finfold formation.

Larval supply of shorefishes to nursery habitats around Lee Stocking Island, Bahamas. I. Small-scale distribution patterns

Plankton nets moored in tidal channels around Lee Stocking Island, Bahamas, were used to monitor larval supply from Exuma Sound to benthic habitats on Great Bahama Bank in the winter months (December–February) of 1990–1991 and 1991–1992. A total of 10376 fishes were collected in 1990–1991 from 58 taxa; in 1991–1992, 13358 fishes were collected from 56 taxa. Vertical distributions of 16 dominant taxa suggested that most settlement-stage fishes were concentrated in surface waters Six taxa showed no yearxdepth interaction; of Fese, five were sigmficantly more abundant in the surface nets. Eight of the ten taxa with significant yearxdepth interactions displayed a tendency to be more abundant in surface layers than in sub-surface collections during the first year, but were more evenly distributed across surface and sub-surface collections in the second year of sampling. Larval supply of six taxa showed significant coherency over spatial scales from 0.5 to 1.5 km. Over scales up to 5 km, however, larval supply became largely decoupled at the daily level. Significant inter-annual variability in the vertical and horizontal distributions of settlement-stage fishes suggests that behavior may play a major role in determining larval supply in tropical shorefishes.

Use of tropical cleaner fish to control the ectoparasite Neobenedenia melleni (Monogenea: Capsalidae) on seawater-cultured Florida red tilapia

Abstract The juvenile bluehead wrasse (Thalassoma bifasciatum), the neon goby (Gobiosoma oceanops) and the cleaning goby (Gobiosoma genie) were evaluated for their abilities to remove ectoparasitic monogeneans (Neobenedenia melleni) from seawater-cultured Florida red tilapia. Initial and final infection levels (number of monogeneans/fish) were monitored for individual tilapia maintained with and without cleaner fish in three 8-day trials. Initial infection levels varied widely among trials, with averages (± s.e.) of 412 ± 103, 103 ± 45 and 291 ± 130 in trials 1, 2 and 3, respectively. Final infection levels on tilapia maintained without cleaners (controls) were significantly (P 0.05). The results demonstrate that cleaner fish, particularly the gobies, may be a viable biological method for controlling monogenean parasitosis in seawater-cultured tilapia.

Habitat use by fishes after tidal reconnection of an impounded estuarine wetland in the Indian River Lagoon, Florida (USA)

Most of the wetlands located along the Indian River Lagoon (IRL) ineast-central Florida (USA) have been impounded since the 1950s and1960s to reduce mosquito reproduction. Impounded marsh (i.e.,impoundment) dikes physically separate the wetlands from the estuary toallow artificial flooding of the impoundments during the mosquito breedingperiod (May to October). Presently, Rotational ImpoundmentManagement (RIM) is the preferred impoundment management techniquein the IRL. Impoundments maintained under RIM have culverts installedthrough the dikes which are kept closed during the mosquito breedingseason (to control mosquitos) and are allowed to remain open for theremainder of the year (to allow tidal flow). A 24.3 ha impoundment8 km north of Sebastian Inlet that had been isolated from the IRL for over39 years was studied for 12 months to determine habitat use by fishes aftertidal reconnection and the implementation of RIM. Fish sampling wasconducted with a seine in the perimeter ditch and with clover and minnowtraps in the upper marsh and tidal creek areas of the impoundment. Waterlevel, impoundment bottom topography, and the seasonal nursery functionof the impoundment were factors that contributed to observed patterns offish habitat use during the study. Within the first 15 weeks of perimeterditch sampling, an increase from 9 to 40 species was observed. Transientspecies used the perimeter ditch almost exclusively and entered theimpoundment primarily during the spring open period. Juvenile Pogonias cromis (Linnaeus), Elops saurus Linnaeus, Centropomusundecimalis (Bloch), and Megalops atlanticus Valenciennes were themost abundant recreationally important species, respectively. Habitat useby the most abundant resident species (Gambusia holbrooki Girard,Poecilia latipinna (Lesueur), Cyprinodon variegatus Lacepède, andFundulus confluentus Goode & Bean) was influenced primarily bywater level fluctuations. Resident species used the upper marsh and tidalcreek habitats during summer flooded periods and the cyprinodontids leftthe interior surface of the impoundment last as water levels decreased. Thisstudy is the first to document the recovery of fish populations in areconnected impoundment north of Sebastian Inlet using both active andpassive sampling techniques.

Diet of age-0 tarpon (Megalops atlanticus) in anthropogenically-modified and natural nursery habitats along the Indian River Lagoon, Florida

As human development in coastal areas increases, the role of anthropogenically-created habitats in the life history of marine organisms is becoming increasingly important. We examined the diet of age-0 tarpon, Megalops atlanticus, in and around man-made mosquito control impoundments along the Indian River Lagoon in east-central Florida, with a particular focus on identifying dietary patterns associated with tarpon size and nursery habitat type (i.e., between perimeter pool habitats in established impoundments and newly-created restoration marsh habitats). Age-0 tarpon were found to consume a wide variety of prey organisms, and exhibited considerable dietary variation among study sites. Smaller juvenile tarpon consumed a limited number of small prey taxa, while larger individuals fed on a greater range of prey taxa and sizes. Overall, copepods and fishes were the dominant prey items; however, the consumption of these organisms varied considerably among size classes and sites. There was no clear difference in tarpon diet between the two types of habitat we examined. The ability of juvenile tarpon to utilize such a diverse range of prey organisms may allow populations to inhabit a variety of habitats, including man-made marshes. When natural systems have been degraded or destroyed, human-altered habitats can assume a nursery role for the species.

Acute lethal and teratogenic effects of tributyltin chloride and copper chloride on mahi mahi (Coryphaena hippurus) eggs and larvae

Acute and chronic bioassays were used to evaluate the lethal and sublethal effects of copper chloride and tributyltin chloride on mahi mahi (Coryphaena hippurus) embryos, a pelagic life stage often found in the surface microlayer where anthropogenic contaminants can accumulate. Acute bioassay testing determined the median lethal concentration (LC50) for the test organism after 48 h of exposure. Chronic toxicity tests were used to determine the measurement of sublethal parameters, such as developmental abnormalities after 72-h exposures to the toxicants. Embryos were collected 4 h postfertilization and subsequently exposed to 1, 5, 25, 50, and 100 microg/L of copper chloride and 3, 10, 20, 30, and 50 microg/L of tributyltin chloride. Analysis of hatch rate percentage determined that the mean 48-h LC50 of copper chloride and tributyltin chloride was 32.8 and 16.7 microg/L, respectively, based on the pooled data of four experiments with four replicates for each metal. Consistent abnormalities, such as yolk sac swelling, spinal deformities, and decreased hatch rates, were observed for each metal. Teratogenic responses to copper chloride and tributyltin chloride demonstrate the need to investigate further the impacts of pollution in the open oceans to a species indigenous to, and commercially important to, the Florida (USA) coasts. This information could then lead to the future development of a surface microlayer bioassay using mahi mahi embryos.

Effects of Climate Change on Fishery Species in Florida

Recreational and commercial fishery species in Florida and elsewhere are under serious stress from overfishing and many types of habitat and water quality degradation. Climate change may add to that stress by affecting an array of biological processes, although the range of some subtropical and tropical species may expand northward in the state. It is expected to trigger sea level rise and changes in hurricanes and precipitation levels in Florida and elsewhere. Perhaps the most significant impacts of climate change on fishery species will also associated with changes in seagrasses and mangroves that function as Essential Nursery Habitats. Seagrasses in estuarine and coastal areas are limited by water depth and light penetration. Increases in sea level and in precipitation‐induced turbidity may restrict the extent of seagrass habitats and their role in fishery production. Expanded efforts to reduce nutrient and sediment loading into seagrass habitats may help minimize the potential loss of a valuable fish ...

Identifying pre-spawning aggregation sites for bonefish (Albula vulpes) in the Bahamas to inform habitat protection and species conservation

Many species of tropical marine fish aggregate to spawn, and the dynamics of these aggregations make them especially susceptible to overfishing and habitat loss. Spawning aggregations tend to attract reproductive adults from a large geographic area, sites are traditionally used across generations, and larval dispersal can help supply regional fish stocks. Thus, anthropogenic impacts to spawning sites can have population-level consequences over local and regional scales. A critical component in the challenge to conservation of aggregation-spawning species is identification and subsequent protection of spawning sites. Here we summarize fieldwork conducted to create a protocol for identification of pre-spawning aggregation sites for bonefish, Albula vulpes, in The Bahamas. The mixed-methods, field-based protocol includes Traditional Ecological Knowledge, assessment of spawning readiness, tracking using acoustic telemetry, behavioral observations, and mark-recapture, that combined meet the requirements for identifying pre-spawning aggregation sites. Pre-spawning site identification, in conjunction with information on other life stages and habitats, is essential for successful spatial management strategies. Since bonefish and many other tropical fishes that form spawning aggregation are ‘data poor’ and occur in regions where enforcement of fishery regulations is lacking, spatial management is often the best conservation strategy. This protocol builds upon similar previous efforts to identify spawning sites for groupers and snappers, and will contribute to information needs for conservation is an essential component in the conservation of aggregation-forming species such as bonefish across broad spatial scales.

Bonefish in South Florida: status, threats and research needs

Bonefish (Albula vulpes) support a world-renowned fishery in South Florida, USA. However, fishing guides and anglers have been reporting significant declines in bonefish angling quality over that past three decades. In the absence of any long-term bonefish stock and ecosystem assessments, the cause of this decline in the fishery is unclear. Here we summarize our current knowledge of bonefish ecology in Florida and discuss potential causes of fishery decline. Reductions and alterations in freshwater flows from the Everglades have caused major changes in bonefish habitat, including acute (anoxic conditions) and chronic (changes in benthic flora and fauna) effects in Florida Bay and Biscayne Bay. Various pollutants from agricultural and urban runoff may also be impacting bonefish population(s) directly and/or indirectly throughout their range. Efforts to locate juvenile A. vulpes in Florida have been largely unsuccessful to date, suggesting abundances may be low, and/or juveniles have unknown habitat requirements in Florida. Further, bonefish larvae may be sourced from adult individuals outside of Florida in areas such as Cuba or Mexico, in which case bonefish conservation in other regions is highly relevant to the Florida population. Extreme weather events may have also contributed to the decline; an extreme cold spell in 2010 caused significant bonefish mortality and coincided with documented declines in the fishery. The fishery may also be impacting the population. We outline research needs and potential approaches to better understand the causes of the bonefish decline in Florida and restore populations of this ecologically and socioeconomically important species.