David L. Nieland

Reproductive Biology and Annual Variation of Reproductive Variables of Black Drum in the Northern Gulf of Mexico

Abstract Black drums Pogonias cromis were sampled from commercial and recreational catches in the northern Gulf of Mexico from July 1987 to September 1990, Seasonal onset of spawning, evidenced by the presence of postovulatory follicles in ovarian tissue sections and by elevated gonadosomatic indices, occurred in January of each year (one female with hydrated oocytes was sampled in December 1988). Atretic oocytes observed in mid to late April indicated imminent cessation of spawning. Two of 115 females less than age 5 had achieved sexual maturity; all females age 5 and older were mature. Fifty percent maturity of females was attained at 640–649 mm fork length and all females larger than 690 mm were mature. Male black drums entered the breeding population at a younger age (>50% maturity at age 4) and a smaller size (50% maturity at 610–620 mm). Multiple oocyte stages observed throughout the annual spawning seasons verified groupsynchronous oocyte development and multiple batch spawning. Estimated batch fec...

Age, Growth, and Reproduction of Spotted Seatrout in Barataria Bay, Louisiana

Abstract Spotted seatrout Cynoscion nebulosus (604 males, 1,453 females) were collected from Barataria Bay, Louisiana, from January 1994 to November 1995 for analyses of age, growth, and reproduction. It was confirmed that opaque annuli in sagittal otoliths accrete once a year during the period from November to April. Age among both sexes varied from 0 to 5 years; females dominated the population at age 2 but had disappeared from it at age 5. Females were significantly larger than males at all ages. Instantaneous mortality, annual mortality, and survival were, respectively, 1.40, 0.75, and 0.25 for females and 0.60, 0.45, and 0.55 for males. Spotted seatrout spawn over a 6-month period beginning in April and continuing through September, as indicated by elevated gonadosomatic index values and the recrudescence of oocyte maturation. Essentially all male and female spotted seatrout become reproductively mature the first summer after hatching. The presence of multiple oocyte maturation stages during the spaw...

Reproductive Biology of Female Spotted Seatrout, Cynoscion nebulosus, in the Gulf of Mexico: Differences among Estuaries?

Although the reproductive biology of spotted seatrout, Cynoscion nebulosus, has been documented across the northern Gulf of Mexico, longitudinal comparisons across its range are not available. We evaluated aspects of female spotted seatrout reproduction in five estuaries ranging from Charlotte Harbor, FL (CHFL) to Redfish Bay, TX (TX). Seasonal temperature profiles were similar among the five estuaries, but spring salinities were lower in Apalachicola Bay, FL (AFL) and St. Louis and Biloxi Bays, MS (MS) (range 7.5–15.0‰) than in CHFL, Barataria Bay, LA (LA) and TX (range 16.6–31.7‰). The length of the spawning season varied among estuaries: five months in MS and AFL, six months in LA and TX, and seven months in CHFL. Peak gonodosomatic index (GSI) values varied from May to July among estuaries. The smallest sexually mature females captured ranged from 235 mm TL in LA to 285 mm TL in AFL. Mean relative batch fecundity (# eggs g−1 ovary-free body weight) was significantly higher (ANOVA, p < 0.5) in TX (390 ± 39) and LA (397 ± 26) than in MS (103 ± 10). Spawning frequency, determined by the percentage of females in the late developing ovarian class with postovulatory follicles, ranged from 4.2 to 7.7 d and was not significantly different when all months were combined. However, significant differences during March, April and September (χ2, p < 0.01) showed that spotted seatrout from CHFL and AFL spawned less frequently than those from other estuaries. Overall, MS and AFL fish have the shortest reproductive season, fewer number of spawns and appear to obtain sexual maturity at a slightly larger size. Five hypotheses to explain these differences are presented: variations in time of sampling, temperature, habitat structure, genetics and salinity. Differences in salinity profiles appears to be the most plausible explanation.

Preliminary Evaluation of the Use of Phosphogypsum for Reef Substrate. I. A Laboratory Study of Bioaccumulation of Radium and Six Heavy Metals in an Aquatic Food Chain

Abstract Phosphogypsum (PG), a solid by-product of phosphoric acid production, contains radionuclides and trace metals in concentrations which may pose a potential hazard to human health and the environment. to investigate the possibility of bioaccumulation of radium and six heavy metals over time when aquatic organisms experience both trophic and environmental exposure to PG, we designed a laboratory experiment representing three levels of an aquatic food chain. During the 135 day experiment, a meiobenthic copepod species (Amphiascoides atopus) was cultured in the presence of PG. the copepods were subsequently fed to grass shrimp (Palaemonetes vulgaris and P. pugio) which were in turn fed to gulf killifish (Fundulus grandis); both the grass shrimp and the killifish also experienced an environmental PG exposure. Other than elevated radium levels in the experimental grass shrimp, the experiment demonstrated little effect of environmental or trophic exposure to PG on microinvertebrates, macroinvertebrates, ...

Preliminary Evaluation of the Use of Phosphogypsum for Reef Substrate. Ii. A Study of the Effects of Phosphogypsum Exposure On Diversity and Biomass of Aquatic Organisms

Abstract The effects of cement consolidated phosphogypsum (PG) on marine organisms was investigated under natural conditions in four 1000 m2 estuarine ponds. Two ponds were seeded with 160 kg of PG arranged in aggregations of blocks and two ponds received similar mass of sand/cement blocks. Meiofauna were sampled quarterly and PG did not affect total meiofauna or major taxa (nematodes and copepods) density. Abundant species of copepods either were slightly increased in ponds with PG or were inconsistently affected. All ponds were drained after one year. Three species of macroinvertebrates and 15 species of fishes were collected. Diversity indices showed modest but inconsistent variation among ponds. Only Pond 1 (control) and Pond 4 (experimental) had similar species abundances and all ponds showed unique distributions of biomasses among species. Thus, no differences in community structure attributable to the presence of PG could be detected among benthic invertebrates, natant invertebrates, or fishes.