Seasonal egg production of whitemouth croaker (Micropogonias furnieri) in the Río de la Plata estuary, Argentina-Uruguay

The reproductive biology of the whitemouth croaker (Micropogonias furnieri) inhabiting the estuarine waters of the Río de la Plata (Argentina-Uruguay) was studied by using histological analysis of the ovaries. Samples were collected during the spawning peak and the end of two breeding seasons (November 1995–Feb-ruary 1996 and November 1997–March 1998). Micropogonias furnieri is a multiple spawner with indeterminate annual fecundity. Spawning frequency, determined by using the percentage of females with postovulatory follicles, was about 31% in November 1995 and 25% in February 1996. At these frequencies, a female on average spawned a new batch of eggs every 3–4 days during the spawning season. Batch fecundity was fitted to a power function of length and a linear function of ovary-free female weight. The number of hydrated oocytes decreased at the end of the breeding season, coinciding with an increase of atresia. Annual egg production for a 40-cm-TL female was estimated to be between 3,300,000 and 7,300,000 eggs. In addition to the seasonal decrease in fecundity and spawning activity, a decline in egg size and weight toward the end of the breeding season was also observed.

Physiological ecology of juvenile chinook salmon (Oncorhynchus tshawytscha) at the southern end of their distribution, the San Francisco Estuary and Gulf of the Farallones, California

Juvenile chinook salmon, Oncorhynchus tshawytscha, from natal streams in California’s Central Valley demonstrated little estuarine dependency but grew rapidly once in coastal waters. We collected juvenile chinook salmon at locations spanning the San Francisco Estuary from the western side of the freshwater delta—at the confluence of the Sacramento and San Joaquin Rivers—to the estuary exit at the Golden Gate and in the coastal waters of the Gulf of the Farallones. Juveniles spent about 40 d migrating through the estuary at an estimated rate of 1.6 km/d or faster during their migration season (May and June 1997) toward the ocean. Mean growth in length (0.18 mm/d) and weight (0.02 g/d) was insignificant in young chinook salmon while in the estuary, but estimated daily growth of 0.6 mm/d and 0.5 g/d in the ocean was rapid (P≤0.001). Condition (K factor) declined in the estuary, but improved markedly in ocean fish. Total body protein, total lipid, triacylglycerols (TAG), polar lipids, cholesterol, and nonesterified fatty acids concentrations did not change in juveniles in the estuary, but total lipid and TAG were depleted in ocean juveniles. As young chinook migrated from freshwater to the ocean, their prey changed progressively in importance from invertebrates to fish larvae. Once in coastal waters, juvenile salmon appear to employ a strategy of rapid growth at the expense of energy reserves to increase survival potential. In 1997, environmental conditions did not impede development: freshwater discharge was above average and water temperatures were only slightly elevated, within the species’ tolerance. Data suggest that chinook salmon from California’s Central Valley have evolved a strong ecological propensity for a ocean-type life history. But unlike populations in the Pacific Northwest, they show little estuarine dependency and proceed to the ocean to benefit from the upwelling-driven, biologically productive coastal waters.

Recruitment season, size, and age of young American eels (Anguilla rostrata) entering an estuary near Beaufort, North Carolina

Net catches from 1985–86 to 1994–95 at Pivers Island, North Carolina, indicated that glass-eel stage American eels (Anguilla rostrata) were recruited to the estuary from November to early May, with peak numbers in January, February, and March. There was no declining trend in recruitment over the years of sampling. Except for one year, there was no clear seasonal decrease in mean length. But shorter glass eels were older than longer glass eels, as judged by age within the glass eel growth zone of the otolith, suggesting that smaller fish took longer to arrive. The mean age of glass eels collected from the lower estuary and a freshwater site 9.5 km upriver differed by 8.4 d (36.2 vs. 44.6, respectively). Outer increments (30–35) of the otolith growth zone of glass eels from North Carolina were significantly wider than corresponding increments of otoliths from New Brunswick. Mean total ages of North Carolina, New Jersey, and New Brunswick elvers were 175.4, 201.2, and 209.3 d, corresponding to mean lengths of 55.9, 60.9, and 58.1 mm TL, respectively. The mean durations of glass-eel growth zones (44.6, 62.3, and 69.8) were in close agreement with those from previous studies, but total ages were not. This suggested that perhaps some finer (leptocephalus stage) increments were not detected by light microscopy, differences occurred in seasonal increment deposition, or absorption of the otolith material may have taken place during metamorphosis, rendering the aging of larvae inaccurate. Judging from the long recruitment period and seasonal uniformity in both mean age and length found in our study, the spawning period of American eels may be somewhat more protracted than previously considered.

Late Holocene environmental variability in the upper San Francisco Estuary as reconstructed from tidal marsh sediments

EXTRACT (SEE PDF FOR FULL ABSTRACT): Tidal marsh sediments collected from Browns Island in the lower Sacramento/San Joaquin Delta, California, are used to reconstruct environmental variability over the past 6.8 ka. Calibrated radiocarbon dates provide chronostratigraphic control. Trace metal analyses, grain-size variability, organic content, and macrofossils are used to define short- and long-term variations in relative salinity and inundation frequency. Aggradation began in subtidal fresh water conditions about 6.8 ka. Subtidal aggradation of clayey silts continued until about 6.3 ka, when conditions shifted toward a lower intertidal brackish marsh environment. By 5.1 ka, a brackish marsh plain had evolved, with surface water freshening after 4.1 ka. Conditions returned to brackish similar to the present after 2.3 ka.

Physical, chemical, and biological characterization of water year types in the San Francisco Bay estuary [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): Twenty-three years of physical, chemical, and biological data were used to characterize conditions associated with wet, normal, dry, and critical water year types in the upper San Francisco Bay estuary.

The influence of climate on phytoplankton communities in the upper San Francisco estuary

EXTRACT (SEE PDF FOR FULL ABSTRACT): The 1977 climate shift was characterized by low chlorophyll a concentrations and a shift in phytoplankton community composition throughout the upper San Francisco Bay estuary. ... For climate to be a driving force in phytoplankton communities, it must affect mechanisms that control biomass and community composition. The influence of climate on environmental conditions and phytoplankton community composition among water-year types was examined using 19 years of physical, chemical, and phytoplankton data collected monthly at 15 stations throughout the estuary.

Prawn seed resources and its farming potentialities in Sunkeri back waters (Kali Estuary - Karwar)

Prawn seed resources of Sunkeri back waters indicated the availability of Penaeus indicus, P. monodon, Metapenaeus dobsoni and M. monoceros. The monthly variation in seed composition, its correlation with environmental parameters and the aquaculture potentialities are reported

Composition and distribution of benthos in Kali Estuary, Karwar

The composition and abundance of meio and macrobenthos in 5 stations of Kali estuary were studied during September 1981 to September 1982. In all sixteen meiobenthic and fourteen macrobenthic taxa were identified and the salient features in their temporal and spatial distribution, species dominance and percentage occurrence are discussed.

Report on two types of leptocephalus-eel from Vellar Estuary (Bay of Bengal)

Two types of leptocephalus-eel, identified as ophichthyid larva and Muraenesox cinereus, collected from the Vellar estuary, India, are described. M. cinereus larvae are common in the estuary during November-January whereas ophichthyid larvae are very rare, collected on one occasion (January) only.

Tidal and diel influence on zooplankton occurrence in the Mandovi estuary, Goa

Distribution and abundance of zooplankton over the tidal cycle were studied in the Mandovi estuary, Goa, during August and December 1971 and May 1972. Tide induced salinity fluctuations were obvious with high values during spring tides. Salinity was low during August, apparently due to precipitation and land run off but increased subsequently. The mean biomass values for the day and night collections were 13.6 and 19.8 ml/100 m super(3) respectively. Occurrence of most of the zooplankton taxa and species was related to diel rhythm and tidal oscillations. However, overall mean zooplankton standing stock at both the stations were same (16.3 ml/100 m super(3)) indicating that estuarine zooplankton maintained their position during tidal exchanges. Variations in occurrence of common groups and species of zooplankton over the tidal cycle are discussed.

Environmental inventory and the distribution of inorganic nutrients in a tropical estuary of the south-west coast of India

Dissolved nutrients (PO sub(4)-P, NO sub(3)-N, NO sub(2)-N and SiO sub(4)-Si) estimated in the surface and bottom waters of five selected stations of the Paravur Lake, Kerala, India, during February 1987 to January 1988 revealed distinct seasonal variations. Rainfall and land drainage play significant roles in the nutrient economy, particularly NO sub(3)-N and SiO sub(4)-Si, of this water body. Abnormally high values of PO sub(4)-P indicated extremely polluted condition at the wetting zone of the lake during the premonsoon season. SiO sub(4)-Si showed significant negative relationship with salinity.

Seasonal variation in the physico-chemical properties of Rushikulya estuary and its effect on the occurrence of Chanos fry

Seasonal variation in some physico-chemical properties of Rushikulya estuary was studied. The surface water temperature varied from 20 to 34.5 degree C, the transparency of the water from 6.3 to 12 cm, the salinity from 28.3 to 32.8 % and the pH from 6.77 to 7.35. The transparency and salinity showed bimodal distribution. Occurrence of the Chanos fry were correlated to it.

Algae and water pollution in Mahi Estuary

Distribution of phytoplankton, chlorophyll A and phaeophytin was studied at different locations in the Mahi Estuary, Gujarat, India during 1982. The water quality at the discharge point was poor while the region away from it was relatively unpolluted. The results indicated a wide range of variation in phytoplankton population (7.68-5010, 96 x 10 super(4) cells/l, chl. a 2.22-58.22 mg/m super(3) and phaeophytin [0.20-10.21 mg/m super(3)]. The ratio of chl. a/phaeophytin were remarkably low at highly polluted stations. Higher abundance of the genera Oscillatoria and Nitzschia were recorded at polluted stations. The diversity of species at the unpolluted station was higher (1.56) as compared to the polluted station (1.07).

Physicochemical and biological cycles in a tide dominated, nitrogen-polluted temperate estuary

Spatio-temporal variations in the physicochemical and biological parameters in the Morlaix estuary on the Brittany coast of France were studied. Hydrographically, the estuary can be classified into 3 segments: the upper estuary where stratification always persists, the lower estuary where vertical homogeneity is permanent, and a middle estuary where there is a regular oscillation of stratification and homogeneity during every tidal cycle, stratification being associated with slack waters and homogeneity, with ebb and flood. Nitrogen pollution in the estuary is very intense.