Postlarval ecology of the blue shrimp (Litopenaeus stylirostris) and brown shrimp (Farfantepenaeus californiensis) in the Colorado River Estuary.

The study describes habitat use by penaeid shrimp larvae that enter the Colorado River Delta. A location was chosen in the Santa Clara Channel in the core zone of the Upper Gulf of California and Colorado River Delta Biosphere Reserve, where collections were done during three consecutive days of each spring tide from May to October 2000. A 505-µm net was anchored and left in the water for 10 minutes when the height of the tide was 1 m above the level of the channel, during both flood tide and ebb tide. Blue shrimp (Litopenaeus stylirostris) and brown shrimp (Farfantepenaeus californiensis) postlarvae were caught in proportions of 80% and 20%, respectively. The postlarval abundance of blue shrimp was significatively greater during flood tide than during ebb tide in May, June and September, but significatively greater during ebb tide than during flood tide in July and August. The blue shrimp postlarval sizes were significatively greater during ebb tide than during flood tide. No differences in the abundance of brown shrimp postlarvae were found between flood and ebb tides. It is concluded that the Colorado River Delta is a breeding area for blue shrimp, but not for brown shrimp

Reproductive period of the brown shrimp Farfantepenaeus californiensis (Holmes, 1900) in the Agiabampo coastal lagoon system, Sonora/Sinaloa, Mexico

Knowledge of the biological role of the brown shrimp, Farfantepenaeus californiensis, in coastal lagoons is lacking. This species has been classified as oceanic that may or may not enter coastal lagoons in early stages and if it does, it migrates back to the ocean when it attains a size of 35 mm total length (TL). Recently, the brown shrimp has been caught in the Agiabampo coastal lagoon system, in Sonora/Sinaloa (Mexico), and the objective of this study is to describe the reproductive period of this species in that system. Monthly sampling campaigns were carried out from January to December 2002, during five consecutive days. Tows in 24 geopositioned stations were done during high and low tide using 15-m-wide trawl nets. A total of 27,694 organisms were analyzed, with a male:female ratio of 4:3. Based on the proportion of mature females, we determined two reproductive periods: one from June to July (summer) and another from October to November (autumn); however, the average abundance was 20 org ha–1 in summer and 2 org ha–1 in autumn. The average size of mature females was significantly smaller (P < 0.05) in summer (129.9 mm TL) than in autumn (134.5 mm TL). Size at first maturity was 145 mm TL in both periods. An important result that contributes to the biological knowledge of F. californiensis is evidence that part of the population matures inside this coastal lagoon and presents one important spawn deposition per year

Temporal variation in the abundance of postlarval and juvenile blue shrimp (Litopenaeus stylirostris) and brown shrimp (Farfantepenaeus californiensis) in the Colorado River estuary

The temporal variation in the abundance and species composition of penaeid shrimp postlarvae and juveniles was studied in a tidal channel of the Colorado River estuary. Biweekly sampling during flood and ebb tide was conducted from March through November 2000. Postlarvae of the blue shrimp, Litopenaeus stylirostris, were observed beginning in May, with highest densities in early June during flood tide. A much smaller peak in densities occurred in late September, with few postlarvae found in October and November. Juvenile L. stylirostris were present in highest densities during ebb tide in mid-June, with smaller peaks in mid-July and late September. Densities of postlarval and juvenile brown shrimp, Farfantepenaeus californiensis, were much lower than those of L. stylirostris and without clearly defined peaks. The growth rate of juvenile L. stylirostris appeared similar to rates (30–60 mm month–1) reported for penaeid shrimp from the Pacific Ocean, Gulf of Mexico, and Australia. Management decisions affecting the Upper Gulf of California and Colorado River Delta Biosphere Reserve need to be cognizant of the importance of May and June as critical months in the use of the estuarine tidal channels by these commercially important species

THE RELATIONSHIP OF PLASMA pH AND ANION PATTERN TO MERCURIAL DIURESIS

Summer mortalities have been observed in French shellfish areas (including Normandy) since 1994, but origin of this syndrome remains unclear and is suspected to be caused by a combination of several interacting extrinsic (biotic and abiotic) and intrinsic (genetic, physiological, immunological) factors. The French research program, MOREST aimed to identify the origin of oyster summer mortality along the French coast, focusing on the interactions between oysters, their pathogens, and the environment. The present study analyzed spatio-temporal variation in growth, condition and mortality in spat, and half-grown and market-sized oysters reared from February 2000 to October 2003 at six stations within two different areas in the Bay of Veys, Normandy: Grandcamp (GR), and Gefosse (GE) that is more estuarine. These biological parameters were compared between years, age groups, and areas. Results showed that shell growth was significantly lower in the station highest on the shore and similar in the four other sites, whereas tissue growth and condition index were higher in the Gefosse area. Results also showed large interannual, interage, seasonal and spatial variation in oyster mortality. In 2001, mortalities were markedly higher than in other years and all batches and sites were affected by high mortality rates. Moreover oysters suffered much higher mortalities in their second and third years than as spat, and the difference between age classes was accentuated when mortality was high. Increases in mortality occurred when the gonad was most extensively developed and the peak coincided with the spawning and postspawning periods when gonad volume began to decrease. Spatial variability showed that mortality was higher in Gefosse than Grandcamp. Chronology and spatial variations in mortality highlighted the importance of timing and confirmed that mass mortalities may be closely linked to reproduction. The risk seems to be associated with high reproductive effort, partial spawning, and/or slow gonad resorption. Spatial variation also suggests that the study sites experience varying degrees of stress caused by biological changes and probable differences in water quality reflecting the influence of freshwater input in Gefosse where mortality is higher