Reproductive biology of the blue spot mullet Valamugil seheli (Forskal) from Mangalore Region, southwest coast of India

The blue spot mullet Valamugil seheli spawns once a year between August and February with peak spawning during October - November. Males attain maturity at 250.5 mm and females at 256.5 mm total length. Males outnumbered females in the commercial catches, although the sex-ratio (M:F=1:0.90) in the population showed no significant deviation. The fecundity of this species varied from 108378 to 910350 eggs with an average of 327944. Linear relationships were found between fish length, gonad weight and fecundity; and between fish length, fish weight and ovary weight

Diel feeding patterns, rate of gastric evacuation and foods of Indian sandwhiting, Sillago sihama in Mulki estuary, west coast of India

Diel feeding chronology of sandwhiting, Sillago sihama was examined from stomach collections taken during the months of April, July and December'99 in Mulki estuary along Dakshina Kannada coast, India. Significant differences in mean stomach content weight were found between several consecutive 3 hour periods with peak fullness occurring in early morning and evening hours. The rate of gastric evacuation of natural food (crustacea, polychaetes and fish) was measured in the field was best described by an exponential model, with an estimated evacuation time of 8.0 h at a temperature of 28.5 ± 1.2°C. Stomach content analysis indicated that this species is a carnivore on a wide range of benthic, epibenthic and planktonic prey. The principal food items of S. sihama were crustaceans, polychaetes and fish. Fishes less than 100 mm TL preferred mainly crustaceans while larger ones depends on polychaetes, crustaceans and fish. The feeding activity of S. sihama was influenced by tidal cycle

Community structure of net phytoplankton along surf zone of Mangalore during southwest monsoon season

445-448Data collected from surf waters of Mangalore revealed the time scale variation of hydrographical parameters and phytoplankton community. Salinity and plant nutrients specially nitrate and silicate exhibited a conspicuous fluctuation in relation to intensity of precipitation. Surf water was characterized with much higher levels of limiting nutrients than the Redfield ratio. Diatoms dominated numerically among phytoplankton in the surf waters followed by dinoflagellates and blue green algae. Lower salinity associated with high load of nutrients favored the growth of bloom forming centric types of diatoms. While diverse forms of diatoms, dinoflagellates and blue green algae occurred with increasing salinity in surf waters. Shannon’s species diversity varied from 0.049 to 2.125 and Shannon’s evenness index varied from 0.020 to 0.735. Diversity indices indicated gradual increase in diversity and evenness values in relation to variation of salinity and nutrient

An assessment of Dinophysis blooms in the coastal Arabian Sea

Dinoflagellate blooms of the genus Dinophysis occur regularly in the coastal Arabian Sea. By producing toxins, which may accumulate in marine bivalves, they impose threat to human health. Using time-series data on environmental variables (e.g., nutrients, sea surface temperature and salinity) and concurrent Dinophysis abundances for the surface waters along the coast of the southeastern Arabian Sea during the period 1990–2010, we investigate whether potential climate change signals play a role in driving blooms of Dinophysis spp. A logistic Generalized Linear Model was adopted to test the effect of environmental variables on Dinophysis abundances over a range of threshold values (102–105 cells m−3) for blooms. Some of the extreme events occurred during the pre-monsoon (March–May) periods. Model validation suggested a threshold of 105 cells m−3 to be better than other thresholds in examining the Dinophysis abundances, and the variation in this threshold is explained by sea surface temperature, salinity, dissolved inorganic nitrogen to phosphorus ratio and total suspended solids (turbidity). Fate of the Dinophysis blooms in the coastal Arabian Sea for different climate change scenarios is discussed