Stock assessment of soldier catfish Osteogeneiosus militaris along the northwest coast of India

Value of length growth parameters L∞, K and t(sub)0 from age-length relation obtained from length-frequency analysis for the soldier catfish stock were estimated to be 47.6 cm, 0.51 per year and 0.03 year respectively. The age at recruitment (t [sub]r) was 0.58 year and the age at first capture (t[sub]c) 0.83 year. The total mortality (Z) was 0.88 including the present natural mortality (M) of 0.84 and fishing mortality (F) of 0.04. The total stock of this fish along the Northwest coast of India was assessed to be 32,413 tons and the MSY 5,426 tons which is much higher than the current catch of 863.8 tons. The potential yield (P[sub]y) of 38.7 g per recruit could be obtained at the optimum of exploitation (t[sub]y) of 2.84 years.

Estimates of growth, mortality, recruitment pattern and MSY of important resources from the Maharashtra coast

Based on the data collected from the year 1987-1991 the growth, mortality and recruitment pattern of eighteen species of fish, two species of cephalopods and four species of penaeid prawns have been presented in the present communication. The total mortality coefficient, (Z) varied from lowest of 1.20 for O. cuvieri to a highest of 10.78 for P. stylifera. The natural mortality coefficient, (M) varied from 0.52 for T. thalassinus to 3.44 for S. crassicornis. The average annual yield of eighteen species of fish, four species of prawns and two species of cephalopods are 65.083, 38.404 and 11.373 tons as against the MSY of 83.023, 72.460 and 10.475 tons respectively. The MSY estimated for the total fish stock is 1.77.753 tons whereas the present yield is 1.14.859 tons. This indicates that higher yield can be obtained by increasing the effort.

A study on food and feeding habits of Nemipterus japonicus (Bloch) off Bombay coast

The gut content of Nemipterus japonicus revealed that this fish is a carnivorous bottom feeder, feeding mainly on crustaceans, fishes, salps and polychaetes, with marginal variations in females. The intensity of feeding increased with the advancement of maturity till stage 5 except in stage 3 where the intensity of feeding indicated a decrease.

Stock dynamics of horse mackerel, megalaspis cordyla (Linnaeus) along northwest coast of India

The stock dynamics of horse mackerel, Megalaspis cordyla, along the northwest coast of India has been studied using length frequency data recorded from commercial landings and trawl catches of research-cum-training vessel M.F.V. Saraswati. The growth parameters for this species has been estimated to be L∞=54 cm and K=0.49 per annum. The natural and fishing mortality for the stock have been worked out to be 0.93 and 0.91 per annum respectively. The study indicated that the stock is fished at a safer fishing mortality level F sub(0.1), lower than F sub(msy) level.

Population dynamics and stock assessment of the spider prawn, Nematopalaemon tenuipes Henderson along the Maharashtra coast

Nematopalaemon tenuipes is an important component of non-penaeid prawn resources of the northwest coast of India. During 1979-82 period, it contributed 29.9% to the non-penaeid prawn and 5.6% to the total fish landings of Maharashtra. The von Bertalanffy growth parameter L∞, K and t(sub)0 were 77.38 mm, 1.31 and -0.02 year for the males while for the females these parameters were respectively 87.23 mm, 1.30 and -0.01 year. The natural mortality coefficient (M) was 3.54 and 3.52 and the average total mortality coefficient (Z) during the period was 9.09 and 7.79 for the males and females respectively. With the exploitation rates of 0.61 and 0.55 for the males and females during the period, the total stock of the species was 26,270 tonnes and the standing stock was 3,418 tonnes. The maximum sustainable yield (MSY) of the species under the prevailing fishing conditions was 15,744 tonnes which is close to the average yield of 14,726 tonnes from the nets. Hence further increase in effort is not suggested.

Stock assessment and biology of Johnius glaucus (Day) off the northwest coast of India

The stock size and biology of Johnius glaucus (Day) resource off the northwest coast of India were studied for 1982-83 and 1983-84. The total length at the end of 6, 12, 18, 24 and 26 months was 121 mm, 183 mm, 237 mm, 261 mm and 264 mm respectively. The length growth parameters were: L∞=300 mm, K=0.0807 (monthly) and t(sub)0=-0.51 month. The weight growth parameters were: W∞= 317g, K=0.0762 (monthly) and t(sub)0= -0.41 month. The exploited stock mainly composed of 1/2 + and 1+ age groups. The annual Z, M and F were 2.34, 1.49 and 0.85 respectively. The l(sub)b, t(sub)b, l(sub)r, t(sub)r and selection factor K were 155 mm, 0.75 year, 65 mm, 0.25 year and 3.875 respectively. The Yw/R was optimum at the exploitation rate (E) of 0.75 and coded mesh size of 37 mm. The total stock for 1982-83 and 1983-84 was 14,624 and 26,190 tons respectively. The standing stock of 1982-83 and 1983-84 was 5,645 and 10,110 tons respectively. The MSY for 1982-83 and 1983-84 was 6,623 and 11,788 tons respectively. The F and Z were lowest in 0+ age group and highest in 1+ age group.

Macrobenthos off Mahim (Bombay), west coast of India in relation to coastal pollution and aquaculture

Deterioration of water quality clearly indicated a moderate to severe coastal pollution around Mahim whereas a relatively healthy marine environment towards offshore was noticed. Foraminifera, polychaetes, crustaceans and pelecypods were the dominant macro faunal groups encountered in the area. The occasional inhabitants like pennatularians, nemertines, sipunculids, ophiuroids and fish larvae were mostly restricted to offshore regions. Biomass and population density of macro fauna were moderate and showed fluctuating trend. Similarity coefficients of foraminifera (0.89) and polychaetes (0.81) were high for offshore unpolluted stations (3 and 4) as compared to near shore coastal stations (1 and 2). Faunal diversity was relatively more in unpolluted zone. The diversity index (H) was more at station 3 for polychaetes (1.39) and at station 4 for foraminifers (0.54). In general, biomass was high during post monsoon excepting station 1 which was invariably under severe pollution stress throughout the study period. Foraminifera were abundant at sandy bottom while polychaetes preferred muddy (clayey silt) bottom. A noticeable ecological modification associated with faunal abundance and diversity were related to deteriorating marine water quality due to anthropogenic waste disposals. The prevailing water quality around Mahim is unsuitable for any kind of culture practices and also for harvesting economically important marine species.

Preliminary observations on the morphometric characteristics, length weight relationship, food and fedding habits and fecundity of Saurida tumbil (Bloch) off Bombay coast

Fifteen morphometric and four meristic characters of Saurida tumbil were studied and their relationships with total length and head length were established. The length weight relationship worked out to be W= -5.6055 L(super)3.291. The fish is a carnivore, feeding mainly on small fishes, molluscs and crustaceans. Larger fishes are selective feeders on fish. It is a long protracted spawner. Fecundity varied from 6008 to 17384 eggs in specimens of size group 212-420 mm. Fecundity-total length, fecundity-total weight of fish and fecundity - total weight of ovary relationships were worked out to be F=0.9414 L(super)1.6626, F=180.7069 W(super)0.7531 and F=3153.0375 W(super)0.8278 respectively.

Population dynamics of penaeid prawn Penaeus merguiensis off Mumbai coast

Stock dynamics of Penaeus merguiensis was studied using length composition data collected separately for males and females during the period 1995-1998, at New Ferry Warf landing, centre in Greater Mumbai. Food and feeding, sex ratio, fecundity and length-weight relationships were worked out on a representative sub-sample. Asymptotic length (Loo) and growth coefficient (K) were estimated to be 220 mm and 1.80 per annum respectively for males. These parameters were respectively 281 mm and 1. 72 per annum in the case of females. The instantaneous rate of total mortality coefficient (Z) was found to be 9.79 and 7.44 per annum for males and females respectively. The annual natural mortality coefficient (M) was estimated to be 2.80 for males and 2.60 for females. As the exploitation ratio exceeded 0.5 in the case of both the males and females, the study suggests the necessity for reduction in fishing pressure in order to achieve Maximum Sustainable Yield (MSY).

Mortality estimates of Indian ribbon fish Trichiurus lepturus off Maharashtra coast

In view of its new found status in export market, ribbon fish resources need to be continually monitored. Mortality, one of the important parameter is reported for the Indian ribbon fish Trichiurus lepturus Linnaeus in the present communication. The average annual instantaneous rate of total (Z), natural (M) and fishing mortality coefficient (F) were estimated as 2.66, 0.77 and 1.89 respectively for the 1995 to 1997 period. The exploitation rate (U) and exploitation ratio (E) were estimated as 0.66 and 0.71 respectively, which is beyond the optimum thrust reduction in the fishing effort for this stock along the Maharashtra coast is necessary.

Study on the morphometric and meristic characteristics of splendid silver belly Leiognathus splendens (Cuvier) from Bombay coast

Ten morphometric and six meristic characters of Leiognathus splendens (Cuvier) of Bombay Coast have been studied sexwise. Regression and sexwise difference if any between the compared morphometric characteristics have been worked out. Range, mode, standard deviation, co-efficient of variation of 6 meristic characters have been analysed. There was no significant difference between the sexes in morphometric and any deviation in the meristic characters.

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.

Macrobenthos of intertidal zone of Versova along the coast of Mumbai

To assess the biodiversity of macro benthos in the changing environment along the coast of Mumbai, the intertidal zone of Versova was identified. The water quality in this intertidal region was poor with low pH, salinity and dissolved oxygen, and high nitrite, nitrate, phosphate and ammonia. The substratum was sandy with 1.29% organic matter in it. Mean faunal density of 2257 no./m² was recorded during the study which was mainly contributed by polychaetes (83.5%) followed by amphipods (14.5%), while other groups represented were isopods, crabs, hermit crabs, unidentified decapods, pelecypods and gastropods. Average biomass of 34.83 g/m² (93.7%) was contributed by polychaetes. Shannon and Wiener Index (0.4107) indicated heavy pollution in the intertidal area of Versova.

Copper, zinc, iron and manganese in sediments and in the rock oyster Saccostrea cucullata in Mumbai coast

Sediment and oyster (Saccostrea cucullata) samples were collected at Dhanda, a fishing village in Mumbai, Maharashtra. The samples were analysed for copper, zinc, iron and manganese contents. Metal concentrations in the sediments and bioaccumulated levels in oysters were correlated. There is no positive correlation between the total sedimentary levels of metals analysed and the bioaccumulated levels of respective metals in oyster. A positive correlation between the bioavailable fractions of zinc, iron and manganese, and the bioaccumulated levels exists. Copper, however, shows a negative correlation with respect to the bioaccumulated levels.

Studies on length-weight relationship of Gerres filamentosus Cuvier from the estuaries of the southern Karnataka coast

Random samples of Gerres filamentosus Cuvier from the Netravathi-Gurpur, Mulky, Kallayanapura, Mabukala and Kundapura estuaries of the southern Karnataka Coast were collected in the years 2000, 2001 and 2002, and length-weight relationships for each estuary were derived using multiple linear regression technique with one dummy variable. Hence, combined or sex-wise length-weight relationships were obtained after testing for homogeneity and isometric growth condition of fishes for each estuary by t-test. The extent of closeness of length-weight relationships between sexes and among estuaries for different years is explained by a trend line graph. The whole process of multiple linear regression analysis with one dummy variable is a better substitute for the analysis of covariance technique.