Occurrence of whale sharks in coastal waters in the Indian Ocean: an interesting coincidence

Salinity, temperature and pressure are parameters which govern the oceanographic state of a marine water body and together they make up density of seawater. In this contribution we will focus our interest on one of these parameters, the salinity: accuracy in relation to different purposes as well as observation technique and instrumentation. We will also discuss the definition of salinity. For example most of the Indian Ocean waters are within the salinity range from 34.60-34.80, which emphasize the importance of careful observations and clear definitions of salinity, in such a way that it is possible to define water masses and predict their movements. In coastal waters the salinity usually features much larger variation in time and space and thus less accuracy is sometimes needed. Salinity has been measured and defined in several ways over the past century. While early measurements were based on the amount of salt in a sea water sample, today the salinity of seawater is most often determined from its conductivity. As conductivity is a function of salinity and temperature, determination involves also measurement of the density of seawater is now more precisely estimated and thus the temperature. As a result of this method the Practical Salinity Scale (PSS) was developed. The best determination of salinity from conductivity and the temperature measurements gives salinity with resolution of 0.001 psu, while the accuracy of titration method was about ± 0.02‰. Because of that, even calculation of movements in the ocean is also improved.

Status of the gill net fishery for the small pelagic fish species in western, south-western and southern coastal waters of Sri Lanka during 1995-1997

Small pelagic fish species are mainly caught by gill nets operated by fibre reinforced plastic boats fitted with 8-25hp out board engines, traditional crafts fitted with 8-1hp out board engines and non mechanised traditional crafts. Around 28 to 55% of the small pelagic catch in the study area consisted of trenched sardine Amblygaster sirm during 1995-1997 period. Another 26-36% of the catch composed of other Sardinella species such as Sardinella gibbosa, S. albella, S. sindensis and S. longiceps. Engraulids such as Encrasicholina heteroloba, Stolephorus insularis and Stolephorus indicus and Thryssa spp formed around 3-5% of the catch. The major component of this fishery consisted of Clupeids and Engrauhds and over 65 species ranged between smaller Engraulids to incidental rock fish, sail fish, seer fish, sharks, skates and rays. Around 1.4 to 1.9% of the catch consisted of Chirocentrus dorab, Sphyraenaspp, Scomberomorus spp, Lepturcanthus sp and Megalaspis cordyla. Around 1-11% of the catch consisted of incidentally catches of sharks, rays, skates and sail fish. Another 1.6 to 6% of the catch consisted of Selar crumenophthalamus and Rastrelliger kanagurta. The best fishing season appeared to be from June to October in the west coast and August to December in the south coast. The major components of Amblygaster sirm, Sardinella albella and Sardinella gibbosa were caught within the size ranges of 10.0-22.5 cm, 11.0-13.0 cm and 11.0-15.0 cm respectively. However, smaller sized fish of above species of sizes between 6.9 cm to 9.7 cm total length were incidentally caught in the gill nets operated for small Engraulids with a stretched mesh size of 1.6cm. The overall catch rate for the major fish landing centre at Negombo indicated an increase from 38.5 kg/boat trip during 1984-1990 period to 49.5 kg/boat trip during 1995-1997 period. The catch rate for the dominant species Amblygaster sirm has decreased from 28.17 kg/boat trip during 1983-1990 period to 17.47 kg/boat trip during 1995-1997 period at Negombo. The paper also discusses the changing overall catch rates, change in species abundance and possible management consequences that should be considered.

A report of the fisheries catch assessment surveys in the Ugandan waters of Lake Victoria for November 2005

The fisheries of Lake Victoria have undergone many changes in the recent past which have been characterized by shifts in abundance of different fish Species and changes in fishing effort. Monitoring of the population dynamics as well as the magnitude, distribution and trends of fishing effort and fish Catches is probably more necessary now than ever before for sound management of the fisheries of the lake. This will enable the formulation of appropriate fisheries policies and legislation to ensure that the fisheries are sustainable. One of the avenues to collect information to support the above process is through conducting regular Catch Assessment Surveys (CASs). The EU funded Implementation of a Fisheries Management Plan (IFMP) project for Lake Victoria through the Lake Victoria Fisheries Organization (LVFO) is supporting the implementation of regionally harmonized CASs in Lake Victoria. The CASs under IFMP are following a statistically design laid down in Standard Operating Procedures (SOPs) agreed around the whole lake. In the Ugandan part of the lake, the CASs are carried out at 54 fish landing sites selected in the eleven districts sharing the lake. They are jointly conducted by the Fisheries Resources Research Institute (FIRRI), Jinja; the Department of Fisheries Resources (DFR), Entebbe; and the Districts of Busia, Bugiri, Mayuge, Jinja, Mukono, Wakiso, Kampala, Mpigi, Masaka, Kalangala and Rakai. The CAS enumerators are recruited from the fishing communities and work under direct supervision of sub county Fisheries Officers. It is planned to involve the recently formed Beach Management Units (BMUs) in fisheries data collection when modalities for their roles have been streamlined.

A report of the Fisheries Catch Assessment Survey in the Ugandan waters of Lake Victoria for the August 2007 survey

The monitoring of fish stocks as well as the magnitude, distribution and trends of fishing effort and fish catches is required for sound fisheries resources management. Conducting regular Catch Assessment Surveys (CASs) in Lake Victoria is one of the ways through which the partner states sharing the lake are generating information to contribute to the above process. The EU funded Implementation of a Fisheries Management Plan (IFMP) project for Lake Victoria through the Lake Victoria Fisheries Organisation (LVFO) is supporting the implementation of regionally harmonised CASs in Lake Victoria . The CASs under IFMP are following a statistical design laid down in Standard Operating Procedures (SOPs) agreed by the three partner states of the East African Community sharing the lake. In the Ugandan part of the lake, the CASs are carried out at 54 fish landing sites selected in the eleven riparian districts sharing the lake. The National Fisheries Resources Research Institute (NAFIRRI), Jinja; the Department of Fisheries Resources (DFR), Entebbe; and the Districts of Busia, Bugiri, Mayuge, Jinja, Mukono, Wakiso, Kampala, Mpigi, Masaka, Kalangala and Rakai jointly conduct the surveys. The CAS enumerators are recruited from the fishing communities and work under direct supervision of subcounty Fisheries Officers. NaFIRRI seeks to continue strengthening the engagement of the Beach Management Units (BMUs) and other fisheries Co-management Institutions in fisheries data collection .

Morphometry and length-weight relationship of Coilia dussumieri, Valenciennes, 1848 from Mumbai waters

Coilia dussumieri Valenciennes, 1848 a component of 'dol' net fishery forms an important pelagic resource along northwest coast of India. The present communication deals with morphometry and length-weight relationship of this species along Mumbai coast. Morphometric study showed a positive correlation among the compared characters. The length-weight relationship for the species from Mumbai coast was found to be W=0.017L super(2.4223).

Reproductive biology of Otolithes cuvieri (Trewavas, 1974) from Mumbai waters

The reproductive biology of Otolithes cuvieri (Trewavas, 1974) is reported in the present communication. The size at first maturity for the females was estimated to be 275 mm. The spawning activity was observed throughout the year with two peaks occurring in April and June. Two prominent peaks of gonadosomatic index (April and June) also support the view of two major spawning. Relative fecundity ranged from 71,574 to 79,680 eggs per 100g of body weight. Relationship of fecundity with fish length, fish weight and ovary weight of the species has been established as F = -132971 + 1447.441 x L, F = 124195 + 468.798 x W and F = 250517.5 + 3369.029 x OW, respectively. Study of sex ratio by random sampling of the catches indicated the dominance of females in commercial catches of Mumbai coast.

Population dynamics of two jewfishes Jhonius argentatus and Johnieops vogleri) in the coastal waters of Bay of Bengal, Bangladesh

Population parameters of Jhonius argentatus and Johnieops vogleri in coastal waters of Bay of Bengal, Bangladesh were estimated by using FiSAT programme. The von Bertalanffy growth parameters, extreme length (cm) and growth constant K (year ·1) were found to be 46.50 and 0.59 for J. argentatus, and 33.50 and 0.85 for J.vogleri The Loc(cm) and Z/K estimates provided by Wetherall plot were 46.694 and 1.791 for J. argentatus, and 31.25 and 2.623 for J. vogleri. The annual rate of natural (M) and fishing mortality (F) were estimated as 1.12 and 0.78 for J. argentatus, and 1.56 and 1.28 for J. vogleri. Rate of exploitation (E) was estimated as 0.41 for J. argentatus and 0.45 for J. vogleri. About 80.04% of J. argentatus were found to be recruited during peak pulses (April-May) and 19.96% during lean pulses (October-November) and 85.75% J. vogleri during peak pulses (May-July) and 14.25% during lean pulses (September-October). The growth performance index(') was 3.11 for J. argentatus and 1.93 for J. vogleri. The total length and body weight relationship was found to be W = 0.0403 TL25723 for J. argentatus and W = 0.0907 TV3482 for J. vogleri.

Ecology of phytoplankton in the coastal waters of Mangalore, west coast of India

Phytoplankton cell count, percentage composition and species diversity at 4 locations of different depth contours in the coastal waters of Mangalore, west coast of India were studied for a period of 8 months. A total of 27 genera of phytoplankton were recorded from the area of which 20 belonged to diatoms, 6 /dinoflagellates and 1 blue-green algae. On an average the population density was higher at 4 m depth contour (280.48xl04 cells/m3 ) than 8m depth contour (97.79xl04 cells/m3 ). The plankton cell density in the present study is much higher than the earlier observations made elsewhere which might be due to intense blooming of Chaetoceros, Cosctnodiscus, Ceratium, Dinophysis and blue-green algae along this coast during the study period.

Length-weight relationship and condition factor of Perna viridis (Linnaeus, 1758) and Meretrix meretrix (Linnaeus, 1758) from Mumbai waters

Length weight relationship of the two commercially important molluscs P. viridis and M. meretrix was found to be W=-0.40263L super(2.044719) & W=-0.04359L super(2.2315498) respectively. Condition factor was recorded to be less than 1.0 for most part of the year in P. viridis and for M. meretrix it ranged from 0.39 to 4.61. The present study reveals that there was allometric growth in both the species and the growth was not satisfactory since it showed lower K-value during most part of the year.

Biology of Bombay duck, Harpodon nehereus (Ham., 1822), from Mumbai waters, India

Morphometric and meristic study of Harpodon nehereus (Hamilton, 1822) from Mumbai waters indicated that the specimens belonged to a homogenous population. Based on the meristic study, the fin formula can be written as B sub(23-269), D sub(12-139), P sub(11-139), V sub(9), A sub(13-15), C sub(19), L sub(40). Length-weight study revealed an allometric relationship, presented as Log W= -3.1362 + 3.6059 Log L. The analysis of food and feeding habits revealed the species to be voracious, carnivorous and cannibalistic, feeding mainly on Acetes spp., juveniles of H. nehereus itself, prawns and Coilia dussumieri. The feeding intensity was found to be the maximum during September and November, and also in mature specimens which may be the preparation for the ensuing spawning activity. Reproductive biology indicated two peak spawning seasons in November and March. However, the species as a whole has prolonged breeding season and spawning occurs throughout the year. Average fecundity was estimated as 314 ova/g body weight of fish and the length at which 50% of female specimens mature (Lc sub (50)) was calculated as 255 mm.

Some aspects of the biology of Johnieops sina (Cuvier, 1830) from Mumbai waters

Investigations on food and feeding of Johnieops sina indicated that it feeds mainly on penaeid prawns, Acetes spp. and fishes. Penaeid prawns were found to be its preferred food item. The spawning activity was observed throughout the year with two peaks in February and August, supported by prominent peaks of gonadosomatic index in the same months. The minimum size at first maturity for females was 153 mm. The absolute fecundity ranged from 28,495 to 135,346 eggs for the ovaries weighing 1.30 to 9.49 g.

Natural diet of penaeid prawns in the coastal waters of Mumbai

Foregut contents of eight commercially important species of penaied prawns namely Penaeus merguiensis, Metapenaeus affinis, M. monoceros, M. brevicornis, Parapenaeopsis stylifera, P. hardwickii, P. sculptilis and Solenocera crassicornis were investigated from inshore, nearshore and offshore fishing grounds of Mumbai. Feeding intensity and index of preponderance (IP) of the dietary items were compared statistically for the species, sexes, fishing areas and maturity condition of females. All the species except M. monoceros and P. sculptilis showed that females were better fed than males. The feeding intensity in the three depth-zones was different for M. affinis, M. brevicornis, M. monoceros, P. hardwickii and S. crassicornis, and uniform for P. merguiensis, P. stylifera and P. sculptilis. Acetes spp., prawn remains, polychaetes, benthic crustaceans, foraminifers and fish remains were the important food items of the prawns. Dietary comparison between the two sexes of the species did not show any difference, but mature females of M. monoceros and P. sculptilis had different diets. Comparison of food items for all the species together showed significant difference between the three areas. Crustacean diet was the favorite in the inshore and nearshore, and polychaetes in the offshore waters. All the species except P. hardwickii showed difference in their dietary composition in the three depth-zones. It is concluded that these coexisting species are primarily carnivorous and exhibit diverse food preferences in different depth-zones by browsing on interstitial organisms, chasing epipelagic prey, raptorial predation, scavenging on dead organisms or adopting different temporal abundance to avoid inter-specific competition for food.

Nitrogen-fixing aerobic bacteria and their nitrogenase activity in north Mumbai coastal waters

The effect of the physicochemical parameters of water and soil on the distribution of nitrogen-fixing bacteria and their nitrogen-fixing capacity was studied. Four species of nitrogen-fixing bacteria, e. g. Azotobacter chroococcum, A. vinelandii, A. beijerinckii and A. armeniacus, were recorded from water and soil samples of Mumbai coast. A higher number of bacterial populations were observed in sediment than in water samples. A positive correlation was observed between the dissolved organic matter and nitrogen fixing bacterial populations of water as well as between available phosphorus and the nitrogen-fixing bacteria of sediment. The nitrogen-fixing capacity of A. chroococcum was found to be 1.076 nmol C sub(2) H sub(4)/l/d and that of A. vinelandii was 0.965 nmol C sub(2) H sub(4)/l/d. Station 1 showed higher level of nitrogenase activity in comparison to other four stations.

Heavy metals in certain commercially important finfish off Mahim in Mumbai coastal waters

The coastal water of the metropolitan city of Mumbai has deteriorated due to the indiscriminate discharge of untreated sewage and industrial waste in huge quantities. Mahim creek is one such locality surrounded by a large number of industrial units discharging heavy metals. The accumulation of the heavy metals Cu, Cd, Zn and Pb in finfishes (Coilia dussumeri, Lepturacanthus savala, Harpodon nehereus and Johnieops elongates) from this locality along with that in the sediment was studied. The rate of accumulation of Cu was high compared to Cd, Zn and Pb. A gradual increase in the bioaccumulation of heavy metals was noticed in fishes with increase in average body weight and length, perhaps due to biomagnification. A declining trend in concentration of heavy metals horizontally from inshore to offshore was observed in these fishes.