Diets of thornback ray (Raja clavata) and tope shark (Galeorhinus galeus) in the bottom longline fishery of the Azores, northeastern Atlantic

Tope shark (Galeorhinus galeus) and thornback ray (Raja clavata) are the two most captured elasmobranch species by the Azorean bottom longline fishery. In order to better understand the trophic dynamics of these species in the Azores, the diets of thornback ray and tope shark caught in this area during 1996 and 1997 were analyzed to describe feeding patterns and to investigate the effect of sex, size, and depth and area of capture on diet. Thornback rays fed mainly upon fishes and reptants, but also upon polychaetes, mysids, natant crustaceans, isopods, and cephalopods. In the Azores, this species preyed more heavily upon fish compared with the predation patterns described in other areas. Differences in the diet may be due to differences in the environments (e.g. in the Azores, seamounts and oceanic islands are the major topographic features, whereas in all other studies, continental shelves have been the major topographic feature). No differences were observed in the major prey consumed between the sexes or between size classes (49−60, 61−70, 71−80, and 81−93 cm TL). Our study indicates that rays inhabiting different depths and areas (coastal or offshore banks) prey upon different resources. This appears to be related to the relative abundance of prey with habitat. Tope sharks were found to prey almost exclusively upon teleost fish: small shoaling fish, mainly boarfish (Capros aper) and snipefish (Macroramphosus scolopax), were the most frequent prey. This study illustrates that thornback rays and tope sharks are top predators in waters off the Azores.

Food habits and consumption rates of common dolphinfish (Coryphaena hippurus) in the eastern Pacific Ocean

An ecosystem approach to fisheries management requires an understanding of the impact of predatory fishes on the underlying prey resources. Defining trophic connections and measuring rates of food consumption by apex predators lays the groundwork for gaining insight into the role of predators and commercial fisheries in influencing food web structure and ecosystem dynamics.We analyzed the stomach contents of 545 common dolphinfish (Coryphaena hippurus) sampled from 74 sets of tuna purse-seine vessels fishing in the eastern Pacific Ocean (EPO) over a 22-month period. Stomach fullness of these dolphinfish and digestion state of the prey indicated that diel feeding periodicity varied by area and may be related to the digestibility and energy content of the prey. Common dolphinfish in the EPO appear to feed at night, as well as during the daytime. We analyzed prey importance by weight, numbers, and frequency of occurrence for five regions of the EPO. Prey importance varied by area. Flyingfishes, epipelagic cephalopods, tetraodontiform fishes, several mesopelagic fishes, Auxis spp., and gempylid fishes predominated in the diet. Ratios of prey length to predator length ranged from 0.014 to 0.720. Consumption-rate estimates averaged 5.6% of body weight per day. Stratified by sex, area, and length class, daily rations ranged up to 9.6% for large males and up to 19.8% for small dolphinfish in the east area (0–15°N, 111°W–coastline). Because common dolphinfish exert substantial predation pressure on several important prey groups, we concluded that their feeding ecology provides important clues to the pelagic food web and ecosystem structure in the EPO.

The influence of seasonal precipitation and temperature variations on runoff in California and southwestern Oregon

EXTRACT (SEE PDF FOR FULL ABSTRACT): There is considerable seasonal-to-interannual variability in the runoff of major watersheds in the Sierra Nevada, Coastal, and Cascade ranges of California and southwestern Oregon. This variability is reflected in both the amount and timing of runoff. This study examines that variability using long historical streamflow records and seasonal mean temperature and precipitation. ... Precipitation is the only significant predictor for both amount and timing of runoff in the low elevation basins. As elevation increases, the models rely more and more on temperature to explain amount and timing of runoff.

Regional context of the climate of H.J. Andrews Experimental Forest, Oregon

H.J. Andrews Experimental Forest is a 6400 ha forest of Douglas fir, western hemlock, and Pacific silver fir located in, and typical of, the central portion of the western slope of the Cascade mountain range of Oregon. The forest is one of 19 sites in the Long-Term Ecological Research (LTER) program sponsored by the National Science Foundation. ... Because of the scientific significance of Andrews Forest, it is important to investigate the temporal variability of annual and seasonal temperature and precipitation values at the site and identify past times of anomalous climatic conditions. It is also important to establish quantitatively the relationships between the climate of Andrews Forest and that of its surrounding area and, hence, place the climate of Andrews Forest into its regional context.

Potential solar radiation at H.J. Andrews Experimental Forest, Oregon

EXTRACT (SEE PDF FOR FULL ABSTRACT): Potential (clear-sky) radiation receipt is modeled for the slopes of the H.J. Andrews Experimental Forest Long-Term Ecological Research site in the foothills of the southern Cascade mountains of central Oregon. The modeling method developed by Williams is selected and applied to the forest area for the times of the solstices and equinox as well as mid-month times in January, February, April, and May in order to completely characterize the seasonal change of potential radiation at the location. ... It seems that Lookout Creek approximately divides the Andrews Forest into an area of relatively high potential radiation to the north of the creek and relatively lower potential radiation values to the south of the creek. Potential radiation values seem to be associated with the Andrews GIS data layers of debris flows and predominant tree species zones.

Biological productivity and fishery potential in the coastal waters off Bombay

Fishery potential of the nearshore waters of Bombay is estimated from the observed values of biological productivity at different trophic levels. The rate of primary and secondary production is relatively higher in the polluted coastal waters of Versova, Mahim and Thana. Observed mean benthic standing stock in the polluted creek waters is far less than the relatively unpolluted coastal regions off Bombay. Results suggest that the higher productivity at the lower trophic levels due to pollution, may not end up with high tertiary production. Therefore, such polluted regions are to be classified as special ecosystems where the transfer coefficient may be far less than the assumed 10% conversion factor.

Marine pollution and zooplankton: some recent trends in marine pollution studies

The presence of even very minute quantities of pollutants may become harmful either due to their direct effect on zooplankton or indirectly due to the transfer of the pollutants to other trophic levels through zooplankton. The recent trend in marine pollution studies is therefore to find out the effects of very minute quantities of these pollutants on marine zooplankton and the methods of their accumulation and transfer to the organisms of higher trophic level including man. A review of laboratory and field studies concerning the effects of pollutants such as hydrocarbons, crude oil, heavy metals, pesticides and heated waste water on the survival, breeding, movement, faecal pellet production, growth and development on marine zooplankton is presented.

East African Freshwater Fisheries Research Organization Annual Report 1972

Feeding habits of many animals have been used widely in animal classifications. This is so, because the type of diet an organism requires demands structural specialisation which will utilise the available resource. Many animals may however have many structural modifications to enable them to be described as omnivourous or generalised feeders such as H. empodisma and H. riponianus (GREENWOOD 1960) which may show varying degrees of structural and adaptational intermediacy between two trophic groups. Generally, however, the diet of many animals including fish changes as the animal grow larger. The change in structural modifications is usually correlated with changes in the diet. In fishes the change may involve change from tricuspid to biscuspid and finally to unicuspid type of teeth. The degree of modification in the structure depends on the diet, thus Haplochromis that feeds on soft tissues of snails only requires modifications in oral dentition while Haplochromis that feeds on both soft tissues and shells of snails require modification in the lower pharyngeal bone for grinding purposes. Other modifications connected with food utilisation may be located in the alimentary canal. (I) The fish species that are commercially exploited are Protopterus aethiopicus, Clarias mossambicus, Tilapia esculenta, Tilapia amphimelas and Tilapia hybrids. The other fish species present in the lake but not commercially exploited are: Gnathonemus sp. Alestes sp. Labeo sp., Barbus paludinoses, Barbus jacksoni, Barbus lineomaculatus, Barbus regersi, Leptogrlanis sp., Schilbe sp., Haplochromis spp. and Hemihaplochromis sp. (2) Protopterus sp. and Clarias sp. are mostly caught with hooks on long lines. There has been a steady increase in number of hooks on the lake. Since the stocks of Protopterus and C/arias in the lake have a limit, we should control the number of hooks used by each of the fishermen in order to avoid overharvesting. (3) All the previous studies on Lake Kitangiri fisheries suggested the use of gill nets with mesh size greater than 88.9 mm in order to avoid the capture of immature Ti/apia spp. But if the fishermen are to obtain economic gains from the fishery, the optimum mesh size for use is 88.9 -101.6 mm. (4) The gillnet is a passive gear with very beneficial selective characteristics. Unfortunately the drive-in fishery which exists on Lake Kitangiri more or less destroys the gillnet selectivity characteristics. It is therefore recommended that the beating of water with poles be discouraged and stopped. (5) There is need for provision of stable fishing canoes to replace the unstable bottle palm dug-out canoes which are currently being used and which are very risky to operate. (6) The fish processing facilities on Lake Kitangiri are still inadequate. Most of the fish is sun dried, Since sun drying is very difficult during the rainy season, most fishermen carry out intensive fishing during the dry season, Concentrating most of the fishing effort in anyone season instead of spreading evenly this effort over the whole year could damage the age structure of the exploitable stocks. (7) There are considerable fluctuations in the volume of water of the lake. The feasibility of regulating the water loss through the effluent Sibiti river should be investigated by the Water Development Department. (8) Damming the Sibiti river is an expensive undertaking and therefore, the Rural Development Bank of Tanzania should be asked to assess the economic feasibility of such a project.

Morphological overlap of fish community in Vamanapuram River, south Kerala

The morphological characteristics and overlap of fish community in Vamanapuram River have been studied in detail. In the 12 study sites, 19 fish species were encountered. Based on the body shape, four different types are apparent. The elongate bodied fishes (RBD<1.5) like Hemiramphus xanthopterus and Xenentodon cancila are grouped under one category. The deep bodied fishes (RBD>3.5) like Puntius filamentosus, P. ticto, P. vittatus, P. melanampyx, P. sarana, Etroplus maculatus and E. suratensis come under a separate category. Fishes with round to square cross section like Garra mullya and Glossogobius giuris form a separate group. All the other species are grouped as generalized bodied fishes. The morphological overlap studied for the Vamanapuram fish community showed that out of 190 combinations, 30 combinations have high overlaps (≥ 67). P. melanampyx has maximum number (6) of high overlaps. Puntius spp., which constituted 49.5% of the total population, have a mean morphological overlap of 52%. The morphological overlap of fish species in relation to the trophic structure is discussed in detail.

On the importance of Mesopodopsis zeylanica (Crustacea, Mysidacea) as food of fish.

This investigation was aimed at ascertaining the actual consumers of Mesopodopsis zeylanica, to assess its importance in the trophic relationship within the habitat.

A study on the piscifauna of the Idukki Reservoir and catchment area

From the area under report 17 species, 15 endemic and 2 exotic, of freshwater fish have been identified. Of these, 8 species are commonly found in the catches and are of fishery significance. The fact that small fish species which have no fishery importance also support life in other trophic levels of this ecosystem is well exemplified by the interaction of the birds and mammals with these species. A scientific management and monitoring of the reservoir waters as well as the remaining segments of forests are recommended to salvage the wild life and vegetation from a possible rapid deterioration within years.

Impact of plankton structure on primary productivity in two beels of West Bengal, India

Planktonic community in floodplain wetlands embodies the energy transfer through this phase and indicates trophic status of lake. Originally rich bottom coupled with a conducive physicochemical environment encourages fast colonization of the plankton population. Present investigation was carried out in two floodplain wetlands having characteristics of open (Amda beel) and closed (Suguna beel) system. The physicochemical parameters of water and soil of the investigated heels were by and large conducive for planktonic growth. The density of plankton population varied between 1,346 and 2,170 u/l in Suguna bed whereas in Amda beel it ranged from 1,030 to 1,802 u/l. Seasonal fluctuations in water column were conspicuous and mostly dependent on the replenished resources and volume, A mixed and balanced population of diversified fauna constituted the plankton population of the investigated ecosystems. Mostly the diversity was observed to be maximum during winter seasons with coincidence of favorable temperature, dissolved oxygen and other physico-chemical parameters of water besides optimum solar penetration. Richness of planktonic structure in closed system (Suguna) resulted in higher fish production (1,570,05 kg/ha/yr) than that of open system (Amda) (384.4 kg/ha/yr).

Assessing potential of production in Lake Choghakhor

Phytoplankton productivity is the common and important factor being considered in determining the overall status of a given body of water. This is because they are found at the base of an energy or food chain, being the basic source of primary food in a given aquatic system. Hence, information on their contribution is essential in indicating how much biomass energy will be available to all other living resources in the system. Though the primary productivity of shallow lakes is characterized by mixed populations of phytoplankton and submersed aquatic vegetation in the open water. Lake Choghakhor, is a shallow lake, located in Chaharmahal-Bakhtiyari Province. This lake is the most important ecosystem in the region especially for waterfowl populations, has a recreational value and supports tourism and fisheries. During last decade Choghakhor has been influenced by some man-made impacts such as water level fluctuation, agricultural discharge and fish (Cyprinids) introduction causing a serious problem in its trophic states. So water quality for physical, chemical and biological was monitored in five sampling stations, from April 2003 to March 2004. As biological parameters we studied phytoplankton, epiphytic algae, and zooplankton and macrobenthose community structure. Chlorophyll a content for phytoplankton and epiphytes was measured to estimate production of these groups (biomass over time). Also we determined biomasses of submersed macrophytes and macrobenthose and primary production of phytoplankton (dark and light bottles technique) to estimate fish production. The results of this study showed Lake Choghakhor did not undergo stable thermal and oxygen stratification, and the lake water was mixed throughout the study (the lake mixing regime is polymictic). Now submerged plants especially Myriophyllum spicatum has covered almost the entire lake and dense macrophyte beds (Polygonom amphibium), located on the east southern end of the lake appear to act as a sink for these nutrients. Lake Choghakhor appeared to be in a macrophyte dominated clear water state with low TP (annual mean: 24± 15μg.l-1) and chlorophyll a (annual mean: 3±1.28μg.l-1) concentrations and very high Secchi depth. The grazing pressure of dominant pelagic filtering zooplankton Daphnia longespina did not seem to be significant in determining the low phytoplankton crop expressed as chlorophyll a. We expect that sequestering of nutrients by submerged plants and associated epiphytes are the dominant stabilizing mechanisms suppressing the phytoplankton crop of Lake Choghakhor.

Impact of mangrove conversion

The article presents the impact of mangrove conversion on fisheries and on coastal areas. The mangrove areas which serve as nursery grounds for important species of fish and crustaceans are also rich feeding ground for many species from various trophic levels. Thus, the destruction of mangroves could affect the availability of fry and broodstock and, consequently, aquaculture production and fisheries. While in coastal areas, the destruction of mangroves increased the risk of coastal erosion from storm surges and winds, accelerates the erosion of riverbanks, exposes acid sulfate soils, leading to poor production and mass mortality of stocks, and affects the freshwater supply through salt intrusion upstream among others.

The major aquatic systems of the Victoria and Kyoga lake basins

The Victoria and Kyoga lake basins form the major aquatic system of this study (Fig. I). The two lake basins share a common evolutionary history and have similar native fish faunas (Graham 1929, Worthington 1929). The two main lakes have also had similar impacts by introduction of Nile perch Lates niloticus and therefore these two lakes can be considered to be similar for ichiogeographical purposes. These lake basins have many satellite lakes isolated from one another and from the main lakes Victoria and Kyoga by swamps and other barriers. Some of these satellite lakes still possess stocks of endemic fish species which are almost extinct from the main water bodies. It was therefore considered that understanding of these lakes would contribute to the knowledge base required to solve some of the problems experienced in Lake Victoria and Kyoga especially the loss in trophic diversity arising. The study was carried out in these two main water bodies (Kyoga and Victoria) and on other satellite lakes e.g Wamala, Kachera, Mburo, Kayanja and Kayugi in the Victoria lake basin and lakes Nawampasa, Nyaguo, Agu, Gigate, Lemwa and Kawi in the Kyoga lake basin (Figs. 2, 3, 4, 5 & 6).