Ashmole's halo: direct evidence for prey depletion by a seabird

Kedukang fish (Hexanematichthys sagor) is a consumable fish that is widely caught by fishermen and the community. Kedukang fishing is carried out every day in the Percut River, resulting in a decline in its population. This study aims to analyze the population by looking at density, sex ratio, growth pattern, gonad maturity level, gonad maturity index and fecundity of kedukang fish and analyze the relationship between physical-chemical factors of waters with population density of Kedukang fish. Samples were taken using purposive sampling method at 3 observation stations with 2 repetitions. Fish samples were taken using a net fishing gear installed at low tide and lifted at high tide. The results showed that the population density of kedukang fish in Percut River was low ranging from 0.048-0.123 ind/m2. The sex ratio kedukang fish at each observation station has an average of 1:0.5. The growth pattern of fish is allometric negative. The frequency distribution of fish length ranged from 21.5-47.9 cm. The greatest number of fish caught had a length range of 30.3-34.7 cm as many as 9 fish. The level of gonad maturity kedukang fish is dominated by TKG V. The average gonad maturity index of female kedukang fish is highest at the TPI location which is 20.729% and the highest fecundity at station II which is 4622.6. The relationship between the density of the kedukang fish population is very strong and positively correlated with DO, light intensity and nitrate. The population density of kedukang fish was strongly and negatively correlated with pH and phosphate.

Temperature variation is an important factor in Everglade wetlands ecology. A temperature fluctuation from 17 degrees C to 32 degrees C recorded in the Everglades may have significant impact on fish dynamics. The short life cycles of some of Everglade fishes has rendered this temperature variation to have even more impacts on the ecosystem. Fish population dynamic models, which do not explicitly consider seasonal oscillations in temperature, may fail to describe the details of such a population. Hence, a model for fish in freshwater marshes of the Florida Everglades that explicitly incorporates seasonal temperature variations is developed. The model's main objective is to assess the temporal pattern of fish population and densities through time subject to temperature variations. Fish population is divided into 2 functional groups (FGs) consisting of small fishes; each group is subdivided into 5-day age classes during their life cycles. Many governing sub-modules are set directly or indirectly to be temperature dependent. Growth, fecundity, prey availability, consumption rates and mortality are examples. Several mortality sub-modules are introduced in the model, of which starvation mortality is set to be proportional to the ratio of prey needed to prey available at that particular time step. As part of the calibration process, the model is run for 50 years to ensure that fish densities do not go to extinction, while the simulation period is about 8 years. The model shows that the temperature dependent starvation mortality is an important factor that influences fish population densities. It also shows high fish population densities at some temperature ranges when this consumption need is minimum. Several sensitivity analyses involving variations in temperature terms, food resources and water levels are conducted to ascertain the relative importance of temperature dependence terms.

We attempted to discern the contributions of physical habitat, water chemistry, nutrients, and contaminants from historic lead–zinc mining activities on the riffle-dwelling benthic fish community of the Spring River, a midwestern warmwater stream that originates in Missouri and flows into Kansas and Oklahoma. The Spring River has a fish community that includes the Neosho madtom Noturus placidus, a species federally listed as threatened. Although anthropogenic factors such as contaminants limited populations and densities of fishes, an integrated assessment of natural and anthropogenic factors was necessary to effectively estimate the influence of the latter. Fish populations in the Spring River, especially Neosho madtoms, seem to be limited by the presence of cadmium, lead, and zinc in water and in benthic invertebrate food sources and by physical habitat. The population density and community structure of fish in the Spring River also seem to be related to water chemistry and nutrients. Concurrently, diminished food availability may be limiting fish populations at some sites where Neosho madtoms are not found. Many of the natural factors that may be limiting Neosho madtom and other riffle-dwelling fish populations in the Spring River probably are characteristic of the physiographic region drained by the upper reach and many of the tributaries of the Spring River. Our results indicate that competition between the Neosho madtom and other species within the riffle-dwelling fish community is an unlikely cause of Neosho madtom population limitation in the Spring River.

Evaluating the cascade dam construction effects on endemic fish habitat and population status in spawning sites of Lancang River (in Tibet), China

This paper proposes and studies a comprehensive control model that considers fish population density and its current growth rate, providing new ideas for fishing strategies. First, we established a phytoplankton-fish model with state-impulse feedback control based on fish density and rate of change. Secondly, the complex phase sets and impulse sets of the model are divided into three cases, then the Poincaré map of the model is defined and its complex dynamic properties are deeply studied. Furthermore, some necessary and sufficient conditions for the global stability of the fixed point (order-1 limit cycle) have been provided even for the Poincaré map. The existence conditions for periodic solutions of order-k(k≥2) are discussed, and the influence of dynamic thresholds on system dynamics is shown. Dynamic thresholds depend on fish density and rate of change, i.e., the form of control employed is more in line with the evolution of biological populations than in earlier studies. The analytical method presented in this paper also plays an important role in analyzing impulse models with complex phase sets or impulse sets.

The invasion of U.S. east coast salt marshes by common reed (Phragmites australis) and the efforts to remove it and restore marshes to their natural vegetation (Spartina spp.) can directly impact mummichog (Fundulus heteroclitus) as this abundant species is critically linked to marsh habitat. We estimated population density, growth, and biomass to determine production of mummichog in treated Phragmites (''Treated,'' now dominated by Spartina), untreated Phragmites, and naturally occurring Spartina habitats in Delaware Bay using throw traps for small fish (mean 5 24.1 mm standard length or SL, 95% CI 5 10-38) and tag/recapture for large fish (mean 5 36.5 mm SL, 95% CI 5 18-64). Mean population density of small fish on the marsh surface was significantly higher in the Spartina (20.2 fish m 22 ) and Treated (14.1 fish m 22 ) habitats than in the Phragmites (0 fish m 22 ) habitat. Population density of large fish was similar among all three habitats (mean 5 0.9-1.7 fish m 22 ). Mean absolute growth rates of large fish were significantly higher in the Spartina (0.24 mm d 21 ) and Treated (0.24 mm d 21 ) habitats than in the Phragmites (0.13 mm d 21 ) habitat. Mean monthly mummichog production during June to September varied among habitats with Spartina highest (1.22 g dw m 22 mo 21 ), Treated intermediate (0.51 g dw m 22 mo 21 ), and Phragmites lowest (0.07 g dw m 22 mo 21 ). Small fish were the largest contributor to the production estimates in Spartina and Treated habitats. The Phragmites habitat had little or no standing water at low tide (i.e., optimal habitat for small fish was lacking), and thus, it had the lowest production for mummichog. These results also indicated that Treated marshes were more similar to Spartina than to Phragmites habitat; therefore, it appears that habitat quality and mummichog production can be increased with restoration.

Fish density models are essential tools for fish ecologists and fisheries managers. However, applying these models can be difficult because of high levels of model complexity and the large number of parameters that must be estimated. We designed a simple fish density model and tested whether it could predict fish densities in lotic systems with meaningful levels of accuracy and precision. We built our 6-parameter model on 2 key assumptions: 1) fish population density is a power function of mean body mass (i.e., the self-thinning relationship), and 2) energetic resources are transferred from lower to higher trophic levels at a nearly constant rate (i.e., trophic transfer efficiency). We estimated the self-thinning and trophic transfer efficiency parameters by randomly sampling from values reported in the primary literature. Remaining parameters were net primary production, trophic level, the production∶biomass ratio, and mean body mass. We used empirical parameter estimates and fish density estimat...

The development of an ant colony's foraging range

The significance of risk assessment in determining the boundaries of foraging ranges of deer mice and voles was examined by comparing the distances to which resident animals were willing to follow shifting feeding stations providing equal rewards beyond their previous foraging ranges in an area with abundant cover (forest), and in one where cover was lacking (frozen lake surface). Previous foraging ranges were estimated on the basis of livetrapping and the "rediscovery distances" for the moving stations. In three experiments the distance at which animals stopped visiting the stations ("giving-up distance") averaged 3.3 times farther where cover was abundant (forest) than where it was absent (lake). In a fourth experiment, reduction of supplementary food available within the original ranges extended the giving-up distance where cover was present but had relatively little effect on giving-up distance and almost no effect on rediscovery distance where cover was absent. Supplying cover more than tripled giving-up distances on the lake. The distance at which boxes were visited was affected by snowfall, ambient temperature, food supply, and availability of cover. Results emphasize the importance of risk assessment in defining foraging range, and suggest that hoarding permits choice among energy maximization and time minimization strategies.

The coral reef of Cabo Pulmo is located at the southern tip of the Baja California Peninsula, near the big tourist development in Los Cabos, Mexico. The reef and adjacent areas are highly valued by sport and artisanal fishermen, by aquarium collectors, and by skin and scuba divers from many countries, because it is the most pristine and scenic, and also the most threatened, submarine habitat in Baja California. Research and assessments carried out since 1988 have shown an increasing environmental impact of extractive actions resulting in a decline of coral cover and density of fish, mollusc and other marine populations, generating negative effects in the only coral reef in the Gulf of California. The main purpose of this study was to develop a rigorously planned management strategy to improve the health of the environment and the quality of life of the human population of Cabo Pulmo. The first objective was to evaluate the system and its environmental components as well as the economic and social ones, and their changes in the last 20 years. The methods used included micro region zoning through a Geographical Information System and capacity of use evaluation, integrating the physical, biological, economical and social characteristics of the study area. Based on the evaluation of indexes of fragility, pressure, and vulnerability, 31 environmental units were proposed. Results showed that the predominant environmental policy would be a conservation and protection policy in 48%, sustainable management within 40% of the total area, and restoration in 12%. The sites with the highest human impact would need an environmental management policy, with the encouragement of sustainable tourism, while eliminating and further excluding any extreme use or high density traditional tourism. Many workshops and meetings have been organized to recommend management actions focusing on sustainable tourism and to discuss how to tailor Tourism and Environment 59 www.witpress.com, ISSN 1755-8336 (on-line) WIT Transactions on State of the Art in Science and Engineering, Vol 69, © 2013 WIT Press doi:10.2495/978-1-84564-808-4/006 specific features. After more than 20 years, a recent evaluation of this coralline system, now a National Park, demonstrated that the quality of life of the local inhabitants has improved, and that there is a healthier ecosystem, with coral recovery, many sea turtles, whales, sharks, other fish and invertebrates.

Seagrass meadows are often important habitats for newly recruited juvenile fishes. Although substantial effort has gone into documenting patterns of association of fishes with attributes of seagrass beds, experimental investigations of why fish use seagrass habitats are rare. We performed two short-term manipulative field experiments to test (1) the effects of food supply on growth and densities of fish, and (2) effects of predation on the density and size distribution of fish recruits, and how this varies among habitat types. Experiments were conducted in Galveston Bay, Texas, and we focused on the common estuarine fish, pinfish Lagodon rhomboides. In the first experiment, replicate artifical seagrass and sand plots were either supplemented with food or left as controls. Recruitment of pinfish was significantly greater to seagrass than sand habitats; however, we detected no effect of food supplementation on the abundance of recruits in either habitat. Pinfish recruits in artifical seagrass grew at a significantly faster rate than those in sand habitats, and fish supplemented with food exhibited a greater growth rate than controls in both sand and artifical grass habitats. In our second experiment, we provided artificial seagrass and sand habitats with and without predator access. Predator access was manipulated with cages, and two-sided cages served as controls. Recruitment was significantly greater to the cage versus cage-control treatment, and this effect did not vary between habitats. In addition, the standard length of pinfish recruits was significantly larger in the predator access than in the predator exclusion treatment, suggesting size-selective predation on smaller settlers or density-dependent growth. Our results indicate that the impact of predation on pinfish recruits is equivalent in both sand and vegetated habitats, and thus differential predation does not explain the higher recruitment of pinfish to vegetated than to nonvegetated habitats. Since predators may disproportionately affect smaller fish, and a limited food resource appears to be more effectively utilized by fish in vegetated than in unvegetated habitats, we hypothesize that pinfish recruits may select vegetated habitats because high growth rates allow them to achieve a size that is relatively safe from predation more quickly.

The experiment was carried out under three treatments each with two replications. Fish population density was 80 fish per decimal (silver carp 32, tilapia 32 and mrigal 16) under treatment-1, 120 fish per decimal (silver carp 48, tilapia 48 and mrigal 24) under treatment-2 and 160 fish per decimal (silver carp 64, tilapia 64 and mrigal 32) under treatment-3. The average initial length and weight of the fingerlings of silver carp, tilapia and mrigal were 7.49, 5.12, and 5.56 cm and 8.00, 2.00 and 1.50 g respectively. The ponds were fertilized fortnightly with cowdung, urea and TSP (triple super phosphate) at the rates of 5 kg, 60 g, and 90 g per decimal, respectively. During the experimental period, the range of water temperature (30.20 to 32.90°C), transparency (28 to 38 cm), dissolved oxygen (8.20 to 10.60 mg/L), pH (6.90 to 7.90), total alkalinity (92.00 to 127.00 mg/L), free CO2 (1.00 to 1.60 mg/L), phosphate-phosphorus (1.00 to 1.90 mg/L), and nitrate-nitrogen (1.90 to 3.90 mg/L) were within the productive range and more or less similar in all the ponds under three treatments. There were 25 genera of phytoplankton under five major groups and 10 genera of zooplankton under three major groups in the experimental ponds. The calculated net fish production of the ponds under treatment-1 was 2.62 ton/ha/yr and that of the ponds under treatment-2 was 4.42 ton/ha/yr and that of the ponds under treatment-3 was 5.18 ton/ha/yr. The net fish production under treatment-2 and treatment -3 were 195.58% and 229.20% higher than that of treatment-1, taking net fish production under treatment-1 for 100%. According to profit-cost analysis the ratios of net profit and total cost under treatments 1, 2, and 3 were 1:0.25, 1:0.45, and 1:0.44. According to growth and production treatment-3 is the best, and according to the profit-cost analysis, treatment-2 (ratio 1:0.45) is the best but it is almost same to that of treatment-3. So, the population density of 160 fish per decimal (under treatment-3) might be considered best. It seems that proper determination of stocking density of different fishes in polyculture is very important to increase fish production.DOI: http://dx.doi.org/10.3329/pa.v23i1-2.16566Progress. Agric. 23(1 & 2): 63 – 73, 2012

Seabird foraging ranges as a preliminary tool for identifying candidate Marine Protected Areas

River rehabilitation initiatives have become commonplace in European water courses as a result of European Union Water Framework Directive requirements. However, the short‐term responses of fishes to such work have thus far been varied, with some river rehabilitation efforts resulting in demonstrable improvements in diversity and size structure, whereas others have resulted in little or no change. Electrofishing and channel character surveys were conducted annually between 2009 and 2014 on a reach of the River Glaven (North Norfolk, UK) before and after rehabilitation work (embankment removal in 2009 and re‐meandering in 2010) as well as on a control reach immediately upstream. To assess the effects of rehabilitation work, before‐after‐control‐impact analysis tested for changes in channel character (geomorphology, substratum composition, and mesohabitat structure) and in fish species richness, relative abundance, population density, and size structure (calculated after fish data entry into the UK Environment Agency's National Fisheries Population Database). Following re‐meandering work (i.e., treatment), habitat heterogeneity and depth variation increased in the treatment reach, but fish responses were not significant except for biomass and density increases of brown trout Salmo trutta and abundance decreases of European eel Anguilla anguilla, in the treatment but not the control reach. These results are consistent with comparable river rehabilitation initiatives elsewhere, and they suggest that larger‐scale rehabilitations are probably needed to produce greater increases in fish density and diversity. It is recommended that future rehabilitation initiatives address catchment‐scale factors that can enhance ecosystem recovery, for example, removal of barriers to colonization, and increases in connectivity and water quality issues linked to eutrophication, elevated fine sediment inputs, and various pollutants.

Density-dependent depletion of prey during the breeding season may affect breeding performance and colony development in seabirds and colonial waterbirds. Breeding Great Cormorants Phalacrocorax carbo sinensis are central place foragers, so parental flight distances to profitable foraging grounds and thus parental provisioning of offspring are likely affected by local food availability. Chick body condition in a given colony may therefore be influenced by the distance to feeding areas, changes in fish stocks and fish distribution as well as the number of Cormorants from neighbouring colonies using the same feeding areas. At three Danish Great Cormorant colonies with overlapping foraging ranges and variable access to shallow marine areas, Vorsø (VO), Mågeøerne (MA) and Stavns Fjord (SF), we investigated variation in mean chick body condition (n = 9697) in relation to colony location, year, colony size and estimated density of foraging conspecifics during 1993–2007. Foraging areas available to VO colony parents had the highest theoretical densities of conspecifics and the VO chicks were invariably in poorer condition than the chicks at the other two colonies. Chick body condition was negatively correlated with estimated foraging density, especially within a foraging range of 20 km. Body condition between all three colonies was weakly correlated over the years, suggesting that changes in macro-environmental conditions (e.g. fish density) only had moderate impacts on food availability, independently of Cormorant numbers. We conclude that both the geographical location of colonies, the size of the colony itself and the nearest neighbouring colonies and the associated variation in density of foraging Cormorants were major drivers of variation in chick body condition between colonies and years.