Density Of Small Fishes Research Articles

Preventing extinction in <i>Rastrelliger brachysoma</i> using an impulsive mathematical model

<abstract><p>In this paper, we proposed a mathematical model of the population density of Indo-Pacific mackerel (<italic>Rastrelliger brachysoma</italic>) and the population density of small fishes based on the impulsive fishery. The model also considers the effects of the toxic environment that is the major problem in the water. The developed impulsive mathematical model was analyzed theoretically in terms of existence and uniqueness, positivity, and upper bound of the solution. The obtained solution has a periodic behavior that is suitable for the fishery. Moreover, the stability, permanence, and positive of the periodic solution are investigated. Then, we obtain the parameter conditions of the model for which Indo-Pacific mackerel conservation might be expected. Numerical results were also investigated to confirm our theoretical results. The results represent the periodic behavior of the population density of the Indo-Pacific mackerel and small fishes. The outcomes showed that the duration and quantity of fisheries were the keys to prevent the extinction of Indo-Pacific mackerel.</p></abstract>

A preliminary analysis of the correlation of food-web characteristics with hydrology and nutrient gradients in the southern Everglades

We estimated trophic position and carbon source for three consumers (Florida gar, Lepisosteus platyrhincus; eastern mosquitofish, Gambusia holbrooki; and riverine grass shrimp, Palaemonetes paludosus) from 20 sites representing gradients of productivity and hydrological disturbance in the southern Florida Everglades, U.S.A. We characterized gross primary productivity at each site using light/dark bottle incubation and stem density of emergent vascular plants. We also documented nutrient availability as total phosphorus (TP) in floc and periphyton, and the density of small fishes. Hydrological disturbance was characterized as the time since a site was last dried and the average number of days per year the sites were inundated for the previous 10 years. Food-web attributes were estimated in both the wet and dry seasons by analysis of δ15N (trophic position) and δ13C (food-web carbon source) from 702 samples of aquatic consumers. An index of carbon source was derived from a two-member mixing model with Seminole ramshorn snails (Planorbella duryi) as a basal grazing consumer and scuds (amphipods Hyallela azteca) as a basal detritivore. Snails yielded carbon isotopic values similar to green algae and diatoms, while carbon values of scuds were similar to bulk periphyton and floc; carbon isotopic values of cyanobacteria were enriched in C13 compared to all consumers examined. A carbon source similar to scuds dominated at all but one study site, and though the relative contribution of scud-like and snail-like carbon sources was variable, there was no evidence that these contributions were a function of abiotic factors or season. Gar consistently displayed the highest estimated trophic position of the consumers studied, with mosquitofish feeding at a slightly lower level, and grass shrimp feeding at the lowest level. Trophic position was not correlated with any nutrient or productivity parameter, but did increase for grass shrimp and mosquitofish as the time following droughts increased. Trophic position of Florida gar was positively correlated with emergent plant stem density.

Small fish communities in two regions of the Liangzi Lake, China, with or without submersed macrophytes

Small fish communities were compared between the vegetated and vegetation-free regions of the Liangzi Lake, a shallow lake along the middle reach of the Yangtze River, China. Fish were sampled using 10 x 10 m(2) block nets and poisoning. Three samples were taken from either the near shore area or lake centre of each region. A total of 19 fish species were collected; all species occurred in the vegetated region but only 12 occurred in the vegetation-free region. The dominant small fish were Carassius auratus auratus in the vegetated region and Ctenogobius giurinus in the vegetation-free region. Diversity, density and biomass of small fishes were significantly higher in the vegetated region than in the vegetation-free region in both near shore and lake centre areas. In the vegetated region, density and biomass of small fishes was significantly higher, while species diversity significantly lower in the near shore area than in the lake centre. In the vegetation-free region, density of small fishes was significantly higher in the near shore area than in the lake centre area, but species diversity or biomass was unaffected by location.

Fish Associations with Four Habitat Types in a South Dakota Prairie Stream

ABSTRACT Fish were collected from riffles, runs, pools and woody habitats in the Vermillion River, South Dakota, to examine the temporal dynamics of habitat use during non-flood summer months. The densities of small fishes (30–75 mm; cyprinids and young-of-the-year individuals) were greatest in riffles and woody habitats during periods of moderate discharge (1.14 and 1.44 m3/s); however, their densities were greater in rimes than other habitats during late summer low flow (0.49 m3/s). Large fishes (> 75 mm; juvenile and adult individuals of several species) were distributed evenly among habitats across flow levels. During moderate stream flows, 89% and 95% of the individual species and size classes exhibited random use of habitats. In contrast, 35% of the individual species collected during late summer low stream flows exhibited preferences for two or three habitats, but only one species (central stoneroller Campostoma anomalum) exhibited a preference for a single habitat type (riffles). We found little evidence for the existence of discrete habitat guilds of fish because neither individual species nor groups of species consistently associated with a single habitat type. We suggest a community-level approach based on the combined densities of small and young-of-the-year fishes, rather than an individual species or guild approach, be used to define fish associations with habitat in hydrologically variable prairie streams because discrete patterns of habitat use exist at the community level.