Differentiation in morphometric traits of Chanos chanos stocks along the Indian coast

233-238Stocks of Chanos chanos (Milkfish) are identified based on the morphometric traits from four different locations from the Indian coast. A total of 246 fish samples were collected for the present study from the East coast (Mandapam Lagoon and Chilika Lake) and West coast (Mandovi–Zuari estuarine system and Cochin backwaters). Digital imaging techniques were employed to extract 18 morphometric characters from the specimens. Principal component analysis showed that horizontal depth measurements, dorsal fin length and pelvic fin length were helpful in differentiating the milkfish populations. First and second principal components explained the variance of 37.62% and 31.26 % respectively. Cross-validated results of the discriminant analysis showed the overall classification rate of 90.4%. The present study decoded the differentiation and occurrence of separate stocks of milkfish in Indian waters. The findings of the present study could be utilized for conservation and management of the species

Reproductive Behaviour and Urinary Signals in the Round Goby Neogobiud Melanostomus

In studying chemical communication, it is important to characterize how olfactory signals are released and dispersed by the producer before investigating how signals are interpreted by the receiver. In the present study, I used dye injections and a particles image velocimetry technique to characterize the release and dispersion of urine signals by male round gobies. I found that male round gobies release urine signals passively and do not modulate their urination in the presence of reproductive females. Additionally, males use repeated tail flippings to generate currents that disperse pheromones in the environment and enhance the detection of this coumpounds by females. Thus, males can advertise their reproductiveness without leaving the nest. Ultimately, the characterization of round goby pheromonal communication will improve our understanding of the role of chemical signals in animals and will be an important asset for the control of the invasive round goby in the Great Lakes

Encounters in the Zooplankton: Implications for Pelagic Ecosystem Dynamics

Many important phenomena in the plankton are driven by encounters among individuals. These encounters are mediated by the relative motion of zooplankters, either through the swimming ability of organisms, the small-scale hydrodynamic turbulence, or both. Through selected case studies, in this chapter, we illustrate how encounter rates influence the predator-prey interactions and reproduction, two of the major processes regulating the zooplankton population dynamics. Estimations on the encounter rates among zooplankters were made on the basis of the Gerritsen-Strickler and Rothschild-Osborn models, which consider non-turbulent and turbulent conditions, respectively. In a first case, we show how the predatory impact of siphonophores is over the fish larvae, in the southern Gulf of Mexico. In the absence of water turbulence, a predator encounters 38–40 prey in a day at surface waters, but under the influence of the wind, encounters can increase between 1.2 and 3.3 times depending on the wind velocity and prey speed. In a second case, we examined the encounters between a copepod predator and a cladoceran prey, the dominant groups in the meromictic lagoon of Clipperton atoll. Here, a predator can encounter a high number of prey (until 441) in a day, due to the high density of prey. Turbulence conditions enhance encounter rates, but even if encounters are high, it does not mean that a predator can ingest a high number of prey. In a third case, we analyzed the mate encounters of the holoplanktonic mollusk Firoloida desmarestia from the southern Gulf of Mexico, throughout an annual cycle. Results indicated that May is the high reproductive season, a period where a female can encounter 17 males in a day, under turbulent conditions. As F. desmarestia is a low abundant species, the role of wind-induced turbulence proved to be highly important in increasing encounters between mates. These case studies illustrate the importance of encounters among zooplankters in the growth and maintenance of populations in the plankton. Future field and experimental studies are needed to achieve a better understanding of the pelagic ecosystem dynamics

The ratio of plastic to plankton in the Mediterranean Sea

Plastic pollution is a huge problem that is affecting all the oceans of the Earth. Plastic items end into the sea, break into tiny pieces and pollute the marine environment. The aim of this research is to increase our knowledge on this problem by comparing microplastic and zooplankton distributions. Samples from the Mediterranean Sea and Gibraltar Strait have been collected and analyzed. Plastic fragments have been extracted, weighted, photographed, measured and analyzed with a hyperspectral camera. The planktonic part of the samples has been analyzed identifying the main typology of organisms, taking pictures of the samples and analyzing them with ImageJ to take the measures. Data analysis was focused to the plastic to zooplankton ratio. The results have highlighted that most of the plastic to plankton ratios occurred in the in 1mm-10mm size range, and half of the stations in the Mediterranean sea presented values higher than 1, meaning than there is more plastic than plankton in that size range, for 50% of the Mediterranean. The ratio was higher during the day, due to the ascent of zooplankton during night. The results clearly show that the rank of greater danger is between 1mm to 10mm, and for this reason future samplings should focus on a net for this specific size range, to make sampling more simple and effective. A pollution indicator was created, based on the data collected all around the Mediterranean Sea, which could help find out future danger classifications, and choose the best adoptable strategies to solve the problem. Furthermore, the fact that the higher ratio has been found during the day can help future plastic sampling to focus on this time lapse. Concluding, the data provided by this research will be useful to better understand the degree of plastic contamination of our oceans and give updates to develop quality guidelines according to the Marine Strategy Framework Directive

Physical and Biological Drivers of Juvenile Fish Distributions in Unstructured Shallow Tropical Nearshore Habitats

The structural complexity of aquatic habitats can influence the ecological processes that occur within them, as fine-scale topographic features act as refugia for small fishes, buffering the effects of environmental stressors. Accordingly, the habitat requirements of juvenile demersal fishes in shallow littoral zones are often defined by their associations with distinct benthic microhabitats, such as densely vegetated substrates. However, an array of ecologically-important juvenile fishes also associate with topographically-homogeneous, sparsely-vegetated substrata. Absent the benefits offered by structural refugia, such fishes may be more affected by environmental variability and may have evolved distinct strategies for coping with stressors. I examined this hypothesis by assessing the factors shaping juvenile fish assemblages across the littoral zones of a subtropical island, where I predicted that flow-related stress and positive social interactions would be influential in governing the distributions of species occupying open, unstructured habitats. Spatio-temporal variability in the strength of wave-and tide-driven water movement were among the principal drivers of habitat use for a variety of juvenile fishes, exerting the most pronounced effects on species with an aversion to dense benthic vegetation (i.e., Bothus spp., and Albula vulpes), with little impact on species inhabiting seagrass (Haemulon spp. and Halichoeres bivittatus). Spatial segregation between A. vulpes and its cryptic congener Albula goreensis was unrelated to benthic habitat characteristics but well-explained by differential relationships with wave exposure, suggesting that niche partitioning between these functionally-indistinct species was mediated by flow. After accounting for phenotypic clustering caused by an extensive suite of environmental filters, residual correlations in species abundance were dominated by strongly- asymmetric positive associations, primarily between soft-bottom benthivores and Eucinostomus spp. Interspecific relationships were weak among seagrass-associated taxa. Disparities in the foraging behaviors and putative vigilance-keeping abilities of Eucinostomus spp. and its associate A. vulpes implied that the large organizational influence of eucinostomids could be explained by their capacity for producing risk-related information, which more vulnerable species exploited. Collectively, these findings support the hypothesis that fishes using unstructured habitats are more exposed to flow-related stress than those occupying complex habitats, and likewise that they employ alternative antipredator strategies, relying on social mechanisms to reduce predation risk

Evidence of Cnidarians sensitivity to sound after exposure to low frequency underwater sources

Jellyfishes represent a group of species that play an important role in oceans, particularly as a food source for different taxa and as a predator of fish larvae and planktonic prey. The massive introduction of artificial sound sources in the oceans has become a concern to science and society. While we are only beginning to understand that non-hearing specialists like cephalopods can be affected by anthropogenic noises and regulation is underway to measure European water noise levels, we still don’t know yet if the impact of sound may be extended to other lower level taxa of the food web. Here we exposed two species of Mediterranean Scyphozoan medusa, Cotylorhiza tuberculata and Rhizostoma pulmo to a sweep of low frequency sounds. Scanning electron microscopy (SEM) revealed injuries in the statocyst sensory epithelium of both species after exposure to sound, that are consistent with the manifestation of a massive acoustic trauma observed in other species. The presence of acoustic trauma in marine species that are not hearing specialists, like medusa, shows the magnitude of the problem of noise pollution and the complexity of the task to determine threshold values that would help building up regulation to prevent permanent damage of the ecosystems.Postprint (published version

Bio-Inspired Robotic Fish With Vision Based Target Tracking

The lionfish is an invasive species that out-competes and overcrowds native sh species along the eastern seaboard of the United States and down into the Caribbean. Lionfish populations are growing rapidly. Current methods of monitoring lionfish populations are costly and time intensive. A bio-inspired robotic fish was built to use as an autonomous lionfish tracking platform. Lionfish are tracked visually using an onboard processor. Five different computer vision methods for identification and tracking are proposed and discussed. These include: background subtraction, color tracking, mixture of Gaussian background subtraction, speeded up robust feature (SURF), and CamShift based tracking. Each of these methods were compared and their accuracy analyzed. CamShift based tracking is determined to be the most accurate for this application. Preliminary experiments for system identification and control design are discussed

Hydrodynamic stability of swimming in ostraciid fishes: role of the carapace in the smooth trunkfish Lactophrys triqueter (Teleostei: Ostraciidae)

The hydrodynamic bases for the stability of locomotory motions in fishes are poorly understood, even for those fishes, such as the rigid-bodied smooth trunkfish Lactophrys triqueter, that exhibit unusually small amplitude recoil movements during rectilinear swimming. We have studied the role played by the bony carapace of the smooth trunkfish in generating trimming forces that self-correct for instabilities. The flow patterns, forces and moments on and around anatomically exact, smooth trunkfish models positioned at both pitching and yawing angles of attack were investigated using three methods: digital particle image velocimetry (DPIV), pressure distribution measurements, and force balance measurements. Models positioned at various pitching angles of attack within a flow tunnel produced well-developed counter-rotating vortices along the ventro-lateral keels. The vortices developed first at the anterior edges of the ventro-lateral keels, grew posteriorly along the carapace, and reached maximum circulation at the posterior edge of the carapace. The vortical flow increased in strength as pitching angles of attack deviated from 0°, and was located above the keels at positive angles of attack and below them at negative angles of attack. Variation of yawing angles of attack resulted in prominent dorsal and ventral vortices developing at far-field locations of the carapace; far-field vortices intensified posteriorly and as angles of attack deviated from 0°. Pressure distribution results were consistent with the DPIV findings, with areas of low pressure correlating well with regions of attached, concentrated vorticity. Lift coefficients of boxfish models were similar to lift coefficients of delta wings, devices that also generate lift through vortex generation. Furthermore, nose-down and nose-up pitching moments about the center of mass were detected at positive and negative pitching angles of attack, respectively. The three complementary experimental approaches all indicate that the carapace of the smooth trunkfish effectively generates self-correcting forces for pitching and yawing motions — a characteristic that is advantageous for the highly variable velocity fields experienced by trunkfish in their complex aquatic environment. All important morphological features of the carapace contribute to producing the hydrodynamic stability of swimming trajectories in this species

Animal perception in gravel-bed rivers: scales of sensing and environmental controls on sensory information

Animals make decisions based on the sensory information that they obtain from the environment and other organisms within that environment. In a river, this information is transported, transmitted, masked, and filtered by fluvial factors and processes, such as relative roughness and turbulent flow. By interpreting the resultant signals, animals decide on the suitability of habitat and their reaction to other organisms. While a great deal is known about the sensory biology of animals, only limited attention has been paid to the environmental controls on the propagation of sensory information within rivers. Here, the potential transport mechanisms and masking processes of the sensory information used by animals in gravel-bed rivers are assessed by considering how the physical nature of sensory signals are affected by river hydromorphology. In addition, the physical processes that animals have the potential to directly perceive are discussed. Understanding the environmental phenomena that animals directly perceive will substantially improve understanding of what controls animal distributions, shifting emphasis from identifying correlations between biotic and abiotic factors to a better appreciation of causation, with benefits for successful management