Location Of Release Sites Research Articles

Radioseguimiento post recuperación de erizos europeos (Erinaceus europaeus Linnaeus, 1758) en el Parque Natural de la Sierra de Collserola (Barcelona)

The western European hedgehog is in decline in Collserola Natural Park (Barcelona) for various reasons, including the loss of habitats due to urbanisation and infrastructure impact, barrier effect and roadkills on the main road network. Between 2006 and 2008 a radiotracking study was undertaken on 15 hedgehogs (7 ♂♂ and 8 ♀♀) released from the wildlife recovery centre of the Can Balasc Biological Station with the aim of (i) understanding the adaptation and survival capabilities of the recovered individuals after release; (ii) comparing the dispersal response between different release areas; and (iii) characterising the different problems with which they are faced in order to improve their conservation. Hedgehogs released in woodland areas dispersed significantly further during the first days immediately following release when compared to hedgehogs released close to farms, either with or without densely vegetated torrents close by. Eventually however, released individuals tended to show similar dispersal ranges independent of the initial release site surroundings. Dispersal ranges varied widely, generally between 5 and 100 ha (mean 55.3±117.0 ha), but with extreme cases of 0.21 ha and 465 ha. The mean maximum dispersal distance was just over 1 km, and an absolute maximum of 3.9 km in one case. A tendency was observed for dispersal towards more ecotonic peripheral and periurban areas of the park. Dispersal to and use of these areas has consequences for hedgehogs due to the sharp boundary that exists between protected and urban space and the dangers that the latter represents. Of the 15 hedgehogs tracked it was possible to confirm the mortality of at least five of these (33%) during the first two months following their release, the specific causes of death being varied and similar to the main causes of hedgehog admission to the wildlife recovery centre: attacks by carnivores, roadkill, an accident in an industrial zone and other unknown causes. Recommendations are given on the location of release sites in order to reduce dispersal and minimise mortality, and also on reducing the admission of healthy hedgehogs to centres by a well-meaning public.

Location of Release Sites and Calcium-Activated Chloride Channels Relative to Calcium Channels at the Photoreceptor Ribbon Synapse

Vesicle release from photoreceptor ribbon synapses is regulated by L-type Ca(2+) channels, which are in turn regulated by Cl(-) moving through calcium-activated chloride [Cl(Ca)] channels. We assessed the proximity of Ca(2+) channels to release sites and Cl(Ca) channels in synaptic terminals of salamander photoreceptors by comparing fast (BAPTA) and slow (EGTA) intracellular Ca(2+) buffers. BAPTA did not fully block synaptic release, indicating some release sites are <100 nm from Ca(2+) channels. Comparing Cl(Ca) currents with predicted Ca(2+) diffusion profiles suggested that Cl(Ca) and Ca(2+) channels average a few hundred nanometers apart, but the inability of BAPTA to block Cl(Ca) currents completely suggested some channels are much closer together. Diffuse immunolabeling of terminals with an antibody to the putative Cl(Ca) channel TMEM16A supports the idea that Cl(Ca) channels are dispersed throughout the presynaptic terminal, in contrast with clustering of Ca(2+) channels near ribbons. Cl(Ca) currents evoked by intracellular calcium ion concentration ([Ca(2+)](i)) elevation through flash photolysis of DM-nitrophen exhibited EC(50) values of 556 and 377 nM with Hill slopes of 1.8 and 2.4 in rods and cones, respectively. These relationships were used to estimate average submembrane [Ca(2+)](i) in photoreceptor terminals. Consistent with control of exocytosis by [Ca(2+)] nanodomains near Ca(2+) channels, average submembrane [Ca(2+)](i) remained below the vesicle release threshold (∼ 400 nM) over much of the physiological voltage range for cones. Positioning Ca(2+) channels near release sites may improve fidelity in converting voltage changes to synaptic release. A diffuse distribution of Cl(Ca) channels may allow Ca(2+) influx at one site to influence relatively distant Ca(2+) channels.

Release Strategies for Estuarine Species with Complex Migratory Life Cycles: Stock Enhancement of Chesapeake Blue Crabs (Callinectes sapidus)

Responsible stock enhancement requires rigorous experiments to develop release strategies that account for movement of all life-history stages among habitats across inshore-offshore and estuarine gradients. However, crab stock enhancement research to date has focused primarily on hatchery production, with only limited field assessments of the efficacy of releases to increase the target population. This paper summarizes ongoing research to develop effective release strategies for hatchery-reared juveniles to augment the spawning biomass of Chesapeake Bay blue crabs, which has declined > 80% in 15 years and appears to be recruitment limited. Our release experiments focused on three factors: (1) components of preparation and release, which included life stage and size at release, pre-release conditioning to minimize differences between hatchery and wild crabs, and micro-habitat and micro-timing of release; (2) stocking variables, particularly seasonal timing of release and stocking density; and (3) site selection and coordination, including release macro-habitat and location of release sites along environmental gradients, emphasizing coordination of release site and fishing pressure with migration corridors linking nurseries to spawning areas. In the first 5 years of research, we demonstrated that small (1,000–10,000) cohorts of hatchery reared, 20 mm, 7th-instar juvenile blue crabs can be tagged and released into small (1–10 ha) coves, and that these cohorts can be followed successfully to quantify growth, survivorship, and productivity of the enhanced population. We also determined the timing and routes of migration using a tag-reward system with the cooperation of fishers. Our multifaceted research strategy provides a model for responsible approaches to stock enhancement of other species with complex migratory life cycles.

Mechanisms of axon guidance: membrane dynamics and axonal transport in semaphorin signalling

The intricate geometry of neuronal networks poses many unique cell-biological problems regarding the way a growing axon responds to its environment. Several groups of ligand-receptor pairs have been identified to regulate such processes. In this study, we take class 3 semaphorins as an example and review what is known about the intracellular movements of semaphorins throughout neuronal cells, transport support structures and location of release sites. We discuss how their receptor trafficking may contribute to regulate membrane dynamics underlying growth cone motility and the physiological contribution made by class 3 semaphorins-induced acceleration of axoplasmic transport on neurite development.

Quantitative Evaluation of 5-Hydroxytryptamine (Serotonin) Neuronal Release and Uptake: An Investigation of Extrasynaptic Transmission

Whether neurotransmitters are restricted to the synaptic cleft (participating only in hard-wired neurotransmission) or diffuse to remote receptor sites (participating in what has been termed volume or paracrine transmission) depends on a number of factors. These include (1) the location of release sites with respect to the receptors, (2) the number of molecules released, (3) the diffusional rate away from the release site, determined by both the geometry near the release site as well as binding interactions, and (4) the removal of transmitter by the relevant transporter. Fast-scan cyclic voltammetry allows for the detection of extrasynaptic concentrations of many biogenic amines, permitting direct access to many of these parameters. In this study the hypothesis that 5-hydroxytryptamine (5-HT) transmission is primarily extrasynaptic in the substantia nigra reticulata, a terminal region with identified synaptic contacts, and the dorsal raphe nucleus, a somatodendritic region with rare synaptic incidence, was tested in brain slices prepared from the rat. Using carbon fiber microelectrodes, we found the concentration of 5-HT released per stimulus pulse in both regions to be identical when elicited by single pulse stimulations or trains at high frequency. 5-HT efflux elicited by a single stimulus pulse was unaffected by uptake inhibition or receptor antagonism. Thus, synaptic efflux is not restricted by binding to intrasynaptic receptors or transporters. The number of 5-HT molecules released per terminal was estimated in the substantia nigra reticulata and was considerably less than the number of 5-HT transporter and receptor sites, reinforcing the hypothesis that these sites are extrasynaptic. Furthermore, the detected extrasynaptic concentrations closely match the affinity for the predominant 5-HT receptor in each region. Although they do not disprove the existence of classical synaptic transmission, our results support the existence of paracrine neurotransmission in both serotonergic regions.

Habitat Use and Movement of Young Paddlefish (Polyodon spathula)

ABSTRACT We used radio telemetry to determine movement and habitat use of 19 paddlefish (Polyodon spathula) stocked into the Neches River system, Texas. Thirteen fish weighing 0.5–0.8 kg were released in April 1990 in the upper reaches of B.A. Steinhagen Reservoir and six fish weighing 2.4–3.7 kg were released in October 1990 in the lower reaches of B.A. Steinhagen Reservoir. Fish were tracked from April 1990 to September 1991. Five fish died within four months of release. There was a significant relation between: 1) habitat type and both water depth in which fish were found and their distance to shore and 2) season of year and both water depth in which fish were found and their distance to shore. These relations suggest seasonal patterns of habitat use. Farthest upstream movement was 270.4 km and farthest downstream movement was 161.3 km. Eleven fish remained upstream of the dam and six fish moved through reservoir floodgates or over the spillway into the lower Neches River. Our findings indicated: 1) paddlefish size relative to size of implanted radio transmitter may have a bearing on survival. 2) young paddlefish may migrate great distances shortly after stocking and 3) location of release site may influence direction of paddlefish dispersement.

Distribution of adult recaptures from hatchery-reared Atlantic salmon (Salmo salar) smolts released in and off-shore of the River Surna, western Norway

The hypothesis that motivation of adult salmon to enter fresh water is dependent on the location of release site was tested. Three groups of smolts were released into a river; into a fjord outside the river and into the open sea. Numbers and percentages of adult salmon caught in the commercial marine fisheries were highest for smolts released from sites outside the river. Adults from smolts released in the river did not migrate farther upstream than adults released from marine sites. Adults homed to the area of smolt release, whether or not the fish were released in sea or fresh water. The results also showed that both recapture rates and straying increased with increasing release distance from fresh water.Consequently, both rates of recapture and straying of ocean ranched Atlantic salmon are strongly dependent on release location.