192 research outputs found
The Arctic Cisco (Coregonus autumnalis) Subsistence and Commercial Fisheries, Colville River, Alaska: A Conceptual Model
The arctic cisco (Coregonus autumnalis), known regionally by its Inupiat name qaaqtaq, is the principal target of fall subsistence and commercial fisheries that operate in the Colville River along the Alaskan Beaufort Sea. Our conceptual model of the fisheries is based on more than two decades of continuous scientific study conducted in conjunction with oil industry growth on the North Slope. It expands upon an existing body of published literature to discuss additional factors that affect fishery yields. Long-term data indicate that arctic cisco spawn in Canadaâs Mackenzie River system. Young-of-the-year are transported westward into Alaska by wind-driven coastal currents. Arctic cisco successfully recruit to Alaskaâs Colville River when summer winds blow from the east with an average speed greater than 5 km/h. The successful recruitment of these young arctic cisco to central Alaska is a prerequisite for the eventual entry of harvestable five- to eight-year-old fish into the regionâs subsistence and commercial fisheries. Recruitment into the fisheries also requires that fish survive in central Alaska for the five to six years it takes for them to grow to a harvestable size. Once these fish are recruited into the fisheries, annual harvests are strongly dependent on salinity conditions within the fishing grounds. Although fishing mortality occurs, the loss of older fish from the region is attributed largely to the emigration of sexually mature fish back to Canada.Le cisco arctique (Coregonus autumnalis), connu rĂ©gionalement sous le nom de qaaqtaq en inupiat, est la principale cible des pĂȘcheries commerciales et de la subsistance dâautomne de Colville River, le long de la partie alaskienne de la mer de Beaufort. Notre modĂšle conceptuel des pĂȘcheries repose sur une Ă©tude scientifique rĂ©alisĂ©e sans arrĂȘt pendant plus de deux dĂ©cennies Ă la lumiĂšre de lâessor connu par lâindustrie du pĂ©trole sur la cĂŽte Nord. Il sâappuie Ă©galement sur de la documentation publiĂ©e et englobe dâautres facteurs qui ont une incidence sur le rendement des pĂȘcheries. Les donnĂ©es de longue date laissent entendre que le cisco arctique fraie dans la partie canadienne du rĂ©seau du fleuve Mackenzie. Les jeunes de lâannĂ©e sont transportĂ©s vers lâOuest, en Alaska, par les courants de dĂ©rive du littoral. Le cisco arctique rĂ©ussit Ă se recruter dans la rĂ©gion alaskienne de Colville River lorsque les vents dâĂ©tĂ© soufflent de lâest Ă une vitesse moyenne de 5 km/h. Le recrutement rĂ©ussi de ces jeunes ciscos arctiques vers le centre de lâAlaska est un prĂ©alable pour lâentrĂ©e Ă©ventuelle des poissons pĂȘchables de cinq Ă huit ans en vue de la subsistance de la rĂ©gion et de la pĂȘche commerciale. Le recrutement implique Ă©galement que les poissons doivent survivre dans le centre de lâAlaska pendant les cinq Ă six annĂ©es quâil leur faut pour atteindre une taille se prĂȘtant Ă la pĂȘche. Une fois que ces poissons sont recrutĂ©s dans les pĂȘcheries, les rĂ©coltes annuelles dĂ©pendent beaucoup des conditions de salinitĂ© prĂ©sentes aux pĂȘcheries. MalgrĂ© le taux de mortalitĂ© par pĂȘche, la perte de poissons plus ĂągĂ©s dans la rĂ©gion est grandement attribuable Ă lâĂ©migration au Canada de poissons prĂȘts Ă se reproduire
Bowhead Whale (Balaena mysticetus) Migration and Calling Behaviour in the Alaskan Beaufort Sea, Autumn 2001â04: An Acoustic Localization Study
The westward migration of bowhead whales (Bering Sea stock) was studied during autumn 2001â04 as part of an oil industry monitoring program. An array of Directional Autonomous Seafloor Acoustic Recorders (DASARs) was deployed northeast of the Northstar oil production island near Prudhoe Bay, Alaska. Underwater sounds were recorded continuously for 24â35 days per year, mainly in September. More than 130 000 bowhead calls were detected, and the directional capability of DASARs allowed triangulation of whale position for ~93 500 calls. The migration pathway was closer to shore in 2003â04 than in 2001â02. Calls were clumped in space and time, and there was significantly more calling at night than by day. From 65% to 82% of calls were simple frequency-modulated calls, and the percentage of complex calls was positively related to the daily number of calls. No songs were detected, but in 2004 there were numerous call sequences consisting of repeated identical calls in series and generally lasting up to a few minutes. The DASAR methodology provides detailed information on the temporal and spatial distribution of calling whales and on their acoustic repertoire.La migration Ă lâouest de la baleine borĂ©ale (population de la mer de BĂ©ring) a Ă©tĂ© Ă©tudiĂ©e durant quatre automnes (2001-2004) dans le cadre dâun programme dâĂ©tude de lâindustrie pĂ©troliĂšre. Un rĂ©seau dâenregistreurs sous-marins autonomes et directionnels (DASAR) a Ă©tĂ© dĂ©ployĂ© au nord-est de Northstar, une Ăźle artificielle dâexploitation pĂ©troliĂšre prĂšs de Prudhoe Bay en Alaska. Des enregistrements sous-marins continus ont Ă©tĂ© rĂ©coltĂ©s pendant 24 Ă 35 jours chaque annĂ©e, principalement pendant le mois de septembre. Plus de 130 000 appels de baleines ont Ă©tĂ© enregistrĂ©s et la capacitĂ© directionnelle des DASAR a permis de dĂ©terminer par triangulation la position des baleines pour ~ 93 500 de ces appels. Le corridor de migration sâest avĂ©rĂ© plus proche de la cĂŽte en 2003-2004 quâen 2001-2002. Les appels des baleines Ă©taient groupĂ©s dans le temps et lâespace et il y avait significativement plus dâappels la nuit que le jour. Soixante-cinq Ă 82 % des appels appartenaient au type dit « simple », et le pourcentage dâappels du type « complexe » Ă©tait positivement corrĂ©lĂ© au nombre journalier dâappels. Aucun chant nâa Ă©tĂ© dĂ©tectĂ©, mais les enregistrements de 2004 contenaient de nombreuses sĂ©quences dâappels composĂ©es de sĂ©ries dâappels identiques rĂ©pĂ©tĂ©s pendant 30 minutes et plus. Lâutilisation des DASAR a permis dâobtenir des renseignements dĂ©taillĂ©s sur la distribution spatiale et temporelle de baleines borĂ©ales vocalisant ainsi que sur leur rĂ©pertoire acoustique
Assessment of Effects of an Oil Pipeline on Caribou, Rangifer tarandus granti, Use of Riparian Habitats in Arctic Alaska, 2001-2003
Elevated oil field pipelines may alter Caribou (Rangifer tarandus granti) movements and delay or prevent access to insect relief habitat. In an attempt to determine if the 40-km elevated Badami pipeline in northern Alaska changed Caribou use of riparian habitats at the three river crossings where the pipeline is buried, we quantified Caribou habitat use at all three crossings using time-lapse video cameras and aerial distribution surveys over three summers. We compared habitat use, behavior and duration of observations among pipeline and non-pipeline sites. We used a block experimental design with cameras at four sites at the three river crossings to evaluate differences in numbers of Caribou per day at pipeline and non-pipeline sites. At each crossing, four cameras were positioned, with one pair of cameras next to the pipeline (pipeline sites) and one pair of cameras 1.8-3.2 km upstream from the pipeline (non-pipeline sites); where cameras monitored the river bank and channel (river habitat) and the tundra within about 200 m of the river (tundra habitat). Peak numbers of Caribou per day occurred during early July 2003 and mid-July 2001 and 2002. Large numbers of Caribou recorded north of the pipeline during aerial surveys did not usually correspond with increased number per day recorded by cameras suggesting Caribou probably also crossed the pipeline outside of the riparian areas. We assessed local changes in riparian habitat use by comparing the numbers of Caribou per day in river and tundra habitats at pipeline and non-pipeline sites and found no difference. We assessed regional changes in riparian habitat use by comparing numbers of Caribou per day at pipeline sites and at non-pipeline sites and found no difference. Caribou groups spent an average of 1 minute longer at tundra pipeline sites and groups spent 30 seconds longer feeding and trotting at pipeline sites, but these differences were not significant
Effects of Gas Flaring on the Behavior of Night-migrating Birds at an Artificial Oil-production Island, Arctic Alaska
We studied movement rates and the general flight behavior of bird flocks seen on radar and recorded visually at Northstar Island, Arctic Alaska, from 13 to 27 September 2002. Most of this period (13 â 19 and 21 â 27 September) had no gas-flaring events, but a major gas-flaring event occurred on the night of 20 September. Movement rates of targets on radar and of bird flocks recorded visually in the first ~50% â 60% of the night were much lower during the non-flaring period than during the night of flaring, whereas rates in the last ~40% â 50% of the night were similar in all periods. The general flight behavior of birds also differed significantly, with higher percentages of both radar targets and bird flocks exhibiting straight-line (directional) flight behaviors during the non-flaring periods and higher percentages of radar targets and bird flocks exhibiting non-straight-line (erratic and circling) flight behaviors during the gas-flaring period. During the night of gas flaring, the bright illumination appeared to have an effect only after sunset, when flocks of birds circled the island after being drawn in from what appeared to be a substantial distance from the island. On both radar and visual sampling, the number of bird flocks approaching the island declined over the evening, and the attractiveness of the light from flaring appeared to decline. The visibility of the moon appeared to have little effect on the behavior of birds. Because illumination from extensive gas-flaring is such a strong attractant to migrating birds and because most bird flocks fly at low altitudes over the water, flaring booms on coastal and offshore oil-production platforms in Arctic Alaska should be positioned higher than the mean flight altitudes of migrating birds to reduce the chances of incineration.Nous avons Ă©tudiĂ© les taux de dĂ©placement et le comportement de vol gĂ©nĂ©ral des troupeaux dâoiseaux captĂ©s par radar ou consignĂ©s visuellement Ă lâĂźle Northstar, dans lâAlaska de lâArctique, du 13 au 27 septembre 2002. Pendant presque toute cette pĂ©riode (du 13 au 19 et du 21 au 27 septembre), il nây a pas eu de brĂ»lage de gaz Ă la torche, mais la nuit du 20 septembre, il y a eu un important brĂ»lage de gaz Ă la torche. Les taux de dĂ©placement des cibles radar et des troupeaux dâoiseaux consignĂ©s visuellement pendant la premiĂšre tranche dâenviron 50 % Ă 60 % de la nuit Ă©taient beaucoup moins Ă©levĂ©s pendant la pĂ©riode oĂč il nây avait pas de brĂ»lage Ă la torche que pendant la nuit oĂč il y a eu brĂ»lage Ă la torche, tandis que pendant la deuxiĂšme tranche dâenviron 40 % Ă 50 % de la nuit, les taux de dĂ©placement Ă©taient semblables pendant toutes les pĂ©riodes. Le comportement de vol gĂ©nĂ©ral des oiseaux a Ă©galement affichĂ© une diffĂ©rence considĂ©rable. De plus grands pourcentages de cibles radar et de troupeaux dâoiseaux adoptaient un comportement de vol rectiligne (direct) pendant les pĂ©riodes oĂč il nây avait pas de brĂ»lage Ă la torche, et de plus grands pourcentages de cibles radar et de troupeaux dâoiseaux affichaient un comportement de vol non rectiligne (erratique et indirect) pendant la pĂ©riode oĂč il y a eu brĂ»lage Ă la torche. La nuit du brĂ»lage Ă la torche, la vive illumination nâa semblĂ© avoir un effet quâaprĂšs le coucher du soleil, quand les troupeaux dâoiseaux encerclaient lâĂźle aprĂšs avoir Ă©tĂ© attirĂ©s depuis un endroit qui semblait trĂšs lointain. Tant pour lâĂ©chantillonnage prĂ©levĂ© par radar que par consignation visuelle, le nombre de troupeaux dâoiseaux sâapprochant de lâĂźle diminuait dans le courant de la soirĂ©e, et lâattrait de la lumiĂšre Ă©manant du brĂ»lage Ă la torche semblait Ă©galement diminuer. La visibilitĂ© de la lune semblait avoir peu dâeffet sur le comportement des oiseaux. Puisque lâillumination provenant du brĂ»lage prolongĂ© Ă la torche exerce une si grande force dâattraction chez les oiseaux migrateurs, et puisque la plupart des troupeaux dâoiseaux volent en basse altitude au-dessus de lâeau, le torchage effectuĂ© sur les plateformes pĂ©troliĂšres cĂŽtiĂšres et extracĂŽtiĂšres dans lâAlaska de lâArctique devrait ĂȘtre positionnĂ© plus haut que les altitudes moyennes de vol des oiseaux migrateurs afin de rĂ©duire les risques dâincinĂ©ration
Bird Use of Northern Alaska Oilfield Rehabilitation Sites
Breeding bird response to habitat rehabilitation after anthropogenic disturbance has received little attention in the Arctic. The North Slope of Alaska is an important breeding ground for many populations of migratory birds and has also supported major oilfields since the late 1960s. The most obvious impacts of industrial development to nesting birds are direct habitat loss and fragmentation resulting from the construction of infrastructure, along with increased mechanical noise, vehicle traffic, and other forms of anthropogenic disturbance. In response to state and federal requirements, efforts have been made to rehabilitate abandoned portions of the oilfields. We compared bird use at rehabilitation sites and at nearby paired reference sites. Densities of shorebirds and passerines varied between rehabilitation sites and reference sites, but waterfowl densities did not. Specifically, passerine and shorebird densities were higher at reference sites in the early or mid-season and lower at reference sites in the late season. Additionally, birds on rehabilitation sites were primarily observed foraging and resting, while behavior observed on paired reference sites was more diverse and included courtship displays, nesting, and aggression. Further, rehabilitation sites supported significantly fewer nests and fewer species than recorded at reference sites. Our findings suggest that sites 3 to 10 years post rehabilitation do not provide bird habitat comparable to nearby reference sites and, by extension, do not provide shorebird and passerine habitat comparable to that found prior to development. However, rehabilitation sites appear to provide adequate habitat for waterfowl and are important to shorebirds and passerines as foraging areas. Continued monitoring will be needed to establish the long-term suitability of rehabilitation sites, compared to reference sites, as breeding habitat for birds.Dans lâArctique, la rĂ©ponse des oiseaux nicheurs Ă la remise en valeur de lâhabitat aprĂšs des perturbations dâorigine anthropique a Ă©tĂ© peu Ă©tudiĂ©e. Le North Slope de lâAlaska est un lieu de reproduction important pour de nombreuses populations dâoiseaux migrateurs. Des champs pĂ©troliers dâenvergure y ont Ă©galement Ă©tĂ© amĂ©nagĂ©s depuis la fin des annĂ©es 1960. Les incidences les plus Ă©videntes du dĂ©veloppement industriel sur les oiseaux nicheurs sont la fragmentation et la perte directe dâhabitat dĂ©coulant de la construction dâinfrastructures ainsi que lâaugmentation du bruit mĂ©canique, de la circulation de vĂ©hicules et dâautres formes de perturbations anthropiques. En raison des exigences de lâĂtat et de lâadministration fĂ©dĂ©rale, des efforts ont Ă©tĂ© dĂ©ployĂ©s pour remettre en valeur les zones abandonnĂ©es des champs pĂ©troliers. Nous avons comparĂ© lâutilisation par les oiseaux des lieux remis en valeur Ă des lieux de rĂ©fĂ©rence jumelĂ©s des environs. Les densitĂ©s dâoiseaux de rivage et de passereaux variaient dans les lieux remis en valeur et les lieux de rĂ©fĂ©rence, mais ce nâĂ©tait pas le cas des densitĂ©s de la sauvagine. Plus prĂ©cisĂ©ment, les densitĂ©s de passereaux et dâoiseaux de rivage Ă©taient plus Ă©levĂ©es aux lieux de rĂ©fĂ©rence en dĂ©but ou en milieu de saison, et moins Ă©levĂ©es aux lieux de rĂ©fĂ©rence en fin de saison. De plus, les oiseaux de lieux remis en valeur ont surtout Ă©tĂ© vus en train de se nourrir ou de se reposer, tandis quâaux lieux de rĂ©fĂ©rence, leurs comportements Ă©taient plus variĂ©s et comprenaient des comportements de parade nuptiale, de nidification et dâagression. Par ailleurs, les lieux remis en valeur abritaient un beaucoup moins grand nombre de nids et moins dâespĂšces que les lieux de rĂ©fĂ©rence. Selon nos constatations, de trois Ă dix ans aprĂšs les travaux de remise en valeur, ces lieux ne prĂ©sentent pas, pour les oiseaux, un habitat comparable aux lieux de rĂ©fĂ©rence des environs et, par consĂ©quent, ils ne fournissent pas aux passereaux et aux oiseaux de rivage un habitat comparable Ă celui qui sây trouvait avant le dĂ©veloppement industriel. Toutefois, les lieux remis en valeur semblent prĂ©senter un habitat adĂ©quat pour la sauvagine et revĂȘtent de lâimportance comme lieux de ravitaillement pour les oiseaux de rivage et les passereaux. Une surveillance continue sâavĂšre nĂ©cessaire afin dâĂ©tablir la convenance Ă long terme des lieux remis en valeur, comparativement aux lieux de rĂ©fĂ©rence, comme habitat de nidification pour les oiseaux
Evaluation of Percent Cover Requirements for Revegetation of Disturbed Sites on Alaska's North Slope
On the North Slope of Alaska, attempts have been made to revegetate areas damaged by development. Some revegetation projects strive to achieve specific performance standards based on percent vegetation cover. This study uses data collected from 60 sites over 16 years to compare revegetating sites and natural reference sites. Results demonstrate that percent cover in most revegetation settings has the potential to reach levels comparable to those of reference sites, depending on how cover is defined. Linear models that explain between 48% and 84% of the variability in data show that planting cultivar seeds and fertilizing can increase cover (p < 0.05 for all models) and that cover continues to increase over time (p < 0.05 for all models), provided that cover is defined to include all live plants and plant litter. Ordination analysis separates reference sites from most revegetating sites along two significant axes (Monte Carlo tests, p < 0.01 with 100 randomizations). Comparison of ordination results with plots of change in plant cover over time shows that plant cover offers only limited insight into plant community development. If percent cover is to be used as a performance standard, it should be clearly defined, and the link between percent cover and restoration objectives should be carefully considered. Although this paper focuses on North Slope revegetation projects, the issues that are addressed have implications for all projects with performance standards calling for specific percent cover by vegetation.Le versant Nord de l'Alaska a fait l'objet de tentatives de reverdissement dans des zones endommagĂ©es par l'exploitation. Certains projets de remise en Ă©tat s'efforcent d'atteindre des normes de rendement spĂ©cifiques qui s'appuient sur le pourcentage de tapis vĂ©gĂ©tal. Cette Ă©tude fait appel aux donnĂ©es collectĂ©es Ă 60 emplacements sur une durĂ©e de 16 ans afin de comparer les sites de reverdissement avec des sites tĂ©moins laissĂ©s Ă l'Ă©tat naturel. Les rĂ©sultats montrent qu'Ă la plupart des endroits de reverdissement, le pourcentage de tapis vĂ©gĂ©tal a le potentiel d'atteindre des niveaux comparables Ă ceux des sites tĂ©moins, selon la dĂ©finition du tapis vĂ©gĂ©tal. Les modĂšles linĂ©aires, qui expliquent entre 48 et 84 % de la variabilitĂ© dans les donnĂ©es, montrent que le fait de planter des semences de cultivars et de mettre de l'engrais peut accroĂźtre le tapis (p < 0,05 pour tous les modĂšles) et que ce dernier continue d'augmenter au fil du temps (p < 0,05 pour tous les modĂšles), Ă condition d'inclure toutes les plantes vivantes et la litiĂšre vĂ©gĂ©tale dans la dĂ©finition du tapis vĂ©gĂ©tal. L'analyse d'ordination permet de distinguer les sites tĂ©moins de la majoritĂ© des sites reverdis selon deux grands axes (tests de Monte Carlo, p < 0,01 avec 100 randomisations). La comparaison des rĂ©sultats de l'ordination avec les courbes de changement dans la couverture vĂ©gĂ©tale en fonction du temps rĂ©vĂšle que la couverture n'offre qu'un aperçu limitĂ© de l'Ă©volution du peuplement vĂ©gĂ©tal. Si le pourcentage de tapis doit servir de norme de rendement, il faut en donner une dĂ©finition prĂ©cise, et examiner en dĂ©tail le lien entre le pourcentage de tapis et les objectifs de restauration. Si cet article se concentre sur les projets de remise en Ă©tat du versant Nord, les questions qu'il soulĂšve ont des implications pour tous les projets oĂč les normes de rendement prĂ©voient un pourcentage spĂ©cifique de tapis vĂ©gĂ©tal
Effects of a Hazing-Light System on Migration and Collision Avoidance of Eiders at an Artificial Oil-Production Island, Arctic Alaska
During migration, Common and King Eiders (Somateria mollissima and S. spectabilis) cross the Beaufort and Chukchi Seas of Arctic Alaska. Because they may become attracted to lights, eiders are susceptible to collision with structures, including offshore oil facilities. We used ornithological radar in 2001 â 04 to characterize the behavior of eiders migrating past Northstar Island, an oil-production island near Prudhoe Bay, Alaska, and to assess the effects of a hazing-light system on migrating eiders. âEiderâ radar targets exhibited pulsed, irregular periods of movement; movement rates were higher when sea ice was present, without precipitation, and during tailwinds and crosswinds but were not affected by lights. Velocities (ground speeds) were higher when ice was present and with strong tailwinds. They were lower at night when the lights were on, but higher during the day when the lights were on. Radar targets exhibited little variation in flight behavior as they passed the island; the proportion of non-directional behavior was larger when ice was present, with tailwinds, with weak winds, and near the full moon when it was not visible. Lights had no effect on flight behavior. Birds tended to exhibit more course changes as they approached the island, greater angular changes when they changed course, and larger net increases in passing distance as a result of those course changes when the lights were on; however, none of these differences were statistically significant. Overall, the hazing lights at Northstar did not disrupt the birdsâ migratory movements but resulted in increased avoidance of the island.En pĂ©riode de migration, lâeider Ă duvet et lâeider Ă tĂȘte grise (Somateria mollissima et S. spectabilis) survolent la mer de Beaufort et la mer des Tchouktches dans lâAlaska de lâArctique. Comme ils sont attirĂ©s par les lumiĂšres, les eiders risquent dâentrer en collision avec des structures, y compris les installations pĂ©troliĂšres au large. De 2001 Ă 2004, nous avons utilisĂ© un radar ornithologique pour caractĂ©riser le comportement des eiders qui migrent au-delĂ de lâĂźle Northstar, une Ăźle de production pĂ©troliĂšre prĂšs de Prudhoe Bay, en Alaska, et pour Ă©valuer les effets dâun systĂšme dâĂ©clairage de dispersion sur les eiders en migration. Les « eiders » ciblĂ©s par le radar prĂ©sentaient des pĂ©riodes de mouvement pulsĂ©es et irrĂ©guliĂšres; les taux de mouvement Ă©taient plus importants en prĂ©sence de glace marine, en lâabsence de prĂ©cipitation et en prĂ©sence de vent arriĂšre et de vent latĂ©ral, mais nâĂ©taient pas touchĂ©s par les lumiĂšres. Les vĂ©locitĂ©s (vitesses au sol) Ă©taient plus Ă©levĂ©es en prĂ©sence de glace et de forts vents arriĂšre. Elles Ă©taient plus basses la nuit lorsque les lumiĂšres Ă©taient allumĂ©es, mais plus Ă©levĂ©es le jour lorsque les lumiĂšres Ă©taient allumĂ©es. Nous avons observĂ© peu de variation quant au comportement de vol des cibles atteintes par le radar pendant quâelles survolaient lâĂźle; la proportion de comportements de vol non directionnels Ă©tait plus importante en prĂ©sence de glace, de vent arriĂšre, de vent faible et lorsque la pleine lune nâĂ©tait pas visible. Les lumiĂšres nâont pas eu dâimpact sur le comportement de vol. Lorsque les lumiĂšres Ă©taient allumĂ©es, les oiseaux avaient tendance Ă changer de direction plus souvent durant leur vol Ă lâapproche de lâĂźle et Ă effectuer de plus grandes variations angulaires lorsquâils changeaient de direction, puis prĂ©sentaient une nette augmentation de la distance de passage Ă la suite de ces changements de direction. Toutefois, aucune de ces diffĂ©rences nâĂ©tait statistiquement importante. En gĂ©nĂ©ral, les lumiĂšres de dispersion de lâĂźle Northstar nâont pas nui aux mouvements migratoires des oiseaux, mais ces derniers ont davantage Ă©vitĂ© de voler prĂšs de lâĂźle
Changes in Fish Catch Rates in the Presence of Air Gun Sounds in Prudhoe Bay, Alaska
Air guns used in oil industry seismic surveys have the capacity to change fish catch rates, but no previous work has demonstrated this effect in shallow water or in Arctic oilfields. Long-term monitoring of fish catches using four fyke nets allowed assessment of changes in catch rates during a 2014 seismic survey in Prudhoe Bay, Alaska. Fyke net locations were instrumented with both conventional hydrophones and vector sensors. Catch rates were generally within the range of those found in 27 previous sampling seasons. The effect of air guns on eight species was assessed using a modified Before-After/Control-Impact analysis, with historical data and 2014 data as the Before-After components of the analysis and days without and with air gun activity as the Control-Impact components. Results showed significant changes associated with air guns in catch rates at one or more nets at p < 0.1 for all eight species and at p < 0.05 for seven of the eight. Changes included both increased and decreased catch rates, perhaps reflecting displacement of fish in response to air gun sounds throughout the study area. Measured sound pressure levels associated with air gun pulses were low and usually undetectable close to the fyke nets, reflecting the loss of low frequencies in shallow water (~1.5 m). Attempts to measure particle velocities failed when wind-driven surface waves overwhelmed vector sensors. However, fish responses may have been related to changes in particle motion associated with air gun sounds.Les armes Ă air comprimĂ© dont on se sert pour faire les levĂ©s sismiques dans lâindustrie pĂ©troliĂšre ont la capacitĂ© de changer le taux de capture des poissons, mais aucune Ă©tude nâa jamais dĂ©montrĂ© lâeffet de ces armes dans les eaux peu profondes ou dans les champs pĂ©trolifĂšres de lâArctique. La surveillance Ă long terme des prises de poissons Ă lâaide de quatre verveux a permis dâĂ©valuer les changements en matiĂšre de taux de prises pendant un levĂ© sismique qui a eu lieu Ă Prudhoe Bay, Alaska, en 2014. Les emplacements de verveux ont Ă©tĂ© munis dâhydrophones classiques et de capteurs de vecteur. De maniĂšre gĂ©nĂ©rale, les taux de prises coĂŻncidaient avec la gamme rĂ©pertoriĂ©e au cours des 27 saisons dâĂ©chantillonnage prĂ©cĂ©dentes. Lâeffet des armes Ă air comprimĂ© sur huit espĂšces a Ă©tĂ© Ă©valuĂ© au moyen dâune analyse modifiĂ©e avant-aprĂšs/contrĂŽle-impact, les donnĂ©es historiques et les donnĂ©es de 2014 reprĂ©sentant les composantes avant-aprĂšs de lâanalyse, puis les jours avec et les jours sans activitĂ© dâarmes Ă air comprimĂ© reprĂ©sentant les composantes contrĂŽle-impact de lâanalyse. Les rĂ©sultats ont permis de constater dâimportants changements liĂ©s Ă lâemploi dâarmes Ă air comprimĂ© pour ce qui est des taux de prises Ă un ou plusieurs verveux, Ă p < 0,1 pour les huit espĂšces, et Ă p < 0,05 pour sept des huit espĂšces. Les changements se sont caractĂ©risĂ©s Ă la fois par des taux de prises plus Ă©levĂ©s et moins Ă©levĂ©s, ce qui reflĂ©tait peut-ĂȘtre le dĂ©placement des poissons en raison du son des armes Ă air comprimĂ© dans la zone visĂ©e par lâĂ©tude. Les niveaux de pression sonore mesurĂ©s en lien avec les impulsions dâarmes Ă air comprimĂ© Ă©taient faibles et habituellement indĂ©tectables Ă proximitĂ© des verveux, signe de la perte des ondes kilomĂ©triques dans lâeau peu profonde (~1,5 m). Les tentatives de mesure des vitesses acoustiques des particules ont Ă©chouĂ© lorsque les ondes de surface poussĂ©es par le vent submergeaient les capteurs de vecteur. Toutefois, la rĂ©action des poissons aurait pu ĂȘtre liĂ©e aux changements sur le plan du mouvement des particules dĂ©coulant du son des armes Ă air comprimĂ©
Itinerant electron metamagnetism in LaCoSi
The strongly exchange enhanced Pauli paramagnet LaCoSi is found to
exhibit an itinerant metamagnetic phase transition with indications for
metamagnetic quantum criticality. Our investigation comprises magnetic,
specific heat, and NMR measurements as well as ab-initio electronic structure
calculations. The critical field is about 3.5 T for and 6 T for , which is the lowest value ever found for rare earth intermetallic
compounds. In the ferromagnetic state there appears a moment of about 0.2
/Co at the Co-sites, but sigificantly smaller moments at the 4d
and Co-sites.Comment: 11 pages, 5 figures, PRB Rapid Communication, in prin
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