900 resultados para Maintenance intervals
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The development of the ecosystem approach and models for the management of ocean marine resources requires easy access to standard validated datasets of historical catch data for the main exploited species. They are used to measure the impact of biomass removal by fisheries and to evaluate the models skills, while the use of standard dataset facilitates models inter-comparison. North Atlantic albacore tuna is exploited all year round by longline and in summer and autumn by surface fisheries and fishery statistics compiled by the International Commission for the Conservation of Atlantic Tunas (ICCAT). Catch and effort with geographical coordinates at monthly spatial resolution of 1° or 5° squares were extracted for this species with a careful definition of fisheries and data screening. In total, thirteen fisheries were defined for the period 1956-2010, with fishing gears longline, troll, mid-water trawl and bait fishing. However, the spatialized catch effort data available in ICCAT database represent a fraction of the entire total catch. Length frequencies of catch were also extracted according to the definition of fisheries above for the period 1956-2010 with a quarterly temporal resolution and spatial resolutions varying from 1°x 1° to 10°x 20°. The resolution used to measure the fish also varies with size-bins of 1, 2 or 5 cm (Fork Length). The screening of data allowed detecting inconsistencies with a relatively large number of samples larger than 150 cm while all studies on the growth of albacore suggest that fish rarely grow up over 130 cm. Therefore, a threshold value of 130 cm has been arbitrarily fixed and all length frequency data above this value removed from the original data set.
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The development of the ecosystem approach and models for the management of ocean marine resources requires easy access to standard validated datasets of historical catch data for the main exploited species. They are used to measure the impact of biomass removal by fisheries and to evaluate the models skills, while the use of standard dataset facilitates models inter-comparison. North Atlantic albacore tuna is exploited all year round by longline and in summer and autumn by surface fisheries and fishery statistics compiled by the International Commission for the Conservation of Atlantic Tunas (ICCAT). Catch and effort with geographical coordinates at monthly spatial resolution of 1° or 5° squares were extracted for this species with a careful definition of fisheries and data screening. In total, thirteen fisheries were defined for the period 1956-2010, with fishing gears longline, troll, mid-water trawl and bait fishing. However, the spatialized catch effort data available in ICCAT database represent a fraction of the entire total catch. Length frequencies of catch were also extracted according to the definition of fisheries above for the period 1956-2010 with a quarterly temporal resolution and spatial resolutions varying from 1°x 1° to 10°x 20°. The resolution used to measure the fish also varies with size-bins of 1, 2 or 5 cm (Fork Length). The screening of data allowed detecting inconsistencies with a relatively large number of samples larger than 150 cm while all studies on the growth of albacore suggest that fish rarely grow up over 130 cm. Therefore, a threshold value of 130 cm has been arbitrarily fixed and all length frequency data above this value removed from the original data set.
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We combined the analysis of sediment trap data and satellite-derived sea surface chlorophyll to quantify the amount of organic carbon export to the deep sea in the upwelling induced high production area off northwest Africa. In contrast to the generally global or basin-wide adoption of export models, we used a regionally fitted empirical model. Furthermore, the application of our model was restricted to a dynamically defined region of high chlorophyll concentration in order to restrict the model application to an environment of more homogeneous export processes. We developed a correlation-based approximation to estimate the surface source area for a sediment trap deployed from 11 June 1998 to 7 November 1999 at 21.25°N latitude and 20.64°W longitude off Cape Blanc. We also developed a regression model of chlorophyll and export of organic carbon to the 1000 m depth level. Carbon export was calculated for an area of high chlorophyll concentration (>1 mg/m**3) adjacent to the coast on a daily basis. The resulting zone of high chlorophyll concentration was 20,000-800,000 km**2 large and yielded a yearly export of 1.123 to 2.620 Tg organic carbon. The average organic carbon export within the area of high chlorophyll concentration was 20.6 mg/m**2d comparable to 13.3 mg/m**2d as found in the sediment trap results if normalized to the 1000 m level. We found strong interannual variability in export. The period autumn 1998 to summer 1999 was exceeding the mean of the other three comparable periods by a factor of 2.25. We believe that this approach of using more regionally fitted models can be successfully transferred even to different oceanographic regions by selecting appropriate definition criteria like chlorophyll concentration for the definition of an area to which it is applicable.
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The Indian Ocean covers approximately 73.5 * 10**6 km**3 from 25°N to 67°S and from 20° to 120°E. Several legs of the Deep Sea Drilling Project (DSDP) and the Ocean Drilling Program (ODP) have operated in its waters, many penetrating the Cretaceous. Most of the scientific drill sites are DSDP related and thus pre-dated modern biostratigraphic conventions. Foraminifers and calcareous nannoplankton were by far the dominant fossil groups studied in the earlier work, supplemented occasionally by studies of other fossil groups, The results of the Ocean Drilling Project phase are yet too young to be fully integrated but have been based on a broader range of techniques and fossil groups. During most of the Cretaceous, the proto-Indian Ocean basin lay in middle to high latitudes. Thus, it is unrealistic to expect successful routine application of low-latitude zonations. No planktonic foraminifer zonal scheme has been developed for the Indian Ocean basin for several reasons. There are no sections with complete or even significant partial sections to allow development of such a zonation. Carbonate compensation depth (CCD) effects have been marked in most sections, and significant intervals are devoid of planktonic foraminifers. The Indian Ocean now covers a great latitudinal range from tropics to polar regions and, at first glance, no scheme can be expected to be applicable over that entire range. In the Cretaceous the area was much smaller, though expanding progressively, and the paleolatitude range was quite small. Calcareous nannoplankton have proved valuable in dating Indian Ocean Cretaceous sediments and have, perhaps in contrast with the foraminifers, been consistently a more reliable means of applying zonal schemes developed elsewhere. For the Albian-Aptian, zonations based on well-known benthic foraminifer lineages (Scheibnerova, 1974) have been useful when nothing else was available or effective. Palynology has been used little, but where used, has proved excellent. It has the added value of providing valuable information on nearby terrestrial vegetation as the fossils were resistant to dissolution. Normally, when different fossil groups have been applied to a section, the results have been compatible or compatible to an acceptable degree. There are a few instances where incompatibility is noteworthy, and Site 263 is a classic example, as even two calcareous nannoplankton studies show irreconcilable differences here. All groups gave different results, but one benthic foraminifer analysis agreed with one calcareous nannoplankton study.
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Mode of access: Internet.
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F only available in microfiche.
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Texas Department of Transportation, Research and Technology Transfer Office, Austin
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Texas State Department of Highways and Public Transportation, Transportation Planning Division, Austin
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Texas State Department of Highways and Public Transportation, Transportation Planning Division, Austin
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Federal Highway Administration, Washington, D.C.