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A new sledge net system using propulsion vehicles has been developed to sample more efficiently the demersal juveniles of marine organisms. A net attached to a sledge maneuvered by a SCUBA diver who uses operating switches on a steering handle to adjust the altitude of the sledge and the position of the tickler chains to ensure that the footcloth of the mouth of the net remains in constant contact with the bottom surface. Video camera, flow meter, compass, and dive computers are positioned on the sledge net in the view of the diver. Given that the system can attain speeds of 70 cm s−1, the net can be employed to capture highly mobile fish. Unlike most boat-based net sampling methods, the use of propulsion vehicles means that there are no sound or vibration disturbances due to the boat and tow ropes typically used to maneuver these types of sampling nets. Marine fauna was collected at monthly intervals over a two-year period in a sampling area along the southern coast of Hokkaido, Japan. A total of 2641 specimens comprising 61 species and including five species which were the first records for the region were collected. These findings suggest that the new sledge net system employing propulsion vehicles was effective for sampling demersal juveniles, particularly in situations where sledge nets towed by boats or push nets cannot be deployed. 相似文献
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《African Journal of Marine Science》2013,35(3):429-439
The major causes of large whale entanglement in South Africa are static fishing gear, especially the type associated with the West Coast rock lobster Jasus lalandii industry, and large-mesh gillnets that are set off the coast of KwaZulu-Natal (KZN) to reduce shark attacks (shark nets). The prevalence of entanglements is seasonal with the peaks in activity coinciding with the breeding migrations of humpback whales Megaptera novaeangliae and southern right whales Eubalaena australis, the two large whale species that are the most prone to entanglement. Generalised linear models with a Poisson or quasi-Poisson distribution were used to describe the relationship between the number of incidents and time. Taking into account the combined length of shark-net installations per year as an offset variable, entanglement of humpback whales in shark nets increased at 15.1% per year (95% CI = 9.5–21.6%) from 1990 to 2009. This is comparable to the rate of increase in the numbers of this species migrating past the KZN coast, between 1988 and 2002 (9–11%). The number of reported incidents of southern right whales entangled in gear other than shark nets also increased between 1990 and 2009. This was accounted for by the increase in numbers of this species in South Africa (7% per year), so in neither case are the two species at increasing risk of individual entanglement, and anthropogenic factors including entanglement do not seem to be affecting the recovery of these whale populations. Nevertheless, there is concern regarding the vulnerability to entanglement of a small assemblage of humpback whales that habitually visits the West Coast in spring and summer. The continued recovery of whale populations is likely to lead to greater levels of anthropogenic interaction and heighten the need for adequate mitigation measures. The KZN Sharks Board and the South African Whale Disentanglement Network (since 2006) have respectively released (disentangled) 81% and 23% of confirmed entangled individuals, and recorded relevant information on entanglement incidents. Such information is critical for developing mitigation measures and monitoring the prevalence of entanglement. 相似文献
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By utilizing a 3-D atmospheric circulation resolving method, the authors studied the air-sea
interactive linkages between the tropical Indian Ocean and the Pacific Ocean in 1979-2008 El
Ni?o-Southern Oscillation (ENSO) events. Their findings showed that evident 3-D gear-coupling
characteristics existed in the 1979-2008 ENSO events. Their resolving analyses also suggested that the
general circulation showed stronger and wider sinking motions over the eastern Indian Ocean-western
Pacific during the mature phase of 1979-2008 ENSO events, compared with the vertical velocities from the
U.S. National Centers for Enviornmental Prediction (NCEP) reanalysis data. With their 3-D analysis
method, the vertical velocity was resolved by two components, i.e. zonal and meridional components. It
was found that the zonal component of the vertical velocities showed a strong sinking motion while the
meridional components showed an upward motion during the prevailing phases of the ENSO events. In the
tropics, the zonal component of the vertical velocities was found greater than the meridional component,
reflecting the dominant characteristics of the vertical velocity, and the overall outcomes showed a strong
sinking motion, although the two components also partially offset each other in the processes. Compared
with the vertical velocities from NCEP reanalysis, the vertical motions calculated with the 3-D resolving
analysis method demonstrate some advantages. 相似文献
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渔用合成纤维及其网线和绳索是构成渔具的基本要素，其强度性能对渔具的力学性能、渔获性能、使用寿命和制造成本具有重要作用。为了满足海洋渔业不断发展的需要，我国陆续颁布了一批国家及行业质量标准，并在实践中逐步接近ＩＳＯ标准或国际名牌产品标准，使渔具纤维材料性能有了较大的提高。本文通过对国内外渔具合成纤维材料强度性能的比较和分析，认为：（１）国产合成纤维长丝的有关性能与日本产品无显著差异；（２）国产ＰＡ胶丝性能普遍较好，并优于英国产品，而ＰＡ长丝捻线与国外产品尚有较大差距；（３）ＰＥ线产品性能普遍超过ＱＪ／ＣＮＦＣ０２９２标准，但仍低于ＳＣ１４１—８５标准要求；（４）国产ＰＡ长丝三股绳索性能与德国产品接近而高于日本产品；（５）ＰＥ和ＰＶＡ三股绳索性能仅略高于日本产品；（６）渔具新材料的研制及其在渔业中的开发应用与国外相比，尚有较大差距，应得到足够重视。 相似文献