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Some studies have attributed forest shrinkage to population growth, economic development, conversion of forest land to agricultural
use and harvesting of trees for timber and fuelwood. But the statistical support for these hypotheses is not strong. This
paper attempts to test the above hypotheses statistically in the case of Bangladesh. Factor analysis extracted 4 important
factors—(a) exploitation of forests for timber, fuelwood, tea, and shrimp production, (b) demographic pressure in agriculture,
(c) economic development, and (d) expansion of crop lands—as causes of deforestation. The statistical test supports the hypotheses
that the exploitation of forests for timber, fuelwood, tea and shrimp production, and conversion of forests to crop lands
have a negative influence on forest cover. Economic development and demographic pressure in agriculture are also negatively
correlated with forest cover. Results of regression analysis show the conversion of forests to agricultural land is the most
important cause of deforestation. Other important causes, in order of their relative importance, are the relative price of
forest products, population growth, economic development, demographic pressure in agriculture, increasing production of shrimps,
export of tea and shrimps, increasing production of timber and fuelwood, and expansion of tea lands. The statistical tests
support the above relationships. 相似文献
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Tetsuya Takatsu Toshikuni Nakatani Takanori Miyamoto Kouji Kooka & Toyomi Takahashi 《Fisheries Oceanography》2002,11(2):90-101
The spatial distributions and feeding habits of Pacific cod ( Gadus macrocephalus ) larvae, and the spatial distributions of copepod nauplii and copepodites, their main prey, were examined in Mutsu Bay from February to March during 1989–92. Yolk-sac larvae were caught at 30–45 m depth at the bay mouth. Larvae without yolk were collected at 8–45 m depth at the bay mouth and the inner part of the bay, and large larvae were chiefly found in the bay. This geographical pattern in larval size may have been because of transport to the inner part of Mutsu Bay by the Tsugaru Warm Current. The dominant taxa of copepod nauplii and copepodites in the diet and the environment changed each year. Larvae fed mainly on abundant taxa in the environment, suggesting that larvae are opportunistic feeders. Nauplii and copepodites were abundant in the bay, especially in 1992. Copepodites were slightly more abundant in the diet of cod larvae in 1992 than in 1991, but this difference was smaller than in the environment. In addition, larvae with empty digestive tracts were scarce in 1991 and 1992. Prey concentrations in the bay in 1991 and 1992 seem to have been high enough to sustain most Pacific cod larvae. 相似文献
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Masafumi KIMURA Toyomi TAKAHASHI Tetsuya TAKATSU Toshikuni NAKATANI Tatsuaki MAEDA 《Fisheries Science》2004,70(4):537-545
ABSTRACT: Effects of hypoxia on the principal prey and growth of flathead flounder Hippoglossoides dubius were studied in Funka Bay. Of the three dominant year-classes that occurred in recent years, the 1995 year-class was small in total length at age ≥ 3 and low in condition factor at age ≥ 2. Ophiuroids (almost Ophiura sarsi ), which were the dominant prey in the 1980s, were of little importance and instead, crustaceans such as mysids, natant decapods and pelagic amphipods, bivalves and fish were important prey items for H. dubius in 2000–2001. In addition, the feeding intensity of H. dubius in 2000–2001 was lower than that in the 1980s. These facts are closely related to a reduction of prey abundance, particularly ophiuroids. It seems that the hypoxia that occurred in the central part of the bay during the summer and autumn of 1995–1997 caused the poor food supply and low growth rate at ages 2–4 of the 1995 year-class. 相似文献
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Annual variation in otolith increment widths of walleye pollock (Gadus chalcogrammus) larvae in Funka Bay,Hokkaido, Japan 下载免费PDF全文
Yota Kano Tetsuya Takatsu Yutaro Hashimoto Yuta Inagaki Toshikuni Nakatani 《Fisheries Oceanography》2015,24(4):325-334
To clarify relationships between year‐class strength and larval growth of walleye pollock (Gadus chalcogrammus), and oceanographic conditions in the Pacific stock off Hokkaido and Tohoku, Japan, we undertook conductivity/temperature/depth (CTD) observations and investigated larval densities, larval otolith increment widths and larval prey densities (of copepod nauplii) of the 2008, 2009, 2010 and 2011 yr classes in Funka Bay. Oyashio Coastal Water (OCW) flowed into the bay in late February in 2008, 2010 and 2011, and the mean water temperatures decreased to 1.9–3.1 °C in March. OCW was not observed in 2009, and it was warm in late February (≥3.4 °C). Increment widths of lapillar otoliths during the yolk‐sac stage were wide in 2009 and 2011, medium in 2010 and narrow in 2008. Increment widths during the first‐feeding stage tended to become wider as the hatch month progressed, and the annual variation during the first‐feeding stage was larger than that of the yolk‐sac stage. The densities of the primary food for the larvae were high in 2008 when larval increment widths were narrowest, so the effect of prey abundance on larval growth appeared to be small. The ranking of the larval abundance in March was nearly coincident with that of the increment width during the larval stage. We, therefore, suggest that the larval growth rate is associated with the mortality rate and that the growth–mortality hypothesis may be applicable to walleye pollock in Funka Bay. Feeding success under warm water conditions may be an important factor that contributes towards high growth rates. 相似文献
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Community forest management (CFM) has received increasing worldwide attention from governments, researchers and educational
institutions over the past two decades. Many governments, especially in developing countries, have prioritized CFM over traditional
forest management systems. In Thailand, CFM is not recognized by the legal system; however, there are de facto CFM practices under common property resource regimes. CFM has in essence been practiced here for hundreds of years by local
people, and represents an important aspect of Thai culture. This study aims at evaluating CFM in Thailand in the context of
sustainable development. To meet the objective, the study gathered information through focus group discussions with various
stakeholders: academics, Forest Department staff, and members of the Chang Tok Tay community forests. From the study, it emerged that forest resources are critical for the livelihoods and survival of rural
people, and so they have protected forests to ensure sustainable livelihoods. This study identified that prospects for sustainable
CFM in Thailand are bright because: (i) community members are highly motivated and are sufficiently interested to protect
trees because they are well aware that their livelihoods are under threat from depleting forests; (ii) tradition and culture
of rural people support their relation with nature; (iii) non-timber forest products (NTFPs) play a crucial role in local
livelihoods for subsistence and necessitate protection of the forest watershed, which is vital to support their occupations;
(iv) spiritual rituals such as those where Buddhist monks bind yellow cloth on trees play a vital role in protecting trees,
something rare in other countries. The study further identified various hindrances to achieve sustainable CFM: (i) legal support
for CFM is absent; (ii) the Royal Forest Department (RFD) cannot transfer appropriate technology to community people due to
lack of legal support; (iii) scope for developing effective strategies for sustainable CFM by combining traditional knowledge
with existing scientific knowledge is limited; (iv) a formal institutional arrangement for CFM does not exist; and (v) community
members’ access to the hard technology of CFM is limited. Therefore, in addition to legalizing CFM, a formal institutional
framework for elaboration, implementation and control of CFM is essential to achieve sustainable CFM in Thailand. 相似文献
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Yuki Yamamoto Taku Yoshiyama Keitaro Kajiwara Toshikuni Nakatani Takashi Matsuishi 《Fisheries Science》2018,84(3):425-433
Overfishing can affect life history traits, resulting in population collapse and oftentimes a decrease in length-at-age and maturation size in fish populations. However, little is known about the recovery mechanisms and time scales of these traits in exploited wild populations. In the study reported here, we documented long-term shifts in growth and mature size in Miyabe charr Salvelinus malma miyabei associated with a history of recreational fishing in Lake Shikaribetsu for approximately 80 years. Downsizing in the charr was observed when the charr population collapsed due to intensive recreational fishing. However, subsequent moratoriums and the introduction of fishing regulations, especially the implementation of a catch-and-release policy, during the following 10–30 years facilitated the recovery of population size, length-at-age and mature fish size. This study provides important insights into the biological changes and required recovery time scales of a heavily harvested population and supports management and conservation strategies. 相似文献
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