Variability of a cyprinid lake ecosystem with special emphasis on the native fish fauna under intensive fisheries management including common carp (Cyprinus carpio) and silver carp (Hypophthalmichthys molitrix)

The lake investigated (Lake Heiliger See near the town of Angermünde, North-East Germany) is small (10.2 ha) but deep (z_max = 12 m, ? = 6.5 m). During summer the thermocline is at a depth of 4-5 m, and the hypolimnion is filled with H₂S already by mid-June, making 60-75% of the bottom area inaccessible to fish. The native fish fauna is dominated by planktivorous roach (Rutilus rutilus). A test stocking of silver carp (Hypophthalmichthys molitrix) together with an unplanned and erroneous stocking of common carp (Cyprinus carpio), coupled with an incorrectly calculated strong stocking of eel (Anguilla anguilla), which assumed that the total lake area yielded fish food organisms, brought about a strong depression of the food biomass available to native fish. Both silver carp and common carp showed a pattern of behaviour which only partly agreed with results obtained in experimental ponds prior to lake stocking. At least for 10 years there was a very low zooplankton biomass (mostly below 1 mg/l fresh weight) caused by silver carp and a strongly reduced benthos biomass (frequently below 1 g/m² fresh weight) caused by common carp and eel on H₂S-free bottom areas. Despite this extreme situation, which lasted for 20 years and is rarely found in lakes elsewhere, it was not possible to demonstrate negative effects on the native fish fauna comprising 16 species. Also the dominance pattern seems uninfluenced in the long run. A strong decline of the catchable roach stock was observed for some years, but the stock reappeared soon in comparable quantity. During the time of roach stock depression the individual growth of roach (and common carp) was particularly low. Nevertheless, roach succeeded in reproduction during this time in spite of the reduced zooplankton and detritus concentrations. Fry numbers per year ranged from 500-15 000 individuals/ha. The pike perch (Stizostedion lucioperca) was perhaps the most endangered species of all those living at small population numbers in the lake, since its fry is confined to the limnion where competition from silver carp and adult roach and perhaps predation by roach is highest. However the pike perch stock remained unchanged at the low level of 1950, the time prior of carp and eel stocking. All other rare species of Lake Heiliger See spawn in the littoral zone where fry survival conditions were less impacted. In summary, we present more evidence that the fish fauna of cyprinid lakes is more robust than in salmonid lakes. The regulation capacity of fish communities of eutrophic lakes seems to be able to offset even severe direct and indirect influences of fisheries management.     

Luminescence chronology of late pleistocene loess-paleosol and tephra sequences near Fairbanks, Alaska

Thermoluminescence (TL) and infrared-stimulated luminescence (IRSL) sediment-dating methods have been applied to paleosol- and tephra-bearing loess sequences younger than marine oxygen isotope stage (MIS) 7 at three important sites. TL ages indicate the development of significant paleosols ∼75,000 and ∼30,000 yr ago in the loess sequence at the Gold Hill site. Relatively minor soil development occurred ∼70,000 and ∼48,000 yr ago. Like the ∼75,000-yr-old soil, the 30,000-yr-old soil is apparently of global extent, and consistent in timing with inferred warm intervals elsewhere (e.g., Greenland, Europe, western and central China). At Birch Hill, replicate TL dating of primary loess combined with two earlier TL results from the same site, and with an earlier mean fission-track-glass-shard age of 140,000 ± 10,000 yr for the associated Old Crow tephra, yield a more precise numeric age of 142,300 ± 6600 yr for this Alaska/Yukon chronostratigraphic marker ash bed. Three of the TL ages at the Halfway House site are difficult to interpret, but combined with other evidence, they indicate: (1) the upper 5-6 m of loess from Halfway House is not part of the Gold Hill Loess (equivalent to pre-MIS 5 age) as long thought by T.L. Péwé, but rather is much younger; (2) the regionally significant variegated tephra, found in the Fairbanks and Klondike areas and previously thought to be older than MIS 5, has an age of 77,800 ± 4100 yr (late MIS 5).     

Trace-element geochemistry of individual glass shards of the Old Crow tephra and the age of the Delta glaciation, central Alaska

Two widespread tephra deposits constrain the age of the Delta Glaciation in central Alaska. The Old Crow tephra (ca. 140,000 ± 10,000 yr), identified by electron microprobe and ion microprobe analyses of individual glass shards, overlies an outwash terrace coeval with the Delta glaciation. The Sheep Creek tephra (ca. 190,000 yr) is reworked in alluvium of Delta age. The upper and lower limiting tephra dates indicate that the Delta glaciation occurred during marine oxygen isotope stage 6. We hypothesize that glaciers in the Delta River Valley reached their maximum Pleistocene extent during this cold interval because of significant mid-Pleistocene tectonic uplift of the east-central Alaska Range.     

Lake victoria: The water hyacinth (Eichhornia crassipes [Mart.] Solms), its socio-economic effects, control measures and resurgence in the Winam gulf

The aquatic weed Eichhornia crassipes [Mart.]Solms was introduced in Lake Victoria from Rwanda via the Kagera River by the activities of man. After originally infesting Lake Victoria (Uganda), it eventually spread into the Winam gulf, where its proliferation was spectacular, resulting in an enormous public outcry. The aim of this study was to find out how a beach/bay covered by a weed carpet affected the life of a lakeshore community, if there were any seasonal changes in carpet sizes and to establish if the water hyacinth is a friend or an enemy. Surveys were conducted in selected beaches between June 1995 and November 1999. When surveys were complete, it became clear that this weed is nomadic, except in lagoons and beaches that had little external interference. The open waters remained generally clear due to constant wave action. Interviews conducted on selected beaches/bays indicated that weed carpets impacted both positively and negatively, i.e. they disrupted fishing activities, transport, irrigation, water treatment, enhanced breeding grounds for vectors of human diseases, impacted on biodiversity and had become a source of raw materials for making furniture, paper and artefacts. After successful biological control by the Kenya Agricultural Research Institute (KARI), resurgence and succession were observed. The impact of water hyacinth on the life of the lakeshore communities in the Winam gulf is serious and needs to be quantified. Further research is necessary to establish whether this weed is an enemy or a friend of the lakeshore communities.     

Post-glacial relative sea level, isostasy, and glacial history in Icy Strait, Southeast Alaska, USA

We use the radiocarbon ages of marine shells and terrestrial vegetation to reconstruct relative sea level (RSL) history in northern Southeast Alaska. RSL fell below its present level around 13,900 cal yr BP, suggesting regional deglaciation was complete by then. RSL stayed at least several meters below modern levels until the mid-Holocene, when it began a fluctuating rise that probably tracked isostatic depression and rebound caused by varying ice loads in nearby Glacier Bay. This fluctuating RSL rise likely reflects the episodic but progressive advance of ice in Glacier Bay that started around 6000 cal yr BP. After that time, RSL low stands probably signaled minor episodes of glacier retreat/thinning that triggered isostatic rebound and land uplift. Progressive, down-fjord advance of the Glacier Bay glacier during the late Holocene is consistent with the main driver of this glacial system being the dynamics of its terminus rather than climate change directly. Only after the glacier reached an exposed position protruding into Icy Strait ca. AD 1750, did its terminus succumb - a century before the climate changes that marked the end of the Little Ice Age - to the catastrophic retreat that triggered the rapid isostatic rebound and RSL fall occurring today in Icy Strait.     

Late Pleistocene and Holocene glaciation of the Fish Lake valley,northeastern Alaska Range,Alaska

We reconstructed a chronology of glaciation spanning from the Late Pleistocene through the late Holocene for Fish Lake valley in the north‐eastern Alaska Range using ¹⁰Be surface exposure dating and lichenometry. After it attained its maximum late Wisconsin extent, the Fish Lake valley glacier began to retreat ca. 16.5 ka, and then experienced a readvance or standstill at 11.6 ± 0.3 ka. Evidence of the earliest Holocene glacial activity in the valley is a moraine immediately in front of Little Ice Age (LIA) moraines and is dated to 3.3–3.0 ka. A subsequent advance culminated at ca. AD 610–900 and several LIA moraine crests date to AD 1290, 1640, 1860 and 1910. Our results indicate that ¹⁰Be dating from high‐elevation sites can be used to help constrain late Holocene glacial histories in Alaska, even when other dating techniques are unavailable. Close agreement between ¹⁰Be and lichenometric ages reveal that ¹⁰Be ages on late Holocene moraines may be as accurate as other dating methods. Copyright © 2009 John Wiley & Sons, Ltd.     

Vegetation succession in deglaciated landscapes: implications for sediment and landscape stability

Landscapes exposed by glacial retreat provide an ideal natural laboratory to study the processes involved in transforming a highly disturbed, glacially influenced landscape to a stable, diverse ecosystem which supports numerous species and communities. Large‐scale vegetation development and changes in sediment availability, used as a proxy for paraglacial adjustment following rapid deglaciation, were assessed using information from remote sensing. Delineation of broad successional vegetation cover types was undertaken using Landsat satellite imagery (covering a 22 year period) to document the rate and trajectory of terrestrial vegetation development. Use of a space‐for‐time substitution in Glacier Bay National Park, Alaska, allowed ‘back‐calculation’ of the age and stage of development of six catchments over 206 years. The high accuracy (89.2%) of the remotely sensed information used in monitoring successional change allowed detection of a high rate of change in vegetation classes in early successional stages (bare sediment and alder). In contrast, later successional stages (spruce and spruce–hemlock dominated forest) had high vegetation class retention, and low turnover. Modelled rates of vegetation change generally confirmed the estimated rates of successional turnover previously reported. These data, when combined with the known influence of terrestrial succession on soil development and sediment availability, suggest how physical and biological processes interact over time to influence paraglacial adjustment following deglaciation. This study highlights the application of remote sensing of successional chronosequence landscapes to assess the temporal dynamics of paraglacial adjustment following rapid deglaciation and shows the importance of incorporating bio‐physical interactions within landscape evolution models. © 2014 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

阿拉斯加北坡区域地质演化及油气资源

在收集国内外资料的基础上, 分析研究阿拉斯加北坡地区的构造演化过程, 地层序列及演化阶段, 并对本区石油勘探历史, 地质特征和油气资源进行了总结。确定了4个主要地层序列, 分别为富兰克林层序(密西西比系之下), 埃尔斯米尔层序(密西西比系-三叠系), 波弗特层序(侏罗系-下白垩统)和布鲁克斯层序(下白垩统-第四系)。阿拉斯加北坡地区经历了比较复杂的演化过程, 北坡盆地即位于此。盆地主要经历了3个演化阶段, 分别为埃尔斯米尔造山阶段、同裂谷阶段和前陆阶段。本区具有石油远景的岩石大多在密西西比纪及之后的地层中, 它们记录了整个被动大陆边缘、裂谷和前陆盆地构造阶段地层序列和地质方面的演化。本区油气潜力巨大, 勘探历史悠久。石油和天然气的未探明储量分别为244.9×108桶和2.905×1012 m3, 页岩油约9.4×108桶, 页岩气约1.19×1012 m3。      

Taiwan's response to international fisheries management after 2005 as influenced by ICCAT and fishers' perception

It is widely recognized that fishing states are obliged to exercise flag state responsibility over their vessels. In an attempt to become a responsible fishing actor, Taiwan has endeavored to manage its distant water fishing fleet in accordance with international fisheries management. However, the long-standing problems of illegal, unreported and unregulated (IUU) fishing, fish laundering, and fishing overcapacity, which remained unsolved during the 1990s and early 2000s, brought its management capability into doubt. Failure to address these problems undermined the credibility of all management measures and ultimately resulted in a recommendation adopted by International Commission for the Conservation of the Atlantic Tunas (ICCAT) in 2005. This recommendation significantly affected Taiwan's distant water fishing policy. This paper examines how Taiwan assimilated this outside force into its fishing policy as a new response to international fisheries management and how fishers perceived this response. It shows that Taiwan's efforts in controlling distant water fisheries marked a big change, specifically manifest in three noticeable actions - reducing excessive bigeye-targeted efforts, deterring IUU fishing, and strengthening fisheries management. The study advises that management of small tuna vessels be effectively exercised and recommends future actions on providing subsidies for fishers to partially offset costs incurred by rule compliance, streamlining their administrative work, enhancing communication with them, putting more enforcement and meaningful penalties in place. Finally, the study indicates the existence of an interaction in the international fisheries management scheme, potentially favoring Taiwan to bargain for fishing rights and a favorable status in the participation of regional fisheries management organizations (RFMOs) in the future if it continues to exercise effective control of distant water fisheries.     

Managing fishing capacity in tuna regional fisheries management organisations (RFMOs): Development and state of the art

Overcapacity is a major threat to the sustainability of tuna resources. Diverse actions are being carried out by tuna RFMOs to counteract this problem. This paper reviews and analyses both the historical development of fishing capacity management in tuna RFMOs and their state of the art practices. Despite the fact, that thus far, management measures have not yielded the expected results for capacity reduction, they provide a good basis for improved management of capacity at regional and global levels.