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Bottom trawl fishing is a controversial activity. It yields about a quarter of the world's wild seafood, but also has impacts on the marine environment. Recent advances have quantified and improved understanding of large‐scale impacts of trawling on the seabed. However, such information needs to be coupled with distributions of benthic invertebrates (benthos) to assess whether these populations are being sustained under current trawling regimes. This study collated data from 13 diverse regions of the globe spanning four continents. Within each region, we combined trawl intensity distributions and predicted abundance distributions of benthos groups with impact and recovery parameters for taxonomic classes in a risk assessment model to estimate benthos status. The exposure of 220 predicted benthos‐group distributions to trawling intensity (as swept area ratio) ranged between 0% and 210% (mean = 37%) of abundance. However, benthos status, an indicator of the depleted abundance under chronic trawling pressure as a proportion of untrawled state, ranged between 0.86 and 1 (mean = 0.99), with 78% of benthos groups > 0.95. Mean benthos status was lowest in regions of Europe and Africa, and for taxonomic classes Bivalvia and Gastropoda. Our results demonstrate that while spatial overlap studies can help infer general patterns of potential risk, actual risks cannot be evaluated without using an assessment model that incorporates trawl impact and recovery metrics. These quantitative outputs are essential for sustainability assessments, and together with reference points and thresholds, can help managers ensure use of the marine environment is sustainable under the ecosystem approach to management.  相似文献   
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Journal of Soils and Sediments - To understand the impact of geochemical sedimentation history for arsenic (As) distribution in the sediment profiles of the Hetao Basin, we (1) evaluated sediments...  相似文献   
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Large sized biopores (diameter >2 mm) in the subsoil can be created by tap roots, which leave voids after their decay, or by the burrowing activity of anecic earthworms which may benefit from the temporary lack in tillage in perennial cropping systems. However, the interactions between root growth and earthworm activity in the process of biopore formation during perennial ley cropping are not well understood. The aim of this field study was to quantify the development of the abundance of the anecic earthworm Lumbricus terrestris and the biopore density during the cultivation of lucerne (Medicago sativa L.), chicory (Cichorium intybus L.) and tall fescue (Festuca arundinacea Schreb.) grown for either one, two or three years. An increased abundance of L. terrestris was already recorded after two years of continuous ley when compared with one year cultivation. The ley crop species had only minor influence on the abundance of L. terrestris. Biopore densities of both diameter classes under study (2–5 mm and >5 mm) were not significantly affected by the duration of ley cropping. In contrast, biopore densities were influenced by ley crop species. More biopores of diameter class 2–5 mm were recorded after chicory than after fescue. Lucerne cropping resulted in intermediate biopore density. Additionally, in an incubation experiment under field conditions, we quantified whether L. terrestris preferentially created new biopores or colonized abandoned, previously existing ones. After three weeks of incubation, one third of the adult individuals incubated in the experimental area created new biopores at 0.4 m soil depth. A similar percentage of individuals colonized previously existing biopores, partially widening the lumen of smaller sized biopores. The remaining individuals remained in the topsoil. Sub-adult individuals rarely formed new pores. Half of the introduced sub-adults remained in the topsoil. We conclude that in crop rotations new biopores can be generated during perennial ley cropping by taproot systems of ley crops, but that a two to three- year period without tillage is not sufficient for populations of anecic earthworms to make a marked contribution to biopore density in the subsoil. The relevance of anecic earthworms for altering physical and chemical properties of biopores during ley cropping still needs further investigation.  相似文献   
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  1. Understanding population size and trend is critical information in species management and conservation. To enable accurate population trend estimates, consistent robust monitoring of a species is essential, particularly for a species such as the New Zealand (NZ) sea lion, Phocarctos hookeri , which has experienced an almost continuous decline in pup production since the late 1990s.
  2. This research examines the pup production estimates for all known breeding sites for this species, and using a stage‐structured matrix population model, estimates population size and trend between 1995 and 2015.
  3. Overall, it is estimated that 2,316 pups were born in 2015, a decrease of 13% since 1995 and a 27% decline since the highest pup production estimate in 1998. This decline has been driven by the significant decline of 48% at the main breeding area, the Auckland Islands since 1998.
  4. Using the stage‐structured matrix population model a total species population size of 11,767 sea lions (95% CrI: 10,790–12,923) was estimated. This is the lowest population size of any sea lion species. Trend data for the Auckland Islands indicated that pup and population numbers have decreased at 1.9% yr?1 in the last 20 yr, while total species population decline is 0.6% yr?1.
  5. Estimates of population trends for this species have been hindered by inconsistent monitoring at most breeding sites. This study strengthens the growing field of research highlighting the need for consistent long‐term monitoring for the conservation management of endangered species.
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  1. The noble crayfish (Astacus astacus) is an endangered freshwater species in Europe. The main threat is from lethal crayfish plague, caused by the oomycete Aphanomyces astaci that has been spread over Europe by introduced North American crayfish species, acting as chronic carriers of the disease.
  2. Most of the remaining noble crayfish populations are found in the Baltic Sea area, and there is an urgent need to implement conservation actions to slow down or halt the extinction rate in this region. However, limited knowledge about the genetic structure of populations in this area has so far precluded the development of conservation strategies that take genetic aspects into consideration.
  3. Key objectives of this large-scale genetic study, covering 77 locations mainly from northern Europe, were to describe the contemporary population genetic structure of the noble crayfish in the Fennoscandian peninsula (Sweden, Norway, and Finland), taking postglacial colonization history into account, and to evaluate how human activities such as stocking have affected the genetic structure of the populations.
  4. Analyses of 15 microsatellite markers revealed three main genetic clusters corresponding to populations in northern, middle, and southern Fennoscandia, with measures of genetic diversity being markedly higher within populations in the southern cluster. The observed genetic structure probably mirrors two main colonizations of the Baltic Sea basin after the last glaciation period. At the same time, several deviations from this pattern were observed, reflecting past human translocations of noble crayfish.
  5. The results are discussed in relation to the conservation and management of this critically endangered species. In particular, we recommend increased efforts to protect the few remaining noble crayfish populations in southern Fennoscandia and the use of genetic information when planning stocking activities, such as reintroductions following local extinctions.
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