Balanced harvest: concept, policies, evidence, and management implications

Balanced harvest has been proposed to reduce fishing impact on ecosystems while simultaneously maintaining or even increasing fishery yield. The concept has attracted broad interest, but also received criticisms. In this paper, we examine the theory, modelling studies, empirical evidence, the legal and policy frameworks, and management implications of balanced harvest. The examination reveals unresolved issues and challenges from both scientific and management perspectives. We summarize current knowledge and address common questions relevant to the idea. Major conclusions include: balanced harvest can be expressed in several ways and implemented on multiple levels, and with different approaches e.g. métier based management; it explicitly bridges fisheries and conservation goals in accordance with international legal and policy frameworks; modelling studies and limited empirical evidence reveal that balanced harvest can reduce fishing impact on ecosystem structure and increase the aggregate yield; the extent of balanced harvest is not purely a scientific question, but also a legal and social choice; a transition to balanced harvest may incur short-term economic costs, while in the long-term, economic results will vary across individual fisheries and for society overall; for its application, balanced harvest can be adopted at both strategic and tactical levels and need not be a full implementation, but could aim for a “partially-balanced” harvest. Further objective discussions and research on this subject are needed to move balanced harvest toward supporting a practical ecosystem approach to fisheries

Studies on prolactin-secreting cells in aging rats of different strains. I. Alterations in pituitary histology and serum prolactin levels as related to ageing.

Serum PRL levels and histologically tumor-free pituitary glands of 91 aging rats of the BN/BiRij strain, the WAG/Rij strain and their F1 hybrid were studied. In rats with pituitary glands without signs of hyperplasia, serum PRL levels were, in comparison to rats of 15-24 months, increased 25-29-month-old female BN/BiRij rats and showed a decline with further aging. This rise and decline during aging correlated with changes in the PRL cell volume density and in ultrastructural signs of their synthetic activity. Rats with hyperplastic pituitaries showed similar age-related changes in serum PRL levels, but these levels were higher. Concerning the hyperplasia, some strain differences were found. In BN/BiRij rats anti-r-PRL positive hyperplasia, and in WAG/Rij and F1 rats, anti-r-PRL negative and anti-r-PRL positive hyperplasia were present. All foci of hyperplasia were negative for anti-ACTH and anti-h-GH. In male rats no age-related changes of serum PRL levels could be established, although a decline of PRL cell volume density in the oldest rats is indicated. We conclude that the absence of a continuous age-related rise of serum PRL levels in our animals is caused by exclusion of animals with pituitary tumors

Fisheries, the inverted food pyramid

A global assessment of fishing patterns and fishing pressure from 110 different Ecopath models, representing marine ecosystems throughout the world and covering the period 1970 to 2007, show that human exploitation across trophic levels is highly unbalanced and skewed towards low productive species at high trophic levels, which are around two trophic levels higher than the animal protein we get from farming. Overall exploitation levels from low trophic species were less than 15% of production, and only 18% of the total number of exploited groups and species were harvested above 40% of their production. Generally well managed fisheries from temperate ecosystems were more selectively harvested at higher exploitation rates than tropical and upwelling (tropical and temperate) fisheries, resulting in potentially larger long-term changes to the ecosystem structure and functioning. The results indicate a very inefficient utilisation of the food energy value of marine production. Rebuilding overfished components of the ecosystem and changing focus to balancing exploitation across a wider range of trophic levels, ie balanced harvesting, has the potential to significantly increase overall catches from global marine fisheries

Changes in the EGFR amplification and EGFRvIII expression between paired primary and recurrent glioblastomas

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