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  • 1990-1994  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of applied phycology 3 (1991), S. 11-18 
    ISSN: 1573-5176
    Keywords: Gelidium ; Pterocladia ; harvesting ; yield ; biomass ; management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This work brings together the scattered information on marine plant harvests and the colloid extraction industry in Portugal, as an initial contribution to the improvement of resource management. The first phase of exploitation of marine plant resources started prior to the 14th century, with the gathering and sale of storm-tossed seaweeds for fertilizer. The harvest of seagrasses and algae at Ria de Aveiro was of great economic importance. The second phase of resource exploitation began with the wider scale harvest of agarophyte species for colloid extraction. Portugal is at present the third largest harvester of the agarophytes Gelidium and Pterocladia (2500 t annually), and it is the fifth largest agar producer (350 t annually). Other colloid-producing species, including Chondrus crispus and Mastocarpus stellatus, are also harvested for export. The total agarophyte landings, agar production and income from agar exports is far below the maximum levels attained in the early 1970s. The status of stocks in each different harvest zone on the continental coast and the Azores is examined. Although there is an effective management structure for the Portuguese marine plant resource, research is needed to provide a sound biological basis for management.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 260-261 (1993), S. 269-276 
    ISSN: 1573-5117
    Keywords: Gelidium sesquipedale ; population dynamics ; demography ; matrix models ; size classes ; harvest ; seaweed
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A matrix model describes the annual dynamics of a commercial (harvested by plucking) Gelidium sesquipedale population off Cape Espichel, Portugal. Vital rates were measured from a frond population divided into size classes; annual transition probabilities among them were calculated. Transition probabilities under harvest by cutting are derived by assuming that all harvested fronds are cut to the first size class, and none are plucked. Simulations of the annual population dynamics for harvest by both plucking and cutting are used to assess which harvest strategy will optimize yields. Assuming the same efficiency for both strategies, cutting fronds to 7 cm (as mechanical harvesters do) results in a higher population growth rate (λ = 1.08 to 1.35) than occurs with the plucking technique (λ = 0.85). Simulations of population recovery show the number of fronds in each size class available the next harvest season will be higher when cut than plucked. This model can also optimize yields by predicting the more efficient season opening, and harvesting cutting height.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 1993-06-01
    Print ISSN: 0018-8158
    Electronic ISSN: 1573-5117
    Topics: Biology
    Published by Springer
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  • 4
    Publication Date: 1991-03-01
    Print ISSN: 0921-8971
    Electronic ISSN: 1573-5176
    Topics: Biology
    Published by Springer
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