The ecosystem impacts of fisheries have become an important concern in fisheries management
and one of the most important issues in fisheries science. The objectives of this thesis were i) to
evaluate the use of trophic models in the analysis of the ecosystem responses to fishing small
pelagic forage fish; ii) to forecast the 'fishing down marine food web' phenomenon in Brazil;
and iii) to conduct an in-depth analysis of the sardine, Sardinella brasiliensis, fishery off
southeastern Brazil to examine hypotheses of ecosystem changes following stock collapse, and to
evaluate how uncertainties of ecological processes influence the choice of harvest strategies and
controls in this fishery. Dynamic simulations of mass-balance trophic models were used to
compare the ecosystem responses to fishing forage fishes across different types of marine
ecosystems, and to examine the stability characteristics of ecosystems when impacted by
fisheries. The comparative analysis among trophic models indicated that as 'wasp-waist' species
in upwelling ecosystems, small pelagics will only sustain much more conservative exploitation
rates than the levels that have brought about historical stock-collapses. In the upwelling
ecosystem off southeastern Brazil, sardine has been historically the main target of commercial
fisheries, although 'fishing down marine food webs' for small pelagic fish species is not yet an
overall observed phenomenon in Brazil. The collapse of the sardine fishery in the late 1980s has
apparently favored a competing small pelagic fish (anchovy, Engraulis anchoitd) in the
ecosystem. The combined effect of fishing and environmental effects makes it difficult,
however, to characterize the changes in the sardine population and the ecosystem, and to predict
the results of rehabilitation measures for the stock. On the other hand, the explicit recognition of
these ecological uncertainties allows a sound choice of precautionary strategies for the fishery,
and a better scrutiny of research programs to improve management. In this context, trophic
models will have a complementary role to single-species models in the analysis of the broad
consequences of fishing policies, and in the test and formulation of hypotheses about the causes
of observed changes in marine ecosystems.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/10998 |
| Date | 05 1900 |
| Creators | Vasconcellos, Marcelo |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Relation | UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/] |
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