SEMINAR: MBF602 Seminar Fracesca Forrestal Friday 9/24 4p

["sidney hartley" <shartley@rsmas.miami.edu>]

Effects of Capture-Based Aquaculture of Bluefin Tuna (Thunnus thynnus
thynnus) on a Western Mediterranean Ecosystem 

 

The Eastern stock of Atlantic bluefin tuna (Thunnus thynnus thynnus) has, in
recent decades, declined to probably a quarter of its virgin biomass, mainly
driven by excessive catches mediated by the growth of the capture-based
aquaculture of this species in the Mediterranean. This study addresses the
potential food-web effects on trophic linkages in the ecosystem through the
removal of both small pelagic fish species and wild bluefin tuna for
capture-based aquaculture operations. An ECOPATH model of the Southern
Catalan Sea (Western Mediterranean) was modified to include a bluefin tuna
farm supplied entirely from fish captured in the area modeled (Coll et al,
2006). Six scenarios were developed to simulate possible changes to the
system using ECOSIM, including the continued growth of aquaculture
operations, as well as changes to the total allowable catch for bluefin tuna
as set by ICCAT. The current level of aquaculture production of bluefin tuna
in the Catalan Sea does not produce detectable effects in the ecosystem.
Simulation scenarios that include the level of production already present in
a similar ecosystem to the south, in the Murcia region, resulted in large
fluctuations of both bluefin tuna biomass and yield, as well as for many of
the species in the modeled ecosystem. Increases in biomass of lower trophic
level functional groups were observed along with reductions in biomass from
higher trophic level predators. Jellyfish and benthopelagic fish exhibited
an increase in biomass, the largest being 8.76% for jellyfish and 69.76% for
benthopelagic fish, while wild bluefin tuna biomass decreased by 87.26%.
Atlantic bonito and swordfish showed similar rates of decline in biomass
levels. Some of these effects are caused by the shift of bluefin tuna prey
species introduced by the caging of wild fish. Bluefin tuna eat a greater
diversity of prey in the wild in comparison than in the cages. These
outcomes stress that removal of biomass at top and intermediate trophic
levels can have unforeseen outcomes on the structure of the ecosystem, due
to the complexity of the food web. Results suggest that, in the case of the
Western Mediterranean Sea, increasing bluefin tuna farming activities will
likely contribute towards further degradation of an already highly exploited
marine ecosystem. 

 

BSc. Marine Biology UC Santa Cruz May 2006

 

MSc.  MAF/MBF University of Miami June 2010

 

Entered Program:  Fall 2010

 

Advisors:  David Die and Elizabeth Babcock 

 

 

Sidney L.S. Hartley

University of Miami

Rosenstiel School of Marine and 

Atmospheric Science

Division of Marine Biology and Fisheries

4600 Rickenbacker Causeway

South Grosvenor 315

Miami, Fl 33149

p: 305.421.4176

f: 305.421.4600

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