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Fish for Food and Ecosystem Function: Fisheries, Trade and Key Ecosystem Processes in Coral Reefs
Stockholm University, Faculty of Science, Department of Systems Ecology.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fish is a key source of food and income to millions of people living along tropical coastlines. They also play essential roles underpinning key ecosystem processes in coral reefs. For example, herbivorous fish keep algae in check that otherwise may outcompete corals, reducing the reef’s social-ecological values. New fishing methods and globalization have turned fish into global commodities, threatening the ecological resilience of many reefs. This thesis addresses the delicate balance between social and ecological aspects associated with fisheries and trade with reef fish in Zanzibar, Tanzania. Paper I examines how parrotfish contribute to keeping reefs free from algae and shows a non-linear relationship between fish body size and function, hence illustrating that maintaining large fish individuals on coral reefs is particularly important. Gear-based management (GBM) has been suggested as an alternative to no-take marine protected areas (MPAs) to sustain ecosystem processes without threatening fishers’ livelihood. Paper II investigates fishers’ use of different gears and how these gears select different functional groups of fish. Results indicate that gear restrictions could be used to reduce fishing pressure on particularly important groups of fish, but also that such an approach is far from simple. MPAs and GBM are both restrictions targeting fishers, but with increasing global demand for reef fish, it is neither realistic nor fair to place the sole burden of sustainable fisheries on them. Papers III & IV analyze the value chain of fish, from fishers to traders and consumers. Results show that the Zanzibar fishery targets a wide range of fish species and sizes, intended for different markets. The thesis concludes that a sound understanding of the functional properties of fish and more nuanced approaches to regulate fishing may contribute to the management of reef fisheries, but that sustainable solutions will require that measures are taken far beyond the oceans.

Place, publisher, year, edition, pages
Stockholm: Department of Systems Ecology, Stockholm University , 2012. , 58 p.
Keyword [en]
fish, food, key ecosystem processes, functional groups, coral reefs, trade, gear, small-scale fisheries, social-ecological systems, Zanzibar, Tanzania, Western Indian Ocean
National Category
Natural Sciences
Research subject
Natural Resources Management
Identifiers
URN: urn:nbn:se:su:diva-75102ISBN: 978-91-7447-469-5 (print)OAI: oai:DiVA.org:su-75102DiVA: diva2:514185
Public defence
2012-05-15, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 09:30 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Submitted.

Available from: 2012-04-23 Created: 2012-04-05 Last updated: 2012-04-17Bibliographically approved
List of papers
1. The non-linear relationship between body size and function in parrotfihes
Open this publication in new window or tab >>The non-linear relationship between body size and function in parrotfihes
2008 (English)In: Coral reefs (Print), ISSN 0722-4028, E-ISSN 1432-0975, Vol. 27, no 4, 967-974 p.Article in journal (Refereed) Published
Abstract [en]

Parrotfishes are a group of herbivores that play an important functional role in structuring benthic communities on coral reefs. Increasingly, these fish are being targeted by fishermen, and resultant declines in biomass and abundance may have severe consequences for the dynamics and regeneration of coral reefs. However, the impact of overfishing extends beyond declining fish stocks. It can also lead to demographic changes within species populations where mean body size is reduced. The effect of reduced mean body size on population dynamics is well described in literature but virtually no information exists on how this may influence important ecological functions. The study investigated how one important function, scraping (i.e., the capacity to remove algae and open up bare substratum for coral larval settlement), by three common species of parrotfishes (Scarus niger, Chlorurus sordidus, and Chlorurus strongylocephalus) on coral reefs at Zanzibar (Tanzania) was influenced by the size of individual fishes. There was a non-linear relationship between body size and scraping function for all species examined, and impact through scraping was also found to increase markedly when fish reached a size of 15-20 cm. Thus, coral reefs which have a high abundance and biomass of parrotfish may nonetheless be functionally impaired if dominated by small-sized individuals. Reductions in mean body size within parrotfish populations could, therefore, have functional impacts on coral reefs that previously have been overlooked.

National Category
Ecology
Identifiers
urn:nbn:se:su:diva-15616 (URN)10.1007/s00338-008-0394-3 (DOI)000260616400027 ()
Available from: 2008-12-06 Created: 2008-12-06 Last updated: 2017-12-13Bibliographically approved
2. The influence of different fishing gear on ecosystem processes in artisanal coral reef fisheries
Open this publication in new window or tab >>The influence of different fishing gear on ecosystem processes in artisanal coral reef fisheries
(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Research subject
Natural Resources Management
Identifiers
urn:nbn:se:su:diva-75100 (URN)
Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2012-04-12Bibliographically approved
3. Trading with resilience: parrotfish trade and the exploitation of key-ecosystem processes 
Open this publication in new window or tab >>Trading with resilience: parrotfish trade and the exploitation of key-ecosystem processes 
2011 (English)In: Coastal Management, ISSN 0892-0753, E-ISSN 1521-0421, Vol. 39, no 4, 396-411 p.Article in journal (Refereed) Published
Abstract [en]

Parrotfish play two important roles in coral reef social–ecological systems; first as important sources of food for reef dependent people, and second by underpinning the ecological function of herbivory (i.e., grazing of algae) on coral reefs. Overfishing of herbivores can be detrimental to coral reef ecosystems because their removal may allow algae to outcompete corals. However, little is known about the drivers behind the exploitation of parrotfish. We describe the trade of parrotfish in Zanzibar with the aim to visualize the linkages between ecological function, market price, and socioeconomic drivers behind their exploitation. Three interesting findings emerge. First, parrotfish are an important part of the fish trade in Zanzibar and are traded at all market scales (from local consumers to international tourists). Second, size is an important determinant of price, with larger fish generating much higher values. Third, size determines which market parrotfish are sold to. Overall the study shows that all sizes of parrotfish are exposed to exploitation, leaving no size-refuge for escaping harvest. In light of an increasing global demand and high market prices, we thus propose that traditional fisheries management be complemented with assessments of both ecological understanding and socioeconomic dynamics to take into account of global market drivers behind parrotfish exploitation at local scales.

Keyword
coral reef, fisheries, parrotfish, resilience, trade
National Category
Environmental Sciences
Research subject
Natural Resources Management
Identifiers
urn:nbn:se:su:diva-66909 (URN)10.1080/08920753.2011.589226 (DOI)000299927200004 ()
Available from: 2011-12-21 Created: 2011-12-21 Last updated: 2017-12-08Bibliographically approved
4. Tracing value chains to understand effects of trade on coral reef fish in Zanzibar
Open this publication in new window or tab >>Tracing value chains to understand effects of trade on coral reef fish in Zanzibar
Show others...
(English)Article in journal (Refereed) Submitted
National Category
Natural Sciences
Research subject
Natural Resources Management
Identifiers
urn:nbn:se:su:diva-75101 (URN)
Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2012-04-12Bibliographically approved

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