Wai Lung Cheung
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Graduate Student Supervision
Doctoral Student Supervision
Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
The impacts of climate change on fish stocks are heightened in the tropics, where catch losses are projected to be three to four times the global average. Yet, there are large sub-regional variations in the drivers and magnitudes of shifting species distributions and their implications for fisheries. In this thesis, I aim to better understand the impacts of climate change on fisheries in the Eastern Tropical Pacific Ocean, from Mexico to Peru. First, I applied a species distribution modeling approach to project future impacts on species caught by the main fisheries in the region. Species are projected to shift towards the equator, seeking the more favorable, cooler habitats associated with the Humboldt and equatorial upwelling systems, as well as towards more oxygenated, inshore waters, away from the expanding oxygen minimum zones. Second, I developed and evaluated the performance of a Biogeographically derived Metabolic Index (BDMI). The BDMI can be generalized to assess the combined effects of warming and deoxygenation on the habitat viability of marine fishes and invertebrates. Thirdly, I applied two catch-based indicators derived from the BDMI to analyze the sensitivity of pelagic fisheries in the Eastern Tropical Pacific to warming and deoxygenation between 1970 and 2009. Temperature was the main factor driving oxygen limitation in pelagic catches. In contrast, when I applied these indices to the demersal community along the oxygen minimum zones off the Costa Rican Pacific coast, ambient oxygen was the main factor driving the responses of the exploited community, although species distributions were sensitive to changes in both temperature and oxygen. In both pelagic and demersal environments, I identified potential temperature and oxygen thresholds that separate different exploited communities with different sensitivities to changing temperature and oxygen levels. Overall, I conclude that warming and deoxygenation will likely impact fisheries resources in the region, revealing the importance of expanding our capability and credibility in projecting future changes. By modeling the mechanisms underlying the non-linear responses of biological communities to ocean warming and deoxygenation, the analytical approaches developed in this thesis can facilitate the detection, attribution and projection of climate impacts, including biogeographical shifts and three-dimensional habitat compression.
Climate change impacts on marine life in the world ocean are expected to increase over the 21st century. In this thesis, I investigated the effects of climate change on biomass flows in marine food webs and their consequences on ecosystem structure and functioning. First, the transfer efficiency and biomass residence time are estimated in the world’ shelf seas from 1950 to 2010. Based on the projected ocean warming under two climate scenarios, I highlighted that biomass transfers may be faster and less efficient by 2100 without mitigation of greenhouse gases emissions. Then, using a modelling framework called EcoTroph that is based on a representation of biomass flow, I projected the future of consumer biomass in marine food webs. From the projected changes in temperature and primary production, marine animal biomass is estimated at each trophic level on a 1° x 1° grid of the global ocean from 1950 to 2100. The projections showed that the projected alteration of biomass flows may lead to a global decline in consumer biomass by 2100 under the “no mitigation policy” climate scenario, with more pronounced impacts at higher trophic levels. In the European waters, the EcoTroph model forced by a coupled hydrodynamic-ecosystem model is used to investigate the potential climate change effects on the ecosystem structure and functioning. The results revealed that biomass and catch may decrease by 2100 under the “no mitigation policy” scenario and if fishing mortality remains constant at its current value. Overall, this thesis showed that climate change would alter biomass flows in marine ecosystems, causing a decrease in the future ocean animal biomass and direct repercussions on fisheries.
Under the United Nations Law of the Seas and the delineation of Exclusive Economic Zones (EEZs), fish stocks that cross neighbouring EEZs are known as transboundary stocks. The sustainability of these stocks depends on international cooperation. However, cooperation is faced with the challenges of insufficient understanding of where and how much fisheries resources are transboundary and climate change is shifting the distribution of marine species. My main objective is to understand the impacts of climate change-induced shifts on transboundary fish stocks distributions and their management, thereby informing international fisheries governance to prepare and respond to climate change. I rely on multiple data sources and numerical modelling to project species distributions under different scenarios of climate change.I found that 67% of the species analyzed are transboundary and that between 2005 and 2014, fisheries targeting these species within global‐EEZs caught on average 48 million tonnes per year, equivalent to USD 77 billion in fishing revenue. As climate change alters ocean properties, the distribution of these species’ transboundary stocks are projected to shift to higher latitude, deeper waters or follow local environmental gradients. Specifically, 60% of the global transboundary stocks will have shifted beyond their historical distribution by 2020, and by 2075, all EEZs are projected to have a shifting transboundary stock. Moreover, the shared proportion of the catch of transboundary stocks between neighboring EEZs will change by 2030 relative to the historic proportion. The changes in the distribution and share proportion of transboundary stocks can potentially impacts the management of the related fisheries. For example, Canada and the United States manage important transboundary stocks. However, by 2050, the proportion of the total catch of some transboundary fish stocks shared between the two countries are expected to change relative to the present, even under a low greenhouse gas emissions scenario.My findings improve our understanding about the current status of transboundary stocks and highlight the challenges that fisheries management will face in a changing climate. Finally, I identify potential adaptation options for transboundary fisheries management such as side payments, dynamic rules, and interchangeable quotas that can improve their sustainability under climate change.
Mariculture is growing rapidly over the last three decades at an average rate of about 3.7% per year from 2001 to 2010. However, questions about mariculture sustainable development are uncertain because of diverse environmental challenges and concerns that the sector faces. Changing ocean conditions such as temperature, acidity, oxygen level and primary production can affect mariculture production, directly and indirectly, particularly the open and semi-open ocean farming operations. This dissertation aims to understand climate change impact on future seafood production from mariculture. Firstly, I update the existing Global Mariculture Database (GMD) with recent mariculture production and create a farm-gate price database to match the production data. I show that global mariculture production in 2015 was 27.6 million tonnes, with a farm-gate value of USD 85 billion. Secondly, I develop quantitative models to predict the present-day global suitable marine area for mariculture. The results show that total suitable mariculture area for the 102 farmed species is 72 million km²: 66 million km², 39 million km² and 31 million km² for finfish, crustaceans and mollusc respectively. Thirdly, I predict climate change impact on suitable marine areas and diversity. Results show that climate change may lead to a substantial redistribution of mariculture species richness, with large decline in potential farm species richness in the tropical to sub-tropical regions. Fourthly, I predict global mariculture production potential (MPP) under climate change. Results suggest that global mariculture production potential will decrease substantially by 16% in the 2050s relative to 2020s under the business as usual scenario. Finally, I develop a set of shared socioeconomic pathways for mariculture to assess the plausible future scenarios for sustainable mariculture under global change. The results highlight that future mariculture development and sustainability will depend on the efficiency of four domains; science and technology; society; governance and economics.Overall, the dissertation shows that climate change is a major threat to seafood production from mariculture. Climate change effect will depend on the species that are farmed, their locations and the farming operation/technology employed. Future research on the sustainable development pathway for mariculture should further expand on socio-economic modelling and projections.
Coral reefs are important ecologically and socially but are threatened by local human impacts and future global climate change. Effective management promotes climate resilience but must take into account the unique multi-scale characteristics of coral reef ecosystems. This dissertation assessed historic trends in coral reef fish assemblages across the Caribbean, to determine the impacts of climate change and role of key environmental drivers in shaping these trends and investigated the influence of these drivers on future reef fish biodiversity. Firstly, using ecosystem indicators, I analyzed historical fisheries catches to assess the potential effects of ocean warming and habitat availability on Caribbean reef fish assemblages. I found that changes in community assemblages were higher than global average for all tropical fisheries and could be explained by increases in sea surface temperature and fishing effects. A negative interaction between reef habitats in each country and sea surface temperature in relation to changes in catch composition, suggesting that habitats may reduce the sensitivity of fish communities to warming. Secondly, using species distribution models, I projected changes in coral reefs under climate change in terms of their morphological complexity. Results showed that under a no-mitigation scenario reef complexity declines significantly, with the most morphologically complex species, Acropora sp., showing northward shifts in relative prevalence. Finally, I conducted multi-scale comparisons of the influence of reef complexity with other environmental variables on current and future Caribbean reef fish biodiversity. Reef fishes showed an affinity for higher temperatures, primary productivity and lower dissolved oxygen at the global scale, but tended toward more alkaline areas hosting reefs, with species showing mixed affinities toward dissolved oxygen. Regional models projected more rapid declines in biodiversity, though declines from global models were larger. Global and regional models projected similar magnitudes of range expansion, though invasions were projected mainly in higher latitudes for global models while regional models projected invasions in lower latitudes around reef-associated areas. Overall, my thesis provides new knowledge for climate-resilient conservation planning by highlighting the utility of multi-scale approaches and the role coral reef habitats may play in protecting reef fish assemblages against the impacts of climate change.
Master's Student Supervision
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
Climate change is altering the physical and biogeochemical properties of the ocean, with implications for the biogeography, phenology, biodiversity and ecosystem functions of marine organisms, as well as for the human societies that depend upon them. Shifting species distributions, among various biological responses to climate change, may exacerbate ongoing challenges to food security, nutritional health and culture for many coastal indigenous First Nation communities. Developing appropriate, nuanced, and context-specific adaptation responses to climate change, however, requires an understanding of how climate-driven ecosystem changes act and interact with other non-climatic factors. Effective adaptation strategies also need to be developed in partnership with community members to identify people’s values, needs, and knowledge of local system dynamics and challenges. Through a collaborative effort with the Tla’amin (ɬəʔamɛn) Nation, this research aims to support the development of adaptation strategies by identifying the perceived mechanisms or pathways through which climate-driven ecosystem changes could affect local seafood access and consumption, and by identifying how these climate effects interact with other factors affecting local seafood availability and access to harvest. This thesis applied a participatory systems mapping approach to co-develop a conceptual model of the key dynamics in the Tla’amin traditional marine food system with Tla’amin Elders, legislators, managers, and community members with expertise in fisheries, traditional food harvest, resource management, and health. I used this model to trace climate stressor-impact pathways and construct a logic-based influence diagram (a modified “fuzzy” cognitive map (FCM)) focusing on the factors affecting food fish harvest. Climate change impacts on the consumption of traditional foods were perceived via both direct and indirect pathways, with reinforcing feedback loops brought about by reduced exposure and experience to traditional foods. Climate effects on local abundance, availability, and safety of fish and shellfish, accompanied by potential consequences for harvest restrictions, were found to compound onto existing constraints to physical and temporal access to the harvest of traditional marine foods. Understanding these multifaceted local climate impacts may help inform future identification and implementation of adaptation strategies for traditional seafood harvest in the face of climate change.
No abstract available.
Recent studies have demonstrated ways in which climate-related shifts in the distribution and relative abundance of marine species are expected to alter the dynamics and catch potential of global fisheries. While these studies focus on assessing impacts to commercial fisheries, few efforts have been made to quantitatively project impacts to small-scale fisheries that are economically, socially and culturally important to many coastal communities. This study uses a dynamic bioclimate envelope model to project scenarios of climate-related changes in the relative abundance, distribution and richness of 98 exploited marine fishes and invertebrates that are of commercial and cultural importance to First Nations in coastal British Columbia, Canada. Declines in relative abundance are projected for most of the sampled species (n = 84 to 95; x̅ = -15.0% to -20.8%) under both the lower and upper scenarios of climate change, with poleward range shifts occurring at a mean rate of 2.9 and 4.5 kilometres decade-1 for fishes and 2.7 to 3.4 kilometres decade-1 for invertebrates within BC’s exclusive economic zone. While cumulative declines in catch potential are projected to occur coastwide (-4.5 to -10.7%), estimates suggest a strong positive correlation between relative catch potential and latitude, with First Nations’ territories along the north and central coasts experiencing less severe declines than those to the south. Furthermore, a strong negative correlation is projected between latitude and the number of species exhibiting declining abundance. These trends are shown to be robust to alternative species distribution models, and highlight key management challenges that are likely to be encountered under climate change. Drawing from an interdisciplinary literature review of First Nations’ traditional fisheries management strategies and historical responses to changes in the availability of aquatic resources, a scenario-based framework is applied to explore climate-resilient pathways for First Nations’ fisheries given quantitative projections. Findings suggest that joint-management frameworks incorporating First Nations’ traditional ecological knowledge could aid in offsetting impacts and developing site-specific mitigation and adaptation strategies. This interdisciplinary framework thereby facilitates proactive discussions of potential mitigation and adaptation strategies deriving from local fishers’ knowledge that could be used to respond to a range of climate change scenarios.