Rebuilding mixed stock fisheries: lessons from the U.S. West Coast

Thesis (Master's)--University of Washington, 2020Management of commercial fisheries is imperative to global food security, economies, and sustainability. However, common management frameworks are often challenged when species with differing sustainable exploitation rates are caught simultaneously in a mixed stock fishery. The tradeoffs which emerge are often magnified when overfished stocks are persistent in the system. As observed in the U.S. West Coast groundfish fishery, the priority to rebuild overfished stocks according to a strict timeline can result in forgone yield of abundant species and negative impacts on communities. In this thesis, I retrospectively analyzed alternative rebuilding scenarios for the West Coast to test if a management approach based on meeting fishing mortality targets could result in fewer tradeoffs for stakeholders while still meeting conservation objectives. I then developed a two-area single species age structure model to evaluate if marine closures can be used as an alternative management approach to single-species catch limits and provide adequate rebuilding protection while minimizing forgone yield of abundant stocks. The analyses on alternative management approaches described in this thesis can be applied to global fishery managers as they address similar challenges in their respective fisheries

Investigating lipid–lipid and lipid–protein interactions in model membranes by ToF-SIMS

With the chemical imaging capability of ToF-SIMS, biological molecules are identified and localized in membranes without any chemical labels. We have developed a model membrane system made with supported Langmuir–Blodgett (LB) monolayers. This simplified model can be used with different combinations of molecules to form a membrane, and thus represents a bottom-up approach to study individual lipid–lipid or lipid–protein interactions. We have used ternary mixtures of sphingomyelin (SM), phosphatidylcholine (PC), and cholesterol (CH) in the model membrane to study the mechanism of domain formation and interactions between phospholipids and cholesterol. Domain structures are observed only when the acyl chain saturation is different for SM and PC in the mixture. The saturated lipid, whether it is SM or PC, is found to be localized with cholesterol, while the unsaturated one is excluded from the domain area. More complicated model membranes which involve a functional membrane protein glycophorin are also investigated and different membrane properties are observed compared to the systems without glycophorin

Localization of Sphingomyelin in Cholesterol Domains by Imaging Mass Spectrometry

The location of each lipid in a palmitoyloleoylphosphatidylcholine/18:0 sphingomyelin/cholesterol monolayer system is laterally resolved using imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS) without the necessity of adding fluorescent labels. This system of coexisting immiscible liquid phases shows cholesterol domains with sizes and shapes comparable to those in the fluorescence microscopy literature. The results show that SM localizes with cholesterol and that palmitoyloleoylphosphatidylcholine is excluded. Moreover, the segregation is not complete, and there is a small amount of both phospholipids distributed throughout

Mass Spectral Imaging of Glycophospholipids, Cholesterol, and Glycophorin A in Model Cell Membranes

of flight secondary ion mass spectrometry (ToF-SIMS) and the Langmuir-Blodgett (LB) technique have been used to create and analyze reproducible membrane mimics of the inner and outer leaflets of a cellular membrane to investigate lipid-protein and lipid-lipid interactions. Films composed of phospholipids, cholesterol and an integral membrane protein were utilized. The results show the outer membrane leaflet mimic (DPPC/cholesterol/ glycophorin A LB film) consisting of a single homogeneous phase whereas the inner membrane leaflet mimic (DPPE/cholesterol/glycophorin A LB film) displays heterogeneity in the form of two separate phases. A DPPE/cholesterol phase and a glycophorin A phase. This points to differences in membrane domain formation based upon the different chemical composition of the leaflets of a cell membrane. The reliability of the measurements was enhanced by establishing the influence of the matrix effect upon the measurement and by utlilizing PCA to enhance the contrast of the images