Years of unregulated fishing activity have resulted in low abundances of elasmobranch species in the Saudi Arabian Red Sea. Coastal populations of sharks and rays in the region remain largely understudied and may be at risk from large-scale coastal development projects. Here we aim to address this pressing need for information by using fish market, unmanned aerial vehicle and baited remote underwater video surveys to quantify the abundance and diversity of sharks and rays in coastal habitats in the Saudi Arabian central Red Sea. Our analysis showed that the majority of observed individuals were batoids, specifically blue-spotted ribbontail stingrays (Taeniura lymma) and reticulate whiprays (Himantura sp.). Aerial surveys observed a catch per unit effort two orders of magnitude greater than underwater video surveys, yet did not detect any shark species. In contrast, baited camera surveys observed both lemon sharks (Negaprion acutidens) and tawny nurse sharks (Nebrius ferrugineus), but in very low quantities (one individual of each species). The combination of survey techniques revealed a higher diversity of elasmobranch presence than using either method alone, however many species of elasmobranch known to exist in the Red Sea were not detected. Our results suggest that aerial surveys are a more accurate tool for elasmobranch abundance estimates in low densities over mangrove-associated habitats. The importance of inshore habitats, particularly for batoids, calls for a deeper understanding of habitat use in order to protect these environments in the face of unregulated fishing, mangrove removal, and anticipated developments along the coastline of the Saudi Arabian Red Sea.

Chondrichthyans—sharks, rays, skates, and chimaeras—influence top down control of food webs and connect disparate ecosystems, yet populations of many species around the world have experienced sharp declines in abundance. Marine protected areas (MPAs) have a long history of conserving marine biodiversity, but their effectiveness to protect representative and critical habitat for threatened species on a global scale is controversial and hindered by a lack of biological and ecological data for the majority of chondrichthyan species. In this thesis, I use non-invasive baited remote underwater video (BRUV) and citizen science diver data to explore diverse chondrichthyan communities in two countries, South Africa and Costa Rica, with data-poor chondrichthyan fisheries and limit conservation funding, and the relationships of these chondrichthyans to biotic and abiotic factors in their habitats in and around MPAs. First, through a literature review, I find substantial taxonomic and geographic biases in understanding of reef shark biology, ecology, and conservation, which impair ability to implement effective conservation measures for these species. After identifying these research gaps, I used BRUVs to explore the diversity of a chondrichthyan hotspot in South Africa, finding many poorly understood endemic chondrichthyans. I discovered strong associations of the chondricthyan community to different habitat types (sand versus reef and kelp habitat), which resulted in poor diversity within one of the region’s larger MPAs—a whale sanctuary whose focus on large charismatic whales left mostly poorer quality sand habitat protected. However, a high occurrence of chondrichthyans within a neighbouring MPA suggested even small MPAs can conserve a high abundance of smaller species, especially if residency can be demonstrated. I then used the BRUV data to examine the relationships amongst these chondrichthyans and the community of other marine animals within the region, finding strong co-occurrence patterns that suggest chondrichthyans, particularly the endemic catsharks, could serve as effective ‘umbrella’ species for conservation in this region where little other information is available for conservation planning and monitoring. Finally, at Cocos Island, an MPA off Costa Rica, I discovered similarly strong, species-specific associations to another aspect of habitat: temperature. I found significant and species-specific responses to the El Niño–Southern Oscillation (ENSO). For example, the scalloped hammerhead Sphryna lewini counts declined by 224.7% during strong El Niño conditions and by 14.7% with just a 1°C rise in SST, while the benthic whitetip reef shark Triaenodon obesus had a weaker response, dropping by only 7.9% and 4.4%, respectively. In general, strong El Niño events reduced sightings within the MPA, providing some of the first indications of how a rising frequency and intensity of these events will impact the spatial distribution of both chondrichthyans and their habitat in the Eastern Tropical Pacific. Overall, this thesis provides insight into the factors influencing chondrichthyan abundance and diversity, demonstrating the importance of considering both biotic and abiotic factors during MPA design and the need to study these factors across diverse taxonomic groups and ecosystems. / Graduate / 2021-05-08

This project had two primary goals: (1) to explore opportunities to further a deep-ocean vehicle’s reach using alternative pressure spheres, and (2) to implement an existing deep-ocean vehicle (lander) in active scientific research. I gained a greater understanding of the limitations and design choices made for existing pressure spheres using Finite Element Analysis (FEA). My simplified FEA model predicted sphere failure for the existing 30% Fiber Glass 70% Nylon injection molded spheres at an external pressure of 3,954psi or 2,690m ocean-depth (only a 7.38% error compared to the tested minimum failure depth), so I determined it a valid model. I also explored alternative designs and materials that could be used for pressure spheres in deep-sea applications. Existing pressure sphere models filled with an incompressible fluid failed at 12,670psi or 8,621m ocean-depth - over three times the depth of the same sphere filled with air. Next, I varied the sphere thickness of existing spheres to determine its impact on depth rating. While the increased thickness did provide an increase in depth rating, there were diminishing returns as the sphere was made thicker. I deemed both of these design options infeasible for our application. To consider the use of laminated composite spheres, the addition of an equatorial ring was required to manufacture O-ring seals safely and reliably. A simple cylindrical equatorial ring model using a stainless-steel ring had a predicted failure at 3,017psi or 2,053m ocean-depth. While this model predicted failure at 637m shallower than the sphere without the ring, it was the only ring material tested to reach the rated depth for the existing pressure spheres (2km), so I concluded stainless-steel is the best ring material. A spherical stainless-steel equatorial ring design was then analyzed which predicted failure at 3,915psi or 2,664m ocean-depth – only 8.3% less than the original sphere with no ring. Because of its successful performance and near identical results to the original model, I determined a stainless-steel spherical equatorial ring is the best option for laminated composite sphere sealing. Finally, I analyzed three different kinds of laminated composite pressure spheres: two carbon fiber and one fiber glass. Each laminate was designed to be quasi-isotropic and as close to 0.8” thick as possible to keep it consistent with the original sphere design. The sphere made of 584 Carbon Fiber with a lay-up of: [[-45/45/0/90]6]s was found to predict failure at 10,000psi or 6,804m ocean-depth, more than 2.5 times that of the original sphere. Next, a model made of 282 Carbon Fiber with a lay-up of: [[-45/45/0/90]11]s predicted failure at 9,242psi or 6,289m ocean-depth – more than 2.3 times as deep as the original pressure spheres. Lastly, a sphere of 7781 Fiber Glass with a lay-up of: [[-45/45/0/90]11]s predicted failure at 6,630psi or 4,511m ocean-depth – about two-thirds the depth of the 584 Carbon Fiber composite, but more than 1.6 times the depth of the original sphere. While real-life applications of these materials would include design modifications and manufacturing imperfections which would lower their maximum depth rating, these results are highly encouraging and show that all three materials could be viable options for future production. Additionally, through partnership with Dr. Crow White and his marine science undergraduate students, I completed numerous deployments for a Before and After Controlled Impact (BACI) study on the area of the proposed windfarm off the coast of Morro Bay, CA. Many modifications were made to the existing lander which enabled it to successfully be implemented in these studies including a new bait containment unit, light color filters, a GPS tracking device, and a large vessel recovery device. A total of 5 pier deployments and 3 boat deployments were conducted by my team over the course of 6-months. Planning for these deployments included accounting for budgeting, weather, permitting, and multi-organizational logistics while working with both NOAA and the Cal Poly marine operations staff.