Chondrichthyan Population Biology

For many species of management concern, we lack the data to perform complete assessments of extinction risk or population status. To address this gap, I developed methods to inform assessments of population productivity and conservation and management status for chondrichthyans (sharks, skates, rays, and chimaeras). Within this data-limited group, I focused on chimaeras because their natural history was almost entirely unknown, and they have fascinatingly unique biology. Using museum specimens and remotely operated vehicle footage, I found that much of the biodiversity in this group was unresolved, which led to the identification and description of a new species of chimaeroid, the Galapagos ghost shark Hydrolagus mccoskeri.

To evaluate the intrinsic vulnerability of chimaeras to exploitation, I collected spotted ratfish (Hydrolagus colliei) from the US West Coast and developed novel techniques for describing their natural history. To determine their population productivity, I combined classic reproductive biology with endocrinology, life history theory, and metaanalysis to show that they have fairly low fecundity but may not be as long lived as other chondrichthyans. I synthesized data from a fishery-independent survey, using zero-inflated generalized linear models to estimate spatiotemporal changes of ratfish populations in response to fishing and climate. Putting this all together, I used information about life history, spatial distribution, fishing effort, and abundance of spotted ratfish to assess their vulnerability to population depletion. I found that although ratfish have life-history characteristics that indicate great vulnerability to overfishing, they can recover from substantial fishing mortality. This evidence of rapid recovery shows that some chondrichthyans actually have strong population stability. To further investigate the patterns and drivers of population productivity and extinction risk of chondrichthyans that arise from life-history diversity, I used Monte Carlo methods to estimate uncertainty in skate population growth rates, while also identifying metrics of their natural history that may be indicators of productivity for this data-poor taxon.