Evaluating and enhancing the taxonomic resolution of shark and ray (Subclass Elasmobranchii) catch statistics in the Mediterranean and Black Seas (1950-2014)
To sustainably manage fisheries, the stock biology, ecology, and its past and present human exploitation must be known. To monitor fisheries, the Food and Agriculture Organization of the United Nations began collecting and harmonizing country catch reports in the late 1940s. In 1950, it issued its first global annual catch statistics, which have continued until the present. This official reported catch has been shown to vastly underrepresent the entirety of the world's catch. The small-scale fisheries sectors (i.e., artisanal, subsistence, and recreational) are largely unreported, in addition to incidental catches of non-target species, much of which is discarded. The latter component of the catch is often comprised of species that are more biologically vulnerable to overfishing than target species. Sharks and rays (subclass Elasmobranchii) are one such group of species. One in four elasmobranch species are estimated to be threatened with extinction, primarily as a result of overfishing. Unfortunately, elasmobranch catch data are notoriously underreported and imprecise.
This thesis sought to elucidate the elasmobranch catches of the Mediterranean and Black Seas, where over half of shark and ray species are threatened with extinction but data deficiency and ambiguity consistently limit conservation action. A Taxonomic Resolution Index (TRI) was calculated for the catches of 24 countries over 65 years (1950-2014) to evaluate the quality of catch reporting over time. The TRI revealed that less than a quarter of commercial elasmobranch taxa are represented in Mediterranean and Black Seas catch data, and reporting quality has hardly improved. While many countries have improved their reporting since the 1950s, the original leaders (e.g., Malta and Georgia) have seen their position worsening over time.
The species composition of reconstructed historical elasmobranch catch was also investigated. The fishery characteristics of species-specific catches were modeled and used to estimate unknown species-specific proportions within aggregated catch categories (e.g., "sharks and rays"). Over half a million tonnes of species-specific catch was disaggregated, increasing the species-specific proportion of reported catches by over 10%. These results, combined with a literature review, imply weak implementation and enforcement of existing protective regulations, despite precipitous declines of elasmobranchs in the Mediterranean and Black Seas.