The Red Sea has long been recognized as a global hotspot of marine biodiversity.
Ongoing overfishing, however, is threatening this unique ecosystem, recently leading to
the identification of the Red Sea as one of three major hotspots of extinction risk for
sharks and rays worldwide. Elasmobranch catches in Saudi Arabian Red Sea waters are
unregulated, often misidentified and unrecorded, resulting in a lack of species-specific
landings information, which would be vital for the formulation of effective management
strategies. Here we employed an integrated approach of fisheries dependent and
independent survey methods combined with molecular tools to provide biological,
ecological and fisheries data to aid in the assessment of the status of elasmobranch
populations in the Red Sea. Over the course of two years, we conducted market surveys
at the biggest Saudi Arabian fish market in Jeddah. Market landings were dominated by,
mostly immature individuals - implying both recruitment and growth overfishing.
Additionally, we employed baited remote underwater video (BRUVS) and longline
surveys along almost the entire length of the Red Sea coast of Saudi Arabia as well as at
selected reef systems in Sudan. The comparison of catch per unit effort (CPUE) data for
Saudi Arabian Red Sea BRUVS and longline surveys to published data originating from
non-Red Sea ocean systems revealed CPUE values several orders of magnitude lower for
both survey methods in the Red Sea compared to other locations around the world.
Finally, we infered the regional population structure of four commercially important
shark species between the Red Sea and the Western Indian Ocean.We genotyped nearly
2000 individuals at the mitochondrial control region as well as a total of 20 microsatellite
loci. Genetic homogeneity could not be rejected for any of the four species across the
spatial comparison. Based on high levels of region-wide exploitation, we suggest that, for
management purposes, the population structure of all four species should be considered
as single stock in the three marginal seas surrounding Arabia. Overall, our combined
results indicate a severe depletion of sharks in Saudi Arabian Red Sea waters, likely
caused by drastic overfishing of elasmobranch populations.
|Date of Award||May 2014|
- Biological, Environmental Science and Engineering
|Supervisor||Michael Berumen (Supervisor)|
- Red Sea