Scientific longline surveys inherently carry a low level of mortality for the target species. Some species generally do better than others during capture, usually split between those that can pump water over their gills (e.g. tiger and Caribbean reef sharks) and those that have to be swimming in order to ventilate (e.g. Atlantic and Caribbean sharpnose sharks). Water temperature also plays a key role. So it was a big surprise for use to find a large, mature, female Caribbean reef shark dead on the longline with no outward signs of trauma – especially as several other reef sharks on the line were all fine.
During the necropsy we found the stomach of the shark packed full of plastic. Some boat had obviously dumped their waste over the side and the scent attracted the shark. Caribbean reef sharks are known to voluntarily evert their stomachs in order to clean their digestive tract – however it would appear that the plastic was so tightly packed in this was not possible. The plastic would have prevented the shark digesting and food, rapidly weakening it and this weakened state likely led to its death during the survey.
The biggest pressure on shark populations globally is fishing – however here in The Bahamas commercial longline fishing is banned. This essentially provides protection form commercial fishing interests in Bahamian national waters. This sad example goes to show that over fishing is not the only threat to sharks.