Drum lines use cutting-edge shark science

History was made when the KZN Sharks Board dropped the Dolphin Coast’s first drum line into the sea off Salt Rock Beach on Monday, November 9.

Not only did this mark a new, greener era in bather protection but also the first time anywhere in the world, hook timers were used on drum lines.

A hook timer is a small battery powered device that records the exact time of day or night a shark is caught and gives scientists a clear indication of how long a shark can survive once caught.

“We will use this information to help us better manage drum lines,” said Dr Matt Dicken, senior scientist at the KZN Sharks Board.

He said the hook timers will help them, among other things, figure out which bait sharks are caught quicker, under which environmental conditions drum lines work best and whether or not sharks are caught more often over a reef.

Unfortunately theft of Sharks Board equipment is a problem and Dicken urged the public to leave the hook timers alone and report theft of these to the Sharks Board.

Drum lines are not expected to increase shark mortality. Dicken said research with tiger sharks showed no difference in survival time between sharks caught in the nets versus those caught on drum lines.

The drum lines are baited with red mullet and jacopeva caught as bycatch by hake trawlers. Each drum line is baited with one fish weighing about half a kilogram and with every second 214 metre long net being replaced with four drum lines, about 53.5 metres apart from each other. The total bait per set of drum lines is only two kilograms, which is too little to be considered as chumming.

“The amount of bait on our drum lines is not enough to attract more sharks. Fishermen drop far more bait in the water surrounding our gear,” said Dicken.

The urgency of the drum lines was clearly illustrated when a skate and a loggerhead turtle were found entangled in the first net that was replaced, when the Courier accompanied the Sharks Board boats this week. The skate was released unharmed but the loggerhead could not be revived.

“Since the introduction of drum lines on the Hibiscus Coast seven years ago, the bycatch of non-targeted harmless species (dolphins, whales, turtles and the like) has been reduced by 50 percent and there have been no shark incidents during that time,” said Mike Anderson-Reade, KZN Sharks Board head of operations.

He said the reason drum lines were only introduced to the Dolphin Coast now was because the Sharks Board does not hunt for bait and a large enough steady supply of bait from hake trawlers could not be guaranteed seven years ago. He said the Sharks Board now had the capacity to stockpile enough bait to see them through times that it is scarce.