How Vulnerable are Sharks in Commercial Fishing? 12 Species Examined

Shark populations are continuing to decline and now, scientists have taken a closer look at how fishing might be impacting them. They've examined the survival rates of 12 shark species when captured as unintentional bycatch in commercial longline fishing and have found that some sharks may be more at risk than once thought.

The scientists analyzed over 10 years of shark bycatch data from the western Atlantic Ocean and Gulf of Mexico tuna and swordfish longline fisheries. This allowed them to examine how survival rates of sharks were affected by fishing duration, hook depth, sea temperature, animal size and the target fish.

So what did they find? Survival rates varied greatly across species. Tiger sharks, for example, had 95 percent survival. Other species, though, showed significantly lower survival rates in the 20 to 40 percent range; these included the night shark and scalloped hammerheads.

"Our study found that differences in how longline fishing is actually conducted, such as the depth, duration, and time-of-day that the longlines are fished can be a major driver of shark survival, depending on the species," said Austin Gallagher, lead author of the new study, in a news release. "At-vessel mortality is a crucial piece of the puzzle in terms of assessing the vulnerability of these open-ocean populations, such of which are highly threatened."

The researchers didn't just take survival into account, though; they also kept reproductive potential in mind. In the end, they found that the species most at risk were those with both very slow reproductive potential and unusual body features, such as hammerheads and thresher sharks.

"Our results suggest that some shark species are being fished beyond their ability to replace themselves," said Neil Hammerschlag, one of the researchers. "Certain sharks, such as big eye threshers and scalloped hammerheads, are prone to rapidly dying on the line once caught and techniques that reduce their interactions with fishing gear in the first place may be the best strategy for conserving these species."

The findings are published in the journal Global Ecology and Conesrvation.