A NEW LOOK AT SHARK DEPREDATION

 

Shark depredation, defined as a shark striking and eating part or all of a fish that has been hooked by a commercial or recreational fisherman, has been a hot issue in recent years.

It has even led to legislation in Congress, where Rep. Robert Whitman (R-VA) introduced the so-called “SHARKED Act,” H.R. 4051, which would, if passed and signed into law, require the Secretary of Commerce (in reality, the National Marine Fisheries Service) to establish a task force comprised of representatives from regional fishery management councils and regional marine fisheries commissions, state fishery managers, the National Marine Fisheries Service and individuals knowledgeable about the highly migratory species fishery, shark management and behavior, and shark ecology.  Such task force would meet to examine the shark depredation issue, and would be required to issue a report of its findings within two years after the bill’s passage.

The House of Representatives passed the SHARKED Act in February.  It now awaits action in the Senate, where passage is far from assured.

The impetus behind the SHARKED Act is a perceived increase in shark depredation, particularly of fish hooked by recreational fishermen.  A recent article in Marlin magazine asserted that

“these events are becoming more frequent, to the point in certain fisheries where it’s nearly assured that you’ll lose at least a significant portion of your catch to sharks…

“The Webster’s definition of depredation is ‘1: to lay waste, plunder, ravage.  2: to engage in plunder.’  That’s certainly fitting to what’s currently happening in places like North Carolina’s famed yellowfin tuna fishery—a mainstay of its extensive charter fleet—as well as South Florida during sailfish season or the Gulf of Mexico’s red snapper fishery.  Sharks are drawn to an area by the sound of boat engines and quickly learn to take advantage of hooked tuna, snapper or sailfish, turning them into an easy meal.  In addition to the frustration that sharks cause, there is also a worry that they can have a significant negative effect on many different fisheries, leading to stricter regulations intended to offset or avoid shark interactions, as well as losses among the local charter fleets.  After all, why spend hundreds or thousands of dollars to go fishing only to see your prized catch right before your eyes?

As the Marlin article notes, the shark depredation issue is nothing new.  It has been

“a part of sport fishing long before Hemingway’s fictional Santiago won his battle with a giant blue marlin, only to lose most of his prize at boatside as immortalized in his literary classic The Old Man and the Sea.”

But in the past few years, such depredation has risen to the forefront of anglers’ concerns.  A real hostility toward sharks has emerged in many fisheries, particularly in the southeast and Gulf of Mexico.  However, it isn’t completely clear whether the increase in shark depredation has been exaggerated by the recreational fishing community.  And if the increase is real, researchers need to decide whether it is caused by an increase in the number of sharks, a change in shark behavior, and/or other, yet to be determined factors.

A newly published paper that originally appeared in Fish and Fisheries on May 24 takes a new look, and sheds some new light, on the depredation issue.

Titled “Depredation:  An old conflict with the sea,” and authored by James Marcus Drymon, et al, the paper examines the depredation issue by focusing on depredation in the northern Gulf of Mexico off Alabama, and using fishery-independent data to evaluate some of anglers’ assumptions about the issue.

The paper, like the Marlin magazine article, begins by acknowledging that shark depredation in recreational fisheries is an old problem, dating back to the 1930s, when Ernest Hemingway and other blue water anglers were striving to land unmutilated giant bluefin tuna off the island of Bimini.  Offshore anglers had no love for sharks in those days, with Hemingway openly admitting that he dealt with potential depredators by luring them to the surface with a big chunk of bait and then shooting them with a Thompson submachine gun.

However, the paper then notes,

“in many ways, this conflict has become more complicated.  In Hemingway’s time, sharks were at best a nuisance, and at worst a danger.  The modern shark conservation ethos did not yet exist because none was needed.  At the time, sharks were considered an ‘underutilized resource’, and attempts to develop and incentivize US shark fisheries were underway.  Shark fishing expanded throughout the 1970s and 1980s, and shark conservation efforts did not begin in earnest until the early 1990s, after several shark populations had already been overfished…

“While several explanations were offered, when asked which factors were primarily driving this increase [in shark depredation], the anglers most often expressed two sentiments, ‘overpopulation’ of sharks (i.e. shark population increase) and/or learned behavior by sharks could explain the recent increase in depredation reported by anglers.  [citations omitted]”

The paper’s authors addressed the first perception—that shark populations were increasing—by examining data from a bottom longline survey conducted off Alabama during the years 2012-2022, and examining the catch-per-unit-effort of sandbar sharks, a species that is responsible for a significant share of the depredation in the region.  Although the still-overfished sandbar population seems to be slowly increasing, the catch-per-unit-effort showed wide year-to-year variations, and did not indicate a clear increase in abundance.

To address the question of whether sharks were adapting, and effectively learning how to depredate more effectively, the researchers turned to additional fishery-independent data, in this case the depredation rate of red snapper caught in the same bottom longline survey that provided the sandbar shark data.  However, that data indicated that the rate of red snapper depredation actually decreased significantly over the relevant period.

As the paper’s authors observed,

“If sharks were learning to depredate, we would expect an increase in the rate of red snapper depredation over time as more sharks learned the behavior.  However, the declining trend in red snapper depredation does not appear to support the idea that an increase in learned behavior among sharks can explain the increase in depredation perceived by anglers.”

While the paper’s authors don’t deny that both an increased shark population and learned behavior might contribute to depredation, they further observed that

“The trends detailed above suggest that increases in shark populations and/or learned behavior in sharks do not fully explain the increase in shark depredation documented by anglers.  Something else may be contributing to the increased conflict…Using angler effort NOAA’s Marine Recreational Information Program, we can see a clear increase in the number of charter-for-hire fishing trips off Alabama in recent years.

“While far from a smoking gun, the above exercise highlights the complexities of this human-wildlife conflict.  In 1935, Hemingway was one of a small group of anglers fishing a virgin stock of bluefin tuna in Bimini.  Today, there are more anglers on the water than any time in history, and the stocks they target are far from virgin biomass.  Are there more sharks in the [Gulf of Mexico] than there were 20 years ago?  Very likely.  Are there more sharks in the [Gulf of Mexico] than there were in Hemingway’s time?  Likely not.  [citations omitted]”

And that temporal perspective matters when it comes to sharks, because the researchers noted that younger anglers don’t really have any experience with a healthy shark population.

“[In another study,] there was clear evidence of shifting baselines; that is, the gradual acceptance of a reduction in the abundance or size of a species.  Older anglers viewed changes in shark sizes more accurately than younger anglers; specifically, only individuals over 60 years of age remembered a time when larger sharks were more common.  [citations omitted]”

I can certainly relate to that comment; having passed the 60-year point a while ago, and having participated in the Atlantic shark fishery for close to 50 years, I remember sharks—most particularly duskies and shortfin makos—that were far larger and much more abundant than what we see in the same northeastern waters today.  I even recall the late 1960s, when female sandbar sharks an honest seven feet long were occasionally caught in Long Island Sound, off Connecticut’s southwestern corner, something that hasn’t occurred in a very, very long time.

Thus, I also recall a level of shark depredation, even on fish caught from the New England party boats that I once fished on, that is far higher than people experience today.  Yet people with far fewer years of experience look at me askance when I suggest that the current level of depredation is really nothing new.

The findings of the paper’s authors, which focused on a single region, single shark species, and single target of depredation, may or may not be transferrable to other fisheries and other places.  Depredation may have multiple causes, depending on the region and the fishery involved.

Yet perhaps more than anything else, the authors’ final conclusion rings true:

“[P]erceived conflict is as potent as real conflict.  Arguably, it may not matter if depredation in the [Gulf of Mexico] has increased or decreased; the overwhelming perception from stakeholders is an increase in depredation, and this is the perceived (or real) conflict that must be addressed.  [citation omitted]”

We can only hope, and help to ensure that when the issue is addressed by fishery managers, facts, and not emotions, prevail.