Great White shark populations could be recovering along North American coasts, but concern still exists for species' vulnerability

Tuesday, August 12, 2014, 12:02 PM - Shark populations have been in serious decline in recent years, mainly due to the fact that humans kill tens of thousands of them every day, but researchers are now noticing that populations of certain types of sharks, especially Great Whites along the coast of California, may be showing signs of recovery.

Roughly three years ago, scientists studying white shark populations along the U.S. west coast conducted a study of white shark populations at two 'aggregation points' along the California coast. Constructing a model to estimate the number of adult and sub-adult white sharks at the Farallon Islands and Tomales Point, using data collected about the number of animals seen and identified year to year, they found 219 sharks present. While this provided no insight into the status of the white shark populations at the time, their results apparently still set off warning bells with conservationists, who called for white sharks to be added to the endangered species list. Currently, they are ranked as 'vulnerable' on the IUCN Red List of Threatened Species, and have been since since 1996.

However, adding a species to the endangered list is a serious undertaking, as it places substantial demands on governments, according to George Burgess, the director of the Florida Program for Shark Research. So, to determine whether the sharks were truly in need of this kind of protection, his group attempted to use several studies of populations to estimate the entire population of sharks - of all sizes and ages - that would produce the number of sub-adult and adult sharks recorded by the 2011 study. The hope was that this would give a more complete look at what the white shark populations were along the California coast.

"Listing species that are not under the threat of biological extinction diverts resources away from species genuinely at risk," Burgess said in a University of Florida News statement. "We want to use our resources for the neediest species."

Examining the data from the 2011 study, along with studies of populations all along the west coast of North America, from Mexico to Alaska, and referencing studies in other parts of the world as well, they constructed a model to estimate the population.

According to University of Florida News, the team "conducted a demographic analysis to account for all life stages for the sharks at Farallon Islands and Tomales Point and found that the total population is most likely at least an order of magnitude higher – rather than just over 200 sharks there likely were well over 2,000."

In an email exchange with The Weather Network, Stanford researchers Randall Kochevar and Taylor Chapple (lead author of the 2011 study) explained that the two studies actually show good agreement with each other, due to the differences in what each was counting - sub-adults and adults vs. all age groups together.

With some of their own research in hand, and adding the study by Burgess' group, the National Marine Fisheries Service - who would be the ones to finalize a recommendation to the IUCN to add white sharks to the endangered list - estimated the entire white shark population in the eastern North Pacific as around 3,000 members.

"We determined there were enough animals that there was a low to very low risk of extinction, and in fact, most developments suggest an increasing population," Heidi Dewar, a research biologist with the NMFS, told University of Florida News.

White sharks are far from completely safe, though. Although protections are in place to help their populations recover, they continue to be listed as a vulnerable species, partly due to the fact that there have been noticeable declines in world populations, yet due to the mobility of the species, exact population numbers are still unknown at this time. According to Burgess, their findings bring hope about the overall recovery of the white shark, given that other shark species are not doing well at all.

"White sharks are the largest and most charismatic of the predator sharks, and the poster child for sharks and the oceans in general," said Burgess in the statement. "If something is wrong with the largest, most powerful group in the sea, then something is wrong with the sea, so it's a relief to find they're in good shape."

However, Chapple, a postdoc scholar at Stanford University's Hopkins Marine Station, warns that making judgments about the status of white sharks from studies is difficult.

"Caution should be taken when interpreting any status implications from these findings," he wrote in an email conversation with The Weather Network. "We cannot make any statements about the status of white sharks off California or the northeast Pacific from either of these studies as they represent only a single point in time."

"However, with additional years of data we hope to soon be able to estimate the trend and status of these sharks," he added.

This latest study, by Burgess and his group, was published in June in the online journal PLOS ONE (click here), while the original study was published in Biology Letters (click here).

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Meanwhile, another study on the other side of North America, led by Toby Curtis of NOAA and the NMFS, examined white shark sightings of all kinds throughout time, from the 1800s on up to the present. The results of this study found that white shark populations in the North Atlantic were also showing signs of recovery. According to Curtis and his NOAA colleague Jose Castro - who works with the Southeast Fisheries Science Center - populations were in abrupt decline starting in the 1970s, due to improved diplomatic relations between China and the West, and also with the release of the movie Jaws.

"The movie Jaws is probably one of the most influential movies in history. And, at first, it set up a shark-killing frenzy," Castro said in an interview. "You know, people looked at sharks as malevolent creatures feeding on mankind. And, so it set off an ecological catastrophe of people killing every shark they could. You know there were shark fishing tournaments that had categories...you could get a prize for the most sharks killed. And that lasted for about 20 years."

It wasn't until 1993 that regulations were put into place to prevent the mass slaughter of white sharks.

"The signs of recovery are coincident with the fisheries regulations," Curtis said in the interview, "so we think that the conservation measures have really benefited the white sharks and helped them rebuild."

Another reason for the increase in population may be due to the increase in seal populations along the New England coast over the past decade or so, since seals are a primary source of food for white sharks.

As with the Pacific study, while these signs are encouraging, it can't be said that white shark populations have fully recovered just yet.

"The news has been using terms like 'surging' and 'booming' and 'exploding' shark populations, and it's certainly not anything like that," said Curtis. "It's been a gradual recovery over a 20-year period. It's positive signs that the population is growing, but we're not there yet."

This study, also published in June in PLOS ONE, can be found here.

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