Born in the USA

Sharks are often described as some of the most threatened animals on the planet today. In general shark populations all over the world, have been decimated by massive overfishing and habitat destruction. But, whilst it is important to understand that this is an incredibly important issue and it is absolutely vital that we ensure fisheries are made more sustainable and Endangered species are offered the protection they need, it is not all doom and gloom for sharks. In fact, in some places, such as the USA, conservation measures have already started to have an impact and sharks are starting to bounce back! So how badly did shark populations decline in the USA? How are they being protected? And how are these management plans having an impact?

Populations of Vulnerable spinner sharks are slowly growing in the east of the USA (Image Credit: Lewis Burnett / Shutterstock)

Once Upon a Time in America

In the United States, shark stocks were decimated between the mid-1970s and early-1990s - as much as 60%–99% reduction for some species. This was as a result of dwindling commercial fish stocks, which redirected the fisheries industry towards targeting sharks and because recreational shark fishing became popular after the release of Jaws in 1975 (Peterson et al, 2017).

Blacktip sharks have become more abundant along the USA east coast since protective measures were introduced in 1993 (Image Credit: Martin Prochazkacz / Shutterstock)

We Are the Kids in America

However, a shark fishery management plan (FMP) was established by the National Marine Fishery Service (NMFS) in the USA in 1993, in order to tackle these horrifying declines. This legislation sought to regulate both commercial and recreational shark fishing in federal Atlantic Waters (Peterson et al, 2017).

After a fishery management plan was implemented in 1993, bonnethead sharks in the east USA have become more abundant (Image Credit: Eric Kilby / WikimediaCommons)

And there may be some good news today... it appears that certain shark populations in the USA may be recovering! A recent study discovered that the "relative abundance" of several species of sharks has gone up since the protections came into place (Peterson et al, 2017).

Excitingly, scientists have found that, not only were populations of the sandbar shark (Carcharhinus plumbeus), blacktip shark (C. limbatus), blacknose shark (C. acronotus), sharpnose shark (Rhizoprionodon terraenovae) and bonnethead (Sphyrna tiburo) all going up in the waters off the east coast of the USA, but the abundance of the tiger shark (Galeocerdo cuvier) had increased by 3% and the spinner shark (C. brevipinna) had increased by as much as 14%! This study can give us hope that protective measures can result in the recovery of shark populations (Peterson et al, 2017).

After huge declines from the 1970s to the 1990s, several species of sharks are now showing increased relative abundances since protective measures were introduced in the USA in 1993 (Peterson et al, 2017).

America's Most Wanted

Whilst the scientists were hopeful that there were signs of recovery in the USA Atlantic coastal shark stocks, they suggested that doesn't mean we should slow down and continued protections will be vital. They recommended a mixture of species-specific measures, limiting selective extraction and large-scale management plans would be advisable in the future:

Scientists think tiger shark populations have bounced back well since protections in the USA, as they have large litters of pups relatively quickly (Image Credit: le bouil baptiste / Shutterstock)

Species-Specific Protective Measures

The researchers noted that, whilst the populations of all species were increasing, there were differences in how rapidly each species was able to recover after protection. For example, the tiger shark was able to recover so successfully due to their high "fecundity"; a single female tiger shark is able to produce an average of 41 pups every two years in the Atlantic. Species with lower fecundity were not able to increase so dramatically. Generally, the populations of larger coastal shark species remained depressed initially after implementation of the FMP, whilst smaller species which had younger age-of-maturity, were able to bounce back more quickly (Peterson et al, 2017).

Sandbar sharks are recovering slowly because fisheries extracted a lot of young sharks before protective measures were introduced in the US in 1993 (Image Credit: Jeff Kubina / WikimediaCommons)

Limitations on Selective Extraction

The scientists also advised that selective extraction of certain portions of the population, can limit recovery after the implementation of protective measures. Many species of sharks segregate by size and/or sex, with males and females occupying different habitats, and neonate and juvenile animals living in an entirely separate area from the adult animals, in "nursery habitats". Therefore, certain life-stages are often extracted in disproportionally high frequency by fisheries, as the area the fisheries target contains one particular group or the fisheries may be limited in which individuals they may extract based on size. For example, the scientists suspected that the slow recovery of the sandbar shark was caused by fisheries' targeting juvenile animals prior to the implementation of the FMP. Upon protection, there was a lag in sandbar recovery because recruitment into the adult population was low, limiting further reproduction (Peterson et al, 2017).

Scientists recommend that large scale management plans will be necessary to bolster the spinner sharks' very slow growing populations in the USA (Image Credit: pedro barbero / Shutterstock)

Large-Scale Management Plans

Whatsmore, the researchers noted that the increases recorded for the bonnethead and the Atlantic sharpnose shark were regional and that the increase of spinner shark abundance was actually very gradual. They hypothesised that, because multiple different management measures had been implemented for their protection, population recovery in these species was variable by area (Peterson et al, 2017).

If we are able to continue to protect threatened sharks, implement further management plans and monitor the populations, hopefully in a few more years, we will see that shark populations have only continued to rise. We will need to be patient, but this study shows us that our efforts can and will pay off!

Endangered blacknose sharks are increasing in abundance in the USA thanks to the implimentation of protective measures in 1993 (Image Credit: D Ross Robertson / WikimediaCommons)

If you would like to stay up-to-date with shark conservation in the USA, you can check out Save the Sharks or follow them on Facebook.

References

Peterson CD, Belcher CN, Bethea DM, Driggers III WB Frazier BS & Latour R (2017). Preliminary recovery of coastal sharks in the south-east United States. Fish and Fisheries, 1–15. Access online.

By Sophie A. Maycock for SharkSpeak