|Humans have done far more damage to great white
shark populations than they have done to us.
(Credit: Tobey Curtis)
|Most Western Atlantic shark populations are well
below historic numbers. (Source)
It may take many decades to rebuild overfished populations due to the low productivity of most sharks (slow growth, late maturity, few offspring, etc.). For example, it is projected to take 60 years for sandbar shark and nearly 100 years for dusky shark populations in the U.S. to rebuild to pre-fishing levels. However, rebuilding horizons such as these are dependent on effective fisheries management. Many countries that contribute to global shark harvests lack the ability to implement or enforce regulations on shark fisheries, and much of the catch and trade goes undocumented. These limitations paint a dire picture for the future of sharks in our world’s oceans.
A basket of shark fins can be worth thousands
of dollars. (Credit: Tobey Curtis)
|A bull shark (Carcharhinus leucas) being caught by longline in the Gulf of Mexico. Some large coastal shark populations have declined more than 80 percent over the last few decades. (Credit: Tobey Curtis)|
Similar management measures implemented in regions of Australia and South Africa have resulted in population increases in several species of commercially-valuable sharks and rays. Even the iconic great white shark appears to be benefitting from years of protected status. The white shark is among the most highly-protected sharks in the world, and has been prohibited from harvest in numerous countries since the 1990s. Relative abundance indices in Australia and the east and west coasts of the U.S. all display upward trajectories over the last decade. Recovering shark populations are a good sign for ecosystems that historically contained higher abundances of these key predators. Their presence helps promote ecological stability through “top-down” predatory pressures on prey populations.
|Sharks play critical ecological roles in our oceans, helping to control prey populations and balance ecosystems. Here a white shark (Carcharodon carcharias) successfully captures a Cape fur seal off South Africa. (Credit: Tobey Curtis)|
Collectively, these recent observations offer some rays of hope (pun intended) for the recovery of shark populations. It is possible for shark stocks to rebuild from low levels of abundance. It is possible to have sustainable shark fisheries when precautionary measures are used. Without proper management, however, the inevitable outcome is the collapse of shark populations and the commercial fisheries that depend on them. Not to mention the long-lasting alterations to the ecology of our oceans. Hopefully we can avoid more negative outcomes with improved management, monitoring, research, and international cooperation.
PhD Candidate, School of Marine Sciences, University of Massachusetts
Thank you Tobey for this excellent guest post. We encourage our colleagues to consider writing a guest post…you write the text, we do the rest!