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Are they here or not: Severely reduced fish species can be hard to protect

Kerwath, S. E., Parker, D., Winker, H., Potts, W., Mann, B., Wilke, C., & Attwood, C. (2019). Tracking the decline of the world’s largest seabream against policy adjustments. Marine Ecology Progress Series610, 163-173.

The passenger pigeon was once so numerous that John James Audubon, the famed bird observer of the 1800s, said that he observed a group so massive that it blocked out the sun. As they were easy to hunt and seemingly endless, no one worried about the passenger pigeon, until in 1900, a boy in Ohio shot what was later identified as the last wild passenger pigeon, and in 1914, the final passenger pigeon, Martha, died of old age in the Cincinnati Zoo. Like that, an American icon was gone.

But this is an oceanography website. What do passenger pigeons have to do with anything? Like the passenger pigeons, the fish in the ocean were once seen as endless, a resource so large that humans couldn’t possibly begin to impact it. But as we have developed more fishing technology and have come up with better ways to look at fish populations, we know that this is not true (although we may have been able to learn this lesson from the demise of the humble passenger pigeon). However, now we know enough to be concerned about our impact on these species. Some studies estimate that about two-thirds of the world’s fisheries are over-exploited, and some more dire studies suggest that without changes, there may be no fish species that can be harvested sustainably by 2048. So we put in regulations. We try to tell people how much they can catch. We try to keep an eye on these species. But does it work? A new paper released by Dr. Sven Kerwath and his colleagues in South Africa analyzes how effective policies have been in protecting the red steenbras (Petrus rupestris). What they show is how difficult it can be to make decisions about a fish species that is already so depleted that it is hard to tell how many there are left.

The red steenbras

A red steenbras, the largest seabream. Populations of red steenbras in South Africa are estimated to have declined by about 96% between 1985 and 2011. Photo from Wikimedia Commons.

The red steenbras is the largest fish in its family, Sparidae. It can reach 78 inches long and weigh 154 pounds, although finding a fish that size at this point would be practically unheard of. Although the red steenbras is the apex predator in the reefs around South Africa, meaning it is at the top of the food chain, it’s been a popular fish for both commercial and recreational fisheries. They also don’t reproduce quickly; it takes a fish 7 years to reach sexual maturity. In the 20th century, red steenbras populations collapsed, and it was listed as endangered by the IUCN in 2014. In addition, the fish have gotten smaller, with the reported size of the fish that are caught decreasing by 50% between 1984 and 2012. Unlike the passenger pigeon though, the South African government has been actively trying to save the species.

Since 1984, new regulations have been put in place for the fishing of red steenbras every few years, including imposing closed seasons (when nobody is allowed to catch the fish), size limits, catch limits, and even a full moratorium in 2012. This moratorium, however, was later removed from the recreational fishing. Despite these efforts, the red steenbras, by all accounts, has continued to decline.

Tsitsikamma, the mid-point that divided the two study regions along the coast of South Africa. Unedited photo from Roger Gordon.

Traditional ways of measuring fish become incredibly difficult with a dwindling species because they are so rarely caught. This makes it difficult to determine if regulations are actually protecting the fish. To combat this, Dr. Kerwath and his colleagues set up two new ways of measuring red steenbras. The first is called standardized probability of encounter (SPE). In this case, they measured how likely a fishing vessel was to catch a red steenbras in any of its catches, not how many red steenbras they caught. This helps account for changes in regulations that dictate how many fish you can catch at one time.

The second unit of measurement was a content analysis (CA) used for the recreational fishery; essentially, they analyzed a local angling magazine to look at trends in the size of the fish that were reported. Larger fish would be more indicative of a healthy stock, whereas smaller fish mean that fish aren’t living long enough to grow large. Both of these techniques allowed them to get a sense of how the fish were doing without having to catch many. They divided their study region into two areas, the South-West (Cape Point to Tsitsikamma), and East (Titsikamma to Durban).

They found in general that commercial fishing boats were very unlikely to encounter red steenbras; in the most likely region in the South-West, there was only a 3% chance of encountering the fish, and in the East, only a 13% chance. Looking at the impact of the commercial fishery versus the recreational fishery, they found that recreational fishers were making a much bigger dent in the current population. Recreational fishers averaged a catch of 0.106 fish per boat day, which was four times higher than the commercial fishery. It doesn’t sound like much, but if calculated over a year, this means the recreational fishery catches about 336 fish each year, which can have a big impact on an already struggling species.

More unfortunately, looking at the standardized probability of encounter (SPE) and the content analysis (CA) showed that none of the previous regulations were able to halt the decline of the red steenbras.

Why is this so hard?

A black sea bass exhibiting classic signs of barotrauma, injuries that fish get when they are pulled to the surface from a great depth. This is due to the dramatic pressure changes the fish has to cope with, which can sometimes make it’s eyes or stomach expand. Photo from Florida Sea Grant.

Regulations can fail for a number of reasons. The simplest is the lack of enforcement, but sometimes they fail because of how they are designed. Bag limits, in which fishers can only catch a certain number of fish, can encourage them to only keep the largest fish and throw the smaller ones back. Red steenbras often live deeper than 70m, and dragging them to the surface traumatizes their body due to the change in pressure. A fish that has been released is not technically caught, but probably still won’t survive.  In addition, creating a closed season might not necessarily work unless it is targeted for the perfect time, like breeding season. However, having new ways to measure the quantity of fish can help show whether or not these regulations are helping earlier on.

So what can be done? One possible solution is the creation of a series of Marine Protected Areas (MPAs). This would create spaces where juvenile fish could escape fishers and grow to reproductive size. MPAs have been shown to keep fish populations healthier, and can even increase fishing in surrounding areas. In addition, we can all be more conscious of the seafood we eat. Is it from a sustainable source? Is there a better alternative? By refusing to support fisheries that are over-exploiting the oceans, we can seek to ease some of the pressure we are putting on the oceans, and give us a chance to work on better ways to protect the seas.


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