East Africa’s reefs being fished at unsustainable rates, study finds

Originally published on Mongabay.com - read on Mongabay

Fish populations in coral reefs off Kenya, Tanzania and Mozambique are being harvested at unsustainable rates, new research has found.

In the study published in the journal Marine Ecology Progress Series, researchers found that at 38% of the coral reefs they surveyed in the region had fish stocks below sustainable levels. When sampling bias was accounted for, they estimate that 70% of the region’s coral reefs have been fished to below sustainable levels.

Author Tim McClanahan, senior conservation zoologist at the Wildlife Conservation Society, surveyed fish populations at 238 sites along the East African coastline over 12 years. At each site, McClanahan counted fish, identified their species, and estimated their size in order to calculate their total biomass — a skill he has been refining for more than 30 years.

“To count coral reefs is not the easiest thing,” McClanahan said. “Coral reefs are fairly chaotic and it gets more chaotic the more fish there are.”

This is the first study of its kind and scale to be conducted in East Africa’s coral reefs and provides a worrying insight into the region’s fish stocks.

“The findings are grounded on sound data sets collected in many sites along the coast,” said Edward Kimani, Research Scientist at Kenya’s Marine and Fisheries Institute, who was not involved with the study.

East Africa’s fisheries are monitored by scientists at national fisheries departments, but their analyses are based predominantly on yield data reported by fishers. Their work is further complicated by the absence of reefs unaffected by fishing, which would provide baseline figures for comparison.

“There are essentially no stock assessments in East Africa, which is a problem because you don’t know what the status of the sustainability is without these,” McClanahan said.

Fisheries support thousands of jobs and livelihoods for coastal communities. If reefs were allowed to recover, they could support greater yields. Image by Rajesh Pamnani via Flickr (CC BY-NC-ND 2.0)

The coral reefs off East Africa’s coasts are mainly exploited by small-scale artisanal fishers, casting nets or spearfishing from small boats. A variety of initiatives, many supported by the U.N. Food and Agriculture Organization and the World Bank, have focused on expanding these fisheries through improved infrastructure, but without a concurrent improvement in fisheries management and monitoring.

“I think there’s this confusion that just because [the fishermen] are poor or not highly educated or don’t have sophisticated technology that they can’t overexploit their fishery, but they can,” McClanahan said.

Optimistic scenario

To create a baseline, McClanahan surveyed sites in the region’s marine protected areas (MPAs), some of which have been managed as “no take” zones for the last 30 to 40 years. Once he had a baseline, he could then compare fish biomass from fished coral reefs to that in the MPAs.

In a separate paper, McClanahan and his colleagues found that East Africa’s previously fished areas that are now closed had only around 40% of the fish biomass of remote tropical reefs in areas like the Seychelles.

“The [baseline] I’m using in the paper is somewhere, maybe even half, of what it might have been,” McClanahan said. “So when I say these reefs have been over exploited, I’m being conservative towards fishermen and fisheries and not at all conservative towards nature.”

And that’s not the only reason the study’s estimates are potentially optimistic. The data used in the paper come from sites McClanahan has studied over the last 12 years. As a marine ecologist interested in the impact of fishing restrictions and closures, he has inevitably sampled sites with less fishing activity. When McClanahan used a computer model to see what would happen if the reefs were randomly chosen rather than selected, the percentage of unsustainably fished reefs rose from 38% to 71%.

Whilst many of McClanahan’s conservation-focused academic colleagues would rather he report the worst-case scenario, he says he has good reason for staying within the limits of his data: as in many places around the world, fisheries in East Africa are a political issue.

“Fisheries support thousands of jobs and livelihoods for coastal communities,” says Kimani. “National fisheries contribute significantly to food and nutrition in Kenya.”

Manage for recovery

Another recent study, published in the Proceedings of the National Academy of Sciences, found that fish stocks in fisheries that are intensively monitored and managed are actually now on the rise, reversing the global trend of decline. By contrast, fisheries with limited management, like in East Africa, have on average higher harvest rates and declining stocks, highlighting the need for proper fisheries management.

McClanahan has been trying to change attitudes and shift policy in the region based on scientific evidence and open discussion. For the last 22 years, he has hosted a Fishers Forum in Kenya for 200 of the most influential people in the country’s fisheries sector. But challenging an ingrained philosophy of expansion is not easy.

“Recovery has to become the new management goal,” he said. “That requires restrictions on fishing gear, restrictions on fishing effort and restrictions on fishing space, that is closures.”

McClanahan has been criticized for his calls to reduce access, but he says fishers would be better off if the fish stocks were allowed to recover. His previous research showed that a subsidy for fishers introduced by the Kenyan government in 2010 actually had the effect of reducing their income by 7% as the stock was further exploited and yields dropped.

McClanahan has calculated that Kenya’s current coral reef fish biomass of 20 tons per square kilometer can only support four boats per square kilometer. In MPAs where fishing has been banned for 30 years, the fish biomass has now recovered to more than 100 tons/km2. If stocks in Kenya’s coral reefs were allowed to recover to half that amount, 50 tons/km2, then McClanahan estimates they could support 11 boats/km2.

And recovery doesn’t have to mean closures. McClanahan’s past research has shown that restricting fishing nets and trap sizes — to ensure juvenile fish and small undesirable fish species can escape — can also be a very effective way to allow the reef biomass to recover while allowing fishing to continue and ultimately boosting fishermen’s income.

“I’m arguing for an empirical approach to this problem, not a political or emotional approach, because otherwise we’re not going to be adaptive,” he said.

Citations

McClanahan, T. R. (2019). Coral reef fish communities, diversity, and their fisheries and biodiversity status in East Africa. Marine Ecology Progress Series, 632, 175-191. doi:10.3354/meps13153

Hilborn, R., Amoroso, R. O., Anderson, C. M., Baum, J. K., Branch, T. A., Costello, C., … Ye, Y. (2020). Effective fisheries management instrumental in improving fish stock status. Proceedings of the National Academy of Sciences, 117(4), 2218-2224. doi:10.1073/pnas.1909726116

McClanahan, T. R., & Kosgei, J. K. (2019). Outcomes of gear and closure subsidies in artisanal coral reef fisheries. Conservation Science and Practice, 1(10). doi:10.1111/csp2.114

McClanahan, T. R., Schroeder, R. E., Friedlander, A. M., Vigliola, L., Wantiez, L., Caselle, J. E., … Cinner, J. E. (2019). Global baselines and benchmarks for fish biomass: comparing remote reefs and fisheries closures. Marine Ecology Progress Series, 612, 167-192. doi:10.3354/meps12874