Basten Gokkon, Jakarta – The wild populations that sustain a significant Indonesian fishery are more depleted than the government had estimated, as highlighted by a recent scientific study. The authors have called for a reevaluation of the method used to assess fish stocks to address the overexploitation of these populations.
The stocks of eight economically valuable fish species living close to the seafloor in Indonesia in 2020 were unhealthy, with most of them showing a decline in measurements of their spawning capacity, indicating unsustainable fishing rates of those deep-slope demersal populations, according to the paper published in the journal Fisheries Research. The findings were 1.4-2.4 times lower than stock estimates of those species provided by the Indonesian Ministry of Marine Affairs and Fisheries, it added.
"We see the urgency to understand how we can use simple metrics to assess different fisheries in Indonesia," Elle Wibisono, a fisheries scientist from the University of Rhode Island in the U.S. who is a lead author of the research, told Mongabay in an email interview.
"Indonesian fisheries are frequently characterized as "data-deficient," especially for length-weight or detailed data. So we want to address the challenge of how we can formulate a science-based fishery management in this data-deficient landscape," she added.
The group of researchers, composed of scientists, experts and government officials from the U.S. and Indonesia, assessed eight species roaming the deep slope of the seabed, including the Malabar blood snapper (Lutjanus malabaricus), the goldbanded jobfish (Pristipomoides multidens) and the crimson snapper (L. erythropterus), and focused on two main types of fishing gear, namely droplines and longlines. The Indonesian deep-slope demersal fisheries are economically valuable and contribute to the well-being of millions of people, the paper said.
The team then applied a framework combining catch rates (CPUE) and the ratio of the amount of spawn produced (SPR) to analyze those fish species with the respective fishing gear to "give a clearer picture of the stock status than either of them alone," the paper said.
They found that none of the studied stocks showed increasing or stable CPUE trends along with high SPR values, which meant that none of them appeared to be healthy or sustainably exploited. They also found significant discrepancies between their calculations and estimates by the Indonesian fisheries ministry, which they attributed to many factors, such as methods and data used to assess the fish stocks.
"However, the most possible explanation is the inclusion of species that are not typically part of the studied deep demersal fisheries," the study said. "In any case, it would be worth investigating if the values provided by the MMAF might be too high given the indications of poor stock status found in this and previous studies of the fisheries."
Wibisono said that without a robust framework indicating the need to use multiple indicators to reach the final conclusion, different priorities could lead to picking and choosing between only using CPUE or only using SPR to make a management decision. For example, she said, a production-focus policymaker could choose to make decisions based on the CPUE, such as allowing the same if not more fishing efforts in a fishery with high CPUE, while a more precautionary policymaker might choose to use SPR.
"I think the main point of the paper is to show that fishery indicators are useful albeit imperfect approximations of the condition of a fishery, and one way to improve our understanding is by using or combining multiple indicators. It can be dangerous to just rely on one indicator," Wibisono said.
Indonesian deep-slope demersal fisheries have helped position Indonesia to be the world's second-largest exporter of snapper species, with a combined domestic and international market value of $382 million and $176 million just for the top two species, L. malabaricus and P. multidens, respectively. The fisheries are multispecies and multigear, predominantly targeting snappers and groupers between 50 meters and 500 meters (164 feet and 1,640 feet) and using mostly droplines and longlines. The fishing grounds for the fisheries include some of Indonesia's important waters such as the Java Sea, the Makassar Strait and the Arafura Sea.
The Indonesian fisheries ministry is developing a harvest control strategy for deep-slope demersal fisheries on top of the ongoing fisheries management tools, the paper noted. The authors said their findings could greatly enhance the capabilities of civil society, nongovernmental organizations, the private sector or other researchers to be more actively involved in commenting on and discussing the draft harvest control strategy in public discussions with the ministry as it gathers input on the draft.
"Translating scientific findings and all of their nuance into a layperson language is challenging," Wibisono said. "However, at its core, we want to share that just because we/you/fishers are catching plenty, it does not mean that there is still a lot of fish left in the ocean."The crimson snapper (L. erythropterus). Image by Hamid Badar Osmany via Wikimedia Commons (CC BY 3.0 DEED).
[Basten Gokkon is a senior staff writer for Indonesia at Mongabay.]
Dimarchopoulou, D., Wibisono, E., Saul, S., Carvalho, P., Nugraha, A., Mous, P. J., & Humphries, A. T. (2023). Combining catch-based indicators suggests overexploitation and poor status of Indonesia's deep demersal fish stocks. Fisheries Research, 268. doi:10.1016/j.fishres.2023.106854