In an article published in the journal PLOS ONE, Brazilian scientists show that one of the effects of overfishing in Arraial do Cabo, Rio de Janeiro state, Brazil, is the replacement of large and valuable species with smaller ones for which there was previously little demand.
According to the authors, the decline in stocks of Pomatomus saltatrix (bluefish), Epinephelus marginatus (brown grouper), Caranx hippos (crevalle jack) and Seriola fasciata (amberjack) was followed by an increase in the catch of fish of lesser commercial value. but more abundant species, such as Trichiurus lepturus (belt fish), Balistes capriscus (gray triggerfish), Aluterus monoceros (leather jacket unicorn) and Priacanthus arenatus (Atlantic obese).
In the article, which focuses on SSF, the authors note that fishermen need to spend more time at sea to get the same returns as in the past, and that younger people are switching to other sources of income such as tourism and are often encouraged by their families to stop fishing.
Focusing on large-bodied fish can cause major predators such as groupers, sharks and tuna to decline and even lead to local extinction of some species, the article points out. The first author is Carine O. Fogliarini, researcher at the Laboratory of Macroecology and Marine Conservation of the Federal University of Santa Maria.
Also signed by Vinicius J. Giglio Fernandes, a researcher at the Federal University of São Paulo (UNIFESP) with a FAPESP postdoctoral fellowship, the article confirms the existence of a well-known trend that scholars call fishing in the food web.
“The decline in stocks of species with a higher trophic level [larger species and apex predators] leads to increased fishing of small-bodied species at a lower trophic level. Overfishing ultimately leads to focus on the smaller species at the bottom of the food chain. In an article published in 2014 we had already highlighted the decline of several species of mesopredators [mid-level carnivores], including groupers and bluefish, and now, by combining the knowledge of local fishermen and landing data, we have shown that higher tier species are overfished in Arraial do Cabo and the average size of landed species is decreasing, “Mariana said. G. Bender, who directs the UFSM Marine Macroecology and Conservation Laboratory and is the last author of the article.
To confirm this latest finding, the researchers used the mean trophic level (MTL) as a metric and decided to estimate its decline over a 16-year time series. “Put simply, when this number drops significantly, it is a sign that we are fishing for many more low-level species,” said Fogliarini. “We had some difficulties with MTL because it is a general metric that takes into account the average trophic level of biomass landed and its variation over time. So we divided MTL into four categories: all species landed; species from one level trophic [TL] higher than 4; TL equal to 3.5 or higher; and TL less than 3.5. “
The researchers observed a downward trend in MTL and landings of species with a TL above 4 and a TL of 3.5 or above. “Catches with a TL above 4 tended to rise and then fall sharply,” Bender said. “This means that landings of species with a TL above 4 were actually decreasing and tended to be replaced by species with a lower TL.”
The study also suggests that assessing changes based on a single indicator, such as MTL, can mask outcomes and that the use of different approaches, including local knowledge, can make changes more explicit.
The researchers interviewed 155 artisanal fishermen in Figueira, Monte Alto, Praia Grande, Praia dos Anjos, Prainha and Pontal, corresponding to 10.3% of the artisanal fishing communities concerned. They classified the respondents into four groups: less experienced (under 20 years of experience), intermediate (21-35 years), experienced (36-40 years) and very experienced (over 40 years).
“Fishermen with more years of experience have recognized significantly more overfished species than those with fewer years of experience,” said Fogliarini. “We have observed the same pattern for the number of species recognized as target species. The more experienced the fisherman is, the more species are mentioned as new local fisheries targets.”
Researchers identified 37 species as overexploited, led by oily fish in all experience categories (45%), but grouper and crevalle jack were the most cited by the most experienced group. “They’ve been fishing for grouper in the region for many decades and it’s important to the local economy. Grouper and crevalle jack have always been very popular there, but both species are increasingly scarce,” Bender said.
Beltfish ranked second among overfished species and first among new target species. “According to more experienced fishermen, the species initially had no value and was buried in the sand when landed as a by-catch, but gradually a market emerged for the species, which became a new target and was eventually overfished,” he said. observed Fogliarini.
The second most cited species among the new targets is the gray triggerfish, followed by the Argentine conger (Conger orbignianus), the unicorn skin vest and the obese Atlantic. “The same downward trend reported for bluefish, belt, grouper, crevalle jack and amberjack was confirmed by the landing data we were able to access,” said Fogliarini. “We also found that younger fishermen reported more new target species than older ones, and this also matched the most recent landing data we had.”
Reasons for overfishing
According to the respondents, the reasons for overfishing were the increase in the number of fishermen and fishing vessels, the presence of industrial vessels in the area and unsustainable fishing techniques such as trawl and purse seine.
Maritime fisheries data from the Rio de Janeiro Fisheries Monitoring Project for the period January-June 2020 shows that 59.9% of the artisanal catch in Arraial do Cabo was obtained by purse seine, with a boat pulling out the net from the fishing boat to surround the fish. The hook and line finished second, and the beach seine finished third.
“In purse seine fishing, they use different boats and pull the net on the beach, where they land their catch. We also know about shark fishing, where they surround the fish and drag it onto the beach. This is highly predatory because it catches a lot of pregnant females.” Fogliarini said.
Data and public policy
According to Bender, the data from the monitoring project analyzed by the researchers was for too short a period (16 years, between 1992 and 2008), and more recent data exists but has not been accessed. Stronger public policy is needed to ensure continuous monitoring, as well as the production and availability of data.
“Monitoring is patchy in Brazil in the sense that it is not done everywhere and it is not continuous. Ideally it should be periodic [once a month, for example] and include inspection of landings at various points along the coast, because catches vary in composition from place to place, “Bender said.” And above all, it should be species-based and as detailed as possible, avoiding the use of common or popular names, which is the current methodology and makes it difficult to build stock scenarios for the entire coast. There may be several species in a generic category such as “grouper”, which however refers to different species in the states of Bahia and Santa Catarina. Common names can change from one region to another. “
For Fogliarini, consumers are also very important. “Few initiatives seek to reach the consumer, yet it is demand that determines what is captured,” he said. “We need consumer awareness campaigns. Much remains to be done to achieve a reasonable level of awareness of fish consumption.”
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Carine O. Fogliarini et al, Telling the Same Story: Fisheries and Landings Data Reveal Changes in Fisheries on the Southeast Coast of Brazil, PLOS ONE (2021). DOI: 10.1371 / journal.pone.0252391
Citation: Study reveals a decline in catches of predatory fish on the southeastern coast of Brazil (2021, 30 August) recovered on 30 August 2021 from https://phys.org/news/2021-08-reveals-decline-predatory- fish-southeastern.html