squamosissimus caught in the Chavantes reservoir (São Paulo state): originally from the North region
it may be competing with and contributing to a decline in the population of native species
it has become a key fishing resource in much of the country (photo: Edmir Daniel Carvalho/CAUNESP)
when it was first recorded in the Jaguarai reservoir in São Paulo state
the Silver croaker (Plagioscion squamosissimus) has established and increased its population in the Paraíba do Sul Basin to the detriment of native fish species
By André Julião | Agência FAPESP – The Silver croaker (Plagioscion squamosissimus)
a fish native to the Amazon (corvina or pescada-branca in Portuguese)
is the most probable cause of a sharp fall in the diversity of native species in the Jaguari reservoir
all of which are part of the Cantareira Water Production System and the Paraíba do Sul Basin in São Paulo state
As a top predator in the food network, the invader has negatively affected local biodiversity by bringing about detrimental changes to its taxonomic, functional and phylogenetic structure, according to a study published in Biological Invasions by researchers at São Paulo State University (UNESP)
They analyzed fish monitoring data collected by power utility CESP (Companhia Energética de São Paulo)
which has recorded the presence of the species in the reservoir since 2001
The data analyzed is for a period ending in 2016
squamosissimus has become the most abundant fish species in the reservoir
CESP does this monitoring of fauna to comply with environmental licensing rules for operation of the dam and power plant enforced by IBAMA
Every four months its technicians install nets at predetermined locations in the reservoir (between Jacareí and São José dos Campos) and on the Peixe and Jaguari
“We analyzed 15 years of monitoring data and found the abundance of native predators, particularly the Thin dogfish (Oligosarcus hepsetus), to have declined significantly as P. squamosissimus preyed on smaller fish and became more abundant”, said Igor Paiva Ramos last author of the article and a professor at FEIS-UNESP
it is not possible to tell from the available data whether the decline of O
since both this species and the invader may prey on the same fish
The former typically inhabits standing water bodies
Invader species are a global problem and occur in environments of all kinds
the annual damage caused by non-native animals
plants and microorganisms has been estimated at BRL 15 billion (now about USD 2.9 billion)
the researchers stress that other introduced species appear in the records for the Jaguari reservoir
and Oreochromis niloticus and Coptodon rendalli
both of which are tilapias and originally from Africa
reinforcing the conclusion that native diversity has dwindled due to P
The diversity loss observed by the authors applies to all three dimensions considered when this type of impact is assessed – taxonomic
Species richness losses during the period analyzed were noted
alongside substitution of many rare specialist species by a few generalists
and significant differences were found in species composition and abundance in the local fish community
with entire evolutionary groups disappearing
There are no simple solutions to the problem
The species is seen as a key fishing resource for both subsistence and sport
Eradicating it could cause social problems
“The species has become very common throughout Brazil
It replaces native species and now plays a very important social role in local economies,” Ramos said
he proposed measures similar to those taken in other countries to deal with invader species
One such measure would be to permit hunting of this species throughout the year without size limits or a ban during the reproductive period
with the aim of eradicating it or at least reducing its abundance
federal and state laws restrict fishing not just of native species
but also of invasive species to some extent
“This ends up perpetuating the species that are harmful to local fauna,” Orlandi Neto said
Ramos pointed out that eradication of invaders does not necessarily lead to a return of the natives
“We don’t know whether another invader will take the place of P
The environment has been modified to such an extent that it may no longer be suitable for former inhabitants,” he said
The article “Long-term impact of an invasive predator on the diversity of fish assemblages in a neotropical reservoir” is at: link.springer.com/article/10.1007/s10530-023-03243-9