Long-term trends of fishery landings and target fish populations in the lower La Plata basin

Abstract

The La Plata basin is the second largest basin of South America and has supported important river fisheries for more than a century. In this paper, we evaluate for the first time the historical trends of landings of 21 fish taxa and the recent population trends of 27 species of commercial fishes in the lower La Plata basin (Argentina). We compiled three kinds of data sets: Total fishery landings (between 1934 and 1986) and exports (1994‒2019), fisheries monitoring programs of Chaco and Santa Fe provinces in the Paraná River (2009‒2019), and surveys of fish populations in the Upper (Corrientes, 1993‒2020) and Middle (EBIPES, 2005‒2020) Paraná River. The analysis of the historical landings showed more species declining in the lower portion of the basin than in the upper basin. Regarding recent population trends, Pimelodus spp., Hoplias spp., Salminus brasiliensis, Luciopimelodus pati, and Ageneiosus spp. declined in more than one region, while Megaleporinus spp., Pterodoras granulosus, and Oxydoras kneri showed stable to positive trends, with the other species varying in their trends between regions. These tendencies could be associated to a combination of factors such as overfishing and environmental changes that would require an ecosystem approach for their adequate management.

Environmental history of one of the largest freshwater neotropical fish (Zungaro jahu) from otolith isotopic analysis

“…The isotope signatures of the upper Paraná are not distinguishable from those of the lower Paraná (Avigliano et al, 2020). However, the landings of the last five decades are restricted to latitudes lower than 30° S (middle and upper Paraná) (Baigún et al, 2003; Scarabotti et al, 2021), suggesting that the otolith isotopic values compatible with the upper/lower Paraná correspond to the upper Paraná, and not to the lower area of basin. Furthermore, forays into waters with high 87 Sr/ 86 Sr ratios such as the Paraguay‐Pilcomayo‐Bermejo appear to be relatively brief (Figure 3), suggesting that fish do not perform extensive migrations into those regions.…”

“…The Manguruyú Zungaro jahu (Ihering, 1898) is one of the largest neotropical fishes, exceeding 160 cm in length (Mateus & Penha, 2007), and is endemic to the La Plata Basin (Argentina, Bolivia, Brazil, Uruguay, and Paraguay) (Boni et al, 2011). One century ago, catches of up to 162 cm were recorded in the Río de la Plata Estuary (Southern limit of the La Plata Basin) (Donagh, 1937), but from the 1970 s onwards, the adult specimens disappeared completely from the lower basin (Scarabotti et al, 2021). Currently, the landings are limited to the subtropical and tropical areas of the La Plata Basin, mainly in the upper end of the middle Paraná, and in the Paraguay sub‐basin (Baigún et al, 2003; Scarabotti et al, 2021).…”

“…One century ago, catches of up to 162 cm were recorded in the Río de la Plata Estuary (Southern limit of the La Plata Basin) (Donagh, 1937), but from the 1970 s onwards, the adult specimens disappeared completely from the lower basin (Scarabotti et al, 2021). Currently, the landings are limited to the subtropical and tropical areas of the La Plata Basin, mainly in the upper end of the middle Paraná, and in the Paraguay sub‐basin (Baigún et al, 2003; Scarabotti et al, 2021). Due to the drop in abundance and reduction in distribution during the last decades, several states have prohibited the commercialization of Z. jahu (Fuentes & Mantinian, 2021), which is currently considered a vulnerable species (SP, 2014; Van Damme et al, 2009).…”

“…There is no information available on migrations, nursery or breeding areas, the presence of eggs or larvae in ichthyoplankton, or diet of Z. jahu , so its life history is practically unknown. This is partly due to the fact that catches are scarce or non‐existent in much of the basin (Scarabotti et al, 2021), with the exception of upper Paraguay (Great Pantanal) (Mateus et al, 2004; Mateus & Penha, 2007). In the Cuiaba River, Great Pantanal, the Z. jahu reproductive period is associated with low water, at which time high densities of larvae have been reported (Ziober et al, 2012).…”

Ecosystem services provided by the exotic bivalves Dreissena polymorpha, D. rostriformis bugensis, and Limnoperna fortunei

“…Many midsized fishes that feed on golden mussels are in turn consumed by larger, piscivorous fishes with high commercial and recreational value, suggesting that mussels are likely to have a positive impact on these large species as well (reviewed in Boltovskoy & Correa, 2015 ; Karatayev et al, 2015b ). In addition, similar to dreissenids, golden mussels transfer large amounts of organic matter from the pelagic to the benthic domains through their feeding and filtering activities and the formation of feces and pseudofeces, which likely boosts the biomass of many iliophagous species, including the sábalo ( Prochilodus lineatus ), an intensively exploited and strictly iliophagous species which represents up to > 60% of the overall fish catches and biomass in the Río de la Plata basin, and ~ 80–90% of Argentine freshwater fish exports (Boltovskoy et al, 2006 ; Scarabotti et al, 2021 ).…”