Definition of no‐fishing zones and fishing effort limits to reduce franciscana bycatch to sustainable levels in southern Brazil

Abstract

Franciscana dolphin Pontoporia blainvillei bycatch has been high for near six decades in western South Atlantic, with large regional variation. In 2012, the Brazilian Government‐regulated gillnet fisheries in south and southeast Brazil by reducing fishing effort and establishing no‐fishing zones. However, there is evidence that the magnitude of franciscana bycatch remains high and unsustainable. The aims of this study were to identify hotspot areas of franciscana bycatch associated with two main gillnet fisheries and to propose no‐fishing zones combined with limited total allowable fishing effort (i.e. total net length per season) in order to meet management objectives in southern Brazil. A hierarchical Bayesian model using integrated nested Laplace approximation (INLA) was employed based on 1427 reported settings from 1999 to 2003 and 2006 to 2009. Hotspot zones were detected and are proposed as no‐fishing zone during the white croaker Micropogonias furnieri and striped weakfish Cynoscion guatucupa gillnet fishing seasons. Their extents represent 6% (1466.8 km2) and 19% (4493.7 km2) of the fishing ground (23 204.1 km2) during croaker and weakfish fishing seasons respectively. The total allowable fishing effort estimated outside the no‐fishing zones were estimated at 541 km (95% credible interval (CrI) [339; 940]) during croaker and 688 km (CrI [312; 2,166]) during weakfish fishing seasons, one order of magnitude lower than the current total fishing effort. The drastic reduction of total fishing effort estimated in this study is largely due to weak protection measures since the gillnet fisheries became the major conservation concern for franciscana by the end of 1970s in southern Brazil. Although the implementation of the proposed exclusion zones and limiting fishing effort will strongly impact the status quo, they were based on the best scientific evidence and on a clearly defined management goal to reduce the risk of the franciscana population’s collapse in southern Brazil.

A Synthesis of the Ecology, Human-Related Threats and Conservation Perspectives for the Endangered Franciscana Dolphin

“…Evidence, however, indicates that the level of franciscana's fishing-related mortality in Brazil remains high, in the order of several hundreds to a few thousands, which is not different from the numbers observed in years that preceded the regulations (e.g., Prado et al, 2013Prado et al, , 2016Cremer et al, 2018a). Moreover, a recent case study showed that even with full compliance, the current fishing regulations cannot reduce franciscana bycatch to sustainable levels in southern Brazil (Prado et al, 2021). Therefore, these regulations are proved insufficient to reduce fishing-related mortality to sustainable levels due to either or both lack of enforcement and, hence, compliance, and insufficient reduction in fishing effort.…”

“…Meanwhile, an immediate and significant bycatch reduction, as a result of a drastic decrease of the total fishing effort, and habitat restoration is, perhaps, the only short-term options for reducing the risk of franciscana's collapse (e.g., Prado et al, 2021). These authors identified two bycatch hotspots areas in Rio Grande do Sul state coast (part of FMA III), south of Brazil, and recommended that they should be designated as no-fishing zones for gillnets.…”

“…One of the recommended gillnet no-take area is off the Albardão region, a strong candidate to become a marine protected area as it represents an important feeding and breeding ground for endangered loggerhead sea turtle and elasmobranchs, respectively (Vooren and Klippel, 2005;Monteiro et al, 2016). Prado et al (2021) also recommended that total fishing effort outside these areas should drop considerably. These sort of management options are extremely unpopular among fishers (e.g., Murray et al, 2000;Brownell et al, 2019), especially if the closure areas encompass significant proportions of their fishing grounds, which is the case in the study of Prado et al (2021).…”

“…Prado et al (2021) also recommended that total fishing effort outside these areas should drop considerably. These sort of management options are extremely unpopular among fishers (e.g., Murray et al, 2000;Brownell et al, 2019), especially if the closure areas encompass significant proportions of their fishing grounds, which is the case in the study of Prado et al (2021). In fact, any action with higher likelihood of effectiveness will, necessarily, result in lowering absolute fishing effort or changing location of main fishing grounds, which, in turn, may have negative socio-economic impact.…”

Intrapopulation variation in the diet of franciscana dolphin (Pontoporia blainvillei) off southern Brazil

“…The species is classified as ‘Vulnerable’ in the IUCN Red List of Threatened Species throughout its range (Zerbini et al ., 2017), principally as a consequence of incidental mortality in fisheries. Within the study area (Franciscana Management Area III), along the Rio Grande do Sul (RS) state coast – southern Brazil, this species has been experiencing unsustainable rates of bycatch in gillnets for at least four decades (Moreno et al ., 1997; Ott et al ., 2002; Secchi et al ., 2003; Secchi & Fletcher, 2004; Prado et al ., 2013, 2016, 2021). At a regional level, franciscana dolphins are listed as ‘Critically Endangered’ in the study region (Rio Grande do Sul State, Decree No.…”