From plentiful to critically endangered: Demographic evidence of the artisanal fisheries impact on the smalltail shark (Carcharhinus porosus) from Northern Brazil

Abstract

The smalltail shark, Carcharhinus porosus, was the most abundant elasmobranch species in fisheries off Brazil's northern coast (BNC) in the 1980s, but its population has been declining since the 1990s. For this reason, a demographic analysis is necessary to determine the extent of this decline and the fishing effect on the BNC's population. Therefore, we performed a stochastic demographic analysis of the population in the BNC, and considered its global center of abundance. Smalltail shark specimens (n = 937) were collected with gillnets in Maranhão state, eastern BNC, in the 1980s with sizes ranging between 29.6 and 120.0 cm total length. Most of the individuals (90.6%) caught were juveniles (< 6 years-old), and the mortality and exploitation rates showed that the species was overexploited (92.3% above the fishing mortality corresponding to the population equilibrium threshold). The smalltail shark's biological characteristics, such as slow growth and low fecundity, demonstrate that it is one of the least resilient species among similar sized coastal sharks in the region. All these factors yielded an annual decrease of 28% in the intrinsic population growth rate, resulting in a population decline of more than 90% in only 10 years, and much higher for the current period. This set of features comprising fishing recruitment occurring upon juveniles, overfishing, and intrinsically low resilience make the population unable to sustain fishing pressure and severely hamper biological recruitment, thus causing this drastic population decline. Furthermore, several local extinctions for this species in the northeastern and southeastern regions of Brazil highlight its concerning conservation scenario. Therefore, since similar fisheries characteristics occur throughout its distribution range, C. porosus fits the criteria E of the IUCN Red List for a critically endangered species and urgent conservation measures are needed to prevent its extinction in the near future.

Two thirds of species in a global shark fin trade hub are threatened with extinction: Conservation potential of international trade regulations for coastal sharks

“…Fins of these coastal species can be small (i.e., < 10 cm), are commonly found in the Hong Kong markets (Cardeñosa et al., 2020c), and arrive to Hong Kong in containers with millions of fins (D. Cardeñosa, personal observation). Therefore, even though individual fins from many of these species do not fetch particularly high commercial value, in large quantities, low‐value fins still provide a lucrative enterprise, potentially creating incentive to retain bycatch or even target these species (Ba et al., 2015; Santana et al., 2020; Quinlan et al., 2021). Whether a high‐ or low‐value species, our study indicates that international trade is potentially an ultimate threat.…”

Myliobatis goodei: Carlson, J., Charvet, P., Avalos, C., Blanco-Parra, MP, Briones Bell-lloch, A., Cardenosa, D., Chiaramonte, G.E., Cuevas, J.M., Derrick, D., Espinoza, E., Mejía-Falla, P.A., Morales-Saldaña, J.M., Motta, F., Naranjo-Elizondo, B., Pacoureau, N., Paesch, L., Pérez Jiménez, J.C., Rincon, G., Schneider, E.V.C., Simpson, N.J., Talwar, B.S. & Pollom, R.

“…In northern Brazil, artisanal fisheries pressure is high and 44% of target stocks were likely to be overfished by the end of the 2000s (Vasconcellos et al 2011). The combination of intense and unmanaged artisanal and commercial fishing in that area has led to the disappearance of several elasmobranch species in the region, including Largetooth Sawfish (Pristis pristis), Smalltooth Sawfish (Pristis pectinata), Daggernose Shark (Isogomphodon oxyrhynchus), and Smalltail Shark (Carcharhinus porosus) (Charvet and Faria 2014, Lessa et al 2016, Reis-Filho et al 2016, Santana et al 2020. In northeastern and eastern Brazil, artisanal fisheries are intense, gillnetting is the predominant artisanal gear, fishers there report that stocks are overexploited, and other sharks have been depleted (Guebert-Bartholo et al 2011, Reis-Filho et al 2016.…”

Is restricting catch to young sharks only more sustainable? Exploring a controversial management strategy for bull, tiger, blue and bonnethead sharks

“…In fact, widespread underestimation of shark captures hinders stock assessments and implementation of management strategies (Cashion et al, 2019). As a result, many shark populations have decline around the world (Baum & Myers, 2004; Lawson et al, 2020; Lessa et al, 2016; Santana et al, 2020; Santander‐Neto et al, 2021), with significant increases in extinction risk being estimated (Dulvy et al, 2014). Currently, ~75% of shark species are threatened to some level (Pacoureau et al, 2021).…”

“…In the face of this data‐poor situation, demographic modelling has emerged as an alternative tool to provide and evaluate potential management measures by determining important quantitative population parameters and identifying the most vulnerable life stages (Cortés, 1998; Simpfendorfer, 2004; Cortés et al, 2015). Demographic modelling does not require extensive catch and effort data, but rather uses basic life‐history information that is easier to obtain and more readily available, such as growth parameters, fecundities and estimated mortalities to project population growth rates and other important demographic parameters (Bradshaw et al, 2018; Caswell, 2018; Santana et al, 2020; Smart et al, 2017). In addition, incorporation of the random effects of environmental stochasticity and variation in life‐history traits in demographic models enables measurement of uncertainty (McAuley et al, 2007; Smart et al, 2017).…”

“…Slow growth rates, large asymptotic sizes, low fecundity and late maturations cause shark populations to grow at remarkably slow rates even when unexploited (Schindler et al, 2002;Cortés, 2008;Dulvy et al, 2008;Field et al, 2009;Smart et al, 2017;Grant et al, 2018Grant et al, , 2020Erhardt & Weder, 2020). Consequently, even low levels of fishing mortality can lead to disturbances in population dynamics such as decreased recruitment strengths and cause declines (Schindler et al, 2002;Smart et al, 2017;Santana et al, 2020;Tsai et al, 2020). In addition, there is only scant evidence pointing to compensatory effects of exploitation on shark population parameters such as increased fecundities and earlier maturation (Frisk et al, 2005).…”