Most sharks occupy high trophic levels in marine ecosystems, thus exerting a key influence on their structure and function (1990; Compagno, 1984). Yet, contrary to most fishes, sharks generally have a K-selected life history strategy, which means slow growth rates, late maturity age, low fecundity, long gestation period, few offspring, and long-life spans (Dulvy et al., 2014; Wheeler et al., 2020). This, allied to a general tendency for segregation by age and sex, makes them especially vulnerable to human impacts (Baum et al., 2003; García et al., 2008; Ferretti et al., 2010; Roff et al., 2016). In fact, shark populations have been plummeting over the past few decades, namely driven by intense fishing pressure, with key implications for their sustainability and conservation (Queiroz et al., 2019; Dulvy et al., 2021; Pacoureau et al., 2021).

Understanding the habitat-use patterns of sharks, namely through identification of key aggregation sites and nursery grounds, is essential to recognize the potential effects of human activities on these populations and design effective conservation and management strategies (Knipp et al., 2010; Speed et al., 2010; Diemer et al., 2011; Henderson et al., 2016; Queiroz et al., 2016; Heupel et al., 2019; Queiroz et al., 2019). Among several hypotheses concerning the role of nursery areas, it is generally accepted that such areas provide enhanced food availability and protection against predation (Springer, 1967; Branstetter, 1987; Heupel and Simpfendorfer, 2002; Heupel et al., 2007). According to Heupel et al. (2007), three criteria must be met so that a particular marine area can be considered as a shark nursery ground, namely: i) preference – sharks are found more often in the specific area than in neighboring ones, ii) residency – sharks tend to remain in the area (or return) for extended periods, and iii) consistency – the area or habitat is used repeatedly by sharks over the years.

While great efforts have been made to identify and describe sharks’ nursery areas around the world, there are still strong climate, habitat, and taxonomic bias in the literature (Heupel et al., 2019). Moreover, and because the identification of such important nursery areas is often dependent on long-term sample size datasets, most studies do not comply with all three criteria defined by Heupel et al. (2007), fulfilling only one or two criteria. For the Atlantic African region in particular, seven potential shark nursery areas were described over the past decade, all of them being for single species (see Supplementary Table 1 ). These pertained to areas used by angel sharks (Squatina squatina) in the Canary Islands, leafscale gulper sharks (Centrophorus squamosus) in Mauritania and Namibia, and great white (Carcharodon carcharias), smooth hound (Mustelus mustelus), and blue (Prionace glauca) sharks in South Africa (see details and respective references in Supplementary Table 1 ).

Communal nurseries are locations where juveniles of multiple shark species occur and the adults are mostly absent (Simpfendorfer and Milward, 1993). Yet, in such nurseries, the juveniles face a tradeoff between lower predation risk and increased competition – while the latter is potentially reduced via partitioning of food resources (Kinney et al., 2011). Within this context, here we describe, for the first time, a potential multi-species/communal shark nursery area in the Atlantic African region. More specifically, we describe the first potential nursery of milk (Rhizoprionodon acutus), scalloped hammerhead (Sphyrna lewini), blacktip (Carcharhinus limbatus), Atlantic weasel (Paragaleus pectoralis), and nurse (Ginglymostoma cirratum) sharks in Sal Rei Bay (SRB), Boa Vista Island, Cabo Verde. Here we assess: (i) the diversity of shark species occurring in the SRB; (ii) the size frequency distribution of juvenile sharks; (iii) inter and intra-year patterns in the relative abundance of juvenile sharks (catch per unit of effort data); and (iv) the spatial variation in species composition and abundance around Boa Vista Island based on interviews to local fishermen.

The present study shows that SRB is used by juveniles of, at least, 5 threatened shark species. According to the IUCN Red List of Threatened Species (IUCN, 2022), S. lewini is designated by as “Critically Endangered”, P. pectoralis as “Endangered”, and R. acutus, C. limbatus and G. cirratum as “Vulnerable”. Furthermore, although not caught during the present surveys, information acquired through citizen science and preliminary data based on baited remote underwater videos (BRUVs), suggest the presence of juveniles of other shark species, namely spinner (Carcharhinus brevipinna) and lemon (Negaprion brevirostris) sharks (see Supplementary Figure 5 ).

The high consistency of the results obtained based on local fishermen’s knowledge clearly showcases that shark juveniles are found more often in SRB than in other coastal areas of the island ( Figure 4 ). This preference is potentially related to the fact that SRB is a shallow, relatively wave-protected area (mostly with less than 10 m of depth). Because the predominant direction of waves in Boa Vista Island is from the Northeastern quadrant (Gomes, 2019) under the influence of the Canary Current (Peña-Izquierdo et al., 2012), SRB has relatively low wave action, especially during summer months. Moreover, there is a small islet at the north side of the bay that provides further protection ( Supplementary Figure 2 ). By contrast, most other areas in Boa Vista Island are high-energy exposed shores without noticeable barriers (e.g., reefs or small islets) (Gomes, 2019).

SRB is repeatedly used by juvenile sharks over the years ( Figures 1 , 2 ), with higher CPUE values during summer and autumn periods. With this information, we are confident that SRB fully meets both criteria I (i.e., sharks are found more often in the specific area than in neighboring ones) and III (i.e., the area is used repeatedly by sharks over the years), as defined by Heupel et al. (2007). While no definite conclusions can be drawn regarding criterion II (i.e., sharks tend to remain in the area for extended periods), the observation of neonates with umbilical scars at different healing stages (preliminary findings) together with the general range of sizes observed ( Figure 4 ) suggest that these animals are likely to make use of the bay for at least a few weeks after birth, and, thus, likely to meet criteria II. In this context, and although direct efforts to definitively confirm criterion II are still required (e.g., mark-recapture studies, remote tracking, stable isotope analysis), we argue that the importance of the SRB as a potential nursery area for multiple threatened shark species must not be understated.

Ensuring the effective protection of the SRB potential nursery area is of the utmost relevance as all identified shark species – in particular scalloped hammerheads and Atlantic weasel sharks – are threatened by anthropogenic pressures, and vulnerable to extinction over the near future (IUCN, 2022). There are many types of potential marine protected areas (MPAs), from full to minimal protection, from the ones that exist in practice (implemented) to the ones only on paper (Grorud-Colvert et al., 2021). The SRB is partially encompassed by two of the Boa Vista Island protected areas, however these do not focus on the marine realm, and are not MPAs but “natural reserves” – over 80% of their extension corresponds to terrestrial area (Cabo Verde Parliament, 2014a; 2014b). Indeed, the Boa Esperança Natural Reserve and the Morro de Areia Natural Reserve do include “peripheral areas for marine protection” that extend up to 300 m offshore (Cabo Verde Parliament, 2014a; 2014b). Yet, the latter represent only a small fraction of the SRB (10%), with an area of c. 2.7 km² (see Supplementary Figure 2 ). At the same time, these natural reserves are still pending implementation, which means that they do not yet have any management instruments in place (e.g., management plans) (Boa Vista Municipality, 2022). The latter is especially significant as benefits of MPAs are highly dependent on their effective implementation and management (Grorud-Colvert et al., 2021). Also, the lack of enforcement further undermines the effectiveness of MPAs, as observed in other islands of Cabo Verde (Vasconcelos et al., 2015).

New opportunities and risk also arise from the recently approved coastal and marine spatial plan of Boa Vista Island – Plano de Ordenamento da Orla Costeira e Mar adjacente da ilha da Boa Vista (POOCM) (Cabo Verde Parliament, 2020). The POOCM establishes a planning unit for SRB (the Sal Rei Bay Integrated Management Area) whose general goals are to: (1) minimize the risk of environmental impacts; and (2) regulate fishing, nautical sports, and other recreational activities to make them compatible with the protection and valorization of marine ecosystems. Still, human activities such as artisanal fisheries, aquaculture, renewable energy, and maritime transportation are generally allowed in the planning unit (Cabo Verde Parliament, 2020). At the same time, while the POOCM has several references to the protection of sea turtles and marine mammals, no references are found for sharks, reflecting the lack of attention to this particular taxonomic group. Also, the POOCM is to be further implemented by dedicated management plans and regulations that are still to be developed, and which sometimes take long to be put in place because of social-political factors (Frazão Santos et al., 2021). Finally, the close proximity to two “tourism development zones” (the Integral Tourism Development Zone of Chave and Integral Tourism Development Zone of Morro de Areia) makes the SRB further vulnerable to human pressures and impacts (Cabo Verde Parliament, 2008; 2009).

Further action is therefore needed to ensure the effective conservation of shark populations, and broader benthic and pelagic ecosystems, in the SRB. Such protection will largely depend on the specific conservation measures and monitoring plans that are put in place, but also on capacity building and awareness raising actions targeting national and international ocean users and stakeholders. Only then will it be possible to ensure an equitable and sustainable use and conservation of the SRB.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Ethical review and approval was not required for the animal study because It entailed surveys on local artisanal bycatch fishery.

RR conceptualized the study. RR, EN, VP, CS, JV, JP, MB, TR, JC and CF collected field data. RR and TM performed data analyses. RR and CF wrote the original draft of the manuscript. All authors reviewed and edited the manuscript. All authors contributed to the article and approved the submitted version.