Using historical and citizen science data to improve knowledge about the occurrence of the elusive sandbar shark Carcharhinus plumbeus (Chondrichthyes – Carcharhinidae) in the Adriatic Sea

Abstract

The Mediterranean Sea is an extinction hotspot for sharks, skates, and rays, with at least half of all species being threatened. The sandbar shark Carcharhinus plumbeus is among the most threatened species and is declared endangered (EN) in the Mediterranean according to the IUCN Red List of Threatened Species. The Adriatic Sea was previously proposed to be an important nursery area for this species based on sporadic sightings of neonates and juveniles. However, this species is generally considered to be rare in this region, and reports of its presence are scarce. Here, we present new records for the sandbar shark in the Adriatic Sea and review spatial and temporal data accumulated from literature, museum specimens, and citizen science initiatives in an attempt to assess the distribution and seasonality of this species. The majority of the records were from neonate and juvenile sandbar sharks, and three hotspots for their occurrence could be identified: (1) the Emilia-Romagna region, (2) the Veneto region, and (3) the Gulf of Trieste. Our data indicate a high concentration of sandbar sharks around the delta of the Po river, emphasising the need for scientific surveys in this confined area in order to confirm a possible nursery ground. Data collected by citizen science initiatives reveal that this species is still present in the Adriatic Sea and might be more abundant than previously thought, underlining the potential of citizen science as a valuable tool to monitor the distribution of rare and endangered species.

First record of neonatal sandbar shark Carcharhinus plumbeus (Nardo, 1827) (Carcharhiniformes: Carcharhinidae) from the Southern Adriatic Sea

“…Such conclusion is directly supported by the fact that all the fisherman on our trawler also identified the shark as "peshkaqen pëllumb" which is the local neme for Mustelus spp. Furthermore, a significant increase in the use of social networks delivered numerous records of previously lessknown or very rare species (TAKLIS et al, 2020;GAJIĆ et al, 2022), including sandbar sharks in the Adriatic Sea (JAMBURA et al, 2021). Thus, lack of cooperation between researchers and fishermen could be another reason for lack of data on records (LIPEJ et al, 2000).…”

“…Medium-sized and large species inhabiting the coastal shallow waters, such as sandbar shark, are the most exposed to fisheries, habitat destruction and pollution (FERRETTI et al, 2008;DULVY et al, 2014;GAJIĆ et al, 2020). Despite being a common species in the Mediterranean Sea (JAMBURA et al, 2021), sandbar shark is facing severe anthropogenic pressures, including overfishing (DULVY et al, 2021), and is even considered locally extinct in certain parts of the Mediterranean (i.e., CAPAPÉ et al, 2000;KABASAKAL, 2015, KABASAKAL 2019.…”

Observations of juvenile sandbar sharks Carcharhinus plumbeus (Nardo, 1827) around the Bojana River delta (Southern Adriatic Sea)

“…Most of the records of this species in this area were reported from its northern region, especially around the delta of the River Po (Lipej et al, 2008;Jambura et al, 2021), while it has also been recorded in the middle Adriatic Sea (Dragičević et al, 2010). The high number of neonates and juveniles in this area lead several authors to propose that the Northern Adriatic basin might serve as a nursery area for this species (Costantini & Affronte, 2003;Lipej et al, 2008;Jambura et al, 2021). The presence of this species in the Southern Adriatic Sea has been indicated before, but on the basis of only a few specimens (Jambura et al, 2021).…”

“…The sandbar shark is the only species of the genus Carcharhinus that is known to inhabit the Adriatic Sea (Kovačić et al, 2020). Most of the records of this species in this area were reported from its northern region, especially around the delta of the River Po (Lipej et al, 2008;Jambura et al, 2021), while it has also been recorded in the middle Adriatic Sea (Dragičević et al, 2010). The high number of neonates and juveniles in this area lead several authors to propose that the Northern Adriatic basin might serve as a nursery area for this species (Costantini & Affronte, 2003;Lipej et al, 2008;Jambura et al, 2021).…”

“…The high number of neonates and juveniles in this area lead several authors to propose that the Northern Adriatic basin might serve as a nursery area for this species (Costantini & Affronte, 2003;Lipej et al, 2008;Jambura et al, 2021). The presence of this species in the Southern Adriatic Sea has been indicated before, but on the basis of only a few specimens (Jambura et al, 2021). Here, we report additional records of the sandbar shark from the delta of the River Bojana and discuss its potential role as an important habitat for this rare shark species.…”