Global review of bull shark Carcharhinus leucas (Valenciennes, 1839) museum specimens: summary of records, geographic analysis, and assessment of their scientific value

Background Museum specimens provide critical data for taxonomy, systematics, biogeography, and conservation. Well-preserved vouchers are essential for documenting both historical and contemporary distributional records, supporting a better understanding on species distribution in a world undergoing constant environmental changes. Regarding the euryhaline bull shark, Carcharhinus leucas , voucher specimens reliably confirm occurrences in areas where the species' status was previously unclear and clarify the identity of morphologically similar shark species found in freshwater environments. This study aims to provide a synthesis of C. leucas voucher specimens, assessing their scientific significance and identifying priority regions for future sampling to address knowledge gaps in the occurrence and distribution of the bull shark. New information This study is one of the few available comprehensive global reviews of museum specimens for an extant shark species. By reviewing public databases and the primary literature, we collated information on 964 Carcharhinus leucas voucher specimens housed in ichthyological collections worldwide, of which 830 (86.1%) were associated with spatial metadata that allowed for geolocating of specimens. Among the specimens with spatial information, 6.3% (n = 52) were collected in freshwater, 49.0% (n = 407) in brackish estuarine habitats, 43.9% (n = 364) in marine environments, and 0.8% (n = 7) lacked precise locality so were not attributable to one of these categories. Our spatial analysis revealed several regions where collection efforts for C. leucas should be prioritized, including the Pacific and Atlantic coasts of South America, the Southwest Atlantic region of Africa, and the entirety of the Indian Ocean coast. The examination of this material confirmed the species' presence in locations where its occurrence was previously uncertain, and pre-dated its known occurrence in the Brazilian Amazon. Furthermore, our investigation revealed that some vouchers are imprecisely geolocated, either by the original collectors or during subsequent curation, highlighting the need for optimized spatial precision and caution when utilizing these data for scientific studies. Key findings of our study new to science: 1. A total of 964 Carcharhinus leucas vouchers (excluding fossils and genetic samples) were identified across global natural history collections. 2. Critical sampling gaps were identified in the Global South, particularly along the Atlantic and Pacific coasts of Central and South America, the Atlantic and Indian Ocean coasts of Africa, and vast regions of Asia (Indian and West Pacific). 3. Distributional data do not support the presence of C. leucas north of Bahía Magdalena (southern Baja California, Mexico); records north of this limit remain unconfirmed. 4. Direct examination of material verified the species' presence in Samoa (Polynesia, Southwest Pacific Ocean) and the Azores Archipelago (Portugal, North Central Atlantic Ocean). 5. Three previously undocumented estuarine/riverine records were identified for Puerto Rico (n = 2) and Colombia (n = 1). 6. The first record of C. leucas in the Amazon River (Belém, Pará, Brazil) was pre-dated to 1903, ten years earlier than previously reported in the scientific literature (1913). Simultaneously, this specimen also represents the first documented record of the species for Brazil. 7. Historical vouchers from riverine locations currently inaccessible to migratory fish (due to anthropogenic barriers) provide empirical evidence of habitat degradation and loss of fish biodiversity.