Molecular identification and first demographic insights of sharks based on artisanal fisheries bycatch in the Pacific Coast of Colombia: implications for conservation

Abstract

The Pacific coast of Colombia is characterized by mangrove ecosystems which play a crucial role as possible nurseries for juvenile sharks. However, trophic food webs from coastal ecosystems are heavily disturbed by increased fishing pressure, which affects numerous shark species. In this region of the Eastern Tropical Pacific (ETP), fisheries’ data from coastal areas are scarce and unspecific, as most sharks from artisanal fisheries are landed decapitated and finless, making their morphological identification difficult. For the establishment and implementation of effective regional conservation and management policies, information on the diversity and population dynamics of shark species is crucial. We therefore sequenced the mitochondrial NADH2 gene of 696 samples taken from fishermen’s landings of shark’s bycatch along the Colombian north Pacific coast. We were able to identify 14 species of sharks, two of the most abundant species were Sphyrna lewini and Carcharhinus falciformis, both evaluated on IUCN the Red List of Threatened species (Critically Endangered and Vulnerable) and CITES regulated. We found low genetic diversity in the sampled area increasing the concern for both species in the region, even more considering that the majority of individuals were juveniles. Our results showed the importance of genetic markers for first population genetic insights as a complementary tool during the decision-making process in management plans. For this specific region, strategies such as the delimitation of conservation priority areas or the regulation of fishing gears could help improve the sustainability of shark populations in the Colombian Pacific.

Vulnerability of Eastern Tropical Pacific chondrichthyan fish to climate change

“…Overfishing, however, is the most pervasive threat to chondrichthyans globally, placing this group as one of the most threatened marine groups due to overexploitation (Dulvy et al., 2014, 2021; Field et al., 2010; Pacoureau et al., 2021). Pelagic species such as silky sharks ( C. falciformis ) and devil rays (Mobulidae) already experienced a considerable reduction in abundance in the ETP (Croll et al., 2016; Villate‐Moreno et al., 2022). Climate change projections indicate decreases in suitable habitat for species caught in pelagic fisheries in the ETP, the movement of invasive species from tropical to temperate waters, and an increase in local losses in abundance along the ETP platform due to climate change (Clarke et al., 2021).…”

Genetic population dynamics of the critically endangered scalloped hammerhead shark (Sphyrna lewini) in the Eastern Tropical Pacific

“…Understanding the population genetic dynamics and genetic diversity of scalloped hammerhead aggregations, and of this critically endangered shark across its ETP distribution, can provide insight into its biology, genetic health and resilience, and is of conservation management relevance (Hoban et al, 2021 ; Thomson et al, 2021 ). Eight previous studies examining the population genetic structure and phylogeography of scalloped hammerheads, from local to global scales, have included samples from at least one location in the broader eastern Pacific (Castillo‐Olguín et al, 2012 ; Daly‐Engel et al, 2012 ; Duncan et al, 2006 ; Green et al, 2022 ; Nance et al, 2011 ; Quintanilla et al, 2015 ; Rangel‐Morales et al, 2022 ; Villate‐Moreno et al, 2022 ). These studies have added to the body of knowledge about this species in this region, but their inferences have been constrained by either samples obtained from only one or a few sites, small samples sizes collected opportunistically from fisheries landings (given difficulties of sampling threatened megafauna), and in some cases sample sets pooled across variable demographic groups (YOY, juveniles, adults), factors which can lead to erroneous conclusions about population structure and dispersal patterns (McClain et al, 2022 ; Phillips et al, 2021 ).…”