Preliminary Observations of Population Genetics and Relatedness of the Broadnose Sevengill Shark, Notorynchus cepedianus, in Two Northeast Pacific Estuaries

Abstract

The broadnose sevengill shark, Notorynchus cepedianus, a common coastal species in the eastern North Pacific, was sampled during routine capture and tagging operations conducted from 2005–2012. One hundred and thirty three biopsy samples were taken during these research operations in Willapa Bay, Washington and in San Francisco Bay, California. Genotypic data from seven polymorphic microsatellites (derived from the related sixgill shark, Hexanchus griseus) were used to describe N. cepedianus genetic diversity, population structure and relatedness. Diversity within N. cepedianus was found to be low to moderate with an average observed heterozygosity of 0.41, expected heterozygosity of 0.53, and an average of 5.1 alleles per microsatellite locus. There was no evidence of a recent population bottleneck based on genetic data. Analyses of genetic differences between the two sampled estuaries suggest two distinct populations with some genetic mixing of sharks sampled during 2005–2006. Relatedness within sampled populations was high, with percent relatedness among sharks caught in the same area indicating 42.30% first-order relative relationships (full or half siblings). Estuary-specific familial relationships suggest that management of N. cepedianus on the U.S. West Coast should incorporate stock-specific management goals to conserve this ecologically important predator.

Population genetics reveals global and regional history of the apex predator Galeocerdocuvier (carcharhiniformes) with comments on mitigating shark attacks in north‐eastern brazil

“…The understanding of the population genetic structure of the species is of great importance because it reveals information about the geographic limits of populations by analysing the gene flow between locations. This approach can be also used as possible drivers for their conservation (Castro et al., 2007; Reiss et al., 2009; Dudgeon et al., 2012; Bellafronte et al., 2013; Chapman et al., 2015; Quintanilla et al 2015; Sigsgaard et al., 2016; Domingues et al 2018a; Flanagan et al., 2018; Carmo et al., 2019), given the possibility of identification of evolutionary and management units (Domingues et al., 2019; Dudgeon et al., 2012; Giles et al., 2016; King et al., 2015; Larson et al., 2015; Laurrabaquio‐A et al., 2019). Studies on the levels of genetic variation of species also allow estimating effective population size and can help to enlighten questions about species vulnerability, especially for exploited marine species and sharks, as fishing and environmental changes can cause a decline in populations and the reduction in the genetic variability (Garcia et al., 2008; Allendorff et al 2014; Rosa et al., 2014; Rosa et al., 2017; Pinsky & Palumbi, 2014; Ferrette et al., 2015).…”

“…Knowledge on genetic structure is also greatly relevant for the conservation of sharks, given that evolutionary lineages can be masked by conserved external morphologies (Gaither et al., 2016), and also due to the fact that several species across the world show signs of stock depletion (Baum et al., 2003; Burgess et al 2005; Myers et al., 2007; Dulvy et al., 2008; Davidson et al., 2016; Roff et al., 2018). As such, population genetics have been studied for several species helping to identify cryptic species, endogamy, low genetic diversity, fitness reduction and endangered populations, and being of great use in species management and conservational plans (Amos & Balmford, 2001; Domingues et al., 2019; Dudgeon et al., 2012; Frankham et al., 2008; Giles et al., 2016; Karl et al., 2011, 2012; Larson et al., 2015).…”

Estimating population parameters of broadnose sevengill sharks (Notorynchus cepedianus) using photo identification capture‐recapture

“…This either supports the idea that new individuals were moving into Sawdust Bay over the duration of the study or that the sampling was not extensive enough to sight all individual sharks in Sawdust Bay at a time. N. cepedianus is thought to use certain areas for specific purposes ( e.g ., breeding, pupping, foraging) with individuals moving between sites as required (Ebert, 1986; Larson et al ., 2015). Sawdust Bay might provide a seasonal foraging area in this case.…”

“…Due to the study period being limited to 18 months, it was not possible to confirm site fidelity in consecutive summers. Previous studies with longer sampling periods ( e.g ., Barnett et al ., 2011; Williams et al ., 2011, 2012) have found that N. cepedianus display seasonal migrations, but return to the same site year after year (Larson et al ., 2015). It is therefore plausible that individual sharks return to Sawdust Bay over several years.…”

Potential global distribution of a temperate marine coastal predator: The role of barriers and dispersal corridors on subpopulation connectivity

“…At the global scale, patterns of genetic structure among most N. cepedianus subpopulations showed historical divergence and subsequent isolation between Oceania, Eastern Pacific, and South Atlantic basins (Schmidt‐Roach et al 2021), a pattern that is common to other globally distributed coastal shark species (Benavides et al 2011; Bester‐van der Merwe et al 2017). However, genetic connectivity within individual ocean basins was evident, and individual sharks can travel up to 1800 km implying highly mobile behavior and large regional displacements (Barnett et al 2011; Williams et al 2012; Larson et al 2015). Although N. cepedianus is capable of large scale movements, transoceanic dispersal may not occur (which information to date suggests) because of the species' benthic habitat association (Barnett et al 2010 a ) with engrained coastal habitat use patterns, combined with high fidelity to feeding grounds (Barnett and Semmens 2012; Irigoyen et al 2018).…”