Juvenile Greenland sharks Somniosus microcephalus (Bloch & Schneider, 1801) in the Canadian Arctic

Abstract

Life-stage-based management of marine fishes requires information on juvenile habitat preferences to ensure sustainable population demographics. This is especially important in the Arctic region given very little is known about the life histories of many native species, yet exploitation by developing commercial and artisanal fisheries is increasing as the ice extent decreases. Through scientific surveys and bycatch data from gillnet fisheries, we document captures of rarely reported juvenile Greenland sharks (Somniosus microcephalus; B200 cm total length [TL]) during the ice-free period in the Canadian Arctic. A total of 22 juvenile animals (42 % of total catch; n = 54), including the smallest reliably measured individual of 117 cm TL, were caught on scientific longlines and bottom trawls in Scott Inlet and Sam Ford Trough over three consecutive years. Molecular genetic nuclear markers confirmed species identity for 44 of these sharks sampled; however, two sharks including a juvenile of 150 cm TL were identified as carrying a Pacific sleeper shark (Somniosus pacificus) mitochondrial cytochrome b (cyt b) haplotype. This represents the first record of a Pacific sleeper shark genetic signature in Greenland sharks in Eastern Arctic waters. Juvenile sharks caught as bycatch in gillnet fisheries were only observed offshore in Baffin Bay surrounding a fishery closure area, while larger subadult and mature Greenland sharks ([200 cm TL) were caught in all fishing locations, including areas where juveniles were observed. The repeatable occurrence of juvenile Greenland sharks in a fjord and their presence at two offshore sites indicates that these smaller animals either reside in nurseries or have defined home ranges in both coastal and offshore regions or undertake large-scale inshoreoffshore movements.

Origins of the Greenland shark (Somniosus microcephalus): Impacts of ice‐olation and introgression

“…Our results show that the nearly morphologically identical sister species Greenland shark and Pacific sleeper shark can be genetically distinguished using a combination of mtDNA and nuclear markers, but interspecific hybridization (introgression) between these two species is probable and has likely been ongoing since initial divergence. Our results confirm the fourth reported instance of interspecific hybridization among elasmobranchs (Hussey et al., ; see also Morgan et al., ; Walter et al., ; Cruz et al., ), which is likely more common among this group of fishes than previously thought. Our findings, considering a range of substitution rates for the genetic markers employed here, are consistent with a more recent Greenland shark and Pacific sleeper shark speciation event occurring between 1 and 2.34 Ma, more recently than the closure of the Isthmus of Panama.…”

“…These results are consistent with a scenario of introgressive hybridization. This could explain the occurrence of Pacific sleeper shark mtDNA in Greenland sharks sampled in Scott Inlet in the Canadian Arctic (previously reported by Hussey et al., ) and found in other Arctic and sub‐Arctic areas such as Cumberland Sound and Maxwell Bay. The occurrence of admixed sharks in temperate and subtropical waters begs the question as to the source and origin of the Pacific sleeper shark alleles found in Greenland shark.…”

“…Our genetic analyses clearly demonstrate the existence of two genetically differentiated mtDNA and nDNA lineages of Somniosus in the Northern hemisphere, largely consistent with the current recognized species ranges (MacNeil et al., ). However, cytonuclear discordance (initially reported among juvenile S. microcephalus in the Canadian Arctic, see Hussey et al., ) was present in eight individuals in this study; seven individuals from the known S. microcephalus distribution (MacNeil et al., ) and in an additional individual sampled well outside the known distribution (i.e., Gulf of Mexico). These data provide evidence for at least three classes of genetically admixed (i.e., hybrid) individuals that account for roughly 2% of the somniosid individuals in this study.…”

“…() demonstrated that Pacific sleeper sharks and Greenland sharks can be distinguished from one another, with the former exhibiting no geographic structure among samples collected across the Pacific Ocean or more southerly latitudes. More recently, genetic characterization of juvenile Greenland sharks from the Canadian Arctic revealed individuals carrying Pacific sleeper shark mtDNA haplotypes (Hussey et al., ). This finding, taken with a growing list of cytonuclear discordance and/or genetic admixture among closely related elasmobranchs in the literature, suggests that hybridization among Somniosus species is possible (Hinojosa‐Alvarez, Walter, Diaz‐Jaimes, Galván‐Magaña, & Paig‐Tran, ; Kashiwagi, Marshall, Bennett, & Ovenden, ; Morgan et al., ; Walter et al., ).…”

Annotated checklist of the sharks, batoids and chimaeras (Chondrichthyes: Elasmobranchii, Holocephali) from waters of Russia and adjacent areas

“…Remarks: No information is available on type specimens (Eschmeyer, 2014 (Gubanov et al, 1986;Fedorov and Parin, 1998;Amaoka et al, 1989;Sheiko and Fedorov, 2000;Balanov, 2000;Benz et al, 2003;Love et al, 2005;Chereshnev et al, 2005;Rooper and Wilkins, 2008;Shinohara et al, 2009Shinohara et al, , 2014Orlov and Baitalyuk, 2014); Arctic coast of Alaska in the eastern part of Chukchi Sea (Benz et al, 2003;Stevenson et al, 2007;Mecklenburg et al, 2011); probably East Siberian and Beaufort seas Chereshnev and Kirillov, 2007); juvenile specimens from Arctic waters of Greenland (Hussey et al 2014). Marine species.…”