Analysis of vertebral chemistry to assess stock structure in a deep-sea shark, Etmopterus spinax

Abstract

Deep-sea sharks play a valuable ecological role helping maintain food web balance, yet they are vulnerable to commercial fishing because of slow growth rates and low reproductive capacity. Overfishing of sharks can heavily impact marine ecosystems and the fisheries these support. Knowledge of stock structure is integral to sustainable management of fisheries. The present study analysed vertebral chemistry using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to assay concentrations of 7Li, 23Na, 24Mg, 55Mn, 59Co, 60Ni, 63Cu, 66Zn, 85Rb, 88Sr, 138Ba and 208Pb to assess stock structure in a deep-sea shark, Etmopterus spinax, in Norwegian and French waters. Few studies have applied this technique to elasmobranch vertebrae and the present study represents its first application to a deep-sea shark. Three stocks were identified at the regional scale off western Norway, southern Norway, and France. At finer spatial scales there was evidence of strong population mixing. Overall, the general pattern of stock structure outlined herein provides some indication of the spatial scales at which stocks should be viewed as distinct fisheries management units. The identification of an effective multi-element signature for distinguishing E. spinax stocks utilizing Sr, Ba, Mg, Zn and Pb and the methodological groundwork laid in the present study could also expedite future research into stock structure for E. spinax and deep-sea elasmobranchs more generally.

Element composition of shark vertebrae shows promise as a natural tag

“…Moreover, it is unclear, for example, what role diet has in affecting both the condition of an individual and vertebral element composition, where both are likely to be affected by extrinsic factors such as temperature (Webb et al 2012), although diet did not vary among experimental treatments in the present study. This is consistent with hypothesised among-element differences in how vertebral elements are affected by intrinsic as opposed to extrinsic factors (McMillan et al 2017b), with Mn and Li linked to metabolism (Watanabe et al 1997) and osmoregulation (Fleishman et al 1986) respectively. In teleost otoliths, variations in composition and element incorporation of Mn : Ca and Li : Ca have also been related to intrinsic factors directly (e.g.…”

“…Overall, apatite is poorly crystallised relative to other biogenic calcified structures, and its chemical properties (i.e. element incorporation) are expected to differ from those of otoliths and other structures (see McMillan et al 2017aMcMillan et al , 2017b, with both biogenic (from Serratia sp. bacteria) and non-biogenic hydroxyapatite showing stable strontium and cobalt sorption under a range of pH conditions (Handley-Sidhu et al 2016).…”

Skating on thin ice: Identifying the need for species‐specific data and defined migration ecology of Rajidae spp.

“…Owing to the fact that elasmobranchs lack otoliths, vertebrae have been adopted as an alternative tissue type to broadly quantify lifetime movement and migration patterns for a number of species (Carlisle et al., ; Estrada, Rice, Natanson, & Skomal, ). Similar to otoliths, vertebral annuli are incrementally deposited (Cailliet, Radtke, & Weldon, ), thus, the measurement of biogeochemical tracers in the organic matrix (primarily collagen) of each incremental band can broadly trace changes in habitat use, diet and inform stock structure (McMillan et al., ), which for some species, may change as a function of year class and/or size (Estrada et al., ). For example, Carlisle et al.…”

“…In addition, McMillan et al. () identified three separate stocks of velvet belly lanternshark ( Etmopterus spinax , Etmopteridae) between western Norway, southern Norway and France using vertebral trace metal microchemistry as a proxy for movement. As the extent to which movement generally occurs in skates remains unrefined, such information would be extremely useful to augment contemporary fisheries management, especially in cases where ecosystem approaches to fisheries management are practiced.…”

Effects of sample cleaning and storage on the elemental composition of shark vertebrae

“…The trace elemental composition of vertebrae is increasingly used to reconstruct the environments previously encountered by elasmobranchs and has been used to validate growth band deposition rate . Despite the surge in recent studies that have utilized vertebral elemental chemistry, few have systematically investigated how cleaning and storage procedures may alter the primary elemental composition of hydroxyapatite structures.…”