Identification of Hatchery‐Reared Lake Sturgeon Using Natural Elemental Signatures and Elemental Marking of Fin Rays

Abstract

Stock enhancement programs often involve the introduction of hatchery‐reared fish into wild environments, with the goal of increasing the abundance of a particular stock. To measure the success of stocking efforts for depressed populations, hatchery‐reared individuals must be distinguishable from naturally spawned fish, potentially many years after release. Biological tags are attractive due to their ability to batch‐mark whole cohorts in a cost‐effective manner, with minimal disruption to hatchery procedures and reduced handling stress inflicted on individuals during the marking process. Elemental marking may occur naturally or via deliberate manipulation of the concentration of specific elements to create recognizable elemental signatures in the hard structures of fish (e.g., fin rays and otoliths). In this study, elemental signatures in the fin rays of known hatchery‐released Lake Sturgeon Acipenser fulvescens (ages 1–7) were quantified via laser ablation (LA) inductively coupled plasma–mass spectrometry (ICP‐MS) to assess whether the ambient water chemistry in a groundwater‐fed hatchery would create an elemental signature that facilitated discrimination of hatchery‐reared individuals from those naturally spawned in the wild. The concentrations of divalent trace elements, particularly Mn, within the first growth band of hatchery‐reared fish were significantly different from those of wild conspecifics, allowing us to accurately classify hatchery‐ versus wild‐spawned individuals with 99% success. In addition, we conducted a preliminary experiment to test the validity of two separate 24‐h immersions in 86Sr and 137Ba (immersions were conducted 30 d apart) to induce multiple combination marks in the fin rays of juvenile Lake Sturgeon. Fin rays collected 60 d after the second immersion were analyzed for isotopic ratios via LA ICP‐MS, and results indicated that elemental marking at both time points was achieved with 100% success. Induction of a combination of isotopic signatures could enable hatcheries to track the success of families or stocking groups within a single year‐class or across multiple year‐classes.

Using seasonal oscillations in fin ray microchemistry to chemically age Lake Sturgeon

“…Like previous studies, distinguishing the first growth zone may have also led to inaccuracies in traditional ages, specifically for rays that were sampled at Sea Falls, Manitoba (n = 54; ages 5-8). Samples from this location had hatchery signatures (Loeppky et al 2020); therefore, when ages were assigned chemically, it was possible to identify the first year of life (first growth zone) without reader bias, which may have led to higher classification success. Known-age agreement was higher for ages estimated using the chemical interpretation method, but both methods resulted in over 80% agreement within ±2 years, which is similar to other Lake Sturgeon aging studies that have used multiple readers (e.g., three readers had 75% agreement within ±2 years: Izzo et al 2021).…”

“…Samples from this location had hatchery signatures (Loeppky et al. 2020); therefore, when ages were assigned chemically, it was possible to identify the first year of life (first growth zone) without reader bias, which may have led to higher classification success.…”

“…Rays were prepared for laser ablation–inductively coupled plasma–mass spectrometry (LA‐ICP‐MS) following methods that were outlined by Loeppky et al. (2020) and adapted from Smith and Whitledge (2011). At room temperature, rays were embedded in epoxy resin (5:1 EpoxiCure resin : EpoxiCure hardener) and were allowed to harden for 24 h or more.…”

“…Rays were analyzed for trace element concentration via LA‐ICP‐MS (Perkin‐Elmer DRC II) following the methods outlined by Loeppky et al. (2020). Epoxy rings containing multiple fin rays were placed individually in the ablation chamber.…”

“…Elements that oscillated seasonally corresponding with annuli were identified and used in the chemical aging methods outlined below. It is important to note that all Manitoban fish had hatchery signatures due to their time spent in well water (see Loeppky et al 2020), which significantly altered the chemistry (specifically for Mn) in the first year of life (Figure 3). Because of this, elemental profiles from the region 1 population were manipulated to remove the area of the signature corresponding with hatchery residence.…”