Short communicationSimple biopsy modification to collect muscle samples from free-swimming sharks
Graphical abstract
Introduction
Research programs investigating the biology and ecology of marine animals are increasingly calling for the development and use of non-lethal sampling techniques (Fossi et al., 2010; Jardine et al., 2011; Smith et al., 2018). This is especially pronounced for studies of elasmobranchs (Heupel and Simpfendorfer, 2010; Hammerschlag and Sulikowski, 2011; Marshall and Pierce, 2012), owing to their generally low abundance and high conservation concern (Dulvy et al., 2014).
Gaining a robust understanding of diet, habitat use, population size, and stock structure is vital as it underpins appropriate conservation and management strategies (outlined in Carrier et al., 2018). Additionally, quantifying the load of natural (Meyer et al., 2016) and anthropogenic (Marsili et al., 2016; Fossi et al., 2017) toxins on elasmobranchs is increasingly important as human activity and urbanisation encroaches on a growing array of marine habitats. Paralleling the call for non-lethal sampling, smaller tissue quantities (<1 g) can now be used in studies investigating trophic ecology (Boecklen et al., 2011; Meyer et al., 2017; Pethybridge et al., 2018; Munroe et al., 2018), population structure (Smith et al., 2018), and ecotoxicology (Marsili et al., 2016; Fossi et al., 2017). There has been a push to develop minimally invasive, in situ sampling devices targeting free-swimming animals (Reeb and Best, 2006; Robbins, 2006; Noren and Mocklin, 2012; Smith et al., 2018) as these offer alternatives to collecting tissue via lethal sampling or restraining animals, which can be logistically difficult and stressful for large species.
Advances in biopsy probe design (e.g. Reeb and Best, 2006) and firing devices (including pole spears, rifles, crossbows, and spearguns) have largely been applied to sampling marine mammals from the surface (reviewed in Noren and Mocklin, 2012). Some of these designs have been adapted for underwater sampling, e.g. for elasmobranchs >1 m total length (e.g. Robbins, 2006; Daly and Smale, 2013). This includes the biopsy probe outlined in Daly and Smale (2013), which relies on suction to extract tissue cores. Underwater, suction is created as water is not compressible, and is thus expelled out of ventilation holes as the probe penetrates the skin. A rubber band covering the holes acts as a one-way valve (Fig. 1A), preventing backflow into the probe, therefore creating the necessary suction to retain the tissue core as the probe is withdrawn. However, this suction mechanism does not work above the surface. Air is compressible, and the rubber band which acts as a valve underwater, creates a tight seal, preventing the air in the probe from being expelled through the ventilation holes. Upon withdrawal, the air re-expands, not creating the required suction to retain a tissue core. Obtaining adequately sized tissue cores from above the surface offers a number of practical advantages (research is not constrained by in-water limitations including communication, nitrogen accumulation, and temperature), increasing sampling opportunities. Here, we assess the effectiveness of a water-balloon adaptation to enable the use of the Reeb and Best (2006) biopsy probe (assessed in Daly and Smale, 2013) to target white shark Carcharodon carcharias from above the water's surface.
Previously, large elasmobranchs such as whale sharks Rhincodon typus and white sharks have been biopsied from the surface with various probes using a hatch door system, mechanically slicing off the tissue core (described in Jaime-Rivera et al., 2013). The tissue collected has often been limited to skin and sub-dermal tissue (the thick layer of elastin and collagen underlying the skin) (e.g. Castro et al., 2007; Carlisle et al., 2012; Rohner et al., 2013; Fossi et al., 2017), however, the underlying muscle is the preferred tissue for a number of trophic analyses, e.g. stable isotopes (Hussey et al., 2015) and fatty acid analysis (Every et al., 2016). As such, the quantity of muscle retained by these biopsy devices can limit the type and number of analyses that can be conducted (Meyer et al., 2017). Responsible sampling, including maximizing the output from collection opportunities, is a financial, scientific, and ethical imperative (Heupel and Simpfendorfer, 2010). Thus, we compare the amount of sub-dermal and muscle tissue obtained from the surface-adapted and underwater biopsy probes to determine the efficacy of the water-balloon adaptation in successfully collecting sufficient tissue for multiple biochemical analyses.
Section snippets
Biopsy equipment
The standard biopsy probe, manufactured by Rob Allen Dive Factory (www.roballen.co.za) in Durban, South Africa, attaches to the end of a spear and is typically fired underwater. In our study, the probe was attached to a 1.3 m steel spear, shot from a 1.1 m long Beuchat speargun powered by a 20 mm diameter elastic rubber. The probe consisted of a hollow 1 cm diameter stainless steel tube with a sharpened front edge to puncture the skin (Daly and Smale, 2013; Fig. 1). The biopsy probe tip screwed
Results
The two biopsy methods retained similar quantities of muscle (surface: 0.36 ± 0.21 vs. underwater: 0.44 ± 0.37 g, P = 0.170, Fig. 4), which was not influenced by shark total length (P = 0.131). Eighty-eight percent of total biopsies (38 of the 43 from both underwater and above the surface) contained sufficient muscle for stable isotope, genetic, fatty acid, and ecotoxicology analyses. Although not explicitly tested within this study, failure rate and haemorrhaging rate were both estimated to be
Discussion
The underwater and surface-adapted biopsy probes had the same estimated success rates (90%) and was similar to other underwater probes including the one tested by Daly and Smale (87% in Daly and Smale, 2013) and both probes tested by Robbins (2006) (87% and 91%). The surface-adapted biopsy performed similarly to those tested in Jaime-Rivera et al. (2013), which had reported success rates of 80%, 95%, and 100% for the biopsy device using a trap door mechanism to retain tissue cores. As the
Conclusion
The novel adaptation of an existing underwater biopsy probe enables its use from the surface with no significant difference in muscle or sub-dermal tissue retention. Both biopsy methods obtained ample tissue for a number of biochemical analyses to investigate trophic ecology, population structure, and ecotoxicology of chondrichthyans. With the described modification, this biopsy probe can now be used both underwater and above the surface, providing more opportunities for effective, non-lethal
Declaration of interest
The authors have no competing interests to declare.
Acknowledgements
The authors thank Rob Allen and the team from Rob Allen Dive Factory (www.roballen.co.za) in Durban, South Africa, for manufacturing the biopsy probes and providing the diagrams in Fig. 1. We appreciate the ongoing support of the white shark cage-diving operators, including the teams at Rodney Fox Shark Expeditions, Adventure Bay Charters, and Calypso Star Charters. We also thank the Save Our Seas Foundation (Switzerland, grant ID #RPF14/553), Holsworth Wildlife Research Endowment (Australia),
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