Tagging Methods

Tagging commenced in April 2018 and will continue until April 2024 at five sites (all ~ 500–1000 m²) off southern Sydney, and another on the southern NSW coast (see previous post on research sites). Three sites were ocean-exposed (Little Bay and Merry Beach are more exposed than Kurnell), while two of the remaining five were protected within Botany Bay and one was a rock-platform swimming pool (i.e. Mahon Pool). Three of the Botany Bay sites (at Congwong Bay) were chosen along the west-facing shoreline at 50 and 200 m apart. Sites were thus spatially separated by 0.05, 0.2, 1, 3 and 200 km.

Part way through the work, second locations at Kurnell, Little Bay and Congwong 3 were created as two subsites separated by 50m to 100m (K1,K2;  LB1,LB2;  C3,C3N) to examine local movements and any growth differences between adjacent locations, as with C1 and C2. Some analysis is being done both with subsites combined and separated, to tease out smaller scale habitat differences.

Each site was opportunistically sampled throughout various months (classified into four austral meteorological seasons). Up until 31 January 2024 I spent 220 full or partial days in the field diving and tagging (Table 1) and obtained  over 22,000 length measurements for Lunella torquata.

Table 1. Research days for tagging and non-tagging sampling for 11 locations at 6 sites in Southern Sydney and Kioloa, NSW, Australia. Numbers of length measurements are for L torquata only.

At most sampling visits, a powered boat with an air compressor was anchored off the site (at depths of less than 10 m) and I dived with a floating air hose and collected snails in small-meshed bags. I moved at alternate 45^o paths from shallow to deeper water and then generally re-traced my steps on a slightly different zig-zag track to achieve a more comprehensive but still haphazard collection. A substantial number of dives were snorkelling without compressed air.

I hand collected up to 300 L. torquata from the bottom during 30–90 minute dives. Specimens were held in collection bags at the side of the vessel, or onboard in a 40-litre seawater holding tank. Individuals of Turbo militaris were collected opportunistically, except for Mahon Pool, where they were targeted.

All snails were removed from the collecting bags and measured to the nearest millimetre for shell diameter along the maximum axis, (”length” for convenience). All snails were examined carefully for previous tags which can be overgrown with epibionts and not easily noticed. Initially, all recaptures were set aside and kept for boiling, dissection and sexing, but from 2023, most recaptures were re-tagged and replaced to enable some multiple-tagging/multiple-recapture data. For these latter taggings, sex data is not available.

While the numbers with multiple recaptures are small, to avoid confounding or biasing the data with multiple entries for a single snail, only the initial length and final length were used for those snails in primary analyses.

Specimens selected for tagging were cleaned with a towel (or wire brush or serrated knife if heavily encrusted) before being tagged. The growing margin was usually not covered with epibionts so a wipe with a towel was sufficient in most cases for L torquata and in all cases for the smoother-shelled T militaris.

Un-numbered tags were manufactured from flexible plastic containers (shampoo, detergent, food) in various colours and shapes (unique to each tagging at each site). They were cut small, designed to be glued (using cyanoacrylate) between ridges on shells to minimise abrasion and loss. Polymerisation of the glue apparently requires some moisture so the shells did not need to be completely dry. The gel forms of superglue were easier to work with (it bonds instantly with skin) but took longer to set dry.