Twenty embryos were randomly sampled from each incubator prior to 50% hatch in both temperature groups (day 29 at 2.8 °C and day 56 at 0.5 °C). Embryos were transferred with a minimum amount of water to a 100 mL glass graduated cylinder filled with diluted seawater (28‰) at either 0.5 °C or 2.8 °C and the time it took for the embryo to sink 5.5 cm was recorded. The 28‰ seawater was found to be appropriate for observing sinking speeds of the positively buoyant embryos reared at 34‰. The time and distance that embryos descended in the water column were converted into a sinking speed (cm/s). Further conversion of sinking speed to embryo specific gravity was performed using Stoke's Law of fluid dynamics in the following equation:

where the kinetic velocity of seawater (µ) at 28‰ was extracted from Table 25 in Riley and Skirrow96 based on temperature, g is the acceleration due to gravity, an average embryo diameter (d) of 1.63 mm measured from a sub-sample of embryos, and ρw is the density of seawater97.

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