Transgenerational marking of cephalopods with an enriched barium isotope: a promising tool for empirically estimating post-hatching movement and population connectivity

Quantifying the movement of very small and young individuals, determining sources of recruitment, and identifying the contribution of populations from different regions and periods to fished stocks is a major ecological challenge. Transgenerational isotope labelling (TRAIL), a technique which enables offspring to be marked on a mass scale, is applied for the first time to cephalopods, facilitating field studies quantifying population connectivity. Four species were used: Sepioteuthis australis, Euprymna tasmanica, Octopus pallidus, and Octopus maorum. Gravid females were injected with the enriched stable isotope 137Ba in different body tissues at several different doses. Isotopic ratios 138Ba:137Ba were then quantified using laser ablation inductively coupled plasma-mass spectrometry on the hard structures (statoliths and stylets) of offspring produced by the injected females. Day-old hatchlings from both squid species had statoliths with isotopic ratios significantly different from natural ratios and control animals, but variability in the ratios in hatchlings produced by different females was independent of dose or injection location. No differences were observed in the statoliths and stylets removed from hatchlings and juveniles, respectively, from the two octopus species, although isotopic shifts were evident in the hard structures of the adults injected. The use of TRAIL is a technique that offers considerable potential to advance the understanding of post-hatching dispersal and population connectivity in cephalopod populations