MEPS 726:131-148 (2024)  -  DOI: https://doi.org/10.3354/meps14473

ABSTRACT: Many long-lived, deep-sea species of the higher latitudes possess protracted egg and larval phases leading to dispersal across large geographical areas. The timing of ontogenetic life-history shifts is vital for understanding dispersal potential, a key driver of spatial patterns and stock structure of Patagonian toothfish Dissostichus eleginoides on the Patagonian Shelf. The early life-history patterns from hatching until settlement into a demersal habitat remain elusive and largely unexplored. We applied a complementary approach using otolith microstructure and trace element analysis (by laser ablation-inductively coupled plasma mass spectrometry) to infer time-resolved elemental profiles that reflect the early ontogeny of age-0+ toothfish from key nursery areas on the Patagonian Shelf. Results revealed significant ontogenetic shifts across the early life history. Key biological benchmarks were identified, including (1) the hatch date distribution (predicted mean = 3 October ± 8.47 d); (2) a period of natal dispersal (0-50 d post hatch [dph]; 22 November); (3) entry of pelagic larvae onto the Patagonian shelf (50-100 dph; 1 January); (4) settlement into a demersal habitat (100-120 dph; 31 January); and (5) the start of a downslope ontogenetic migration along pathways to the continental slope (>120 dph). The results provide important considerations in terms of the complexity and protracted nature of early life-history stages in Patagonian toothfish as a complex process, informing future research objectives relating to the identification of the stock origin on the Patagonian Shelf.

KEY WORDS: Otolith microchemistry · Otolith microstructure · Stock structure · Connectivity · Southwest Atlantic · Patagonian toothfish · Dissostichus eleginoides