Environmental drivers of Patagonian toothfish (Dissostichus eleginoides) spatial-temporal patterns during an ontogenetic migration on the Patagonian Shelf

Abstract

Abstract Understanding the spatial and temporal dynamics in marine fish populations is essential for the development of effective adaptive management strategies. Many marine fish species undergo ontogenetic shifts in abundance, with the utilization of productive shelf-based habitats during early life-history stages. For instance, in the shelf ecosystem around the Falkland Islands, a dynamic Patagonian toothfish population undertakes an early life-history ontogenetic migration after recruitment from spawning areas off southern Chile and the Burdwood Bank. To better understand the spatial-temporal dynamics for this species, Bayesian species distribution models were used to (1) identify oceanographic drivers of recruitment success; (2) assess the spatial-temporal distribution patterns; and (3) describe the habitat preferences and ecological interactions during a six-year study period (2015–2020) on the Patagonian Shelf. The presence of seasonal mesoscale eddies linking the Sub-Antarctic Front with the Falkland Current appear to be of primary importance for the survival of toothfish eggs and larvae on the shelf after transport from offshore spawning areas over the Burdwood Bank and southern Chile. Results indicate persistent recruitment hotspots for newly-settled Patagonian toothfish to the north-east, along with opportunistic areas to the south and west of the Falkland Islands, coinciding with the main areas of upwelling and high productivity. During years of low recruitment, juveniles are largely constrained to sheltered inshore regions to the north-west of the Falkland Islands. Spatial distribution patterns during post-settlement ontogenetic migrations are progressive, characterised by age-structured hotspots that differ according to depth, current velocity, oxygen, mixed-layer thickness, the abundance of competitors (icefish – Champsocephalus esox) and prey (rock cod – Patagonotothen ramsayi). The temporal shift in the range and intensity of hotspots is linked to levels of recruitment and subsequent cohort strength, which in turn appears to be driven by oceanographic processes. Understanding the environmental influences on recruitment dynamics is a key step in assessing connectivity within these discrete spatial groups on the Patagonian Shelf, and how their variability can influence the adult population over time.