Oral Presentation Australian Society for Fish Biology & Australian Freshwater Sciences Society Conference 2026

Settling in: effects of natural and artificial structures in urbanised estuaries on fish settlement (145357)

Jessica JN Nguyen 1 , Matt MR Rees 2 , Daniel DEH Hewitt 3 , Matt MT Taylor 4 , Nathan NK Knott 2 , Will WFF Figueira 3 , Iain IMS Suthers 1
  1. University of New South Wales, Kensington, NSW, Australia
  2. Fisheries, NSW DPIRD Fisheries , Husskison , NSW, Australia
  3. School of Life and Environmental Sciences, William Figueira, Sydney, NSW, Australia
  4. Fisheries, NSW DPIRD Fisheries , Port Stephens , NSW, Australia

Larval fish face high mortality when settling into benthic habitats making this early life stage a critical bottleneck shaping recruitment success.  Urbanisation  has impacted natural shorelines, with artificial infrastructure like jetties, groynes and seawalls altering the seascape that larval fish encounter as they settle and recruit to estuaries. Yet, the consequences of this infrastructure for fish populations remain unknown. Groynes are a ubiquitous artificial structure in Gamay (Botany Bay) with 39 distributed across the bay to minimise coastal erosion. We examined how natural and artificial structures shape fish abundance and diversity in comparison with natural habitats. Specifically, we examined how distance from a groyne influences larval fish abundance and size-structure, and whether this varies on the up or down stream sides to prevailing tidal currents for Sand Whiting (Silago ciliata) and Sea Mullet (Mugil cephalus). We found that larval fish abundance is higher near structured habitat whether it is natural or artificial. In addition, we found higher abundances on the side that faces the prevailing tidal current (i.e., the ‘updrift’ side), consistent with expected passive particle accumulation. Our study provides novel insights on how urbanisation can affect the settlement process and may influence spatial patterns in population abundance of fisheries species that are recreationally and culturally important.