Complex life histories discovered in a critically endangered fish

Area of Science:

• Ecology
• Ichthyology
• Conservation Biology

Background:

• California's Delta Smelt (Hypomesus transpacificus) faces extinction in the San Francisco Estuary.
• Existing management models assume a semi-anadromous lifecycle, which recent research questions.

Purpose of the Study:

• To investigate the life-history strategies of Delta Smelt.
• To inform conservation and management efforts for this endangered species.

Main Methods:

• Utilized laser-ablation otolith strontium isotope microchemistry to analyze fish phenotypes.
• Employed unsupervised algorithms and hierarchical clustering to refine life-history classifications.

Main Results:

• Identified three distinct life-history phenotypes: freshwater resident (FWR), brackish-water resident (BWR), and semi-anadromous (SA).
• In the last resilient year-class, SA fish constituted the majority (81%), with FWR (12%) and BWR (7%) comprising smaller proportions.
• Discovered at least four additional sub-phenotypes within the SA group, varying by natal origin, dispersal age, and adult salinity exposure.

Conclusions:

• Delta Smelt exhibit diverse life-history strategies, challenging the traditional semi-anadromous model.
• Incorporating these varied strategies into conservation plans is essential for preventing Delta Smelt extinction.