Complex life histories discovered in a critically endangered fish

James A Hobbs,Christian Denney,Levi S Lewis,Malte Willmes,Eva Bush

doi:10.1038/s41598-019-52273-8

James A Hobbs, Christian Denney + Show 3 more

Open Access

https://doi.org/10.1038/s41598-019-52273-8

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Abstract

Effective conservation of endangered species requires knowledge of the full range of life-history strategies used to maximize population resilience within a stochastic and ever-changing environment. California’s endemic Delta Smelt (Hypomesus transpacificus) is rapidly approaching extinction in the San Francisco Estuary, placing it in the crossfire between human and environmental uses of limited freshwater resources. Though managed as a semi-anadromous species, recent studies have challenged this lifecycle model for Delta Smelt, suggesting the species is an estuarine resident with several localized “hot-spots” of abundance. Using laser-ablation otolith strontium isotope microchemistry, we discovered three distinct life-history phenotypes including freshwater resident (FWR), brackish-water resident (BWR), and semi-anadromous (SA) fish. We further refined life-history phenotypes using an unsupervised algorithm and hierarchical clustering and found that in the last resilient year-class, the FWR (12%) and BWR (7%) comprised a small portion of the population, while the majority of fish were SA (81%). Furthermore, the semi-anadromous fish could be clustered into at least four additional life-history phenotypes that varied by natal origin, dispersal age and adult salinity history. These diverse life-history strategies should be incorporated into future conservation and management efforts aimed at preventing the extinction of Delta Smelt in the wild.

Highlights

Effective conservation of endangered species requires knowledge of the full range of life-history strategies used to maximize population resilience within a stochastic and ever-changing environment
The Delta Smelt (Hypomesus transpacificus) is one of the most socio-politically important species in the Western United States and is nearing extinction in the wild[19,20,21,22]. This small, 2–3 inch cucumber-scented fish is endemic to the upper San Francisco Bay-Delta Estuary (SFE), where spawning habitat coincides with the State Water Project (SWP) and Central Valley Project (CVP) pumping facilities which provide fresh water for 23-million people and irrigation for a multi-billion-dollar agriculture industry[21]
We examined otolith 87Sr/86Sr profiles of Delta Smelt caught between September 2011 and May 2012 by monitoring surveys, in what was the last year of high abundance for this species up to date (Fig. 2)

Summary

Introduction

Effective conservation of endangered species requires knowledge of the full range of life-history strategies used to maximize population resilience within a stochastic and ever-changing environment. The semi-anadromous fish could be clustered into at least four additional lifehistory phenotypes that varied by natal origin, dispersal age and adult salinity history These diverse life-history strategies should be incorporated into future conservation and management efforts aimed at preventing the extinction of Delta Smelt in the wild. The Delta Smelt (Hypomesus transpacificus) is one of the most socio-politically important species in the Western United States and is nearing extinction in the wild[19,20,21,22] This small, 2–3 inch cucumber-scented fish is endemic to the upper San Francisco Bay-Delta Estuary (SFE), where spawning habitat coincides with the State Water Project (SWP) and Central Valley Project (CVP) pumping facilities which provide fresh water for 23-million people and irrigation for a multi-billion-dollar agriculture industry[21]. Recent analyses of long-term monitoring data suggest Delta Smelt do not migrate, rather the species exhibits a resident life history consisting of localized “hot spots” of abundance in brackish and fresh water (Fig. 1b)[29,30,31,32]

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