Complex life histories discovered in a critically endangered fish

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.

Use of affinity analysis to guide habitat restoration and enhancement for the imperiled delta smelt

“…That assumed relationship asserts that habitat for delta smelt becomes increasingly available at higher freshwater outflow levels, when the low-salinity zone in the estuary is at its greatest areal extent. The assumptions underlying that relationship have been shown to not be valid (Murphy & Weiland 2019) and evidence that some delta smelt freely move between higher-salinity and lower-salinity situations in the upper estuary has been documented (Hobbs et al 2019). The analyses presented here indicate that delta smelt have no affinity for South Suisun (Table 4) and that while salinity conditions in highflow circumstances are frequently limiting in North Suisun, prey availability is more frequently limiting there ( Table 8), such that improving salinity conditions and not prey availability will not improve habitat quality.…”

“…Conservation planners intend to restore and enhance delta smelt habitat in order to bolster fish numbers and enhance the likelihood of its persistence. Meeting that objective is inhibited by an ab sence of relevant information -the delta smelt's actual numbers can only be speculated upon (see Bennett 2005, Kimmerer 2008, Newman 2008, Kimmerer et al 2009, its patterns of dispersal are the subject of ongoing debate (Sommer et al 2011, Murphy & Hamilton 2013, Hobbs et al 2019, and the causes of its imperilment appear to be many (e.g. Feyrer et al 2007, Nobriga et al 2008, Grimaldo et al 2009, Winder & Jassby 2011.…”

Factors Controlling Calanoid Copepod Biomass and Distribution in the Upper San Francisco Estuary and Implications for Managing the Imperiled Delta Smelt (Hypomesus transpacificus)

“…Copepod productivity is a primary factor limiting the recovery of delta smelt (IEP MAST 2015; Hamilton and Murphy 2018). The location of delta smelt varies by life stage and through-Delta flows that vary by year and season (e.g., Murphy and Hamilton 2013;Hobbs et al 2019). Thus, the focus of management actions could simply be to improve the circumstances where the fish are most commonly found; that is, to improve the spatial and temporal overlap of the distribution of delta smelt with suitable levels of copepod biomass.…”

Haie auf dem Teller

“…Griffithś Team analysierte die Barcodes von Stichproben in Fish&Chips‐Läden in Großbritannien sowie auch einige Ware von Großhändlern . Die Mehrheit der untersuchten Fischfilets stammten von dem Dornhai ( Squalus acanthias , Abbildung ).…”