Influence of an impacted estuary on the reproduction of an endangered endemic fish

Health and nutrition of individuals are tied to reproductive success, which determines population viability. Environmental variability and anthropogenic effects can affect the health and nutrition of a species leading to reproductive repercussions which can hinder recovery of endangered populations. Indices of health and nutrition were examined for an imperiled species, delta smelt, Hypomesus transpacificus, in relation to their reproductive status to evaluate the effects of hydrologic conditions in the San Francisco Estuary and Sacramento-San Joaquin Delta. Adult delta smelt were collected by the Fall Midwater Trawl and Spring Kodiak Trawl during monthly monitoring surveys run by the California Department of Fish and Wildlife from 2011 to 2018 spanning from the head of the Carquinez strait to the Sacramento Deep Water Ship Channel. The hydrologic conditions during this period ranged from high precipitation (2011 and 2017) to drought (2012-2016). Drought, via indirect effects from contaminant concentrations and food availability, is hypothesized to influence the health and reproductive success of delta smelt. Each individual was examined for size (length, weight, and condition factor), health (gill and liver pathology/indices), nutritional (RNA/DNA and liver glycogen depletion estimated histologically), and reproductive indicators (gonadosomatic indices [GSI], oocyte developmental stage, clutch size, oocyte size, and oocyte weight). Fork length and condition factor both had strong, positive correlations with reproduction. Glycogen depletion was correlated with higher oocyte mass, oocyte area and GSI, indicating females low in liver glycogen had higher reproductive metrics. Gill and liver lesion severity, which often increases with contaminant exposure, were negatively associated with oocyte area and GSI. Delta smelt in Suisun Marsh and Cache Slough had the longest fork length and highest condition factor measures. Delta smelt in Cache Slough had the highest reproductive metrics and proportion of post-spawned females and late-stage oocytes. Drought did not appear to influence reproduction but reduced population size.