Analysis of Limiting Factors Across the Life Cycle of Delta Smelt (Hypomesus transpacificus)

SCOTT A. HAMILTON and DENNIS D. MURPHY

The authors developed a life-cycle model from multiple factors influencing the success of the imperiled delta smelt. After reviewing previous models and analyses, the authors identified a set of factors that could help explain the erratic fluctuations in food availability, predation by introduced species, and entrainment. The analytical approach provides a transparent and intuitive framework to consider population trends, and has the potential to assist with the evaluation of proposed recovery measures.

Long-Term Seasonal Trends in the Prey Community of Delta Smelt (Hypomesus transpacificus) Within the Sacramento-San Joaquin Delta, California

JOSEPH E. MERZ, PAUL S. BERGMAN, JOSEPH L. SIMONIS, DAVID DELANEY,
JAMES PIERSON and PAUL ANDERS

The authors examined zooplankton community dynamics in the San Francisco Estuary, California. They present the first evidence of a shift in zooplankton species that are key prey items of delta smelt, which may have exacerbated well-documented food limitations of delta smelt since the invasion of the overbite clam. Future conservation efforts in the estuary should consider measures designed to restore the timing and magnitude of pre-invasion phytoplankton blooms.

Guidance on the Use of Best Available Science under the U.S. Endangered Species Act

DENNIS D. MURPHY and PAUL S. WEILAND

The Endangered Species Act’s best available science mandate has been widely emulated and reflects a Congressional directive to ensure that decisions made under the Act are informed by reliable knowledge applied
using a structured approach. The authors contend that more rigorous adherence by the wildlife agencies to the best available science directive and better judicial oversight is essential for effective implementation of the Act, particularly where it has substantial ramifications for listed species, stakeholder segments of society, or both.

Stormwater-related transport of the insecticides bifenthrin, fipronil, imidacloprid, and chlorpyrifos into a tidal wetland, San Francisco Bay, California

DONALD P.WESTON, DA CHEN, MICHAEL J. LYDY

Suisun Marsh, in northern San Francisco Bay, is the largest brackish marsh in California, and provides critical habitat for many fish species. Storm runoff enters the marsh through many creeks that drain agricultural uplands and the urban areas of Fairfield and Suisun City. Five creeks were sampled throughout a major storm event in February 2014, and analyzed for representatives of several major insecticide classes. The results
demonstrate the potential for co-occurrence of multiple insecticides in urban runoff, each with the potential for toxicity to particular species, and the value of toxicity monitoring using multiple species.

The use of surrogates in implementation of the federal Endangered Species Act—proposed fixes to a proposed rule

DENNIS D. MURPHY and PAUL S. WEILAND

The US Fish and Wildlife Service and National Marine Fisheries Service recently proposed to amend existing regulations that implement the Endangered Species Act’s by using surrogates to express the amount
or extent of incidental take of listed species. They propose the use of surrogates, either in the form of a substitute species filling in for a species that is challenging to observe or measure, or a habitat attribute, as proxies for the amount or extent of anticipated take. The authors contend that the proposed rule lacks essential implementation details and describe five essential steps in surrogate selection and validation.

Science and structured decision making: fulfilling the promise of adaptive management for imperiled species

DENNIS D. MURPHY and PAUL S. WEILAND

Thirty years after the appearance of adaptive management in the scientific literature, the concept has gained acceptance as a readily recognized, conceptually simple conservation-planning vehicle, despite its lackluster track record. Successful adaptive management must be implemented as a step-wise, structured approach to incorporating scientific information into decision making.

Eastward Migration or Marshward Dispersal: Exercising Survey Data to Elicit an Understanding of Seasonal Movement of Delta Smelt

DENNIS D. MURPHY and SCOTT A. HAMILTON

Nearly two decades after the listing of delta smelt on the federal and state endangered species act, comprehensive understanding of seasonal movements of the fish in the San Francisco Estuary is still lacking. The authors used publicly available data from trawl surveys on the distribution of delta smelt to infer seasonal dispersal patterns. The authors concluded that dispersal of delta smelt is more restricted than previously thought. This conclusion has real-world implications for efforts to conserve delta smelt.
The authors’ findings support a conservation strategy that focuses on habitat restoration and management efforts for tidal marsh and other wetlands in north Delta shoreline areas.

Longfin smelt: spatial dynamics and ontogeny in the San Francisco Estuary, California

JOSEPH E. MERZ, PAUL S. BERGMAN, JENNY F. MELGO, and SCOTT HAMILTON

The authors utilized sampling data from the Interagency Ecological Program and regional monitoring programs to provide a comprehensive description of the range and distribution of longfin smelt within the San Francisco Estuary, California. This comprehensive data review provides
managers and scientists an improved depiction of the distribution of longfin smelt in the Estuary and future population analysis and restoration planning for this species.

An Investigation of Factors Affecting the Decline of Delta Smelt (Hypomesus transpacificus) in the Sacramento-San Joaquin Estuary

WILLIAM J. MILLER, BRYAN F. J. MANLY, DENNIS D. MURPHY,
DAVID FULLERTON, and ROB ROY RAMEY

The delta smelt is a fish native to the Sacramento-San Joaquin Estuary and is protected under federal and California Endangered Species Acts. Record low abundances have occurred since 2004. The authors address three questions: What effects do environmental factors have on abundance? Do factors that may have indirect effects provide an explanation of abundance changes? How are these effects best accounted for?