Delta Smelt Workshop

One of the goals of the CALFED Science Program is to provide authoritative and unbiased descriptions of scientific knowledge. To fulfill this goal, the Science Program holds workshops designed to provide a forum for discussions and the exchange of information among Scientists, Stakeholders, Agency Staff, and the public about topics important to the region. These workshops synthesize the science related to complex problems and provide advice for undertaking specific complex tasks in support of Delta planning and decision-making.

Workshop Purpose

The 2006 Environmental Water Account Science Review Panel noted that the lack of information on delta smelt spawning habitat and migratory behavior was a key data limitation for water management in the Sacramento-San Joaquin Delta. The CALFED Science Program and the U.S. Fish and Wildlife Service co-hosted a one-day workshop to discuss the state of science on the spawning biology of smelts, and to craft a study design for studying the spawning biology of delta smelt and longfin smelt in the San Francisco Estuary


CALFED Science Program Workshop
Unraveling the Smelt Mystery: Where Do Delta Smelt and Longfin Smelt Spawn and How Do They Get There?

Update - 04/25/08

Our original intent was to produce a report from this workshop that was primarily a research strategy for studying delta smelt and longfin smelt spawning migrations and reproductive biology. However, the current species status has made it very unlikely that studies targeting these fish in the field will be permitted and supplies of cultured adult delta smelt are limited. Therefore, we re-evaluated what type of written product would be most useful. The following are a few key generalizations about the spawning biology of smelts that stemmed from the workshop.

  1. The smelts generally spawn in shallow water. This includes beaches for marine species and river edges or small streams for estuarine/freshwater populations.

  2. The smelts appear to spawn most often on sand or gravel substrates. This conclusion is further supported by several gray literature and book references cited within the delta smelt, longfin smelt, wakasagi (Hypomesus nipponensis), and eulachon (Thaleichthys pacificus) chapters in Moyle (2002).

  3. The smelts are secretive spawners, making overnight forays into spawning microhabitats and leaving them before dawn. This appears to be true for marine beach spawners, estuarine populations and the landlocked Lake Washington longfin smelt. A key potential lesson from this is that delta smelt distributions in the IEP's Kodiak trawl survey, which is conducted during daylight in offshore habitats likely reflect general regions of spawning activity, but say little about the actual spawning sites.

  4. A final possibility is that osmerid eggs may "tumble incubate" (phrase attributed to Doug Hay, Department of Fisheries and Oceans, Canada). Delta smelt, like other members of its family (osmeridae) have adhesive eggs. Thus, it has been presumed that eggs are typically affixed to substrates that do not usually move during the eggs' incubation period (Moyle 2002; Wang 2007). Dr. Hay thinks that the eggs of another smelt species, the eulachon, attach to sand particles which keep them negatively buoyant, but not immobile. This is analogous to what has been observed in the marine surf smelts (Hirose and Kawaguchi 1998). The benefits include dispersal of eggs so that they are not so highly aggregated that they attract predators, but not so broadly dispersed that they hatch in conditions very different from those in which they were spawned. Note, the tumble incubation hypothesis is highly speculative for delta smelt, but we think it should be considered a possibility in the context of habitat restoration or enhancement.


Hirose, T, Kawaguchi, K. 1998. Spawning ecology of Japanese surf smelt, Hypomesus pretiosus japonicus (Osmeridae), in Otsuchi Bay, northeastern Japan. Environmental Biology of Fishes 52:213-223.

Moyle, PB. 2002. Inland fishes of California, revised and expanded. University of California Press, Berkeley, CA.

Wang, JCS. 2007. Spawning, early life stages, and early life histories of the Osmerids found in the Sacramento-San Joaquin Delta of California. Tracy Fish Facilities Studies California Volume 38. U.S. Bureau of Reclamation, Mid-Pacific Region.

November 15, 2007, 8:30a.m. to 4:00p.m.
Delta Conference Room
650 Capitol Mall, 5th Floor
Sacramento, CA 95814

Download the Meeting Notice and Agenda.

This meeting will not be Webcast.

Workshop Product

The Science Program produced a written report on the workshop. The report included:

  • the key points made by each presenter
  • an overview of the scientific uncertainties highlighted during the workshop
  • a general study design for studying the spawning biology of delta smelt and longfin smelt

The report and the speakers' presentations will be posted on the CALFED website.


Dr. Mike Healey, CALFED Science Program
Welcome and Introduction

Matt Nobriga, CALFED Science Program
Where do delta smelt and longfin smelt spawn and how do they get there? Basic background information and workshop intent
8:40-9:00 - presentation

Lenny Grimaldo
California Department of Water Resources/University of California at Davis
What the fish salvage data can and cannot tell us about delta smelt and longfin smelt spawning migrations.
9:00-9:30 - presentation

Dr. Doug Hay, Pacific Biological Station, Fisheries and Oceans Canada
Spawning biology of eulachon
9:30-10:00 - presentation


Dr. Paulinus Chigbu, University of Maryland Eastern Shore
Spawning biology of the Lake Washington population of longfin smelt
10:15-10:45 - presentation

Dr. Nat Scholz
National Marine Fisheries Service Northwest Fisheries Science Center
Chemical contaminant issues for migration and habitat restoration


Panel Discussion Facilitated by Matt Nobriga

Public Comment


Order of agenda items is subject to change. Times are approximate and subject to change.

If you have any questions, please contact Matt Nobriga at (916) 445-0479 or

If you need reasonable accommodation due to a disability, please contact Colleen Kirtlan, CALFED Bay-Delta Program at (916) 445-5511, TDD (800) 735-2929.

Please allow extra time for parking and federal building security screening procedures. Current photo identification is required for building access. Visitors may bring cameras and cell phones with camera capability into the building ONLY with the prior approval of the CALFED Bay-Delta Program and the Federal Protective Service, and their use in the building will be subject to federal restrictions. Please contact Terry Smith, Security Coordinator for the CALFED Bay-Delta Program, cell (916) 716-1904, office (916) 445-5345 or for building access information and camera guidelines.