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Nor-Cal Guides & Sportsmen's Association

Introduction and Summary

The San Francisco Bay-Delta watershed has two native sturgeon species:  the white sturgeon and green sturgeon.  The white sturgeon supports an important sport fishery in rivers and the Bay-Delta.  The green sturgeon is less abundant and is listed under the state and federal endangered species acts.  No harvest of green sturgeon is allowed.  Both species are anadromous fish that migrate from the ocean or Bay to rivers to spawn.  Green sturgeon are considered more marine oriented.  Green sturgeon generally migrate further upstream in rivers and tributaries to spawn.  The white sturgeon is larger and generally more sought after as a game fish.  Both are bottom feeders prone to take smell enhanced bait on river/bay bottoms.  With the influx of non-native clams in the 1980s, the sturgeon have a food source thought to enhance their growth and production.  Both species are sensitive to warm water and do best in cooler (<68^oF) saltier waters of the Bay or ocean.

The freshwater journey to spawn is a risky part of their life cycle.  In freshwater they must use several years of stored energy to reach clear cool rushing water with deep rocky bottoms to lay their sticky eggs.  After several days, the eggs hatch and the tiny fry begin their month-long drift to the Bay, feeding as they go and growing to several inches.  It’s that time that determines the fruits of the spawning trek.  In drier years, their eggs and fry die from a lack of flow and warm waters, but in the wetter years the cool, fast currents transport them to the Bay by summer.  In the Bay or nearby ocean, they grow ten to 15 years before they make their first spawning journey to the rivers. Unlike salmon, they are long-lived and can spawn in multiple years.

The frequency of these wet years and their optimal conditions in the Bay determine the number of adults that are in the multiage population.  Although the sport fishery may take 5 to 10 percent of the total adult population in any one year, the greatest threat (at least to the white sturgeon) other than drought years are years when the Bay gets too warm in summer and algae blooms consume much of the oxygen in the water, resulting in large die-offs of resident juvenile and adult sturgeon.

In this report, we focus on the actions necessary to sustain the sturgeon population and keep it viable in a future characterized by climate change.  The factors that are most important are adequate flows and suitable water temperatures in the Sacramento River, the Delta, and Bay.

In the rivers, it is the flows and water temperatures that are key to survival in the spring and early summer prior to spawning, during the spawn, and in the early rearing stages following the spawn.

The Delta is important in late spring and early summer.  In most years under present water management, young sturgeon simply do not survive the Delta because of inadequate flows, high water temperatures, predation, and entrainment into water diversions.

Summer is the critical time in the Bay.  A healthy Bay where most of the sturgeon reside in summer and fall is key to sustaining the sturgeon populations through most of their life cycle.   The Bay is subject to the Super Moons whose tides drain the warm Delta water into the Bay, stimulating algae blooms.  Like the rivers and Delta, the Bay needs adequate freshwater inflow to sustain the food chain and keep the Bay cool (<68^oF) with adequate dissolved oxygen to sustain sturgeon through the summer.

Otherwise, we must do what we can to beef up the population in bad times with a conservation hatchery, rescues of young and adult sturgeon, and strong limits on the sport fishery.  Our top priority is to protect the existing spawning stock of adults older than 15 years.  Second, is ensuring adequate recruitment of subadult sturgeon 4-to-15 years of age will be moving into the adult spawning stock in the coming years.  Third, is improving survival of eggs, larvae, and juveniles to improve recruitment of the age-0 to age-3 juveniles into the population.  To accomplish these actions effectively, we need a stronger science-oriented effort to monitor and assess all the key population and habitat elements that will guide the recovery program.  The entire package will look familiar, given many of the actions are the same as those prescribed for salmon, steelhead, and smelt. All native fishes of the Central Valley and Bay-Delta suffer from the same maladies that beg the same solutions.

This report focuses on assessing the present state of the populations because such information is generally lacking for sturgeon compared to other species.  There is really no recovery plan for sturgeon that identifies actions that would protect and recover the populations.  There are strong pressures building to eliminate the popular sport fishery and list the white sturgeon under the state and federal endangered species acts.  While we believe that sport-fishery harvest is an important factor in sturgeon population dynamics, other factors should be addressed before the fishery is eliminated. Also, the fishery is one of the principal sources of information on the status of the sturgeon populations.

Population Review and Assessment

The population of adult white sturgeon in the SFE has been estimated at 50,000 to 200,000 from 1980 to 2005, but in recent years has been only 20,000 to 50,000 (Figure 1).  After the recent Bay die-offs the population may be down near or even below 10,000.  Hope is that wet years 2017, 2019, and 2023 bring strong brood years that sustain the population over the next decade.

Recruitment of age-0 white sturgeon has been assessed from an Index from Bay Otter Trawl Survey (Figure 2).  The index shows a gradual decline in recruitment as well as sporadic recruitment in wetter years.  The catch represents many sampling stations (Figure 3) visited monthly over a year.  Catches are sporadic within months and between years (Figure 4).  Most of the catch occurred in the west and north Delta (#700 stations) (Figure 5).  The lowest catches occurred in the North, Central, and South Bays.

The population of Southern Green Sturgeon (sDPS) is small, with only a portion entering the San Francisco Bay Estuary (SFE) each year to spawn.  The remainder may be found along the coast from Mexico to Alaska.  Age-0 recruitment is indexed for green sturgeon from screw trap collections at Red Bluff (Figure 6).

The number of green and white sturgeon caught, released, and kept per year from 2007 through 2018 is summarized in Table 1.