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Delta Fish Populations - The Research of Delta Science Fellow Matt Young

May June 2014

Motivated by concerns about the health of resident fish populations in the Delta and evidence that some species, such as the Sacramento blackfish and tule perch, are in decline in shallow nearshore waters of the Delta, Delta Science Fellow Matt Young decided to make their decline the focus of his graduate research.

Since 2003, the Delta Science Fellows Program, in conjunction with California Sea Grant, has paired graduate students and postdoctoral researchers with Bay-Delta agency scientists and senior research mentors in order to address research priorities and pressing science questions of the Bay-Delta system.

Young, a student researcher getting his Ph.D. at U.C. Davis, says he isn’t looking at the “sexy endangered species,” (Delta Smelt and Chinook salmon) he’s looking at other species that are declining, “but nobody seems to care.”

“I asked about these species and no one could give me a good answer,” he said. “If I asked someone about tule perch, what are they doing, what affects them, I invariably got shrugs.”

That’s why he’s researching these lesser known species, trying to determine if their decline is due to non-native species or some other change in the system. One of the big controversies in the Delta currently is the role of non-native fish in the decline of native species and the default answer is that invasive fish are bad.

“What my work is showing thus far is that it’s likely that some non-native fish aren’t that bad,” Young said, “and that their interactions with the natives that I’m studying are quite limited, having little-to-no impact.”

Native fish aren’t sampled regularly or efficiently, so available data on these species are poor. What data do exist shows a pretty marked decline, at least Delta-wide; however, some existing data show some regions where the fish might be doing well. Young has discovered that some of those species (Sacramento sucker, tule perch, prickly sculpin) are doing really well, particularly in the Cache Slough complex, but Sacramento blackfish, hitch, and Sacramento pikeminnow are as rare there as elsewhere.

One of the things he’s specifically investigating with his Delta Science grant is the role of native and non-native fish in Delta food webs, while exploring the possibility for competition between native and non-native species.

“Every food web has gaps, holes where for whatever reason there is a resource that is not being fully exploited by some kind of consumer,” he said.

The type of analysis Young is doing helps to identify which non-native species fill those holes, and which non-native species may be replacing the role of a native species in that food web. If native and non-native species utilize the same resources, or fill the same role within a food web, that potentially sets them up for competing with one another for those same resources.

He has identified groups of species that may be competing for resources and by identifying what these fish have been eating and analyzing the nutrients in their muscle tissues, he can tell which fish are using which resources and identify those whose resource use overlaps.

“It looks like some of those native fish that are doing well, particularly tule perch and prickly sculpin, don’t compete for resources with other fish they share habitat with,” he said. “Whether that’s a mechanism for their success is unclear. That’s what I hope to investigate further.”

One of the important aspects of studying declining species is being corrective or proactive. “It’s relatively easy to get funding to study endangered species,” Young said, “but once you have the money, it’s hard to do something because of regulatory limitations and often the species are often already in dire straits by that point. If you can identify them before they’re endangered, it’s cheaper for taxpayers, for conservation management, and just as effective in terms of helping the species.”

Young hopes that his research helps focus the conversation regarding their declines.

“If my research finds that invasive species don’t matter then maybe we can focus on other avenues of decline; potentially exploring, or eliminating causes of native decline,” he said. “Understanding more about the basic biology of these fishes should help focus that conversation.”

Young has already started collecting samples for similar studies looking at how these kinds of relationships change across space.

“Maybe non-native fish don’t matter in these two areas, but in other areas, they do, so we can start looking for other factors that affect that,” he said.

Possible other factors include: food availability or limitation in certain regions and other environmental changes such as flow, habitat loss, etc. His further work is based on comparing the resource use of different species in regions where food is readily available, versus in areas where food is likely limiting.

Young’s findings may help managers understand the processes that sustain, and potentially rebuild, native resident nearshore fishes in the Delta. He hopes to present his results at the 8th Biennial Bay-Delta Science Conference in October.

An avid runner and white water rafter, Young hails from Tulare, Calif. “I think that’s why so much of the Delta fascinates me,” he said, “I came from an area at least partly dependent on Delta water—there’s a connection of place which helps.”

Coequal goals

The Delta Stewardship Council was created in legislation to achieve the state mandated coequal goals for the Delta. "'Coequal goals' means the two goals of providing a more reliable water supply for California and protecting, restoring, and enhancing the Delta ecosystem. The coequal goals shall be achieved in a manner that protects and enhances the unique cultural, recreational, natural resource, and agricultural values of the Delta as an evolving place." (CA Water Code §85054)