Pelagic Fish Declines

Delta Science Fellow Julien Moderan (right) and graduate student Karen Kayfetz collect water samples from the San Francisco Estuary. Credit: T. IgnoffoDelta Science Fellow Julien Moderan is searching for clues as to why so many pelagic fishes in San Francisco Estuary are declining, despite efforts to protect them.

To do so, he is looking at “baby food” for fishes – the tiny, usually microscopic, drifters, known collectively as zooplankton, that are gobbled up by fishes during their larval and juvenile life stages. Some species, such as delta smelt, feed on zooplankton throughout their life.

He and his colleagues speculate that zooplankton shortages have left fishes hungry and thus more likely to perish. Without a repair to the food chain, fish recovery is unlikely.

This zooplankton species is found in the estuary's low-salinty zone.“My research attempts to identify shifts at the base of the pelagic food web that may be affecting fishes, ” said Moderan, a postdoc at the Romberg Tiburon Center with Wim Kimmerer. “We want to see if this can be observed in archived zooplankton samples, ” collected before and after the pelagic organism decline.

Below is a summary of his Delta Science Fellowship project and findings to date, which will be updated and distributed by California Sea Grant Communications for the State of the San Francisco Estuary Conference this fall.

Another species of zooplankton found in the Delta that is a key prey item. Credit: W. Kimmerer LabDetecting Changes at the Base of the Pelagic Food Web in the San Francisco Estuary

Julien Moderan, Delta Science Fellow 2011-2013

Background

Since about 2004, populations of delta smelt, longfin smelt, juvenile striped bass, and threadfin shad have dropped significantly in the Sacramento-San Joaquin Delta for no obviously apparent or as yet substantiated reason, though food shortages at the base of the food web are among the factors theorized to be contributing to the pelagic organism decline.

Project

This project examines historical zooplankton samples, as well as new field data, to explore trends and variability in zooplankton diets since the 1970s and their implications for the pelagic food web at large. The hypothesis: There has been a shift in the base of the food web from nutritious, large phytoplankton species to less-nutritious bacteria-degraded vascular plant debris.

Such a shift, if it can be detected (analyses are ongoing) would mean less food for the larger zooplankton species that are the dietary staples of larval fishes. It would also be consistent with other observations that strongly suggest the estuary is food-limited. There is, for example, less total phytoplankton in the estuary’s low-salinity zone, and smaller phytoplankton species have become more abundant than larger ones.

The Asian clam was discovered in San Francisco Bay in 1986. Its prodigious ability to filter phytoplankton may deprive other animals of food. Credit: A. Cohen Researchers are analyzing historical zooplankton samples to look for clues on fish declines. Credit: J. Moderan A tray with zooplankton sorted by species and put in tin capsules for stable isotope analyses. Credit: J. Moderan Researchers filter particulate organic matter from water samples to identify sources of food for small animals. Credit: J. Moderan
Pelagic Publishing Ltd Amphibian Biology, Volume 11 Part 3: Status of Conservation and Decline of Amphibians: Eastern Hemisphere: Western Europe
Book (Pelagic Publishing Ltd)

Fish Stocks/ Windpower/ Wave Generators

2006-11-14 00:23:43 by jaybug39

I have read that ocean fish stocks will be gone in a few years. And I have been thinking since I heard that Massachusetts refused to build wind turbines in Long Island Sound as they were unattractive, why not build some in the pacific where we could create national sea life refuges?
This would help out coastal communities in several regards. Some people would come see the turbines, much like some people visit lighthouses. The energy produced would ease any difficulties coastal communities may face from their currently existing long distance power transmissions. And they would get the benefit of knowing that fish will be around in the future


You might also like:

Lehar Cyclone hit andhra in bay of …
Lehar Cyclone hit andhra in bay of …
Fishing in the Saint Martins Island of …
Fishing in the Saint Martins Island of …
Striped Marlin Bait Ball | Pelagic Life
Striped Marlin Bait Ball | Pelagic Life
Underwater World Of Bay Of Bengal …
Underwater World Of Bay Of Bengal …
Bay of Bengal - Promenade …
Bay of Bengal - Promenade …
Mudskipper, Bay of Bengal
Mudskipper, Bay of Bengal

Related posts: