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Fish Fertilizer

Anecdotal accounts tell of salmon once so plentiful in California's Central Valley streams that farmers spread salmon carcasses onto their fields to fertilize crops. While those days are long gone, salmon still posthumously nourish their natal environments. As we navigate the streams draining the San Joaquin basin during late fall and early winter, occasionally accompanied by the unmistakable aroma of decaying fish, we often witness this process of "fertilization" in action, as returned Chinook make their final contribution to watersheds in the Central Valley and Pacific Northwest. Returning salmon contribute organic matter and nutrients to their natal streams in a number of ways, including their own metabolic processes, their release of eggs and sperm, serving as food to their predators, and the decomposition of their carcasses.

 

A surprising variety of animals feed on salmon carcasses. In addition to bears, wolves, otters, raccoons, skunks, and foxes, the likes of shrews, mice, squirrels, deer, and a large number of bird species opportunistically indulge in salmon (Willson and Halupka 1995). All of these species act as vectors for marine-derived nutrients as they spread, by way of metabolic waste, "fish fertilizer" far beyond river channels and adjacent riparian habitat. Any uneaten carcasses decay and release nutrients into the soil and water. During a stroll along suitable spawning reaches this time of year, one can often spot the fuzzy evidence of microbial decomposition.

 

Pacific salmon accumulate the vast majority of their body mass (>90%) while feeding in the ocean, so it may seem intuitive that migrating salmonids provide a substantial nutrient subsidy when they return to their freshwater rearing areas. About two decades ago, advances in the field of stable isotope analysis gave researchers novel tools to trace marine-derived nutrients through riverine and riparian ecosystems. Marine environments (and therefore the salmon's diet and the salmon itself) have a much greater proportion of the heavier nitrogen isotope 15N, relative to 14N, than freshwater, air, or land. Scientists can use these differences to estimate the proportion of marine-derived nutrients (mainly nitrogen and phosphorus) in tissues of animals and plants.

 

Thanks to such studies, we now know that many plant and animal communities depend on salmon runs as a source of energy to a rather astonishing extent. For example, following the return of pink salmon to a stream in southeastern Alaska, nearly all of the nitrogen contained in resident rainbow trout, aquatic insects algae, and microbes was marine-derived, as well as a quarter of the nitrogen in the leaves of riparian vegetation (Kline et al. 1990). While Chinook populations of the Sacramento-San Joaquin basin are more modest than the salmon runs of Alaska, animals and plants still benefit from the autumnal nutrient subsidy, and even cultivated crops such as wine grapes grown adjacent to a Central Valley stream can (indirectly) derive up to a quarter of their foliar nitrogen from returning salmon (Merz and Moyle 2006).

 

Juvenile salmon benefit from the nutrient boost provided by their decomposing ancestors through increased densities of invertebrates to eat and enhanced riparian vegetation providing cover and refuge. As such, the nutrients from spawning salmon may serve as a positive feedback mechanism that maintains long-term salmon production and riparian habitat; conversely, decreased salmon production may be self-perpetuating (Cederholm 1999, Naiman et al. 2002).

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Some assembly required 
For many, the New Year is  the mark of new beginnings and wishes of a prosperous year ahead. For us at FISHBIO, January means it's time for our annual task of installing rotary screw traps (RST) to monitor juvenile salmon and steelhead (see Catch me if you can, The count is on). Each winter, we haul the traps out of storage, carefully inspect them, and make any necessary repairs, such as replacing pop-rivets or damaged parts. Then we load the RSTs onto specially built trailers and transport them from our shop to the field sites for assembly. At most sites, we can assemble the traps in the water close to their sampling locations, then drift or tow them into position. Occasionally, if access is limited, we have to assemble the trap on shore and use a crane to lift the entire apparatus into the river.

Using hand tools and knowhow, our crew makes quick work of putting traps together and getting them ready for sampling (see video). To assemble an RST, we first position the cone (large cylindrical drum) between two pontoons, then bolt crossbars to the pontoons. The cone has an aluminum shaft running down the middle that we insert into nylon collars at the bow and stern of the trap-this allows the cone to rotate freely under the power of passing water. The mouth of the cone, which measures 5 or 8 feet in diameter, points upstream. We mount an A-frame pulley system at the bow...  Read more > 
IN THE NEWS: Recent stories you might have missed...
Gillnetters sue over Columbia fisheries reform plan

The Columbian    

Commercial fishermen have turned to the Oregon Court of Appeals to challenge a recent change  in the state's gillnet fishing rules. In addition to a petition that asks the Oregon court to review the validity of the changes, a lawyer for the fishermen sent a letter to the Washington Fish and Wildlife Commission, asking it to push back a gillnet rule change decision expected Saturday. On Dec. 7, the Oregon Fish and Wildlife Commission voted to ban the use of gillnets to catch fish on the main stem of the lower Columbia River... Read more>

First spring Chinook caught on Columbia
The Seattle Times

The Lower Columbia River below I-5 is open for spring chinook fishing, and reports are swirling about the first fish of the season being caught this week.

"We heard an early spring chinook might've been caught on the Cowlitz through a verbal and photo verification," said Joe Hymer, a state Fish and Wildlife biologist. "We don't know for sure if it was a spring or winter fish." It's usually around now when you hear of spring chinook caught, although the height of this fishery doesn't occur until March and April.... Read more > 

Overfishing causes Pacific bluefin tuna numbers to drop 96%  
The Guardian
The bluefin tuna, which has been endangered for several years and has the misfortune to be prized by Japanese sushi lovers, has suffered a catastrophic decline in stocks in the Northern Pacific Ocean, of more than 96%, according to research published on Wednesday. Equally concerning is the fact that about 90% of specimens currently fished are young fish that have not yet reproduced. Last week, one fish sold in Japan for more than 1m... Read more >
White sharks headed for California endangered species list

U~T San Diego

The California Department of Fish and Game will recommend that the Northeast Pacific population of white sharks be listed as a threatened or endangered species under the state's Endangered Species Act.

The state officials said there is "sufficient scientific information" to indicate that the petition action may be warranted. Now it will recommend that the Fish and Game Commission accept the petition and list the white shark... Read more >   

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