Creature Feature: California Golden Trout

California has long been known as the ‘golden state’. This could be attributed to its golden sunshine, the golden hills that the summer brings, or the gold flakes that line its streams. Thus it is only fitting that the official state fish is the California Golden Trout (Oncorhynchus mykiss aguabonita). It is one of three beautiful subspecies of rainbow trout which are native to only a few high-altitude stream systems of the Sierra mountains1. According to the Department of Fish and Wildlife, it is regarded as one of the most beautiful trout on the planet.  In fact, it is so popular that it has been transplanted to other high altitude lakes—some as far as Wyoming—for sport-fishing purposes1,2.

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A young golden trout (Oncorhynchus mykiss aguabonita) [Source]
These California natives have a body that fades from a deep olive green to bright gold. They are adorned with a red-orange lateral line, and have black speckles at the base of the tail. With golden flanks that glisten against the water, it is uncannily reminiscent of gold flakes at the bottom of stream beds. Despite the flashy coloration, golden trout are active at all times of the day, and are known to have few natural predators. It has been proposed that this bright coloration may have evolved as camouflage against the lighter colors of the volcanic substrates found in their native streams. This claim seems to be supported by the observation that trout relocated to lower elevations lose some of their luster and take on duller colors3.

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The Golden Trout Wilderness, home of the California Golden Trout [Source]
Unfortunately, the golden trout has been in a state of decline for decades. In 1991, it was first added as a candidate to the U.S. Fish and Wildlife’s list of endangered species4. After years of being ignored, the conservation organization Trout Unlimited filed a petition to the U.S. Fish and Wildlife stressing the importance of classifying the golden trout as endangered4,5. Scientific reports since 2008 have validated the urgency for the endangered status of this endemic species6,7. Despite the supporting evidence, efforts of conservationists, and classification by California agencies as endangered, the golden trout continues to be classified merely as threatened by the Endangered Species Act8.

The continuous decline of these trout has primarily been caused by human-induced activities. The most prominent threat is hybridization of the species as a result of mating with introduced non-native trout2,8. Hybridization is when two species (or sub-species) are able to mate and produce offspring which retain genes from both parental lines. Over long periods of time this can be problematic as it can reduce the genetic variation found within a native population. This can cause genetic isolation in those populations which may have consequences on the evolutionary mechanisms that maintain genetic diversity.

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Range of the Kern River Rainbow Trout sub-species in the southern Sierra Mountains of California. [Source]
Pesticide treatments have been used in the past to prevent hybridization by eliminating non-native trout and offspring hybrids1. These methods have had varying levels of success as these treatments also impact native trout. In certain lakes, techniques such as gill-netting have been more successful in removing these hybridized fish. More focused efforts like these could be useful in developing conservation strategies for species that face hybridization challenges. It is possible that un-hybridized populations of golden trout still persist, although likely in small numbers with limited genetic diversity. We must be mindful and conscientious if we are to ensure the long-term survival of this beautiful California mascot.

[By: Josie Hubbard]


References:

1https://www.wildlife.ca.gov/Conservation/Fishes/California-Golden-Trout 

2http://calfish.ucdavis.edu/species/?uid=117&ds=241

3Needham, P. R., & Gard, R. (1959). Rainbow trout in Mexico and California: with notes on the cutthroat series(Vol. 67). University of California Press. Full text: https://babel.hathitrust.org/cgi/pt?id=uc1.32106005864142;view=1up;seq=242 

4https://www.sierraforestlegacy.org/FC_SierraNevadaWildlifeRisk/GoldenTrout.php 

5https://www.tu.org/press_releases/2000/tu-asks-feds-to-list-california-golden-trout-as-endangered 

6Moyle, P. B., Katz, J. V., & Quiñones, R. M. (2011). Rapid decline of California’s native inland fishes: a status assessment. Biological Conservation144(10), 2414-2423.

7Moyle, P. B., Israel, J. A., & Purdy, S. E. (2008). Salmon, steelhead, and trout in California. Status of an Emblematic Fauna. A report commissioned by California Trout.

8https://pisces.ucdavis.edu/content/oncorhynchus-mykiss-aguabonita

Main featured image [Source]

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