Hypomesus nipponensis
Encyclopedia
Also called wakasagi, Hypomesus nipponensis is an important food fish native to the lakes and estuaries of Hokkaido, Japan, although it has been introduced to other locations, including the San Francisco Delta of the United States.
Wakasagi are raised in fisheries, and are very similar in appearance to H. transpacificus
.
in 1997 based on claimed morphological differences. Later studies failed to find these morphological differences, and was then regarded as an ecotype
of H. nipponensis. A 2007 genetic analysis supported this classification, and recommended that H. chishimaensis not be given its own binomial
designation.
and Kyushu
, the Japanese wakasagi (although at the time, both the California-native delta smelt and the Japanese smelt were both thought to be separated members of the same species, H. olidus), was introduced to California
water reservoirs by the California Department of Fish and Game
to provide more prey for stocked rainbow trout
after attempts to introduce native Delta smelt
to three foothill reservoirs failed. In 1959 the CDFG imported 3.6 million fertilized eggs attached to palm
fiber mats from a population in Suwa Lake, located east of Tokyo; many of them dead on arrival. The fiber mats were placed in streams feeding into six lakes and reservoirs that appeared to be ecologically suitable for the smelt. It was thought at the time that these reservoirs could be chemically treated to eradicate the fish if they were found to be undesirable. In 1972 and 1973 about 77,000 fish from the Shastina Reservoir were moved to the Almanor Reservoir in Plumas County. All attempts to introduce the fish were successful, except the Dodge
and Big Bear Reservoir introductions, the latter of which may have been partially attributable to chemical treatments meant to eradicate stunted crappie
and goldfish
.
and San Pablo Bay
s.
and life history
, wakasagi smelt present several potential threats to the endangered Delta smelt. Besides direct competition for nutritional resources and the possibility that wakasagi may prey on the eggs and larvae
of Delta smelt, hybridization could either dilute the species or cause population decline due to sterilizing effects. In fact, a few hybrids have been captured in the wild, although all of them were first generation
crosses and no evidence of back-crossing has been found, which would suggest that the hybrids were not viable. Misidentification of the species is an additional concern, which could lead to inaccurate assessments critical to making policy decisions; however this problem may be mitigated if genetic marker
s are used for identification.
In addition to their negative effects on Delta smelt, the spread of wakasagi significantly reduced Kokanee
fisheries, but helped increase growth rates of other salmons and trout fisheries.
Wakasagi are raised in fisheries, and are very similar in appearance to H. transpacificus
Delta smelt
Delta smelt, Hypomesus transpacificus, is an endangered slender-bodied smelt, about long, of the Osmeridae family. Endemic to the upper Sacramento-San Joaquin estuary of California, it mainly inhabits the freshwater-saltwater mixing zone of the estuary, except during its spawning season, which...
.
Sub-species
Hypomesus chishimaensis was described as being a new species in the lakes of Kunashir and IturupIturup
Iturup is the largest island of the South Kuril Islands. It is the northernmost island in the southern Kuril/Chishima islands, and though it is presently controlled by Russia, Japan also claims this island...
in 1997 based on claimed morphological differences. Later studies failed to find these morphological differences, and was then regarded as an ecotype
Ecotype
In evolutionary ecology, an ecotype,Greek: οίκος = home and τύπος = type, coined by Göte Turesson in 1922 sometimes called ecospecies, describes a genetically distinct geographic variety, population or race within species , which is adapted to specific environmental conditions.Typically, ecotypes...
of H. nipponensis. A 2007 genetic analysis supported this classification, and recommended that H. chishimaensis not be given its own binomial
Binomial nomenclature
Binomial nomenclature is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages...
designation.
Introduction to the United States
Native to the lakes and estuaries of Hokkaido, Japan and introduced to the lakes on HonshuHonshu
is the largest island of Japan. The nation's main island, it is south of Hokkaido across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyushu across the Kanmon Strait...
and Kyushu
Kyushu
is the third largest island of Japan and most southwesterly of its four main islands. Its alternate ancient names include , , and . The historical regional name is referred to Kyushu and its surrounding islands....
, the Japanese wakasagi (although at the time, both the California-native delta smelt and the Japanese smelt were both thought to be separated members of the same species, H. olidus), was introduced to California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
water reservoirs by the California Department of Fish and Game
California Department of Fish and Game
The California Department of Fish and Game is a department within the government of California, falling under its parent California Natural Resources Agency. The Department of Fish and Game manages and protects the state's diverse fish, wildlife, plant resources, and native habitats...
to provide more prey for stocked rainbow trout
Rainbow trout
The rainbow trout is a species of salmonid native to tributaries of the Pacific Ocean in Asia and North America. The steelhead is a sea run rainbow trout usually returning to freshwater to spawn after 2 to 3 years at sea. In other words, rainbow trout and steelhead trout are the same species....
after attempts to introduce native Delta smelt
Delta smelt
Delta smelt, Hypomesus transpacificus, is an endangered slender-bodied smelt, about long, of the Osmeridae family. Endemic to the upper Sacramento-San Joaquin estuary of California, it mainly inhabits the freshwater-saltwater mixing zone of the estuary, except during its spawning season, which...
to three foothill reservoirs failed. In 1959 the CDFG imported 3.6 million fertilized eggs attached to palm
Arecaceae
Arecaceae or Palmae , are a family of flowering plants, the only family in the monocot order Arecales. There are roughly 202 currently known genera with around 2600 species, most of which are restricted to tropical, subtropical, and warm temperate climates...
fiber mats from a population in Suwa Lake, located east of Tokyo; many of them dead on arrival. The fiber mats were placed in streams feeding into six lakes and reservoirs that appeared to be ecologically suitable for the smelt. It was thought at the time that these reservoirs could be chemically treated to eradicate the fish if they were found to be undesirable. In 1972 and 1973 about 77,000 fish from the Shastina Reservoir were moved to the Almanor Reservoir in Plumas County. All attempts to introduce the fish were successful, except the Dodge
Dodge Reservoir
Dodge Reservoir, located in Lassen County, was created in 1937 by the owners of the Dodge Ranch. It covers an area of approximately , among Great Basin high-desert sagebrush and California Juniper. The surrounding habitat is Sagebrush steppe, and is part of the Northern Basin and Range ecoregion...
and Big Bear Reservoir introductions, the latter of which may have been partially attributable to chemical treatments meant to eradicate stunted crappie
Crappie
Crappie is a genus of freshwater fish in the sunfish family of order Perciformes. The type species is P. annularis, the white crappie...
and goldfish
Goldfish
The goldfish is a freshwater fish in the family Cyprinidae of order Cypriniformes. It was one of the earliest fish to be domesticated, and is one of the most commonly kept aquarium fish....
.
Progression into delta
Although a retrospective analysis of preserved Delta smelt samples caught in 1972 and 1982 from the Delta region has shown that wakasagi had been invading the estuaries in undetected quantities since at least the early 1970s, wakasagi expansion from these original introduction sites southward was not tracked until several years later. In 1994 they were detected at the State Water Project pumping plant for the first time, and by 1998 the fish could be found throughout the estuary including the SuisunSuisun
Suisun may refer to:Geography*Suisun Bay in California in the United States*Suisun City, California, in the United States*Suisun Marsh in California in the United StatesOther places*Suisun Valley AVA, California wine region in Solano CountyShips...
and San Pablo Bay
San Pablo Bay
San Pablo Bay is a tidal estuary that forms the northern extension of San Francisco Bay in northern California in the United States. Most of the Bay is shallow; however, there is a deep water channel approximately in mid bay, which allows access to Sacramento, Stockton, Benicia, Martinez, and...
s.
Consequences
Because the two species are very similar in morphologyMorphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
and life history
Biological life cycle
A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
, wakasagi smelt present several potential threats to the endangered Delta smelt. Besides direct competition for nutritional resources and the possibility that wakasagi may prey on the eggs and larvae
Larvae
In Roman mythology, lemures were shades or spirits of the restless or malignant dead, and are probably cognate with an extended sense of larvae as disturbing or frightening...
of Delta smelt, hybridization could either dilute the species or cause population decline due to sterilizing effects. In fact, a few hybrids have been captured in the wild, although all of them were first generation
First generation
The term First Generation can refer to:*First generation immigrant, a citizen or resident who is an immigrant or has immigrant parents*Anything of the earliest kind, often used when describing computers or technology....
crosses and no evidence of back-crossing has been found, which would suggest that the hybrids were not viable. Misidentification of the species is an additional concern, which could lead to inaccurate assessments critical to making policy decisions; however this problem may be mitigated if genetic marker
Genetic marker
A genetic marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify cells, individuals or species. It can be described as a variation that can be observed...
s are used for identification.
In addition to their negative effects on Delta smelt, the spread of wakasagi significantly reduced Kokanee
Sockeye salmon
Sockeye salmon , also called red salmon or blueback salmon in the USA, is an anadromous species of salmon found in the Northern Pacific Ocean and rivers discharging into it...
fisheries, but helped increase growth rates of other salmons and trout fisheries.