silver salmon

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Beneficial

Oncorhynchus kisutch has a moderate environmental impact in the Great Lakes.

Realized:
Although stocking of Pacific salmonines has occurred for nearly half a century in the Great Lakes, relatively little research into or assessment of the environmental consequences has been completed (Crawford 2001).

An early study on the effects of coho salmon spawning in rivers examined the presence of benthic invertebrates before and after spawning in the Platte River, a 25-mile river which flows into Lake Michigan (Hildebrand 1971). Hildebrand (1971) found that spawning significantly reduced the number and weight of invertebrates•ft-2 over the short term due to disturbance of bottom material. Total abundance and weight were reduced relative to controls by 66% and 78%, respectively, in the December following the autumn 1967 spawning (Hildebrand 1971). By May 1968, the number of organisms (but not the weight) was still significantly reduced relative to controls (Hildebrand 1971).

Crawford et al. (2001) pointed out that salmonids have the potential to alter the energy and nutrient cycles of the Great Lakes system through increased energy transfer between open water and streams/tributaries. This energy transfer includes the addition of nitrogen and phosphorous to tributaries through decaying salmonine carcasses (Parmenter and Lamarra 1991, Rand et al. 1992), as well as the addition of salmon eggs and dead fish as a food source in streams. Rand et al. (1992) found that phosphorus released from salmon carcasses was responsible for >50% of the total phosphorus discharged in some Lake Ontario streams during parts of the spring.

Coho salmon competes with native lake trout (Salvelinus namaycush) (Page and Laird 1993). Fausch and White (1986) suggested that juvenile coho salmon also has the ability to outcompete both native brook trout (Salvelinus fontinalis) and non-native brown trout (Salmo trutta) for food and space in Great Lake tributaries based on laboratory stream experiments involving competition for profitable stream positions. The authors also observed that coho salmon emerge earlier in tributaries, which may give them a competitive advantage in size over brook and brown trout (Fausch and White 1986).

The introduction of Pacific salmonines is deemed responsible for the introduction of Renibacterium salmoninarum, which has caused breakouts of bacterial kidney disease in lake trout and has also infected brook trout, lake whitefish (Coregonus clupeaformis), and bloater (C. hoyi). However, the specific role of coho salmon in this introduction is unknown (Crawford 2001; see fact sheet for R. salmoninarum).

Potential:
The diet of coho salmon is diverse, including invasive species such as alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax), and native species such as yellow perch (Perca flavescens), emerald shiner (Notropis atherinoides), ninespine stickleback (Pungitius pungitius), cisco (Coregonus artedii), and many aquatic invertebrates (see Crawford 2001). It is thus possible for coho salmon predation to affect these species or the food web in general. Although coho salmon are thought to be less voracious than chinook salmon (Oncorhynchus tshawytscha), controversy has existed in the Great Lakes regarding the effects Pacific salmonines have had on the forage fish base, on which other recreational/commercial species depend (Brown et al. 1999).

There is little or no evidence to support that Oncorhynchus kisutch has significant socio-economic impacts in the Great Lakes.

As this is an intentionally stocked sport species, there are no negative effects on human health and recreation to report.

Oncorhynchus kisutch has a high beneficial effect in the Great Lakes.

Realized:
Coho salmon was stocked in all of the Great Lakes by 1968 as a control of alewife populations and as a sport fish (Eddy and Underhill 1974). It contributed substantially to the recreational fishery, although currently, it is only stocked in Lake Michigan and in small numbers in Lake Ontario (Kocik and Jones 1999; USFWS/GLFC 2010; NYDEC 2011). According to the 2005 Survey of Recreational Fishing in Canada, coho salmon is still harvested by anglers in much of the Great Lakes system, but is less prominent than chinook salmon and many native recreational species (Fisheries and Oceans Canada 2008). However, historically, coho salmon was among the most-fished Pacific salmon in Lake Superior, especially during winter ice fishing (Bence and Smith 1999). As of 2008, coho salmon was also fished commercially by tribal groups in Lake Superior (U.S. Geological Survey [USGS] 2010). No stocking of coho salmon has been documented (as reported by the Great Lakes Fish Stocking Database (USFWS/GLFC 2010)) in Lake Erie since 2003, Lake Ontario since 2006, Lake Superior since 2007, or Lake Huron since 1989 (USFWS/GLFC 2010).

Regulations (pertaining to the Great Lakes region)
Direct Regulations:
Great Lakes states and provinces have their own specific fishing regulations. Generally, the overall goals and objectives of Pacific salmon fishing regulations are the same throughout the region i.e., to maintain or enhance a healthy and sustainable salmonid fisheries. Pacific salmon fishing regulations include daily and season bag limits, size limits, permitted baitfish, manner of taking i.e., snagging or hook and line, and designated season dates (See New York DEC, Pennsylvania F&BC, Ohio DNR, Michigan DNR, Indiana DNR, Illinois DNR, Minnesota DNR, Wisconsin DNR, Ontario MNR, and Quebec MRNF websites for specific fishing regulations). 

Indirect Regulations:
Typically, Pacific salmon regulations are not species specific, but rather regulate the salmonid fisheries as a whole. Indirect Pacific salmon regulations include mandated salmonid pathogen screening tests and baitfish regulations.
Mandatory salmonid pathogen screening tests are implemented in all Great Lakes states and provinces. The importation, exportation, and transportation of Pacific salmon is highly regulated to control the spread of infectious diseases and parasites such as VHS, BKD, and whirling disease (See USGS nonindigenous diseases and parasites fact sheets for state and provincial regulations).

State and provincial baitfish regulations have aided in preventing the spread of infectious disease. Specific and or stricter regulations are placed on baitfish species that are known carriers of salmonid pathogens.

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control
Biological
Pacific salmon prey heavily upon two non-native species in the Great Lakes, the alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax).   Alewives remain a key food source and crucial to the survival of Pacific salmon.  Over the past several decades, Pacific salmon populations have fluctuated with fluctuating alewife populations. Managing one species significantly impacts the other. Pacific salmon and alewives have significant environmental, socio-economic, and beneficial effects in the Great Lakes and therefore integrated management is essential. Rainbow smelt are also a major component of Pacific salmon diet. Similar to alewives, Pacific salmon and rainbow smelt management should be integrated.  Rainbow smelt have a high environmental impact and high beneficial effect in the Great Lakes. The presence or absence of this species significantly alters predator-prey relationships and competition between native species. Managers can also attempt to increase less harmful native prey species stocks while allowing harmful invasive prey species to decrease.  Implementation of this bio-control has potential significant beneficial effects in the Great Lakes with few negative impacts (See USGS fact sheets on alewife and rainbow smelt).

Of the 23 nonindigenous diseases and parasites in the Great Lakes, Aeromonas salmonicida, Renibacterium salmoninarum, Myxobolus cerebralis, and Novirhabdovirus sp. infections have been realized in Great Lakes Pacific salmon, while Heterosporosis sp. and Piscirickettsia cf. salmonis infections have been realized clinically or outside the Great Lakes. Glugea hertwigi, a microsporidian, is known to cause mortality in rainbow smelt. Therefore, Pacific salmon management must include the management of the above pathogens and parasites (See USGS fact sheets on Aeromonas salmonicida, Renibacterium salmoninarum, Myxobolus cerebralis, Novirhabdovirus sp., Heterosporosis sp., Piscirickettsia cf. salmonis, and Glugea hertwigi for information on Great Lakes impacts and management).

Physical
Aquaculture facilities manage wild and cultured Pacific salmon stocks through wild stock assessments and other methods. Managers are then able to make informed decisions on stocking strategies. Research, pathogen screening, and pathogen treatment, etc. is conducted in aquaculture facilities (See state and provincial DEC, MNR, DNR, and corresponding agency and department websites for information on salmonid aquaculture and state hatcheries).

Chemical
Chemical controls for Pacific salmon are not intended to eradicate or kill the species but rather to protect it against infectious disease. Typically, depending on the target species, chemicals controls are only effective in aquaculture or similar systems. Examples of chemicals used and include cefuroxime, chlorination, and disinfectants.

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

Voucher specimens: Montana (USNM 104701).