Species of Concern
Shortjaw Cisco Status Assessment
Below is the Executive Summary and Abstract, click here for a PDF of the complete 81-page shortjaw cisco status assessment (1.26MB)
Status of the shortjaw cisco (Coregonus zenithicus)in Lake Superior
Final Report to the Species-at-Risk Program
The shortjaw cisco (Coregonus zenithicus) is a widespread species in the salmonid subfamily, Coregoninae. Originally described from Lake Superior at Duluth, Minnesota by Jordan and Evermann in 1909, it was subsequently discovered in most of the Laurentian Great Lakes and many smaller lakes in central North America. Mature adults generally approach 300 g in mass, and exceptionally large fish can reach 1.0 kg. The biology is best known in the Great Lakes (including Lake Nipigon) where the species was once a major component of thriving commercial fishery, occupying depths between 40-200 m.
The shortjaw cisco was once a common chub species in Lakes Huron, Michigan, and Superior, but populations were extirpated in Lakes Erie, Huron and Michigan and greatly reduced in Lake Superior as a result of commercial overharvest. Shortjaw ciscoes have a widespread distribution throughout central Canada and have been reported from at least 22 lakes in Canada extending from Ontario to the Northwest Territories. The species was last verified in Lake Erie prior to 1970, in Lake Michigan in 1975, Lake Huron in 1982, and was never reported from Lake Ontario. In 2004, and again in 2005, a few individuals were identified from commercial catches in Georgian Bay, Lake Huron, but it is not known if these represent remnant stocks or migrants from Lake Superior (N. Mandrak and T.N. Todd, pers. Commun.). At the present time in the United States, viable populations of shortjaw ciscoes may exist only in Lake Superior and while they were once the dominant chub species there, they are now the rarest member of the chub assemblage. Small populations of uncertain status also occur in a few small lakes on the U.S.and Canadian border.
No protection is provided for shortjaw cisco populations in the United States, nor has there been any attempt to regulate the chub (deepwater ciscoes) fishery or to manage and recover the stocks. In Canada, the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) listed shortjaw ciscoes as Threatened, but no specific protection has been provided for the shortjaw cisco in Canada except for general protection afforded through the Fisheries Act.
Population Sizes and Trends
Shortjaw ciscoes have been an important part of the food fishery in the Great Lakes since at least the mid-1800s. Landing records, on the whole, were not recorded by species, but were lumped into a general category, “chubs”, for all the deepwater cisco species that excluded the shallow-water lake herring. In Lake Superior, shortjaw cisco was the dominant chub species and was the target of a commercial chub fishery that thrived from the late 1800s through the mid-1970s. In 1921 Koelz found that shortjaw cisco represented 90% of the chub assemblage but even as late as 1953, shortjaw cisco was numerically the most common chub species in most areas of Lake Superior and were especially abundant in the eastern half of the Lake. Research assessment monitoring showed that populations declined precipitously in the 1960s and 1970s during the most intensive period of commercial harvest in the Lake’s chub fishery history. By the early 1980s the fishery collapsed, and since the early 1970s bloaters have been the dominant chub species in Lake Superior. Today, the shortjaw cisco represents less than 1% of the chub assemblage of Lake Superior.
The species still persists in Lake Superior, but has declined in relative abundance from nearly 90% of the chub catch in the 1920s to about 50% of the catch in the early 1950s to about 25 % of the catch in the late 1950s, to 6-11 % in Michigan waters in the 1970s. Two small collections made in Michigan waters in 1997 revealed abundances of 5 % and 11 %, in the same range as the 1970s. In 1999-2001, USGS resampled areas sampled by Koelz in 1920-1921 and found that shortjaw cisco abundance had declined from greater than 90% to less than 1%. Similar comparisons of assessment sampling conducted by Smith in 1953 with assessment sampling conducted by USGS in 1999-2003 showed that abundances declined from >50% of the catch to <4% of the catch.
In Lake Superior, shortjaw cisco have been found to occur in waters of 40 to 200 m in depth, however, recent assessment data show that peak densities occur at depths of 80-160 m. In comparison to other chubs, the depth distribution of shortjaw cisco overlaps considerably with bloater (40-160 m) and kiyi (80-200 m).
In Lake Superior, spawning occurs in either the spring or the fall. Fecundity of shortjaw cisco is likely similar to that of other deepwater species such as the bloater, ranging from 3,230 eggs for a fish 241 mm total length.
As in most fish species, shortjaw cisco grow quickly in their first year of life. While the sexes have been found to have similar growth in length, females grew faster in weight than the males. In Lake Superior, maturity occurs in about the fifth year, compared to the third or fourth year for lake herring. Like most coregonines, shortjaw cisco are opportunistic, particulate feeders that generally ingest prey one item at a time. Because shortjaw cisco live in deepwater habitat, limnetic crustacea (copepods and cladocerans) and benthic organisms (Mysis and Diporeia) are the most common items they are likely to encounter.
While commercial over-harvest is the most important factor known to be responsible for the decline of the shortjaw cisco and other chub species in the Great Lakes, other factors contributed or now may be deterring the recovery of stocks. In Lake Erie, profound ecological changes occurred that shifted the lake environment to a more mesotrophic condition, and while the physical conditions of Lakes Michigan and Huron have not changed as dramatically over the past 100 years (with the notable exception of Saginaw Bay), the biological community has become considerably altered by the introduction of many exotic species across several trophic levels. Reproductive capability of shortjaw cisco stocks were compromised in the early 1900s when the commercial fisheries targeted the larger individuals at first, and as densities of large fish dwindled, mesh sizes were periodically reduced to target smaller and smaller individuals as a means of maintaining catch levels. Introduced rainbow smelt and sea lamprey populations in Lake Superior peaked well after the start of the decline of shortjaw cisco stocks but their late arrival and continued increases after the decline indicate they may have an impact impeding recovery of shortjaw cisco by imposing unnatural sources of competition and predation. Rainbow smelt compete for food resources and larger individuals prey on larval coregonids; sea lamprey predation continues to take a toll not only on larger species such as lake trout, burbot, and lake whitefish, but also smaller species such as chubs and lake herring. Abiotic factors such as weather and thermal changes (e.g., those associated with global warming) in the lakes have also been suspected to play a role in population destabilization.
Special Significance of the Species
The shortjaw cisco along with the lake herring, appear to be the ancestral colonizing species for most of the post-glacial distribution region of the Mississippi Refugium. Within the Great Lakes, the shortjaw cisco represented one lineage in the most spectacular radiation of sympatric forms in northern lakes. It is a unique form with a distribution that is intimately tied with post-glacial hydrology, and is thus of great scientific interest. Food fisheries in the Great Lakes, especially included this species as part of a highly desirable and commercialized smoked chub market, but it was not considered more desirable than other cisco species of its same size and condition.
The absence of Coregonus zenithicus from Lakes Michigan (since 1975), Huron (since 1982, see earlier note about 2004 and 2005 occurrence), and Erie (since 1957) supports a conclusion that the species has been extirpated in these lakes. The decline of the species in Lake Superior during the 20th Century, coupled with its extirpation in the lower Great Lakes, should be viewed with alarm. The species is vulnerable to excessive food harvest, habitat degradation, and impact by introduced exotic species throughout its range. Low numbers of shortjaw cisco remain in Lake Superior, which suggests that the potential for recovery is good. However, recovery is unlikely to occur or to be sustained if protection is not afforded. Population levels of shortjaw cisco and other chubs should be monitored systematically throughout Lake Superior to determine population trends and population structure. Other studies focused on determining life history and identification of specific stocks (e.g., fall and spring spawning stocks) should be fully supported to provide information critical to development of recovery and management actions. The ultimate goal should be to fully recover shortjaw cisco stocks so that a well managed and valuable fishery can be supported indefinitely.
The shortjaw cisco (Coregonus zenithicus) was once a common chub species in Lakes Huron, Michigan, and Superior, but populations were extirpated in Lakes Huron and Michigan and greatly reduced in Lake Superior largely as a result of commercial overharvest. We previously reported on a study conducted during 1999-2001 in Lake Superior, where we evaluated shortjaw cisco abundance in five areas in the U.S. waters of Lake Superior, and compared our results with a similar assessment conducted by W. Koelz in those areas in 1921-1922. Koelz found that shortjaw cisco was the dominant chub species at all of his survey locations in the 1920s. During 1999-2001, shortjaw cisco were present in four of the areas sampled but abundances were not significantly different from zero. To follow up that study, we proposed searching for historic capture records of shortjaw cisco that could potentially detail the rapid decline of the commercial chub fishery in the 1970s. We were successful in finding several sources of capture data and were also able to incorporate additional nearshore and deepwater trawl survey data collected by us in 2001-2003. The oldest historical dataset discovered was that from the 1953 survey of Lake Superior conducted by Stanford Smith, et al. They found that like Koelz, shortjaw cisco were widespread, abundant, and the dominant chub species of the lake. Their surveys provide invaluable baseline information on distribution and densities of shortjaw cisco, habitat associations, and gear catch efficiencies. Records from the years following the establishment of the Lake Superior Biological Station in 1957 also proved to be an invaluable resource. Small mesh gillnet surveys conducted in the Apostle Islands between 1958 and 1973 showed the abundance of shortjaw cisco plummeted in the early 1960s and were essentially at zero by 1970. Small mesh gillnet assessments conducted in Isle Royale between 1958 and 1992 showed a similar pattern to that in the Apostle Islands; however, shortjaw populations declined rapidly in the late 1960s and reached near zero levels by 1980. Records of the commercial catch of deepwater chubs in Lake Superior showed a period of increased yield between the late 1950s and 1980 and then abruptly dropped to low levels by 1990. Most of the residual catch of chubs after 1980 probably represents harvest of bloater chubs. The intense fishing pressure that occurred during 1958-1980 closely tracks the rapid depletion of shortjaw cisco in Lake Superior and supports previous assertions that population declines were the result of overfishing. Recent deepwater surveys in 2001-2003 show that shortjaw ciscos are still widely distributed in Lake Superior but at very low densities. The greatest frequency and densities were found in eastern Lake Superior and only a few specimens were taken in the western half of the lake.
The widespread, but low numbers of shortjaw cisco found in recent years suggests that recovery may yet be possible, but management strategies should be adopted to ensure that recovery. Population monitoring should continue to assess population trends and to evaluate success of recovery efforts.
Above is the Executive Summary and Abstract, click here for a PDF of the complete 81-page shortjaw cisco status assessment (1.26MB)