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COSEWIC Assessment and Update Status Report on the Deepwater Sculpin (Western and Great Lakes-Western St. Lawrence Populations) in Canada

Population Sizes and Trends

Inland Lakes

Most locations where deepwater sculpin are found have not been sampled extensively or sequentially and, as a result, it is difficult to estimate population sizes and trends of deepwater sculpin. Therefore, population data on deepwater sculpin throughout their range (including the distinct lineages present in both Upper Waterton and Fairbank lakes) are mostly limited to presence/absence data that must be interpreted with caution. In the 2004 survey of deepwater sculpin across inland lakes in Canada, search effort and methods were designed to specifically target deepwater sculpin (T. Sheldon, unpubl. data). Previous sampling efforts relied largely on trawling (Dadswell 1972), with varying degrees of success.

Collapsible, square minnow traps were designed to lie flat on the lake bottom, resulting in a larger catch area along the very bottom of lakes. Fifteen to thirty minnow traps were baited with dog food and cyalume sticks, and set in each lake for a minimum duration of 12 hours. In addition, a 1.0 cm stretched mesh gillnet was set for 12 hours and a minimum of two bottom trawls of ten minutes in duration were also conducted on each lake, weather permitting. All sampling was conducted in the deeper regions of each lake. Table 2 summarizes the lake-by-lake sampling effort and the number of deepwater sculpin captured in each location.

Of the lakes sampled in 2004, deepwater sculpin were found in 16 of 23 lakes where they were previously reported (Table 2, Fig. 9). They were not found in seven lakes where they were previously found, and found in four lakes where they were not previously reported (Table 2, Fig. 9).

Thirty lakes where deepwater sculpin have been reported, but not sampled in 2004, have only been sampled incidentally and the current status of populations in these lakes are unknown.

Great Lakes

Estimates of population size are not available for the Great Lakes; however, fairly intensive long-term index sampling programs provide quite good measures of relative abundance.

Lake Superior

Deepwater sculpin biomass for American and Canadian waters, as determined by fairly long-term indexing programs (Fig. 7, Table 4), indicates quite low densities and some minor decline over time, particularly in the longer data sets from American waters (Bronte et al. 2003). They considered that deepwater sculpin indices were likely not indicative of actual densities and trends, as depths covered by the index sampling programs reach only the shallowest portions of their depth distribution. Nevertheless, deepwater sculpin appear to be present, fairly widely distributed, and are caught consistently, albeit at quite low densities. There is evidence that they are slightly more abundant in Canadian waters, although this indexing program is quite short (11 years).

Figure 7: Indices of Abundance of Deepwater Sculpin in the Upper Great Lakes for a Three-decade Period from the 1970s to the 2000s

Figure 7: Indices of abundance of deepwater sculpin in the upperGreat Lakesfor a three-decade period from the 1970s to the 2000s.

Indices are not continuous but are just measures of abundance for the particular periods indicated; data sets are of varying lengths. Illustration of data presented in Table 4.

Lake Michigan

Deepwater sculpin appear to be much more abundant (Fig. 7, Table 4) in Lake Michigan than in any of the other Great Lakes. In an indexing program from 1973 to 2004, deepwater sculpin increased in abundance, reaching a peak in the 1980s (1983-87) (Madenjian et al. 2002), declining to a lower, but relatively uniform, level from 1989 to 1995 and slightly increasing until 2002.


Table 4: Indices of Abundance for the Deepwater Sculpin in the Upper Great Lakes
YearLake SuperiorLake Michigan
Lake Huron
U.S watersCanadian waters
1973    1.44 
1974    2.89 
1975    7.43 
1976    8.77 
1977    6.76 
19782.370.006  6.23 
19794.450.020  11.25 
19807.580.048  17.95 
19816.700.028  15.77 
19821.820.003  11.68 
19834.400.014  24.55 
19848.010.033  16.17 
19859.500.019  20.43 
19869.890.024  15.97 
19873.580.011  26.28 
19883.780.012  15.96 
19984.230.0138.060.021 3.4
2000    5.55 
2001    10.8950.1
2002    10.5630.4
2003    9.3146.1
2004    7.5363.1

For Lake Superior, numbers and biomass are indicated, separated by U.S. and Canadian waters. Biomass index is provided for Lake Michigan, and mean catch per 10-minute trawl tow is provided for Lake Huron. Lake Superior index is provided by Charles R. Bronte, U.S. Fish and Wildlife Service, New Franken, WI, and described in Bronte et al. 2003; Lake Michigan index is provided by Charles P. Madenjian, U.S. Geological Survey, Ann Arbot, MI, and described in Madenjian et al. 2002; Lake Huron index is provided by Jeff Schaeffer, USGS Great Lakes Science Center, Ann Arbor, MI.

Lake Huron

The results of a recent, relatively short-term, index-netting program for Lake Huron (Fig. 7, Table 4) indicated that deepwater sculpin were relatively widespread with 300 to 400 individuals caught per 10 minute trawl (J. Schaeffer, unpubl. data). In recent years (since 1999), catches appear to have declined and abundance may be reduced; the Lake Huron Fisheries Assessment Unit has not seen a sculpin in their assessment program since 1998 (Lloyd Mohr, Ontario Ministry of Natural Resources, personal communication 2006).

Lake Erie

Reports of deepwater sculpin in Lake Erie have been rare and have always been only larval individuals (young-of-the-year) (Roseman et al. 1998). Two specimens were incidentally caught in a larval fish sampling program in Ohio waters of western Lake Erie in 1995. The individuals were only 15 and 17 mm total length. While these young may have come from vessel ballast water or a reproducing population in Lake Erie, the fact that 21 similar-sized juveniles were collected upstream in the St. Clair River in 1990 indicates that their occurrence probably resulted from downstream transport from Lake Huron (Roseman et al. 1998). Indeed, the results of the index-netting program in Lake Huron suggests that in 1995 the upstream population was at record-high levels (Fig. 7, Table 4), providing additional support for the assumption that transport from Lake Huron was involved. It must be emphasized, however, that the reproductive status of the populations in Lake Erie is unclear as no adults have ever been observed in that lake.

Lake Ontario

The deepwater sculpin was once very abundant in the deep waters of the main basin of Lake Ontario (Dymond et al. 1929). In fact, they were so abundant in Lake Ontario that at one time, they were considered to be a nuisance for commercial lake trout gill net fisheries. The archived samples catalogued at the Royal Ontario Museum for the period 1926 to 1941 confirm their presence (Table 5, Fig. 8). However, they were not reported in southern Lake Ontario between 1943 and 1971, and Christie (1973) reported that the last specimens identified from northern Lake Ontario were taken in 1953. From 1953 to 1973, a few samples were brought in by commercial fishermen as a rarity, but three fish were also caught during an international deepwater trawling program in 1972 (Table 5, Fig. 8). Its rarity led Scott and Crossman (1973) to consider it to be extirpated. However, Crossman and Van Meter (1979) listed it as being present in 1972-75, probably because of the samples caught in 1972, although they noted that it was extremely rare and considered endangered. From that time until 1996, it was not reported, although very limited deepwater trawling was conducted. In 1996, one gravid female was caught in the outlet basin in a relatively shallow index trawling program. This individual signalled the reappearance of the species after a 25-year hiatus (Casselman and Scott 2003). Catching this single fish in a relatively shallow indexing program encouraged a targeted search in deep water that year. Limited targeted trawling in the 90-to-110-m depth range produced two more individuals (Table 5, Fig. 8).


Table 5: Deepwater Sculpin from Lake Ontario (N = 167) Archived and Catalogued at the Royal Ontario Museum (ROM), Originally Acquired by, and Archived at, the OMNR Glenora Fisheries Station from 1926 to 1996
YearDateVicinityLatitudeLongitudeNSampling SourceROM Catalogue No.
Gill netTrawlStomach
192629 Oct.Port Credit43o27’a79o27’a21 12753(1), 2754(1)
192701 JulyPort Credit43o28’a79o18’a1313  3792
192718 JulyPort Credit43o28’a79o17’a3939  3628
192729 Aug.Port Credit43o28’a79o17’a2626  3790B
192701 Oct.Port Credit43o28’a79o18’a3232  2669(1), 3790A(31)
1927 Port Credit43o28’a79o18’a392 3720113
192812 JulyMain Duck Island43o42’a76o38’a22  4876(1), 4877(1)
193018 Feb.Port Credit43o28’a79o18’a44  6795
1931 Bowmanville43o39’a78o40’a11  8125
194102 Sept.Niagara-on-the-Lake43o24’a79o05’a11  13321
195328 Aug.Salmon Point43o42’a77o14’a11  70625
196122 Aug.Point Traverse43o40’76o45’11  23129
196328 Aug.Salmon Point43o42’a77o14’a44  70626b
197221 JuneCobourg43o45’278o08’.62 2 70627
197208 Sept.Cobourg43o43’.078o06’.91 1 70627
199626 JuneOutlet basin44o02’.6376o51’.391 1 70628
199620 Sept.Point Traverse43o44’.6176o49’.961 1 70629
199626 Sept.Cobourg43o47’.0378o03’.671 1 70630
Total    171127638 

Year, date, and vicinity of capture are provided, along with sampling source, coordinates (either recorded or estimated), and ROM catalogue numbers. Samples from 1953, 1961, and 1963 were provided by Stanley Rankin, commercial fisherman, Salmon Point, Prince Edward County, Ontario. Unpublished data assembled by J.M. Casselman, Department of Biology, Queen’s University, Kingston, Ontario.

a Latitude and longitude estimated from headings and depth.
b Glenora acquisition numbers indicate that three specimens were received in 1963; however, sample contains four individuals.

Figure 8: The Distribution of Deepwater Sculpin in Lake Ontario Based on Specimens (N=167) Archived and Catalogued at the Royal Ontario Museum (ROM), Originally Acquired by, and Archived at, the OMNR Glenora Fisheries Station from 1926 to 1996

Figure 8: The distribution of deepwater sculpin in Lake Ontario based on specimens (N=167) archived and catalogued at the Royal Ontario Museum (ROM), originally acquired by, and archived at, the OMNR Glenora Fisheries Station from 1926 to 1996.

Samples archived at the ROM are indicated by closed circles showing approximate origin of sample and year, with number of samples in parentheses. Closed triangles are samples originally archived at the Glenora Fisheries Station, illustrated as above. Open star indicates recent reappearance in 1996 in routine trawl indexing (30 m); closed stars indicate two sculpin captured in targeted deepwater trawling conducted in 1996 (91 and 96 m). Unpublished data assembled by J.M. Casselman, Department of Biology, Queen’s University, Kingston, Ontario.

Figure 9: 2004 Survey Results for Deepwater Sculpin Compared to Historical Records

Figure 9: 2004 survey results for deepwater sculpin compared to historical records.

A deeper trawling program in American waters conducted by the United States Geological Survey (USGS) produced one sculpin in 1998 at 150 m in an alewife assessment program off Thirty-Mile Point in Lake Ontario (Owens et al. 2003). This deepwater sculpin, caught off the southwest shore, was the first sighting of this formerly abundant fish in American waters since 1942 (Stone 1947). Targeted sampling in deep water produced three more individuals in 1999 and one in 2000 (Owens et al. 2003). Regardless of these recent occurrences, many continue to regard the species to be extirpated from Lake Ontario (e.g., Eshenroder and Krueger 2002). However, this is not the case. In fact, a single individual was caught in 2004, and 13 were caught in routine USGS alewife and mid-lake assessment trawling programs in 2005.

Since the recent reappearance of three fish in Lake Ontario in 1996, a total of 19 individuals have been collected. It could be argued that these appearances are related to increased trawling effort. However, this was not the case for the first individual collected in 1996, since it was caught in the eastern basin in a routine trawling program that had been begun in the early 1960s. The appearance of this individual was interpreted to reflect an increase in abundance of deepwater sculpins in deep water, so a target program that trawled deep water (90-110 m) was initiated immediately and two more individuals were caught. By contrast, fairly deep trawling in the eastern basin in the 60-m depth range in the early 1990s, as part of a juvenile lake trout indexing program, did not produce any deepwater sculpin (J. Casselman, unpubl. data). In fact, the recent appearance in 1996 and 1998 came from individuals of the 1994 and 1995 year-classes (Casselman and Scott 2003). Casselman et al. (1999) suggested that during the early 1990s, there was a substantial shift in the open-water fish community, at least in Lake Ontario. The reappearance of deepwater sculpin was one of a whole set of population and community changes.

It is apparent that deepwater sculpin are not extirpated from Lake Ontario. Their presence, albeit in very low numbers, through the 1950s, 1960s, 1970s and, most recently, the 1990s, suggests that the present resurgence is due to increased reproductive success by a remnant population rather than to colonization by juveniles drifting from Lake Huron or ballast water transfer of larval individuals from the upper Great Lakes. Downstream transport of larvae, which probably explains the appearance of larvae in western Lake Erie in 1995, probably does not explain their presence in Lake Ontario, although Roseman et al. (1998) speculated that this could also be a plausible explanation for their occurrence in Lake Ontario.

The few individuals that are found in Lake Ontario are large and in appropriate habitat. Decreased deep-water fishing effort in the 1980s and early 1990s may have led to an assumption of extirpation. Nevertheless, they are present, albeit in very low numbers. Although they are very rare, mature, gravid individuals are present and seem to be increasing in abundance, particularly in 2005 sampling in U.S. waters (13 individuals). A number of year-classes have been identified through age assessment, and very recently, in 2005, small individuals have been caught quite frequently in U.S. waters. Although continuous colonization cannot be conclusively ruled out, the appearance of gravid females, small young fish, and the increased appearance of recent year-classes provides strong circumstantial evidence that abundance is increasing and successful reproduction is occurring.

Rescue Effect

The potential of a healthy population of deepwater sculpin returning to Canadian waters within lakes that occur on both sides of the Canada-U.S. border is high should the Canadian population become extirpated and the American population persist; however, conditions affecting the species on one side of the border may also affect it on the other side, thus diminishing this potential. Furthermore, there is virtually no potential of immigration or introduction of deepwater sculpin into inland lakes should these populations become extirpated.