Grass pickerel (Esox americanus vermiculatus) COSEWIC assessment and status report: chapter 9

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Population sizes and trends

• Quebec
• Ontario

Some authors writing about conditions in the habitats farther south suggest that, compared to earlier accounts, it is possible that population sizes and territory occupied are diminished (Ming 1968). A problem involved in such time-period comparisons is that, in the past, this form was poorly known and often mistaken for the young of larger esocids.

Trautman (1981) indicated a decline in populations in Ohio in the period starting before 1901 to 1921. However, his distribution map included populations not known previously in the period 1922-1955. There were a smaller number of such populations noted for 1955-1980. It is difficult to be certain whether these data represent shifts in population numbers or intensification of collecting effort.

Since 1970, the species has been collected in several new locations in Canada, and repeat sampling at some sites suggests that the populations there are as strong as they were previously. At a few locations there appears to be a decline in numbers (see below).

Quebec

Although there is a 1985 record extending the range a short distance downstream in Lake St-Louis, the grass pickerel appears to be very rare and declining in Quebec (Dumount pers. comm.). Extensive sampling in Lake St-Louis from 1988 to 2003 (100 seine hauls around Île Perrot and the Archipelago of Îles de la Paix in 1988-1989; 57 gill net sets in 1988-1990; 46 seine stations and 78 gill net stations in 1997, 50 seine hauls around Îles de la Paix and Dowker Island in 2003) yielded only a single specimen in 1988.

Sampling effort in Lake St-François (46 stations in 1968 in deep water, 43 seine net stations and 73 gill net stations in 1996) yielded no grass pickerel.

Ontario

The species is extant at several locations (Jones Creek, Niagara River tributaries, Point Pelee) that have been sampled repetitively on several occasions. Collecting at some Ontario sites suggests population sizes are rather large for the nature of the habitat. For example, 58 specimens (30-220 mm TL [total length]) were captured in a pond on Long Point in 1973 (Royal Ontario Museum [ROM] 28989), and 99 adult specimens (120-216 mm TL) were captured in a seine haul in a small creek on the Niagara Peninsula in 1982 (ROM 43510) and 101 in 2003 (Yagi 2004). Apparently new, or previously unknown, populations were reported recently in drains of the Welland River, Maxwell Creek, Sydenham River, and the upper waters of the Gananoque River system (St. Lawrence River).

Unlike the Quebec situation, effort farther upstream in Lake St. Francis on the Ontario side was successful in capturing a single specimen in 1994 in Cooper’s marsh (ROM 69378).

The majority of records from Jones Creek, the St. Lawrence River and eastern end of Lake Ontario occurred prior to 1984. This is likely the reflection of more intensive sampling by individuals such as G.C. Toner and E.J. Crossman between 1934 and 1960. Grass pickerel have also been captured in more recent and less intensive sampling programs. It is likely that the species is stable here.

Note: In 1979 there were no grass pickerel caught in 9 sample stations on the Upper Niagara tributaries. In 2003 all of the 1979 stations were re-sampled as closely as possible to the 1979 sites and grass pickerel represented 3.88% of the total catch (n = 72 of 1854 fish) in those stations. Tables table1 and table2 after Radford (2003).

Yagi (2004) described the situation in the Niagara peninsula as follows (see also Table 3): “Consistent and repeatable fish community station data for our inland tributaries for the purposes of trend through time analysis is not readily available. For example, our best comprehensive study is a one time sampling effort in 1979 of the Upper Niagara tributaries, which has been repeated in its entirety for the first time in 2003. Relying solely on this information to establish a fish community trend is dangerous at best, as the water quality, habitat, watershed land use, invasive species presence and even weather conditions can account for a significant amount of the variation between these years”.

Pre-1979 sampling of the Upper Niagara tributaries shows Miller Creek with an abundance of grass pickerel in one location. In 1979 there were no grass pickerel caught in 9 sample stations on the Upper Niagara tributaries. No standardized fish sampling was completed on those stations in the years following except for Usshers Creek in 1999. In 2003 all of the 1979 stations were re-sampled as closely as possible to the 1979 sites and grass pickerel represented 3.88% of the total catch (n = 1854 fish) in those stations” (see Tables 1, 2).

The data in Table 1 suggests that grass pickerel have not declined in the upper Niagara River tributaries and may actually have increased (although note caution in interpreting this data, above and Table 3). Since there is little historical data available for the Welland River tributaries, it is not possible to determine trends there.

The species was known to occur in tributaries of the lower Grand River around Dunnville in 1949-1959. In 2001-2003, nearly every drain that could be shocked in the Dunnville area was electrofished by the Grand River Conservation Authority. During this sampling several juvenile individuals of Esox were captured in two drains. These were identified as northern pike (K. Killins, Grand River Conservation Authority; Cambridge, Ontario, personal communication). This evidence suggests that there has been a decline of grass pickerel in the lower Grand River.

In upper Twenty Mile Creek (western Lake Ontario), where grass pickerel occurred in the 1990s, intensive collecting in 2003 yielded much fewer grass pickerel. The habitat appeared changed as a result of bridge repairs (N. Mandrak, Department of Fisheries and Oceans, Burlington, Ontario; personal communication).

At Point Pelee, the grass pickerel continues to show up in low numbers in surveys since the capture of 21 specimens in 1949. In 1997, 6 individuals were captured in 5 of 15 collections (Royal Ontario Museum (ROM), unpublished data) and, in 2002, 9 individuals were captured in 3 of 117 collections (H. Surette, University of Guelph, Guelph, Ontario; personal communication). Differences in the higher frequency of capture in the 1997 survey may be caused by differing techniques (primarily electrofishing in 1997 vs. primarily trap netting and seining in 2002). But it may also reflect a declining population of grass pickerel in Point Pelee. 

In Lake St. Clair, recent surveys by ROM and the Walpole Island First Nation documented many captures of the species in marshes at the northern end of the lake. In 1999, 80 specimens were captured at 23 of 91 sites; in 2001, 43 specimenswere captured at 8 of 10 sites; and, in 2002, 5 specimens were captured at 2 of 5 sites. The species was particularly abundant in diked marshes (ROM, unpublished data).

The population in the Old Ausable Channel appears to be stable. In 1997, 4 specimens were captured at 4 sites, and in 2003, 8 specimens were captured at 7 sites.

The status of the Severn River population is uncertain but the species is rare there. In 1987, 20 specimens were caught and live-released by the Ministry of Natural Resources in the South Kahshe River. In 1988, 2 specimens were captured in Kahshe Lake (G. Arnett, Ministry of Natural Resources, Bracebridge, Ontario; personal communication). In 2001, walleye index-netting surveys in Kahshe Lake captured no grass pickerel (Bob Bergmann, Ministry of Natural Resources, Bracebridge, Ontario; personal communication). It could not be easily determined if the randomly located sample sites were in suitable grass pickerel habitat (i.e. shallow heavily vegetated). There is no evidence of recent surveys in Sparrow Lake (B. Allen, Ministry of Natural Resources, personal communication).