March 2006

Changes in the Turtle Lake ecosystem from seventies to 2005

Brian Jackson, Area Biologist

To whomever chances upon and reads this, this is a number of interesting observations about the Turtle Lake ecosystem, some quantifiable and some not.

Background

Turtle Lake is part of the Turtle/Crowrock/Dashwa chain of lakes. These lakes have a combined area of 4100 ha and are separated by relatively wide channels that are easily passable by boats. They are located approximately 25 km northwest of Atikokan and are accessible by four public boat launch sites (1 on Dashwa, 3 on Turtle Lake) from Hwy. 622. Lake surveys were completed on the lakes around 1968 and the lakes were found to be relatively unproductive (MEI value of 1.5 – 2.7) with moderate water clarity (secchi depth of 3.2 – 3.7 m (10.5 – 12’)) and fairly deep (average depths of 7.4 – 13.5 m (24-45’)) (Table 1). The lakes are classed as oligotrophic (or unproductive) lakes.

Table 1. Selected limnological characteristics of Turtle Lake and Crowrock Lake.

Lake Characteristics	Turtle Lake	Crowrock Lake
Surface Area (ha.)	1153	1820
MEI	2.6	2.7
Average Depth (m)	7.8	7.4
Maximum Depth (m)	20.1	50.3
Secchi Depth (m)	3.2	3.5
T.D.S. (mg/L)	20.3	31.8
Growing Degree Days >5^oC (GDD>5^oC)	1500	1475

The original large fish community was made up of lake trout, northern pike, whitefish, burbot , white sucker and various cyprinids and other small fish.

Observations of ecosystem changes through time

70’s

- Smallmouth bass were introduced into the system sometime in the late seventies/early eighties and had become well established throughout all three lakes by the mid/late eighties.

- Cottaging started on the lake in the early eighties with 45 lots being developed. Some of these have gradually turned into permanent residences over time.

80’s

- terns arrived on the lake some time in the mid eighties (some question about exactly when they arrived but most people seem to agree that it was after the cottagers and the bass). Establish colony on rock island west of Turtle Narrows.

- Walleye were introduced into the system by adult transfer in 1987. Established themselves initially at the north end of Crowrock Lake.

90’s

- (getting into the period that people tend to have better memories of what happened and what conditions were like and some actual data)

- cottagers and regular lake users generally characterize the inshore community as dominated by smallmouth bass with lots of small fish (shiners, perch etc) present. General reports of good bass fishing in Turtle Lake and reports of bass splashing and chasing minnows every evening in Turtle Narrows are common. Bass tournament moved from Nym Lake to Turtle/Crowrock/Dashwa system in 1994 with high catches of smaller sized bass recorded (annual data collection of tournament data from 1994 to present, summarized in 2000 report)

- The lakes were closed to walleye angling in 1992 to allow the fish to establish a population able to sustain angling harvest. Beginning in the early nineties, anglers reported consistently catching walleye from the north end of Crowrock Lake (at the mouth of the Little Turtle and Gamble R.) but only occasional catches throughout the rest of Crowrock, Turtle and Dashwa Lake. Between 1997 and 2000, walleye fry were introduced into Turtle Lake by the Atikokan Sportsmen’s Conservation Club (total number of approximately 6 million walleye fry).

- Walleye were rare in Turtle Lake (none caught in 1995 netting and just starting to show up (0.4 walleye/trap net) in 2000) although numbers were increasing significantly in Crowrock Lake through this period. (Data summarized in 2 reports).

- Tern colony very active with ~50+ birds (no actual numbers and guesses generally vary from 50 on up).

2000’s

- Between May and September of 2000, an aerial survey was conducted over the Atikokan area on a weekly basis to record angler activity. The estimated angling effort from these counts is 5.56 angler hrs/ha for Turtle Lake, 3.29 hrs/ha for Crowrock Lake and 2.39 hrs/ha for Dashwa Lake (i.e. moderate to low effort associated primarily with bass fishing).

- Walleye numbers increase dramatically in Turtle early in decade. Good numbers of small walleye were caught in 2000 SPIN netting in Turtle Lake.

- Walleye season opened in system in 2001 and fishing is excellent for larger than average walleye for first couple of years, especially in Turtle Narrows area.

- Walleye angling declines, both in terms of size and numbers. Decline is probably due to a combination of increased angling pressure (lake had been closed to walleye angling until 2000) and normal population cycling following introduction.

- Bass anglers begin to report fewer bass caught. Tournament angling success appears to be declining between 2001-2003 and 2004-2005.

- Data from the Atikokan bass tournament suggest that condition of smallmouth bass from the system (i.e. weight of a 30 cm bass) has declined in recent years. Declines in condition could be related to reductions in prey supply (less food available for growth) or increases in competition for food.

- Cottagers report seeing much fewer small fish around their docks (shiners, perch etc.). They also report seeing less surface feeding activity by smallmouth bass in areas like Turtle Narrows in the evenings.

- The terns abandon colony site on Turtle around 2004. There is no known new colony established nearby (i.e. they are not known to just have moved to the next lake over) although there may be increases to individual tern nesting sites in the general area (i.e. there may have been more terns nesting as pairs on Lower Marmion Lake 25km to the southeast).

Completely hypothetical, untested hypothesis:

Loss of tern colony may be related to the increase in walleye numbers which caused a decline in the food source for the terns (i.e. small fish in shallow water). Whether this is a long term decline in small fish numbers due to “too many” predators in the littoral zone of the lake (introduced walleye, introduced bass and native pike) or a short term decline due to walleye numbers exceeding resources capability remains to be seen. Interestingly, large numbers of small fish were found in the shallows of the lake with high numbers of smallmouth bass (eighties and nineties) even though they have been found to cause declines in minnow abundance when smallmouth bass are present with rock bass in large numbers (Vander Zanden et al, 1999). In fact, the tern colony established itself after the introduction of bass and the decline in small fish numbers and loss of the colony did not appear to occur until after the establishment of a walleye population. There is a possibility that YOY bass may have been an additional prey item for terns.

Of course there are lots of unknowns that may also account for loss of the tern colony. In hindsight, this would have been an excellent study site for monitoring changes in fish community species/abundance following changes in introduced species. Consideration should be given to monitoring fish communities and other species dependent on fish when changes in predator fish species are planned or known to occur (such as walleye or bass introductions).