The Damsa Chronicles 4: New Technology Advances...

The Damsa Chronicles 4: New Technology Advances - How Are These Exceptional Fisheries Created?

The exceptional brook trout fisheries created by Damsa were due, in part, to new technology developed for sexually altered trout. Protocols originally developed for salmonid aquaculture applications were applied to Lake Nipigon strain brook trout, the brook trout strain with the world record size genes. These techniques involved sexual manipulations of stock including monosexing and sterilizing brook trout to produce fish suitable for stocking that had certain desirable characteristics (see Donaldson 1996, Donaldson et al. 1991).

Trophy (5 lb+) Lake Nipigon strain brook trout grown in small Canadian Shield lakes in Northwestern Ontario. A - female offspring from sex reversed female parent, B - hormonally sterile, C - sex reversed female in fall spawning colours, D - female triploid, E,F - untreated

Damsa sterilized trout three different ways: physically removing their reproductive organs: gonadectomies (McLean 1991), heat shocking the eggs to create fish with three sets of chromosomes instead of two: triploidy (Ihssen et al. 1990) and exposing to steroids: hormonally (Parks and Parks 1991). "All female" brook trout stocks were created using the milt of "sex reversed males" (females treated with androgen to turn them into males) with eggs of untreated females (Donaldson et al. 1991. Some "all female" stock was developed using direct exposure to low levels of estrogen (Parks and Parks 1991). Sex reversed male stock was developed by exposing "all female" trout to low concentrations of androgen (Solar et al.1984).

Increased trophy size was hoped for and was a major consideration for utilizing sterile stocks in fishery development as there is field and aquaculture evidence to show that sterile trout can grow bigger than their sexually mature counterparts. The largest lake trout ever captured in the wild weighed in at 46.4 kg (102 pounds) and was sterile. And the new Ontario record rainbow trout caught in 2005 had failed to spawn in its nine-year life according to Jon George, OMNR, Thunder Bay. This fish weighed 40.7 pounds - less than 1.5 pounds from the world record. Sterile triploid rainbow trout have also grown to impressive sizes in other recreational fisheries.

With sterile fish, energy that would otherwise go into egg and sperm development and spawning activities per se could be redirected into increased growth. Our studies did not show that sterile brook trout consistently outgrew their counterparts, but that growth (and survival) was related to the chemical and biological quality of the trout's environment - and the form of sterility used. In some stockings the largest fish captured was sterile; in others they were not. All treated and untreated stocks had fish that grew in excess of five pounds, a trophy by almost any standard.

In general, there were more trophy sterile trout than untreated trout (age 5) in each lake - up to 42% (data not shown), but this does not necessarily reflect higher survival rates for sterile fish per se. Detailed studies by researchers at Cornell University show much higher numbers of trophy fish in waters where the outlet is blocked to prevent stocked trout from emigrating to spawn (Josephson et al. 2001, Josephson et al. 2002). At sexual maturity - typically two to three years for Nipigon strain trout - brook trout will attempt to spawn. Many sexually mature fertile fish that have been stocked in lakes with no suitable waters to spawn will emigrate at spawning times. Typically in our stocked waters it can be expected that the fish will head downstream to spawn as most stocked lakes are small headwaters with no inflowing streams of any consequence. During higher fall flows in spawning periods sexually mature trout will easily slip over the beaver dams but will be unable to return due to the beaver dam barrier.

As the vast majority of stocked lakes are subject to beaver activity, the loss of trophy brook trout may be considerable. From the literature it can be expected that about half of the sexually mature fish will emigrate but lake to lake variations can be large and one may expect that some lakes lose upwards of 90% of these fish (see Josephson et al. 2001). The studies at Cornell University were the first to show that the use of all female triploid brook trout can increase trophy fisheries in stocked lakes (Warrillow et al 1997).

Wayne Groom stands on top of the beaver dam at the outflow of Thunder Lake. With little flowage and high barriers, trout that emigrate to spawn will be unable to return to the lake.

Previously we showed higher yields in Damsa stocked waters in comparison to many government stocked lakes in the Thunder Bay district. Part of the explanation of why there can be much higher catch rates in Damsa waters comes from the use of winterkill lakes which have an intrinsically higher productivity - about twice that for the typical lake stocked by OMNR. Winterkill lakes are shallower than self sustaining trout lakes - other factors being equal - and shallower lakes produce more food for trout (Vezina 1978).

As the vast majority of stocked lakes are subject to beaver activity, the loss of trophy brook trout may be considerable. From the literature it can be expected that about half of the sexually mature fish will emigrate but lake to lake variations can be large and one may expect that some lakes lose upwards of 90% of these fish (see Josephson et al. 2001). The studies at Cornell University were the first to show that the use of all female triploid brook trout can increase trophy fisheries in stocked lakes (Warrillow et al 1997).

Shallower lakes result in higher yields - but also lower late winter dissolved oxygen levels that can be lethal to trout. Artificially aerating shallow waters will improve yields.

Previously we showed higher yields in Damsa stocked waters in comparison to many government stocked lakes in the Thunder Bay district. Part of the explanation of why there can be much higher catch rates in Damsa waters comes from the use of winterkill lakes which have an intrinsically higher productivity - about twice that for the typical lake stocked by OMNR. Winterkill lakes are shallower than self sustaining trout lakes - other factors being equal - and shallower lakes produce more food for trout (Vezina 1978).

With respect to trophy fisheries the technology utilized by Damsa has several ecological and biological advantages over that currently employed in many stocking programs. In addition to providing quality angling opportunities, the ability to determine fish sex has important ecological implications for fish stocking programs. Where these species are absent, monosex and sterile fish can be stocked without risk to the genetic integrity of the fish communities and minimal risk to ecosystems because they can not reproduce. Where these species or others with which they may hybridize are present, the addition of sterile fish can not dilute or alter the gene pool of existing stocks. It is partly for this reason there is a substantial interest and application of sexually manipulated salmonid stocks in recreational fisheries in British Columbia and Alaska. In British Columbia, all female triploid (sterile) brook trout are stocked in many inland lakes to minimize the potential for interbreeding with bull trout (T. Yesaki pers com). In waters that Damsa stocked, some lakes drained into Brule Creek, a popular brook trout stream for local anglers. These lakes were stocked with sterile or monosex brook and rainbow trout to ensure that the integrity of the native brook trout fishery was not put at risk.

The ability to limit potential effects of stocking nonnative strains to one life time can be an important consideration in ecosystems where other ecological effects may occur from stocking (Simon and Townsend 2003). In western North America for example, stocking with nonnative trout has revealed negative associations with amphibians including frogs and salamanders (Dunham et al. 2004). Moreover, stocked trout in many lakes have successfully reproduced (eg. Wiley 2003). Recovery of these lakes to pre stocking ecological conditions is extremely difficult, if not impossible without severe economic and ecological costs, thus, limiting management options for future lake ecology directions. Where/when the ecological liabilities of stocking trout outweigh the benefits, cessation of stocking sexually manipulated trout stops further adverse effects, as the trout would be eliminated from the aquatic community.

Sterile stock can live longer than their sexually mature counterparts, in part due to their better condition entering winter. High mortalities during winter to sexually mature trout in comparison to immature trout has been correlated with lower lipid levels in late fall (Hutchings et al. 1999). The spawning process depletes fat stores, making sexually mature fish more vulnerable to starvation and death. In our studies the longest-lived fish were sterile with a maximum age of 10+ years in comparison to untreated stock maximum of 7+ years.

Stocking certain lakes can result in stunted populations - a not infrequent occurrence in western North America lakes.

Stocking with sexually altered trout also prevents stunting of populations which is a situation also prevalent in many western North American lakes and streams where brook trout have been introduced. In some lakes, brook trout populations are dominated by 40 g (about 1.5 ounces) brook trout (Donald and Alger 1989). It is thought that too many high quality spawning areas in a given water body can lead to stunted populations. By preventing reproduction and adjusting stocking rates, larger trout can result.

Sterile/monosex brook trout can provide superb angling opportunities throughout the year. Because the fish do not spawn in the fall with their untreated counterparts, they are in better condition for fall angling (Photograph 1C). Sexually mature salmonids caught incidently during or after spawning periods are frequently in poor condition with eroded fins and males marked from fighting. Sterile trout can effectively extend the season for angling in comparison to natural populations where angling ends in early fall to protect spawning fish. For angling purposes, the fall can be a particularly satisfying time to be on the water. Brook trout readily come to the fly, annoying insects are fewer, and fall forest colours can be spectacular.

In addition to technology developed using sterile stock, other Damsa protocols can include stocking of bigger fish than current government protocols which also results in a higher return to angler. Trout stocked at lengths greater than 30 cm are much less vulnerable to predation by birds, particularly loons, a predator which can greatly impact trout survival in these lakes and by other brook trout, as brook trout are also known to be cannibalistic (Armstrong and Davis 1995).

Finally the technology utilized by Damsa may reduce the risk of mercury poisoning to fish - consuming wildlife - where such risks exist or are created. Threats of mercury poisoning to indigenous wildlife from aquatic organisms is receiving substantial national and international attention but there has been less focus on the role of government fish stocking programs and their potential to increase or decrease such risks. For example, the Ontario Government typically stocks more than 650 lakes annually (Steve Kerr, OMNR (about 80 in total in the Thunder Bay District with brook trout, some on alternate years).

Mercury accumulated in stocked brook trout may place wildlife at risk.

Results from the Ontario Sport Fish Monitoring Program for 75 locations in Ontario indicate, however, that mercury accumulates in many brook trout in Ontario waters to levels which exceed the Canadian Tissue Residue Guideline (CTRG) for the protection of mink (0.092 ppm) - by up to a factor of ten (Photograph 5). Brook trout also exceed the CTRG for otters (0.22 ppm) the common loon (0.172), and the red-breasted merganser (0.115 ppm). Apparently there is no data for Thunder Bay district lakes for stocked brook trout other than some limited sampling we carried out at the end of the study on some Damsa study lakes. Our results suggest that mercury will accumulate in brook trout stocked in accordance with current government stocking protocols to levels which exceed CTRG values for some wildlife (Parks 2005).

Exceeding CRTG values does not necessarily mean that wildlife populations are definitely adversely affected. But the risk for wildlife poisoning is substantially increased and further examinations of populations potentially at risk are clearly warranted, particularly as Environment Canada (2003) has noted that mercury exists in Canada at levels that are causing deleterious impacts on wildlife. Further, mercury levels in fish are high enough to put wildlife such as loons, kingfishers, herons, osprey and mink at risk of adverse health effects. As mercury levels in Ontario Fish are certainly amongst the highest in Canada and populations already at risk include: herons, loons, kingfisher, mergansers, otters (Kent et al. 1998, Scheuhammer 1998, Mierle 2000).

Lakes used for stocking brook trout frequently include acid stressed waters, as brook trout are amongst the most tolerant of fish to low pH conditions. Because of this tolerance, brook trout can be stocked where other sport fish fail to survive. Additionally, many waters in Ontario stocked with brook trout are highly coloured due to the presence of organic acids. Both these characteristics - increased colour and acidity favour higher levels of mercury in fish - other factors not withstanding.

Sexually mature stocked brook trout can be particularly prone to predation by mink and other large predators during spawning periods. As mentioned earlier, sexually mature trout will likely emigrate to small creeks to spawn when suitable spawning locations in the lake are lacking. Here the trout are very vulnerable. According to researchers at Cornell University, about 70% of these fish are lost per week to opportunistic predators such as mink and otters (D. Josephson pers. comm.). It is these larger brook trout that contain the most mercury. Based on the precautionary principle, governments may wish to evaluate the risks of their stocking programs to wildlife, as their stocking policies may unwittingly be contributing to adverse effects on wildlife.

Trout stocked at larger sizes would reduce risks of mercury poisoning as mercury concentrations in brook trout reared in aquaculture settings (Cassidy et al. 2003) are substantially less than for those fish typically grown in the wild (Guide to Eating Ontario Sport Fish 2005-2006). Damsa grew brook trout to trophy sizes in aquaculture settings that had mercury values ( < 0.04 ppm), well below those values that could pose risks to wildlife. Risks could also be reduced perhaps if sterile stock were utilized as these fish are not as vulnerable to predation during spawning periods and based on bioenergetic modelling considerations should accumulate less mercury than their sexually mature counterparts (Rodgers 1994).

While a number of advantages to using sexually altered trout for recreational fisheries have been identified here, it should be noted that sexual alterations do have physiological consequences to the resulting stocks, which can affect their growth, performance and survival. Triploid trout do not appear to do as well as untreated fish in some marginal habitats. Additionally some triploids have not appeared to have the same sport qualities as other triploids or their untreated counterparts. That said, in certain environments there is evidence that triploids can consistently outgrow their untreated counterparts. Clearly much research remains to clarify the optimum roles for sexually altered brook trout applications in recreational fisheries.

Finally it should be noted that these fisheries created by Damsa are designed to conform to the guiding principles of sustainable development as outlined in the "Strategic Plan for Ontario Fisheries - SPOF 11. As such, the fisheries are intended to meet OMNR's Statement of Environmental Values. In particular, the fisheries are not anticipated to compromise any future use of present waters used for stocking and in many cases the aquatic environment is improved.

The fisheries also utilize the ecosystem approach to resource management as outlined in the guiding principles for the Ministry of the Environment.


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Cassidy, M., A. Matu and G. Downing. 2003. Baseline risk study of potential chemical contaminants in Ontario farm-raised rainbow trout. Ontario Ministry of Agriculture and Food (OMAF), Food Safety Policy Branch, Guelph, Ontario

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Mierle, G., E.M. Addison, K.S. McDonald and D.G. Joachim. 2000. Mercury levels in tissues of Otters from Ontario, Canada:Variation with age , sex and location. Environmental Toxicology and Chemistry 19 (12):3044-3051

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Wiley, R.W. 2003. Planting trout in Wyoming high-wilderness waters. Fisheries 28(1):22-27

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