Carmine shiner (Notropis percobromus) recovery strategy: chapter 4

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3. Threats To The Survival Or Recovery Of The Species

3.1 Overview

Carmine shiners spawn in relatively warm, clear water and frequent shallow, flowing water with clean rocky substrates. They may be threatened by activities that alter the turbidity or flow of water. Flow impoundment, agricultural drainage that increases sediment loads, streambed gravel removal, and stream channelization are examples of activities that have been implicated in the decline or disappearance of the rosyface shiner within its distribution (Smith 1979; Trautman 1981; Humphries and Cashner 1994; Houston 1996). Increased bank erosion and consequent siltation probably have negative effects on eggs, fry, and food supply.  Shoreline alterations associated with cottage development might adversely affect these minnows. Incidental harvests by bait fish harvesters and species introductions also may be a concern.

3.2 Threats assessment

The Carmine Shiner Recovery Team undertook a detailed threats assessment for each waterbody where the species is known to occur. Four primary categories of threat were identified:

• overexploitation,
• species introductions,
• habitat loss/degradation, and
• pollution.

A brief description of the methods and assessment of threats to carmine shiner in each of these waterbodies is provided in Appendix A. The results are discussed below and summarized in Table 1.

3.2.1 Overexploitation

Carmine shiner could potentially be exploited as a bait fish.  Bait fisheries include both live and dead (frozen) bait operations.  All commercial bait fishing in Manitoba is regulated and requires an annual license from Manitoba Water Stewardship. Licensed commercial bait fishers may harvest fish for dead bait use from any Crown water within their allocated bait blocks, some of which may encompass areas where carmine shiners have been found.  Live bait harvest, on the other hand, can only occur within specific waters approved by Manitoba Water Stewardship. Most of the commercial bait fish harvest in southeastern Manitoba is directed at collecting live bait fishes (B. Scaife, MB Water Stewardship, pers. comm. 2004).

Generally, live bait harvest is directed at non-shiner species, which are hardier, have a higher survival rate, and frequent different habitats from shiners. While the use of live traps allows for sorting and release, carmine shiners are difficult for fishermen to identify and may be easily damaged by handling.  The Whitemouth, Bird and Winnipeg rivers are not approved for live bait fish harvest and as such, carmine shiners are not likely to be affected by such operations.

Dead (frozen) bait harvesting is of greater potential concern as shiners are generally the targeted species. The gear used for these harvests (e.g., seines) is more likely to kill or harm the bait fish than that used for live-capture, but these methods are seldom used in the medium to small stream habitats where carmine shiners are most often found (K.W. Stewart, pers. comm. 2004),  Although the harvest from specific waters is currently unknown, commercial bait fishermen with allocations in the Whitemouth and Bird rivers have not indicated any frozen production on their annual production report forms (B. Scaife, pers. comm. 2004).  Frozen production, however, is known to occur from some areas on the Winnipeg River.  Although unlikely, this could potentially include the Pinawa Channel where carmine shiners have recently been reported.

In addition to commercial bait fishing, licensed anglers may harvest bait fish for their own use from any Crown water including live bait where it is permitted.  Live bait, however, may not be transported away from the waters in which it was caught.

Table 1. Carmine shiner threats assessment summary by location.

The potential for incidental harvest of carmine shiners by bait fishing operations does exist, particularly for frozen production but this is not believed to represent a significant threat to the species at this time (Table 1).  The focus of the existing fishery on live bait operations which are not permitted in areas where carmine shiner occur and the logistical constraints of fishing for frozen production from carmine shiner habitats are likely to limit the potential interaction between bait harvesters and carmine shiners.  Although some frozen bait production may occur in the Winnipeg River, carmine shiner are only know to occur within the Pinawa Channel where any collection would be difficult.  Notwithstanding, monitoring and research are recommended to verify this analysis and to examine measures that might further mitigate any potential effects.   Public education is also necessary to ensure that commercial fishermen and anglers know where carmine shiners may occur, how to identify them, and how to reduce the potential for incidental harvest.   In addition, further management actions could be directed as necessary at reducing any potential impacts associated with the bait fishery.

3.2.2 Species Introductions

Species introductions could pose a threat to carmine shiner populations through predation, competition and food chain disruption. They might also carry diseases and parasites that are new to carmine shiner populations and could adversely affect them. The significance of this threat is likely moderate in the Whitemouth River and unknown elsewhere. The potential for mitigating the impacts of species introductions once they occur is likely low (Table 1).

Potential sources of introductions include: interbasin water transfers, possibly associated with hydrostatic pipeline testing; as live bait used by anglers; and through the stocking of game fishes.  The import of live bait into Canada is illegal and requires strict enforcement by Canada Customs. Walleye (Sander vitreus) have been stocked in Whitemouth Lake since 1960, and brook trout (Salvelinus fontinalis) were stocked there in 1961-62 (D. Leroux, MB Conservation, pers. comm. 2005; see also http://www.gov.mb.ca/conservation/fish/). The Birch River has been stocked with rainbow trout (Oncorhynchus mykiss), brook trout, brown trout (Salmo trutta), and walleye, with poor survival (Clarke 1998). Brown trout have been stocked in the Pinawa Channel. Smallmouth bass and rainbow smelt (Osmerus mordax) have been introduced to the Winnipeg River system. The effects of these piscivores on carmine shiner populations are unknown, although elsewhere smallmouth bass and carmine shiners do coexist. The potential for transfer of species from the Lake of the Woods watershed via overland drainage exists but is presently unlikely given the prevalence of beaver dams and bogs that separate the respective watersheds.

3.2.3  Habitat Loss/Degradation

Habitat loss and/or degradation associated with flow regulation, channelization, shoreline development, landscape changes and climate change is likely in some reaches of the rivers inhabited by carmine shiners, and may pose a threat to the species. At present, it is probably the most significant threat to survival of the carmine shiners, but it is difficult to assess given the uncertainties in the species’ distribution and habitat requirements. The potential for mitigation varies with the type of threat and the affected waterbody (Table 1).

Flow alteration 

Because carmine shiners frequent shallow riffles with clear water in summer, flow alterations that affect these conditions may pose a threat to their existence. Hydroelectric development has altered flow in the Winnipeg River. Development on the river mainstem began in 1909 at Pointe du Bois, and ended in 1955 with the completion of the station at McArthur Falls (http://www.hydro.mb.ca). These stations are still in operation and are unlikely to be removed in the foreseeable future. Another station on the Pinawa Channel was completed in 1906. It was retired in 1951 and has been partially razed. These developments impounded reaches of the river creating forebays, flooding vegetation, and eliminating rapids. Whether these changes increased turbidity and decreased riffle habitat sufficiently to cause a decline in the abundance of carmine shiners in the system is unknown. Over time, the turbidity may decrease as flooded shorelines stabilize.

Other activities such as land drainage for farming, highways, and peat extraction; the installation of weirs and river crossings; and removal of nearby vegetation for forestry or agriculture may also affect drainage and thereby flow patterns. The effects of many of these activities on shorelines and runoff may be mitigated to some extent. Water removal for domestic use, for lawn or agricultural irrigation, and for watering livestock can also reduce flow, particularly during dry years. The impacts of these activities can be mitigated by restriction or control of water withdrawals from, or diversions of water into, water bodies where the carmine shiner may occur.

Overall, the threat posed to carmine shiners by flow alteration is uncertain. The mitigation potential is likely moderate to high for most activities except for conditions affected by hydroelectric development.

Shoreline development

Development of the shoreline in areas that provide spawning habitat for carmine shiners, or immediately upstream, could adversely affect spawning habitats by causing physical disturbances or changes in water quality. Clearing of riparian vegetation to the water’s edge for cottage or agricultural development, for example, can destabilize banks and increase erosion. Allowing livestock access to the river’s edge can also disturb habitats and increase silt and nutrient loading, as can ditching and drainage for local highways. Indeed, most of these effects have been documented along the lower Birch River (Clarke 1998). Fortunately, most impacts of these activities on stream habitats can be mitigated using existing technology and best management practices. Mitigation would typically include the establishment of riparian buffers, livestock fencing or otherwise restricting access, and the deployment of appropriate erosion control techniques. Shoreline development was deemed to be a moderate threat for the Whitemouth River system and uncertain elsewhere. The potential for mitigation is moderate to high in the Whitemouth River and elsewhere.

Landscape changes 

Forestry, agriculture, peat extraction, and highway development all have the potential to change landscapes in ways that alter the patterns and quality of runoff entering waters that support carmine shiners. These changes include, in particular, the removal of vegetation, grading of overburden, drainage of wetlands, stream channelization and ditching, and the construction of physical barriers (e.g., dams, roadways, culverts). Sound project design and management, establishment of appropriate riparian buffers, and effective monitoring can mitigate many of the potential impacts of these types of activities on stream habitats. The significance of landscape changes to carmine shiners is uncertain, with moderate to high potential for mitigation.

Climate change

The effects of climate change on carmine shiners are unknown. These effects may be positive or negative depending on the direction, extent, and timing of any changes in water temperature and hydrology that affect the species’ habitats. The Birch River, where low flow and low oxygen conditions already occur in summer and winter (Clarke 1998), may be the most vulnerable to any changes. The potential for mitigating threats from climate change is low as this is a global issue requiring global solutions.

3.2.4 Pollution

The threat posed to carmine shiners by point and non-point sources of pollution is uncertain. Examples of some pollutants that could affect the species include farm fertilizers, herbicides, and pesticides. Nutrient enrichment by runoff from barnyards or intensive livestock operations is an ongoing problem that is being addressed by the Province of Manitoba and Prairie Farm Rehabilitation Administration (PFRA). Clarke (1998) found elevated levels of phosphorus (0.2 mg∙L^-1 TDP) and nitrogen (0.99 mg∙L^-1 nitrate/nitrite) in the lower Birch River in April 1996, but not at other times of the year. These levels are probably elevated through mobilization of agricultural chemicals by spring runoff. Before leaks were repaired, the Birch River also received chlorinated water leaking from the Winnipeg Aqueduct (Clarke 1998). The potential to mitigate or recover from pollution impacts is moderate to high except where long-range transport is the main source of pollutants, since these substances are ubiquitous.

3.2.5 Other Threats

Scientific sampling may also pose a threat to the carmine shiner. This threat is likely low and has a high potential for mitigation as it is carefully regulated through the issuance of scientific collection permits under SARA. To date, there is no evidence that routine scientific sampling in the Whitemouth River has had any impact on carmine shiner populations.   

Natural hybridization may occur between carmine shiners and other shiners in Manitoba. A substantial decline in the proportion of carmine shiners on the spawning grounds might lead to decreases in reproductive success or complete assimilation of the carmine shiner populations. The significance of this natural threat is likely low, as is the potential for mitigation should it occur (Table 1).

4. Knowledge Gaps

The conservation or recovery of carmine shiner populations in Manitoba is hampered by a lack of knowledge of the species’ biology, life history and habitat requirements that prevents an accurate evaluation of potential threats. The taxonomic identity of these fish, their distribution, reproductive potential, seasonal habitat use, spawning requirements, and interactions with other species remain uncertain. Their tolerance to potentially limiting environmental factors, such as extremes of temperature, turbidity, and flow are also uncertain.