8.2 Seismic line density

Last Updated: 
June 4, 2015

This indicator measures cumulative linear disturbance in km/km2, in each terrestrial ecoregion of the NWT. The types of linear disturbances included are - seismic lines, roads and power lines. This indicator, however, is most likely reporting on seismic lines, as they form the vast majority of the data used to calculate density.

Seismic lines and fire scars in the Taiga Plains
Seismic lines and fire scars in the Taiga Plains – see VEGETATION for details on natural disturbances like fire.

Seismic data for this indicator has been obtained from the National Energy Board (NEB, August 2012), Dehcho Land Use Planning Committee (IRS-based interpretation - c.2001), GNWT (Forest Management Division - harvest access), and several individual proponents. The NEB data is released periodically and includes lines that are at least 5 years old, and date back to 1958. Road and power line data were from Natural Resources Canada (CanVec Version 9), Environment Canada (Landsat-based interpretation - c.2009). Ecoregions are defined at level IV under the ecosystem classification system developed by ENR1.

This indicator was reported as Fragmentation Density in 2010, renamed back to seismic line density in 2011. The information and data on fragmentation was used and retained in the new indicator on woodland caribou see focal point SPECIES AT RISK.

NWT Focus

Seismic lines are the single largest landscape disturbance caused by humans in the NWT. In many parts of the NWT, they are the only indication of human disturbance in large areas of otherwise undisturbed forest land. In western Canada, seismic line and road density estimates are used as an indicator of habitat fragmentation for some forest-dwelling species.  Fragmented habitat results in less use by some species. For example, studies in Alberta indicate that Woodland caribou occurrence decreases with increasing seismic line density. Assessments of caribou movement strongly suggest they prefer to be at least 100 meters away from seismic lines. There is also evidence to suggest that caribou in close proximity to seismic lines are at higher risk of being killed by wolves2,3.

Current view: status and trend

An unknown number of additional seismic lines were created in the NWT between 2013 and today. As well, an unknown proportion of the old seismic lines included in the data set used for this indicator have varying levels of regeneration and have differing levels of visibility and preceptibility on the landscape. By comparing the NEB data set of pre-1999 lines with maps of visible seismic lines obtained from satellite images for the Dehcho, it was found that the NEB data is incomplete. There are also several areas where the differing data sources provide duplicate features, although the duplication was removed as much as possible when combining all linear disturbance datasets. Density calculations were performed using this combined comprehensive dataset, and represents an historic cumulative extent of seismic line density. As such, these estimates should be considered as more of a cumulative historical baseline.

The Mackenzie Delta and Richards Island Coastal Plains in  the Southern Arctic Ecozone have the highest seismic line densities at 6 km/km2 and  2.38 km/km2 respectively.  Other areas of high seismic impact are the Liard Valley and Cameron Hills.

Map 1. Representation of the data used to estimate densitites of cumulative linear disturbance from 1958 to 2013. Map by ENR, GNWT with data from NEB, NRCan, and various others. Seismic lines in the Beaufort Sea and on the Arctic Islands were not used to estimate densities for this indicator, but are included in this map for completeness.

NWT Linear disturbance
NWT Linear disturbance

Map 2. Density of cumulative linear disturbances in the NWT calculated for each Level 4 Ecoregion in the mainland of NWT (only). Source: ENR, GNWT with data from NEB, NRCan and various others.

Linear disturbance density (mainland NWT) by Level 4 EcoRegion
Linear disturbance density (mainland NWT) by Level 4 EcoRegion

Looking forward

The density of seismic lines presented here only reflects seismic lines created up to approximately 2013, and therefore the density figures are already dated. 2D and 3D seismic line programs were carried out between 2013 and 2015, although activity has been slower than previous years. Available details for these recent seismic programs can be found in the HUMAN ACTIVITIES focal point.  


This indicator will continue to track changes in seismic line “footprint” using the information provided by oil-gas companies to the National Energy Board, by obtaining information through the other sources. The actual effects of increasing seismic line densities on wildlife and other components of NWT ecosystems are being studied and will be reported in this indicator in the future2,4,5. To improve upon this indicator, discussions will consider how to assign ages to lines, when to remove the lines from the cumulative dataset, and how to incorporate wildland fire impact on linear feature regeneration.

Looking around

Some land use plans contain mechanisms to look at seismic line density and how it affects boreal caribou. For more information on land use planning, go to PROTECTED AREAS AND LAND USE PLANS focal point. How to quantify and use information about seismic line density is being explored by other jurisdictions, including Alberta.

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Technical Notes

Level IV ecoregions are a sub-division of ecozones (Level 2 Ecoregions). Each level IV ecoregion is considered unique in its combination of climate, geomorphology, geology, and ecosystem components.

 

Found an error or have a question? Contact the team at NWTSOER@gov.nt.ca.


References:

Ref. 1. ENR. 2007-2013. NWT Ecosystem Classiciation. Yellowknife, GNWT.

Ref. 2. Gunn, A., et al. 2004. Boreal caribou habitat and land use planning in the Dehcho region, Northwest Territories. GNWT.

Ref. 3. James, A.R.C., and A.K. Stuart-Smith. 2000. Distribution of caribou and wolves in relation to linear corridors. Journal of Wildlife Management 64:154-1591.

Ref. 4. Ashenhurst, A.R., and S.J. Hannon. 2008. Effects of seismic lines on the abundance of breeding birds in the Kendall Island Bird Sanctuary, Northwest Territories, Canada. Arctic 61:190-198.

Ref. 5. Machtans, C.S. 2006. Songbird responses to seismic lines in the western boreal forest: a manipulative experiment. Can. J. Zool. 84:1421-1430.