Speaking notes/Brief to the Senate Committee on Fisheries and Oceans, March 21, 2012

Submitted by:           Debbie MacKenzie, Chair
                                Grey Seal Conservation Society

Thank you for giving me the opportunity to speak to you about grey seals. My name is Debbie MacKenzie and I represent the Grey Seal Conservation Society.

The main thing I want to bring to your attention is a growing body of credible science that describes physical processes through which seals make positive contributions to the health of ocean ecosystems. Recently, a series of peer-reviewed scientific publications has described and measured fertility-boosting “ecosystem services” provided by marine mammals, including by seals. (1, 2, 3, 4, 5)

First, through their diving, surfacing, feeding and bodily excretion patterns, marine mammals actively transport significant quantities of plant fertilizer from deeper waters to the sunlit surface water. This stimulates the growth of plankton, the uptake of atmospheric carbon dioxide by the ocean, and the production of food and oxygen for many consumers including their own prey fish. Secondly, marine mammals and other swimming sea creatures contribute to turbulent mixing of the seawater, which also enhances biological productivity. (6, 7)

These two pathways of indirect positive impacts of seals on fish were previously assumed to be trivial. Ocean modellers have traditionally assumed that the life-sustaining jobs of physically lifting sunken plant fertilizers to the surface water and mixing seawater were accomplished solely by non-living physical forces, that is, by weather patterns and ocean currents. However, these “physical” processes are also managed separately by the power of living, moving animals. Large, deep diving animals like whales and seals make the greatest contributions, and their presence has a significant positive impact on ocean fertility and health. Further, marine mammal activity can counter-act stagnant, nutrient-depleted “stratified” surface water conditions, which can invite the growth of harmful algae blooms, which are another growing concern. (8)

Scientists have estimated that the massive removal of whales and seals from the Antarctic Ocean has diminished that region’s capacity to support plant and animal life, including krill, and lowered its capacity to draw down carbon dioxide from the atmosphere. Deep diving sperm whales contribute significantly to open ocean productivity and to the burial of carbon in the deep sea. Closer to home, scientists have found that whales and seals in the Gulf of Maine actively transport a quantity of nitrogen into the surface waters that exceeds the amount delivered by all the region’s rivers. (1) This is especially beneficial during summer when phytoplankton (plant) growth is limited by a shortage of nitrogen in the surface water. Although they call it “the whale pump,” the scientists noted that seals have the same effect and they calculated the nutrient cycling benefit provided to the Gulf of Maine by 1,731 grey seals. Applying this same type of analysis to 400,000 grey seals in eastern Canada will demonstrate how a significant contribution to the health of the ecosystem in this region is currently being made by grey seals.

This information has important implications for ocean resource managers. The authors concluded that “marine mammals provide an important ecosystem service by sustaining productivity in regions where they occur in high densities” and that “an unintended effect of bounty programs and culls could be reduced availability of nitrogen in the euphotic zone and decreased overall productivity.”

Stressful environmental conditions are currently affecting or projected to affect the survival of marine fish (9, 10), making it particularly important that ocean managers place a high priority on preserving the strength of the positive ecosystem services delivered by marine-mammals. This new evidence of the positive impact of seals on fish stocks is reinforced by and helps to explain recent events on the Eastern Scotian Shelf, where multiple groundfish stocks defied the predictions of “modellers” and the fishing industry by showing remarkable signs of rebuilding while sharing their habitat with an unprecedented density of “voracious” grey seals. (11, 12) It is not unreasonable to conclude that the impact of the dense grey seal herd on the Scotian Shelf has been to raise the “carrying capacity” of the area for groundfish.

DFO scientists and others are frustrated by the inability of currently used fish “population analysis models” and “ecosystem models” to predict the impact on fish populations of fisheries management interventions and of naturally occurring ocean processes. (13, 14, 15, 16) Models now in use are just too crude. A crucial factor and quantifiable ocean process, that is entirely missing from the models now used to make projections, is the positive feedback dynamic that naturally exists between large ocean animals and the plankton. For food web modellers, changing models to incorporate this information will mean a huge adjustment in their thinking and challenging a major underlying assumption that current models were built on. Regardless, this must be done if fisheries scientists hope to improve accuracy in their modelled forecasting of sea life.

We now see the southern Gulf of St. Lawrence cod stock continuing to decline as the Eastern Scotian Shelf cod stock rebuilds, while both cod stocks co-exist with large and increasing numbers of grey seals. This apparent paradoxical response of cod to seals suggests to me that environmental stressors negatively affecting cod are more severe inside the Gulf than outside. Differences between the two areas include important water quality parameters, in particular the fact that a large oxygen-depleted “dead zone” has been spreading for years in the deep waters of the Gulf, which has already forced cod to abandon part of its former range in the region.

When seals eat fish that have been rendered vulnerable to predation by other stress factors, seal removal is not an appropriate response and will not effectively prevent “natural mortality.” In my view, this type of scenario most likely underlies the apparent increased consumption of larger over-wintering cod in the Cabot Strait by grey seals, and such a situation does not justify culling seals. It has been argued that removing grey seals from the southern Gulf of St. Lawrence would not threaten the future of the seal species because large numbers are thriving on the Scotian Shelf. The same argument applies to cod. Deliberately removing the seals, however, will come at an ecological cost that we cannot afford, and doing so may very likely make matters worse yet for the cod.

I recommend that this committee urge the Minister to perform his mandate under the Oceans Act to promote the “understanding of oceans, ocean processes, marine resources and marine ecosystems….” by setting the terms of reference now for fruitful new research, through which:

(1) DFO is asked to calculate and report on the current value of ecosystem services now provided by the grey seal herd, particularly in terms of enhanced primary productivity

(2) DFO is asked to calculate and report on the projected plankton response to any proposed grey seal cull, including the knock-on impact on plankton-dependent species

(3) DFO is asked to develop new population and ecosystem models incorporating the positive pathways of effect between marine mammals and ecosystem primary productivity,

(4) DFO is asked to assess and report on the current risk of the occurrence of harmful algae blooms associated with stagnant surface water conditions, especially inside the Gulf of St. Lawrence, and to offer science advice on the potential value of the presence and activity of the grey seal herd in mitigating this health hazard, and

(5) DFO is asked to evaluate and report on the potential effectiveness of air-breathing marine predators in curtailing “dead zones” in semi-enclosed waterways such as the Gulf of St. Lawrence.

Please also advise the Minister that Canada’s “broadly articulated recovery plan” for fisheries must include a plan to refrain from using any interventions that will impair processes known to enhance primary productivity, including the living presence of seals.

Finally, beyond the risk of ecological damage posed by any deliberate substantial reduction in seal numbers, there are other risks inherent in any grey seal cull or commercial grey seal marketing proposals, which also support my recommendation that these initiatives be abandoned. Current seal marketing challenges will not be easily overcome, and may become worse as relevant facts are examined more closely. Two problem areas are adequately controlling food safety hazards and the potentially inhumane slaughter of grey seals.

Canada must rethink the commercial usefulness of seals as a “resource”. Concrete recognition that marine mammals provide valuable ecosystem services that benefit everyone is spreading in both the scientific literature and the general media. Canada’s acknowledgement of the important ecosystem services provided by this living “resource” should help the fishing industry understand why its desire for a grey seal cull cannot be granted. Ecotourism focused on seals has significant untapped potential in Atlantic Canada. Besides actively enhancing the health of their own environment, grey seals are intelligent and interesting, and they are some of the only large wild animals in this part of the world that urban people can ever expect to see today.


  1. Roman, J., McCarthy, J.J. (2010) The Whale Pump: Marine Mammals Enhance Primary Productivity in a Coastal Basin. PLoS ONE 5(10):e13255.doi:10.1371/journal.pone.0013255 (accessed online at http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.0013255 )
  2. Kanwisher, J.W., and Ridgeway, S.H., (1983) The Physiological Ecology of Whales and Porpoises. Scientific American 248:110-120
  3. Nicol, S., Bowie, A., Jarman, S., Lannuzel, D., Meiners, K.M., and VanDerMerwe, P. (2010) Southern Ocean iron fertilization by baleen whales and Antarctic krill. Fish and Fisheries 11(2): 203-209 (“allowing the great whales to recover might actually increase Southern Ocean productivity through enhancing iron levels in the surface layer.”)
  4. Willis, J. (2007) Could whales have maintained a high abundance of krill? Evolutionary Ecology Research 9:1-12 (“this reverses the predictions of mass balance ecosystem models”)
  5. Hucke-Gaete, R. (2011) Whales Might Also be an Important Component in Patagonian Fjord Ecosystems: Comment to Iriate et al. AMBIO (2011) 40:104-105 (“primary productivity enhancement is by no means irrelevant or dismissible as previously thought”)
  6. Dewar, W.K., Bingham, R.J., Iverson, R.L., Nowacek, D.P., St. Laurent, L.C., and Wiebe, P.H., (2006) Does the marine biosphere mix the ocean? Journal of Marine Research 64:541-561
  7. Katija, K. (2012) Biogenic inputs to ocean mixing. The Journal of Experimental Biology 215:1040-1049 (accessed online at http://jeb.biologists.org/content/215/6/1040.full.pdf+html )
  8. Anderson, D.M., Cembella, A.D., Hallegraeff, G.M. (2012) Progress in Understanding Harmful Algal Blooms: Paradigm Shifts and New Technologies for Research, Monitoring, and Management. Annu. Rev. Mar. Sci. 2012, 4:143-76
  9. DFO 2010. 2010 Canadian Marine Ecosystem Status and Trends Report. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2010/030 (Revised) (this includes information on trends in the Gulf of St. Lawrence which include increasing water temperatures, increasing oxygen-stress and plankton changes consistent with “less productive ecosystems”)
  10. Royal Society of Canada, 2012. Sustaining Canadian Marine Biodiversity: Responding to the Challenges Posed by Climate Change, Fisheries, and Aquaculture.
  11. DFO. 2009. DFO Maritimes Summer research vessel survey.
  12. Frank, K.T., Petrie, B., Fisher, A.D., Leggett, W.C. (2011) Transient dynamics of an altered large marine ecosystem. Nature 477:86-89
  13. DFO. 2009. Proceedings of the National Workshop on the Impacts of Seals on Fish Populations in Eastern Canada (Part 2), 24-28 November 2008. DFO Can. Sci. Advis. Sec. Proceed. Ser. 2009/020
  14. Swain, D.P., Benoit, H.P, Hammill, M.O. (2011) Grey Seal Reduction scenarios to restore the southern Gulf of St. Lawrence cod population. DFO Can. Sci. Advis. Sec. Res. Doc. 2011/035 (“a caveat is that grey seal reductions could have impacts on other components of the ecosystem which in turn could have a negative effect on cod productivity.”)
  15. O’Boyle, R., Sinclair, M. (2012) Seal-cod interactions on the Eastern Scotian Shelf: Reconsideration of modeling assumptions. Fisheries Research 115-116 (2012) 1-13
  16. Hammill, M.O., Swain, D. 2011. A Controlled Experiment (Strawman draft) to Test the Impact of Removals of Grey Seals on the Mortality of Southern Gulf Cod. DFO Can. Sci. Advis. Sec. Res. Doc. 2011/013 (“Under the proposed experiment clear longterm cod and seal management objectives must be identified, minimum realistic and ecosystem modeling simulations must be completed to identify possible benefits and impacts…”)




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