28 Grey Seal Abundance
Data Type: Tabular Data
Spatial Scope: Scotian Shelf
Duration 1960-2021
Source: den Heyer, C. E., Mosnier, A., Stenson, G. B., Lidgard, D. C., Bowen, W. D., & Hammill, M. O. (2024). Grey seal pup production in Canada (DFO Can. Sci. Advis. Sec. Res. Doc. 2023/078). Fisheries and Oceans Canada, Canadian Science Advisory Secretariat.
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28.1 Introduction to Indicator
Grey seal populations in Atlantic Canada have been periodically estimated since the 1960s using a combination of visual and aerial surveys of seal pups. Data from this region comprises one of the longest and most robust datasets of pinniped abundance in the world. The Scotian Shelf grey seal herd includes breeding populations in Coastal Nova Scotia and on Sable Island – the largest single breeding population of grey seals in the world, and the source of over 75% of Canada’s entire pup production (Heyer et al. 2024; Bowen, McMillan, and Blanchard 2007).
Pup production in the Scotian Shelf herd increased exponentially from the 1960s-1990s, after which the rate of increase began to slow in the mid 2000s (Bowen, McMillan, and Blanchard 2007). By the 2020s, population estimates appear to be leveling off as the population appriaches its hypothesized carrying capacity (Hammill et al. 2023).
Population estimates for the Scotian Shelf herd are produced from ensembled estimates of four formulations of an integrated population model, which use different assumptions of survival and mortality. The model uses data on pup production, pregnancy rates, removals, survival, and ice-related mortality rates; the model consists of three main components: a demographic model indicating maturity-at-age, a population dynamics model, and a mark-recapture model that indicates survival probabilities of individuals (Hammill et al. 2023).
28.2 View Data
library(plotly)
data@data %>%
plot_ly(x = ~year, y = ~median_value) %>%
add_ribbons(ymin = ~lower, ymax = ~upper,
line = list(width = 0),
fillcolor = 'rgba(180, 180, 180, .4)',
name = "Uncertainty Interval",
text = ~paste0("Uncertainty Interval (1000s): ", round(lower), " - ", round(upper)),
hoverinfo = "text") %>%
add_lines(y = ~median_value,
name = "Annual Median",
line = list(color = "rgba(50, 50, 50, 1)", width = 2), hovertemplate = "Modeled Abundance (1000s): %{y:.2f}<extra></extra>"
) %>%
layout(yaxis = list(title = "Abundance (1000s)",
fixedrange = TRUE),
xaxis = list(title = "Year"),
hovermode = "x unified",
title = "Grey Seal Abundance for Scotian Shelf"
) %>%
config(displayModeBar = F)(#fig:plot-grey_seals)Grey seal population restimates in the Scotian Shelf, 1960–2021.
28.3 Summary and Trends
Trend and summary values are automatically generated; data were last updated on marea package install on 2026-02-10
As of the most recent data entry in 2021, grey seal abundance was estimated at 310.68 thousand seals, which is the highest predicted value to date from the timeseries.
Estimated seal abundance has increased since monitoring began in 1960, beginning with exponential increase in the first few decades. The rate of increase has declined between the 1990s and 2000s, and the population is now thought to be leveling off towards a carrying capacity for the reigon.
28.3.1 Summary Table
Summary values for the grey seal abundance are found in the table below (Table 28.1)
| Metric | Value | Description |
|---|---|---|
| Most Recent Value (2021) | 310.68 | The 2021 estimate is the highest model-projected seal abundance value in the time series. |
| Recent Trend (2011 – 2021) |
5.31 per year | In the last ten years, seal abundance has increased by 5.31 thousand per year with a Very Strong trend (p < 0.01). |
| Overall Trend (1960 – 2021) |
5.78 per year | Since the beginning of the timeseries, seal abundance has increased by 5.78 thousand seals per year with a Very Strong trend (p < 0.01). |
| Timeseries Record High | 310.68 | The highest value in the timeseries was recorded in 2021. |
| Timeseries Record Low | 1.86 | The lowest value in the timeseries was recorded in 1960. |
28.4 Relevance to Research and Stock Assessments
Grey seal population changes are directly relevant to seal harvest in Atlantic Canada. Canada does not assign a specific total allowable catch limit for seals, instead employing a precautionary approach wherein harvest guidance is structured so that the population does not decline past the precautionary reference level of 70% of the largest population size (Hammill et al. 2023). Estimated allowable individuals harvested to remain above the reference level depend on the age-structure of the harvest, but conservative estimates for the Scotian Shelf population alone are above 20,000 per year. Still, grey seal harvest in Canada remains small, below 5,000 individuals per year from 2002-2024 (Fisheries and Oceans Canada 2025).
Seals are also generalist predators, and can influence the populations of other important harvest species. In the Scotian Shelf, top-down forcing by seal predation has shown to impact the marine environment, in addition to environmental factors (Sinclair et al. 2015). While not thought to be a major factor in the collapse of cod in Atlantic Canada in the 1990s (Mohn and Bowen 1996), rising grey seal populations might be limiting the recovery potential to cod stocks by exerting increasing predation pressure on already-limited populations (Trzcinski, Mohn, and Bowen 2006).