Science Advisory Report  2010/047

Recovery Potential Assessment of Spotted Gar (Lepisosteus oculatus) in Canada

Summary

• The current and historic Spotted Gar distribution is limited to seven distinct locations of the Great Lakes basin: Lake St. Clair, Point Pelee National Park, Rondeau Bay, Long Point Bay, Hamilton Harbour, East Lake and North Channel. Four of these locations are represented by a single record (Lake St. Clair, Hamilton Habrour, East Lake and North Channel) (Figure 1). Current Spotted Gar population sizes are unknown.
• Adult Spotted Gar are typically found in shallow waters (Canadian records ranged from 0.23 to 2.6 m) of wetlands, marshes or flooded riparian areas. Dense vegetation appears to be a mandatory component of adult Spotted Gar preferred habitat. There are very limited data on habitat requirements for young-of-the-year (YOY) and juvenile Spotted Gar, necessitating the inference of these requirements from the adult life stage. Spawning occurs in the nearshore areas adjacent to preferred adult habitat.
• To achieve ~99% probability of persistence, given a 15% chance of catastrophic decline (50% decline in abundance), requires ~1400 adult Spotted Gar and at least 360 ha of suitable habitat. The definition of “extinct” has a large impact on Minimum Viable Population (MVP) size. If an extinction threshold of 10 females is considered, MVP becomes ~14000 adults requiring 3500 ha. Extinction risk is elevated exponentially when suitable habitat is at or below the minimum area for population viability.
• In the absence of additional harm or recovery effort, a population at 10% of MVP has a 95% chance of recovering within 45-66 years (depending on frequency of catastrophic events). Increasing survival of YOY and juveniles (the most efficient strategy) by just 10% improves recovery time to 23-29 years.
• The greatest threats to the survival and persistence of Spotted Gar in Canada are related to habitat modification and destruction, aquatic vegetation removal, increases in nutrient loading, and increases in turbidity and sediment loadings resulting from agricultural and urban development. Lesser threats that may be affecting the survival of Spotted Gar include the introduction of exotic species, and incidental harvest through the baitfish, recreational, and commercial fishing industries.
• Cumulative harm to annual survival of YOY and juvenile stages should not exceed 8%. Cumulative harm to adult survival or reproduction should not exceed 14 or 16%, respectively. Harm that affects multiple vital rates should be restricted further. For example, cumulative harm to survival of all life stages should not exceed 5%. Recovery time is delayed exponentially by any amount of harm above or below these thresholds.
• There remain numerous sources of uncertainty related to Spotted Gar population size, structure and the level of connectivity between populations. There is very little information available on preferred habitat of juvenile Spotted Gar. Numerous threats have been identified for the Spotted Gar, although the direct impact that these threats might have on Spotted Gar populations is currently unknown.

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