untested assumptions in fisheries management: the role of ... · nonnative species like rainbow...
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Untested Assumptions in Fisheries Management:the role of competition in
Brook Trout declines?
Brian MorrisonFisheries Biologist
Ganaraska Region Conservation Authority
November 22, 2012
Alternate Titles
The Trout Management Menagerie:
50 Shades of Grey
Brian’s roadmap to Brook Trout Armageddon
Historical Overview
• Rivers contained Brook Trout and Atlantic Salmon
• Overfishing, deforestation, dams, habitat loss, and pollution eliminated or reduced abundance of original fish community by 1900
Historical Overview Cont.
• American Eel – upwards of 50% of Lake Ontario nearshore biomass
• Sea Lamprey• Harbour Seal• Possibly Burbot, Whitefish, Lake Trout
utilizing tributaries?
Lake Ontario Brook Trout
• Originally had adfluvial and riverine populations• In 1832 “Brook Trout were so plentiful, they were
caught with a bucket in Orono Creek”• 1870’s - Wilmot described the fish (Brook Trout)
as “exceedingly scarce" in southern Ontario in and "in the older settled sections quite extinct”
• 1879 - Wilmot states “speckled trout (Brook Trout) must soon become a luxury of the past in the older and more cleared sections of Ontario”
Lake Ontario Brook Trout
• 1881 – “…the time is gone by forever for the growth of salmon and speckled trout in the frontier streams of Ontario”
• 1884 – Wilmot’s hatchery closed
Brook Trout
• A belief that Brook Trout are headwater specialists in southern Ontario
• Managers have followed the ‘shifting baseline syndrome’, truncating abundance and life history diversity
• Working with relict populations – trout crumbs
Power 1980
Curry et al. 2010
Cobourg Creek
• 123 km2 watershed• Two major dams• Numerous small
barriers (N=66)• Naturalized Chinook,
Coho, Brown, Rainbow
• Stocking location for ATS
• FMP in development
FMP Development
• Began in 2006• Concern over perceived Brook Trout
declines in mid-70’s• Decline correlated when RBT were lifted
above Pratt’s Dam ~200/yr• MNR management priority to use existing
barriers as species partitions
Corbett
0
50
100
150
200
250
300
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
Num
ber o
f Ind
ivid
uals
Year
Brook Trout
Cobourg Creek Lamprey Barrier
Avg = 28
Brook Trout Stocking
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
Num
ber o
f Yea
rling
s
Year
Brook Trout Yearlings Stocked into Cobourg Watershed
Water Temperature
Cobourg Creek 1919
Benthic Information
• Use exuviae and rock flipping to determine relative abundance or presence of Isogenoides frontalis (BioMap = 4)
• Rock flipping to determine presence of Epeorus sp.
Epeorus pleuralis - 4 Isogenoides frontalis - 4
Benthic Information
Habitat
• Headwater streams
• Higher order channels
M. Ewaschuk photos
Competition
• Brook Trout outcompete Brown Trout (Korsu et al. 2010)
• Brown Trout outcompete Brook Trout (Fausch & White 1981)
• Brook trout outcompete Chinook Salmon (Levin et al. 2002)
• Growth decline in Brook Trout following RBT emergence (Rose 1986)
• Has the use of barriers as partitions increased abundance of Brook Trout?
Information Needs
• Better understanding of existing life history diversity and behavioural patterns (e.g. potential age of smolting, repeat spawning)
• Identification of where migratory fish spawn• Use of a ‘reference’ approach – utilize other
index programs as a guide for management (e.g. Lake Superior tribs)
• Long-term monitoring of core populations
Information Needs Cont.
• An expanded view of what Brook Trout habitat looks like in southern Ontario
Roadmap for recovery• Reconnect populations and habitats, facilitate
metapopulation dynamics• Manage for abundance, spatial distribution,
productivity, and diversity (life history and genetic)• These are the four pillars of population resiliency! • Support habitat and increasing natural landscape
cover• Protect from harvest when population sizes are
small• We have been managing for a graduated decline in
abundance and productivity
Food for thought
• “That those who promote the conservation and restoration of native species should do so with a…sense of humility… Reading through the letters and public pronouncements of the men who were most responsible for spreading nonnative species like rainbow trout throughout the world in the nineteenth century, I have been struck by the similarity of the rhetoric to those who promote native species restoration today. They, too, were sure they were doing the right thing for the world”.
Patricia Nelson Limerick 2010
