Atlantic Salmon in Maine (2004) / Chapter Skim
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2 Salmon Life History and Ecology
2 Salmon Life History and Ecology
Pages 23-46
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From page 23... ...
. The widespread hemispheric decline in salmon, even in streams with high-quality habitat where exploitation has been restricted or prohibited, points to a strong climatic impact in either the riverine or the oceanic portions of the salmon life history or both (Cairns 2001, Hutchinson and Mills 2000, Reddin et al.
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From page 24... ...
24 routes. migration Fund-U.S.
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From page 25... ...
. Large stocking efforts in the Penobscot River, especially of smolts, led to a brief period of annual returns numbering 3,0005,000 fish, but returns to the Penobscot and the other DPS rivers have declined precipitously since the early 1990s (Figure 2-4 [returns versus time]
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From page 26... ...
Topics covered in this section include salmon life history, historical and recent changes in abundance, and distribution and migrations. Then, the characteristics of environments that comprise salmon habitat are described: (1)
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From page 27... ...
These are rod and trap catches combined for the Penobscot River and primarily rod catches for other rivers. These numbers represent minimum estimates of adult returns.
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From page 28... ...
(b) Minimum estimates of number of fish returning to seven of the DPS rivers.
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From page 30... ...
SALMON LIFE HISTORY This subsection provides basic information about the natural history of the Atlantic salmon necessary to understand problems facing their continued existence. The first topic is a description of the sequence of developmental stages and their timing in an individual Atlantic salmon.
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From page 31... ...
. The parrsmolt transformation is of key importance because the smolt faces the energetic challenge of seaward migration and the osmoregulatory challenge of the transition from freshwater to seawater.
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From page 32... ...
Understanding the life cycle of Atlantic salmon is complicated by their alternative life-history strategies. For example, before reproductive maturity, these alternatives include variable durations in the stages before their seaward migration and variable numbers of years growing in the ocean (see Table 2-2)
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From page 33... ...
Because salmon migrate between ocean and freshwater environments, they are subjected to the vagaries of two ecosystems during different parts of their life history. This anadromous life history greatly increases the number of factors that could affect population size.
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From page 34... ...
, they probably acquired adaptations to the distinct physical and environmental challenges of local waters. Local adaptations, established by strong homing and selection pressures, are a known property of salmon populations throughout the world (Allendorf and Ryman 1987, Taylor 1991)
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From page 35... ...
Electronic tagging data near the mouth of the Bay of Fundy indicate most smolts are in the upper 10 m (G. Lacroix, unpublished data, 2001; see methods in Lacroix and McCurdy 1996)
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From page 36... ...
. If post-smolts leaving the Down East rivers and Penobscot Bay exhibit similar behavior, a likely pathway would involve passage westward along the shelf to the central coast (Penobscot Bay region)
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From page 37... ...
Unlike Atlantic salmon populations across the Canadian border from Maine, where 1SW fish are common among spawning adults, about 94% of adults returning to Maine are 2SW fish (USASAC 1999)
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From page 38... ...
These interfaces in the Atlantic salmon are the gills, gut, kidneys, and skin, and they are important for two reasons: First, it is these interfaces that are most susceptible to infection and insult; and, second, the roles of these sites change to meet the challenge imposed by the transitions between freshwater and seawater. At no site is this more obvious than in the gills.
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From page 39... ...
Once this developmental stage has been reached, photoperiod and to a lesser degree temperature regulate neuroendocrine changes that bring about physiological changes in the spring. Releasing factors such as temperature, flow, and turbidity may have rapid effects (dashed arrows)
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From page 40... ...
When migration timing and optimal environmental conditions coincide (solid lines) , adult returns are high (total returns, 166)
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From page 41... ...
The environmental information used by smolting Atlantic salmon to time outmigration is complex and likely includes temperature, rainfall, and water flow, and the behavior of other smolts as "proximate cues" or "releasing factors" (Jonsson 1991, McCormick et al.
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From page 42... ...
. The third study showed that migrating Atlantic salmon smolts in the Connecticut and Penobscot rivers lost their high salinity tolerance and gill Na+/K+-ATPase activity as the rivers warmed at the end of spring, whereas Atlantic salmon smolts in the more northern and colder Conne River and Catamaran Brook retained their smolt characteristics longer (McCormick et al.
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From page 43... ...
The temperature and biota associated with this circulation pattern provide a relative continuity of habitat between the Maine DPS rivers and the winter feeding grounds in the Labrador Sea. By contrast, rivers to the west of Penobscot Bay empty into an aquatic regime that is distinctly different during warm months of the year, approximately May to October.
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From page 44... ...
Climate can affect the dynamics of juvenile salmon populations in freshwater nurseries through modulation of growth rates, principally by the effect of temperature on growth. Habitat is a limiting factor in the production of juvenile salmon, and the factors that affect the pace at which cohorts move through rearing habitat the overall production of pre-recruits to the stocks (Bardonnet and Baglinière 2000)
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From page 45... ...
. If adaptations to initiate the migration to sea are not robust to climate variability, the consequence for regional stock groups may be profound, especially for stocks at the margins of salmon distribution that may already have low return rates.
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From page 46... ...
The spring thermal habitat areas associated with post-smolt survival of central European salmon stocks are derived from large ocean areas where the distribution of SST is affected by the NAO (Dickson and Turrell 2000)
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