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Abundance and Distribution

Abundance and distribution of Atlantic salmon within the range of the GOM DPS have drastically declined from the historical levels of the 1800s (Fay, et al., 2006). NOAA and USFWS (2009) described the historical distribution of Atlantic salmon in the DPS.  Their range included most of the Androscoggin River except above Rumford Falls and Snow Falls on the Little Androscoggin River; the Kennebec River except above Grand Falls on the Dead River; the Penobscot River except above Big Niagara Falls, Grand Pitch on Webster Brook, and Grand Falls on the Passadumkeag River; and all portions of the Downeast rivers.  Historical distribution is estimated to have covered 45,980 square kilometers (km2), or 50 percent of the State of Maine (91,652 km2).  Approximately 19,311 km2 (42 percent) of this historical habitat is thought to be occupied now (NOAA 2009). 

Data sets tracking adult abundance back to the 1800’s are not available throughout this historical time period, but observations and catch data provide important reference points to compare to current population estimates.  For example, Foster and Atkins (1869) estimated that roughly 100,000 adult salmon returned to the Penobscot River prior to the 1860s before dams  reduced adult returns.  Based on U.S. Fish Commission Reports, Baum (1997) reports commercial catches of 10,016 fish in the Penobscot in 1880 and approximately 20,000 fish per year from 1870 to 1890.  He also assembles a comprehensive time series of adult sport catch data from Maine dating back to 1936 that includes rivers outside the current GOM DPS.  This time series of sport catch data in Maine rivers shows a few hundred fish (maximum 480) per year were caught from 1936 to 1976, with more in the 1980s (maximum: 1,396)

 Contemporary abundance estimates (USASAC 2016) are informative in considering the current recovery status of the GOM DPS.  After a period of population growth in the 1970s, adult returns of salmon in the GOM DPS steadily declined through the 1990s, leveling at around 1,000 adult returns since 2000 ( (USASAC, 2016)


 Figure 3-1. Atlantic salmon adult returns for the Gulf of Maine DPS, 1966 – 2016 (Data Source, USASAC 2017).

Wild vs. Hatchery Returns

A recovered GOM DPS will ultimately require wild adult spawners because they represent the self-sustaining portion of the population that will require minimal ongoing management and investment of resources.  Until that time, naturally reared offspring are central to the recovery goal.  The term ‘‘naturally reared’’ includes fish originating from wild spawners and hatchery egg or fry (USASAC 2013).  Hatchery fry are included because they are not marked and cannot be visually distinguished from fish produced from natural spawning (termed “wild”).  The term “hatchery-reared” includes fish that are stocked as either parr or smolts from CBNFH or GLNFH, and although stocking these life stages is important in preventing extinction and increasing adult escapement, they cannot be counted toward recovery goals.  Figure 3-2 illustrates naturally reared adult returns relative to the total adult returns to the Gulf of Maine DPS from 1967 to 2016.  

Figure 3-2.  Total Atlantic salmon adult returns and the proportion of naturally reared returns to the Gulf of Maine DPS, 1966-2016 (Data Source, USASAC 2017).

The Purpose of the Stocking program:

The Federal hatcheries, Craig Brook NFH and Green Lake NFH, are the life-support system for the GOM DPS.  These two hatcheries reduce short-term extinction risks to the GOM DPS. The goal of the conservation hatchery program is to maintain abundance and diversity of the GOM DPS.  The three strategies used are:

1.  Stocking large numbers of smolts aimed at increasing adult returns, thus reducing demographic risks (i.e., extinction risks) to populations that would otherwise be smaller.

2.   Stocking large numbers of multiple life stages to reduce the risks of catastrophic loss.  The assumption is that at least one cohort is always at sea and could be collected as broodstock in the case of a catastrophic event in fresh water (e.g., a large contaminant spill) or in a hatchery (e.g., disease outbreak).

3.   Stocking large numbers of hatchery fish at the fry stage to maximize exposure to natural environmental factors throughout a majority of the life history.  Increasing exposure to natural selection pressures provides some assurance of maintaining genetic fitness.

Recent adult population estimates of Atlantic salmon in the GOM DPS are lower than returns in the 1970s and 1980s (Figure 3-3).  The current percentage of fish that are naturally reared continues to be small (approximately 5 percent in recent years).  The conservation hatchery program has assisted in slowing the decline and helped stabilize populations at low levels, but has not contributed to an increase in the overall abundance of salmon and has not been able to halt the decline of the naturally reared component of the GOM DPS.


Figure 3-3.  Atlantic salmon adult returns by SHRU 1966-2016 (Data Source, USASAC 2017).

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