The Facts about Atlantic Salmon: What Makes Wild Maine Salmon Unique? NO GRILSE (or at least very few)
Questions & Answers
1/9/2000 — —
What’s a grilse?
A grilse is an Atlantic salmon that spends only one year in the ocean before returning to its home river to spawn. Adult salmon that spend two years in the ocean before returning to spawn are simply called “salmon” or “two sea-winter salmon.”
What do grilse look like?
Grilse look like Atlantic salmon, only much smaller. They are generally 22 to 24 inches long and between 3 and 5 lbs. in weight. In comparison, salmon that spend two years in the ocean are much larger (28-34 inches long) and weigh twice as much (8-12 lbs.) as grilse. Most grilse are males and in some Canadian rivers, are almost exclusively males.
Do Maine salmon rivers have grilse?
Yes, but very few in comparison to most other Atlantic salmon populations in North America and Europe. In Canadian rivers just north of Maine, such as the St. John and Miramichi, up to half of their salmon runs are grilse. In Maine, between one in ten and one in 100 returning salmon are grilse. Rivers in southern New England, such as the Merrimack and Connecticut, also have very low numbers of grilse. This is not surprising since these rivers’ salmon runs were re-established by using Atlantic salmon from Maine’s Penobscot River.
Why do Maine salmon rivers have so few grilse?
Biologists are not sure. However, this special trait of Maine salmon has been long recognized by scientists, anglers and the aquaculture industry. Historic records dating back to the 19th century indicate Maine salmon rivers have never had more than a few grilse in their salmon runs, a trend which continues to this day.
What is the significance of this trait?
This trait of Maine salmon to produce very few grilse has a number of significant economic, biological and political implications.
Significance for aquaculture
The fact that most Maine salmon spawn after two years in saltwater is important for the aquaculture industry, which desires large salmon for market rather than small salmon. According to Joseph McGonigle of the Maine Aquaculture Association, salmon aquaculturists routinely introduce Atlantic salmon of Penobscot River origin into their broodstock populations to lower their “grilse rates” and produce more large salmon in their pens.
Significance for anglers
Aside from their tremendous leaping and fighting ability, Atlantic salmon have been called the “king of gamefish” because they provide anglers with the chance to catch a very large fish (10-20 lbs.) on light tackle in a scenic, freshwater river. For this reason, salmon anglers greatly prefer catching large salmon rather than much smaller grilse. Maine is fairly unique in that its wild salmon are almost all large, two sea-winter salmon with very few grilse.
Significance for the species
For those who are curious if Maine’s wild Atlantic salmon populations are really “different” from Atlantic salmon in Canada or Europe, the habit of Maine rivers to produce 90-95 percent large salmon and very few grilse is an important and very real distinction. This distinction indicates that Maine’s salmon have followed a different evolutionary track than their relatives to the north and east, one that compels nearly all of our salmon to spend two years or more at sea. This distinction has been clearly shown through past stockings of Miramichi, St. John and other Canadian salmon in some Maine rivers. When these stockings actually produced returning adults, a large component of the runs were small grilse instead of large salmon, just as they would in their “home” Canadian river. For this reason, stockings of Canadian salmon were used in Maine sporadically and only during years when funding and staff were not available to collect wild Maine salmon for broodstock.
Equally important is that the persistent habit of Maine salmon to produce far fewer grilse than Canadian rivers casts serious doubt on claims that Maine’s wild salmon have been “homogenized” due to past stockings of Canadian salmon in Maine rivers. If the salmon in Maine rivers today were truly of Canadian origin, they would have similarly high grilse runs as the Canadian rivers. They do not.