In 1999 a very interesting and informative article was written for the Atlantic Salmon Journal entitled The Case for Releasing Grilse by Atkinson and Moore. These men were DFO scientists who did a lot of work with the Miramichi’s Atlantic salmon by reading the growth rings on the scales of 11,500 salmon sampled between 1994 and 1998. Nathan Wilbur of the ASF recently brought this information to my attention because of the ongoing debate surrounding the killing of grilse. The article is jammed with what any Miramichi salmon junkie would think of as fascinating info. If you are interested in the various life cycles of Miramichi salmon I urge you to read the full article which is available at this link.
Atkinson and Moore approach the benefits of releasing grilse from two directions. One is the value of leaving grilse alive for spawning. Dead fish don’t spawn is a statement much maligned by sectors of the angling community who feel that fishing without harvesting an occasional fish is empty, but none-the-less, dead fish really do not spawn, and it takes both males and females to spawn. Grilse are the river’s main source of males for spawning. The large number of grilse also provides for natural selection and genetic diversity. The other direction from which Atkinson and Moore approach the issue is in considering the effect that releasing grilse can have on the quality of the angling, meaning the amount of larger salmon created within the population by releasing the smaller ones. After all, one of the main differences between Atlantic salmon and their Pacific brethren is that the Pacific fish all die after spawning anyway – dead fish don’t grow either. That is not true with Atlantics, in fact some Miramichi fish have been documented through scale reading as making as many as 8 repeat trips to the river gaining in size with every return.
Young salmon called parr live two to three years in the Miramichi system, then turn to silvery smolts in their final riverine spring and swim to the ocean. Salmon returning to the river for the first time are called multi sea winter “MSW” maiden spawners. The greatest number of maiden spawners are 1 MSW – one winter at sea – fish or grilse. Grilse are about 15% female in the Southwest Miramichi system, and 20% female in the Northwest branch. The other maiden spawners are almost entirely 2 MSW fish that average around 10 pounds, and are 90% female in the Southwest and 82% female in Northwest. There are a very tiny number of 3 MSW virgin spawners, but in the Miramichi and most other salmon rivers they are anomalies. It is all a bit more complicated than this in that the percentages of males versus females in both branches varies between the early and late runs, and there are lots of exceptions to the averages. This information is 20 years old, I expect that things haven’t changed all that much, though undoubtedly there are cyclical variations in all these statistics and always have been.
After spawning many or most of these fish – now called kelts – stay in the fresh water portions of the river for the winter and drop back to the ocean in the late spring. Some of these fish rebuild their size and strength and return to the river again during that same summer and spawn in the fall. These are called consecutive spawners. Other kelts head straight out to sea and stay there one or two years before returning to spawn again. These are called annual spawners.
If we look at the Miramichi run of the large or 2+ MSW fish – all salmon other than 1 MSW fish or grilse – we find that in any given year between 14% and 57% of these fish are repeat spawners. The mean is 27% which strikes me as quite a large number, and, as of 1999 that number was increasing. Also, in both branches of the Miramichi 72% of these large salmon are females. Here is an important little twist. The 28% that are males is nearly double the percentage of males found in the 2 MSW virgin spawner run. The reason for this is that clearly a lot of grilse survive to come back as repeat spawners. Additionally two thirds of the male grilse kelts stay at sea for two years and not just one before returning to spawn a second time. According to Atkinson and Moore, during that time the growth rate is very impressive and upon return these fish are 32.5 inches long and weigh 14.5 pounds. At my camps on the Miramichi and Cains Rivers we catch a few cock salmon each year that are between 14 and 20 pounds, and no fish in the salmon world are more determined on the end of a line than these creatures. According to Atkinson and Moore’s research a very high percentage of these fish are rebuilt, male grilse kelts.
While the probability of a grilse living to go back to sea – living two years in the ocean, and then returning as a mid-teen sized cock salmon – is only about 4.5% for males and double that or 9% for females, according to Atkinson and Moore’s data once they have spawned a second time their chances for a third return leap up to 41%! Also, that is 4.5% of what is, in most years, the largest group of salmon to enter the river by far – the male portion of the grilse run. The message is quite clear that if we release our grilse we will not only have more and a better diversity of spawners on the beds that fall, but more really large fish in succeeding seasons – plus we get to angle for them along the way.