Two or three noted features from a number of Scottish & Northeast England rivers point to some of the reasons for later runs of the grilse, and overall changing patterns of the salmon runs.
Much smaller grilse coming in with the main runs, whenever they occur - some fish down to 2lbs or so...but the average size of such grilse are smaller, as there are more really small fish within the group.
The grilse are not just miniature versions of the normal small barrels either, there are many grilse noted to be really thin or slim (undernourished).
The sea birds & others (comorants & seals etc) who would 'naturally' feed in the estuaries or in the coastal regions are much more commonly seen 'inland' ie well up into the main river system.
There have been those fish with the red-vent problem.
These factors point to poor feeding at sea in the season since they had left their natal river & estuary as smolts.
As the primary role of ALL salmon is to reproduce the species, their cycle is birth from the egg, then eat, eat & eat more in the natal streams & rivers, avoid predation, and then travel outside the river to the sea where the necessary food-fuel will be found so that they may mature to breeding size & age, and then return to their rivers for the sole purpose of repeating the start of the breeding life cycle.
We all know that such salmon growth & survival to spawn may be interrupted at any stage, and as such, perhaps of 3000-odd fertilised eggs, the ravages of predation, starvation, disease, flood & whatever else can be thrown at them by 'natural' means, these 3000 eggs may be only expected to result in one successfully returning & spawning adult pair to repeat the cycle.
Nature does have a natural surplus, to allow for the possibility of significantly unusual mortality events (drought, flood, whatever). Such unusual events are UNUSUAL, and, by definition, not expected to be an additional mortality feature every year!
However, if additional 'burdens' are placed upon a fragile system, a system struggling to maintain sufficient spawning numbers to replenish the breeding stock, the overall stock will decline, and eventually, unchecked, there will be insufficient numbers to even to result in a single breeding pair, and river species extinction results.
When there was a huge initial stock, perhaps in the early part of the 20th century, it would appear that however many of the salmon in the runs were 'harvested' by the commercial netsmen & the chapping classes on the rivers with rods, there was always enough for next year, and the next.
Always & never are dangerous words!
And always ran out some time ago.
Other commercial agricultural enterprises (and commercial salmon netting of wild fish is no different) have recognised for hundreds of years that the farmer has to either rest the land, rotate crops, or replenish the soil with manure/fertiliser etc.
The wheat harvests just cannot go on year after year, decade after decade, without putting back into the soil the essential nutrients for the crops to grow.
Whilst there may be some evidence of 'spoiling' of the nursery habitats of the salmon eggs, to fry, to alevin, to smolts etc, by poor forestry & agricultural practices, there is far more evidence that the essential 'main' foods needed to produce large healthy breeding adult salmon whilst feeding in the sea have indeed been devastated - completely filtering the high seas & coastal regions of shrimps, krill & sandeels & the like by commercial netsmen who gather such 'harvest' to create fish-paste pellets for yet more commercial fishermen to feed to aquacultured fish (including salmon!
), and to prepare such shrimp/krill/sandeel mulch into pet foods!
The high seas and coastal regions are less full of the essential building blocks for the migrating & feeding salmon to be beefed up into the necessary breeding stock.
The spiral is relentless, and the fate of wild salmon may be already sealed.
Unfortunately, even 100% catch & release of rod-caught river salmon & grilse may not be sufficient to save the stocks (it will help), but other more drastic & hard hitting alterations to man's 'harvest-greed' would have to be instituted.
Stop commercial netting - sea, estuarine & river - full stop! No exceptions.
Stop commercial salmon aquaculture where such nets are within 100 miles of the migratory routes of wild salmon & seatrout.
Mike
), and to prepare such shrimp/krill/sandeel mulch into pet foods!