Inshore commercial fishing boats are the number one predator

[dunadd]

Cormorants, otters etc have been around for millennia - they're not responsible for the collapse in sea trout and salmon numbers. Pollution of rivers has been - but many rivers have been getting less polluted in the UK and others never had much pollution.

Since statistics started being kept on sea trout numbers in Scotland (1952), there was a big fall from the mid-1960s (first salmon farms set up) and another from the late 1980s. In 1984 the UK government removed a legal ban on inshore commercial boat fishing. Previously they couldn't fish closer to shore than 3 miles.

If you google the pre-print of the study 'Concurrent Collapses of Demersal Fish and Sea Trout (Salmo trutta) on Scotland’s West Coast following the Removal of the

“Three-Mile Fishing Limit”', it shows that as stocks of sea fish collapsed, sea trout since 1984 have declined at the same rate. The laws on what species can and can't be caught by fishing boats make little difference as they'll just dump them overboard, already dead, or sell them illegally.

Also see this Scottish government report www.gov.scot/publications/sea-trout-fishery-statistics-2019/

Of course invasive species that aren't native will have an impact too, but commercial fishing boats and trawlers fishing deep sea and near the shore , and using more and more advanced sonar have a massive one.

If we want sea trout numbers to recover we should be lobbying the Scottish, Welsh, NI and UK governments to restore the ban on inshore commercial fishing - and reduce the allowed number and size and annual catch of offshore commercial fishing boats too. Sea trout can't evolve at the rate that commercial fishing technology can.

[daiben]

Nice post dunadd,



Whilst I broadly agree with the your conclusion, I wouldn't dismiss the important contribution that fish eating birds, agricultural pollution,winter floods, obstruction to spawning ground etc. are making to an already declining migratory fish population.
I hope we haven't yet reached the point where this sad decline in Sea Trout populations is irreversible but I fear time is rapidly running out.

[dunadd]

Hi Daiben , thanks. You make good points on agricultural pollution and hydro-electric schemes etc blocking access to spawning grounds and flooding in winter damaging them too.

I don't doubt some bird species will eat some trout and sea trout - I just doubt they're the main factor since they co-existed with and predated on salmon and sea trout for millions of years. Though it may well be that the decimation of sea fish species by drift net trawlers in the deep sea, and inshore fishing boats as well, have driven many birds like gulls and cormorants inland as fish big enough for them to survive on become rare on the coast, which could be further reducing sea trout numbers.

Since any brown trout can potentially become a sea trout, as long as wild brown trout survive in rivers, there is hope that sea trout could recover at some point in future. But I completely agree that sea trout could be almost wiped out in our lifetime, and without big changes, probably will be, which would be a very sad thing to see.

The first fishing I ever did around age 10 was for trout and sea trout in a burn in the highlands, and the thrill of (almost) catching a big silver sea trout (i got it on the bank but it jumped back in) stayed with me. Today I'm glad that one got away and regret that I later killed one I caught during a spate in order to show my family it (they weren't even impressed).

I hope people fishing for sea trout at sea take this into account as much as people fishing for them in freshwater, and use barbless hooks and release any fish they catch alive.

[rodney]

FEBs don’t distinguish between adult and juvenile brown trout, sea trout or other species, they eat all river fish.



I would suggest any angler interested in this topic should watch the presentation in 2018 on YouTube by Niels Jepsen who has done a great deal of research into the impact cormorants have had on fish and smolt predation in Scandinavia. It’s depressing and available at this link. www.youtube.com/watch?v=7u-RCGNsYW8



I’ve been in touch with Niels Jepsen again recently and he kindly sent me an update on latest data and I paste some of his reply here:

“I did publish some new grave results, documenting a very high impact from cormorants on in-river fish, especially juvenile salmonids, reducing winter survival from 70% to 5-20%.



New results from this winter shows even higher predation with as much as 98% of all fish eaten from October to March.



We are now really feeling the hurt on our river fisheries and what you describe is very common here now as well, it as a genuine disaster.

Our coast fishing is also in free fall – decline, due to super heavy predation on almost all life stages"

I can’t attach NJ’s Powerpoint file as too large for this site. But have included a pdf paper Jepsen_etal_2018.pdf (715.44 KB)by him and others from 2018 that documents the drastic impact even a few cormorants can have on populations of resident river fish.