Why are fish growing bigger?

[ayjay]

Bruno Broughton:

 

I would love to be able to add that growth hormones in bait have helped - what evidence do you have for this thoery, AJP?

I was thinking specifically of Barbel and luncheon meat and the work done by Ray Walton and some others mainly on the Royalty barbel but also on the Lea.

[Steve Burke]

As I posted when I posed the question, I suspect that there's a combination of reasons for the growth in some species. Indeed, Bruno has listed a whole host of possibles.

 

The 2 that I suspect are most influential are fertilisation of the water and, to a lesser extent, climate change.

 

Anglers' baits no doubt play a part, but to a lesser degree than perhaps some think. For instance the weights of fish have increased on several waters I know that have rarely ever been fished, let alone seen HNV baits!

 

Having said that, I do accept that bait has made a difference, but would suggest that this is especially so on waters that are overstocked and so need the extra food. And, let's face it, most stillwaters are now overstocked, and not just commercial "puddles" either!

 

We're therefore looking for factors that affect most waters, not just a few.

 

Nitrates and phosphates get into the water table itself and so could well be prime candidates. Individual waters in agricultural areas would be particularly enriched. The increase in fish weights certainly seems to have occured at the same time that the use of farm chemicals has soared.

 

It may also be signifant that different species have been affected more than others.

 

For instance big barbel were present in the Hampshire Avon in Richard Walker's day, and some were caught out of season by salmon anglers. Barbel, like carp, are more widespread now, so perhaps it's not surprising that more big ones are caught. However, the maximum weight of barbel has little changed.

 

Chub are no bigger now than 50 years ago. Having said that they are definitely bigger than 20 years ago, when a 4lber was considered a specimen by many chub hunters. My best of 5-01½ came in the early 80s, and in fact until the last fortnight was the biggest caught that season by a Chub Study Group member! The reason was possibly poor spawning years. Certainly a 5lb chub then is equivalent to a 6lber now.

 

Likewise the top weights of perch and pike haven't significantly increased. However, there are more big pike being caught perhaps, largely because of the opening of trout reservoirs. Big perch are much more common, but here the fact that we're have no major outbreaks of perch disease for 20 years is a major factor. Once again though the maximum weight has barely changed.

 

Could it be significant that the 3 species that have been most effected (bream, carp and tench) have done especially well in gravel pits? Many of these have been dug in the last 50 years and, when I was a lad most were relatively barren and weed free. Now, probably because of fertilisation from chemicals, they are usually weedy and full of life.

 

Additionally, these 3 species do well in higher water temperatures. It's not just the hotter summers that are important here, but also the warmer winters that allows them to feed for more of the year.

 

Newt's observation about US carp is an interesting one, and he mentions that the northern states have hot summers and cold winters. Could carp also be growing bigger in the northern states because of less competition from other species, Newt?

 

Whatever the reasons I find the question fascinating and look forward to more observations from members. Forums like these seem a particularly good place to discuss such a subject.

[Bradford Angler]

I had the same thought about the pike . . apart from the usual reservoir pike washed up . . has the current record been challenged recently or are pike on the incresae sizewise . . don't think they are in the north anyway ?

[macca29]

Along with the other comments I think the river fish are bigger due to the influx of the cormorant to fresh waters.

These are eating the small fish leaving more space and natural food for the older fish which grow bigger.

Sounds daft but just a thought

[Bruno Broughton]

More interesting material worthy of a few comments.

 

Against the general background of few, larger fish, it is hardly surprising that pike sizes have not increased in the last decade or two. Pike need ample, regular supplies of food, not occasional blow-outs on specimen-sized fish. They also tend to grow best in clear-water fisheries, the sort of conditions that do not favour good spawning success by many of their potential prey species.

 

The exceptions, of course, are clear-water fisheries with lots of bite-sized fish, excactly what is provided by many trout reservoirs and gravel pits maintained for trout through regular introductions of rainbows.

 

The particular problem with stillwater roach and bream is that one of the consequences of eutrophication is greater plant growth. If these plants are suspended algae, which make the water appear green or green-brown for much of the year, the psawning success of roach and bream can be excellent. With greater competition for food from their fellows, the ultimate size of the fish is restricted.

 

If spawning success is intermittent or virtually non-existant (by which I mean that naturally-bred fish do not survive long enough to become catchable by anglers), the fish that do survive tend to grow much better. This is the more so if the fishery is productive. Clear-water fisheries - and many gravel pits in particular - fulfill these criteria.

 

I suspect that bream benefit in these conditions because they can survive long enough to attain large sizes. One reason for this is that they become too large for most predators, except otters, maybe. That is not the case with roach, which cannot outgrow the size limit for a range of fish predators. Certainly, I have aged far fewer roach of 10-12 years or older than was the case 20 years ago, and this leads me to strongly suspect that they are just not there.

 

The situation in rivers is more complicated, but relatively small species must struggle to survive the flood flows in many of our rivers Thanks to the blight of land drainage and flood prevention schemes, many rivers - even in lowland areas - are more 'flashy' than ever before. Typically, a flood event is now accompanied by a rapid rise in water levels and extremely high flows which subside equally rapidly; compare that with the more gentle rise and fall of flood water that used to be typical of many lowland rivers. Smaller species almost certainly get washed away, and they probably never get large enough to withstand flash floods.

 

Pockets of specimen-sized roach remain, but generally the situation is far from ideal. Can anyone name (say) half a dozen rivers where the roach fishing, or the dace fishing, is better than it was 20 or 30 years ago. I don't mean odd swims or short stretches; I mean substantial stretches of rivers. I'm blowed if I can. Yet I can do so for both barbel and carp.

 

[ 31. January 2004, 02:23 PM: Message edited by: Bruno Broughton ]

[Nugg]

Originally posted by Bruno Broughton

Certainly, I have aged far fewer roach of 10-12 years or older than was the case 20 years ago, and this leads me to strongly suspect that they are just not there.

 

Bruno can you say that the few fish that have attained this age, are bigger than 20 years ago?

 

Also, nitrates have been mentioned, but lets not forget that great advances have been made in water quality over the years, there is far less industrial pollution these days, which may or may not aid growth, dependent on whether the fish were killed outright or not.

[poledark]

I would suggest that we should look for one common factor in this. As stated by most posters there are a variety of possible factors affecting a variety of different water types and fish types.

To me the one thing they all have in common is milder winters, probably leading to a longer feeding/growing season.

 

Den

[fenboy]

Sometimes, somebody writes something that has you nodding your head in agreement all the way through. Bruno's posting did just that.

He's right about dace, too. Is that because they had a lot of success in many rivers following the columnaris outbreak of the late 60s which wiped roach out of the equation and hence there was less competition on the small rivers where they succeeded? That was certainly the case in West Norfolk, were the dace had it all to themselves through the 70s on the chalk-fed tributaries that flowed est into the Great Ouse.

But what about rudd? Where have they all gone?

It is interesting to note, incidentally, that bream and tench sizes have remained much the same through history in southern Ireland, where agriculture is mainly non-arable and, therefore, there aren't so many fertilisers washed into the rivers and loughs.

As an aside, why are Irish perch nearly always small? The waters are usually clear and have loads of small fish... but a pounder is usually a good one.

Keep up the good work, Bruno.

[Jeff S]

fenboy:

 

As an aside, why are Irish perch nearly always small? The waters are usually clear and have loads of small fish... but a pounder is usually a good one.

Found myself nodding as well. So many factors but can it be narrowed down to one? I believe it is a variety of those factors. Each one contributes to or balances in some way.

 

Fen, it's the same with perch in the US. You rarely hear of them over a pound. What is the secret ingredient?

 

[ 01. February 2004, 10:37 AM: Message edited by: Jeff S ]

[malevans]

Answer is obvious to me. The nice one don't end up mounted on walls in glass cases so they grow and get bigger. But whilst the protien baits etc contribute, they would have no effect if most 6lb tench ended up on their captures dinning room wall.