Why are fish growing bigger?

[Steve Burke]

This follows on from Nathan's topic on big fish.

 

Why do you think some species of fish are growing much bigger than in years gone by?

 

It's not all species of course, but the record weight for many has substantial increased since I started fishing over 40 years ago.

 

It's probably a combination of reasons of course, and I've got my own ideas. But let's here from others first.......

[Guest sslatter]

Many fish now living in an "unnatural" situation? Being regularly fed high protein baits etc. "artificially" introduced into the water? Thenceforth being mollycoddled and "protected", and further fed?

 

Some of the fish photos I see nowadays make me cringe..some fish have got bigger stomachs than humans. Can't be right. Not naming any species or anything, but..

[wunnus]

I agree that the increased use of high protein baits has got to be a strong factor.

 

The overweight specimens that often adorn the mags are certainly a recent phenomena. The stuffed specimens of the past do not seem to have as much flab on them.

 

But in part this must also be due to the fact that many live shelterd environments. The high economic value of such specimens to their owners means that the food webs in those waters favour them. They live in an artificial environment tuned to their needs.

 

Another factor has to be that many of our streams in lowland England are high in nitrates. This promotes rapid vegetation growth and hence the food supply in our rivers is there as well. (insects etc like the weed)

hmmm time to reflect some more...

[kendo]

definitely high protein baits.

[Lid]

Those damn signal crayfish make good food for chub, perch (and presumably pike), so that could be why we are seeing some bigger perch and chub in rivers.

[ayjay]

There are no crayfish in the Stour or Avon yet,but plenty of big chub.

 

Tench were probably the first species to start throwing up bigger specimens,quite some time ago now,and I would think that this was before the introduction of large quantities of high protein baits.Likewise on the Ouse, a few anglers started to catch big barbel and it was only after this that the circus moved in with the bait buckets.

 

I think it is a combination of many factors,including warmer winters,various hormones in the water,growth hormones in bait,high protein baits,and probably several more that I can't think of at the moment. (It's late, I'm tired )

[fenboy]

Milder winters have got a lot to do with it. Fish don't semi-hibernate any more. I well remember the frustration more than 20 years ago when I couldn't fish certain drains and stillwaters for weeks on end in winter. It just doesn't happen any more.

 

Boilies play a part in heavily-fished stillwaters. But not rivers and drains. So what's going on there? Possibly less competition: there are fewer small fish around these days.

 

Also, fish live longer. Keepnet design is better, so survival rates of coarse fish have improved.

 

Pike grow bigger because 99 per cent are returned to the water. Thirty years ago, 50 per cent weren't.

 

But I agree that eutrophication from excess nitrates is largely responsibhle. The waters are richer and therefore more productive. Same happens on the land, which is why farmer apply so many nitrates in the first place.

 

Incidentally, Steve, all fish are "growing bigger". That's because it's impossible for a fish to grow smaller...

[Bruno Broughton]

If we look at fish growth from a very basic viewpoint, the crucial factor is the quantity of food available to and eaten by each individual fish.

 

So...

 

This should lead us to examine:-

 

1. the amount of food, and

2. the number of fish

 

Influences that merely increase the amount of food available could cause the population number to increase - more fish of the same size. It is ALSO important that there are fewer fish, leading to a scenario in which these fish have more food each.

 

We are fortunate to live in times where both influences have coincided. The real driver for most of the weight increases has been the management of the land. If land is fertilised, this makes land plants grow. When the same fertilisers enter water, they are equally good at making water plants grow. In the last 40 years there has been a trend of increasing water enrichment (known as 'eutrophication') as a consequence of what has happened on the land. It is not just nitrates that are responsible; phosphates are of equal or even greater importance.

 

On specific fisheries, the bait factor may be of importance, but this is not universal. By the way, I disagree that it has been high protein content of baits that has been responsible - most coarse fish cannot digest or utilise protein content of more than 50% (usually less), and if their food contains a lot more than this, it simply passes out as poo. But ample supplies of good-quality bait has played a role in some fisheries.

 

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

 

Crayfish? On a few fisheries, maybe, but this is not universal.

 

There is no single factor that has acted to reduce fish numbers, but the following (in no particular order) have been of lesser or greater importance at specific fisheries:-

 

increased predation on fish by fish-eating birds (and on eggs by crayfish)

 

deliberate fish cropping exercises

 

increased land drainage and river channelisation (causing wash-out of fry)

 

fluctuating temperatures at/immediately after spawning (egg/fry mortalities)

 

 

Against this background, the milder winters have helped to maintain the metabolism of fish at higher level than would otherwise be the case, enabling them to benefit from the extra food available to each.

 

The deliberate targetting of large fish, and the use of tackle capable of landing them, are other (but marginal) influences.

 

The question could be different: at 'natural' fisheries not established or maintained by stocking, has the number of catchable fish increased or decreased in the same period? The answer paints a somewhat different picture of the status of UK fisheries... but for the same reasons cited above.

[Newt]

Interesting as usual Bruno. A question though.

 

Against this background, the milder winters have helped to maintain the metabolism of fish at higher level than would otherwise be the case, enabling them to benefit from the extra food available to each.

 

Certainly warmer water = higher metabolic rate in cold blooded critters that live in water.

 

Certainly they have to eat more to fuel the increased rate or else lose weight and maybe die of starvation.

 

But is there really a net weight increase or do the two factors a)eat more b)burn more pretty much cancel each other out?

 

I've noticed that carp in the US, for instance, tend to average larger size/weight (at least the reported catches) in the northern US than in the southern US. Those areas tend to have longer and colder winters than the UK along with hotter summers.

[Dick Dastardly]

More interesting to me is why some species are bucking this trend.I personaly dont think Pike are growing that much bigger.I am talking more over the last 100 years than last 30 here.But more specificly the Roach.With the exception of a few carp waters Roach in general aint no bigger are they?Certainly not to the same extent as all(?) the other species.

When a lot of the "great" anglers of the last centuary were at their peek ie Walker,the Taylors,Stone etc etc a 10lb Bream was unheard of.Now many many waters hold them.Same with Tench a 5lb fish being a monster,not so now.BUT now same as then a 2lb Roach seems to be just as rare.Why? or dont you agree? :confused: