Otter friend or foe

[Anderoo]

Admittedly, such pictures might be out there, but I couldn't find any - anyone else want to have a try?

 

Afraid not - but I do have quite a few pictures of unremarkable perch lying next to rods

 

 

 

I've seen 2 otters around here, one on the Windrush, 1 on the Thames. I've never seen one eating anything, but I have caught several fish with what I suspect is damage caused by failed otter attacks, especially chub (chewed tails, missing scales). But I don't get emotional about it.

 

[Vagabond]

Aye, otoliths in scats would be the way to go. They are little lumps of calcium carbonate and protein found in the inner ears of fish, and they'll pass right through an otter.

 

Mm'yes. But, surely the otter will have to have eaten the fish's skull for that to happen, and there must be a limit to the size of a fish-head the otter is prepared to eat whole. So what I am saying is that what an otter is prepared to swallow will govern what is found in the scats. So what is in scats might be biased in favour of small fish.

 

It seems likely that an otter eating a large fish (lets not argue at this stage whether it killed the fish or found it dead or dying - that does not affect the argument) will chew the best bits but eschew (forgive the pun) the larger bones and skull, and perhaps larger scales.

 

If you want evidence of otters eating larger fish, then scales might give the answer.

I'm not into scatology (or scatomancy ) so don't know how well scales survive digestion - but assuming they do........

 

The scales of even large salmon and trout are tiny in comparison with the size of the fish, so would get eaten (and show up in the scats ?) . The scales of eels are miniscule.

 

Cyprinids have larger scales, but they might still get swallowed.

 

I have just been up to the spare room and dug out a box of fish-scale slides I made in the days I was looking at growth rates. All from fish caught either by me or my mates.

 

I have measured a few. All measurements to the nearest half-millimetre.

 

Barbel scales are relatively small for a cyprinid. A scale (roughly oval shape) from an 11lb 8oz barbel measures 15.5mm by 12mm

Chub/dace/roach scales are broadly circular.

A scale from a 6lb chub is 22mm diameter

 

Carp scales are huge (scales from doubles were too big for the slides I used ) One from a 9 lb fully scaled mirror was 35 mm by 32mm

 

...and if the otter is dining futher down, in the estuary, a scale from a 5 lb mullet measures 18mm by 15mm. or from a 12lb 8oz bass a scale of 15mm by 13mm

 

Steve, Worms - have scales of this sort of size ever turned up in the scats you have examined ?

Edited November 14, 2011 by Vagabond

[Tigger]

I've seen 2 otters around here, one on the Windrush, 1 on the Thames. I've never seen one eating anything, but I have caught several fish with what I suspect is damage caused by failed otter attacks, especially chub (chewed tails, missing scales). But I don't get emotional about it.

 

 

 

I've seen fish with chunks missing from their fins just like that chub from lots of still and running water venues where there are no otters present so I wouldn't put it down to otters. Those fins do grow back by the way (infact you can see it growing back in the pic) so it's not a problem, just looks unsightly for a spell.

Edited November 14, 2011 by Tigger

[Tigger]

After reading through this thread, I'm glad to see that AN has (again) proved to be more open minded on the subject, than most other forums usually are.

 

To answer the original question, "Are otters friend or foe"? In my opinion they are neither. They are just another piece of the jigsaw, that makes up the natural flora and fauna of our waterside. They are no more a "foe" than pike, perch, chub, kingfishers, heron etc, and less of a foe than many anglers, and angling bodies.

I find it strange and hypocrytical that some sections of angling can complain about the 'stocking' of less than 200 otters over the last 20 odd years. While many of the same people support the stocking of hundreds of thousands of fish, (that are either alien to our shores, or to the locale)! Talk about double standards!!

I can only assume that those who see otters as a "foe", must do so because they see them as competition. Which again seems strange, and more than a little foolish to me.

 

As to the 'loss' of species. During my many years of angling involvment, I have seen peaks and troughs in species numbers, in many waters. There have been years when some species have dominated a water/area, only to eventually fall, and be replaced by another. This is natural, as the conditions/food supply benefits some species more, and the survival rate of those species increase. As conditions change, they will favour another species, and so on, in a natural cycle. It's only when man interfers will this cycle that we have problems. This can be through discharges, abstraction, bank improvement (?), building etc. It can also be by adding a different species into the mix, (something anglers are particularly good at). These will all have an effect on the make up of water, and not always with the result they hoped for.

 

I see that 'The Traveller' has been mentioned (again) as evidence of otters killing/eating large fish. Could those who believe this to be fact, please supply the post mortem evidence as to the condition and age of the fish. I have scoured the 'net for this information but haven't found it. I could be my lack of skill that's caused me to miss it, so I would be grateful for a link.

 

As usual, all this is just my honest opinion.

 

John.

 

 

 

Pretty much spot on with that John

[Worms]

An interesting paper on otter feeding habits here. Especially considering eels weren't particularly scarce when some of these surveys took place. Personally I agree with most of the results shown here with regard to cyprinids being the major food item as opposed to eels. On game rivers bullheads and small trout and salmon parr are the main targets, grayling less so!

 

I'll see if I can dig out a recent paper on the significance of aquatic invertebrates as well....don't hold your breath, house is upside-down and I'm in silly season!

 

p.s, Hi John!

 

Oops, sorry Dave, nearly forgot. The biggest scales that I have found in otter scats were from a pike that I estimated at 6-8lbs, largest cyprinid (chub scales) about 2.5lb.

Edited November 14, 2011 by Worms

[Phone]

Worms,

 

Was interesting, almost 180 degrees from Midwest US.

 

Phone

[Steve Walker]

Experts?

 

No one I think can count themselves as an expert on this subject, I think there is still a lot to learn.

 

What is for sure that views seem to be very polarised as whether that Otter is Friend or Foe.

 

If I remember correctly, Worms makes his living as an expert in a field which includes this subject

[Vagabond]

biggest scales that I have found in otter scats were from a pike that I estimated at 6-8lbs, largest cyprinid (chub scales) about 2.5lb.

 

Now that is very interesting. Chub have comparitively large scales.

A scale from a 2.5 lb chub would have a diameter of about 19mm

Bigger, in fact than a scale from an 11lb pike (14mm x 10mm),

bigger than a scale from an 11.5 lb barbel, (15mm x 12mm)

and far, far bigger than a scale from a 20 lb salmon.

 

So the upper limit of what indigestible bits an otter is prepared to swallow is at least 19mm - that's rather larger than I thought. So my hypothesis (suggested to FT many posts back) that the absence of large scales and bones from the spraints might just mean otters are not prepared to swallow them can only apply to items significantly greater than 19mm across.

 

Ie if otters were consuming double figure barbel, double figure pike, and double figure salmon, then you would expect some scales to show in the spraints. Worms ? Steve ? ever seen/heard of any?

 

The hypothesis might still apply to large carp, however, which have very large scales. Even an otter might think twice before trying to swallow a scale over an inch across.

 

 

Read your link, Worms, very interesting, I fished Slapton Ley for a week in 1953, and again for a week in 1961. There have obviously been some profound changes in the fish population, which I will pursue in a different thread. (Have you got access to Kennedy's paper ? Would appreciate a link)

The broad thrust of Riley's paper as far as otters are concerned, is that they will take whatever fish are most abundant and most easily caught. No change there.

[Steve Walker]

Not so much my area, Dave, all my otoliths were dug out of fish heads, not out of otter poo!

 

Worms might know?

[corydoras]

The broad thrust of Riley's paper as far as otters are concerned, is that they will take whatever fish are most abundant and most easily caught.

That makes sense to me. After all that's what evolution would dictate. No doubt our hunter-gatherer forebears used the same approach when going out to hunt for din-dins. "Aw Mum, not finch and chimps AGAIN"

 

Sorry, I'll get me coat.

Edited November 15, 2011 by corydoras