Yuku free message boards

Bare with me here guys, this is Chris who was covering the Cherwell area for the past few weeks, its cut and pasted, therefore the tables etc have broken up.
Anyone who wants copies just shoot me an email through. There are 3 more documents. As I said just shoot me a pb through and I will forward the full attachments, I haven't had a chance to look at them yet, as I have been moving house.... Only round the corner but may as well have been to Scotland, the amount of hassle there has been!

Dear Mark,

Thanks for highlighting the Barbel Fishing World forum comments to me. They certainly

make interesting reading, and mirror recent comments made to us by other local anglers.

Overall, the themes seem to be fewer, but larger chub, and historically low, and declining

numbers of barbel, along with issues of predation by otters and the effect of signal crayfish.

Other interesting issues of spawning success, water quality, habitat quality and high/low flows

are also touched on. There are some reports of reasonable current fishing too.

I'll try and address some of the issues in turn, although as you know, some of them have no

simple practical solution. I'll begin by looking at what the Environment Agency fish survey

data indicate.

Fish Survey Data

We are always keen to hear reports from anglers, especially those who have fished the river

over a long time period. I know that being out fishing on the rivers can really give you an

excellent understanding of what is going on and also what might be changing. Rod-catches

and direct observations can highlight trends. However as anglers we also know that results

can also be influenced by river conditions, angling pressure, size-selective methods etc.

For that reason, we collect our own fishery survey data in order to assess trends in fish

populations over time. Again, this data is not without its limits. For example, although the

survey locations will remain the same at each site, the standard survey length is around 100m

of river. Water flow/clarity and efficiency of the electric-fishing equipment and operators can

all affect the results too. In terms of barbel, the low numbers encountered on the Cherwell do

not allow an accurate picture of population size, but may highlight trends. For fish which have

been shown to migrate up to 34km in unimpounded rivers, their presence in the sites at the

time of survey is obviously not guaranteed.

We have undertaken fish surveys on the Cherwell for over 15 years, on various sites which

give good coverage of the whole river. In terms of the lower river, the best sites which we

have continuous data for, are Islip and Gosford Bridge (2001-2008). We have other data for

sites at Lower Heyford, Northbrook, Gibraltar, Shipton and Marston over shorter periods,

which I'm happy to provide upon request.

Chub

I've taken the data we have for chub captured in surveys at Islip and Gosford Bridge. Fig. 1

shows the biomass (weight) of chub at each site over the period 2001-2008. Biomass is

shown in grams of fish per square metre of river surveyed. I appreciate this is not an easy

measurement to comprehend from an angling point of view, but it's a standard scale which

allows direct comparison between sites and rivers all over England and Wales. As a rough

guide, for a "Southern English" coarse fish river, 20 grams per square metre of all fish species

combined would be considered a good standard.

Fig. 2 shows the density (number) of chub at each site over the period 2001 to 2008. Density

is the number of fish per square meter of river surveyed. The reason for using both biomass

and density as measurements is that you could potentially capture just one large fish in a

survey and that might give you a very high biomass figure, but it would hide the fact that only

one fish was captured. The density figure allows you to see how many fish are present,

which obviously has implications when you are looking at juvenile fish growing on to replace

the larger, older fish. A density figure of 0.50 fish per square metre of all fish species would

be considered very good, however that would generally consist mostly of species such as

dace, gudgeon, roach, bleak etc.

Density of Chub caught on surveys at Gosford Bridge and Islip from 2001-2008, including

trendlines.

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

2001 2002 2003 2004 2005 2006 2007 2008

Year

Density (n per m2)

Gosford Br.

Islip

Gosford Br.

Trendline

Islip Trendline

Biomass of Chub caught on surveys at Gosford Bridge and Islip from 2001-2008,

including trendlines.

0

5

10

15

20

25

30

2001 2002 2003 2004 2005 2006 2007 2008

Year

Biomass (g per m2)

Gosford Br.

Islip

Gosford

Br.Trendline

Islip Trendline

Fig. 1

Fig. 2

As you can see from Fig. 1 and 2, the biomass and density of chub at Gosford Bridge has

fluctuated but remained relatively stable. Issues worth noting about the 2007 and 2008

surveys were new equipment, which later proved to be less reliable and very high flows

respectively, which may have reduced the efficiency and therefore led to lower results. Both

biomass and density levels for chub are what we would consider to be good. These

encouraging results are backed up by looking at Graphs 1-8 (see Appendix 1), which display

individual lengths of chub captured at each survey. In each survey, a range of sizes of chub

are apparent. This means that large, mature fish are present, along with juvenile chub which

indicate successful recruitment.

The results for Islip given in Fig. 1 and 2 suggest a rather different picture. Both biomass

and density for chub have been at good to high levels but have declined in the last few years,

which seem to mirror the findings of anglers on the forum. As described above, the results in

2007 and 2008 may have been impacted by the equipment and flows, and potentially the

summer floods of 2007 which are likely to have moved both adult and juvenile fish

considerably, as well as reducing successful recruitment from the 2007 year-class. However

the decline appears to pre-date these years.

These results should also be viewed alongside Graphs 9-16 (see Appendix 2), which

indicate a progressive loss of some size ranges of chub at this site. This is especially

apparent from 2005 onwards, and has potential implications for future spawning, recruitment,

and of course the quality of the fishery itself.

At both Gosford Bridge and Islip, there has been an upward trend between 2001 and 2008 of

the average size of individual chub (see Fig. 3). This agrees with angler reports (and also

reports from many other rivers in recent years).

Fig. 3

Mean Length (mm) of individual Chub caught in Surveys at Gosford Br. and Islip

2001-2008, including trendlines

0

50

100

150

200

250

300

350

400

450

2001 2002 2003 2004 2005 2006 2007 2008

Year

Length (mm)

Gosford

Br.

Islip

Gosford

Br.

Trendline

Islip

Trendline

Barbel

I've taken a look at the captures of barbel in all of our Cherwell surveys dating back to 1986,

and presented the data in Table 1. This gives an indication of their distribution along the river

(although it's obviously not exhaustive), and also highlights the limitations in capturing barbel

in a survey - they tend to appear and disappear according to their movements relative to the

survey site and time.

Barbel have been caught at four sites, Gibraltar, Thrupp, Gosford Bridge and Islip. Table

2 shows the number and fork length (measurement in mm from nose tip to centre of tail fork)

of barbel caught. You will see that the site which has held barbel most frequently is Gosford

Bridge. Certainly in 2001 and 2002, this site held numbers of mature and juvenile barbel,

however, these catches have declined more recently. Whether this can be directly translated

into a reduction in population size is impossible to say with certainty; however that would

agree with the angler reports. The barbel from Thrupp in 2008 were captured in a targeted

barbel survey - an area not covered in previous surveys (for further details see Cherwell

Fisheries Action Plan Update pdf - to follow).

.

No barbel have been encountered at Islip since 2001, despite a further seven surveys having

taken place there. Again, whilst not conclusive, this is further evidence of declining, rather

than increasing numbers of barbel.

Year 1986 1989 1995 2001 2002 2003 2004 2005 2006 2007 2008

Site Location

West Farndon Mill ns 0 0 ns ns ns ns ns ns ns ns

Trafford Bridge ns 0 0 ns 0 ns ns ns 0 ns ns

Cropredy 0 0 ns ns ns ns ns 0 0 0 0

d/s Cropredy ns ns ns ns ns ns ns 0 0 0 0

Slatt Mill ns 0 0 ns 0 ns ns 0 0 0 ns

Little Bourton ns ns ns ns 0 ns ns ns ns ns ns

Spiceball Park ns 0 0 ns 0 0 0 0 0 0 0

M40 Roadbridge ns ns 0 ns 0 0 0 0 0 0 0

Twyford Mill 0 0 0 ns 0 0 0 0 0 0 0

Mill House Farm ns ns 0 ns ns ns ns ns ns ns ns

Nell Bridge ns 0 ns ns 0 0 0 0 0 ns ns

Somerton 0 0 0 ns 0 0 0 0 0 ns 0

Lower Heyford 0 0 0 ns ns ns 0 0 0 ns ns

Northbrook ns 0 ns 0 ns 0 0 0 ns ns ns

Rock of Gibralter ns y 0 ns ns ns y y 0 ns ns

Shipton on Cherwell ns ns ns 0 0 ns ns 0 0 0 0

Shipton Weirstream ns ns ns ns ns ns ns ns ns ns 0

Thrupp ns ns ns ns ns ns ns ns ns ns y

Hampton Poyle ns 0 ns ns ns ns ns ns ns ns 0

Gosford Bridge ns ns ns y y y 0 y y y y

Islip ns y ns y 0 0 0 0 0 0 0

Marston ns ns ns ns ns ns 0 0 0 0 0

ns Not surveyed in that year

Surveyed but no barbel caught

y Surveyed and barbel caught

Year 1986 1989 1995 2001 2002 2003 2004 2005 2006 2007 2008

Site Location

Rock of Gibralter ns 700 0 ns ns ns 705 627 0 ns ns

560 701

520 618

520

520

330

Thrupp ns ns ns ns ns ns ns ns ns ns 705

685

374

Gosford Bridge ns ns ns 676 664 628 0 535 316 565 248

532 639 422 366 269

396 633 287 375

352 534 267 245

157 462

153 396

151 271

254

223

215

104

100

98

96

92

88

86

85

80

Islip ns 694 ns 160 0 0 0 0 0 0 0

668 112

102

98

37

Presence or absence of Barbel in Environment Agency Fish Surveys on Cherwell 1986-2008

Fork Length (mm) of Barbel caught in Environment Agency Fish Surveys on Cherwell 1986-2008

Table 1

Table 2

Reasons for changes in chub populations.

I cannot give a definite answer which fully explains the trends indicated both by angler

catches and by our own data. However, we can use current and historical research to make

educated opinions for the reasons. Most of these have been discussed in the forum already -

natural variation in fish populations, predation, habitat quality and floods.

We know that chub (and barbel) populations can vary over time, just through natural variation

in spawning success and survival of the crucial first winter (year-class strength). In a river,

year class strength is usually associated with factors including water temperatures, flow rates

and whether there is sufficient cover for the juvenile fish ('refuge') in the river. Where a strong

year class of chub exists, it will often translate into a good adult population (and therefore

good "specimen" fishing. Chub can be very long-lived - we have aged chub up to 16 years

on the Cherwell, but older fish may be present. In southern England, good coarse fish year

classes in some rivers have originated from 1975, 1976, 1984, 1994, 1995 and 2003.

It may be that some of the specimen chub targeted by anglers on the Cherwell were born in

the early-mid 1990's, and that those have been reaching the end of their lives over the last

few years.

Between the mid-1990's and now, as you will know, some significant changes have taken

place on the river. The first is the colonisation of the signal crayfish, which was first (officially)

recorded on the Cherwell in 1995 and spread very rapidly. The second is the increase in

numbers of cormorants now living inland and the third is recolonisation by otters. If pushed, I

would suggest that the huge numbers of crayfish are likely to have had the greatest individual

effect on the fish populations of the river.

I'm sure you are familiar with the generally perceived ways in which signals can impact fish

(directly via predation on spawn, fry and altering fish behaviour, and indirectly by feeding on

invertebrates, cropping weed and potentially by increasing turbidity). Conversely, signals can

act as a food source for those fish large enough to eat them. I have attached a recent report,

supported by the Environment Agency (see Chub and Crayfish pdf), which looked at the

interactions between chub and signals, and studies the Cherwell and Evenlode as well as two

other Thames tributaries. This is the most relevant study I have seen on this subject, and

strongly supports these perceived impacts. The report is rather technical to read, although

well worth a look if you are interested. In summary, the findings were that the growth rate of

young chub (less than 3 years old) was reduced in the presence of signals, the growth rate of

older fish increased in the presence of signals, and that their diets overlapped for certain size

classes of fish.

Cormorants, mink and otter are all piscivores which will be taking fish of all sizes on the river.

Fish populations have survived with pressure from predators for millions of years and there is

no suggestion that our usual coarse species will be lost to any of these new (or in the case of

otters, re-established) predators. However, for the time being, it's entirely possible that some

of the perceived reductions in chub populations may be the result of pressure in addition to

the signal crayfish impacts, i.e. a cumulative effect of the combined issues.

One of the key factors in avoiding predation is the availability of refuge areas such as fallen

trees, weed beds, undercut banks etc. In our daily work, and during our advice to

landowners, angling clubs and other environmental bodies, the Fisheries team are keen to

stress the importance of these habitats, and press for their retention or improvement where

feasible.

An interesting point is the apparent difference in chub population trends between Gosford

Bridge and Islip. It may be that the habitat, either in terms of spawning areas, or refuge

areas, has allowed the chub to be more resilient to the new impacts at Gosford.

The recent summer flooding events will have undoubtedly affected fish populations in the

Cherwell through downstream displacement, fry survival (as discussed above), and also

possibly by stranding of fish in certain parts of the floodplain. Future survey work will

hopefully give us a better indication of the extent of the impacts of the 2007 and 2008 summer

flooding. If forecasts are correct, more frequent and extreme summer flooding in the future

will emphasise the importance to suitable low-flow refuge areas for fish, and good connectivity

between the river and floodplain, to allow fish to make their natural movements to and from

these areas.

Reasons for changes in barbel populations.

From our data and also from angler's reports over time, it is apparent that barbel have never

been hugely abundant in the Cherwell, when compared to some other rivers. However, that

should not prevent us from being concerned about their apparent decline in recent years.

Indeed, for that fact, as well as their status as an "indicator species" for habitat quality in the

river, and because they are highly sought-after quarry for our anglers, we are keen to address

the issue and to work with others to improve the situation. It seems to me that all of the

pressures outlined above probably apply equally to the barbel in the Cherwell, as much as the

chub (possibly more so, given smaller populations, and higher habitat quality requirements of

barbel over chub).

What the Environment Agency have done recently on the Cherwell

Some of the comments from local anglers suggest that news of our work on the rivers is not

reaching everyone. We do work closely with most of the major angling clubs and

consultatives in the area i.e. The Upper Thames Fisheries Consultative on a regular basis.

However, here are some of the things we have been doing, and intend to do in the future on

the river.

• We continue to survey the river to get fish population data (as used in this report). All

of this information is available upon request.

• We undertook a targeted barbel survey in 2008 in areas not covered by routine

surveys.

• We recently installed two fish refuge backwaters on the Cherwell (one in Banbury

near Spiceball Park and the other at Sunnymead in Oxford). Initial surveys indicate

that they are being well used by juvenile fish of several species (for further details see

Cherwell Fisheries Action Plan Update pdf - to follow Monday).

• We introduced several tons of clean gravel to form a spawning area at Islip, and

pressure-washed existing gravel areas to remove silt from the bed.

• We part-funded and supported the research into the chub/crayfish interactions on the

Cherwell and other rivers.

• We continue to work with the Cherwell Fisheries Action Plan group to address a wide

range of issues on the river.

• We highlighted the barbel issue on the Upper Thames and Cherwell to a PhD student

we are funding (on a national basis) to research the issue of declining barbel

populations on our rivers. We are hoping that their studies will encompass these

rivers and allow us to understand the situation - and potential solutions - more fully.

• We stocked several thousand roach, chub and dace into the river around Cropredy

and Somerton in 2007 and 2008.

• We have worked closely with Thames Water to support the construction of the

Banbury Low-Flow Alleviation Scheme (now operational). When its operation is

triggered by low river flows in Banbury, this will essentially back-pump water for

recirculation through the areas which have historically been most heavily impacted by

a severe lack of water.

• We ran an investigation into turbidity in the Cherwell. This highlighted some

unexpected nocturnal increases in turbidity which could be potentially be related to

night-time signal crayfish activity. We began a further study to test this theory, by

heavily trapping crayfish in a short section of river, whilst continuing the turbidity

monitoring. Unfortunately, summer floods interfered with this research to such an

extent that it had to be postponed.

• We produced a comprehensive "State of the Environment" report for the

Cherwell, covering the period 1998-2005. I have attached this as it covers many of

the topics touched on by forum contributors - river flows, invertebrates, water quality

etc. Space prevents detailed discussion here, but it's certainly worth a look.

What we will be doing in the near future.

• We have plans for another backwater fish refuge in the Northfield Farm area.

• We will continue with landowner discussions to provide a coarse fish bypass channel

around the weir at Gosford Bridge, which will allow more fish access to high quality

spawning and juvenile habitat.

• We intend to introduce and improve more high-quality gravel-spawning areas in

strategic areas.

• We have earmarked fish from our Calverton Fish Farm for stocking into the Cherwell

for 2009 and 2010. These include several thousand chub, roach and about 2,500 1-2

year-old barbel. This is subject to other priorities (i.e. if a major fish-kill on another

river meant we had to restock there instead), but stands at present.

• At a national level, further research into impacts of signal crayfish and potential

control methods is being organised and part-funded by the Environment Agency.

• We are keen to work with other groups, including landowners and clubs, to plan and

deliver targeted habitat improvements or other schemes which will have a beneficial

effect for fish and anglers.

What local anglers can do.

I am glad to see that there are some very positive feelings posted just recently on the forum,

indicating that anglers and/or clubs wish to work together to improve the river.

It is worth restating that the Cherwell Fisheries Action Plan is still running, and that was set up

essentially to allow local anglers and clubs to become involved and agree on realistic goals

for the river, and to jointly work towards getting these achieved. Having attended a couple of

these group meetings, I think it is fair to say that they are now running low on members, and

on momentum. The same, few, hard-working stalwarts are keeping them running.

Tom Sherwood, whose role I am standing in for, is back from leave in the next week, and so

he will resume as Fisheries Officer for the Cherwell at that point. I will therefore leave it for

Tom to suggest the best route to incorporate the momentum which appears to be building, for

it would surely be a shame to lose that.

I hope this report provides you with some useful information. I will e-mail you the missing

Cherwell Fisheries Action Plan Document on Monday. Please call me (or Tom Sherwood

after Tuesday), to discuss any of this further.

Kind regards,

Chris Bell - Fisheries Officer

01491 828358.

chris.bell@environment-agency.gov.uk

18 April 2009

Appendix 1

Graphs 1-8 - Length/Frequency for Chub at Gosford Br. 2001-2008

2008

0 1 2 3 4 5 6

0 100 200 300 400 500

Length (mm)

Frequency

Chub n = 30

2007

0

1

2

3

4

0 100 200 300 400 500

Length (mm)

Frequency

Chub n = 18

2006

0

1

2

3

4

0 100 200 300 400 500

Length (mm)

Frequency

Chub n = 33

2005

0

1

2

3

4

5

0 100 200 300 400 500

Length (mm)

Frequency

Chub n = 14

2004

0

2

4

6

8

0 100 200 300 400 500

Length (mm)

Frequency

Chub n = 43

2003

Chub n=32

0

1

2

3

4

5

0 50 100 150 200 250 300 350 400 450 500

Length (mm)

2002

Chub n=41

0

2

4

0 100 200 300 400

Length (mm)

Frequency

2001

Chub N=34

0

5

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

Length (cm)

0

5

10

0 100 200 300 400 500 600

Length (mm)

Frequency

Chub n = 21

0

5

10

0 100 200 300 400 500

Length (mm)

Frequency

Chub n = 10

Appendix 2

Graphs 9-16 - Length/Frequency for Chub at Islip 2001-2008

2008

0

1

2

3

0 100 200 300 400 500

Length (mm)

Frequency

Chub n = 10

2007

0

1

2

3

4

0 100 200 300 400 500

Length (mm)

Frequency

Chub n = 3

2006

2005

2004

0

2

4

6

8

10

0 100 200 300 400 500

Length (mm) Frequency

Chub n = 40

Chub N=59

0

5

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51

2003

Chub n=36

0

1

2

3

4

5

6

0 50 100 150 200 250 300 350 400 450 500 550

Length (mm)

2002

Chub n=72

0 5

10

15

0 100 200 300 400 500

Length (mm)

Frequency

2001