A study of Climate Change and its effect on the Chub of the River Ribble
At the end of the 2006/7 coarse fishing season, my Ribble chub records showed that the number of chub caught above 5lb had declined and was still declining into the 2007/8 season. I then extrapolated the corresponding data from the FishingMagic Website Venue Thread for the Ribble and it showed a similar decline in chub caught above 5lb. I then started to think about why this might be, and if by looking at the possible sources of change affecting coarse fishing on the Ribble, I might find an answer. The two graphs below are the starting point of this investigation.
The two bar charts show for each year: - Green: No. of chub above 1lb to 4lb - Pink: No. of chub caught between 4lb & 5lb - Blue: No. of chub caught between 5lb & 6lb - Brown: No. of chub caught above 6lb - Yellow: No. of sessions
The Ribble Catchment
The River Ribble rises in the Pennines in the Yorkshire Dales at the confluence of Gayle Beck and Cam Beck and its character is that of a typical spate river. However, just below Settle the river passes across a large flood plain, a more typical feature of a lowland river, locally known as Long Preston Deeps, and here the river meanders and twists across open pasture with little or no protection from the elements. It's also at Settle that the river crosses the Craven Fault and we are out of the open bare limestone hills and into the glaciated valleys of North West Lancashire.
The mid Ribble is joined south of Clitheroe by two major tributaries; the Hodder and the Calder. The River Hodder rises in the Forest of Bowland where it is dammed near to its source to form Stocks Reservoir.
The River Calder, crossing East Lancashire, contrasts to the Hodder in that it is a post-industrialized river, exhibiting pollution from relics of mining, contaminated land run-off and sewage discharges.
From the Calder downriver the Ribble Basin covers a varied landscape shaped by a variety of activities, including livestock farming in the upper catchments to the industrialised urban areas such as Blackburn in the middle catchment. These activities have all had an impact upon the water quality and quantity of the Ribble. Historically, the landscape has also been modified, as watercourses and wetlands were altered to improve land drainage.
The river upstream of the confluence with the Calder is predominately a game river, below the Calder, and including the Calder, it is a mixed fishery and it is in this part of the river that the barbel and chub are the main species targeted by the coarse angler.
Fish Populations
A successful fish population is one that prospers within the limits of its environment. If a water body contains all of the elements needed to satisfy the basic requirements of the fish, then that population is more likely to be successful. In many cases, there will be habitat constraints, predation, competition and disease, as well as variable weather conditions at critical times.
-
Large variations in fish populations occur naturally.
The number of fish surviving their first year of life largely determines their overall contribution to the population. If many fish survive the first year, then that “year class” will be more numerous in later years. The classic “population Pyramid” can be used to illustrate this:
Poor conditions can affect the survival of young fish, and can result in lower numbers being added, or “recruited”, to the adult population.
-
Fish are affected the most by the environment in their first year of life.
The above information was extracted from the on-line EA book 'Coarse Biology & Management'.
Climate Change, Temperature, Food, Growth & Competition
Fish are cold blooded or poikilothermic animals and have the capacity to grow continuously all their lives. The growth rate in fish is not constant; it varies during the year and throughout the life cycle of the fish. In general the growth rate of fish is rapid in the first few years and after attainment of maturity gradually declines, ie, growth is continuous but growth rate declines with age. All growth comes from food and the products of ingestion and is either used for the maintenance or growth. Many factors affect the growth rate; food supply, temperature, stress and behaviour, etc. The metabolism of fish is very dependent upon the external temperature. This is particularly relevant in temperate latitudes where minimal growth is recorded during the colder months. The food supply may be adequate at this time but the digestive processes of fish are much slower at these sub optimal temperatures. The growth of fish is thus much more variable and vulnerable to external factors than mammals.
The above is a Précis of an article 'Growth in Fish with Particular Reference to Chub' written by Dr PB Spillett (Fisheries Research Officer) in a Chub Study Group bulletin from the 70's.
From the above it would seem logical that a mild dose of Global Warming would be beneficial for all aquatic life? However, what we also have to considered is whether any particular species of fish benefits more at the expense of another species, ie:
-
Would barbel feeding throughout the winter be additional competition for chub?
-
If the river temperature was to rise such that river carp were more successful in breeding, thus increasing the competition for food?
-
Could chub, being more predatory than barbel or carp, take advantage of the increase in the young of other species?
-
Spawning is a very debilitating process for a fish and imposes severe stress. If a higher water temperature encourages chub to have multiple spawning then does this reduce the growth rate of a chub?
This graph shows an average rise in river temperature of about three degrees. Although this may be beneficial to plant and invertebrate life, it also enlarges the window of opportunity for carp to spawn, which depending on your point of view may or may not be beneficial?
Spawning times for barbel - May - July, in water 14-20C.
Spawning times for carp - May - July, 16-22C, (multiple spawning).
Spawning times for chub - May - July, multiple spawning, 18C-20C
Climate Change, Flow and Survival
This graph shows the Max flood pulses on the Ribble along with the average water levels demonstrating that there are plenty of opportunities for the river to change the geography and environment of the river. Most chub die in their first year of life, even when conditions are ideal. Environmental and other factors can change conditions, and important habitats can disappear or change. In very bad years, practically no young fish of a species will survive.
The Aftermath of the Jan 7th 2005 floods above Ribchester (Note this was a near 4M flood pulse and not the highest the river has seen in the last 17 years)
|
The Author with a few nice fish from the Ribble - Which species will benefit the most from Global Warming?
|
Some issues regarding Pollution & Predation that have yet to be addressed
Farming Practices
Run-off due to:
- Hill & Fell drainage
-
Soil compaction due to heavier equipment, denser live stocking etc
Pollution due to:-
- Muck/Slurry spreading
-
Silage
Social
- Increase in sewerage requirements due to increases in population
-
Migration from town to country
-
Industrialization
-
Pollution
Accidental or illegal fish stocking
Predation
-
Mink
-
Otter
-
Seal
-
Cormorants
-
Illegal removal of fish
There are several articles that could be written regarding any of the above subjects all of which may affect the future of angling on the Ribble, however, a lot of these are not within our ability to control.
Conclusion
What I didn't expect to find was the large increase in water temperature and to support my own records re water temperatures I asked the EA for the data they had and this confirmed my own findings. The magnitude of the rise came as a surprise; however, I don't have any older historical data therefore I can't say that this is an unusual event. Although one could speculate that this rise in water temperature will continue, please bear in mind that there are other climatic events that could reverse this trend, like the collapse of the Gulf Stream due to the melting ice caps.
Just has I'd finished the draft copy of this article about the reductions in big chub on the Ribble, I've just had a nice couple of 5lb plus chub in the last couple of trips. Let's hope that this continues and I get the chance to continue with my records long enough to show once again an increase in big chub on the Ribble.
My article may seem to end abruptly, but as I've been analysing my records I keep finding more questions to address and the need to collect even more data. Also, as I read more and more about chub, the historical data held by the Chub Study Group is absolutely fascinating and I find even more questions to ask.
I'm sure my studies are making me a better angler, however, like most anglers I also just enjoy fishing and at the end of the day that's the only reason I need to justify what I do.
John McLaren
