Dale Fort Blog Number 10

7 08 2012

 

Imagine a lump of matter with a mass so huge that its gravitational pull distorts the very fabric of space-time.  If you could find this warp in space (or wormhole), you might use it to defy relativity and visit unfeasibly  distant parts of the cosmos

   Adventurous readers may be disappointed to find The Dale Fort Wormhole Project slightly more prosaic.  The wormholes we investigated were not massive warps in space, nor were they the burrows excavated by worms themselves.  We were interested in the holes dug in muddy shores by people seeking bait for fishing.

People have been concerned about the impact of bait-digging on the soft-sediment shores of Milford Haven for at least 40 years.  The Countryside Council for Wales decided that an investigation might be appropriate and they employed Dale Fort Field Centre to carry it out.

  The aims of the study were to find out:

Which species were being collected ?

Where they were being collected from ?

What was the intensity of collection?

Did collecting vary seasonally?

Who was doing the collecting ?

How they were doing it ?

How abundant were the bait species ?

Where did the local bait shops obtain their stocks ?

What Species are Collected and from Where?

   Ragworms and lugworms are the two main species dug for in Milford Haven.  Ragworms are by far the most popular.

Easily the most important site for ragworms is The Gann followed in a distant second place by Angle Bay.  There is evidence of small scale digging at Sandy Haven, Gelliswick, Pembroke Dock and Pennar and a miniscule amount at Lawrenny and Llangwm.

Lugworms are harvested on a much smaller scale than ragworms and at fewer sites.  The main lugworm digging site was at Angle Bay, followed by Sandy Haven.  A few holes were found at The Gann, Gelliswick and Pennar.  Anecdotal information from bait-diggers suggested that sites like Saundersfoot and Pembrey were better for lugworms and more frequently dug for this species.  The only site where there was evidence of collection of razor clams was on the Dale village side of The Gann Flats.  Crabs were collected only from Sandy Haven and Dale.

How Intense is the Collecting and is it Seasonal?

We used a Garmin GPS (Global Positioning System) to map precisely the locations of bait-holes.  At the same time, holes were aged on a scale of 1 to 4, based on the nature of the sediment and the structure of the hole.  This work concentrated on the main sites: The Gann and Angle Bay.  We mapped and aged a total of 35,536 holes.  26,615 of these holes were in The Gann.

 

 

 

 

 

 

There were so many holes in The Gann that we divided the area into 50x50m grid squares and mapped the density of holes (as in the diagram above).  A typical grid square towards the central, most intensively dug area might easily contain over 500 holes.

We used the hole-age data to determine the proportion of holes of different ages to shed some light on the seasonal intensity of digging.  This data seemed to indicate intensive digging towards the end of the winter period, followed by a reduction in digging intensity until autumn.

Who is Doing the Collecting and How do They Do It?

Dale and beaches on the north side of the Haven are mainly visited by diggers from Milford.  We know of only one fulltime professional digger and he says he digs up to 2000 worms a day from The Gann.  Angle is visited by people from the Pembroke/Tenby area.  The less productive sites such as Gelliswick and Pembroke dock/ Pennar are only visited by people who live locally.  The summer period finds occasional holidaying anglers digging on the flats.  For the most part holiday makers probably purchase bait from shops rather than dig it for themselves.  The survey team met only two holidaying anglers over the whole period of field work.

Ragworms and lugworms are usually dug with a fork.  Peeler crabs are collected by turning over stones and boulders.  Razor clams are collected by skilled and fast use of a fork which may be helped by encouraging the animals to the surface by sprinkling salt onto the burrow holes.

How Abundant are the Bait Species?

   The highest density of ragworms was found at Sandy Haven Pill. This site also possessed the worms of lowest average weight of all 9 sites investigated.  The second highest ragworm densities were found at The Gann.  The mean weight of ragworms at The Gann was much higher than at Sandy Haven.  The animals sold by bait farmers seem to weigh 5-6g each. This is similar to the mean weight at The Gann.  It would therefore seem reasonable to suggest that this is the size anglers most desire.  The high density and high mean weights of ragworms found at The Gann, together with ease of access account for its huge popularity among worm digging enthusiasts.

Where Do the Local Bait Shops Obtain Their Stocks?

   We surveyed all the bait shops in West Wales and discovered:

Each shop sells an estimated average of 1265 worms per week

50% of shops sell ½ farmed and ½ locally dug worms

The number of locally dug worms sold per week is 7274 or 48.5 Kg

(= 378248 per year or 2522Kg per year)

Conclusions

If The Gann was populated by fluffy pink seaweed-bunnies that bait collectors impaled on hooks to lure bunny-guzzling dolphins to their doom, there would be much public concern for both the bunnies and the dolphins.  It’s hard to elicit a similar degree of sympathy for worms.  But The Gann is a Site of Special Scientific Interest (SSSI).  It’s (still) an extremely diverse sediment shore.  This diversity depends hugely upon its variety of sediments, some fine, some coarse and some in between.  As well as worms, it’s of vital importance for wading and other birds; it’s home to many interesting seaweeds and molluscs; and it’s got over 26,000 large holes in it.  The effect of all this digging is to mix and homogenise the sediments.  This is bad news for species that need specific conditions (E.g. Coarse sediment).

Species that can cope with these changes can do really well.  One such adaptable species is the ragworm.  It can feed on almost anything in a number of different ways.  It can actively prey on other creatures, it can feed directly on the sediment, it can spin a mucous net and filter food from the water and it can tolerate a variety of physical conditions.  Studies carried out at The Gann in 1960 and 1992 indicate a decline in species richness, coupled with a massive increase in the abundance of ragworms.  You might say that the area has been transformed inadvertently into a giant ragworm farm.

Return here for Blog Number 11 which will probably be another episode in the history of Dale Fort

 

 

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