Wednesday, 9 June 2010

Potting for Crabs and Lobsters

We all love our shellfish from crab and lobster to whelks and prawns. It must be remembered that these, unlike the harvested bivalve species mussels, clams and oysters, have to be caught by trapping or potting methods. This type of fishing can be hugely rewarding but also very dangerous. The short blog post gives a simple explanations into the procedure of catching our favorite seafood.

Traditionally there are two main types of pot in the UK. The creel is constructed from a wooden frame consisting of a rectangular batten base surmounted with ‘D’ shaped hoops or bows and then netted. The entrance or entrances are side mounted and are known as soft eyes together with a stretched band across the pot used for baiting. The inkwell was originally made entirely from wickerwork with a circular base and a neck in the top. These were baited using wooden skewers pushed into the inside of the neck.

There are a large number of shapes and designs both on the near continent and worldwide that have been created to do similar jobs. The standard theory for these differences is the availability of local materials. Today the two major shapes are constructed from metal or plastic frames covered with netting. This netting is usually 3mm black polypropylene with a 75mm mesh but could vary depending on target species. Other designs of various materials are produced, some commercially and some by fisherman, and provided they obey the basic rules they will fish perfectly well. Even if a good pot has been selected many other factors could determine whether a good catch is made.
  • Species not located – The target species may not be present in the area, or not hungry. Other possibilities include mating, moulting, predators in the area, sea conditions or weather conditions.
  • Bait – The bait could be of an incorrect type it could be incorrectly positioned or it may have been dislodged as the pot enters the water. Edible Crabs (Cancer pagurus) and spider crabs (Maja squinado) have a preference for very fresh bait compared to the lobster (Homarus gammarus) that has a liking for stale oily bait.
  • Pots badly positioned on the seabed – This could be due to incorrect weighting. Problems can arise if rocks or other debris block the entrance.
  • Dislodged pots – Could be carried away by sea conditions, tides or towed away by trawlers.
  • Scavengers – The bait could attract scavenger species such as sea lice or conger eels before the shellfish have located the pots.
  • The ropes disturb target species – Due to tide movement.
  • Pot disturbs shellfish – It is common for shellfish to put off pots that are moving with the tide. This is usually down to the weight of the pot.
  • Shellfish feeds on the bait from the outside of the pot – This will be down to poor baiting arrangements or practices.
  • Other shellfish in the pot preventing entry for others – The lobster does not like a large number of spider crabs so may not enter, or the entrance may be blocked by a large spider crab.
  • Shellfish enters and is eaten by other shellfish – The lobster and brown crabs are cannibalistic and will turn on each other.
  • Shellfish eats the bait and then escapes – The spider crab rarely escapes and the brown crab will successfully escape but they are slow to do so. The lobster will enter and leave un-trapped pots at will.
The lobster seems to be happier in dark pots with plenty of room. The pot can be adapted to be darker by double netting, but this will add cost and tide drag to the gear. An increase in pot size would also up the cost as well as adding weight to the pot. Stowage and handling problems could also be created and as ever the final decision will have to be a compromise.

Once a shellfish has entered the pot it can be retained by fitting some form of trap in the pot to prevent escape. In the case of a creel this is done by the use of a parlour. A parlour is a separate compartment at one end of the creel, which is entered via a net funnel with a taught deck and a roof, which closes after entry. This method is highly efficient and have made it possible for some boats to double or treble the number of pots used as they only need to be worked every two or three days. This has had a major effect on some shellfish stocks.

It is not possible to fit a parlour to an inkwell pot. The answer has been a trap across the neck, which prevents exit, or a rubber skirt, which discourages exit.

The majority of pots are usually rigged with a bridle and spinner. The spinner is designed to permit the pot to spin in bad conditions without twisting the back rope. This is a convenient way of attaching or removing the pot from the string.

Pots may be shot singly by very small inshore boats but more commonly they are shot in strings or fleets. These strings may be of up to 80 pots in the case of large offshore super-crabbers. The strings will depend on the size of the boat, the number of crew and the ground being worked. The spinner is attached to the ground rope (back rope) by a short snood (1 – 5 fathom length) with a figure of eight knot at the spinner and then spliced into the back rope. The pots are spaced along the back rope at intervals of between 10 and 15 fathoms. At either end of the back rope there may be an anchor or weight. Either this weight or the last pot is attached to the head rope, which are between 2 and 3 times the depth of the water with some sort of buff, float or dhan flag combination.

The rope is usually hard lay split film polypropylene, though it can be monofilament which is more expensive. Smaller boats will commonly use 10mm rope and larger deep-water boats will use up to 14mm. There is also a tendency for some boats to use leaded ropes for a variety of reasons.
  • There is less drag on the gear as the ground rope is on the bottom.
  • There is less chafe on the ground rope as there is less movement.
  • There is less rope on the surface at slack water, which is important in areas of heavy boat traffic.
  • Disadvantages include cost and strength, as it is weaker for given diameter of rope.
When the gear is hauled it is done by a slave line hauler. This may be mounted either on a ‘P’ bracket or inboard with the rope coming aboard through a snatch block suspended from a davit.

Once hauled the pots need to be cleaned. This entails the removal of shellfish and by-catch to be retained and the removal of undersized shellfish and unwanted by-catch to be returned. The pots are then re-baited and stacked back ready to be shot. When they have all been stacked aboard the pots can be re-shot on the same ground if the catch warrants it or they can be moved elsewhere. It is good practice to use the same man shooting as stacking back because shooting the pots in the wrong order can be very dangerous.

Below are pictures of the target catch: Brown Crab (top), Spider Crab (middle),Native Lobster (Bottom)

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