FISH STOCK ASSESSMENT
Few issues cause more discussion in Angling Clubs than ‘stocking policy’. If the fishery is used partly for match fishing and partly for pleasure fishing, then inevitably there will be different views; perhaps the match anglers wishing to add additional stocks to boost match weights, particularly during the winter months. Conversely there will be the traditionalists and pleasure anglers who argue that the removal of a proportion of the smaller fish should take place to give the larger fish more space and to feed more confidently, etc. Before decisions are made,members need some idea of the total fish weight in the fishery (I.e. the biomass) relative to the size and depth of the fishery It is recommended by many Fishery Consultants that between 900 and 1000 lbs per acre is the optimum for natural fisheries if they do not have facilities for additional oxygen supplies.
So how can the biomass be assessed;-
1. NETTING
Can cause stress to the fish; also snags and trees in the fishery can make it difficult to use nets.
On Very large waters can it also be difficult to identify which area to net; I remember on one netting operation, working with the Environment Agency, six attempts produced NOTHING, whilst the seventh produced thousands of small roach and skimmers; illustrating how fish shoal tightly for safety and security on large waters.
However, despite these problems if undertaken professionally (e.g. by the Environment Agency) netting can provide a wealth of information, not only on the numbers of species but also the structure of the population for each species by age structure. This information can help determine the best course of action for the fishery. (E.g. transfer large numbers of small roach to other waters). Remember,however, approval from the E. A. Is needed for all fish transfers between waters. One netting operation on one of our waters approximately 1 acre in size was netted in two equal sized produced 500lbs of small fish, whist the second half produced a similar quantity of small fish in addition to hundreds of pound of carp and a few quality perch.
2. ELECTRO-NETTING
Must be carried out by trained staff. Courses are available but experience is essential in addition to courses.
3.MATCH WEIGHTS
5 Match weights in the warmer months can provide some indication of biomass. Match weights should be accurately monitored over a long period, rather than shorter periods to establish a more accurate estimate of total the biomass. All members should be told to weigh their catch no matter how small relative to the winning weights. In one of our summer matches a total of 500 lbs was weighed in a water no more than an acre no more than an acre in size, this suggests the stocks are far above the 900-1000 lbs recommended. Match angers still requested additional stocking as their experiences on Commercial Fisheries produced higher weights and their expectations reflected this level of angling success. If stock levels are way above the recommended levels, then additional feeding on a regular basis, particularly during the warmer months will be needed. Regularly monitor the health and weight of the fish caught.
4. THINK OUTSIDE THE BOX
Think of ways in which YOUR fishery can be used to come up with more accurate ways of biomass measurement, if for example a section of the water could be sectioned off and fish transferred to that area, for a short period, to see the results of future weights fall, then it may help in establishing the stock level.
Matches for silver fish to assess the volume of smaller fish using methods that can assess more accurately the volume of smaller fish (e.g. matches using pinkies, maggot and bloodworm are also possibilities).
THINK OUTSIDE THE BOX BUT NEVER NEGLECT FISH HEALTH.
IF FISH TRANSFER OF SMALLER FISH TO OTHER WATERS ARE CONSIDERED LIAISE WITH THE ENVIRONMENT AGENCY AT A VERY EARLY STAGE TO DETERMINE WHAT CAN AND CANNOT BE DONE
Stocking operation F1 CARP
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SMALLER GHOST CARP
THE SUCCESS OF STOCKING WITH DIFFERENT SIZES OF FISH IS VERY IMPORTANT AND SHOULD BE MONITORED AS PART OF THE STOCKING PROCESS . KNOW WHAT SIZE WAS INTRODUCED WHEN AND MONITOR THEIR LENGTHS AND WEIGHT.