The Sea Fish Industry Authority

Transcription

1 . The Sea Fish Industry Authority Seafish Technology Assessment of a novel system for restraining claws of the. Consultancy Report No. CR 145 Author: M S Jacklin Date: June 1998 Seafish Industry Authority 1998

2 . The Sea Fish Industry Authority Seafish Technology Assessment of a novel system for restraining claws of the. Consultancy Report No. CR 145 Author: M S Jacklin Date: June 1998 Summary This report describes the evaluation of a novel method of banding crab claws that was designed primarily with a view to airfreighting product to foreign markets. The aim of the work was to determine the potential for wider application, especially it s suitability for crabs subjected to medium term storage in live holding tanks. The restraints were successful for 24 hours thereafter failing throughout the remainder of the trial. It is suggested that the most likely mode of failure is slippage, as the majority of restraints resemble flattened tubes and exhibited very little damage. The most likely cause of failure is a combination of material characteristics and the cleansing action of the crabs appendages. After 24 hours animals exhibited mortality and claw loss which contiued throughout the trial. The main factor, probably, contributing to mortality was damage caused by unrestrained claws. The equipment was robust and easy to use although it could be operated only in the standing position and band claws individually. A machine designed for seated operation and which could band both claws in one operation would be considered preferable. The results suggest that the commercial utility of this restraint to the vivier trade is limited. The industry needs a restraint that is successful in all commercial situations where animals can be subjected to a range of conditions, for periods of up to three weeks. A design that provided the following preferred design features would probably gain wider commercial acceptance: the ability to be used in the seated position; the ability to band two claws in a single operation; easy release of banded claws; and a system for loading restraints automatically.

3 TABLE OF CONTENTS Page Number Summary 1 Introduction Aims and objectives Approach Methods Results Discussion Conclusions Recommendations Reference Appendix 3

4 1 INTRODUCTION In September 97 a shellfish merchant purchased a novel system for banding the claws of the. The banding system had been developed by the North Atlantic Fisheries College (NAFC), in Shetland, who have been conducting research into novel methods of restraining the claws of brown crab, primarily with a view to airfreighting product to foreign markets. The equipment, Fig 2, Appendix 1, is currently manufactured by HNP Engineers (Shetland) and has been marketed since early Seafish were requested to assist in investigating the suitability of the system for a crab fishery located off the East coast of England. The main interest was the efficacy of the bands on crabs which were subjected to medium term immersed storage in live holding tanks. Previous research by Seafish on restraints for brown crab is described in Seafish report No The work involved evaluating different designs of restraint in specialised conditions, with the aim of producing a design suitable for the U.K. vivier trade. 4

5 2 AIMS AND OBJECTIVES The aim of the work was to investigate the utility of the the system using animals which were sourced from the east coast and maintained under conditions commonly experienced in the live storage and vivier trade. The intention was to determine whether the system had wider commercial application than the one for which it was specifically designed. The objectives of the experiment were to investigate the equipment s mode of operation, and to determine the pattern of mortality, claw loss and failure of the restraint under the following conditions: high animal activity; low animal density; and non replacement of failed restraints. 5

6 3 APPROACH Equipment was obtained from the shellfish merchant and the assessments were carried out ashore in commercial live holding premises and in controlled conditions at the laboratory facilities at Seafish, Hull. Sea trials were not conducted. 6

7 4 METHODS A sample of un-nicked animals, comprising ten male and nineteen female crabs, were sourced from a shellfish merchant located the East coast of England. They had been caught locally, eight hours prior to collection. The animals carapace widths ranged from 120mm- 179mm and the size frequency of the sample is described in Fig.3, Appendix I. Claws were banded using the equipment as follows. A wetted restraint was placed over the three prongs of the applicator. The foot pedal was depressed, opening up the band, and the claw inserted, Fig. 2. The foot pedal was released, ensuring that the band was located in position, as described in Fig.4. The intention was to cover most of the palm to secure the restraint and most of the pincers to minimise movement. Animals were then maintained in seawater at 15 C in a live holding tank measuring 1.5m diameter, giving an animal loading of 9.94 kg per square metre. The animals were inspected regularly over a period of 14 days and the dead removed. The following parameters were recorded: number of live animals, number of claws on live animals and number of restraints on claws of live animals. Restraints that failed were not replaced. 7

8 5 RESULTS The results are presented as percentages in Fig. 1 as follows: the percentage of live crabs remaining (% crabs alive); the percentage of claws remaining on animals (% claws remaining); and the percentage of bands remaining on live claws (% banded claws). These parameters indicate animal survival, claw loss (some animals lost claws but remained alive), and the proportion of live claws which remained banded. The graphs show that, after 24 hours, each paramerter declined in an approxamately linear manner throughout the trial. At the conclusion of the trial (14 days immersion) 81% of the animals were alive, 68% of live claws remained and 37 % of live claws were banded. Some restraints failed almost immediately, whereas others remained on for the duration of the trial. The majority (almost 60%) failed evenly (5% per day) over 14 days. After 9 days immersion 50 % of live claws remained banded. 8

9 Fig 1: Percentage of bands remaining on claws, claws remaining on crabs and survival of crabs with time. 9

10 6 DISCUSSION In evaluating the results it should be noted that they were obtained under conditions similar to the most unfavourable experienced in shore based commercial holding units. The trial was conducted at low animal density as previous work has shown that restraints fail to a greater extent in conditions where crabs can move freely compared to those where they are packed tightly (1). Also, crabs were maintained at a relatively high temperature to encourage animal activity, and restraints that failed were not replaced in order to investigate potential damage from fighting with unrestrained claws. These conditions could occur in situations where storage tanks contain little stock. Endurance The restraints were successful for 24 hours, thereafter failing throughout the remainder of the trial. It is suggested that the the most likely mode of failure is slippage, as the majority of failed restraints resembled flattened tubes and exhibited very little damage. It is unlikely that improper application caused restraint failure; firstly due to the care exercised in applying each restraint, and secondly the pattern of failure would probably be different from that observed. Improperly applied restraints would, most likely, have failed quickly over a short period of time, whereas those applied properly would have remained secure. The observed pattern of failure suggests that other factors are responsible. The most likely cause of failure is the combination of material characteristics (elasticity) and the cleansing action of the crabs appendages. It is possible that the edge and roughened suface of the restraint allowed limbs to gain purchase and ease off the restraint. It is also likely that flexing of the upper pincer contributed as this movement was observed when handling animals. Claw size was not measured, though size variation might have influenced the pattern of failure. Mortality and condition After 24 hours the crabs exhibited mortality which continued throughout the trial. The main factor, most likely, contributing to mortality was damage caused by unrestrained claws as the majority of dead animals exhibited a combination of lost limbs, carapace damage and puncture wounds. Animals also exhibited a high level of claw loss caused, most likely, by fighting with unrestrained claws. All lost claws were undamaged and had been autotomised, a process wherby a gripped claw is discarded in an attempt to secure the survival of the animal. Equipment operation The equipment was considered easy to use, although it could only be operated in the standing position and, during the banding process, required the operative to balance on one foot while using both hands to hold the crab. Operating the equipment on small vessels in this manner might be difficult due to space limitation, and dangerous due to vessel motion unbalancing the operator. A machine designed for seated operation would be considered preferable. 10

11 On releasing the foot pedal removing a banded claw from the pronged applicator often proved difficult, especially when bands were dry. Wetting the bands with seawater eased removal to some degree, but in many cases made little difference. Prongs that did not inhibit removal would quicken the banding proceedure and reduce operator fatigue. The equipment was robust and of uncomplicated design, making it suitable for the environment on a fishing vesel. However, difficulties experienced with the existing model often resulted in protracted banding times. When a banded claw was released in order to reload the applicator (to band the second claw) a crab s typical response was to clasp tightly the hand holding the unbanded claw. This caused inconvenience and additional time was required to free the animal in order to present the second claw correctly to the applicator prongs. A machine that banded both claws in one operation would be preferable as the crab would not have to be released until the end of the proceedure. This could be achieved by designing a machine with two applicator heads. Application to industry The results suggest that the commercial utility of this restraint to the vivier trade is limited. It could be used in distribution chains of less than 24 hours duration and, probably, those of greater duration where conditions inhibit claw and pincer movement. However, in normal commercial situations the band s tendancy to fail after 24 hours would cause mortality, damage and crippled animals, greatly reducing the value of the catch. The industry needs a restraint that is successful in all commercial situations where animals can be subjected to a range of conditions, for periods up to three weeks. The equipment s size and requirement to be operated whilst standing could restrict application to larger vessels. Also, operational difficulties experienced when using the equipment precluded easy use. These limitations could prevent widespread commercial application. A design that provided the following preferred design features would probably gain wider commercial acceptance: the ability to be used in the seated position; the ability to band two claws in a single operation; easy release of banded claws; and a system for loading restraints automatically. 11

12 7 CONCLUSIONS The research has shown that under conditions considered to be representative of normal commercial practices in the UK vivier trade the restraint was unsuccessful causing high mortality, damage and loss of limbs. As currently designed, the commercial applications of this restraint are limited. In most commercial situations the band s tendancy to commence failing after 24 hours would cause early mortality, damage and loss of quality, reducing the value of the catch. The band could be used successfully in distribution chains of less than 24 hours duration and possibly those of greater duration where conditions inhibit claw and pincer movement. The equipment s size and requirement to be operated in the standing position could restrict its utility to larger vessels. Also, operational difficulties experienced when using the equipment precludes easy use. These limiations could prevent widespread commercial application. The research indicates that further work is required on the design of both the restraint and applicator to ensure commercial application and encourage widespread commercial acceptance. 12

13 8 RECOMMENDATIONS Further work is required to determine the mode and cause of the band s failure. Information gained by observing banded crabs using underwater camera/video equipment could aid development of a modified design. It may be that material of a different thickness or exhibiting different elasticity characteristics would be appropriate. Further work is required to ease the release of banded claws from the prongs. One approach would be to coat the prongs with a material exhibiting a low coefficient of friction, such as PTFE. The ability to band two claws in a single operation would be advantageous as would a system that loaded bands automatically. Finally, consideration should be given to designing an applicator that can be operated in the sitting position. 13

14 9 REFERENCE (1).Novel Methods for Restraining the Claws of the Edible Crab (Cancer pagurus) Seafish Report No

15 Appendix I 15

16 Fig 2. System to band claws showing applicator and rubber band. 16

17 Fig 3. Size categories of carapace widths (mm) of animals used for the trials. 17

18 Fig 4. Location of band restraint on claws. 18

19 19