Development of formulated bait for edible crab (Cancer pagurus L.), using by-products from the fisheries and aquaculture industry.
KEY WORDS: edible crab, Cancer pagurus, formulated bait, baited traps, effectiveness, attraction
In the early 1990s the Norwegian edible crab fishery struggled with low profitability, and the annual catch was approximately 1,300 tonnes. To facilitate the development from a subsidized industry towards a modern profitable industry, a national development program was established. In the period from 1990 to 2003 the annual catch increased from 1,300 tonnes to 5,000 tonnes. The edible crab fishery takes place in the period from August to November.
The crabs are caught by traps, and several different models of traps are used, from home made traditional wooden traps, to commercially produced traps in recycled polyethylene (Polymoon Ltd). Some models are equipped with a compartment for the bait, but most are not. All the traps commonly used contain two entrances.
During the Norwegian edible crab fishery around 20 tons of bait, mainly saithe (Pollachius virens), is used daily. In some regions fishermen buy frozen bait from the local filet factory. In other regions however, the fishermen fish their own bait, an activity that is time consuming. If formulated bait were commercially available, the time spent on bait fishery could be used more efficiently either in the crab fisheries or in other fisheries. To our knowledge no formulated or artificial baits for edible crab is available. For other crustaceans, several attempts have been made to develop artificial bait, but none of them is commercially available today (Chanes-Miranda & Viana 2000).
At Norwegian Institute of Fisheries and Aquaculture Ltd, a wet feed for sea urchins and red king crab has been developed. In this feed, fish skin is the major ingredient. Fish skin serves as a protein source in the feed, and furthermore, fish skin gelatin work in combination with the enzyme transglutaminase as a binding agent (Mortensen et al. 2004). The resulting feed is very stable in seawater (very little disintegration and nutrients leakage, Mortensen et al. 2004). In a small-scale pilot study in 1999, this feed was tested as bait for edible crab, with very promising results (own unpublished data).
To become commercially interesting, formulated bait must have equal or lower price than natural bait. The natural baits used today, are suitable (and indeed used) for human consumption as well. According to FAO, the use of certain fish products should be destined only for human consumption (FAO 1997). Therefore, future formulated baits should preferably contain by-products from other industry (e.g., fish filet industry, or aquaculture). Norwegian fisheries and aquaculture industry produce large amount of by-products every year, of which there is little or no alternative application. For some byproducts the industry even has cost connected to their destruction. One of these by-products is called "protein concentrate" (PC). PC is generated during the production of fish meal. On a dry matter basis PC contains 90% protein, whereof >50% is collagen/gelatin. The blue mussel industry produce large amounts of mussels that do not fulfill marked requirements (small size, fouling, cracking, etc), and these form another potential source of low cost ingredient in formulated baits.
We aimed to develop formulated bait for edible crab using the formulated sea urchin/red king crab feed as a basis, and using by-products from the fishery and aquaculture industry as attractants. The performance of the four baits was compared with that of the most commonly used natural bait.
MATERIALS AND METHODS
This study was carried out in two different regions; in the Risvaerfjord/Lekafjord (study area I) in mid Norway (65[degrees]N), and in Eidsfjord (study area II) in the Vesteralen archipelago in northern Norway (68[degrees]) (Fig. 1). A pilot study was carried out in Eidsfjord during the period from 26th November to 3rd December 2002 (hereafter named pilot study). The main studies were carried out in the Risvaerfjord and Lekafjord in the period from September 30 to October 3, 2003 (hereafter named main study I) and in the Eidsfjord in the period November 10 to 14, 2003 (hereafter named main study II). The Risvaerfjord/Lekafjord is located in the core area of the Norwegian edible crab fishery. The Eidsfjord is located close to the northern limit of the edible crab distribution and the area has only been commercially harvested for two seasons (2002 and 2003).
[FIGURE 1 OMITTED]
Four formulated baits were prepared (hereafter named Bait 1-4), and the formulation of the baits is given in Table 1. in all baits, fish skin (45% to 50% of wet weight) and saithe (19% to 49% of wet weight) was the main ingredients. In Bait 1, a meal mixture (shrimp meal, kelp meal, fish meal) was added as attractant. In bait 2, protein concentrate (PC: 15% to 30% dry matter, on a dry matter basis >90% protein whereof>50% collagen/gelatin) was added as attractant in addition to the meals mixture used in bait 1. Blue mussels (Mytilus edulis) and cod (Gadus morhua) roe were used as attractants in Bait 3 and 4 respectively (Table 1). Fish skin gelatin strengthened by the enzyme transglutaminase was used as a binder in all baits. This concept was originally designed for sea urchin feed, and the function of transglutaminase in combination with fish skin gelatin is described in detail in Mortensen et al. (2004). The fish skin was heated (with steam) until it started to disintegrate (temperature >80[degrees]C). The heated fish skin was minced to a viscous liquid. The remaining ingredients were minced, added to the fish skin liquid, and the resulting soup was thoroughly mixed. When the temperature decreased below 35[degrees]C, transglutaminase was added. The mixture was poured into wax coated cardboard forms and left to coagulate as the temperature continued to fall. After 12 h at 4[degrees]C, the gel forming process was completed and the bait was ready for use. Saithe is the most commonly used natural bait in the Norwegian edible crab fishery, and was therefore chosen as reference bait.
We aimed to test the performance of the formulated baits in a realistic setting. Therefore the field experiments were carried out onboard commercial vessels during the season for the edible crab fishery. The two vessels participating in the study were different concerning size and fishing gear used, and adjustments had to be made to fit the experimental set-up to the vessels. As a result, the experimental set-up was not completely standardized.
According to sea maps, the study areas were not topographically uniform. We could therefore not assume that all traps experience the same density of crabs and the same environmental conditions concerning current strength and direction. Furthermore, the densities of scavengers feeding on the bait were assumed to vary within the study area. The fishermen also described their fishing area as variable, containing some very good and some not so good locations. To assess this variation, differences in catch per unit effort (CPUE) between sites within the fishing areas was measured prior to each bait experiment. All traps were baited with saithe, and soaking times were approximately 24 h. The CPUE data obtained will in the following be referred to as 0-measurements.
The 0-measurements showed considerable variation within the study areas (see Fig. 3 later). To ensure that the baits were compared in both what the fishermen described as "good" and "not so good" locations, baits were allocated to traps in a predecided systematic order. Because of current conditions, and thus the size and shape of the plume of smell generated by the bait were unknown, at least 6 consecutive traps in a chain were baited with the same bait.
In the pilot study, the effect of soaking time (the elapsed time between setting and hauling) on CPUE was investigated. The durability of the formulated bait was also investigated and compared with that of saithe. We assumed that the durability of the four baits would be the same in seawater, therefore only one of the formulated baits (Bait 2) was used for the durability test. Furthermore, the performance of bait 1 and 2 were compared with that of saithe. 15 chains with between l0 and 16 traps in each, (a total of 170 traps) were used. The traps were made of polyethylene (30 cm x 35 cm x 80 cm) (Polymoon Ltd), and had an entrance on both ends. For bait I and 2, there were no significant differences between 24 h and 48 h soaking time, and soaking time of 24 h was used. The bait was allocated to the traps in the order described in Figure 2. Bait 1 and 2 changed place the second day, so that all traps baited with bait 1 the first day were baited with bait 2 in the second day and vice versa. Numbers of crabs per chain was counted.
In main study I, the performance of bait 1 and 2, were compared with that of saithe. Eleven chains were used, each containing 21 traps. The traps were made of wood (30 cm x 35 cm x 100 cm), and had an entrance in both ends. The bait was allocated to the traps in the order given in Figure 2, and this order was maintained throughout the study. Soaking time was 24 h. In main study II, the performance of bait 1, 3, and 4 were compared with that of saithe. Thirteen chains, each containing 24 traps were used. The type of trap was the same as those used in the pilot. The baits were allocated to the traps in the order given in Figure 2, and this order was maintained throughout the study. Because of a larger fishing area compared with the previous year (pilot study), soaking time of 48 h was used. In main study I and H, numbers of crabs per trap were counted. The formulated bait was stored frozen after production and was left to thaw before it was chopped into cubes. The natural bait was chopped into chunks when still frozen. In all studies the amount of bait used (both natural and formulated) was in the range 0.4-0.6 kg.
[FIGURE 2 OMITTED]
Data Analysis and Statistics
The fishermen have observed a strong tendency of higher catch in the traps located in the ends of the chains. Therefore data from all end traps were omitted in analyses. To increase the probability that a crab caught in a trap was attracted by the kind of bait used in that particular trap, traps located next to a trap with a different kind of bait, were also omitted, i.e., the first and last trap in a sequence with equal baits. Catch per unit effort (CPUE) (numbers/trap/day) was calculated for each bait. CPUE data did not follow a normal distribution, and to compare CPUE between the different baits, Kruskal-Wallis and Mann-Whitney tests were applied. In all analyses, significance was assumed when P < 0.05.
There appears to be differences in durability between formulated bait and natural bait. After 24 h soaking time, between 20% and 30% of the traps baited with saithe were empty, compared with only 7% of traps baited with bait 2.
The catches were generally higher in study area I. The 0-measurements from main study I showed a CPUE of 6.5, compared with 1.4 in the pilot study and 1.7 in main study II (Fig. 3). The catch in traps baited with bait 1 and 2, had a significantly lower CPUE compared with traps baited with saithe, irrespective of study area (Fig. 3). No significant differences between bait 1 and 2 were observed. The catch in traps baited with bait 3 and 4 had significantly higher CPUE both compared with traps baited with bait 1 and to traps baited with saithe. There appeared to be a higher CPUE in traps baited with bait 3 compared with bait 4, but this tendency was not statistically significant.
This study compares the effectiveness of four different formulated baits to that of natural bait under field conditions. Two of the tested bait formulations were more effective than natural bait. To our knowledge, no artificial or formulated bait for edible crab (Cancer pagurus) is commercially available, and no formulation for artificial bait is published. For other crustaceans such as spiny lobsters: lobsters: and crayfish, several types of artificial baits have been tried (e.g., Huner et al. 1990, Miller 1990, Mohan Rajan et al. 1995), but according to Chanes-Miranda & Viana (2000), none of them have been a commercial success. In his review on the effectiveness of crab and lobster traps, Miller (1990), suggested the following generalization considering the effectiveness of artificial baits: "the best artificial bait is no better than a good natural bait." Although other factors such as price and logistical problems may contribute to the lack of success in commercial fisheries, the lower effectiveness of the artificial baits is the most obvious reason. This is also the argument used by the fishermen themselves.
[FIGURE 3 OMITTED]
In the present study, formulated bait 3 and 4 was significantly more efficient than formulated baits 1 and 2. The better performance of bait 3 and 4 may be caused by their higher content of saithe, which is, according to the fishermen, the best natural bait. On the other hand, there were no differences between bait 1 and 2 despite the fact that the content of saithe was doubled in bait 1 compared with bait 2. For natural baits, the bait quantity is shown to affect catch rate in some studies (Lyons & Kennedy Jr. 1982, Miller 1983), and not in others (Thomas 1954, Zimmer-Faust & Case 1982). Yet other studies indicate that there is a threshold over which the quantity of bait does not affect the catch rate. In the study of Zimmer-Faust & Case (1983), traps baited with abalone muscle in the weight range of 46-372 g had similar catch of Panulirus interruptus, whereas baits in the range 18-3 g yielded progressively lower catch rates. Also for artificial baits laboratory studies have shown that different concentrations of attractant evoke different behavioral response (Miller 1990). The response of the animal increased moderately with order of magnitude increase in concentration of attractant, typically a 2 or 3-fold increase in response to 100-fold increase in attractant concentration (McLeese 1974, Daniel & Bayer 1987, Ache, et al. 1978).
The higher catch rate using bait 3 and 4 may alternatively be attributed to differences in attractant quality of the bait ingredients. Blue mussel (bait 3) and cod roe (bait 4) may function better as attractants than the combinations used in bait 1 (kelp meal, shrimp meal, and fish meal) and bait 2 (kelp meal, shrimp meal, fish meal, and PC). Molluscs are generally considered as good bait (e.g., Jones 1992, Mackie 1982), and mussels from the genus Mytilus, are commonly used as fishing bait (Rius & Cabra1 2004, Smith & Murray 2005). Furthermore, Cancer pagurus is known to consume at variety of molluscan prey in the wild, among those M. edulis (Mascaro & Seed 2001). Carr, et al. (1996), attributed the popularity of molluscs as bait and feed additives to their high concentrations of what the author define as "most frequently cited stimulant" (MFCS). In extracts from Mytilus edilis betaine, taurine, alanine, and glycine was the dominant components (Carr et al. 1996), where betaine, glycine, and alanine are represented among the MFCS. In the study of Carr et al. (1996), the list of M FCS was derived from studies on fish 35 species offish, and to our knowledge no similar studies are carried out for crustaceans. However, marine invertebrates have high sensitivity for the amino acids serine, alanine, histidine, and glycine (Ache 1987), and it is therefore plausible that blue mussels could function well as attractant in bait for edible crab.
To our knowledge, the use of cod roe as attractant in bait for crustaceans is not reported elsewhere in the scientific literature. However, roe from different fish species are well known attractants and commonly used as bait among sport fishers. Own unpublished data have shown that cod roe is particularly efficient as attractant for salmonids. Furthermore, cod roe is used as ingredient in feeds for fish larvae in aquaculture (Garatun-Ttjeldsto et al. 1987, Hamre et al. 2001, Knights 1996), both to enhance nutritional value and palatability. The composition of amino acids in fish muscle shows a great degree of similarity between close related species (Carr et al. 1996). Although not necessarily in the same order, leucine, alanine, glutamic acid, glycine, proline, and serine rank among the top six amino acids in the roe of a number of different species (Iwasaki & Harada 1985, De Silva et al. 2001).
Initially, we assumed that PC would function well as attractant. PC contains high levels of glycine in particular but also high levels of serine, alanine and histidine (Miljoprosess Ltd. pers. comm.). To act as a feeding attractant to scavengers and predators, amino acid fluxes must simulate release from live injured prey and carrion (Zimmer et al. 1999). The PC have had a long way from live fish (boiling, steaming and drying), and it is possible that the release of amino acids into the environment bear no similarity to that of injured prey or carrion.
The type of binder is known to influence the leaking of attractant, (Mackie et al. 1980, Miller 1990, Lokkeborg 1991), and thus the efficiency of the bait. According to Lokkeborg (1991), a binder of high binding power such as gelatin may cause a slow release rate of attractants. In the present study the binder was fish skin gelatin strengthened by the enzyme transglutaminase in all baits. In bait 2, the high content of gelatin in the protein concentrate may have added to the binding power. However, bait 2 did not have a significantly lower efficiency that bait 1, which had an otherwise identical list of ingredients. Without any measurements of leaking, we cannot exclude that differences in efficiency was caused by differences in leakage of attractants caused by binder properties.
After 24 h, the bait was completely disappeared in 20-30% of the traps baited with saithe, whereas the bait was completely disappeared in <10% of the traps with bait 2. There are several location specific factors that could influence the amount of bait remaining in the traps. The traps that were used did not contain a separate chamber for the bait, and the crabs were observed to feed on the bait inside the trap. Furthermore, the remaining amount of bait was highly variable also in traps with no catch, indicating that organism other than the crabs feed on the bait as well. We do, however, believe both bait 2 and saithe were used in a range of different locations and the observed differences in durability are real. The formulated baits have a very similar composition to a previously described wet feed for sea urchins (Mortensen, et al. 2004). During an immersion period of 7 d at 8[degrees]C, only insignificant changes in consistency occurred and the loss of dry matter was 17.6% (Mortensen et al. 2004).
Both baits 3 and 4 were as efficient as the natural bait in the present study. However, we do believe that bait 3, containing blue mussels, is the most promising candidate for further development. The blue mussel industry produces large amounts of not marketable mussels that form a potential source of low cost ingredient. The coming season bait 3 will be produced and tested in large scale in the commercial fisheries. The all round (biological, logistical, and economical) performance of the bait at large will be tested.
This project was funded by The Fishery and Aquaculture Industry Research Fund, Innovation Norway, Norwegian Raw Fish Organization, Norwegian Institute of Fisheries and Aquaculture Research. We want to thank Willy Olsen on the FF "Annie," and Alf Bliko and Einar Bliko on the FF "Alf-Einar" for practical help during field work. Their knowledge of the edible crab fishery was highly valuable in the design of this study. The author thanks Miljoprosess Ltd for good cooperation in development and production of the baits and Alf Albrigtsen at the Fiskeridirektoratet for introducing the edible crab industry and for helping with organizing the field study.
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TRINE DALE, (1) * STEN. I. SIIKAVUOPIO (2) AND KARE AAS (2)
(1) Norwegian Institute of Water Research, Bergen N-5817, Norway; (2) Norwegian Institute of Fisheries and Aquaculture Research, Tromso N-9291, Norway
* Corresponding author. E-mail: email@example.com
TABLE 1. List of ingredients in the baits expressed as a percentage of wet weight. Ingredient/Constituent Bait 1 Bait 2 Bait 3 Bait 4 Fish skin 49.6 49.6 45.4 49.0 Saithe (whole grinded) 37.2 18.6 45.4 48.9 Protein concentrate (PC) 0 18.6 0 0 Kelp meal 2.5 2.5 0 0 Shrimp meal 4.5 4.5 0 0 Fish meal 6.1 6.1 0 0 Blue mussel 0 0 9.1 0 Cod roe 0 0 0 2 Transglutaminase 0.1 0.1 0.1 0.1
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|Author:||Dale, Trine; Siikavuopio, Sten I.; Aas, Kare|
|Publication:||Journal of Shellfish Research|
|Date:||Aug 1, 2007|
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