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Development of a New Conservation Approach for Farmed Sea Scallops Kept in Seawater in Live Wells to Foster the Sale of Princess Scallops on New Markets
Final Report
Société de développement de l'Industrie maricole inc. (SODIM)
AIMAP-2010-Q08
Table of contents
Abstract
The purpose of this project was to determine an adequate protocol that would serve to keep scallops alive in a closed-circuit live well, in either natural or artificial seawater, and to determine the product’s shelf life and evolution in quality. This study was divided into two phases. For Phase 1, the scallops were placed in three different experimental conditions (closed circuit, closed circuit with seawater, and closed circuit with salt-enriched water). Three size categories were used to determine whether there was a difference in the response to containment in terms of scallop size. For each trial, the following analyses were conducted: measurement of vitality, condition index and glycogen concentration in the muscle, and a sensory analysis (appearance, odour, texture, taste). For Phase 2, the scallops were shipped by plane on a round-trip flight lasting several hours (Blanc-Sablon/Sept-Îles round trip) before being put into containment in closed-circuit live wells (only two experimental conditions). For the first year of the tests, the category 1 scallops suffered greater mortality than the others. In contrast, during the second year, size category did not appear to truly influence scallop containment in live wells. The lowest mortality rates occurred in the “open-circuit” and “closed-circuit, water + salts” experimental conditions. As for the time of year, it appears that the months of October and November are conducive to the successful containment of scallops. In fact, by that time, spawning has already taken place and the ambient temperature is close to the scallops’ preferendum, which limits emersion-related stress. The condition of the scallops was very markedly different on the first day and the fourteenth day of the trial. In fact, the scallops were in significantly poorer condition by the end of the trial. The crucial point appeared to occur at around the seventh day of containment. However, sensory tests did not show a particular difference in terms of the scallops’ commercial qualities. According to both the trained panel and the untrained panel, there appeared to be no significant difference in terms of trial day, experimental condition or time of year.
1.0 Introduction
Québec has developed scallop farming know-how in recent years. In fact, coastal areas in Québec have the qualities needed to conduct this kind of production successfully. Scallop farming businesses are primarily located in two areas: on the Magdalen Islands and on the Lower North Shore. To make their product distinct from the scallops harvested by the fishery, scallop farmers sell a single product: the Princess scallop. The particularity of this scallop is that it is sold live, in its shell. The product has already been available for eight years in Québec and has earned a faithful following, particularly amongst upscale restaurateurs. However, production sites are generally located far from major urban centres like Québec City, Montréal, Toronto or Boston where the people who eat scallops live. The new challenge businesses face in their efforts to diversify their sales opportunities is to successfully ship scallops over long distances and hold them in live wells thereafter for sale by distributors. It would be interesting to be able to hold scallops in live wells as is the case for lobster. Although this method of conservation has been fully mastered for the lobster, there are no data at present concerning the optimal parameters for keeping scallops alive under these conditions.
So the purpose of this study was to determine an adequate protocol that would make it possible to keep scallops alive in closed-circuit live wells, supplied with either natural or artificial seawater, and to determine the product’s shelf life and evolution in quality (taste, texture, vitality).
More precisely, this study sought to document and compares the quality of farmed scallops in terms of:
- Different commercial sizes;
- Different rearing conditions (open vs. closed circuit, natural vs. artificial seawater);
- Two different emersion conditions (short and long);
- Different seasons of the year; and
- Different gonad maturation conditions.
2.0 Discussion
2.1 Experimental conditions
By testing three experimental conditions, the goal was to evaluate the feasibility of live scallop containment in closed-circuit, water + salts live wells, as is done with lobster. The lowest mortality rate occurred in the scallops held in the “open-circuit” tank (4%) and in the “closed-circuit, water + salts” (9%) live well. In the “closed-circuit, seawater” live well, the high mortality (14%) is due to the data generated by Trial 4, during which the breakdown of the cooler on the closed-circuit, seawater live well lead to the death of all the scallops contained in this live well.
In statistical terms, there was no difference in mean vitality between the three experimental conditions. However, the scallops held in the “closed-circuit, water + salts” live well had a lower condition index (CI≈9) than the scallops in the other tanks (CI≈10). In fact, this tendency was observed in September and November 2010 (trials 1 and 3) as well as in September, October and November 2011 (trials 5, 6 and 7). Trial 4, conducted in July 2011 was the exception; during this trial, the vitality, condition index and glycogen concentration in the muscles of the scallops held in the “closed-circuit, seawater” live well were significantly lower (about twice as low) than those of the scallops in the other tanks because of the breakdown of the cooler on this tank. In October 2010, the panel of experts determined that the taste of the scallops held in the “closed-circuit, water + salts” live well was less interesting and gave them a score of about 5, which corresponds to “Neither like nor dislike.” In November 2010, the acceptability score for the taste of the muscle of the scallops from the “open-circuit” tank was higher (≈7) than for the “closed-circuit” live wells (≈6). Finally, in October 2011, glycogen concentration in the muscles of scallops held in the “closed-circuit, water + salts” live well was lower (0.62) than that of the scallops from the “closed-circuit, seawater” live well (1.16). Although the CI and glycogen concentration were lower in the scallops from the closed-circuit, water + salts live well, the acceptability score for the taste of the scallops from the “closed-circuit, seawater” live well fell to 5.7 on Day 14 of the trial.
Based on these results, the closed-circuit, water + salts live well appears to be less successful in terms of scallop quality than the other experimental conditions. However, the panellists did not notice any reduction in the sensory qualities of the scallops held in this live well.
2.2 Size categories
Three size categories were tested during this project to evaluate the potential effect of the scallop’s size on its capacity to support containment. In terms of the mortality rate, size had no influence. But size did have an effect on the condition index on several occasions. In September 2010, the scallops in size category 1 had a CI lower than that of the other scallop categories. In addition, during each flight to Gaspé during the 2010 trials, the size 1 category scallops proved to be less resistant to transportation-related stress. In September and October 2011 (trials 5 and 6), the size category 3 scallops had a higher condition index than scallops in the other categories. The gonado somatic index (GSI) show that in September 2011, the scallops were about to spawn since they had very high GSI. In October 2011, the GSI fell, meaning that the scallops had spawned. Spawning may have had less impact on the size category 2 scallops than on their young and older fellows. In September and November 2011 (trials 5 and 7), the glycogen concentration was lower in the size category 1 scallops. This datum may be due to the fact that smaller individuals tend to dip more into their energy reserves than larger individuals (Girault L. et al, 2005). However, simply because there is a drop does not mean that the scallops are of lower quality. In addition, glycogen concentration is a measurement that varies greatly from one individual to the next (Girault L. et al, 2009).
Given these results, size category does not appear to have a decisive effect on the containment of scallops in live wells. However, if a choice has to be made, it would be better to choose size category 2 scallops. In fact, size category 3 scallops are large and do not really correspond to the product we wish to sell, the Princess scallop, and the size category 1 scallops suffer higher mortality. This high mortality may also be due to the transportation conditions during the first year which were harder on the size 1 category scallops than on the other size categories. In addition, the scallops in the different size categories came from different genetic lots. This being said, these lots do not all have the same mortality rates (pers. comm. Pec-Nord).
2.3 Trial days
The different trials were conducted over a period of 14 days each to evaluate the shelf life of scallops maintained in closed-circuit live wells and the impact of containment on product quality. In general, there was a difference in the CI between Day 1 and Day 14; in terms of vitality, the drop occurred on Day 7. For the September 2010 trial, the drop in scallop vitality was significant beginning on Day 12; in the October 2010 trial, this occurred as of Day 7; while in the November 2010 the drop occurred on Day 6. In September 2011, vitality was significantly lower on Day 14 than on Day 1. However, for the same trial, the CI fell significantly beginning on Day 7. In October 2011, there was a drop in vitality and the CI beginning on Day 7, as well as a drop in the taste acceptability score for the muscle of the scallops from the “closed-circuit, seawater” live well between Day 7 and Day 14. In November 2011, vitality fell on Day 7; in contrast, the CI was higher on Day 14 than on Day 1. For the month of July 2011, the CI was significantly lower beginning on Day 5 and the glycogen concentration was higher on Day 1 compared to other days of the trial. These figures are due to the breakdown of the cooler on the closed-circuit, seawater live well.
Measurement of the glycogen concentration in the muscle shows a drop between Day 1 and Day 14. This drop is significant only for Trial 4 (July 2011). It is normal to observe a drop over the course of the trial since the scallops are not fed, but this difference does not appear to be very great.
The CI and vitality are two indicators of the physiological condition of the scallops, but the results show that these two measurements do not fluctuate in the same way. These results show that it is hard to settle for a single indicator to evaluate the conditions of scallops while they are being held in live wells. In fact, vitality, which is measured by the number of claps in two minutes out of the water, is a datum that is very sensitive to short-term stress (Girault L. et al, 2009). Although it is obvious that vitality tends to fall beginning on Day 7 of containment, the CI does not; so it would appear that the physiological condition of the scallops does not really become worse over the course of the trials.
2.4 Time of year
By conducting the trials throughout the harvest season, the goal was to evaluate whether gonad maturity had an impact on the capacity of the scallops to be kept in live wells while maintaining their quality and vitality. As for the mortality rate, the Trial 6 results (October 2011) were better than those obtained for the other periods. The small number of dead scallops during this trial may be due to a number of factors. First of all, during this trial, there were fewer scallops (30 individuals) in the closed circuit live wells than during the 2011 trials (80 individuals). This particularity may explain why mortality was greater in 2010 than in 2011. In addition, Trial 6 marked the beginning of Phase 2 and particular attention was paid to brushing the scallops to prepare them for transportation by cooler prior to the trial. Less fouling in the live wells and tank may have led to improved scallop survival. In October 2011, the scallops had finished spawning so for them, this is a period where they can withstand stress better since they do not have to invest energy in spawning.
The GSI were lower in October-November and transportation was less stressful for the scallops since the ambient temperature is lower at this time of year, closer to the scallops’ preferendum. The tests conducted in July and September 2011 showed higher GSI. So these are periods that should be avoided. Unfortunately, the July 2011 results were distorted by the breakdown of the cooler on the closed-circuit, seawater live well, but a GSI of over 25% supposes that the scallops are less resistant since they are getting ready to spawn and thus, more sensitive. No tests were done in June and August for logistical reasons, but everything leads us to believe that the month of August would not be an ideal period to optimise the condition of scallops kept in closed circuit live wells, notably because of the high ambient temperature.
2.5 Comparison between phases 1 and 2
The October 2011 and November 2011 trials correspond to the Phase 2 tests (trials 6 and 7). Before being put into containment in the live wells, the scallops were shipped by plane (Blanc-Sablon/Sept-Îles round trip). The interest of this second phase was to submit the scallops to real commercial conditions. In fact, a Lower North Shore mariculturer that wants to sell its scallops in a Québec City fish store would first have to ship the scallops and they would be kept in a live well after having endured the stress caused by several hours in transit.
The two Phase 2 trials produced very good results in terms of post-transportation scallop mortality. In addition, the CI and vitality observed during the course of the Phase 2 trials were not lower than those obtained for the Phase 1 trials. Moreover, during the November 2011 trial, the scallops stayed out of the water for two entire days due to a transportation problem. During this time, they were kept at 4°C in a cold room. Despite this incident, the scallops survived 14 days in containment.
Conducting these trials in the fall (October and November) was certainly a factor in their smooth operation. In fact, at this time of year, ambient water temperature is lower than in the summer. It would perhaps be hard for scallops to remain in transit for long periods of time in July and August, particularly since local airports do not generally have cold rooms. Furthermore, September should also be excluded because their high GSI levels make the scallops more sensitive to stress.
3.0 Conclusion
This project served to evaluate the technical feasibility of conserving scallops in this way. The trials conducted in 2010 proved to be less meaningful than the 2011 results. This was notably due to the ammonia rate which was hard to master during the 2010 trials. High scallop density (about environ 80 individuals instead of the 40 used in 2011) might be one reason for these differences. Staff experience probably had an influence and it certainly led to better results during the second year. In fact, the technical staff received no training and their acquired experience undoubtedly played a major role in the success of the 2011 trials.
A drop in vitality was observed beginning on Day 7 in the muscles contained in the closed-circuit live wells, both in the seawater and the salt-enriched water lots. As for the CI, a significant drop was observed, but only beginning on Day 14 and not beginning on Day 7. Vitality measurement remains relatively subjective depending on the person doing the sampling, and is very sensitive to short-term stress (Girault L. et al, 2009).
As for the experimental conditions, the “closed-circuit, water + salts” live well, which corresponds to the conditions in which scallops would be kept in major consumer centres, produced lower scallop CI and vitality data.
However, the results observed in terms of CI and vitality do not appear to have had an impact on the product’s sensory qualities. In general, the trained and untrained panellists did not detect any difference in the quality of the scallop muscles associated with either trial day or experimental condition.
This last point is very important in terms of marketing this new product. To obtain more meaningful results, it would be pertinent to consider conducting a sensory test using consumers to see whether it would be interesting to develop such a market. There are also other technical aspects that require further study, including the optimal density for scallops held in live wells and the establishment of a transportation method adapted to suit the Lower North Shore reality.
This study reached its initial objectives which were to document and compare mortality, vitality, the condition index, glycogen concentration in the muscle and the sensory qualities of farmed scallops of different commercial sizes kept in live wells in artificial or natural (closed circuit) seawater and in an open tank after a short period of emersion (Phase 1) and after a long period of emersion (Phase 2). In addition, the researchers were able to compare the results obtained at different seasons of the year and for different gonad maturation conditions.
4.0 Bibliographical references
Girault, L, Leblanc, M.-J. and Tamigneaux, E. 2009. Optimisation des procédés de manutention postrécolte du pétoncle d’élevage vivant: Augmentation de la durée de conservation et maintien de la qualité du produit. Final report presented to the Ministère de l’Éducation, du Loisir et des Sports (Programme d’Aide à la Recherche Technologique): v + 49 p.
Girault, L., Larrivée, M.-L. and Tamigneaux, E. 2005. Projet expérimental: comparaison de cinq techniques d’élevage de pétoncles géants de la baie de Gaspé. 2001-2004 final report, SODIM, 73 p.
