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A New Spat Collection Strategy for the Lower North Shore: The Gillnet-Type Collector
Final Report
Société de développement de l’industrie maricole (SODIM)
AIMAP-2010-Q07
Table of contents
- Abstract
- 1.0 Introduction
- 2.0 Objectives
- 3.0 Discussion
- 4.0 Conclusions and recommendations
- 5.0 References
Abstract
Mussel spat supply is a key phase that can be a rather costly component of the mussel production process. Moreover, the quantity of young mussels collected can vary markedly from year to year. At some production sites, the water column suitable for mussel spat collection can be fairly shallow. Consequently, this project aims to assess the feasibility and cost/benefit aspect of a new mussel spat collection structure—a gillnet-type structure set up at a mussel production site on the Lower North Shore. This method was compared to the conventional method—suspended collectors—that is generally used. The main goal of this study was to compare collection yield as well as the technical and economic feasibility of conventional 3-foot candle-type collectors to those of 3-foot high gillnet-type collectors with 12" x 12" mesh. The results of this study showed that collection yields were fairly low, both on the conventional 3-foot collectors and on the gillnet-type collectors and that there was a significant spatial difference between the two longlines. Notwithstanding these results, the larger collection surface of the gillnets gives them an economic advantage over the 3-foot conventional collectors. In fact, the gillnets offer more contact surface in a more shallow water column so more young mussels settle there (three times more mussels of suitable size for socking) thus improving the company's ultimate production. It also lowers capital costs, notably by reducing the number of longlines needed (three times fewer) for the same length of collectors.
1.0 Introduction
Aquaculture activities in the Lower North Shore Region primarily focus on the Sea Scallop (Placopecten magellanicus) and the Blue Mussel (Mytilus edulis). The Belles-Amours Farms mussel farming operation is located near Blanc-Sablon, in the Baie des Belles-Amours. This company has farmed mussels for several years. The bulk of its production is sold fresh on the local market. To offset transportation problems and the highly competitive nature of the fresh mussel market, the company wants to diversify its offering of consumer products. Belles-Amours Farms Inc. is currently working on setting up a cannery to produce canned mussels in brine. It also plans on processing vacuum-packed frozen mussels. As a result of diversifying its products, the company expects mussel sales to increase. To support the expected growth, it will need to develop ways to safeguard its spat supply.
Commercial-size mussel production includes one crucial step: that of mussel spat supply. This step is a costly component of the mussel production process. Although since its inception, the company has collected adequate mussel spat in the Baie des Belles-Amours to supply Belles-Amours Farms Inc.'s market needs, considerable annual variations in collection success have been noted. This uncertainty factor is a concern for a company looking to broaden its range of aquaculture products and likely the scope of its sales. Furthermore, the profit margin is generally low for mussel farming operations like this one. It is essential for the company to maximize the yield, whether from a good or bad collection year. Therefore, efforts have been made to optimize mussel spat collection structures. The company previously used 6-foot1 suspended candle-type collectors on surface longlines. However, considerable epifaunal growth was observed on the lower part of these collectors, which negatively affected mussel collection yield and grow-out (Goaziou and Guay 2008). In 1993, Thomas also observed a negative gradient of the mussel spat collection yield with the increase in depth. In many cases, this epifaunal growth, especially clear at depths of 3 feet, resulted in losses due to fall-off of mussels attached to the lower part of the collectors. This fouling also added a great mass to all of the longlines, requiring more flotation material and maintenance time.
As a result of these observations, a study was undertaken to compare the collection yield of this type of structure (6-foot collectors) with two new collector configurations (Guay 2009). These new structures are 3-foot gillnet-type collectors and 3-foot candle-type collectors, which would maximize collection effort in the first 3 feet of the water column. Although the results were revealed in a preliminary study, the project was compromised by mussel predation by ducks and damage to longlines by ice. The current study proposes that the project be reworked with changes made in light of the preliminary results. The results of the initial study suggest that collection on gillnet-type collectors could be economically advantageous because of the larger capture surface on the same part of the water column, as well as decreased capital costs (decrease in the number of longlines for the same total length of collectors). Moreover, there does not seem to be a difference in collection success or mussel size between the 3-foot gillnet-type and candle-type collectors. However, the major difference seems to lie in the collection yield per foot of longline. According to this study, the collection surface of the gillnet-type collectors is double that offered by the 3-foot candle-type collectors. Furthermore, this study demonstrated that the use of collection structures providing an attachment surface at a depth lower than 3 feet should be avoided because of the adherence of fouling and the low collection yield (Guay 2009).
Ultimately, the purpose of the project is to develop a more effective mussel spat collection system, better suited to the conditions prevailing in the Lower North Shore, which could increase mussel spat supply and reduce the costs associated with this stage of production.
2.0 Objective
The main goal of this study is to compare collection yield as well as the technical and economic feasibility of conventional 3-foot candle-type collectors to those of 3-foot high gillnet-type collectors with 12" x 12" mesh.
3.0 Discussion
The results of this study showed fairly low collection yields, both on the conventional 3-foot collectors and on the gillnet-type collectors, and a significant spatial difference between the two longlines. Notwithstanding these results, the larger collection surface of the gillnets gives them an economic advantage over the 3-foot conventional collectors.
An adequate supply of mussel spat is essential and is the first step towards the company's profitability. The Baie des Belles-Amours mussel-farming site has been operating for several years. In 2006–2007, a study was conducted on the site to evaluate the success of mussel spat capture on the collectors (Guay 2009). Three types of collectors were evaluated and compared in terms of mussel collection yield, mussel size and colonization by associated species. This study compared various lengths (3 feet and 6 feet) of conventional candle-type collectors and a new gillnet-type collector with 12" x 12" mesh. Despite issues with mussel predation by ducks and damage to longlines by ice, the study's results shed light on a significant decrease in collection yield and an increase in colonization by associated species for collectors deeper than 3 feet below the surface of the water. However, decreasing the length of the collectors also decreased the amount of spat collected and thereby the final production of mussels. This is why a larger collection surface in the first 3 feet of the water column, through the use of gillnet-type collectors, is a promising avenue for providing an ample spat supply at this site.
3.1 Collection yield and associated species weight
The fall collection yield was two times higher on conventional collectors (405 g/15 cm of collector) than on gillnet-type collectors (193 g/15 cm of collector). This difference between structures may be partially due to a spatial variation confirmed by considerable differences between longlines. The average mussel collection yield (g/15 cm of collector), measured in spring and fall 2011, was from 3 to 15 times higher on longline 2 (spring: 0.94; fall: 456) than on longline 1 (spring: 0.06; fall: 142). Spat collection on collectors in a natural environment can vary spatially and depends on several factors, such as the arrangement of collectors relative to currents (Mallet and Myrand 1995). Furthermore, the collectors and the two longlines were handled in the same way and at the same time during the project.
The fall collection yields, measured as part of the current project, are much lower (between 70 and 315 g/15 cm), with the exception of the conventional collectors on longline 2 (600 g/15 cm), than those measured in fall 2008 during Guay's study (2009), 14 months after the collectors were deployed (average ≈ 500 g/15 cm). The difference between data from the two studies might be related to interannual environmental variability. Mussel spat collection can vary interannually due to environmental factors such as climate, tides and currents (Mallet and Myrand 1995).
The company observed the same spatial differences and the same low percentage of spat collection on its collectors installed in the same area of the bay and collected at the same time (S. Dumas, pers. comm.).
The associated species found on collectors, mostly made up of algae and hydrozoans, were significantly more abundant on the gillnets of longline 2, but only in the spring. It is possible that the abundance of algae and hydrozoans on longline 2 gillnets in the spring contributed to the decreased mussel yield on the longline 2 gillnet come fall. A significant amount of algae and hydrozoans on the collectors can contribute to the fall-off and loss of mussels attached to these associated species (Bourque and Myrand 2007). The weight of the associated species measured in the fall, that is, 14 months after the collectors were deployed, was lower (20–40 g/15 cm) than that measured during Guay's study (2009) (75 g/15 cm on average).
3.2 Mussel size
Although a significant difference was observed between the collector types in fall 2011, it seems less notable than that observed between longlines. As observed for the collection yield, the average size of the mussels was slightly larger on longline 2 than on longline 1, both in the spring and fall. The average size of mussels larger than 5 mm varied between 9.7 and 8.1 mm in the spring and up to 25.3 and 17.5 mm in the fall on longline 2 and longline 1, respectively. As a result, the hypothesis of a spatial variation between the two longlines also seems to have a favourable effect on the mussels from longline 2. It is possible that the currents brought more food (microscopic algae) into the environment adjacent to longline 2, but not longline 1. In addition, as observed on the size structure of the mussels measured in the fall, there was a much greater percentage of mussels larger than 10 mm observed on longline 2 (32% and 60% for conventional and gillnet-type collectors, respectively) compared to longline 1 (<10% for the two types of collectors).
Compared to the size structure measured by Guay (2009), in fall 2008, for the 3-foot conventional collectors, the percentage of mussels larger than 10 mm is much lower than in the current study (approximately 75% in 2008 vs. 10–30% in 2011). Once again, this appears to indicate a significant interannual variation of environmental conditions at the mussel collection site.
The percentage of mussels of suitable size for socking (≥15 mm) at the time of fall harvesting, that is, 14 months after the collectors were deployed, varies more between longlines than between structures: 40–65% on longline 2 vs. 10% on longline 1. Note that longline 2 contained a percentage of mussels of suitable size for socking corresponding to the average typically found at this site (65% for conventional collectors; Guay 2009).
3.3 Bioeconomic assessment
The bioeconomic assessment makes it possible to correlate the production costs of various expenditure items with the yield of mussels of suitable size for socking. Although handling (manufacture, recovery) of mussels takes longer on gillnet-type collectors than on conventional collectors, it turns out to be economically advantageous to collect spat with surface gillnets. Three times fewer longlines are needed to produce the same amount of sockable-size mussels (9750 kg) when using gillnet-type collectors rather than conventional candle-type collectors. The better yield of sockable-size mussels per foot of longline, as well as the reduced number of longlines for gillnet-type collectors essentially has to do with the larger surface area of netting on the same height of the water column.
The production costs calculated in the current report are higher than those assessed in 2008 by Guay (2009), for both types of collectors. This difference relates to the mussel collection yield, which was much lower in the current study. Guay (2009) had measured a collection yield of sockable-size mussels per foot of longline of 4.6 kg/foot of longline for the gillnet and 2.6 kg for conventional collectors, compared to a yield of 1.06 kg/foot of longline for the gillnet and 0.35 kg/foot of longline for conventional collectors in the current study. As discussed, this difference is likely due to an interannual variation of environmental conditions such as current.
Unlike the study carried out in 2008, the current study shows no mussels lost due to either predation by ducks or the presence of ice in the bay.
4. Conclusions and recommendations
The results of this study showed that collection yields were fairly low, both on the conventional 3-foot collectors and on the gillnet-type collectors, likely due to inadequate environmental conditions. Since collection success can vary from one year to the next at a given site, trials focusing on more than one year might have provided more conclusive results.
In addition, conventional collectors show more attractive yields than gillnet-type collectors. Results show that spatial variability is more important than that generated by the choice of structure. Therefore, it is relevant to focus on the economic analysis, which indicates that the gillnet's larger collection surface makes it three times more economically advantageous to use gillnet rather than conventional 3-foot candle-type collectors, due to fewer longlines being required for the same production and a yield of sockable-size mussels proportional to the larger collection surface of the netting. The economic advantage of the gillnets could be increased by mechanizing and adapting some equipment so that mussels could be mechanically harvested from the gillnet-type collectors, since mussels are currently harvested and declumped by hand.
An underground duck-scaring device was also installed on one of the two longlines. It is not certain that there was a cause and effect relationship with the subsequent lack of predation; however, considering previously observed predation by ducks at this site, prevention through deterrence should be a priority.
5. References
BOURQUE, F. et B. MYRAND. Rapport de R-D, Essais de stratégies pour contrer l’effet négatif des algues sur la collecte de moules au bassin du Havre Aubert. MAPAQ, DIT, 2007, no 157. 13 p.
GOAZIOU, Y. et M., Guay. Rapport CACN MLQ-008, Caractérisation des espèces épibiontes et évaluation de la fenêtre du captage du naissain de moules dans les baies des Belles-Amours et de Brador, 2008, 23 p.
GUAY, M. Rapport final MLQ-009, Nouvelle stratégie de captage du naissain de moules en Basse-Côte-Nord. Centre aquacole de la Côte-Nord, 2009 19 p.
MALLET, A.L. and B. Myrand. The culture of the blue mussel in Atlantic Canada, In: Cold-water aquaculture in Atlantic Canada (Boghen AD, ed), Moncton: Canadian Institute for Research on Regional Development, 1995, 255-296.
THOMAS, B. Premiers essais de captage de la moule bleue (Mytilus edulis) dans la baie de Gaspé. Activités 1992-1993. Dir. rech. scient. tech. 52 : 16-17.
1Structure sizes will be indicated in feet and inches in the text, since this is the unit commonly used by mariculturists.
