Freshwater Crayfish 19(1):15–19, 2013 Copyright ©2013 International Association of Astacology ISSN:2076-4324 (Print), 2076-4332 (Online) doi: 10.5869/fc.2013.v19.015
A Simple and Efficient Cooling Method for Post-harvest Transport of the Commercial Crayfish Catch Japo Jussila,1,* Vesa Tiitinen,2 Ravi Fotedar 3 and Harri Kokko 1 1
Department of Biology, University of Eastern Finland, Kuopio campus, P.O. Box 1627, 70211 Kuopio, Suomi-Finland *Corresponding Author.—
[email protected] 2 South Karelian Fisheries Advisory Center, Hietakallionkatu 2, 53850 Lappeenranta, Suomi-Finland 3 Department of Environment & Agriculture, Curtin University, GPO Box U1987, Perth, Western Australia 6845
Abstract.— Factors affecting post-harvest survival were investigated for the signal crayfish, Pacifastacus leniusculus (Dana), catch during onboard transport and subsequent holding at a land storage facility. Based on those results, an onboard transport method was developed. The research and development project was carried out during July, August and September 2010 – 2011 on Lake Saimaa, Finland. The investigation showed that critical factors for survival were air temperature during onboard transport and water temperature during trapping of signal crayfish. To minimise onboard transport stress caused by the elevated temperature and resulting decrease in survival, several transport methods were tested. The commercial catch of signal crayfish was monitored over an entire day and a newly developed, rapid cooling method was compared to existing conventional onboard cooling systems used during transport. When the crayfish catch was rapidly cooled from ambient temperature (20 – 26°C) to 5 – 7°C, it resulted in 100% survival of the crayfish during transport. The improvement in catch survival was estimated at 10%, compared to the conventional transport methods when the holding facility mortality was taken into account. The improved cooling system during boat transport consisted of cooler boxes equipped with -20°C cooling units on the bottom, a mesh to prevent crayfish from being in contact with frozen material and a plastic bag to ensure a cool and moist environment during onboard and road transport. [Keywords.— commercial trapping; onboard transport; signal crayfish; survival]. Submitted: 29 September 2012, Accepted: 24 January 2013, Published: 15 February 2013
INTRODUCTION
transport to market (Whiteley and Taylor 1992; Samet et al. 1996; Spanoghe and Bourne 1997; Jiravanichpaisal et al. 2004).
The professional commercial trapping of the signal crayfish, Pacifastacus leniusculus (Dana), in Finland has been practised in the southern great lakes for the past 10 years (Jussila and Mannonen 2004), including Lake Saimaa. This has been enabled by an increase in signal crayfish production in southern lakes in Finland (Kirjavainen and Sipponen 2004), after the crayfishery collapsed some 100 years ago due to crayfish plague, Aphanomyces astaci Schikora, which devastated the productive noble crayfish populations that existed in Southern Finland (Jussila and Mannonen 2004; Kirjavainen and Sipponen 2004).
Due to long crayfishing working hours and rather hot summer days during recent years in Finland (Finnish Metereological Institute 2012), the crayfish losses during onboard and road transport, and later at holding facilities, have been high. Crayfishermen are using large numbers of traps (up to 200 – 400) and spend up to 12 – 14 hours daily to check traps and handle the catch. Therefore, there have been recent attempts to develop professional crayfish trapping, transport and storage methods to match the requirements of modern expectations. Some of the guidelines have been adapted from previous research that was carried out on post-harvest handling of other crustaceans (Fotedar and Evans 2011), and also utilised traditional knowledge on the handling and stress resistance of freshwater crayfish.
In order to increase the profitability of the signal crayfish fishery in Lake Saimaa, it would be crucial that post-harvest mortality is minimised and marketed crayfish are of prime quality (our unpublished data). The critical time for minimising mortalities would be during handling and transport of the catch on crayfishing boats (Jussila et al. 1997; Paterson et al. 2005) or on the road (Jussila et al. 1999) in order to minimise post-harvest stress (Paterson and Spanoghe 1997; Jussila et al. 2001; Paterson et al. 2005). If the catch is subjected to immediate cooling and minimum handling (Fotedar and Evans 2011), it then reduces the chances for stress induced mortality during later stages during
The aim of this study was first to evaluate the factors causing post-harvest survival changes in the commercial catch of the signal crayfish. The second aim was to develop a cost-effective practice for onboard and road transport of signal crayfish from Lake Saimaa under the most stressful conditions (i.e., warm to hot days with air temperatures between 25 – 35°C) and long crayfish transport periods (8 – 14 hours). 15
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Table 1. Regression equations and correlation between factors and catch survival over 4 weeks while holding in a commercial facility (CrayShower) during the summer of 2010. The analyses have been carried out for the grade I catch, except for the quality rating comparison. Regression could not be estimated when n/a is displayed due to too few variables or data not available. A non-significant correlation is indicated by ns.
Water temp., °C
y = -0.016x2 + 0.576x – 4.3044 (R² = 0.50)
Correlation Coefficient -0.41*
Air temp. max., °C
y = -0.001x2 + 0.049x + 0.4654 (R² = 0.56)
-0.63**
Air temp. min., °C
y = -0.003x2 + 0.091x + 0.3136 (R² = 0.42)
-0.50**
Factor
Wind strength, m s
Regression Equation
y = 0.009x – 0.103x + 1.1338 (R² = 0.14)
ns
Quality rating
n/a
-0.40*
Crayfisherman
n/a
ns
Wind direction, °
n/a
ns
Cloud cover, %
n/a
ns
-1
2
MATERIAL AND METHODS Lake Saimaa Signal Crayfish (Pacifastacus leniusculus) The Lake Saimaa signal crayfish population has several features that make it rather unique among the Finnish signal crayfish stocks, and as a result, a good target for research. Large scale introductions of the signal crayfish were carried out in Lake Saimaa in the mid 1990s. The stocked signal crayfish were probably infected with crayfish plague and during the first half of the 2000s this resulted in infection outbreaks and decreased production throughout Lake Saimaa. Today, the signal crayfish stock shows severe gross symptoms in 50 – 70% of the commercial catch (our unpublished data) and roughly half of the commercial sized catch are graded as commercial grade II, and thus low in value. The stock also carries Psorospermium haeckeli Hilgendorf (Henttonen 2010, personal communication), which has been claimed to weaken the immune system of signal crayfish (Thörnqvist and Söderhäll 1993), possibly further hindering production.
The CrayShower Land Storage Method The land storage method used by the commercial trappers participating in this project, the CrayShower, is a specific storage system developed for freshwater crayfish originally in Western Australia by the Pemberton Fishermen Co-operative in the 1990s and further modified by the Crayfish Innovation Center in Finland. In the CrayShower storage environment, the crayfish are held in plastic containers (for example 50×35×30 cm, L×W×H) with a maximum of two layers of crayfish in each container. Within the CrayShower system, a cool environment with 100% humidity is developed by constant fine water spray that creates a mist within each container. The containers can be stacked on top of each other and are placed in a cooling unit, a cold store or a reefer box, at a temperature of 6 to 8°C. Factors Affecting Post-harvest Survival The survival of the commercial catch stored in the CrayShower, described in the above section, was followed over a four week period during the summer of 2010. Results from two different crayfishermen were followed. The environmental conditions (Lake Saimaa surface water temperature, lake Saimaa regional maximum and minimum air temperature, rainfall, wind strength and direction and cloud cover) were monitored during the crayfish trapping day and factors affecting the survival of the crayfish held in the CrayShower reefer box were analysed. A total of 14 different one day catches were included in the analyses.
Figure 1. Post harvest survival in the holding facility, CrayShower, for grade I and grade II commercial signal crayfish (P. leniusculus), trapped from Lake Saimaa in the summer of 2010. The difference between grade I and grade II survival was statistically significantly different from week 1 onwards (t-test, P < 0.04). Data for both grade I and grade II catch are combined from 14 one day catches.
The catch was graded into two different groups based on the current commercial criteria, as follows: grade I crayfish were healthy with no gross symptoms of crayfish plague (A. astaci), two equal size claws, good coloration (even coloration, mostly brown, typical for signal crayfish) and were responsive to physical stimuli when handled, while grade II crayfish showed minor gross symptoms of crayfish plague, could have lost limbs but were responsive to physical stimuli when handled. Both commercial categories were 11+ cm in total length. Development of the Transport Method Onboard transport methods were developed based on data analyses from the previous summer (2010), where the onboard
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transport temperature was noted to be the critical factor. During the following summer (2011), the post-harvest catch survival and onboard transport conditions were followed and compared to data from the previous summer (2010) in order to support the progress in developing a working system. Conventional transport methods (i.e., plastic container and onboard CrayShower applications), were followed during three different days using a rapidly cooled subset of the catch as a control. The three onboard transport methods investigated were as follows: 1) cooling of the catch with a damp cloth on top, while crayfish were held in a plastic container (hereafter plastic container); 2) crayfish held in plastic boxes stacked on top of each other and sprinkled with lake water (hereafter onboard CrayShower) and 3) crayfish held in foam boxes on top of a layer of ice and damp cloth or plastic mesh (hereafter control container). The crayfish were held at commercial transport densities, roughly 3 kg per container, during transport, with roughly two layers of crayfish in each container. We also tested the control system transport method under simulated conditions (i.e., during a seven hour transport on road and subsequent holding of the crayfish in cool and moist conditions). In this final experiment, we used 30 signal crayfish from a commercial catch in early September, transported for a short time (one hr) in onboard containers (no mortalities during onboard transport) with moist hemp cloth on top. The crayfish were then packed in the foam box (Figure 4), similar to experiments discussed above, with the temperature followed inside the foam box (ThermaData™ Logger, series II) during a six hour road trip and survival was then monitored for a week.
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Figure 2. Temperature profiles during boat transport, plastic container, during summer of 2011. Temperature within the transport environment expressed as lines and ambient air temperature on every hour with a dot. Plastic containers were stacked and lowest container packed roughly two hours prior to the top container. Ice added indicates time when the trapping ceased and remaining ice was poured on the top container.
Prior to packing the crayfish, they were graded according to the local commercial standards and only grade I signal crayfish were used. The quality grading of Lake Saimaa crayfish is essential since more than 50% of the signal crayfish catch shows gross symptoms of crayfish plague (melanisation, tissue erosion and limb loss), and thus are considered substandard for commercial purposes. The transport temperature was monitored using temperature data loggers (ThermaData™ Logger, series II) with the logging interval set to 1 min and an accuracy to 0.1°C. Survival was observed after the catch arrived at the land holding facility CrayShower, and afterwards, up to four weeks of holding in the land holding facility CrayShower. The lake water surface temperature was measured during crayfishing trip (Minitherma™) and air temperature was also monitored using data loggers. Data on ambient conditions were also obtained from the Finnish Metereological Institute, but this data was used in the analyses only if we failed to collect similar data ourselves. Statistical Analyses The grade I catch was used in the analyses, except for the comparisons between grade I and grade II. Both SPSS (v. 17) and Excel were used to analyse the data. Regression was considered statistically significant when P < 0.05. Correlation coefficient significance was rated as * equals P < 0.05 and ** equals P < 0.01. RESULTS AND DISCUSSION Factors Affecting Post-harvest Survival The average post-harvest survival was significantly lower for the grade II catch than the grade I catch (t-test, P < 0.04) from the
Figure 3. Temperature profiles during boat transport, onboard CrayShower, during summer of 2011. Arrival at the shore (A) and after road transport to the holding facility, CrayShower, (B) indicated by vertical bars. CrayShower 1 was packed from the first catches and CrayShower 2 later around noon from the last catches.
first week onwards (Figure 1). A similar decrease in survival has been previously suggested for immunocompromised crustaceans (Fotedar and Evans 2011). In both commercial categories, the post-harvest survival decreased significantly after the second week in captivity. There were no statistically significant differences (t-test, P > 0.05) between grade I or grade II survival for the two crayfishermen, and thus the survival data was pooled for the grade I catch in the following analyses. Both water and air temperature were the main factors affecting commercial post-harvest survival, as shown by the best regression fits and highest correlation coefficients (Table 1), with air temperature and exposure being previously reported as crucial factors influencing post-harvest stress (Samet et al. 1996; Spanoghe and Bourne 1997; Fotedar and Evans 2011). The single most important factor was maximum air temperature during
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Table 2. Mortality comparisons between different transport methods before and after the research and development project conducted during the summer of 2011. The control container allowed for rapid cooling of the catch to < 7°C and the a moist environment helped to calm the crayfish. Boat transport
Holding depot, per day
Combined, first day
Combined, first week
3 – 14.1%
0.08%
3.1 – 14.2%
3.6 – 14.7%
2%
0.2%
2.2%
3.4%
0%
0.38 – 0.65%
0.4 – 0.7%
2.8 – 4.9%
BEFORE R&D, N=5 Plastic container Onboard CrayShower AFTER R&D, N=4 Control container
onboard transport (Table 1, correlation -0.63**), and most of the post-harvest survival decline could be explained by the synergistic effects of air and water temperature during trapping and transport. Grade II crayfish post-harvest survival was significantly lower than grade I (t-test, P < 0.01) (Figure 1 and Table 1). The ambient factors, such as wind strength and direction and cloud cover, did not seem to affect post-harvest survival. The 2010 summer was exceptionally hot and calm, with virtually no wind or cloud cover during the study period, which partially explains the lack of influence from these factors (Table 1). Development of Transport Methods The temperature inside the plastic containers that had a moist hemp cloth as a cooling unit, followed the ambient air temperature (Figure 2). The inside temperature exceeded 20°C at about 9 AM, which was less than three hours into the total seven hour transport time. The initial cooling observed in both onboard transport containers was caused by ice being added on top of the hemp cloth. The temperature was elevated even faster in the topmost container, which was fully exposed to the direct heat of the sun,
Figure 4. The simple crayfish transport method, which was the final version developed for use. The cooling units are placed on the bottom, then the plastic mesh to prevent the crayfish from being in direct contact with the cooling units. The crayfish are placed on the plastic mesh, preferably inside a plastic container or a plastic bag.
with the temperature reaching 25°C at the end of the day. Ice was added to the top container to avoid further heating (Figure 2). In the control container, the temperature declined to 7°C within 90 min of packing, and remained at that level throughout the day. The second system tested, the onboard CrayShower, worked similar to the plastic containers except that the temperature within the onboard CrayShower was not as directly influenced by the ambient air temperature and heat of the sun (Figure 3). The temperature within the onboard CrayShower remained stable, between 18 and 19°C, throughout the day. The temperature within the onboard CrayShower, especially CrayShower 1, was mostly influenced by the surface water temperature, which was used to spray the crayfish, with a slight cooling effect due to the fine spray and evaporation. The crayfish that were caught later in the day (CrayShower 2) showed an instant cooling effect and within an hour, reached a temperature 2°C lower than that at packing time. The final temperature in CrayShower 2 was similar to CrayShower 1, which was used for the whole day. The control container showed similar cooling trends to the first onboard transport experiment (Figures 2 and 3), with rapid cooling below 7°C within one hour after the crayfish were packed, and the temperature remained low throughout the day. There was a slight elevation in temperature in CrayShower 2 during land transport (from A to B, Figure 3), indicating differences in individual container handling by that particular crayfisherman. The best onboard transport system, the final version of the control container, resulted in zero mortality during boat transport for the entire project period (Table 2), as well as over the whole 2012 crayfish season at Lake Saimaa. There was a close to 10% improvement in the survival of the catch. Pacifying and cooling the catch has been previously reported to improve survival in other crustaceans (Jacklin 1996; Morrissy et al. 1999). The survival in the holding facility was slightly lower than the survival seen in crayfish transported using conventional methods (Table 2). This highlights the fact that there is still considerable room for improvement in post-harvest handling methods since there seems to be a tendency for crayfish to experience stress even in the developed rapid cooling transport method described here (Figure 4). The last experiment, where crayfish were instantly cooled and transported imitating onboard transport conditions, verified results from previous experiments. The temperature within the foam box (Figure 4) declined sharply to 6°C and remained at < 7°C for the
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whole seven hour transport period. This additional test resulted in zero crayfish mortality, even one week after capture, thus validating the results obtained under typical conditions at Lake Saimaa. CONCLUSIONS As a result, the best transport method appeared to be the control container, initially selected to be a background control system for the development of a transport method. The system includes foam boxes (Figure 4), which will be equipped with cooling units on the bottom, a plastic mesh to prevent the crayfish from being in contact with frozen cooling units and finally a container or plastic bag to hold the crayfish. The purpose of the container or plastic bag is to keep the crayfish moist and to prevent further handling of individual crayfish, thus minimising stress (Wachter and McMahon 1996; Jussila et al. 1999). Observations indicate that the crayfish become passive inside the container or plastic bag, especially if they are not exposed to light at any stage during transport (our own observation). Later size grading would be less stressful to the crayfish when they are passive, thus resulting in higher survival during holding in a land storage facility. The transport methods used by Finnish crayfishermen are still largely based on traditional methods, even though studies have indicated that recent developments can have commercial benefits. This research and development project has shown that progress can result from simple solutions, and that crayfishermen are eager to benefit from scientifically sound improvements to their current practices, as the rapid cooling system has already been utilised during the 2012 crayfishing season. ACKNOWLEDGMENTS We wish to thank commercial crayfish fishermen from Lake Saimaa for their collaboration. The study was funded by the EU (Eastern Finland Fisheries Group), as EU invests in sustainable fisheries, and Greater Saimaa Fisheries District and the Southeast Centre for Economic Development, Transport and the Environment. The data for daily ambient conditions was kindly provided by the Finnish Metereological Institute. This paper is dedicated to Pedro António da Silva Mendes: bem-vindo! LITERATURE CITED Finnish Metereological Institute (2012). Weather in recent years. http://ilmatieteenlaitos.fi/vuositilastot. [Accessed 21 July 2012]
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Jussila J, Tsvetnenko E, Dunstan B and Evans LH (1997). Total and differential hemocyte counts in western rock lobsters (Panulirus cygnus George) under post-harvest stress. Marine and Freshwater Research 48(8):863–867. Jussila J, Paganini M, Mansfield S and Evans LH (1999). On physiological responses, hemolymph glucose, total hemocyte count and dehydration of marron (Cherax tenuimanus) to handling and transportation under simulated conditions. Freshwater Crayfish 12:154–166. Jussila J, McBride S, Jago J and Evans LH (2001). Hemolymph clotting time as an indicator of stress in western rock lobster (Panulirus cygnus George). Aquaculture 199(1-2):185–193. Jussila J and Mannonen A (2004). Crayfisheries in Finland, a short overview. Bulletin Français de la Pêche et de la Pisciculture 372-373(2):263–274. Kirjavainen J and Sipponen M (2004). Environmental benefit of different crayfish management strategies in Finland. Fisheries Management and Ecology 11(3-4):213–218. Morrissy N, Walker P, Fellows C and Moore W (1999). An investigation of weight loss of marron (Cherax tenuimanus) during live transport to market. Fisheries Research Report 99. Department of Fisheries, WA. Paterson BD and Spanoghe PT (1997). Stress indicators in
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