Urchins

Urchin Culture in British Columbia
Commercial sea urchin harvesting in British Columbia is a recent phenomenon, initiated on a small scale in the 1970’s. Urchins are hand-harvested by divers. Two species of urchins have been the primary target in this fishery, the green urchin, Strongylocentrotus droebachiensis, and the red urchin, Strongylocentrotus franciscanus, with the latter consistently forming the bulk of the landed product. Commercial urchin harvesting expanded rapidly between 1990 and 1992, the year that the fishery peaked and at which point more stringint fishery management regulations were introduced. In 1992 nearly 13,000 tonnes of red urchins were harvested at a total value of $8,661,500, and 978 tonnes of green urchins valued at $4,500,000. Current harvests are approximately 4000 and 100 tonnes for red and green urchins respectively. (Source: Fisheries and Oceans Canada, Fisheries Management, Pacific Region).

British Columbia is only one source of a north-eastern pacific coast urchin fishery. California has traditionaly dominated the urchin fishery while Oregon, Washington and Alaska have smaller scale fisheries. Yields from California’s fishery have declined since 1991 and by 1998 the BC urchin harvest exceeded that of California. The majority of the urchin harvest is exported to Japan. It is the gonads or roe of the urchins which are the edible product and value of the harvest is determined in part by the percentage of roe yield relative to total body weight. Japan is the world’s largest market for urchin roe (importing approximately 60,000 tonnes whole live urchins per year) followed in distant second place by France (1000 tonnes whole live urchins per year). Russia, Chile, Northe and South Korea, and China are among the other major exporters of urchin products to Japan. The price for top quality urchin roe is quite high, with top price paid for high quality roe that meets desired color, taste and texture characteristics. However, the price fluctuates depending on market supply and other factors.

With global declines in wild urchin stocks, the effort to develop culture technology for a variety of species of urchins is well underway. A great deal of urchin culture technology has already been developed in Japan as local wild stocks declined and efforts to rehabilitate those stocks commenced. In Canada research projects to develop urchin culture technology have been initiated on both coasts. Hatchery technology and the ability to produce roe of consistent high quality are the key objectives for this emerging industry.

Species
Although two species of sea urchins are harvested in coastal British Columbia waters, the red (Strongylocentrotus franciscanus) and the green (Strongylocentrotus droebachiensis), the latter is the focus of most current research and development efforts. The green urchin is capable of producing high roe yields of exceptional quality and is the species most amenable to culture conditions.

Green urchins occur along coastal areas of the Northern Hemisphere, both Pacific and Atlantic areas. The natural habitat preferred by urchins consists of rocky substrate, particularly rock with crevices and ledges affording protection from predators such as the sea otter, sea stars, crabs, octopus and wolf eels. Mature urchins feed on various types of macro-algae and large numbers can sometimes be found around kelp beds consisting of Macrocystis, Nereocystis, Laminaria, or other species of marine plants. Urchins occupy a range from extreme low inter-tidal to depths of 100 metres, but will aggregate mainly at the 5-10 metre range where macro-algae would be most plentiful. Green urchins have a wide temperature tolerance range (1oC-20oC) but are limited in distribution by more restricted temperature tolerances of the larvae where spring water temperature cannot exceed 6oC-8oC.

Planning Production
A culture system for urchins depends on the successful integration of all three components of the production cycle: hatchery, juvenile and grow-out. Development of hatchery technology has been relatively successful and large numbers of juveniles can be now be produced for urchin grow-out operations. Island Scallops Ltd. has been involved in developing hatchery techniques and produce juveniles at apporoximately 1cm test diameter for sale or transfer to growers. Several components of the grow-out phase are being investigated with tank design and finishing diet comprising the key factors. With the emergence of cost-effective prepared diets, and efficient culture systems growers might expect to produce a marketable product of 70 gram animals in approximately 14 months under optimal growth conditions. Containment systems held in open water areas, such as oyster trays or other suspended or benthic cages, may also be an option provided the feeding and handling costs are not excessive.

Steps of Production: Seed and Nursery
In order for an urchin culture industry to develop, hatchery production of seed is essential. Maintaining a healthy and productive broodstock is the first step. The broodstock are held in conditions that promote gonad development and permit multiple spawning. Mixing of sperm and egg results in fertilised eggs that hatch after approximately 20 hours.

Within three or four days the pluteus larvae require plankton for nutrition. The larvae remain free swimming for a further 16-30 days depending on temperature. At this point, when they are 0.3mm in size, they will settle onto a surface and undergo metamorphosis. Recent developments in hatchery technology and the use of probiotics have resulted in improved larval survival rates (25% to metamorphosis). (A. Alabi et.al. 2001)

In the hatchery a corrugated polycarbonate material coated with algal growth is usually used as a settlement surface.

The larvae will graze the surfaces of these plates until they reach 3-4mm in size at which point soft seaweed (such as Ulva lactuca) could be introduced. Soon after this the juveniles are transferred to nursery tanks and can be weaned onto kelp (e.g. Laminaria spp.). Six months after fertilization the juveniles may be 10mm and ready for grow-out. Hatcheries recognize the need to keep seed prices low enough to make grow-out feasible and profitable. The target is to have seed cost less than 10% of the farmgate price of marketable animals.
Green Urchin Juveniles Green sea urchin juveniles.

Grow-out
The fundamental issue in the development of grow-out systems for urchin culture is managing the requirement for regular feeding. Due to the high cost of feed and feeding logistics, optimizing growth to target increase in size (somatic growth) or increase in roe yield and quality, will be a key factor in urchin culture systems. In the wild urchins will migrate towards their preferred foods which consists of macro-algae. However, if animals are limited in their ability to migrate toward such food sources, they will graze on almost any surface, a feature which has endeared them to BC oyster farmers, where larval urchins settle in great numbers on oyster lines and trays. Urchins are omnivores and have been known to consume a wide range of organic materials. For example, they will quite happily graze on potatoes and other vegetables. Although that particular diet is not particularly suitable for producing high quality and volume of roe, it does provide a good result for somatic growth. The development of prepared feeds has been greatly assisted by this omnivorous characteristic. Experiments with different feed formulations have been quite successful and resulted in diets which have produced good results in roe yield, roe color, texture and taste. There will continue to be improvements in feed formulations with current projects investigating the appropriate mineral mix in feeds. However the cost of producing the feed as currently formulated is still high and efforts are underway to reduce the cost which will enable profitable grow-out operations to develop.

Most of the indicators for the development of urchin grow-out operations suggest that containment systems will consist of tanks and/or raceways, either floating or land-based, where feeding is direct and feed loss is minimized. It may be possible to integrate on-bottom or suspended cage rearing with a raceway system where the latter might be used strictly for finishing the animals on a diet producing high roe quality and yields. Tank and raceway design is another area where there is a significant amount of experimentation underway. One of the key requirements for tank or raceway design is an efficient system for particulate waste removal that minimizes use and loss of water. Experimental designs with “V” or “Double-V” shaped raceways with waste removal lines along the bottom have undergone trials. Malaspina University-College students, for example, are conducting trials on a “V” raceway.

Tank design experimentation has been the focus of recent research at the Marine Institute of Memorial University in Newfoundland. Research has been based on the need to develop commercial scale tank systems capable of holding over ten tonnes of urchins. Many pilot scale projects have been done and now the need is to make the transition to commercial scale systems. The project assessed a series of existing tank designs and developed a prototype of a new tank design based on the “Double V” concept. Tank systems must accomodate the physico-chemical and biological requirements of large populations of urchins. For example, dissolved oxygen must be maintained at over 80% saturation, temperatures maintained at over 6oC, salinity at 28ppt or higher and total ammonia at less than 0.02mg/L. Biological considerations include maximum density factors, their tendency to cluster in tanks, ability to access and consume all introduced feed, waste removal, and disease control considerations. Stacked flat raceways are the most common type in use but there are problems with waste removal, and therefore tend to require mor maintenance. (Couturier et. al. 2001.)

Island Scallops have been developing a tank design consisting of an oval raceway with flow driven by a small paddlewheel. The intent is to develop a system where water can be recirculated after pond treatment and water replacement would amount approximately 10% of the total volume per week. A recirculation system would use UV-treated water which would reduce the risk of disease which could be inadvertently introduced in flow-through systems.

Stocking densities of urchins in such raceways is complicated by the mobility of the urchins and their tendency to cluster in groups. Stocking densities will need to be optimized to produce adeqaute yields from each tank or raceway. Experiments with stocking densities indicate that the full diameter of the animal, including spines, must be considered when stocking with no more than 80% total area coverage (Alabi 2001). For example a 1cm shell or test diameter urchin will measure close to 2cm in diameter when spines are taken into account. Each animal may occupy an area of 2.5cm2 but will effectively require at least 3cm2. This would mean a stocking density of approximately 3000 urchins per square metre of tank surface area.

Waste removal from the raceways is accomplished by means of a belt filter in the raceway which removes the particulate waste material.

One of the other factors to consider in tank or raceway design is grading the urchins. Urchins display a wide range of growth rates among individuals of a contained population. At present the urchins must be manually removed from the tanks, screend for size, and returned to the tanks. Such handling is labor-intensive but research is underway to develop self-screening systems in the raceways, perhaps by using sea star extract to “chase” the urchins over grading screens.

Prepared urchin diets need to be specially formulated to “finish” the urchins in preparation for market. Roe quality is also dependent on the stage of sexual maturity of the gonads. As the urchins approach reproductive readiness, gametogenesis reduces the level of glycogen-containing nutrient cells. The result is roe of undesirable quality, soft and somewhat bitter tasting. Through control of water temperature and possibly photoperiod, roe quality can be maintained and production optimized. In its non-reproductive phase, urchins are capable of producing high quality roe consisting of glycogen-rich nutrient cells which yield a bright orange roe with desirable taste and texture characteristics. Roe yields are expected to be around 20% of the live urchin weight. There are some commercially available feeds available now that show good promise for high quality roe production. Small additions of kelp to the finishing diet may help to further improve roe quality.

Polyculture And Sea Culture Options
Deep water shellfish culture operations often acquire a natural urchin set on the stock and/or equipment in the water. For oyster growers in particular, these naturally occuring urchins are of enormous benefit. They will graze the equipment and the shell surfaces of the stock, consuming other organisms that may settle there. They will prevent much of the fouling by mussels, barnacles, algae, sponge, tunicates, etc. that would otherwise occur on the oyster lines or equipment. Since the grow-out cycle for certain types of oysters may be two or three years, the urchins that have naturally set on the oysters may achieve near-marketable size. However, due to the limited area of suspended oyster gear and lines, these urchins have a restricted range of mobility and growth is usually food-limited. However, there is great potential for these naturally set urchins to be grown out for market production. Growers may continue to transfer them to new oyster trays or develop a holding system where they can be fed and possibly finished for market. Suspended containers for urchins would have to be designed to facilitate efficiency of feeding the animals with minimal loss of feed. Bottom culture of urchins is also an option that has been investigated. They would need to be contained in cages and would still require feeding. However, feeding prepared diets would not be cost effective in such a system.

Printed sources to consult about urchins:

  • Alabi, A. et.al. 2001. “Status of sea Urchin Research at Island Scallops” in Proceedings of the Sea Urchin Culture Workshop. Malaspina University-College, Fisheries and Aquaculture extension Program.
  • Couturier, C. et.al. 2001. “Design Considerations for Commercial Sea Urchin Rearing Systems” in Proceedings of the Sea Urchin Culture Workshop. Malaspina University-College, Fisheries and Aquaculture extension Program.
  • Hagen, N. 1996. “Echinoculture: from Fishery Enhancement to Closed Cycle Cultivation” in World Aquaculture 27 (4), pp.6-19.
  • Bulletin of the Aquaculture Association of Canada. March 1997 (1).Proceedings Sea Urchin Culture Workshop

Web sites to consult:

  • Fisheries and Oceans Canada:Species and Habitat of Shellfish.
  • Fisheries and Oceans Canada:Diseases and Parasites of Shellfish