Wave Glider Tracks Snow Crabs to Put New Data in Reach
Liquid Robotics — June 23, 2017
Introduction
Coastal communities around the globe are seeking better ways to understand and manage regional ecosystems. They depend on the ocean to sustain economic opportunities, ensure food security, and safeguard fragile environments and species. For harvesters, scientists, and government organizations in Nova Scotia, Canada, timely, accurate, comprehensive data on movements of valued species is essential for designing effective fishery management regimes.
Harvesters, university research groups, and government agencies have been tagging and monitoring aquatic animals for years. But not all tracking methods are practical or cost-effective for highly mobile, yet slow moving animals like crab and lobster. Electronic tagging systems such as acoustic telemetry are attractive because they let investigators track animals without having to recapture them once they are released. Traditionally, bottom-moored acoustic receivers have been used to detect acoustically tagged animals, but these receivers only pick up tags that are within about 1km range. They also had to be periodically retrieved or interrogated via acoustic modems to get the data stored on them. There are economic and practical limits on how many of these receivers can be moored in the ocean, so scientists have been seeking ways of developing “mobile receivers” that could patrol an area and generate the same data that an extensive moored array would deliver.
The Wave Glider is a flexible platform that fits the bill for a mobile receiver. As an autonomous, piloted, long-duration surface vehicle, the Wave Glider can be instructed to patrol specific target areas and deliver timely data on movements of mobile species of marine life within these areas. Wave Gliders have been used for years by Canada’s Ocean Tracking Network (OTN; see below, and www.oceantrackingnetwork.org) in support of national and international research programs. Regionally, the Wave Glider successes have attracted the attention of other organizations, including local crab harvesters and government crab management agencies, who saw great potential for the technology to address their information needs. These groups were excited to take advantage of a new form of monitoring and data collection, and some even invested their own funds to strengthen the initiative and maximize the value of the data.
The richer data collection enabled by the Wave Glider and real-time access to that data has enabled all these participants to learn something about snow crabs that had been previously unknown: their mobility and migratory patterns. And it has brought these diverse groups together and created a positive forum for future work together.
A Research Initiative Grows
Since 2008, OTN at Dalhousie University in Halifax, Nova Scotia, has been deploying acoustic receivers and oceanographic monitoring equipment in key ocean locations and inland waters around the world. A leading global research organization, OTN has established partnerships with a worldwide community of telemetry users to document the movements and survival of aquatic animals carrying a variety of electronic tags (acoustic, satellite, radio, data archival), with a special focus on acoustic technologies. The effort also tracks how changing oceanographic conditions impact marine life by deploying oceanographic and biogeochemical sampling instruments in tandem with tracking equipment.
OTN tracks a variety of keystone, commercially important, and endangered species, including marine mammals (seals, whales), crustaceans (crab, lobster), and fish (sharks, salmonids, tuna, eels). Over 400 international researchers from 20 countries are currently participating in the global network.
OTN is continually refining and enhancing its technology and research approaches. Three years ago, the organization began developing the Wave Glider as a platform to efficiently and cost-effectively (through acoustic modems) pull data on fish detections from acoustic receiver stations attached to the ocean floor. With its mobility, longevity and autonomy the Wave Glider could retrieve data more frequently and with lower costs and risks to staff. The development of the Wave Glider as a mobile receiver flowed naturally from this initial use. The projects nest within a larger OTN glider program that involves both Wave Gliders and Slocum Gliders. The program seeks to expand coastal monitoring to support climate changes studies, understand marine animal movements in the context of environmental conditions, and gather data for other ocean models.
The Wave Glider has proved its worth for supporting the operations and maintenance of acoustic telemetry arrays. Previously, researchers had to spend up to a week at sea retrieving data from fixed receivers. The Wave Glider initiative reduced the average cost of these voyages by 66 percent. Funds once used to harvest data could be redirected to more undersea receivers, expanding research, or other programs.
OTN’s expertise in tracking marine animals was called upon to assist in evaluating potential environmental impacts on crabs and lobsters from the proposed undersea Maritime Link power line that would span the Cabot Strait exit of the Gulf of St. Lawrence. Multiple stakeholder groups needed a better understanding of crab migration patterns, and of determining whether the project could impact the animals, and if yes how to mitigate any issues.
OTN joined forces with stakeholders to monitor snow crab migration in eastern Nova Scotia. The joint effort involved OTN, local fishermen, Canada’s Department of Fisheries and Oceans (DFO) and Emera (the project Proponent) scientists.
Each group has its own information needs about the crabs’ movements, behavior, and population abundance. Emera focused on meeting the impact assessment directives for monitoring and documenting the habits and behavior of snow crab before and after cable installation. OTN sought the best possible data for the scientific community to provide a foundation for sustainable oceans management. Commercial harvesters were working with government agencies to adjust fishing quotas so that they more accurately tracked the spatial distribution of the resource, and DFO required further data to support its conservation and sustainable fisheries mandates.
This work is ongoing, and the Wave Glider is helping each of these groups achieve its most important objectives—and more. It’s also setting the stage for improved collaboration and cooperation between groups with very distinct perspectives and priorities.
Fishermen Gain Visibility, Strengthen Dialogue
Commercial harvesters in Nova Scotia depend on a healthy ecosystem for their livelihood. Snow crab fishing is a major industry in the community, with annual revenues of more than $130 million. Harvesters need to balance production as well as sustainability, bringing in the largest possible harvest without impacting the long-term health of the crab population.
Fishing quotas are a critical mechanism for balancing the long-term environmental and commercial needs of the fishery. With so much at stake, local harvesters are doing all they can to ensure that quotas will maintain sustainable fisheries.
Fishing in the Canadian waters of the North Atlantic is regulated by zones, and each zone is assigned a specific quota every year by the DFO. The agency sets these quotas based on data from an annual biomass survey, and statistical modelling which factors in things like environmental variables. Quotas can vary dramatically between adjacent zones. One zone might allow an annual harvest of 8,000 lbs., while its neighbor might permit 160,000 lbs. It’s not surprising that local harvesters whose activities are limited to specified zones, are not always in full agreement with their assigned quota—especially if it differs with their perception of the potential catch. An annual snapshot of a specific population can’t always reflect migration and other behavior that’s difficult to model.
“Scientists at the DFO have been going out year after year to perform biomass estimates, but if they can’t find crab in their annual surveys, the quota remains low,” says Neil MacMullin, a local fisherman. “Yet we’re going out and having phenomenal catches. My theory was that crab were moving out, and the annual survey has been missing them.”
A New Partnership Yields Results
To help strengthen their case and verify their own informal observations, these fishing groups took the initiative to develop an acoustic tracking program to see if the crabs were moving among zones. The harvesters built partnerships with government and the OTN, paid to tag approximately 100 snow crab at their own expense, and provided their vessels and time to deploy undersea receivers along the fishing zone boundary line. Dr. Fred Whoriskey, executive director at OTN, suggested using the Wave Glider to improve tracking capabilities. The fishing organizations embraced the idea, seeing the Wave Glider’s potential to add value to snow crab data by providing mobile, near real-time tracking and communications.
“When Dr. Whoriskey suggested using the Wave Glider, I thought it was a great idea,” says MacMullin. “We’re not always sure if stationary receivers are tracking properly, because crabs may not pass near them. The Wave Glider can go directly into where fishing is concentrated, and move back and forth across the area. It can tell if a crab has moved into an area. We can get a continuous survey instead of a snapshot.”
The successful initiative is not only providing new information about the behavior of the crabs. It’s setting the stage for continued dialogue and partnerships with all the stakeholders. Plans are already underway to tag additional crab in Spring 2017, and DFO, as well as the OTN and harvesters, are committed to teaming up on the next phase of the project, which will involve how the crabs respond to a new marine protected area in the study region.
DFO Gains Data for Better Science and Resource Management
Canada’s DFO is playing the central science role in the snow crab tracking project. This government agency strives for sustainable fishery management based on robust science. Since its ultimate mandate is sustainability of the fisheries, the organization must be conservation-oriented. When evaluating new data and methodologies, the DFO is cautious, but also open to new information and approaches.
The DFO’s technology and methods had been in use for a long time. There is a comfort in this familiarity, but also a recognition that with more information generated by new technologies, a better job could be done. However, new technologies like acoustic telemetry bring new challenges. For example, acoustic tags glued to crab carapaces are not great for juvenile crabs that moult frequently and shed their tags. Fully grown adult crabs do not moult.
When the DFO and harvesters came together to work on the Wave Glider tracking project, the DFO saw the project as an opportunity to add an important new set of data to its understanding of the local ecosystems.
“We were interested in using the acoustic tags to understand previously inaccessible segments of population, because there was very little information,” says Dr. Jae Choi, DFO Science, Maritimes. Dr. Choi had in previous years used numbered, visible plastic tags to mark animals, and developed a coarse sense of the species’ movements based on subsequent recaptures by the harvesters. This posed a number of problems. “In the past, we could only tag large fully grown male crab. Other populations were very difficult to track,” says Dr. Choi. To conserve spawning potential, managers have limited harvesters to taking only male crabs (sperm is cheap, eggs are precious) so the only movement data available was about males. In the wild, males segregate from females and juveniles, so information about male movements does not help us understand what most of the population is doing.
Revealing the Big Picture with More Data
With the Wave Glider, DFO can access new sources of data about species that had been unavailable using previous methods. The Wave Glider can also provide near continuous data upload and mobile tracking over longer periods of time—a capability that simply wasn’t possible with boat catches or fixed undersea receivers. The autonomous mobile platform can cost-effectively patrol an area for weeks or months to provide an extended view into the behavior and migration patterns of these mobile animals. DFO can also tag other species such as crab predators that are associated with the crab ecosystem, to gain a better understanding about the relationships between different species in the area.
“From a scientist’s perspective, I find it very fascinating,” says Dr. Choi. “We’re looking at a segment of the population for which, previously, we had almost no movement information. Snow crab are an interesting species overall, and this is a window into the juvenile and female crab for which we had previously no information.”
A Springboard for Collaboration and Future Opportunities
The community-driven research program is an important partnership model for helping Canada’s coastal communities sustain economic opportunities, ensure food security, and safeguard ecosystems. Local fishermen are gaining access to data that could potentially impact their industry through a mobile platform that can share data on tagged animals instantly. Scientists and academics at DFO and OTN are expanding their studies and tapping into data that can help them do their jobs better and more cost-effectively.
But among the most exciting developments is the close collaboration between all parties, which culminates in a yearly snow crab summit. The project has brought together a diverse set of groups, all working toward a common goal: gaining the best available science on the health and behavior of a species that’s vital to the region.
The snow crab tracking initiative has helped to strengthen trust and open new channels of dialogue between what can sometimes be very disparate. Nova Scotia’s fishermen, government agencies, scientists, and other stakeholders are looking forward to continued collaboration to enhance their knowledge in the years to come. And we’re excited about how the Wave Glider can continue to enable more of these collaborations in the future.
A version of this article first appeared in Hydro International.
