Economic Viability of a Directed Skate Fishery in the Gulf of Alaska
University of Alaska Fairbanks
School of Fisheries and Ocean Sciences, University of Alaska Fairbanks
- Thomas Farrugia, PhD program
Alaska has relatively healthy skate stocks. The most frequently landed skates in the Gulf of Alaska are the big skate and longnose skate, both of which are taken as nontarget catch in several longline and trawl fisheries. As a result of their abundance and relatively high ex-vessel value, there is a desire by fishers and processors to increase skate landings by allowing more nontarget retention or developing directed fisheries for them. Researchers seek to understand interactions among skate abundance, fisheries, and economics to aid in development of profitable and sustainable fisheries.
Skates are in growing demand worldwide. In the Gulf of Alaska there is increasing economic pressure to develop directed fisheries for big (Raja binoculata) and longnose (Raja rhina) skates. And Gulf of Alaska coastal fishing communities are looking for more opportunities to increase their economic resilience. However, these skate species are long-lived and slow-growing, and they mature late, making them vulnerable to overfishing, and currently they may be retained only as nontarget catch. Before a skate fishery can be opened, the sustainability of the skate resource and economic feasibility of a directed skate fishery need to be examined. This can be achieved best by determining the sustainable skate harvest through a stock assessment, which is then integrated into a bioeconomic model that includes ex-vessel value, costs, and demand for skates.
Why is this an Alaska Sea Grant project?
This research addresses Alaska Sea Grant’s goal of sustained, well-managed and healthy marine ecosystems in Alaska by providing decision-makers with science-based biological and economic information that can be used to inform the setting of quotas and the design of regulations for increasing skate landings. This project could contribute to strengthening coastal Alaska communities by fostering skate fishing within realistic biological and economic constraints, thereby ensuring sustainability and profitability. Finally, the study will address a third Alaska Sea Grant goal by retaining the biological and economic health of this commercial fishery and ensuring that it remain a long-term economic force in coastal communities.
How will researchers conduct their study?
- Gather data from management agencies and develop the stock assessment using Stock Synthesis software.
- Conduct interviews with fishers and processors and collect import-export data from countries and international agencies (e.g., United Nations).
- Integrate the stock assessment and economic data to produce a bioeconomic model that can be manipulated through a harvest function, a demand function, and a cost function.
- Apply this bioeconomic model to scenarios reflecting changes in management structure, prices, costs, and abundance of skates.
Alaska Department of Fish and Game
NOAA Alaska Fisheries Science Center
NOAA Northwest Fisheries Science Center
What researchers learned
Through our research on skates in the Gulf of Alaska, we have learned that although big skates (Beringraja binoculata) are more active than previously thought and can undergo long movements across the Gulf, they are unlikely to move in and out of the Gulf. This provides evidence that it is appropriate to consider the skate population of the Gulf of Alaska as one stock. We then developed the first population dynamics models for big and longnose skates (Raja rhina) in the Gulf of Alaska and found that current levels of harvest are sustainable but large increases in landings are unlikely to remain sustainable. This information was then integrated into the bioeconomic model, which suggests that the most profitable harvest strategy for skates is through non-target landings in bottom trawl and longline fleets.
Alaska Sea Grant study assesses risk-benefit ratio for consuming skate muscle based on nutritional and toxicity analysis
Relevance: Skates are in demand worldwide. In the Gulf of Alaska there is increasing economic pressure to develop fisheries for big and longnose skates (Raja spp.). Fishing communities are looking for opportunities to be resilient through diversifying their economy. Before a skate fishery can be prosecuted, the harvest needs to be sustainable and the fishery must be profitable. Information is needed on harvestable surplus, nutritional value, product form, demand and price, and best harvest strategies. Skates can be an important source of protein and omega-3 fatty acids, but a concern is the level of heavy metals, particularly mercury, in the muscle, which may influence product quality.
Response: Alaska Sea Grant–funded researchers sampled muscle and liver tissues from big and longnose skates harvested off of Kodiak and Cordova and analyzed nutritional content (protein, moisture, lipids, fatty acids), heavy metal (mercury, arsenic, cadmium, lead) and trace element (selenium) load.
Results: Big and longnose skate muscle was composed of lean protein (14.7%) with 1.2% lipids and 83% moisture. Livers were very high in lipids and omega-3 fatty acids. Mercury in the skates had mean levels of 0.21 mg per kg, below Pacific halibut levels. The risk-benefit ratio of skate muscle was slightly positive (3.62%) based on the balance of mercury toxicity and omega-3 fatty acid benefits, indicating a beneficial protein source. These data can be used by the seafood industry in communicating with markets for skate products and to be aware of health concerns. Results were published in the Journal of Food Composition and Analysis in 2015.
Recap: Alaska Sea Grant–funded researchers found a positive risk-benefit ratio for consuming skate muscle on the balance of mercury toxicity and omega-3 fatty acids; the data can be used by the seafood industry to understand market demands for skate products and to be aware of health concerns of consuming skates.
Anticipated benefits: At the conclusion of this project, the following benefits are expected:
- Develop a stock assessment using Stock Synthesis that can be readily used by management agencies (e.g., National Marine Fisheries Service and ADFG).
- Develop a bioeconomic model that can be used by management agencies to predict the possible consequences of different harvest strategies.
- Provide valuable experience in all facets of fisheries management to the graduate student.
- Provide the fishing industry with valuable economic information (e.g., market demands, possible revenues from skate seafood products, best harvest strategies for a sustainable fishery).
Farrugia, T.J., K.J. Goldman, C. Tribuzio, and A.C. Seitz. 2016. First use of satellite tags to examine movement and habitat use of big skates Beringraja binoculata in the Gulf of Alaska. Marine Ecology Progress Series 556:209-221. https://doi.org/10.3354/meps11842
Farrugia, T.J., A.C.M. Oliveira, J.F. Knue, and A.C. Seitz. 2015. Nutritional content, mercury, and trace element analyses of two skate (Rajidae) species in the Gulf of Alaska. Journal of Food Composition and Analysis 42:152-163. https://doi.org/10.1016/j.jfca.2015.03.013