Capturing Spatial Behaviors of Observed and Unobserved Fishing Over Time Using Vessel Monitoring System Data
School of Fisheries and Ocean Sciences, University of Alaska Fairbanks
- Jordan T. Watson, PhD program
Many studies have focused on the response of commercially relevant fish populations in the North Pacific to physical and biological dynamics within their ecosystems (e.g., climate variability, oil spills). We propose instead to focus on the resilience of commercial fishers themselves and to better understand the adaptive capacity of fishing fleets to such dynamics. For example, how far north are fishers willing to follow shifting fish populations? Are fishing trips longer during warmer years and do they subsequently spend less time in local port communities? Such simple questions are predicated on knowing when trips start and stop, where vessels fish, and how many miles they travel. For trips with fishery observers these questions are easy to answer, but observer coverage varies across fleets and years. Vessel monitoring systems (VMS), however, transmit a vessel's location at regular intervals (about 30 minutes) and they have been mandatory on all North Pacific vessels targeting pollock, cod, and Atka mackerel since 2002 (and additional fisheries and sectors in subsequent years). We will use VMS data to reconstruct trips and thus to determine durations and distances traveled for thousands of trips over more than a decade, regardless of observer coverage. Models based on VMS data also enable us to predict when vessels are fishing, and thus we can better characterize how fishing effort is distributed spatially and how resilient those spatial distributions may be over time. Moreover, these models also allow us to compare fishing locations for observed and unobserved vessels. In the context of resilience, this approach will ensure that the characterization of vessel movements and fishing locations is representative of entire fleets and not only the observed portions. This approach can be extended to all Bering Sea and Gulf of Alaska fleets with VMS.
For more project information, please see the 2016 news story ”Pollock fishermen may struggle to maintain catch numbers as oceans change.”
With a changing environment, shifts in the timing of physical and biological processes, locations of marine populations, and the structure of marine ecosystems are inevitable. Many of these changes may require fishers to redistribute their effort in time and space and even to target different species. By examining changing fishing patterns and deliveries, it becomes possible to model how changing fishing locations are impacting the ports and processors where fish are delivered, and how longer trips may affect fishers’ stress and profitability.
Why is this an Alaska Sea Grant project?
As emphasized in the Sea Grant Strategic Plan, Alaska communities, ecosystems, and fisheries are experiencing the impacts of climate change firsthand. Many Alaska community economies are reliant on fish deliveries to processing plants and on the economic contribution from fishing crews while in port. Meanwhile, the current management of fishery ecosystems has developed around historic spatial distributions of fishing effort. As effort responds to ecosystem shifts, different habitats and species (target and nontarget) may become exploited and patterns of vessel deliveries and contributions to port communities (and economies) may change. Our work will characterize how fleets and their spatial distributions are changing over time, providing an opportunity for management strategies to support community and economic resilience.
NOAA Fisheries, Alaska Fisheries Science Center
NOAA Alaska Regional Office
What researchers learned
We examined the U.S. Bering Sea walleye pollock fishery—one of the world’s largest fisheries—to characterize how fishers during the summer B season responded to variability in the fishery landscape (e.g., fish abundance, climate, catch limits, fuel prices) from 2003–2015. When fish were abundant and water temperatures were warm, vessels across the fleet demonstrated similar behaviors. However, as temperatures and pollock abundance changed, the fleet demonstrated two distinct groups of spatial fishing behaviors based on the processor to which a vessel delivered its catch. Vessels whose catches were more likely to be processed as premium fish fillets (versus surimi or other products) were more likely to embark upon briefer trips and to fish closer to port, requiring less fuel and time at-sea. Larger vessels often traveled farther to regions with higher catch rates but smaller, potentially less valuable fish. We refer to vessels that traveled farther in some years as the offshore group and the other vessels as the nearshore group.
The vessels in the two different groups had many operational differences so statistically comparing catch or revenue metrics across the two groups can be challenging. However, we did describe different trends in trip-level results between the two groups in some years. The average catch-per-trip within each of the vessel groups remained relatively constant across years. Meanwhile, during 2008 and 2009, net earnings per trip for the offshore group were substantially greater than the average for that group, and net earnings per trip for the nearshore group were only slightly above average for that group. In general, the nearshore group consisted of smaller vessels that held fewer fish and subsequently earned less revenue per trip. Across years, the average gross and net revenue per trip was about 1.8 times higher for the offshore group. However, because the longer travel distances often seen in the offshore group took more days to complete, average earnings per day for the larger vessels were only about 1.2 times greater for the offshore group. This differential did vary by year and was likely driven by a combination of vessel capacity, fish price (which varied by processor, fish size, and fish quality), and fuel prices.
The two groups of vessels demonstrated different patterns in their spatial fishing behaviors but revealed similar inter-annual trends in catch, revenue, and numbers of trips per vessel. The different spatial behaviors were strongly correlated with both pollock abundance and Bering Sea temperatures given the range of conditions observed from 2003–2015. While the responses of vessels to climate and biological dynamics support the idea of a relatively resilient pollock fleet, we observed only 3 of the 4 primary modes of variability among these two metrics. Cold years with abundant pollock, cold years with less abundant pollock, and warm years with abundant pollock led to well-fitting statistical models. However, we have not observed any warm years with low pollock abundance so it is difficult to propose how fleets may respond to the full range of conditions.
Alaska Sea Grant researchers use variations in fishing vessel trip data as a proxy for a changing marine environment
Relevance: A changing marine environment is resulting in shifts in timing of physical and biological processes, locations of fish populations, and ecosystem structure. The changes may require fishermen to redistribute effort in time and space to target species differently. By examining changing fishing patterns and deliveries, it becomes possible to model how changes impact ports and processors where fish are delivered, and how longer trips may affect harvester profitability. Answers to questions such as, how far north are fishermen willing to follow shifting fish populations, are fishing trips longer during warmer years, and do fishermen subsequently spend less time in local port communities, can help fishery managers, communities, and industry prepare.
Response: Alaska Sea Grant–funded researchers used vessel monitoring system (VMS) data and fisheries observer data to reconstruct fishing trips in the Bering Sea and Gulf of Alaska. VMS transmits vessel locations and have been mandatory on Bering Sea pollock vessels since 2002. Researchers determined durations and distances traveled during more than 24,500 trips made by pollock catcher vessels between 2008 and 2013.
Results: Researchers tested their experimental approach by comparing observer data (available for about half of trips) with estimated trip durations. Their highly accurate method (less than 5% error) gives strong support for reconstructing the behaviors of unobserved trips. They found that larger pollock vessels may be more resilient to shifting pollock distributions because they can travel farther to follow the fish. However, during low abundance years large vessels were not immune to the lower catches per day experienced by smaller vessels.
Recap: Alaska Sea Grant researchers found vessel monitoring data and fisheries observer data closely conformed for assessing pollock vessel trips in the Bering Sea and Gulf of Alaska, and large vessels may have more resilience to fish location shifts caused by environmental change; the research could provide a tool for agencies to evaluate the impacts of different regulatory actions on fishermen and communities.