Black-footed albatrosses are large seabirds that forage across large portions of the Pacific Ocean. Like other seabirds, they can be attracted to “free” food from bait and processing operations of commercial fishing vessels. This can lead to accidentally being caught, particularly by vessels using hook-and-line gear. There are numerous successful efforts by the fishing industry to minimize seabird bycatch. Most of the Alaska hook-and-line fleet is required to use bycatch deterrence measures, including the use of colorful streamers when setting their fishing gear. However, some bycatch still occurs, and until now, our ability to link birds caught in fisheries back to individual breeding colonies has been limited. In this study, scientists used genetic stock identification and found disproportionate bycatch from specific breeding colonies.
“Genetic Stock Identification has been successfully used to study the movement of salmon populations. But it has rarely been applied to seabirds,” said Diana Baetscher, co-lead author and fisheries biologist at the Alaska Fisheries Science Center. “Our study shows the benefits of this cost-effective and efficient genetic technology and analytical method. We can determine specific colonies that black-footed albatross caught in commercial fisheries belong to and support greater population-specific management of this and other migratory species.”
Pinpointing the Most Vulnerable Breeding Colonies
Black-footed albatross are not listed as endangered or threatened under the Endangered Species Act. However, they are long-lived, slow to reproduce, and have only a single chick when they breed. They forage throughout the North Pacific and breed on nine low-lying islands in the Hawaiian archipelago and on three islands in Japan. Breeding colonies are separated by large distances, corresponding to metapopulation structure—a group of spatially separated populations of the same species, which interact at some level. However, individuals typically return to breed at the same colony with their long-term mates.
Throughout their lives, black-footed albatross may encounter invasive species, sea-level rise, and disease on breeding islands. At sea where they forage, they face threats due to fisheries bycatch, marine heat waves, and plastic pollution. Of all these threats, bycatch is the largest documented cause of death for this species.
Previous research has identified genetic differentiation between Hawaiian and Japanese colonies. However, little genetic differentiation among Hawaiian colonies, which make up 97 percent of the breeding population, has been documented.
In this study, scientists used Genetic Stock Identification to link 495 black-footed albatross caught and collected as bycatch in U.S. federally managed fisheries (2010–2022) to six breeding colonies in the Northwestern Hawaiian Islands. Scientists looked for genetic differences among colonies across the whole genome. They then used a subset of these genetic markers to assign each bird to a specific breeding colony with GSI.
Scientists analyzed specimens collected by fishery observers from:
Hawaiʻi deep-set and shallow-set longline fisheries
North Pacific groundfish and halibut fisheries in Alaska
At-sea hake trawl fishery on the west coast of the United States
However, the sample size for the West Coast hake fishery was too small to draw any definitive conclusions.
Scientists examined population structure and genetic differentiation across the colonies. Similar to previous studies, they found little genetic differentiation between the Hawaiian colonies. They investigated whether specific colonies are disproportionately impacted by bycatch relative to population size, and how spatially explicit bycatch interactions may differ by colony. Ultimately, they were able to directly connect at-sea mortalities to specific colonies.
Genetic stock identification revealed a disproportionately high amount of bycatch from the French Frigate Shoals relative to the population size of the colony. About 7 percent of the total black-footed albatross population breeds on the French Frigate Shoals. Midway Atoll (35 percent of the population) and Laysan Island (34 percent of the population) experienced low levels of bycatch relative to their population sizes. This suggests that bycatch could be a greater concern for the small French Frigate Shoals population. Although the French Frigate Shoals population is not genetically distinct, understanding the mortality from fisheries to birds at individual colonies helps with the management of the species.
“Black-footed Albatross only breed on islands,” says Baetscher. “And there are a limited number of islands in their breeding range. It’s important to know if fisheries bycatch may be disproportionately impacting colonies at specific islands to help managers protect the species as a whole, especially as many of the islands may become smaller with sea level rise and increased storm surges, and breeding locations become more limited.”
Based on this dataset of black-footed albatross bycatch, scientists estimate that:
61 percent of the black-footed albatross collected by fisheries observers in the Alaska groundfish fishery are from the French Frigate Shoals colony
60 percent of the black-footed albatross collected by fisheries observers in the Hawaiʻi deep-set and shallow-set longline fisheries are from the French Frigate Shoals colony
For migratory species, such as seabirds, genetic tools give NOAA Fisheries the ability to link threats to specific populations. Resource managers in the U.S. Fish and Wildlife Service, the agency responsible for seabird protection and management can use these tools to inform targeted and more effective conservation measures at colonies and NOAA Fisheries can use this information to help more effectively manage bycatch in U.S. fisheries to keep fishermen on the water. This study demonstrates the viability of using genetic stock identification for populations with very low levels of genetic differentiation. Genetic stock identification is a viable and cost-effective conservation tool for marine species regularly caught in U.S. fisheries.
While this effort holds promise for better understanding the potential implications of U.S. bycatch, the impact from international fleets are virtually unknown. They don’t have the same level of observer coverage as U.S. fisheries in federal waters. International fishing (both regulated and illegal, unreported, and unregulated) present additional at-sea threats for black-footed albatross from the colonies in this study.
This research could provide the U.S. Fish and Wildlife Service, with a better understanding of how different types of threats can interact or compound each other. This could provide increased understanding of overall impacts to individual colonies.
Bycatch is a complex, global issue that impacts the sustainability and resiliency of fishing communities, economies, and ocean ecosystems. NOAA Fisheries is committed to minimizing bycatch in U.S. fisheries to maximize fishing opportunities while protecting ocean ecosystems.
