The Marine Fisheries Research Project team from the Oregon Department of Fish and Wildlife headed out to sea on Aug. 1.
Their destination: Cobb Seamount, about 300 miles west of the Washington coast.
Their goal: to find older female black, canary, or yellowtail rockfish.
Since the early 1990s, fisheries scientists on the West Coast have noticed a peculiar trend in black, yellowtail, and canary rockfish populations: the older females get, the fewer of them there are.
Marine Fisheries Research Project leader Leif Rasmuson and other members of his team boarded Oregon State University's research vessel Pacific Storm for a 47-hour steam to the research site. The trip is part of OSU's Oceangoing Research Vessel Program.
It took the crew two days to reach Cobb Seamount, where they'll spend about 11 days searching for older female rockfish. Additionally, they'll also collect genetic samples, attach satellite tags to fish, and document other marine life, including sunflower sea stars.
The Mounts are calling
There are two leading theories about the whereabouts of these missing females. One is that they die prematurely because of predation, disease, or other natural causes. While fishing pressure has also been considered, fishery data from along the West Coast show that older females have been largely absent from catch data for decades, suggesting fishing alone is unlikely to explain their disappearance.
Another theory is that they are still alive, but living in places where fishers rarely, if ever, fish.
Rasmuson and his team are investigating whether older female rockfish migrate to seamounts, serving as a sort of retirement home for aging female rockfish.
Rockfish are typically found near shore, preferring shallow water and rocky reefs. The peaks of some seamounts rise surprisingly close to the ocean's surface despite being hundreds of miles offshore, creating habitat that could be suitable for rockfish far from the coast. In fact, commercial fishers targeted some Pacific seamounts in the 1980s and 1990s, regularly catching rockfish there. Those historical catches helped inspire Rasmuson's hypothesis.
Even so, the theory raises additional questions. From an ecological perspective, there is no obvious reason why older females would migrate so far offshore. But, as Rasmuson puts it, nature doesn't always make sense:
“If the males aren't going out there, they're not contributing to the population,” he said. “Their larvae aren't going to come back, so they're not going to enter the population. So why would that have evolved for them to just go swim out there and hang out? But evolution's unique and weird and more bizarre things have happened in the world.”
Rockfish life history
Oregon's waters are home to as many as 80 species of rockfish, which vary widely in color, size, and behavior. Some species spend most of their lives near the seafloor, often staying on the same rocky reef for decades. Others live higher in the water column and may migrate many miles throughout their lifetime.
Additionally, some rockfish species can live a very long time. According to NOAA Fisheries, canary rockfish can live up to 75 years, black rockfish average about 60 years, and yellowtail rockfish can live to around 50 years.
To determine a fish's age, fisheries scientists examine its ear bones, called otoliths. Like tree rings, otoliths form annual growth rings that researchers can count. Scientists on the ODFW expedition will collect otoliths from rockfish they catch at Cobb Seamount, and then those otoliths will be examined back on shore to determine how old the rockfish are.
Fisheries scientists have a tongue-in-cheek acronym for older female fish: BOFFFFs, which stands for Big Old Fat Fecund Female Fish.
The idea is simple: as female fish grow older and larger, the more eggs they produce. Older females also produce higher quality eggs, meaning larvae are more likely to survive (rockfish eggs hatch inside of a mother’s body and then the mother gives live birth, a reproductive method known as “ovoviviparity”). Because of this, fisheries scientists often focus more on females than males when assessing a fish population's sustainability.
The absence of older female yellowtail, canary and black rockfish from fishery data is puzzling, but not necessarily concerning.
“It's not a conservation concern in the sense of like, oh, we're worried about this,” assured Rasmuson. “It's a concern just because it's harder to do a good job.”
Rasmuson doesn't think it's especially likely they'll find the older females at Cobb Seamount. Even if they don't, he said the expedition will provide another important piece of the puzzle, helping scientists narrow the possibilities and better understand the lives of these mature, elusive ladies.
