Ocean and sound-going research
is no pleasure cruise. "We pick
With his research team, Buckel, an assistant professor of zoology in the College of Agriculture and Life Sciences, has happened upon an apparently previously unrecognized cohort of bluefish swimming in our state’s salt waters. A cohort is a group of fish that have similar hatch dates.
Buckel studies the effects of several variables on ocean and estuary fish replenishment, specifically why some young fish, called recruits, live to maturity while others don’t.
For juvenile bluefish, factors could be as varied as predators such as striped bass or starvation among fish that enter winter without sufficient energy reserves, he says.
“ Much research has already been done on juvenile bluefish in summer and fall,” Buckel says. “Part of our work concentrates on juvenile bluefish in the winter.”
New York researchers who examined scales from adult bluefish found that scale sizes at the first scale ring — similar to a tree’s concentric growth circles — corresponded to bluefish sizes that represented mainly spring-spawned fish.
Their data suggested that the smaller, summer-spawned bluefish didn’t substantially contribute to the adult stock. Since summer-spawned fish were present in the fall of their first year, researchers hypothesized that they might not be surviving the winter.
To learn why, Buckel’s team first looked at where blues supposedly were in the winter.
In the process, the team — Buckel, lab technician Paul Rudershausen, graduate student Jim Morley and University of North Carolina at Wilmington collaborators — hauled in the bonus research catch. After two winters’ worth of blues trawling they discovered the previously unreported cohort.
“ The third cohort appears to be produced in the late summer or early fall,” Buckel says.
To determine the third cohort’s birth date, Rudershausen uses a microscope to count otolith rings. Otoliths are fish ear bones; juvenile blues produce a ring a day.
This cohort gives investigators an opportunity to test the winter survival hypothesis on fish that are even smaller than the summer-spawned cohort. The researchers will compare energy storage of the three different juvenile cohorts to determine if individuals spawned earlier in the year have an advantage in surviving the winter.
Morley processes the collected fish in the lab and quantifies their energetic condition by determining the density of lipids in each fish’s muscle and liver. He is also studying winter distribution and feeding of young-of-the-year bluefish in the South Atlantic Bight.
“ Smaller individuals of other species born in the same year exhaust their energy reserves more rapidly and consequently do not survive the winter,” Morley notes, so why not bluefish?
The researchers collect juvenile blues from Onslow Bay monthly between September and June, fishing a 40-foot bottom trawl from the UNC-W-based RV Cape Fear, a 70-foot, twin-diesel research vessel.
Ocean and sound-going research is no pleasure cruise. “We pick our days,” Buckel says, gazing out his second-story office window at the whitecaps kicked up by a strong wind.
Buckel’s research team also looks at other fisheries-related questions:
• Rudershausen is developing standards to more accurately distinguish between two species of river herring, the juvenile alewife and blueback herring. He also is conducting a prey selectivity study to assess striped bass predation’s impact on other Albemarle Sound fishes.
• Jack Tuomikoski, a College zoology graduate student, studies the impact of striped bass predation on juvenile river herring and shad in the Albemarle Sound estuary, where adult herring stocks have drastically declined in recent years.
• Kara Schwenke, a College zoology graduate student, studies the age and growth of dolphin (the fish, Coryphaena hippurus, not the “Flipper” variety) captured in North Carolina waters. As dolphin landings have increased dramatically in both recreational and commercial fisheries since the last study was done in the 1960s, the data will be useful for future assessment of western Atlantic dolphinfish populations.
• Harvey Walsh, a College zoology graduate student, studies the distribution and abundance of fall and winter-spawned fish eggs and larvae on the North Carolina shelf, to understand the relationship between environmental factors and recruitment of estuarine-dependent fishes of the Southeastern U.S. continental shelf.
• And in an upcoming project Nate Bacheler, a doctoral student, will use sonic telemetry to determine monthly estimates of natural and fishing mortality rates for red drum.
Buckel and his team work closely with Dr. Joe Hightower,
a professor in the College’s Zoology
and with Dr. Tom Lankford at the Center
for Marine Science at UNC-W, as well as the state Division
of Marine Fisheries and the National
Oceanographic and Atmospheric Administration.