Rocks of ages

APPLE GROVE – West Virginia’s fisheries biologists are happy fish have rocks in their heads.

By study otoliths – rock-like growths in fishes’ ears – Jeff Hansbarger and other Division of Natural Resources biologists are means to accurately settle customarily how aged those fish are. The information is assisting DNR officials revive local walleye to a New River and deliver blue trout to a Ohio River.

“Three factors are of peerless significance in handling fish populations,” Hansbarger explained. “Those factors are recruitment [of youthful fish into a altogether population], expansion and mortality. By examining otoliths, we advantage a improved bargain of expansion and mortality.”

Biologists guard expansion by last fishes’ length, weight and age. Knowing a accurate age allows them to ascertain a fishes’ annual rate of growth. That’s undeniably critical in a New River, where DNR officials are operative to lapse a river’s singular aria of walleye to a former inflection in a river’s ecosystem.

“By last a native-strain walleyes’ expansion rates, we were means to settle fishing regulations that will assistance to strengthen a race as it grows,” pronounced Mark Scott, district biologist for a state’s southeastern counties.

To improved know fish mortality, Hansbarger and his colleagues collect multi-fish deputy samples from a stream or lake, and afterwards inspect a fishes’ otoliths to settle their ages.

“We’re means to settle how many fish are in any ‘year-class,’ that represents all a fish spawned in a given year,” Hansbarger said. “We can settle if any year-classes are missing, and we can calculate a ‘mortality curve’ to settle how prolonged those fish tend to live in that sold environment.”

That’s critical in places such as a Ohio, where otolith studies have dynamic that vast flathead trout can live during slightest 28 years. Such information gives DNR biologists an thought of how prolonged stocked blue trout competence live, and what their expansion rates competence be.

Fisheries scientists used to settle fishes’ ages by plucking a scale, examining it underneath a magnifying glass, and counting a series of yearly expansion rings. The process works, yet Hansbarger says it has drawbacks.

“In times of stress, fish can reabsorb their scales,” he said. “Fish also remove beam from time to time. Scales that have been reabsorbed or have been regrown don’t have a scold series of rings, so they don’t accurately paint a fish’s age. Otoliths do.”

Otoliths – a word comes from a Latin difference “oto” (ear) and “lith” (stone) – are finished of calcium carbonate, a same devalue that creates adult limestone. The stones grow gradually, gaining a small bit of distance any year. Calcium carbonate accumulates faster on a stones during a fish’s primary flourishing deteriorate and slower during a rest of a year. The delayed expansion shows adult as a dim ring. The multiple of one light ring and one dim ring outlines a year in a fish’s growth.

Hansbarger schooled to “read” otoliths when he was an undergraduate biology tyro during a University of South Carolina. Under John Dean, a heading government on fish age and growth, Hansbarger schooled so many about otoliths that Dean eventually devoted him to run a laboratory, and to sight visiting scientists in otolith-reading procedures.

The Charleston local brought that imagination behind to West Virginia when he supposed a pursuit with a DNR. Armed with a microscope, a fiber-optic light theatre and a jeweler’s saw, he set adult an otolith lab.

“The microscope is mine; a customarily losses [to a DNR] were for a lights, a saw and supplies. For about $2,000, a state gained a ability to inspect otoliths,” Hansbarger said.

Otolith research has one poignant downside: The fish being sampled contingency be killed before a otoliths can be collected. Hansbarger pronounced biologists customarily group adult to do a work.

“We customarily have one chairman stealing a otoliths, another numbering a vials, and another holding data,” he explained. “We wash them in Clorox to eat divided any soothing tissue, rinse them off, and put ethyl ethanol on them to dry them out.”

Because otolith-reading procedures are time- and labor-intensive, Hansbarger and his colleagues do many of it in midsummer and midwinter, that are reduction bustling times for fisheries biologists.

“We store a otoliths in vials or silver envelopes until we’re prepared to review them,” Hansbarger said. “To review them accurately, we cut them into sections. Some otoliths are some-more simply review when they’re cut crosswise, others lengthwise, and others during an angle.

“After we territory a otoliths, we grub divided some of a element and make one side well-spoken and flat. The pretence is to grub customarily adequate element to display all of a expansion rings. Once a harsh is done, we put a otoliths underneath a microscope and count a rings.”

Despite Hansbarger’s believe and imagination during examining otoliths, he always has during slightest one other biologist check his readings. “Ninety-five percent of a time, we’re in agreement with a reads,” he said. “When we disagree, we put a otolith in doubt underneath a microscope, take turns looking during it, and disagree behind and onward until we agree. If we can’t agree, we chuck that representation out.”

Biologists’ time costs money. For that reason, DNR officials contingency import any sampling effort’s intensity advantage opposite a cost. “We have to collect and select a ones we wish to combine on,” Hansbarger said.

They also take into clever care either a information gained is value murdering a comparatively vast series of fish.

“For instance, we’re perplexing to grow a series of New River walleyes, so we try to equivocate whacking them. We’ve figured out a non-lethal approach to age walleyes them by examining a expansion rings in one of their dorsal spines,” Hansbarger said.

“The same goes for muskellunge. They’re top-line predators with a really low reproductive rate, so we’ve found a non-lethal approach to age them by examining a rings in a singular ray from a muskie’s pelvic fin.”

Bret Preston, a DNR’s fisheries chief, pronounced a believe gleaned from otolith studies so distant has given biologists a many design of how prolonged West Virginia’s fish class live, and how quick they grow.

“We’re removing to a indicate where we improved know a age-growth relationships, so we substantially won’t have to do as many [otolith work] in a future,” he said.

“Ultimately, though, if we wish to urge a peculiarity of a state’s recreational fishing, we need to make science-based government decisions. When we do, a arrange of information we get [from otolith studies] is what we’ll need to beam us.”