Oceanography News Tip Sheet
AUGUST 22, 1997
RESEARCH SHOWS DROPS IN CRAB POPULATION
PROBABLY NOT ATTRIBUTED TO FISHERY
California Sea Grant Researcher David Hankin is helping to uncover the
mystery behind dramatic fluctuations in the Dungeness crab population.
He and his graduate students at Humboldt State University are studying
the reproductive biology and mating habits of crabs off the coast of
northern California to determine if the intensive male-only harvesting
there has an impact on whether or not females successfully mate. They
have found that male crabs below the 6º inch legal harvesting size
participate extensively in mating, indicating that the fishery has no
direct effect on total egg production by females and is probably not to
blame for periodic population drops. "Northern California is famous
for large-scale population fluctuations," Hankin says. This research,
he adds, "is relevant for assessing the effectiveness of [Dungeness
crab] management." Dungeness crabs are the most heavily harvested
crustacean on the West Coast of the U.S. Females are able to mate only
after they have molted and their bodies are soft. Hankin and his
students tagged nearly 13,000 females over a three-year period and
found that even females who had not molted and mated within the study
period could develop normal egg masses. This study, Hankin says,
showed that female Dungeness crabs can store sperm for at least two
years. Hankin's students are currently studying an internal structure
in the female crab's reproductive tract, called a sperm plug, which
prevents additional sperm from entering a female once she has been
inseminated. Its presence tells the researchers if a female has mated.
"We're finding that virtually all molting females are mating," says
Hankin. Researchers at the University of Helsinki and the University
of California, Davis have recently developed a computer model which
indicates that biological factors, in conjunction with environmental
changes, are most likely responsible for the intense fluctuations in
Dungeness crab populations.
CONTACT: David Hankin, California Sea Grant Researcher,
(O) 707-826-3683; E-Mail: [email protected]
COMPUTER SOFTWARE EVALUATES COSTS AND
BENEFITS OF SEDIMENT REMEDIATION
University of Wisconsin Sea Grant is coordinating the efforts of
researchers at four universities to develop computer software that
could help decision-makers determine the costs and benefits of cleaning
contaminated sediments. The software enables users to enter the type
of contamination and select a dredging method and treatment options,
says Wisconsin Sea Grant Coastal Engineering Specialist and project
manager Philip Keillor. It then calculates the costs and performance
of the selected method to predict how well a chosen clean-up procedure
will work. The software can be used to examine the effects of various
policies and regulations on remediation cost and performance and
provides a summary of each state's waste disposal regulations and a
listing of where software users can go for updates. Keillor notes that
the software will also help managers to optimize site sampling
techniques to avoid the unnecessary costs of excessive sediment
sampling and testing as well as unnecessary removal and treatment of
clean sediment. He has been demonstrating the software to potential
clients such as state regulatory agencies, the EPA, and a few
environmental consultants in several Great Lakes cities. "We've been
getting a generally favorable and enthusiastic response," he says.
"Some want to try it out." Keillor adds, however, that the software is
unfinished. "Additional testing, writing of manuals, and training
workshops are needed to make the software accurate and more
user-friendly," he says. Researchers will soon decide whether or not
to request funds for a final two years of work after studying the
responses of potential users who participated in software
demonstrations this summer.
CONTACT: Philip Keillor, Wisconsin Sea Grant Coastal Engineering Specialist,
(O) 608-263-5133; E-Mail: [email protected]
BURGEONING NORTH CAROLINA BLUEFIN TUNA
FISHERY ATTRACTS SCIENTISTS, FISHERMEN
The waters off of Cape Hatteras, North Carolina have become a
recreational fishing hot spot for bluefin tuna that gather there from
January till March. Along with fishermen, scientists are utilizing the
area to better understand the migratory patterns of the fish which can
live 30 years, exceed 10 feet in length, and weight as much as 1,200
pounds. "Scientists are excited because the fish are here in such high
numbers," says Jim Bahen, North Carolina Sea Grant Marine Advisory
Agent. "This is one laboratory that they never believed would exist."
It is thought that there are two bluefin tuna families residing in
opposite sides of the Atlantic, but is not known if the two stocks
intermingle. To help determine this, a team of scientists from
Stanford University, the National Underwater Research Center, the
Monterey Bay Aquarium, and the National Marine Fisheries Service
recently initiated a bluefin tuna tagging project off of Cape Hatteras.
The results of the study may help managers decide whether or not a
commercial bluefin fishery should be established in North Carolina.
Because the fish are so valuableósome fish bring in as much as $30 a
poundóresource managers have instigated strict regulations toward
keeping stocks healthy. Currently, only recreational hook and line
fishing of bluefin tuna is permitted in North Carolina. The fishery is
attracting recreational anglers from around the world. Preliminary
figures show that recreational bluefin tuna fishing has a
$30 - $40 million-a-year economic impact to towns on the Outer Banks of
North Carolina, Bahen says. He organizes workshops for fishermen on
bluefin tuna and has been involved in tagging the fish. Not only do
charter boat companies reap the benefits of bluefin fishing, he notes,
but local restaurants and hotels turn a large profit during a time of
year when business used to be slow. "A sleepy village on the Outer
Banks has now become a world class fishing spot."
CONTACT: Jim Bahen, North Carolina Sea Grant Marine Advisory Agent,
(O) 910-256-2083; E-Mail: [email protected]
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