Most Accurate Ever
NMFS Northeast Fisheries Science Center
N E W SWoods Hole, Mass. – Scientists and fishermen working together recently conducted the last at-sea stage of what is likely to be the most accurate survey of surfclams and ocean quahogs ever conducted in East Coast waters. The research conducted aboard commercial fishing vessels in August and September will allow scientists to make better use of data collected earlier in the year by survey crews on the government’s research vessel.
The jointly funded research project was conducted by commercial fishermen and government and academic scientists. Participating agencies and organizations include: the National Fisheries Institute (NFI) Clam Committee, the North Atlantic Clam Association, the New Jersey Fisheries Information and Development Center, the Rutgers University Haskin Shellfish Research Laboratory, the Virginia Institute of Marine Science, and NOAA Fisheries.
“The work with the industry will give us the best picture we’ve ever had of how efficient our sampling gear is on different types of bottom and with different species of clams,”said Dr. James Weinberg, a NOAA Fisheries biologist who studies shellfish. “Knowing more about how efficient our dredge is, we will be able to make better estimates of the total abundance of surfclams and ocean quahogs.”
To estimate total biomass of clams in an area, fishery scientists begin by dredging clams in randomly selected portions of the area. Then they figure out what percentage of all clams living in the sampled area are caught by the survey dredge. When they know how efficient their survey dredge is, scientists can then use the catch data from the sampled stations to estimate total abundance in the entire area.
Every three years scientists from NOAA’s Northeast Fisheries Science Center (NEFSC) conduct clam surveys aboard the Delaware II in waters off the Mid-Atlantic states and out to Georges Bank. Scientists use data from the survey along with other information to make stock assessments that include estimates of abundance. Fishery managers use the stock assessments to regulate the commercial harvest of surfclams and ocean quahogs, the main ingredients in clam chowder. The data from the recent collaborative survey are being processed now and will be used in stock assessments that will be completed in 2003.
To make estimates of stock abundance, biologists first must estimate the efficiency of their sampling instrument – in this case, the clam dredge on the Delaware II. It is possible but time consuming to determine the efficiency of the gear using just one vessel. To make precise estimates, the Delaware II would have to spend much of its six-week clam survey running repeated sampling trials in the same area. By using additional vessels provided by the commercial fishing industry, the scientists and fishermen were able to get a good idea of the Delaware II’s dredge efficiency while still surveying the animals throughout their range.
The project began in the early summer when the Delaware II conducted its usual survey in waters from the Delmarva Peninsula to Georges Bank. The Delaware II was equipped with a state-of-the-art sensor package that operates underwater while mounted on the clam dredge. The sensor package, which was jointly purchased by the fishing industry and NOAA Fisheries and was used for the first time this year, gathers a continuous stream of data on dredge performance, bottom temperature, water depth, and ship position. Scientists can use these data to determine the area of ocean bottom sampled by each tow.
“The surfclam and ocean quahog fishermen were happy to help fund the sensor package,” said David Wallace, a representative of the North Atlantic Clam Association. The fishermen also donated their vessels and their own time for the studies. “It is important to the fishing industry that the clam population studies are based on the highest quality data that can be gathered,” Wallace said.
After the Delaware II cruise ended in July, the sensors were mounted on the Jersey Girl and the Lisa Kim, two commercial vessels that conducted dredge efficiency studies in August and September. The commercial vessels sampled for surfclams (Jersey Girl) and ocean quahogs (Lisa Kim) at locations off Long Island, New Jersey and the Delmarva Peninsula where the Delaware II had surveyed earlier. Data from those cruises will be used to make estimates of the Delaware II’s efficiency at catching different species of clams on different types of ocean bottom.
“The catch efficiency of the survey dredge is the largest single scaling factor in the survey for surfclams and ocean quahogs,” said Dr. Eric Powell, a Rutgers University scientists who worked on the collaborative project. “The calibration experiments are designed to provide this critical information. With results from these studies, NOAA Fisheries scientists can make a more accurate estimate of the biomass of clams in the ocean.”
The collaborative project also included a study of “recruitment” of ocean quahogs. (“Recruitment” refers to the entry of juvenile clams into the adult population.) The clam dredges used on the Delaware II and commercial clam vessels normally do not capture juvenile clams. Using specially rigged gear on board a commercial vessel – the Christy – and sampling at stations sampled earlier by the Delaware II, fishermen and scientists collected juvenile quahogs as small as 35 mm.
“Ocean quahogs can live to be 150 years old,” said Dr. Roger Mann, a Virginia Institute of Marine Science biologist. “Within that time frame, we don’t know how often recruitment takes place. While commercial fishermen are allowed to harvest only a small percentage of the standing stock each year – about three percent – we don’t know whether they are harvesting quahogs from a single year class or multiple year classes.”
Working with samples of juveniles collected between North Carolina and Eastern Long Island waters, biologists hope to improve their understanding of the distribution and age-structure of ocean quahog populations. That information should help fishery managers craft regulations that allow fishermen to harvest clams in a sustainable manner.
The 2002 collaborative research is a continuation of an industry/scientist partnership that began in 1997 and is today one of the largest cooperative research programs in the Northeast U.S.