First published in Landings, June, 2014.
For the past two years, the Maine Lobstermen’s Community Alliance (MLCA) managed an inshore herring acoustic survey with the Gulf of Maine Research Institute (GMRI). GMRI has analyzed the acoustic data collected by ten lobstermen spread out along Maine’s coast. Each lobsterman, from Cutler to York, had echosounder equipment, commonly used as fish finders, installed on his boat. The echosounder sends out sound frequencies to identify fish and then records the data onboard the vessel’s computer. When the sound beam hits a school of fish, the particular pattern it makes reveals whether the school is made up of herring or another type of fish. A total of 70 individual near shore surveys were completed over two years, during the months of September, October and November.
“The biggest problem we had [when analyzing data] was cleaning up the noise,” said Graham Sherwood, a research scientist at GMRI and leader of the herring acoustic survey. Each lobster boat participating in the survey was equipped with a through-hull Simrad ES-70 echosounder that recorded how sounds bounced off objects in the water column and bottom. Because the echosounders are designed for large research vessels that glide through water, the slap of the smaller boat hulls against the water was recorded as extra noise.
The data show that the majority of herring schools are in the area off Mount Desert Island. “We had the lobstermen draw where they thought spawning herring would be on a chart at our very first meeting,” said graduate research associate Katie Wurtzell. Wurtzell used the collected data to plot actual herring schools on a chart and then added the lobstermen’s original predictions to that chart. “They line up almost exactly, which is really neat to see,” she said. Lobstermen were given a predetermined set of coordinates to survey.
The goal of this survey was to estimate the biomass of inshore herring. “That’s easier said than done,” Sherwood admitted. “The collected data is patchy – we could miss a spawning school of herring because a boat couldn’t complete the survey due to weather or technical issues.” Herring are the dominant forage fish in the region and account for nearly three-quarters of the bait used by Maine’s lobster industry. The National Marine Fisheries Service (NMFS) has not surveyed inshore herring populations for many years. Without accurate knowledge about inshore abundance, scientists cannot accurately assess overall herring stock health. “This data likely will not be used in herring stock assessments, but it is a great resource to have,” said Sherwood. “This is unique data. No one else has collected weekly data.”
“There was a big learning curve when we started in 2012,” said GMRI research associate and lobsterman Curt Brown. “Each boat had a different issue and we spent a lot of time working with the guys to figure out a solution.” Now that the issues are solved and the collected data have been analyzed, Sherwood, Brown, and Wurtzell are thinking about what comes next.
GMRI received funding to continue the survey work for another two years. The surveys thus will be conducted for a total of four years, which will allow a more comprehensive data set. “With two more years of data we can start asking questions,” noted Sherwood. The first year, 2012, was an unusual year, with record air temperatures and high water temperature in the Gulf of Maine. Sherwood said it will be interesting to see if water temperature plays a role in spawning schools. “Once we have four years of data we can start looking at that,” he said. The funding to continue the survey comes from the Saltonstall-Kennedy Program through NOAA.
Wurtzell, Brown, and Sherwood are also looking into “ground truthing” – a way to verify the collected acoustic data. “It’s a way to add confidence to the data,” explained Sherwood. “We could set a trap near a school of herring and record the number of eggs on it, for example,” Wurtzell said. A lobster trap would be set along the survey transects when schools of herring are found and then hauled in a week or so to see if any herring eggs are on it. “We assume the schools seen in the acoustic data are spawning because all other fish feed up in the water column at night when the survey took place,” she continued. “If we had a way to check for eggs, it would add confidence that they are indeed spawning.”
The MLCA and GMRI will meet with the ten participating lobstermen to show them the results of their hard work and discuss the next steps. “These guys have put so much into this project and we really appreciate that,” said Brown. “We hope everyone will be willing to participate for the next two years and that we can find a way to make them feel it’s worth their time.”Category: Science