June 23, 2020 — The following was released by NOAA Fisheries:
Atlantic surfclams live at depths between 20 and 35 meters, with an optimal temperature range of 16 to 22o C. They are managed as one stock, with two biologically distinct areas. Surfclams in the northern area on Georges Bank are faster growing than southern surfclams, and the populations don’t mix.
Thirty years ago, southern surfclams grew faster than they do now, and lived in shallower waters. They were also bigger than the surfclams on Georges Bank. Now, these dynamics are reversed. Surfclams in the southern areas have moved to deeper waters, and grow more slowly, to a smaller maximum size. These population changes have been observed by fishermen, noted in their logbooks, and appear in research survey data.
In recent assessments, scientists treated the two areas separately, each with its own assessment model. This time, there is one model with two areas. Dan Hennen, lead surfclam assessment scientist at the Northeast Fisheries Science Center, developed this model. He collaborated closely with the surfclam industry and academic partners, like the Science Center for Marine Fisheries, a National Science Foundation Industry/University Cooperative Research Center.
Working together led to a two-area model, which better deals with the challenges of a population with changing dynamics. Understanding how growth is changing led to better diagnostic behavior in our model. This gives fisheries managers more confidence that it accurately reflects what is going on in the population.