Ask An Expert
Taking Stock of New England Fish: Part 1
Mike Palmer is Research Fisheries Biologist in the Population Dynamics Branch of the Northeast Fisheries Science Center.
TalkingFish.org: First, please tell us about your background: how did you become interested in fisheries? How did you end up working in fisheries science?
Mike Palmer: I’ve always been interested in anything related to water. I studied marine science as an undergraduate before a brief career in aquatic toxicology where I investigated mercury contamination in freshwater fish. While the work was interesting, I wanted to return to studying the marine environment, specifically fish populations. In graduate school I focused on fisheries oceanography and how environmental factors such as sea ice extent and the timing of ice melt affect the growth of fish in the Bering Sea. Fisheries oceanography really intrigued me because it’s interdisciplinary: the dynamics of fish populations are complex, and to fully understand them requires an understanding of physical, biological, and human-induced factors.
I was fortunate that my graduate work exposed me to real-world fisheries management by way of my interactions with the North Pacific Fishery Management Council and the Alaskan fishing industry. These experiences impressed on me that fisheries science, particularly with respect to commercially exploited species, directly affects people’s livelihoods. The results matter. It is critical that the science be thorough and accurate, and that the results be properly communicated to the management bodies. It is important that the management bodies understand the strengths and weaknesses of the results and how to best use them to inform management decisions.
Since returning to New England I’ve been involved with a wide variety of fishery science programs including data collection and electronic logbooks, cooperative research and stock assessments. I joined the stock assessment group at the Northeast Fisheries Science Center over five years ago where my time has been split between the Gulf of Maine cod and haddock assessments as well as lending assistance on other groundfish assessments and supporting analyses.
TF: What types of data are used in stock assessments? Is it just NMFS survey tows, or is more information needed? For example, does fishermen-reported catch data or the biology of the particular fish stock you are assessing come into play? Please describe each form of data used and how each gets input into the models and with what weight.
MP: It is a common misconception that the Northeast Fisheries Science Center’s bottom trawl survey is the assessment. In fact, the core of most stock assessments is fishery catch data. Our ability to describe a fish stock’s status is directly related to how detailed and accurate available catch data are. The best source of catch data has always been the fishing industry. While the survey can tell us about trends over time in a population, fishery catches establish how big or small the stock is.
The importance of acquiring accurate data on when, where, how, how many, and what kind of fish are caught cannot be over appreciated. The catch information used in assessments comes directly from dealer reported landings, vessel trip reports, recreational angler surveys, observer reports, and the biological sampling conducted by port samplers.
Survey information, whether collected by the Northeast Fisheries Science Center, state agencies or other institutions, provides indications of general population trends and total mortality, and is a key source of the biological samples needed to form a picture of the age structure of the population, and the average weight and maturity of a fish at a given age.
Data gathered through cooperative research projects and industry-based surveys are also used. Sometimes these data cannot be directly used in the assessment because the time series is too short or the spatial coverage is too small, but the results can address a range of other issues such as the selectivity of fishing gear, spawning periods or discard mortality, all of which figure into the assessment.
There is no simple answer to how the individual pieces of information are weighted in the model. It varies by data source, model type, and the individual assessment. In the more sophisticated models that we use in the Northeast, the data informs the model on how best to weight the information. These models can use the level of precision in the data to determine the relative weights to apply to each piece of data.