Biology Fisheries Methodology Undergraduate Research

SURFO Special: Examining Atlantic cod populations on Northeast Atlantic through morphometric analysis

My name is Angel M. Reyes Delgado, a senior student from San Juan, Puerto Rico majoring in biology. This summer, through the URI GSO Summer Undergraduate Research program, I worked with Dr. Kelton McMahon (advisor), Nina Santos, Joseph Langan and Margaret Heinichen (mentors) on a project to study the morphology of Atlantic Cod (Figure 1) populations from the Northwest Atlantic.

Figure 1: Atlantic cod. Image source:
Figure 1: Atlantic cod. Image source:

According to the National Ocean and Atmospheric Administration (NOAA), Atlantic cod are one of New England’s primary food resources, the fishery has been part of the New England culture throughout the centuries, it is essential for the regional economy and jobs, and the species has an important role in the food web as a top predator. Proper management is important to sustain Atlantic cod populations and studying morphology, the physical shape of living organisms, informs management strategies.

Figure 2: Northwest Atlantic. Gulf of Maine is outlined in red, Georges Bank is outlined in blue.
Figure 2: Northwest Atlantic. Gulf of Maine is outlined in red, Georges Bank is outlined in blue.



Populations of cod have declined due to overfishing and climate change. As of now, fisheries managers are trying to understand the stock (i.e. managed population) structure for rebuilding purposes. Currently, there are two cod stocks in U.S waters, the Gulf of Maine stock and the Georges Bank (GB) stock, the latter of which includes the Southern New England (SNE) sub-population (Figure 2). The peculiar thing about SNE is that cod abundance has increased even though the rest of the GB stock has declined. Even more peculiar is the fact that temperatures are rising in SNE, which is typically a harmful condition for this cold-water species. Together, the different sub-population responses could mean that SNE and GB could be two different populations and might need to be managed separately.

Understanding morphology and behavior is an important tool for fisheries managers to adjust regulations of important species based on their populations. For this reason, we studied cod morphology to answer two important questions about the GB cod stock. The first question is: What are the characteristics of SNE cod and when do they vary? Understanding how cod shape varies with environmental conditions will help us understand their resistance to external stresses such as climate, competition/predation, diet, etc. Our second question is: Do SNE cod look different from GB cod? Answering this question will help determine whether they should be managed together or not, prevent overfishing, and promote sustainable harvest in the future.

In order to look at morphology, we took measurements of many fish. One way to do this is to require a scientist on every boat catching cod to measure every fish caught, but is impractical with respect to man power and time. Instead, we used images taken of cod caught on commercial fishing boats through the NOAA Northeast Fisheries Observer Program, which collects data on commercial fishing trips for scientific and management purposes. The Observer Program gave us access to cod images from many different times and places. We were able to get approximately 400 images of cod from the SNE region, and up to 2,436 images from GB that we used to compare cod morphology through time and locations.

To turn images into morphology data, we processed them with ImageJ, an image analyzing software which allows for detailed and standardized measurements of all the photos and permits preservation of images for future analysis. Twelve landmarks (white dots) were selected manually around different sections of the fish, ending up with 24 length measurements on each fish (Figure 3). Each measurement has important ecological implications, which is the reason we took them all into consideration. Therefore, by measuring these multiple dimensions, we were better able to describe physical characteristics, which are important indicators of ecology.

Figure 3: ImageJ with 12 points and 24 segment measurements.
Figure 3: ImageJ with 12 points and 24 segment measurements.

Morphologic changes within and among sub-populations are used to look for differences between SNE and GB sub-populations of cod. Information yielded from my summer research project can help fisheries managers determine if they are all part of the same population or not, which has implications for whether they should be managed together or separately.

Working virtually and sharing time with my advisor, mentors and other colleagues has been a really awesome and unique experience for me. First of all, it confirms the fact that anything is possible if the initiative and inspiration to realize something is available. Also, it shows that there are awesome professionals out there willing to help all types of rising students that aspire to different careers. Receiving this attention and sympathy motivates me to give the same treatment to future students further on in my own career, especially those from underrepresented areas.

  • Fisheries, N. (n.d.). Atlantic Cod. Retrieved from
  • Cadrin, S. X. (2014). Stock ID Book.

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