Where the Copepods Are: Prey Data Can Improve Right Whale Models

A new peer-reviewed study in Endangered Species Research finds that incorporating maps of copepod aggregations into North Atlantic right whale density models could improve those models' predictions. The study used data on aggregations of three copepod species collected 2003-2017 from Cape Hatteras, North Carolina, to the Scotian Shelf in Canada. Scientists on the Northeast Fisheries Science Center's Ecosystem Monitoring Survey collected that data.

Under the Marine Mammal Protection Act and the Endangered Species Act, NOAA Fisheries studies marine mammals, including endangered North Atlantic right whales. We find ways to reduce risks posed to them by human activities and environmental change to recover and protect species.

Modeling Right Whale Distribution Supports Proactive Management

There are approximately 370 North Atlantic right whales remaining, including only about 70 reproductively active females. Right whales feed on copepods, a type of zooplankton. They forage off the Northeast coast of the United States and Canada in the winter and spring when copepods are most abundant there. Their foraging grounds overlap with shipping, fishing, and other human activities. This puts them at risk of entanglement and vessel strikes, the two primary causes of right whale deaths. Changes in climate and oceanographic conditions are shifting the availability of copepods and thus the distribution of whales. Modeling right whale distribution allows for effective management to prevent human-caused whale deaths and injuries. Examples of this include Right Whale Slow Zones and Dynamic Management Areas.

Scientists predict the distribution of these whales using density surface models based on visual data collected from aerial and shipboard surveys, along with acoustic data. For this study, scientists used aerial and shipboard survey data, which included 5,196 individual whale sightings by seven institutions from 2003-2017.

Right Whales Follow their Favorite Foods

This study used Ecosystem Monitoring Survey data to identify areas where the density of right whales' preferred copepod prey met the whales' feeding needs. Those areas became "prey fields," which scientists added to the right whale distribution model. They evaluated which prey fields boosted the predictive power of the model across the region and during each season.

Right whales only target a few copepod species, primarily Calanus finmarchicus. The structure of their baleen, which they use to capture their prey, limits them to catching plankton about the size of a grain of rice.

The right whale distribution model performed best when scientists added data representing dense aggregations of Calanus finmarchicus, along with two smaller copepod species, Centropages typicus and Pseudocalanus spp. Adding data solely on aggregations of Calanus finmarchicus- right whales' "favorite food" - also improved the model's performance.

The study's lead author, Dr. Camille Ross from the University of Maine, Bigelow Laboratory, and the Anderson Cabot Center for Ocean Life at the New England Aquarium, explained, "As we learn more about the role of smaller prey in right whales' diet, I am hopeful that it will become easier to predict patterns in where these critically endangered whales gather, ultimately benefiting conservation efforts."

Scientists previously used phytoplankton production data observed from satellites in the right whale model as an indirect measurement, or proxy, for prey because copepods eat phytoplankton. Replacing that with direct observations of the specific copepods that right whales eat improved model performance.

When it comes to how much copepod aggregation data helps explain right whale density, time of year matters. Copepod data had the largest influence on predicted right whale distributions from February to May and November to December.

Long-Term Datasets Help Predict and Protect Whales

This study highlights the importance of collecting long-term oceanographic and marine mammal data, such as from NOAA's Ecosystem Monitoring program and marine mammal surveys that go back to the 1970s.

Dan Pendleton, a fish biologist at the Northeast Fisheries Science Center and an author of the study, explained, "Decades-long monitoring programs focused on plankton, fish and whales are critical to developing quantitative models that help NOAA Fisheries manage marine fish and wildlife populations. The results of our study will provide a better understanding of where whales are and where they may go in the future."

North Atlantic right whales have shifted their distribution and feeding grounds since 2010 because of changing climate and oceanographic conditions. In the future, scientists plan to study the impact of copepod prey layers on right whale density before and after this shift.

This study is a collaboration between: