"Some people talk to animals. Not many listen though. That's the problem."

-A.A. Milne

Acoustic Behavior of Fish

Atlantic Cod school of cod
Cod (Photo credit: Dieter Craasmann) Cod haystack (Photo credit: Gilbert van Ryckevorsel)
The passive acoustics group at the Northeast Fisheries Science Center has obtained acoustic data on two species of gadoid fish: the haddock (Melanogrammus aeglefinus) and the Atlantic cod (Gadus morhua). Current efforts are focused on studying acoustic behavior of North Atlantic cod during the spawning season.

Why study cod acoustics?

Atlantic cod is a demersal predatory fish that is important ecologically, economically and culturally in the Northeast. Since cod stocks are still recovering after a crash in the late 1980s/early 1990s, there has been much research into the genetic structure of cod stocks and their movements based on tagging studies. Research into the reproductive behavior of cod is also of increasing importance, since understanding this portion of the cod life cycle could provide valuable information that could improve management of cod stocks.

While the reproductive behavior of cod has been studied for several decades in captive studies, there have been few studies that looked at these behaviors in the wild. During the spawning season, male cod produce low frequency sounds, called grunts, which are thought to function either as a courtship display to females or an aggressive display to competitors.

How can passive acoustic monitoring (PAM) help?

Passive acoustic monitoring (PAM) can serve as a useful monitoring tool that complements traditional survey methodologies (aerial, visual, trawl, etc.). Recording units (MARUs) can be set out for months at a time, and can continue gathering data in conditions that would otherwise limit survey effort. The data gathered from these recorders provides scientists with information on the acoustic presence of a species of interest with known species specific signals. Arrays of recorders can allow data to be gathered that track the spatial presence of a species and possibly fine-scale movements.

What we have done so far?

In a collaborative effort between the passive acoustics group at NEFSC, the Stellwagen Bank National Marine Sanctuary (SBNMS), the Massachusetts Division of Marine Fisheries (DMF) and Cornell University's Bioacoustic Research Program (BRP), a pilot study was conducted by placing a recording unit in the Spring Cod Conservation Zone (SCCZ), a seasonal conservation zone where a spawning aggregation of cod was known to occur during the spring. Cod were recorded on 98% of recording days from the deployment, although the spawning season continued for at least another month after the MARU was retrieved (based on a DMF tagging study). Despite producing sound throughout the deployment, a daily pattern of calling was apparent in the data: cod tended to grunt more often during the day than during the night or twilight hours.
Graph: daily occurence of cod grunts Graph: diel pattern of cod grunts
Figure a) Daily occurence of cod grunts Figure b) Diel pattern of cod grunts

The results of this analysis have been published as Hernandez, K. M., Risch, D., Cholewiak, D. M., Dean, M. J., Hatch, L. T., Hoffman, W. S., Rice, A. N., Zemeckis, D. and Van Parijs, S. M. 2013. Acoustic monitoring of Atlantic Cod (Gadus morhua) in Massachusetts Bay: implications for management and consevation. ICES Journal of Marine Science

What are we currently doing?

Continuing our collaboration with the Stellwagen Bank National Marine Sanctuary (SBNMS), the Massachusetts Division of Marine Fisheries (DMF), and Cornell University's Bioacoustic Research Program (BRP), we also partnered with The Nature Conservancy and local fisherman to look at winter spawning aggregations in Massachusetts Bay, in an area known as the Winter Cod Conservation Zone (WCCZ). The long term goals of this project are to describe both the spatial and seasonal extent of winter cod spawning activity in Massachusetts Bay, and the inter-annual variability in location and timing of spawning events. In the first season of this multi-year project, we deployed five MARUs to monitor the winter spawning season. Working in conjunction with the Massachusetts DMF "active acoustics" we hope to identify where and when cod are spawning.
Map: Proposed 2014 glider tracks
Map of approximate glider tracks during Fall/Winter 2014
We retrieved the first set of MARUs in Spring 2014 and analysis is now ongoing. Fall 2014 marked the start of the second year of this project, and we recently deployed 6 MARUs alongside the Massachusetts DMF "active acoustics" receivers. We are also deploying slocum gliders to track cod presence in Massachusetts Bay this winter. Because cod vocalizations can only be heard 50-100 meters from the source, the gliders will help identify possible cod spawning activity in areas outside of the range of our MARUs.

To complement this new research endeavor, we are also analyzing data collected in and near the Massachusetts Bay Winter Cod Conservation Zone (WCCZ) from 2007-2012 for the presence of spawning cod. Since there is considerable uncertainty as to where current spawning grounds still persist, prospecting archival acoustic data for cod grunts may provide insight into new locations of spawning aggregations that can then be protected.

What are our next steps?

The continuing analysis of cod acoustic data may include additional MARU placement in Massachusetts Bay, as well as sound source level analysis of all recordings. The source level is necessary to determine the detection range of the sound. In 2012, an experimental array of 3 DMONs (developed by the Woods Hole Oceanographic Institution, WHOI) was deployed within the SCCZ to record grunts in order to measure source level. Knowledge of the grunt's source level will allow us to determine how vulnerable cod are to masking by anthropogenic (man-made) sound sources.

We also plan to investigate whether grunt rates can be used as a proxy to estimate the density of grunting cod on a spawning ground. Density estimates are a useful piece of information, and could complement estimates derived from traditional trawling surveys.

Cod Spectrogram

Spectrogram (time vs. frequency) of cod grunts

Partners: MASS Department of Marine Fisheries, SMAST, TNC, NOAA Stellwagen Bank National Marine Sanctuary, Woods Hole Oceanographic Institution

Funders: NMFS Co-operative Research Grant, NOAA Saltonstall-Kennedy

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(File Modified Sep. 06 2016)