Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Changes in forage fish abundance alter Atlantic cod distribution, affect success of the fishery

26.06.2014

A shift in the prey available to Atlantic cod in the Gulf of Maine that began nearly a decade ago contributed to the controversy that surrounded the 2011 assessment for this stock.

A recent study of how this occurred may help fishery managers, scientists, and the industry understand and resolve apparent conflicts between assessment results and the experiences of the fishing industry.


Map showing location of Stellwagen Bank. Credit: USGS

When the dominant prey species of Atlantic cod changed from Atlantic herring to sand lance beginning in 2006, cod began to concentrate in a small area on Stellwagen Bank where they were easily caught by fishermen.

The fishermen perceived the Gulf of Maine cod stock to be abundant in subsequent years as they reported increased ease in catching cod, yet the 2011 stock assessment concluded that the Gulf of Maine cod stock had not increased as expected and that fishing rates had been too high even though catches had not exceeded the quotas. Fishermen were skeptical, and the 2011 assessment conclusions were questioned and criticized.

Writing in the Canadian Journal of Fisheries and Aquatic Sciences, researchers from NOAA Fisheries’ Northeast Fisheries Science Center (NEFSC) show how the fishermens' observations and the assessment results could both be accurate. Their findings reveal why fishermen targeting these cod would conclude the fish were abundant, and also illustrate how commercial catch-per-unit of effort can be a misleading indicator of stock abundance.  

The NEFSC has been routinely monitoring the diet and distribution of cod and many other marine species since 1973 in an ecosystem survey of waters off the Northeast from Maine to North Carolina and eastward into Canadian waters. By collecting, analyzing, and documenting stomach contents of cod taken in the Gulf of Maine during this survey, the researchers can see what cod eat both seasonally and over time.

“Atlantic herring and sand lance are dominant prey for Atlantic cod in the Gulf of Maine. This long, standardized time series of data has been invaluable to our ability to both show and understand where and when predators and prey are distributed across the region,” said David Richardson, an oceanographer at the NEFSC’s Narragansett Laboratory in Rhode Island and lead author of the study. “When sand lance are abundant, they account for a high proportion of the diet of cod. Also, cod tend to be more aggregated when they are feeding on sand lance than when they are feeding on other prey.”

An assessment is an examination of fishery stock conditions used to develop catch limits and other management measures. The 2011 assessment results were also controversial because the 2008 assessment had suggested an uptick in young fish that would grow the stock. Ultimately this growth in the population did not materialize, and the catch limits set based on the 2008 assessment were found to be too high.  

“The sand lance-induced cod aggregations led to a number of challenges in evaluating population trends in Gulf of Maine cod,” Richardson said. “During the 2007 and 2008 spring bottom trawl surveys, extremely high catches of cod were recorded at individual stations on Stellwagen Bank, while the remainder of the stock area had low catch rates. At the same time, the fishing industry was experiencing high catch rates of cod in the same small area on Stellwagen Bank. One of the main conclusions of this study is that the trends in cod abundance in this small region were not truly reflective of the overall resource at the time.”  

Atlantic herring and sand lance have very different habitat and life history requirements that affect their distribution. Atlantic herring are migratory, shifting distribution in response to changing oceanographic conditions like temperature.  Sand lance are burrowers, and have a nightly need to burrow into shallow sandy bottom, such as that found on Stellwagen Bank, an underwater plateau covering about 156 square miles located in the southwestern portion of the cod stock area. 

“Data from the Northeast Fisheries Science Center survey and from the fishery both indicate that an increase in sand lance abundance resulted in cod aggregating in a small and predictable area on Stellwagen Bank where they were easily caught by fishermen,” Richardson said. “The cod were fished in a very small area, approximately 100 square miles, while the entire cod stock area on which the assessment was based is 20,255 square miles.”

Michael Palmer, an assessment scientist in the NEFSC’s Population Dynamics Branch at the Woods Hole Laboratory and a co-author of the study, said the concentration of cod and of the fishing fleet was significant. “Between 1994 and 2010 the number of fishing trips occurring in this small area increased by 191 percent, and the number of trips occurring outside this area declined by 46 percent.”

“This shift in the fishery distribution indicates a large influx of fishing effort into this small area during the same time period that sand lance was abundantly available to feeding cod,” said Palmer. By 2010, 45 percent of all Gulf of Maine cod landings came from this area, compared with 12 percent prior to 2005. 

This dynamic is important not only for cod but also for other species, including whales that have been reported feeding on sand lance in the same area. “The change in the composition of the forage fish community in the Gulf of Maine may have driven distribution shifts, not only for Atlantic cod, but also for other predators feeding on the same set of prey species,” said Richardson.

In addition to Richardson and Palmer, study authors include fishery biologist Brian Smith, who studies the link between fish feeding and offshore benthic habitats and leads the NEFSC’s food web dynamics program.

# # #

NOAA Fisheries Service is dedicated to protecting and preserving our nation's living marine resources and their habitat through scientific research, management and enforcement. NOAA Fisheries Service provides effective stewardship of these resources for the benefit of the nation, supporting coastal communities that depend upon them, and helping to provide safe and healthy seafood to consumers and recreational opportunities for the American public.

NOAA's mission is to understand and predict changes in the Earth's environment, from the depths of the ocean to the surface of the sun, and to conserve and manage our coastal and marine resources. Join us on Facebook, Twitter and our other social media channels.

Shelley Dawicki | Eurek Alert!
Further information:
http://www.nefsc.noaa.gov/press_release/pr2014/scispot/ss1406/

More articles from Studies and Analyses:

nachricht Rutgers-led innovation could spur faster, cheaper, nano-based manufacturing
14.02.2018 | Rutgers University

nachricht New study from the University of Halle: How climate change alters plant growth
12.01.2018 | Martin-Luther-Universität Halle-Wittenberg

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

Im Focus: Hybrid optics bring color imaging using ultrathin metalenses into focus

For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.

But today's glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require...

Im Focus: Stem cell divisions in the adult brain seen for the first time

Scientists from the University of Zurich have succeeded for the first time in tracking individual stem cells and their neuronal progeny over months within the intact adult brain. This study sheds light on how new neurons are produced throughout life.

The generation of new nerve cells was once thought to taper off at the end of embryonic development. However, recent research has shown that the adult brain...

Im Focus: Interference as a new method for cooling quantum devices

Theoretical physicists propose to use negative interference to control heat flow in quantum devices. Study published in Physical Review Letters

Quantum computer parts are sensitive and need to be cooled to very low temperatures. Their tiny size makes them particularly susceptible to a temperature...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Researchers invent tiny, light-powered wires to modulate brain's electrical signals

21.02.2018 | Life Sciences

The “Holy Grail” of peptide chemistry: Making peptide active agents available orally

21.02.2018 | Life Sciences

Atomic structure of ultrasound material not what anyone expected

21.02.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>