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 Smart Data Transformation – Surfing the Big Wave
02.12.2016 | Fraunhofer-Institut für Angewandte Informationstechnik FIT

nachricht Climate change could outpace EPA Lake Champlain protections
18.11.2016 | University of Vermont

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: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>