COMMERCE
Subscriber Services
Classified Ads
Subscribe
Advertise
NEWS
This Month
Editorial
Letters
F/V Safety
Past Issues
ABOUT US
Contact Us
Latest Issue
Subscribe
History
MORE CONTENT
CFN Archives
Links
Each month exclusively in the PRINT edition of CFN
Along the Coast
Ask the Lobster Doc
Bearin’s
Classifieds
Coming Events
Editorial
Enforcement Report
FISH SAFE
Fleet Additions
Letters
Lobster Market Report
New Boats
News Catch
Quahog Market Report
|
Commercial Fisheries News
Volume 34 Number 8
April 2007
Whales, seals, dogfish, cod eat a lot of herring — a whole lot
ROCKPORT, ME – Predators, especially marine mammals and dogfish, are consuming roughly three times as much herring as what’s being harvested by the commercial fishing industry.
Three researchers from the Northeast Fisheries Science Center – Bill Overholtz, Jason Link, and Larry Jacobson – analyzed herring consumption by four predator groups from 1977 to 2002, and Overholtz presented the team’s findings to roughly 100 people gathered for an all-day herring session on March 1 at the Maine Fishermen’s Forum.
The four predator groups analyzed were marine mammals, “medium demersal fish,” large pelagic fish, and sea birds.
Marine mammals topped the list. In 2002, they ate roughly 150,000 metric tons (mt) of herring collectively, with finbacks, humpbacks, minkes, and harbor porpoise being especially noteworthy herring consumers.
One harbor seal by itself doesn’t eat all that much herring, but, Overholtz said, “There are a lot of them so it does add up.” The analysis showed that in 2002, harbor seals ate an estimated 13,000 mt of herring.
Medium demersal fish were the second biggest predator group with dogfish, cod, and silver hake being the top three herring consumers in the category.
In 1991, the research team estimated that dogfish alone ate around 98,000 mt of herring. Consumption by all species in the category peaked in the early 1990s at just over 200,000 mt.
However, the analysis indicated that, since then, the total has dropped. In 2002, medium demersal fish consumed 130,000 mt of herring.
This means marine mammals ate more herring than medium demersal fish, even though dogfish was part of the fish category.
“The marine mammals caught up because the abundance of marine mammals has increased,” said Overholtz.
While nothing came close to the tonnage consumed by marine mammals and medium demersal fish, large pelagic fish and sea birds eat herring, too.
Mako and blue sharks accounted for a small percentage of the large pelagic fish category’s consumption, while the biggest consumer of the group was bluefin tuna. Total herring consumption by this large pelagic fish category increased from roughly 15,000 mt in the late 1970s to 25,000 mt in 2002.
Gannets, shearwaters, and gulls were the top three sea bird consumers. Collectively, sea birds ate roughly 9,000 mt of herring in 2002.
Grand total
Overholtz, Link, and Jacobson began investigating this predator/prey relationship and estimating consumption levels in order to incorporate more ecosystem concepts into herring stock assessments and determine, among other things, the impact of predation on the herring stock complex.
In very general terms, they concluded that the four major predator groups combined consumed on the order of 300,000 mt of herring in 2002.
“Predation removes three times what landings are currently,” said Overholtz.
Furthermore, he said predator demand for herring could increase to something on the order of 350,000 mt in the future if groundfish stocks continue to rebuild and marine mammal populations continue to increase.
What’s available
Overholtz noted that predators didn’t always consume this much herring.
“There are 25 important prey fishes on our coast. Herring is just one of them,” said Overholtz. “Sand lance abundance increased a lot when herring and mackerel were down.”
As the herring resource grew in size, marine mammals and other predators simply took advantage of what was available and ate more herring.
Given the current size of the herring resource, computer models show that a “surplus production” of herring – above the 100,000 mt or so now being harvested – might be available for the commercial fishery, according to Overholtz.
But if predators increase and continue to consume more herring, that would tip the equation and less surplus would be available for the fishery.
“It’s a predator vs. fishery trade-off,” he said.
Janice M. Plante
Back to story list
|
|
Tell us what you think.
