MakoMike
12-16-2010, 01:27 PM
From the Baltimore Daily Record:
More than two months before biologists threw their first net into the water to gauge the success of this year’s striped bass reproduction, Ed Martino had the answer, and he never had to leave his desk.
Rockfish reproduction, Martino determined in May, would be “well below average.”
The researcher with the National Oceanic and Atmospheric Administration’s Cooperative Oxford Laboratory came up with his conclusion by going online and looking at March though May river flows monitored by the U.S. Geological Survey and temperature data from Baltimore-Washington International Thurgood Marshall Airport for the same period, then plugging the information into a mathematical model.
While Martino crunched numbers in his office, a team of biologists from the Maryland Department of Natural Resources waded into the water at 22 locations once a month from July through September. At each site, they did two sweeps through the water with a 100-foot seine net, then counted everything they caught.
When the work was done, the biologists had averaged 5.6 juvenile striped bass per net haul. That was less than half the long-term average of 11.6. After all of their field work, they had reached the same conclusion as Martino.
His model, which was developed with data from the DNR, confirms what biologists have thought for years: The weather during any given spring plays a huge role in determining how many larval striped bass survive to be “recruited” into the overall population. But his model puts an exclamation point to just how important weather is: In looking back to 1985, he can account for more than 80 percent of the annual variability in striped bass recruitment in Maryland, where the majority of the East Coast population is spawned.
This year, the model successfully predicted a poor year even though many fishery biologists — including Martino — thought it would be good.
But that predictability may contain a hint of problems on the horizon for striped bass. Although the coast-wide population remains above target levels, striped bass recruitment in Maryland has been below average for three consecutive years, largely because the weather hasn’t cooperated.
“The bay is full of spawners, but we are seeing a real reduction in recent years in reproduction,” Martino said. “So I think it’s pretty obvious that something else is going on in the environment.”
That “something else” may be found in work done by Bob Wood, the NOAA scientist in charge of the Oxford Lab. Wood suggests that a broader, long-lasting climate pattern called the Atlantic Multidecadal Oscillation may be affecting striped bass and other fish.
The Atlantic Multidecadal Oscillation is an alternating pattern of warming and cooling over large areas of the Atlantic Ocean, similar to the El Nino, La Nina patterns in the Pacific. The shifts affect climate over large regions of North America. Various AMO phases, during which different parts of the Atlantic are warmed or cooled, persist for decades.
During certain AMO phases, which promote wetter winters, cool springs and more frequent nor’easters, the prevailing pattern seems to promote improved reproductive success for anadromous fish, such as striped bass, which live most of their lives at sea but return to freshwater to spawn.
During other AMO phases, which promote drier, warmer springs, the situation is reversed, with fish such as menhaden, that spawn on the coastal shelf and whose larvae use estuaries for nurseries, getting a boost. During those times, striped bass reproduction takes a hit.
Wood says those phase shifts are strongly correlated with the rise and fall of striped bass and menhaden stocks in the past.
Striped bass crashed because of overfishing in the 1980s, which was also a time when the AMO was in a phase unfavorable for their recruitment, so fish being caught were not being replaced. The ensuing rebound of striped bass stocks is often touted as a major fishery management success as managers took drastic actions, including a coast-wide moratorium, to protect the spawning stock. And it was. But Wood’s work strongly suggests that managers also got lucky. Their fishing moratorium coincided with an AMO shift that greatly improved striped bass spawning conditions.
“Had the weather not turned, we would have been waiting longer for that recovery,” Wood said.
Meanwhile, as striped bass recruitment bottomed out in the 1970s and 1980s, menhaden recruitment soared, only to fall to persistent low levels in the 1990s and 2000s as striped bass again benefited from the prevailing climate cycles.
The exact reason why temperature and the timing of river flows is so important is less certain. Martino and Wood theorize the cool temperatures delay the production of plankton until striped bass larvae are most abundant. The high flows may push those plankton and striped bass larvae together so the larvae, which are poor swimmers, have plenty to eat.
Conversely, warmer years benefit larval menhaden, which use the same nursery grounds, but arrive earlier and eat different kinds of plankton.
A better understanding of these long-term patterns can be a huge aid for fishery managers. Had they understood they were in the midst of a down-cycle for striped bass recruitment in the 1980s, for instance, managers might have acted sooner to curb fishing pressure, Wood said.
There are problems in using the information in management, though. The understanding of regional climate patterns is far from complete, and it is much easier to observe what happened in the past than to predict what will happen in the future. As a result, it’s hard to say with certainty whether the last three years of poor reproduction stemmed from a change in the AMO and will persist into the future — or their correlation is just coincidence.
Also, while striped bass recruitment has been poor the last three years, there’s been no boom in menhaden recruitment. The menhaden recruitment index remains below average.
More than two months before biologists threw their first net into the water to gauge the success of this year’s striped bass reproduction, Ed Martino had the answer, and he never had to leave his desk.
Rockfish reproduction, Martino determined in May, would be “well below average.”
The researcher with the National Oceanic and Atmospheric Administration’s Cooperative Oxford Laboratory came up with his conclusion by going online and looking at March though May river flows monitored by the U.S. Geological Survey and temperature data from Baltimore-Washington International Thurgood Marshall Airport for the same period, then plugging the information into a mathematical model.
While Martino crunched numbers in his office, a team of biologists from the Maryland Department of Natural Resources waded into the water at 22 locations once a month from July through September. At each site, they did two sweeps through the water with a 100-foot seine net, then counted everything they caught.
When the work was done, the biologists had averaged 5.6 juvenile striped bass per net haul. That was less than half the long-term average of 11.6. After all of their field work, they had reached the same conclusion as Martino.
His model, which was developed with data from the DNR, confirms what biologists have thought for years: The weather during any given spring plays a huge role in determining how many larval striped bass survive to be “recruited” into the overall population. But his model puts an exclamation point to just how important weather is: In looking back to 1985, he can account for more than 80 percent of the annual variability in striped bass recruitment in Maryland, where the majority of the East Coast population is spawned.
This year, the model successfully predicted a poor year even though many fishery biologists — including Martino — thought it would be good.
But that predictability may contain a hint of problems on the horizon for striped bass. Although the coast-wide population remains above target levels, striped bass recruitment in Maryland has been below average for three consecutive years, largely because the weather hasn’t cooperated.
“The bay is full of spawners, but we are seeing a real reduction in recent years in reproduction,” Martino said. “So I think it’s pretty obvious that something else is going on in the environment.”
That “something else” may be found in work done by Bob Wood, the NOAA scientist in charge of the Oxford Lab. Wood suggests that a broader, long-lasting climate pattern called the Atlantic Multidecadal Oscillation may be affecting striped bass and other fish.
The Atlantic Multidecadal Oscillation is an alternating pattern of warming and cooling over large areas of the Atlantic Ocean, similar to the El Nino, La Nina patterns in the Pacific. The shifts affect climate over large regions of North America. Various AMO phases, during which different parts of the Atlantic are warmed or cooled, persist for decades.
During certain AMO phases, which promote wetter winters, cool springs and more frequent nor’easters, the prevailing pattern seems to promote improved reproductive success for anadromous fish, such as striped bass, which live most of their lives at sea but return to freshwater to spawn.
During other AMO phases, which promote drier, warmer springs, the situation is reversed, with fish such as menhaden, that spawn on the coastal shelf and whose larvae use estuaries for nurseries, getting a boost. During those times, striped bass reproduction takes a hit.
Wood says those phase shifts are strongly correlated with the rise and fall of striped bass and menhaden stocks in the past.
Striped bass crashed because of overfishing in the 1980s, which was also a time when the AMO was in a phase unfavorable for their recruitment, so fish being caught were not being replaced. The ensuing rebound of striped bass stocks is often touted as a major fishery management success as managers took drastic actions, including a coast-wide moratorium, to protect the spawning stock. And it was. But Wood’s work strongly suggests that managers also got lucky. Their fishing moratorium coincided with an AMO shift that greatly improved striped bass spawning conditions.
“Had the weather not turned, we would have been waiting longer for that recovery,” Wood said.
Meanwhile, as striped bass recruitment bottomed out in the 1970s and 1980s, menhaden recruitment soared, only to fall to persistent low levels in the 1990s and 2000s as striped bass again benefited from the prevailing climate cycles.
The exact reason why temperature and the timing of river flows is so important is less certain. Martino and Wood theorize the cool temperatures delay the production of plankton until striped bass larvae are most abundant. The high flows may push those plankton and striped bass larvae together so the larvae, which are poor swimmers, have plenty to eat.
Conversely, warmer years benefit larval menhaden, which use the same nursery grounds, but arrive earlier and eat different kinds of plankton.
A better understanding of these long-term patterns can be a huge aid for fishery managers. Had they understood they were in the midst of a down-cycle for striped bass recruitment in the 1980s, for instance, managers might have acted sooner to curb fishing pressure, Wood said.
There are problems in using the information in management, though. The understanding of regional climate patterns is far from complete, and it is much easier to observe what happened in the past than to predict what will happen in the future. As a result, it’s hard to say with certainty whether the last three years of poor reproduction stemmed from a change in the AMO and will persist into the future — or their correlation is just coincidence.
Also, while striped bass recruitment has been poor the last three years, there’s been no boom in menhaden recruitment. The menhaden recruitment index remains below average.