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NEFSC researcher Larry Alade holds a tagged goosefish, or monkfish, prior to release during a cooperative monkfish migration study with commercial fishermen in 2009 and 2010. Photo Credit: Pasha Ivanov
Click image to enlargeA large female goosefish is measured after being caught during a bottom trawl survey. Photo credit: NOAA Fisheries/NEFSC
Close-up of part of an egg veil. It may look a bit like bubble wrap, but the light tan colored spots, or bubbles, are eggs. The image was taken during a Gulf of Maine shrimp survey on the R/V Gloria Michelle. Credit: NOAA Fisheries/Heidi Marotta, NEFSC
April 19, 2017
Contact: Shelley Dawicki
Monkfish mysteries: Study finds they are serial spawners
Researchers have found that individual goosefish, commonly called monkfish, spawn more than once during a spawning season that can last six months. Their size has also declined over time, leading to a population dominated by young small females with reduced spawning capacity compared to the older, larger females more common in the past.
The findings, published online in the Journal of Fish Biology, compared findings from 1982-1985 and 2009-2012, two very different periods for monkfish. Although often caught by fishermen, monkfish was not a viable commercial fishery until the 1980s, when a market for them developed. Today, monkfish (Lophius americanus) is one of the most valuable finfish fisheries in the Northeast.
Monkfish are known for spawning their egg in masses, called egg veils since they look like bolts of delicate lace billowing in the ocean's current. Each veil can be up to 40 feet long and 5 feet wide, with eggs arranged in a single layer just over one-tenth of an inch thick. The largest females can produce more than two million eggs per veil. The veil is spawned by the female and fertilized by nearby males. Eggs are protected in chambers within the veil and develop over a period of weeks until the veil breaks up and the larvae are released into the water column.
“We have evidence that female monkfish spawn more than once in a season, and perhaps as many as three times,” said Richard McBride, a fishery biologist at the Northeast Fisheries Science Center and lead author of the study. “A female at the New England Aquarium has been observed to produce more than one veil per year, but there were no males in the tank, so it was not clear if this was normal. Now we have observed monkfish in the ocean preparing for serial spawning, which is a common bet-hedging strategy in fishes. Environmental and feeding conditions vary over time, so by spawning several times a year in different seasons, more eggs will likely survive and grow into adult fish, thereby contributing to a more resilient population and fishery.”
McBride and NOAA Fisheries colleagues examined 54 spawning-capable female monkfish, the largest number examined to date. These fish were collected between 2009 and 2012 from the southern management area on the Mid-Atlantic Bight shelf region. Samples were collected by commercial gillnets during February to July, trawl catches during the Northeast Fisheries Science Center’s 2009 Cooperative Monkfish Survey, and from the NEFSC’s spring 2012 bottom trawl survey. Results were compared to 17 samples collected from 1982 to 1985.
“Our comparisons suggest that the females are not producing as many eggs as they used to, partly because they are smaller now, but perhaps because feeding conditions now are different than they were in the 1980s when the last similar study was done,” McBride said. “We looked at the southern management area, which includes the Mid-Atlantic seaboard and southern New England, because we had a previous study for comparison.”
The recent study focused on three areas of reproductive biology: fecundity, spawning frequency, and the seasonality of female spawning. Fecundity means the number of eggs produced in a single spawning. One of the smallest monkfish produced about 230,000 eggs per veil, and one of the largest monkfish produced 2.2 million eggs per veil. The average monkfish producing 3 egg veils per year spawns 5-6 billion eggs in her lifetime, as calculated for the recent period in the southern management area.
Spawning activity by the population was prolonged, occurring nearly year-round, but was most common from March to October. It progresses northward during the year: collections of monkfish larvae peak in May-June offshore of Chesapeake Bay but July-August in the Gulf of Maine, which is in the northern management area.
These results were used to estimate changes since the 1980s in the reproductive potential of the population. The model assumed that spawning frequency increased with age during both time periods. The results showed that the current population reproductive potential is less than 50 percent of what it was in the 1980s study because fecundity per individual is lower and there are fewer large females in the population now.
“We know much more than we used to about monkfish, but there are still some major gaps,” said Anne Richards, a fishery biologist who leads monkfish assessments at the NEFSC and is a co-author of the study. “The gaps include stock structure, migration patterns, and growth rates. We are making progress filling those gaps, but it takes time.”
Richards says there has been some encouraging news. “In 2015 there was a very large year class of monkfish produced in the southern management area, and in 2016 a large recruitment event happened in the northern management area. These year classes are helping to resolve some long-standing questions about monkfish growth and are expected to boost catch rates as these recruits grow into exploitable size. This is good news for both scientists and fishermen.”
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