Kevin Smith
09-29-2009, 07:00 AM
Fishing Folks,
Very interesting reading that may help explain why the stripers are getting thin and why the stripers follow the Menhaden off shore in the winter.
Kevin
Weekend Mistress
CHESAPEAKE BAY ECOLOGICAL FOUNDATION, INC.
2009
ECOLOGICAL DEPLETION OF ATLANTIC MENHADEN
EFFECTS ON ATLANTIC COAST STRIPED BASS
First Year-Round Diet Study Of Large Chesapeake Bay Striped Bass
The Chesapeake Bay Ecological Foundation (CBEF), with initial assistance from East Carolina University (ECU), has been examining striped bass since 2004 to investigate biological characteristics, identify prey species and determine the age classes and size of menhaden consumed by area, season and predator size. The project title is Predator/Prey Monitoring Program (PPMP). Funding has been provided by the U.S Fish & Wildlife Service, Maryland Department of Natural Resources, ECU and CBEF. Striped bass were obtained from Maryland, Virginia, and North Carolina sport fisheries and Maryland commercial fisheries.
Years of diminishing striped bass numbers culminated in threatened species status in Maryland's section of the Chesapeake Bay (upper Bay) in 1984 and a fishing moratorium in 1985. In 1990 the fishery reopened coast-wide under harvest restrictions approved by the Atlantic States Marine Fisheries Commission (ASMFC). Within the upper Bay the historical 12" (total length) minimum size was raised to 18" and a harvest cap imposed for the first time. Within ocean waters the minimum size was set at 28". These actions protected unprecedented numbers of striped bass, dramatically increasing predation on menhaden and bay anchovy.
PPMP has examined over 5000 striped bass since 2004 and accumulated data demonstrate that malnutrition observed in small upper Bay striped bass approximately 6" to 24" is a consequence of ecological depletion (insufficient numbers to provide adequate prey for dependent predators) of bay anchovy and young ages-0&1 menhaden. Diet analyses show that bay anchovy 1" to 3½" (total length) are an essential prey species for striped bass approximately 6" to 16". Sub-adult (ages-0&1) menhaden 3½" to 9" (total length) are essential to the diet of striped bass approximately 16" to 24". Ages-2+ menhaden greater than 10" (>10") are essential to the diet of large striped bass >24". In mid-Atlantic ocean waters ages-3+ menhaden (>12") are essential to the diet of migratory striped bass >28".
Maryland tidal waters provide the principal spawning and nursery areas for Chesapeake Bay striped bass. By late age-3 (approximately 16") most females have emigrated to coastal waters. PPMP examination of upper bay striped bass >16" revealed that over 85% were males. Most striped bass >16" (ages-3+) aggregate in the main stem of Maryland's mid-Bay region from late spring through early fall. During this period prey consumption by small striped bass (16" to 24") is minimal and these fish assimilate body fat accrued in late fall and winter when feeding intensively on ages-0&1 menhaden. Reduced feeding is the result of ecological depletion and geographical distribution of ingestible-size menhaden <9": Most age-0 menhaden <6½" inhabit tributary nursery areas from spring through early fall, and PPMP data collected from 2006 through 2008 indicate that few age-1 menhaden (6½" to 9") are re-entering Maryland's mid-Bay region following their South Atlantic coastal migration. Therefore, ages-0&1 menhaden in the main stem of Maryland's mid-Bay region during spring through early fall are severely depleted. Striped bass movement into Chesapeake Bay tributaries and predation on menhaden increase during the fall as water temperatures decline to approximately 60 degrees F. In late fall age-0 menhaden and bay anchovy begin migrating down the Chesapeake Bay to ocean waters. Many striped bass follow and prey on both species before returning to the upper Bay during the winter.
During 2007 & 2008 body fat indices were recorded for 1,256 resident striped bass caught in the main stem of the upper Bay from June 21 to Oct. 15 and in the Choptank River from May 2 to Oct. 15. The average index value for striped bass 6" to 24" was significantly lower than for striped bass >24". These findings indicate populations of bay anchovy and ingestible size menhaden <9" in Maryland's mid-Bay region from late spring through early fall are too low to provide adequate prey for small striped bass 6" to 24". In contrast, age-2 menhaden >10" inhabit Chesapeake Bay year-round and are utilized as prey by large resident striped bass >24". Migratory striped bass (>28") arriving in the Chesapeake Bay and adjacent Virginia ocean waters during late fall and winter have low levels of body fat. After these fish begin feeding, primarily on sub-adult menhaden and bay anchovy, body fat levels gradually increase. Most body fat is used for gonadal development as post-spawning fat indices are near zero.
The Chesapeake Bay forage base for striped bass 6" to 24" has collapsed due to poor recruitment of bay anchovy and menhaden since the mid 1990's in conjunction with increasing predation by high populations of striped bass, continued over-harvest by the menhaden purse seine reduction fishery (large scale harvest of fish for processing into products such as fish oil and meal), and a management policy oblivious to these interacting factors. Striped bass 6" to 24", which are dependent on ages-0&1 menhaden and bay anchovy, are unable to maintain their weight and health. During years of low menhaden recruitment in the upper Bay the average weight of upper Bay striped bass approximately 18" in length caught in the Choptank River during the fall can be less than 70% of their historical weight - a level symptomatic of starvation. The striped bass recovery following the initiation of the moratorium is now threatened by the ensuing imbalance between prey and predator populations.
The Virginia based menhaden purse seine reduction fishery, which operates in Virginia Chesapeake Bay waters and in ocean areas from North Carolina to New Jersey, competes with striped bass for the declining numbers of ages 1+ menhaden. Responding to mounting concern about "depletion" of menhaden in the Chesapeake Bay, the ASMFC established (in 2006) an annual "Bay harvest cap" of 109,020 metric tons on reduction fishery landings from Virginia Bay waters. Since annual landings from 2006-2008 have averaged 30% below the harvest cap, the cap has been ineffective in conserving menhaden stocks.
PPMP sampling detected that large numbers of striped bass >28" that historically migrated from summer habitat in New England waters to winter feeding grounds off Virginia and North Carolina, have migrated into the upper Bay each fall since 2006 and remained through the spring spawning season - a previously undocumented event. (These striped bass account for a significant portion of upper Bay winter gill net landings). This change in established feeding patterns indicates that menhaden are more available in the Chesapeake Bay than on their historical winter feeding grounds. The depleted coastal stock of ages-3+ adult menhaden currently fails to provide sufficient prey for migratory striped bass >28". (Few age-4+ menhaden remain in the population even though life expectancy exceeds 10 years). Consequently, many migratory striped bass >28" now enter the Chesapeake Bay to feed on the more abundant sub-adult menhaden. This unprecedented competition for food could exacerbate growth and health problems affecting resident striped bass. After spawning, migratory striped bass resume feeding, primarily on age-2+ menhaden, while migrating out of the Chesapeake Bay en route to their summer habitat in northern coastal waters. Migratory striped bass supplement their primary diet of menhaden with high value recreational or commercial species that include the following: blue crab, white perch, spot, Atlantic croaker, weakfish, flounder and American eel.
Migratory striped bass over-wintering in mid-Atlantic coastal waters also prey heavily on the depleted stock of bay anchovies. (During late fall most Chesapeake Bay anchovies migrate to ocean waters). Published data collected through research conducted by PPMP and the Southeast Area Monitoring and Assessment Program shows consumption of bay anchovy (by weight) by over-wintering migratory striped bass in Virginia and North Carolina coastal waters has dramatically declined since 2000. This decline parallels poor recruitment of bay anchovy documented in Chesapeake Bay surveys. PPMP striped bass diet studies substantiate the depletion of bay anchovy in Chesapeake Bay and mid-Atlantic coastal waters.
Ecological depletion of bay anchovy and ages-0&1 menhaden in the Chesapeake Bay has lowered the carrying capacity for striped bass 6" to 24". Numbers of ages-0&1 menhaden in the main stem of Maryland's mid Bay region from spring through early fall are too low to provide adequate prey for striped bass 16" to 24". In the Chesapeake Bay bacterial disease and lesions are prevalent in striped bass, natural mortality has risen, and growth and weight-at-length have declined. Ecological depletion of ages-3+ adult menhaden in mid-Atlantic waters has lowered the carrying capacity for striped bass >28". Migratory and resident striped bass must now compete for limited numbers of similar size prey. PPMP studies of striped bass >18" in Chesapeake Bay and >28" in mid-Atlantic waters found that menhaden constitute over 80% of their annual diet (by weight), and are essential to maintenance of healthy striped bass populations.
You can read more at:
Chesapeake Bay Ecological Foundation, Inc. (http://www.chesbay.org/articles/striped%20bass%20study(1-09).asp)
Very interesting reading that may help explain why the stripers are getting thin and why the stripers follow the Menhaden off shore in the winter.
Kevin
Weekend Mistress
CHESAPEAKE BAY ECOLOGICAL FOUNDATION, INC.
2009
ECOLOGICAL DEPLETION OF ATLANTIC MENHADEN
EFFECTS ON ATLANTIC COAST STRIPED BASS
First Year-Round Diet Study Of Large Chesapeake Bay Striped Bass
The Chesapeake Bay Ecological Foundation (CBEF), with initial assistance from East Carolina University (ECU), has been examining striped bass since 2004 to investigate biological characteristics, identify prey species and determine the age classes and size of menhaden consumed by area, season and predator size. The project title is Predator/Prey Monitoring Program (PPMP). Funding has been provided by the U.S Fish & Wildlife Service, Maryland Department of Natural Resources, ECU and CBEF. Striped bass were obtained from Maryland, Virginia, and North Carolina sport fisheries and Maryland commercial fisheries.
Years of diminishing striped bass numbers culminated in threatened species status in Maryland's section of the Chesapeake Bay (upper Bay) in 1984 and a fishing moratorium in 1985. In 1990 the fishery reopened coast-wide under harvest restrictions approved by the Atlantic States Marine Fisheries Commission (ASMFC). Within the upper Bay the historical 12" (total length) minimum size was raised to 18" and a harvest cap imposed for the first time. Within ocean waters the minimum size was set at 28". These actions protected unprecedented numbers of striped bass, dramatically increasing predation on menhaden and bay anchovy.
PPMP has examined over 5000 striped bass since 2004 and accumulated data demonstrate that malnutrition observed in small upper Bay striped bass approximately 6" to 24" is a consequence of ecological depletion (insufficient numbers to provide adequate prey for dependent predators) of bay anchovy and young ages-0&1 menhaden. Diet analyses show that bay anchovy 1" to 3½" (total length) are an essential prey species for striped bass approximately 6" to 16". Sub-adult (ages-0&1) menhaden 3½" to 9" (total length) are essential to the diet of striped bass approximately 16" to 24". Ages-2+ menhaden greater than 10" (>10") are essential to the diet of large striped bass >24". In mid-Atlantic ocean waters ages-3+ menhaden (>12") are essential to the diet of migratory striped bass >28".
Maryland tidal waters provide the principal spawning and nursery areas for Chesapeake Bay striped bass. By late age-3 (approximately 16") most females have emigrated to coastal waters. PPMP examination of upper bay striped bass >16" revealed that over 85% were males. Most striped bass >16" (ages-3+) aggregate in the main stem of Maryland's mid-Bay region from late spring through early fall. During this period prey consumption by small striped bass (16" to 24") is minimal and these fish assimilate body fat accrued in late fall and winter when feeding intensively on ages-0&1 menhaden. Reduced feeding is the result of ecological depletion and geographical distribution of ingestible-size menhaden <9": Most age-0 menhaden <6½" inhabit tributary nursery areas from spring through early fall, and PPMP data collected from 2006 through 2008 indicate that few age-1 menhaden (6½" to 9") are re-entering Maryland's mid-Bay region following their South Atlantic coastal migration. Therefore, ages-0&1 menhaden in the main stem of Maryland's mid-Bay region during spring through early fall are severely depleted. Striped bass movement into Chesapeake Bay tributaries and predation on menhaden increase during the fall as water temperatures decline to approximately 60 degrees F. In late fall age-0 menhaden and bay anchovy begin migrating down the Chesapeake Bay to ocean waters. Many striped bass follow and prey on both species before returning to the upper Bay during the winter.
During 2007 & 2008 body fat indices were recorded for 1,256 resident striped bass caught in the main stem of the upper Bay from June 21 to Oct. 15 and in the Choptank River from May 2 to Oct. 15. The average index value for striped bass 6" to 24" was significantly lower than for striped bass >24". These findings indicate populations of bay anchovy and ingestible size menhaden <9" in Maryland's mid-Bay region from late spring through early fall are too low to provide adequate prey for small striped bass 6" to 24". In contrast, age-2 menhaden >10" inhabit Chesapeake Bay year-round and are utilized as prey by large resident striped bass >24". Migratory striped bass (>28") arriving in the Chesapeake Bay and adjacent Virginia ocean waters during late fall and winter have low levels of body fat. After these fish begin feeding, primarily on sub-adult menhaden and bay anchovy, body fat levels gradually increase. Most body fat is used for gonadal development as post-spawning fat indices are near zero.
The Chesapeake Bay forage base for striped bass 6" to 24" has collapsed due to poor recruitment of bay anchovy and menhaden since the mid 1990's in conjunction with increasing predation by high populations of striped bass, continued over-harvest by the menhaden purse seine reduction fishery (large scale harvest of fish for processing into products such as fish oil and meal), and a management policy oblivious to these interacting factors. Striped bass 6" to 24", which are dependent on ages-0&1 menhaden and bay anchovy, are unable to maintain their weight and health. During years of low menhaden recruitment in the upper Bay the average weight of upper Bay striped bass approximately 18" in length caught in the Choptank River during the fall can be less than 70% of their historical weight - a level symptomatic of starvation. The striped bass recovery following the initiation of the moratorium is now threatened by the ensuing imbalance between prey and predator populations.
The Virginia based menhaden purse seine reduction fishery, which operates in Virginia Chesapeake Bay waters and in ocean areas from North Carolina to New Jersey, competes with striped bass for the declining numbers of ages 1+ menhaden. Responding to mounting concern about "depletion" of menhaden in the Chesapeake Bay, the ASMFC established (in 2006) an annual "Bay harvest cap" of 109,020 metric tons on reduction fishery landings from Virginia Bay waters. Since annual landings from 2006-2008 have averaged 30% below the harvest cap, the cap has been ineffective in conserving menhaden stocks.
PPMP sampling detected that large numbers of striped bass >28" that historically migrated from summer habitat in New England waters to winter feeding grounds off Virginia and North Carolina, have migrated into the upper Bay each fall since 2006 and remained through the spring spawning season - a previously undocumented event. (These striped bass account for a significant portion of upper Bay winter gill net landings). This change in established feeding patterns indicates that menhaden are more available in the Chesapeake Bay than on their historical winter feeding grounds. The depleted coastal stock of ages-3+ adult menhaden currently fails to provide sufficient prey for migratory striped bass >28". (Few age-4+ menhaden remain in the population even though life expectancy exceeds 10 years). Consequently, many migratory striped bass >28" now enter the Chesapeake Bay to feed on the more abundant sub-adult menhaden. This unprecedented competition for food could exacerbate growth and health problems affecting resident striped bass. After spawning, migratory striped bass resume feeding, primarily on age-2+ menhaden, while migrating out of the Chesapeake Bay en route to their summer habitat in northern coastal waters. Migratory striped bass supplement their primary diet of menhaden with high value recreational or commercial species that include the following: blue crab, white perch, spot, Atlantic croaker, weakfish, flounder and American eel.
Migratory striped bass over-wintering in mid-Atlantic coastal waters also prey heavily on the depleted stock of bay anchovies. (During late fall most Chesapeake Bay anchovies migrate to ocean waters). Published data collected through research conducted by PPMP and the Southeast Area Monitoring and Assessment Program shows consumption of bay anchovy (by weight) by over-wintering migratory striped bass in Virginia and North Carolina coastal waters has dramatically declined since 2000. This decline parallels poor recruitment of bay anchovy documented in Chesapeake Bay surveys. PPMP striped bass diet studies substantiate the depletion of bay anchovy in Chesapeake Bay and mid-Atlantic coastal waters.
Ecological depletion of bay anchovy and ages-0&1 menhaden in the Chesapeake Bay has lowered the carrying capacity for striped bass 6" to 24". Numbers of ages-0&1 menhaden in the main stem of Maryland's mid Bay region from spring through early fall are too low to provide adequate prey for striped bass 16" to 24". In the Chesapeake Bay bacterial disease and lesions are prevalent in striped bass, natural mortality has risen, and growth and weight-at-length have declined. Ecological depletion of ages-3+ adult menhaden in mid-Atlantic waters has lowered the carrying capacity for striped bass >28". Migratory and resident striped bass must now compete for limited numbers of similar size prey. PPMP studies of striped bass >18" in Chesapeake Bay and >28" in mid-Atlantic waters found that menhaden constitute over 80% of their annual diet (by weight), and are essential to maintenance of healthy striped bass populations.
You can read more at:
Chesapeake Bay Ecological Foundation, Inc. (http://www.chesbay.org/articles/striped%20bass%20study(1-09).asp)