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by Ed Cherry
(from Jersey Coast Anglers Association June 2004 Newsletter)
A condensation of some of the topics discussed in A Symposium on Management Issues of Striped Bass in the Chesapeake Bay
Current State Of Chesapeake Bay
The resident striped bass population is considered to be very high and consists of fish mainly through age 5. This population is primarily male.
More than 60% of the population of the bay appears to be affected and infected by a mycobacterium-based disease, and the disease is increasing at an alarming rate.
There is a noticeably reduced forage population of both menhaden and bay anchovies.
There is a suggestion from tagging studies that natural striped bass mortality has increased beginning in 1998
The striped bass population was declared restored in 1995. The striped bass population in Chesapeake Bay at this time remains high. In 1997 recreational and commercial fishermen reported the appearance of diseased fish. However, some current estimates of diseased fish run over 60% of the total bay population. The stock in the Rappahannock River appears to be 80% infected.
The Disease Symptoms:
During late summer and fall, striped bass begin to feed heavily in preparation for the winter and spawning in the spring. Excess food is stored predominantly as fat in the body cavity and as this is used, it is replaced with water. Chesapeake Bay striped bass usually under 24 inches in length are exhibiting a weight at length that is much lower than would be traditionally expected (long skinny fish!), elevated moisture and a lack of mesenteric fat, strongly suggesting poor nutritional health. In 2001 studies indicated that by age 6 striped bass in the bay annually consume 38% less forage and weigh about 40% less than they did in the time period of 1955-59.
Infected fish (mainly over 24 inches) may exhibit external lesions called Ulcerative Dermatitis Syndrome, with some 15% of the population of 18-26” fish exhibiting UDS. The relationship of skinny fish to infected fish is not clear at this time.
Most infected fish may not have external lesions, but many internal organs, primarily the spleen and head kidney exhibit internal granulomas (The body’s defense against pathogens by encapsulating them).
The presence of diseased fish has been recently reported in coastal stocks from New Jersey to Maine. The extent of these infections is presently unknown. There is a feeling since the majority of the coastal stock is made up of females, that their early departure from the bay by age 5 may be a factor in limiting the extent of the coastal stock infection. But again, no one knows. At this time we are dealing with far more questions and unknowns with this disease than there are answers.
Health Concerns:
Striped bass definitely are dying from mycobacteriosis, but it is not in any sense a fish kill as we normally think of it. Because mycobacteriosis is a slow growing infection, it is unlikely anyone would see a major fish kill from mycobacteriosis. The disease probably has its onset in 2-3 year old fish and is most prevalent in 3-5 year old fish. The presence of large quantities of dead and dying fish has not been noted. However the normal scavenging that takes place in the bay probably maintains an appearance of normalcy. However, one must ponder the fate of the crabs and other scavengers that are consuming these disease-ridden fish.
Human Health Concerns:
There does not appear at this time a concern that consumption will cause mycobacteriosis in humans, as these bacteria are killed at 170oF while cooking. However, caution is warranted. Thus, all striped bass should be thoroughly cooked. Do not keep a striped bass with obvious ulcerations!
However, there are health risks in handling diseased fish. Some species of mycobacterium can affect humans. Fishermen should release fish exhibiting ulcerated patches, and wear gloves when handling diseased striped bass. If any cuts, scrapes, or abrasions are on hands or arms, wash with a germicidal soap and water after coming into contact with diseased fish.
Anyone who suspects they may have been exposed to mycobacteriosis from handling infected striped bass should contact their physician. Human infection symptoms are local swelling and raised red areas in the sites of infection in the hands or feet. Long term antibiotic therapy may be needed to eliminate these localized infections of the extremities.
The cause of the disease:
Mycobacterium is a very broad family of bacteria, which includes the organisms responsible for tuberculosis and leprosy (these specific organisms are not implicated in this disease process), causes Mycobacteriosis, the chronic debilitating infection found in striped bass. A new species of mycobacterium called Mycobacterium shottsii is most commonly found in the current samples. However, some 10 different mycobacterium species can be isolated from the diseased fish. It is unknown at this time which of these organisms is involved in the disease development. Of the most prevalent mycobacterium strains it has not been possible to implicate any of them at this time as the causative pathogen.
Possible causes implicated within the disease process:
The current rapid encroachment of man on the bay
Point and non-point pollution
Declining water quality
Poor nutrition
Low oxygen levels, large hypoxic areas in the summer
Water temperatures too high
Too many striped bass
Stress related to predator/prey imbalance
Stress related to too high of a striped bass population
Striped Bass and Atlantic menhaden: is there a predator-prey imbalance in Chesapeake Bay?
The abundance of forage-sized menhaden (ages 0-2) had declined to near its historic low, while striped bass climbed to an historic high in the 1990s. Low ratios of menhaden supply to striped bass demand began around 1995 and coincided with the outbreak of lesions and decreased presence of Atlantic menhaden in diets. In the 1960’s menhaden comprised 80% of the striped bass diet and had dropped to a low of 21% in 2001.
The predation of the bass reduced the stock of bay anchovies by a considerable amount as the bass looked for alternatives to the shrinking menhaden supply. As a consequence the bass have had to settle for forage foods of lesser nutritional value, they are also feeding heavier on spot, blue back herring, white perch, Atlantic silversides, and juvenile croakers. This has put stress on these populations as well. Crabs have become an increasing part of the diet as well as benthic organisms (those small critters in mud). As part of the whole picture there is a declining crab population in the bay, greater turbidity, very high bacterial counts (in the main these are not sewage related), and a greatly lowered flushing action within the bay as the oceans rise.
There is a noticeable lack of 0-2 age Menhaden in Chesapeake Bay, the age range that bass to age 3-4 prefer. They seem to be blaming the lack of forage (Atlantic menhaden and Bay anchovies) in Chesapeake Bay on too many foraging striped bass in the bay contributing to a rampant state of mycobacterium infected fish. Also the rebuilding stocks of weakfish and bluefish have increased the pressure on the stocks of forage species.
It was stated by reducing the predatory demand of striped bass by more than 30% would probably improve the predator/prey ratio, but indicated that this would create a historical over fishing condition, and obviously would not be a solution from a striped bass management perspective.
My Own Personal Thoughts:
While a large amount of time was taken discussing the forage imbalance and disease within the bay, only minimal to no mention was made of the effects of:
Drinking and irrigation water demand on the Chesapeake Bay that cuts down the flow of water and where and how it flushes the bay.
The fact the dams were built affects the way water flows and the temperature of the water.
The dams also affect the migratory patterns of forage and prey species both and have greatly reduced some of their numbers.
The construction of power plants and the damage they do by heating the water and killing prey and forage species alike. The increased handling of the striped bass by both the commercial and recreational sector.
The increased pressure on the harvesting of crabs, oysters, and clams without allowing them to rebuild their stocks. Some discussion was made about the lack of forage on the depleted oyster beds, and the positive effect noted where attempts were made to restore oyster beds.
The encroachment of building construction on the bay creating more non-point source pollution.
Also nowhere in this extensive symposium was mention made to the possible effect of the reduction fleet operating within the bay. In 2003 the reduction fleet removed 124,382 metric tons of a total 166,00 metric ton catch from within the bay, nearly 80% of the total reduction catch. The greatest portion of the catch was made up of Age-1 and Age-2 fish, the very fish the striped bass are likely to forage. This represents approximately 1 BILLION menhaden that are not available for forage or filter feeding. Since 1995 the reduction fleet has removed approximately 1,295 Metric tons or nearly 12 Billion menhaden from the bay. Could there be some correlation with these numbers and the problems we see today?
Nowhere in these discussions was it mentioned about the effect of greatly reduced number of filter feeders within the bay, nor the value of filter feeders to the ecology of the bay. This is a factor that many scientists and fisheries managers seem intent on ignoring. The shrinking population of menhaden, crabs, clams, and of oysters and oyster beds, and the cumulative loss of all of this filter feeding that has been lost permanently to the bay, has to be a major part of the root cause of the declining situation in the bay.
The bay in years past had much larger stocks of striped bass, shad, sturgeon, crabs, clams and oysters all at the same time, but because on the impacts of humans, the ecosystem has been knocked out of balance. It is ridiculous to blame Mother Nature for our disasters, and this is what we are doing when we blame the fish for causing the problem. It is human activities that cause the problem. What we need to do first is try to reduce the impact of human activities on the bay and many of these and other problems will correct themselves.
Can Barnegat Bay Be Far Behind?
For more detailed information on these subjects please refer to http://www.vims.edu/myco/Biblio.html