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Jun 05 2008

Too Many Striped Bass and they are Eating all the Chesapeake Crabs: Fact or Fiction to Save the Dying Commerical Chesapeake Crab Industry?

Published by at 5:57 pm under Fisheries Conservation Talk,Striped Bass

I read an article in the paper today that now the commerical crabbers in the Chesapeake Bay are saying that we have way too many striped bass and they are the reason we do not have enough crabs. I mean come on guys. I actaully heard this argument spun at some of the crab meetings leading up the emergency regulations that just started June 1 to protect female crabs in the Chesapeake Bay.  While I am open to new ideas and would agree that striped bass do eat crabs, it’s certainly not the main portion of their diet and they are certainly not eating enough to cause the crab crash we had. I am not sure how many times it has to be said, but we have been harvesting crabs for the last several years at a rate of 60%  a year, 20% above the sustainable rate. The math is really simple. But like I have said, a person is not going to understand something when their jobs depend on them not understanding.

Having said that, maybe this, most likely fictitious,  PR campaign against striped bass is a way to bring commerical and recreational anglers together. Let’s just run with it and say striped bass are eating all the crabs, why all the sudden? Well probably because a big portion of what they used to eat, menhaden, are being whacked in the lower Virginia part of the Chesapeake by Omega. Now the Maryland commerical watermen and Maryland recreational anglers can unite and get that fishery’s harvest drastically reduced. Hey, then we would have happy rockfish which would mean we would have happy crabbers.

If you want to know what striped bass really rely on for their diet, Jim Price from the Chesapeake Bay Ecological Foundation might be a good person to consult. I have seen his presentations at science conferences and he has some compelling data. A lot of people, generally the commerical interests, criticize his research because they argue it’s not peer reviewed. Fair enough, so maybe we can pontificate on the lack of academic “credentials” the overall study might not have. But, this “technical”argument is just a tactic by the commerical interests to interject doubt, when in “doubt” the bureaucratic process gets hazy and no one on councils, like the ASMFC, wants to step up and make a decision based on something that appears to have “doubt” surrounding it even if the data is in fact sound. I would argue, and I do have a Masters in Psychology and did conduct research, a thesis etc so I think I am somewhat qualified to comment, that the peer review criticism has some merit because for the most part it has not been peer reviewed, however I’d say the data is what it is. Striped bass stomach contents were examined and what was in them was reported. Peer reviewed or not, what was in there was in there. The below chart is what you see when you look at the data (you can click on the picture for a larger view):

Striped Bass Diet

I really do not believe the striped bass are the reason we have a crab collapse in the Chesapeake Bay,  I think over harvesting crabs way above sustainable rates explains that one.  I do not think we need to reduce the striped bass population to save the crabs. I certainly do not think there are too many striped bass, in fact I think we have a potential problem with not enough bigger fish. I do think, given how much striped bass rely on menhaden, we need to reduce the harvest of menhaden in the Chesapeake Bay as well as along the Atlantic Coast. If you think so too, sign the petition we have going here.

In case you are interested below is the full paper that the above chart came from. You can also see it here

CHESAPEAKE BAY ECOLOGICAL FOUNDATION, INC.
2008
ECOLOGICAL DEPLETION OF ATLANTIC MENHADEN
EFFECTS ON ATLANTIC COAST STRIPED BASS
The Chesapeake Bay Ecological Foundation (CBEF) and the Maryland Department of Natural Resources (MD-DNR) have conducted cooperative striped bass studies since the early 1980s. In 2004 CBEF initiated a Predator/Prey Monitoring Program (PPMP) to determine the type of prey and age structure of Atlantic menhaden consumed by striped bass along the Atlantic coast and in the Chesapeake Bay. Funding for the PPMP was provided by the U.S. Fish & Wildlife Service, MD-DNR, CBEF and East Carolina University. Over 4,000 striped bass have been examined and analysis of PPMP and MD-DNR data demonstrate that malnutrition observed in striped bass results from ecological depletion (insufficient numbers to meet nutritional needs of dependent predators) of Atlantic menhaden, their primary forage. Food habit studies of striped bass from Maryland’s portion of the Chesapeake (upper Bay) show that age-0 menhaden less than 6” in total length are crucial to the diet of small striped bass (<18”) during the summer, fall and winter. Both age-0 and sub-adult menhaden (ages 1&2) are crucial to the diet of large resident striped bass (>18”) from fall through spring. Migratory striped bass over 28” in length (approximately 80% females) prey on all age classes of menhaden while in ocean waters and the upper Bay from late fall through spring.

Both sexes of young striped bass live and feed within the Chesapeake Bay system; however, prior to reaching age-4 (about 16”) most of the females migrate to coastal waters. More than 85% of striped bass (16” to 18”) that remain in the upper Bay are males and are at the size when age-0 menhaden become their primary prey. From fall through spring, just prior to reaching age-4, these 3 year old feed heavily on age-0 menhaden and accumulate body fat. This fat is used for gonad development and assimilation during the following summer and early fall when feeding activity by age-4+ striped bass in the upper Bay is greatly reduced. (The PPMP found that although resident striped bass 4 years and older prey heavily on menhaden from fall through spring, they become opportunistic predators during summer and early fall when feeding activity is low and upper Bay water temperatures are relatively high).

Since the mid 1990s consistently poor recruitment has contributed to the ecological depletion of age-0 menhaden in the Chesapeake Bay. Consequently, many striped bass now enter the summer months lacking sufficient body fat to maintain their weight and health until intensive feeding on menhaden resumes in late fall. The average weight of upper Bay age-4 striped bass caught in the Choptank River during the fall is now less than 70% of their historical weight – a level symptomatic of starvation. Weight-at-length of striped bass caught in the Choptank River increases and decreases with high and low recruitment levels of age-0 menhaden, demonstrating that striped bass in this size range are unable to maintain their weight when young menhaden are ecologically depleted. Diet analysis confirm that the number of age-0 menhaden in the stomachs of striped bass caught in the Choptank River increases when the MD-DNR Choptank juvenile menhaden index is high and decreases when it is low.

The PPMP detected that large numbers of striped bass (mostly females >28”) that historically migrated south to the coastal waters off Virginia and North Carolina (winter feeding grounds for large striped bass), migrated to the upper Bay during 2006-07 and 2007-08 and remained over the winter – a previously undocumented event. These large migratory striped bass (>28”) accounted for a significant portion of upper Bay winter gill net landings. They preyed heavily on menhaden from late fall through spring, primarily on sub-adults, indicating menhaden may now be more available in the upper Bay than on their historical winter feeding grounds along the coast. This conclusion is supported by the condition of large migratory striped bass examined from the two areas; those from the upper Bay contained about twice the amount of body fat than those from the coastal ocean. CBEF’s stomach analysis on 98 of these large migratory striped bass caught in the upper Bay during the winter of 2006-07 found that 90 contained a total of 446 menhaden: age-0s were present in approximately 20% of the 90, sub-adults in 70%, and adults in 10%. The body fat index of these 98 striped bass averaged approximately 2 on a scale of (0 to 4), compared to an average body fat index of approximately 1 for 80 migratory striped bass caught during late winter in coastal waters near the mouth of the Bay. The change in historical migration patterns is one of several indicators that the depressed coastal stock of older menhaden is ecologically depleted and no longer provides sufficient prey for large migratory striped bass. (Few menhaden older than age-4 are now present in the population even though life expectancy exceeds 10 years). The use of the upper Bay as a winter feeding ground for many large migratory striped bass (mostly females >28”) has resulted in competition with upper Bay resident striped bass (mostly males) for similar size menhaden. The additional competition for the declining numbers of menhaden, in conjunction with depressed populations of bay anchovy and blue crab, could exacerbate growth and health problems currently affecting upper Bay resident striped bass. The menhaden purse seine fishery and large striped bass compete for the declining numbers of older menhaden – depleting menhaden spawning stock and the prey supply for large striped bass. (During 2006 & 2007 menhaden purse seine landings in the Chesapeake Bay declined sharply to approximately 60% of the previous 20 year average).

After spawning in the spring, large migratory striped bass resume feeding, primarily on age-1+ menhaden, while migrating out of the Chesapeake Bay to northern coastal waters. These adult females now use most of their body fat for egg production – leaving less fat reserves for assimilation during the summer months of reduced feeding activity in New England coastal waters. In late fall they migrate south and arrive on their winter feeding grounds off Virginia and North Carolina in poor nutritional condition. (Weight-at-length of adult female migratory striped bass has been declining in recent years). They feed heavily from fall through early spring, primarily on menhaden, and accumulate body fat essential for weight maintenance and egg development. Following the decline of older menhaden, those migratory striped bass wintering in coastal ocean waters from late fall through early spring now prey heavily on bay anchovy and younger menhaden. Those migratory striped bass that enter the upper Bay prey heavily on menhaden from late fall through spring.

The ecological depletion of Atlantic menhaden has resulted in nutritionally stressed striped bass. Both resident and migratory striped bass now consume increased numbers of alternate prey that have high recreational and commercial value such as blue crab, white perch and weakfish. Cumulative data from PPMP and MD-DNR studies since 2003 show menhaden are crucial to the diet of large striped bass (>18”) in the upper Bay and (>28”) in ocean waters from fall through spring when menhaden constitute over 80% of their diet by weight.

Direct questions or comments to James Price: [email protected]

2 responses so far

2 Responses to “Too Many Striped Bass and they are Eating all the Chesapeake Crabs: Fact or Fiction to Save the Dying Commerical Chesapeake Crab Industry?”

  1. ksmithreon 16 Jun 2008 at 6:22 am

    Because of pollution the water quality of the Chesapeake Bay is horrible.
    Due to this degraded water quality a lack of sun light gets through the water which is needed for sub aquatic grasses to grow.
    These grasses are nursery areas for crabs. They are also good hiding places and offer protection from predation.
    Predation from stripe bass is a problem and a big one. I wish I could post a picture with this comment and you would see what one fish in one day can eat (crabs).
    The Bay has become a nursery for the east coast stripe bass fishery. I would like to see the quotes raised both commercially and recreationally to reduce the numbers.
    When the marine biologist sample the stripe bass and their feeding habits they never go in shore close. When crabs molt many go close to shore. The fish follow them. It is an easy food source. Because there is limited grass the soft crab that has just molted and now weak is easy prey.
    At one time the Bay could sustain all marine life in abundance; but today 40% of the Bay is a dead zone, meaning that in those waters nothing can live. Think about this! All the larvae and microscopic life that is carried by the tide has to pass through the water. What happens when it passes through the dead zone? Getting the picture?
    Instead of blaming the commercial fishermen go to the problem. Pollution!!
    Demand that EPA does what it has promised to do.
    Did you know that in the Commonwealth of Virginia you have a Constitution right to unpolluted water. Article 11 of Virginia’s Constitution. Only 2 things in Virginia are given constitutional protection, education and natural resources. Demand your constitutional rights.
    If the water quality of the Bay is not restored there won’t be a commercial waterman. When the commercial waterman is gone then who will be blamed for the continuing decline in a once abundant resource.
    Ken Smith
    President Virginia Waterman’s Association

  2. Brandonon 15 Jul 2008 at 8:52 pm

    Ken,

    I can not agree with you more, water quality is the main cause of a lot of fish issues we have in the bay. You an I are in violent agreement on that point. I do not blame watermen for our problems in the bay, we all are to blame.

    Due to the poor water quality, fish and crab populations have and will decrease. When that happens harvest limits must be reduced until water quality can be improved. If you do not reduce harvest limits then the math is simple, the population of that fish species will decline at a rapid rate and eventually disappear.

    The situation with the Chesapeake Blue Crab’s decline has been compounded by the fact that it has been harvested at 20% ABOVE the sustainable rate for the last few years. So now we have poor water quality and over harvesting at work, a deadly combination.

    We all have created this problem in the bay, it’s unfortunate that watermen bear the brunt of the pain when these restrictions are put into place, but it’s a reality of our times. Just like the reality of the workers in truck building plants across America are feeling the pain of high gas prices. They too are losing their jobs as a result of all of us using way too much gas and other natural resources. None of this is good, it’s all bad.

    Not all of us that call for reductions in fish harvests do it in spite of watermen, we do it to save the fish for the future.

    The whole we should harvest more rockfish arguement has little basis. I am sure in some places striped bass eat crabs, but it is not their main portion of their diet. Just because they eat a lot of crabs in one tributary of the bay, does not mean you can extrapolate that saying they are the problem. So far all the research I have reviewed and referenced above says the rockfish’s main diet is menhaden. If you believe Rockfish are solely responsible for the decline of the crabs beyond the poor water quality and over harvesting that has taken place then I challenge you to conduct a scientifically valid and peer reviewed study of stomach contents of striped bass throughout the Chesapeake Bay. You do that and prove existing science wrong I’ll change my mind, until then saying things like Rockfish are to blame sounds just as lame as those that blame the crab situation solely on the watermen.

    Brandon

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