KEVIN D. FRIEDLAND
DIRECTOR
UMASS/NOAA COOPERATIVE MARINE
EDUCATION AND RESEARCH PROGRAM
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
BEFORE THE
SUBCOMMITTEE ON FISHERIES CONSERVATION, WILDLIFE AND OCEANS
HOUSE RESOURCES COMMITTEE
Oversight Hearing on
December 13, 2004
Mr.
Chairman and Members of the Committee, I am Kevin Friedland, Director of the
UMass NOAA Cooperative Marine Education and Research program (CMER), a
cooperative program between the National Oceanic and Atmospheric Administration
and the University of Massachusetts.
Thank you for inviting me to testify on the ecological role
of menhaden in the
Before
I respond to your questions, Mr. Chairman, I would like to provide you with
some background information on the Atlantic menhaden. The Atlantic menhaden (Brevoortia tyrannus)
is a member of the herring family and is found in coastal and estuarine waters
from
Most
spawning activity occurs during winter off the
Atlantic
menhaden play an important ecological role. As adults, menhaden are common in
all salinities of the
Atlantic
menhaden also play an important social role in the
Now I would like to address the questions you raised in the letter of invitation.
What is the population
status of Atlantic menhaden in the
While the status of the coast-wide stock of Atlantic
menhaden is healthy and is not overfished, the status of menhaden in the
On the other hand, recruitment, or the number of new fish
added to the population annually, has been poor in recent years. This observation is supported by the data
coming from the stock assessment and from fishery independent survey indices on
the nursery grounds. The stock
assessment estimation of year class strength does not indicate recruitment
failure or the absence of sufficient new recruits to sustain the
population. However, the regional
juvenile abundance indices, although providing a fragmented view of the
potential nursery areas for menhaden along the coast, suggest that recruitment
may have shifted geographically. These
indices suggest the nursery grounds of
For the
Several factors contribute to the uncertainty about the
population status of Atlantic menhaden in the Bay, and like most biological
systems, Atlantic menhaden recruitment is complex. Like so many other marine and estuarine
dependent species, recruitment for Atlantic menhaden appears to be influenced
by climate variation. Recent NOAA
studies suggest a relationship between springtime weather patterns and spawning
success in the Bay. Species that spawn
offshore and have their eggs and larvae transported into the Bay in the late
winter and early spring appear to recruit better with an early onset of warm
and dry conditions and prevailing southwesterly winds brought on by the weather
system known as the Azores-Bermuda High.
Conversely, cool and wet spring conditions apparently hamper recruitment
levels of menhaden within the
The scientific community has identified a number of potential bottlenecks for menhaden recruitment including transport of eggs and larvae across the continental shelf from the spawning grounds to the estuaries, predation on juveniles by other species, poor water quality (low oxygen, high water temperature), and disease. These and other factors may be working in concert to shape recruitment patterns.
Recently, the ASMFC charged its Menhaden Management Board
(Board) and the Menhaden Technical Committee to review the ecological role of
menhaden coastwide and to specifically focus on the population’s status in the
The Technical Committee will soon be analyzing a wide range
of research and management issues. The
first question to be addressed will be whether localized depletion of menhaden
stocks in the
Are menhaden
significant consumers of primary productivity in the Bay?
Yes, menhaden are significant consumers of primary productivity in the Bay. Primary production refers collectively to the food in marine ecosystems produced by phytoplankton. Though not explicitly estimated, we know menhaden are significant consumers of primary production due to their large population numbers, filtration efficiency, and total volume filtered by individual fish.
Atlantic menhaden occupy a unique ecological niche in the food web of the Bay. For a relatively large body size animal they are able to filter extremely small plankton particles. Menhaden ram feed, i.e., they open their mouths and push their gill rakers through the water trapping planktonic organisms. Juvenile menhaden can filter the smallest plankton and are also capable of cropping down large multi-cell phytoplankton and zooplankton.
Menhaden adults in the Bay retain the ability to graze on small phytoplankton, but with lower efficiency than juveniles. New studies of the functional morphology of their gill raker feeding apparatus explain why juvenile fish maintain high filtering efficiency on the small phytoplankton found in the juvenile nursery. As adults, they progressively lose filtering efficiency on the smallest phytoplankton as a tradeoff to be able to filter larger quantities of water. This ensures that the adults can compete with other planktivores in coastal waters.
Menhaden are believed to filter feed during much of the day, so the estimates of the amount of water they filter can quickly become large depending on the size of the resident population in the area. Menhaden exhibit feeding selectivity by modifying their distribution. They are not capable of rejecting individual food particles, so they rely on taste to evaluate the quality of the food they are filtering. They search for productive feeding areas by modifying swimming and turning behavior to find more suitable foods to filter. As a result, menhaden are usually distributed with gradients of phytoplankton.
Not all the material that menhaden ingest is completely digested. As with all animals, menhaden do not convert all foods into growth and the amounts of unused digestive wastes that menhaden eject into their surroundings are unknown. The meaning of these observations is not clear, but they may be significant to the flow of nutrients in the estuaries.
Could changes in the
current management regime of the fishery improve water quality?
Yes, changes in the current management regime of the fishery could theoretically improve water quality, but there is uncertainty as to how, since the question of menhaden recruitment and predation level and water quality is complex.
Because menhaden occupy such an important position in the
pelagic food web of the
Without the benefit of specific modeling advice, we have to rely on qualitative judgments about the impact juvenile and adult fish have on the flow of nutrients in the Bay. Juvenile fish will filter the smallest phytoplankton, especially those associated with eutrophication, and contribute to clearer water column conditions by removing both live and detritus particles. They will also export large quantities of nitrogen and phosphorus used in growth when they migrate in the fall, which will be a net loss of nutrients to these systems represented by those fish that do not return and are harvested elsewhere. These benefits will be most concentrated in the portions of the Bay that serve as the juvenile nursery, which are the salinity transition zones located in the rivers and parts of the upper Bay. Juveniles would not be expected to have a significant effect on the main part of the Bay.
Under the operational assumption that larger populations of menhaden juveniles will contribute to improved water quality, what management measures might increase juvenile abundance? Since there is no directed fishery for juvenile menhaden in the Bay, we can only affect juvenile abundance by improving recruitment or reducing natural mortality on juvenile menhaden. The likelihood of larger recruitments is enhanced by larger spawning stock size, so management measures for the adult stock that increases spawning stock may be beneficial. However, if the recruitment mechanism for menhaden is climate driven, the sacrifices to increase spawning stock may not yield the larger recruitments desired. Reducing the natural mortality on juvenile menhaden will also increase their abundance in the Bay. This could be achieved by better water quality and lower consumption by predators.
Adult menhaden play a different ecological role than the juveniles, thus their anticipated effect on water quality would also be different. The adults more commonly utilize the algal blooms that occur in the Bay main stem and associated water temperature fronts that form between the Bay and its sub-tributaries. They will yield many of the same water quality benefits as previously described for the juveniles, they will clear the water column and incorporate nitrogen and phosphorus as they grow, but they will do so in different parts of the Bay and impact different components of the plankton community. Unlike the juveniles, there is a directed fishery for the adults. Therefore, fishing immediately removes the nutrients used in the growth of menhaden from the system, but reduce their filtering capacity in the system. Finally, the adult population is dependent on successful recruitment, so any management measure that ensures robust spawning stock size would be beneficial.
What is the correct balance between removal and retention of the fish? Is there any benefit in foregoing harvest in that the fish will reappear the following year and reintroduce the nutrients back into the system? Does some level of harvest improve the filtering efficiency of schools by reducing competition? The question of menhaden harvest level and water quality is complex. NOAA recognizes the need to enhance fisheries management plans to explicitly include ecosystem considerations that provides a framework to enhance management performance. These considerations incorporate increased attention to predator-prey relationships, habitats, and understanding the impacts of human activities. Atlantic menhaden is being discussed by multiple partners, including NOAA and ASMFC, in this ecosystem context.
This concludes my testimony, Mr. Chairman. I will be happy to respond to any questions that you or members of the Subcommittee may have.