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Group claims menhaden studies are deeply flawed

Posted on Thursday, April 4, 2013 at 1:17 pm

In the wake of a deeply-flawed 2012 stock assessment that has prevented the Atlantic States Marine Fisheries Commission (ASMFC) from determining the status of Atlantic menhaden, members of the bait and reduction fisheries have written to the ASMFC calling for updated science and better data collection for the menhaden assessment.
To ensure the success of what they called a “critical” 2014 stock assessment, the industry asked the ASMFC to help design and facilitate a coastal aerial menhaden survey this summer. Its purpose is to identify the distribution and age of menhaden along the Mid-Atlantic and New England coast, information that is currently unavailable. An industry spokesperson, Shaun Gehan, called on the ASMFC, as well as recreational and environmental groups that have expressed strong interest in the health of the menhaden stock, to join fishermen in providing resources to facilitate the survey and improve menhaden science.
“The chosen management approach, based on achieving harvest levels associated with a fixed mortality rate, depends on good science in general, and an accurate estimate of current menhaden abundance in particular,” the letter states. Based on the currently available science, it remains unclear whether or not the stock is overfished, which has the effect of “making it impossible to implement the management system as designed.” Determining whether or not menhaden are overfished will not only influence how the species is managed, but will also have significant social and economic consequences for the fishery and communities dependent on it.
One of the significant sources of uncertainty in the assessment involves what type, particularly what age, of fish are being caught by the fishery, also known as “selectivity.” Two types of models are being considered: a “flat top” model and a “dome shaped” model. A flat-top model assumes that fish of all ages are equally likely to be caught, while a domed model assumes that fish become more likely to be caught up to a certain age, after which the likelihood declines. Whether the menhaden fishery follows a domed or flat-top model has a significant impact in determining whether or not the species is overfished, as the estimates of stock size and stock health will shift based on which of the models is used.
The proposed aerial survey is designed to provide insight into which of these models best reflects the pattern of the fishery. A problem with the current data is that there are no direct surveys of menhaden. Instead, menhaden abundance is estimated through landings data provided by the fishery. But this can produce misleading results. Menhaden is a coast-wide species, with fish migrating farther north as they age, while the menhaden fishery is concentrated between the Chesapeake Bay and southern New Jersey. In addition to not being able to catch many older menhaden, the fishery itself specifically targets fish age 2-3. As a result, fishery landings aren’t representative of the population as a whole, and can present a skewed representation of the age structure of the stock.
If an aerial survey finds that older menhaden existed in significant numbers outside of the range of the fishery, it would indicate that older fish are not likely caught, and that a dome-shaped model is most appropriate. The letter concludes that “finding the right answer to this question is critical to determining whether or not the menhaden stock is overfished based on the current assessment.”
To ensure that an aerial survey is completed, the signers of the letter have committed to in-kind and financial support to facilitate the survey. The industry previously funded an aerial survey of the North Atlantic in 2011, but data needs to be collected over an extended time series in order to produce scientifically valid results. The letter requests that the ASMFC evaluate and approve a survey design created by the Virginia Institute of Marine Sciences (VIMS), and that the Commission, member states, and other fishery stakeholders work collaboratively to ensure it is undertaken. It also asks that the data collected pursuant to the approved survey design be included in the next benchmark assessment.

-Released by the Menhaden Fisheries Coalition