May 24, 2013 — The following is an excerpt from the article "Menhaden Science Supports Conservation", published by the organization Wild Oceans:
Are Atlantic menhaden “overfished” or not? For the most important fish in the sea, that’s not what’s most important. What matters for menhaden and other forage species is whether or not we are leaving enough fish in the water to serve their vital role in the ecosystem. And we aren’t. Even the most optimistic scenario says we’re not even close, making the catch limits going into effect this year essential.
In late 2012, the Atlantic States Marine Fisheries Commission decided to cut the coast- wide catch of menhaden by 20 percent. In the same action, the ASMFC raised the bar for defining a healthy population of Atlantic menhaden. The purpose of these changes is to increase menhaden abundance and availability as prey for numerous marine predators along the east coast, including many recreationally and commercially important species.
A new abundance target (what we aim for) and threshold (what we aim to avoid) will guide future management decisions following the next benchmark stock assessment to be completed in 2015. Curious, the commissioners asked the Menhaden Technical Committee to peek at what the status of menhaden might be relative to the new reference points. On February 20th, the TC reported that “there was not sufficient evidence” to determine whether or not the stock is overfished.
This came as somewhat of a surprise, given that the committee of scientists speculated in their July 2012 Stock Assessment Update that, if the new reference points were adopted for management, “the stock would be overfished.” The new-found uncertainty arises from adding a new model with different assumptions about how information gathered from catch reports and surveys relate to what’s really out there in the population at large.
Read the full story at Wild Oceans
Analysis: Early in 2013, the Atlantic States Marine Fisheries Commission’s (ASMFC) Menhaden Technical Committee determined that there is too much uncertainty in the most recent stock assessment results to determine whether or not menhaden are currently overfished. Despite this development, Ken Hinman, in his Wild Ocean article “Menhaden Science Supports Conservation,” asserts that, regardless of whether or not menhaden are overfished, the species is “not even close” to meeting its conservation goals, and that recently imposed, harsh catch limits are necessary.
Mr. Hinman reaches his conclusions on the current state of the menhaden population by relying on estimates that are based on data from the 2012 menhaden stock assessment. However, problems with the assessment limit its usefulness as an accurate representation of the status of menhaden. The assessment is considered severely flawed by the ASMFC, and is not used by the Commission for management purposes. Among other issues, it was found to have overestimated fishing mortality (the number of menhaden caught by the fishery) and underestimated the spawning stock biomass (the number of menhaden that are able to reproduce).
While Mr. Hinman is correct that the model used in the assessment is “the model [the ASMFC] relied on for years,” the results of the 2012 assessment reveal that there are problems with the model and the data used in the assessment that need to be resolved. As a result, the ASMFC concluded that these problems “cast considerable doubt on the accuracy of the estimates from this update stock assessment,” and that it was necessary to have “an expedited benchmark assessment” in which the Menhaden Technical Committee could examine these issues. This expedited benchmark won't be completed until late 2014 or 2015.
There have been several attempts to address the flaws in the current model. One of them involves a variable called selectivity, which is the probability that an individual fish will be caught by the fishery. Selectivity varies based on the age, migration patterns, and size of the fish, along with how the fishery is managed. The selectivity patterns of a fishery will affect how stock assessments estimate population sizes, as they will cause the stock assessments to estimate different levels of fishing mortality. In its recent analysis, the Technical Committee considered two different kinds of selectivity: flat-topped and domed.
Flat-topped selectivity assumes that menhaden become increasingly likely to be caught by the fishery, until the age of 3, at which point they are all assumed to have been caught. This is the selectivity curve currently used in the assessment model. Domed selectivity assumes that menhaden become increasingly likely to be caught until a certain age, then become increasingly less likely to be caught. While it is not currently certain whether a flat-topped or domed model is a more accurate representation of the menhaden fishery, migration patterns of menhaden, which move farther away from the Chesapeake Bay-based menhaden fishery as they age, suggest that domed selectivity is most likely the appropriate approach.
Mr. Hinman's understanding of the status of Atlantic menhaden will benefit greatly from the forthcoming benchmark assessment, whose completion will introduce thorough and more recent findings to a discussion currently clouded by faulty, outdated information. Currently, the most recent reliable data on menhaden comes from the 2010 assessment, which uses data collected through 2008. Because this information is at least 5 years old, the status of menhaden is largely unknown, and will remain so until the next assessment.