WASHINGTON (Saving Seafood) — May 8, 2013 — The paper A Case for Precautionary Management of Forage Fish, presented by Pew’s Peter Baker at the Managing Our Nation’s Fisheries Conference on May 8, is based on several assumptions about “forage fish” and predator species that are unproven. These unproven assumptions, as well as a lack of peer-review of the Lenfest Forage Fish Task Force that the paper extensively cites, should raise significant questions and engender in-depth review before its recommendations become standard practice in fisheries management.
The paper’s recommendations are based around the assumption that “forage fish” is a legitimate and useful categorization of species to be used in fisheries management, and that the various “forage species” can be managed under the same broad guidelines. Specifically, the paper recommends implementing restrictions intended to leave forage species biomass at 75 percent of unfished levels. The paper argues that adopting this conservative management strategy will lead to an increase in the amount of forage available and will benefit predator species.
However, these species have a variety of biological differences, and don’t have much in common outside of their common role in the marine food web. These significant differences–including fecundity, spawning periods, migration, predator-prey relationships, and habitat–are much more relevant variables for fisheries management than a shared trophic role.
It is more likely that different forage species will respond in different ways to management measures. For example, one of the species mentioned in the report, Atlantic herring, has lower levels of fecundity when the stock biomass is high. Another species mentioned, Atlantic menhaden, has historically shown a poor correlation between harvest levels and biomass. Some of the peak years in menhaden biomass, particularly in the early 1980s, followed years of heavy fishing. The paper’s recommendations do not factor in these differences.
The paper’s economic analysis also rests on unproven assumptions about predator species. In asserting that “forage fish” are more valuable if left in the water than if caught, the paper assumes both that all of these fish species left in the water will be consumed by predator species, and that predator species are currently constrained by a lack of forage. For the paper’s assumptions to be correct, the current state of predator species in its analysis would need to be such that they were prevented from growing due to a lack of adequate forage. The report does not provide evidence that this is the case.
And this is simply not true for several predator species. Some, like weakfish, are currently overfished, and an increase in available forage would not be an effective solution to problems facing the stock. Other species, like striped bass, have not historically been abundant at the same time as their forage. Bass are known to have an inverse relationship with one of its primary forage species, menhaden: during periods where striped bass are abundant, menhaden are not, and when menhaden are abundant, striped bass are not. Recent research from Maryland’s Oxford Cooperative Lab suggests that menhaden and striped bass are both affected by the Atlantic Multidecadal Oscillation, a climate pattern of alternating warm and cold ocean temperatures in the North Atlantic. The climate conditions that favor menhaden do not favor striped bass, and conditions that allow for a relative abundance of one species contribute to a relative scarcity of the other.
An increase in forage is also not automatically beneficial to predators, and an increase in predator species is not the only possible outcome. There are instances where a larger amount of forage may have negative influences on predator stocks. For example, an overabundance of Atlantic herring – which feed on cod eggs and plankton — may negatively impact cod reproduction and attempts to rebuild cod stocks. This increase in cod egg predation by herring would exist even as an increase in herring would provide more abundant forage to adult cod.
Regulations are constantly evolving to incorporate new science and research to better manage stocks. Where information is available, managers are involving ecosystem interactions in species regulations. Several stocks, including menhaden and Atlantic herring, are currently managed to account for the needs of predators. Considerations like natural mortality and predation are among the factors that are considered when setting catch limits. These steps are currently being taken under single species management to better account for the needs of the ecosystem.
Read a PDF version of A Case for Precautionary Management of Forage Fish
Works Cited
Collie, Jeremy; Minto, Coilin; Worm, Boris; Bell, Richard, "Predation on Prerecruits Can Delay Rebuilding of Depleted Cod Stocks", Bulletin of Marine Science, vol. 89 No. 0, 2013
Kelly, Kevin H.; Stevenson, David K., "Fecundity of Atlantic Herring (Clupea harengus), from Three Spawning Areas in the Western Gulf of Maine, 1969 and 1982", Journal of Northwest Atlantic Fishery Science, vol. 6, 1985
Martino, Edward J.; Houde, Edward; Wood, Robert; Zhang, Xinsheng, "Disentangling causes of striped bass recruitment variability in Chesapeake Bay: forecasting year-class strength", University of Maryland Center for Environmental Science and NOAA Cooperative Oxford Laboratory