Sealing a Fisheries Fate, NOAA's failure to take into account increased predation Gulf of Maine Fishery

Grey Seals on ice flows in Wellfleet Harbor

Sealing a Fishery’s Fate

The recent NOAA cod counts are part of a disturbing trend of lower than expected counts across a variety of fish species, including, striped bass, cod, and yellowtail flounder, and threatens New England’s traditional fishing industry. Already, the industry has been adversely affected by sector management, which intentionally or unintentionally favors the consolidation of the fishing industry. Sector management policies are exacerbating the decline of the local dayboat industry, and are having a detrimental economic impact upon Cape Cape’s year-round employment.

Now, the cod counts are indicating that the fishery is in worse health than previously believed which could lead to the general collapse of the local groundfishing industry. This is because in order to protect the cod population there will be drastic cuts in the cod quota, or the fishery may be completely closed. A reduction in the cod quota will effectively reduce the entire groundfishing fishery since it is impossible to selectively target one species of groundfish without at least catching some individuals of other groundfish species. So, if a boat is fishing for a species such as haddock, supposedly a healthy fishery (though who knows with the trend of recent fish surveys provided by NOAA, they will inevitably, also catch some cod. In order to protect the cod fishery, the other related fisheries will also have to be closed once the cod quota is met. This will inflict grievous harm on an increasingly fragile industry and could lead to the end of a traditional way of life.

Many fishermen point to issues of accuracy in NOAA’s surveys, specifically since the commissioning of the Bigelow in 2005(NOAA’s current survey ship), as one of the reasons behind the reduced fish counts. However, there is another potential culprit that has largely been ignored by the greater scientific community. The seal population in the Gulf of Maine has exploded in the last twenty years. With the absence of apex predators, excepting a few Great White sharks that have been sighted off of Chatham, the seal population has no natural check on its numbers and is federally protected under the Marine Mammal Protection Act of 1972.

The last official survey of the seal population in the Gulf of Maine was completed over a decade ago in 2001 counted roughly 100,000 individuals. Conservatively, by extrapolating from the observed rate of the growth the population now is at least 200,000 seals (this is below the previously observed rate of growth of 8.7% according to NOAA). On average seals eat between 5-8% of their body weight in fish a day. It can be assumed with the population of seals in the region made up primarily of harbor seals and larger grey seals, that the average seal in the region weighs somewhere around 300lbs (136.36kg). (In the absence of a current survey the specific breakdown of the seal population is unknown.) So a single seal that consumes 6% of its body weight a day eats 18lbs (8.18kg) of fish a day. This means, that over the course of a year the seals conservatively consume 598,000 metric tons of various fish.  For comparison, in 2010 a total of 94,942 metric tons of groundfish were landing in all of New England of which about 5700 metric tons were codfish.  Seals undoubtedly have a more extensive diet than just ground-fish but the point is that NOAA does not know the feeding habits of the Gulf of Maine Seals.

Predation is not the sole detrimental effect the increased seal population is having on the area’s fish populations. There has also been a corresponding increase in what are commonly called, “seal” or “cod” worms. These parasitic worms infect a variety of groundfish species but are particularly fond of cod. Seal worms have been documented to increase the stress on infected fish and contribute to reduced rates of growth and higher mortality rates.

NOAA's most recent cod assessment says in regard to the effects of seals "The working group did discuss the possible impacts of seal predation on assumptions of natural mortality. There is a general presumption that seal populations have been increasing in the region over the past twenty years, though no definitive estimates exist to evaluate the trends or relative scale of a population increase. It is possible that increases in the seal population could lead to increased cod predation which could suggest that M [cod mortality rates] should be temporally increasing in the more recent time period. While these concerns were noted, there is no empirical basis to evaluate the current size of the seal populations and their trends over the last thirty years, nor are there estimates of the rate of seal consumption of cod and how that rate has varied through time. Additionally, while seals are known to prey on cod, they are generalist feeders and the importance of cod in the diet of Gulf of Maine grey seals is unknown. There is limited information that suggests that cod represent only a minor component of harbor seal diet along the Maine coast (Wood 2001)." To put simply, NOAA has no idea as to what effects the seals are having on the cod population, or on the fish populations as a whole, and since they have no idea that they simply do not include it in their calculations!

The failure to account increasing for effects of seal predation and related parasitic infections on the area’s fisheries calls into question NOAA and the New England Fishery Management Council’s understanding of ocean ecology and their ability to form an effective fisheries management strategy. Woods Hole Oceanographic Institute is aware of the potential issues regarding the seal population and the need for additional studies to be held.

It is impossible to look at the oceanic ecology of the Gulf of Maine without quickly realizing that it has been drastically altered by human activities over the last four hundred years. Like many heavily impacted ecosystems, it may no longer be a self-regulating system. The governmental agencies responsible for fisheries management are currently overly focused on direct human disturbances, discounting our indirect effects, and similar disturbances caused by “natural” effects. Proper fisheries management strategies for the Gulf of Maine and many other fisheries around the world can no longer simply be the management of direct human impacts upon a particular fish species (catch limits, days at sea restrictions, etc). Instead, an entirely new strategy is called for where the entire marine system is examined and relationships between its member species (and humans) is carefully mapped and their impacts on one another accessed to prevent overfishing of fish stocks and allowing the fish stocks of the Gulf of Main to recover. There is also a pressing need for more frequent surveys of the marine ecosystem. The current example of the cod population last prior to the most recent survey last being surveyed in 2008 and the seal population in 2001.  NOAA's failure to include the effects of the seal population upon the Gulf of Maine ecosystem is not the lone example of such errors. Furthermore, it is indicative of the systematic failure to properly account for the interrelationships between species.



NOAA Cod assessment
http://www.nero.noaa.gov/nero/hotnews/gomcod/GoM_cod_SAW53_AssessmentReport-WP1_11142011.pdf
Report on Seals
https://darchive.mblwhoilibrary.org/bitstream/handle/1912/3701/WHOI-2010-04.pdf?sequence=1