Forecasting the Genetic Impacts of Net Pen Failures on Gulf of Mexico Cobia Populations Using Individual-based Model Simulations

February 7, 2017

Forecasting the Genetic Impacts of Net Pen Failures on Gulf of Mexico Cobia Populations Using Individual-based Model Simulations - February 7, 2017

Please see the link to the actual report. In summary the study used a model on what would happen to the population of wild cobia in terms of genetic variation if escaped net pen fish would be introduced to the population. With increase number of escapes of fish that are spawned with non native broodstock led to a decrease in genetic variation in wild population. Less genetic variation decreases the ability to adapt, therefor increasing the risk of crashing a population. The papers solution for this is to rotate broodstock every couple of years and to use wild native broodstock. This removes the ability to select for genetic lines.


Net Pen/Salmon Problems Explained - November 10, 2016

The problems salmon raised in net pens plaguing fish and the environment are contained in a thought-provoking article by Outdoor Writer Ted Williams in the latest edition of Fly Rod & Reel magazine.

Williams harkens back to the first days of pen-raised Atlantic Salmon introduced in Norway and spread to Scotland, Iceland, Ireland, the Faeroe Islands, Canada, the U.S., Russia, Denmark, Chile and Australia when the hope was that the commercial venture would relieve commercial fishing pressure on wild stocks while providing tasty salmon fillets for the world’s consumers. The curse of unintended consequences continues the story changing the “Godsend blessing” salmon fishermen worldwide predicted into an environmental and economic 0nightmare after negative event followed negative event.

Williams admits the prediction that consumer and commercial pressure would decrease for wild stocks did occur. But, not in the way, anglers thought. The mix of swarms of sea lice attracted to densely-filled net pens and hybridization of wild stocks via open pen escapees wreaked absolute havoc on wild salmon on both sides of the Atlantic and, in fact, worldwide where net pen farming occurred. Williams’ article explains in plain language the phenomena and delves into the economic boons and busts of the farmed salmon industry.

Escapees, Genetic Mingling & Disease

In his article, Williams cites a February 2016 report from the Norwegian Institute for Nature Research detailing that country’s genetically compromised wild stocks. Of Norway’s 650 salmon rivers, a scant 35 percent had no genetic traces of hybridization by farmed escaped fish. In 2015, the government “reported” 120,000 steelhead trout and 160,000 salmon left the confines of their net pens (although scientists, according to Williams, put salmon escapes for that were closer to 800,000). Pancreas disease, gill disease, and infectious salmon anemia were key pathogens loosed into or contracted from the wild. Complicating the issue was the government warning to anglers not to eat escaped fish due to their diet of delousing drugs, not to mention antibiotic laden uneaten food and feces polluting the sea bottom.

Genetic intermingling by escaped salmon and other species of pen-farmed fish is prevalent everywhere. New Brunswick, Canada’s Magaguadavic river, after three decades of salmon farming, now has net pen escaped fish accounting for 98-99 percent of all salmon populating its waters.

Maine net pen aquaculture suffered the same insults as Norway. Salmon anemia, spread by sea lice, forced the destruction of 1.5 million fish in Cobscook Bay.

The U.S. Endangered Species Act (ESA) forced the state’s salmon farms refocus priorities. Faster growing alien European salmon were jettisoned for North American stock. Open net pens were replaced by better containment pens, but only in that State’s waters. Sea lice infestations in Maine were mitigated due to court-ordered “fallowing” that allowed bodies of water that skipped a period of stocking to cleanse itself of sea lice concentrations.

Sea Lice Infestation

Sea Lice, the tiny parasitic crustaceans that feed on the mucous, epidermal tissue and blood of host fish both wild and farmed, are a constant problem wherever concentrations of net pens exist. They provide double trouble in that they can spell death to thin-skinned wild and hatchery raised salmon and trout smolts heading from river to oceans. Equally as bad is the fact that the parasites transmit and lower immunity towards fatal disease in their hosts.

Huge concentrations of pen-captive salmon and steelhead trout provide the ideal feeding grounds for unnaturally dense sea lice congregations. Their deadly impact on young fish prompted Norwegian hatcheries to tow tanks of young salmon more than 30 kilometers past net pen areas before releasing them in the open ocean. Fish returning to fresh water rivers find the parasites detaching with the change. The problem is traversing past infecting fields created by net pens anchored between fresh water and far ocean salt water. Sure, as advocates of net pens argue, sea lice are a fact of Nature, but not in the swarms created by net pen aggregates.

Pesticides like “Slice” and antibiotics to treat the diseases afflicting net-pen raised fish have been effective for a while. That is until resistance in the sea lice and by disease vectors is established. Treatment is expensive. In Chile, the cost of antibiotics alone is estimated at nearly one US dollar per kilogram of fish produced. In 2014 Chile produced 895,000 tons of fish doused with 563,200 kilograms or 1.2 million pounds of antibiotics. Norway too shells out almost as much for long-term treatment of fish that survive. The cost goes down to pennies where fish die.

One touted “solution” to sea lice is the introduction of “cleaner” fish to eat the little crustaceans as they circulate in the pens. One suggested species is a small wrasse, traditionally a tropical and subtropical fish. Ignored is the idea of the environmental impact of this alien species loosed onto the wild as is inevitable.

Net pens whether open or closed are a bad environmental idea. Sure they make money and lots of it. But at what cost?

Attempts to introduce the technology to lakes farther inland from the oceans are seeing heavy lobbying by industry and pushback by environmental groups and residents fearing negative results to native eco-systems…including recreational anglers. Michigan is the latest state to say no.

The only true solution is moving aquaculture out of net pens and onto land. The argument against such a transition is the high initial cost of construction and on-going energy and maintenance requirements. On the other hand, land-based aquaculture has a number of options to create biosecurity from disease and definitely will not bring the problems associated with sea lice. So is the high investment argument truly that valid?


Join our e-mail list and never miss an update!

IFCNR © 2017 All Rights Reserved. Site Created by