Amerikansk hummer

Recognize an American lobster

It's not always easy to tell the American lobster (Homarus americanus) apart from the European lobster (Homarus gammarus), as both species can vary in appearance.

The clearest sign of an American lobster is that its rostrum (frontal spine) has one or two extra small spines. The European lobster has a single, unbranched rostrum. The spots on the head of the European lobster are completely white, while those on the American lobster are more yellowish. Body color can vary a lot, but generally, an American lobster is more brownish—especially the tail fan (the five plates at the end of the tail). If those plates have a brownish base color, it’s likely an American lobster (see image). If they are blue or dark brown, it’s more likely a European lobster.

At the top an American lobster (Homarus americanus), and at the bottom a European lobster (Homarus gammarus).

(The image is a photomontage. Photo of American lobster: Whitney Cranshaw, Colorado State University, Bugwood.org (Creative Commons Attribution 3.0 License). Photo of European lobster: Arnstein Rønning (Creative Commons Attribution 3.0 Unported license))

Why is the American lobster a threat?

Diseases

The American lobster can carry infectious diseases and parasites that may spread to the European lobster. One example is the bacterial disease Gaffkemia, which is 100% fatal to European lobsters. Shell disease can cause severe damage to the shell and, in serious cases, lead to death. These diseases do not affect American lobsters to the same extent but are life-threatening to European lobster.

Competition

American lobsters live in the same type of environments as European lobsters, creating a high risk of competition for shelter, food, and mating partners.

Hybridization

In Skagerrak, American and European lobsters have already produced offspring together, but the consequences of hybrids spreading in our waters are still unknown.

Since the American lobster can also live at depths of several hundred meters, they may avoid being caught in lobster pots. This allows them to grow undisturbed, making the establishment of American lobsters in Swedish waters particularly difficult to stop.

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Report it!

The American lobster has not yet established itself as a non-native species in Swedish waters. That’s why it’s especially important to contact the Institute of Marine Research (SLU) in Lysekil immediately if you catch a suspected American lobster or diseased lobster.

What to do:

• If you catch a suspected American lobster or one that appears diseased, call SLU’s Institute of Marine Research in Lysekil right away—regardless of the lobster’s size or whether it’s carrying eggs.
• The Institute of Marine Research emergency line: +46 10-478 40 48
• The staff at the Institute of Marine Research will assess your catch, and if the find is relevant, you will be granted permission to bring the lobster ashore.
• SLU offers a reward of 800 SEK per kilo for lobsters suspected to be American, after approval by phone.
• Place the lobster in a plastic bag, keep it cool, and either deliver it to the Institute of Marine Research or store it in a refrigerator until SLU staff can collect it.

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Where does the American lobster come from?

The American lobster is found along the east coast of North America (USA and Canada) and is often imported—alive—to Europe and Sweden. Natural migration from North America is entirely ruled out.

How does the American lobster spread to Swedish waters?

American lobsters may be deliberately released or escape from illegal sea pens. Some captured specimens in Sweden have still had claw bands from North American exporters. In Sweden, it is illegal to store live imported lobsters in the sea.

Make a difference

Prevent further spread in Swedish waters – do not release or store American lobsters in the sea!

How many American lobsters have been caught?

Since the first reports in 2008, a total of 36 American lobsters have been recorded between Marstrand and Smögen.
- 23 were caught in 2014, 19 of them in Gullmarsfjorden.
- 5 were reported in 2015
- 3 in 2016, 2 of which were also from Gullmarsfjorden.
- No American lobsters have been reported since 2017.

SLU’s response and work on American lobsters is carried out on behalf of the Swedish Agency for Marine and Water Management, which monitors the spread of invasive species in marine and freshwater environments.