Protected areas for lobsters increase claw size

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Lobsters in protected areas have bigger claws than lobsters in areas where they are fished, according to a new study. 

“For the first time, a study has shown that protected areas are beneficial to characteristics other than just body size”, explains research scientist Tonje Knutsen Sørdalen. 

It turns out that lobsters in protected areas have bigger claws than the ones that live in areas where they are fished, according to a new scientific article in the journal Evolutionary Applications. The researchers behind the study, who work at the Institute of Marine Research (IMR), the Centre for Coastal Research (CCR) at the University of Agder, and the University of Oslo, believe this is an important discovery:

“This is also good news for lady lobsters, as they prefer males with extra large claws”, says Sørdalen.

Attracts the ladies 

Past research has shown that claw size plays a crucial role in determining which male lobsters are able to mate. Other studies have shown that creating marine protected areas for lobsters results in more, bigger individuals, and that lobsters with big claws are more likely to walk into lobster pots.

The researchers soon suspected that claws play a key role in various processes and that creating protected areas may affect claw size. 
 

Here, outside Flødevigen research station is one of the marine protection areas included in the study. Photo: Anders Martinsen/UAS Norway 

Sørdalen explains that they have documented this very thoroughly. Over the course of three years, they have analysed measurements of almost 2,700 lobsters from the three oldest protected areas along the Skagerrak coast. What they have observed has confirmed their suspicion:

In the protected areas, the lobsters have bigger claws than lobsters of the same size in the surrounding areas, where fishing is allowed. Both sexes had larger claws in the protected areas. However, the difference was biggest in the males. In 37 cm-long males, there was an eight percent difference in claw size.
 

One of the marine protection areas marked in a sea map. Photo: Gulesider Sjøkart 

Show me your claws, and I'll tell you who you are

According to the saying, you shouldn’t judge a book by its cover, but perhaps you should judge a lobster by its claws.

The size of a lobster’s claws also reflects its other characteristics and genes, which in turn affect how well adapted it is to its environment. But why do lobsters in areas where fishing is permitted have smaller claws than their protected cousins?

“The explanation probably lies in the behaviour of the males that makes them vulnerable to fishing”, says Sørdalen. 
 

Big claws can be a blessing and a curse. Photo: Tonje Knutsen Sørdalen/IMR

Strict hierarchy

Although lobsters like to keep their own company, there is a strict hierarchy on the sea floor. Males with particularly large claws have the highest rank, and hence most privileges. For instance, they win the battles for the best hiding places. This is attractive to females looking for a mate. 

So where does it go wrong?

“Well, having a powerful weapon like big claws is accompanied by high levels of aggression and overconfidence. Alpha males are simply more inclined to explore and take risks”, says the research scientist. 

And this is where a tempting lobster pot with a nice-smelling bait comes into the picture. 

“It’s plausible that the alpha males prevent other lobsters from going in, meaning that they themselves end up on the dinner table.”
 

From Bolærne in August 2019, one of the MPA's. Photo: IMR

Also attractive for lobster lovers

In the animal world, so-called sexual selection expresses itself in many ways. Deer with big antlers are preferred by the does, and they excel in fights. And in the same way that big antlers are seen as trophies by hunters, many lobster lovers prefer a juicy lobster claw.

However, there is a risk that claw size will continue to shrink if the fishing pressure carries on increasing, thinks Sørdalen:

“The lobster population is still at record low levels with few signs of improvement. If claw size is genetically determined, the result may be that the genes for large claws disappear.”

In other words, protecting individuals with large claws may not only ensure a more robust population, it may also result in a more valuable catch.

Crown Prince Haakon visited IMR, and got a close meeting with one of the lobsters from the MPA. Photo: Liv Eva Welhaven Løchen/IMR

Protected areas produce results quickly

When the protected area off Flødevigen in Arendal was established, it didn’t take many years for researchers to see a noticeable impact on the population. Sørdalen believes that having more protected areas along the coast could be a good option:

“This study shows that many factors affect a fishery and that there is still lots to learn about some of our best-loved species. It is important for us to understand how species change in response to human influence if we want to establish a good, sustainable management regime. Particularly with marine species, our knowledge is lacking.”
 

Reference

Sørdalen T. K., Halvorsen K. T., Vøllestad L.A., Moland E. & Olsen E.M. (2020) Marine protected areas rescue a sexually selected trait in European lobster. Evolutionary Applications 13 (5):1-12.

Link: https://onlinelibrary.wiley.com/doi/full/10.1111/eva.12992