Foodies are in tears! Why are hairy crabs so thin this Mid-Autumn Festival?

When the autumn wind blows, crabs' feet start to itch, and it's time to eat crabs again.

But I'm sorry, this year's Mid-Autumn Festival, hairy crabs may disappoint you——

"The high temperature has made hairy crabs thin and hungry", "No matter how hard hairy crabs try, they will miss the Mid-Autumn Festival"... What's going on?

01

What impact does high temperature have on hairy crabs?

The official Chinese name of hairy crab is " Chinese mitten crab " (Eriocheir sinensis), which is distributed in many rivers and lakes in China.

Regarding the origin of the name "hairy crab", there is a saying that in the past, fishermen would boil this kind of crab directly in water after catching it and eat it. In Wu dialect, this cooking method is called "煠(zhá)", so it is called "煠蟹", which later evolved into "闸蟹" during the process of transmission.

Another theory is that before catching crabs, one must first build a large gate with bamboo branches and straw, set a net on one side of the gate, and light a lantern at night. The crabs in the lake are lured and swim towards the gate and are caught in the net, so they are called "hairy crabs."

Copyright image, no permission to reprint

Chinese hairy crabs can survive in a temperature range of 5℃-30℃, with the most suitable temperature being 20℃-25℃. When the temperature is higher than 30℃, Chinese hairy crabs will experience symptoms such as anorexia, joint softening, motor weakness, and slow growth . If the temperature is higher than 35℃, they will hardly eat, only consuming the original energy in their bodies, and will not have the strength to molt. However, for arthropods such as Chinese hairy crabs, they need to molt 5 times during their growth cycle to reach the best size for eating.

In the natural environment, animals will try to avoid bad weather to reduce its impact on themselves, such as going to deep water areas, or digging holes and hiding in the mud at the bottom of the river to avoid the high temperature. However, the hairy crabs we eat are almost all artificially cultivated, and the crab ponds are mostly cement pools, so it is difficult to "avoid the heat" by moving or digging holes.

After understanding the living habits of hairy crabs, and comparing them with the high temperatures of over 40°C this summer in Hubei, Hunan, Jiangsu and other places which are the main hairy crab producing areas , it is not difficult to understand why their size has "shrunk" this year and their time to market has been delayed.

The average temperature across the country this summer (June 1 to August 31) was 22.3°C, 1.1°C higher than the same period last year.

This is the highest level in the same period since complete meteorological observation records were kept in 1961. Image source: Weibo @中国天气

Distribution of extremely high temperature days across the country. Image source: Weibo @中国天气

Excessively high temperatures will not only affect the hairy crabs themselves, but also their living environment .

The aquatic plants placed in the crab pond are not only feed for the hairy crabs, but also provide shade for the crabs and purify the water quality. However, the aquatic plants are not resistant to high temperatures and can easily rot and deteriorate .

At the same time, high temperatures can easily cause a surge in the number of plankton in the water. The impact may not be obvious in larger water bodies, but in smaller and relatively closed water environments such as crab ponds, the large appearance of plankton may consume a large amount of oxygen in the water, causing hypoxia in the water , affecting the growth of hairy crabs, and in severe cases may even lead to the death of hairy crabs.

In addition, hairy crabs are very afraid of heat during transportation. If you observe carefully, you will find that the crabs are mailed in plastic foam insulation boxes, and several ice packs are added inside to maintain the temperature and humidity in the box during transportation to prevent the crabs from dying. The continuous high temperature weather also increases the loss of hairy crabs during transportation .

Yangcheng Lake hairy crab pond. Copyright image, no permission to reprint

Of course, rising temperatures are not the only reason for changes in the hairy crab market. Another very important reason is that there has been less rainfall in the south this year .

High temperatures and less rainfall have reduced the amount of water in many lakes and rivers, and the area of ​​water bodies has also been greatly reduced. For example, the water level in some areas of Dongting Lake has reached the lowest level in the same period in history, 7.82 meters lower, and the area of ​​water bodies connected to the Poyang Lake has shrunk by nearly 90% compared with the same period last year . Other waters in the middle and lower reaches of the Yangtze River have also been greatly affected .

Under such circumstances, the water surface available for breeding hairy crabs will decrease, and a decrease in hairy crab production will be a foregone conclusion.

This year, the precipitation in the Yangtze River Basin (358.9 mm) was 32.5% lower than the same period of previous years, the lowest since 1961.

Precipitation in the Taihu Lake Basin (296.8 mm) was 47.3% lower than the same period last year, ranking fourth lowest in the same period in history.

Image source: Weibo @中国天气

This year's high temperatures have also affected sea crabs .

Common sea crabs include swimming crabs, swimming crabs, red star crabs, Japanese crabs, rusty crabs, etc. Unlike hairy crabs, these sea crabs are mainly caught. The catch in Zhoushan, Shengsi and other areas is less than 80% of last year, and the quality is not as good as the same period last year .

The high temperature also increases the loss of these crabs during transportation, further raising the "crab price".

02

How can you pick delicious hairy crabs?

Facing the price of hairy crabs this year, it can be said: "Hairy crabs, it's not easy to say I love you."

But if you still want to enjoy the delicious food, how can you avoid losing both the crab and the money? It is important to know how to choose hairy crabs.

We know that the deliciousness of hairy crabs, in addition to crab meat, mainly comes from "crab roe" and "crab paste". The "crab roe" of female crabs is the orange-yellow hepatopancreas and orange gonads (ovaries), while the "roe" of male crabs is the hepatopancreas. The "crab paste" is the accessory gonads .

Copyright image, no permission to reprint

There are two important indicators that affect the flavor of hairy crabs: fullness and sweetness .

In layman's terms, fullness refers to the amount of meat and roe, while sweetness refers to the flavor of the meat and roe. High-quality hairy crabs have a sweet aftertaste of roe and paste, while crabs of poor quality taste salty or bitter.

The fullness of hairy crabs can be ensured by eating enough plant-based feed, but the sweetness must be supplemented by animal bait .

In order to ensure the taste of this year's hairy crabs and minimize the impact of temperature, crab farmers are trying their best:

For example, aquatic plants such as reeds, Hydrilla verticillata, Elodea, and Vallisneria can be planted in crab ponds. Plants can lower the temperature of some water bodies in the ponds and provide shade and shelter for hairy crabs. The temperature of the water in the crab ponds can be lowered by strengthening the water circulation in the crab ponds. Aerators can be installed to increase the oxygen content of the water in the crab ponds and promote water circulation by stirring.

After all this "trouble", the condition of the hairy crabs in the pond will improve.

Copyright image, no permission to reprint

Before the hairy crabs are put on the market, crab farmers will feed them large amounts of animal bait such as fish, shrimp, snails, and clams to ensure the sweetness of the crabs .

Here I share with you a method of choosing hairy crabs——

There are four characteristics of hairy crabs in good condition:

One is the green back, the crab shell is green, smooth and shiny;

The second is the white belly, the umbilical carapace attached to the mud, crystal white;

The third is yellow hair, the hair on the crab legs is long and yellow, each hair is straight and upright;

The fourth is the golden claws. The crab claws are golden, solid and powerful.

The crab should feel heavy in your hand, so that it is full and not empty. You can also turn the crab over without a rope, with its belly facing up . If the crab can turn over quickly and flexibly, it means that the crab is full of vitality and fresh.

The continued high temperature will indeed cause us some trouble in eating crabs. However, some meteorological experts believe that the continued high temperature like this year will not become the norm, and maybe we can continue to eat crabs happily next year.

Of course, in order to always be able to eat "good crabs" that are both plump and cheap, each of us should also try our best to contribute our part to protecting the environment.

Author: Erzhu

Review | Chen Shengjun Associate Researcher, South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences

Source: Science Popularization China

The cover image and some images in this article are from the copyright library

Reproduction of image content is not authorized