Yangtze River Swordfish is a famous Guijiang fresh in my country. It is known as " Yangtze River Sanqi " together with Yangtze River Anchovy and pufferfish. Every year around Qingming Festival, the best time to catch knife fish . At this time, the meat is the tenderest, the thin bones are as thin as hairs, which is the best. Because the swordfish was first launched, it was listed as the "first of the Three Fresh".
Blade fish has a long history in our country, and it is mostly recorded in ancient books. "Historical Records" "Biography of Merchants and Biography " once described that the sword fishing industry had already emerged during the Western Han Dynasty and residents along the coast liked to eat. But it was such a well-known "famous fish" that quickly fell into depletion in the 1990s, and the spectacular fish flood became history.
The dilemma of the Yangtze River Swordfish: The crisis in the 1970s
The importance of the Yangtze River Swordfish may be beyond everyone's imagination. This fish is famous not only because of its unique meat quality, but also because of its amazing yield. As early as the 1970s, domestic research institutes formed a resource investigation team with the goal of evaluating the resources of sharkfish and trying to find a reasonable way to use them.
According to field investigation, the Yangtze River swordfish firmly ranks as the "Jiangxian Champion" in the middle and lower reaches of the Yangtze River, especially in Jiangsu and Anhui provinces. The swordfish exclusively accounts for 35%~50% of the total fishing volume, which determines the level of fishermen's harvest. In terms of quantity, swordfish replaced large and medium-sized fish with absolute advantage, and the relative importance index (IRI) far exceeds , the four major fish .
Throughout the 1970s and 1980s, the Yangtze River swordfish "lead the lead" in the middle and lower reaches, and the cities of Zhenjiang , Yangzhou , Changshu and other cities benefited greatly. In 1973, the production of blade fish hit a peak of 3,750 tons, which was only the catch of adult fish. According to old fishermen, the yield of juvenile juvenile juvenile juveniles is even better. Most of the juvenile juveniles caught are juveniles, but their economic value is not high. Statistics show that about 10,000 tons of juvenile fish are caught and landed every year, which is 2 to 3 times the output of adult fish, which also reflects the strong resource base of juvenile fish.
Yangtze River swordfish seem endless, but experts still keenly sensed the crisis and realized that the resources of swordfish are not inexhaustible. To achieve high yield and stable production, we must protect the swordfish and the spawning ground.
The concerns of experts are not without scientific reasons. Among the catches, one detail was found by the investigation team: the resource changes of knife fish showed signs of "lower". Taking the swordfish at 3 to 4 years of winter age as an example, the average body length in 1973 was 314.5mm, it dropped to 310.3mm in 1974, and further reached 306.5mm in 1975, which shows that the size of the parent fish is getting smaller and smaller, which means the decline of reproductive power.
On the other hand, the rise of sailboats and trawlers has greatly improved the fishing capacity, and the single-ship productivity is about 5-8 times that of the 1950s. High yield is not the result of the growth of the blade fish population, but because the fishing intensity is even greater, blade fish has been overfished.
Now it seems that the older generation of experts have a certain foresight: "If fishing is uncontrollably, it will surpass the reproductive and regulation ability of knife fish, it will eventually cause changes in resources." Based on this, some experts suggest that knife fish should be caught reasonably, and it is best to catch a fixed quota to protect the young and parent fish of knife fish. At the same time, the management of gates and dams should be improved and supporting fish passing facilities should be built.
But these suggestions did not play a practical role. The results can be imagined that the production of knife fish took a sharp turn for the worse and the decline exceeded expectations. In the 1980s, the production of Yangtze River swordfish plummeted by 90%, with only about 370 tons remaining. In the 1990s, fish floods in Hunan, Hubei and Anhui disappeared one after another, and fish floods in Zhenjiang, Jiangsu also disappeared in 1996.
Zhenjiang knife fish historical catch
Yangtze river knife fish is in a resource crisis, which is a microcosm of the ecological changes of the Yangtze River. Fortunately, the fishing ban system saved the swordfish population at a critical moment, and wild resources were restored, and the fishing ban effect was significant.
catch 400 kilograms in one net! After three years of fishing ban, a large number of Yangtze River swordfish appeared in
my country's protection of Yangtze River swordfish began in 2002. The whole river had banned fish in spring for 3 months. The fishing ban in the middle and lower reaches was from April to June. It was adjusted to March to June in 2015, effectively protecting the breeding period of bladefish.
However, the fishing intensity remains high, and the short-term fishing ban has not fundamentally changed the trend of resource recession.It was not until 2019 that my country provided special protection for swordfish, and all swordfish fishing license was revoked, and the amount of resources began to increase.
To clarify the effect of fishing ban, researchers surveyed the knife fish population of Poyang Lake in 2019 to 2020. The sampling water area was 65km long and 3~14km wide. It was historically the spawning ground for shaved fish. The results show that the number of knife fish in the lake area has increased significantly. The average number of 28 ships caught 8.1 per time, which increased to more than 140 in 2020, and the number of 16 times that of in one year, and the resource recovery was rapid.
People's Daily Online: For the first time in the past decade, a large number of swordfish groups were found in Poyang Lake
Compared with the situation before the fishing ban, the effect is clear at a glance. Because from 2010 to 2014, knife fish in this water were very rare, and a single boat could only catch 1.6 every day (average value), and in 2017 it was only 0.15 , and the fishing efficiency was quite bleak.
knife fish resources are recovered rapidly, which is closely related to the reproductive characteristics. Compared with , saury, saberfish, saberfish has a shorter lifespan, with an average of only 4 to 5 years, with a fast reproduction rate and high egg spawning rate. Therefore, as long as the fishing ban is properly protected, you can see obvious results after three years.
A few days ago, Chinese Academy of Sciences conducted fish monitoring in the Chongming section of Shanghai. A total of 7400 kilograms of were caught in one net. This was never possible in the past! Coincidentally, scientific researchers monitored a knife fish for the second time at Jiayu Station in the middle reaches of the Yangtze River. The specification reached 40cm, and it is estimated that it is 4 to 5 years old and has the ability to lay eggs.
Above mentioned that the Yangtze River swordfish disappeared from Hubei in the 1990s and has now returned to the middle reaches of the Yangtze River after 30 years. This shows that the breeding population is expanding, the migration distance is extending, and the spawning ground in the middle reaches is expected to be "activated". During the ten-year protection period of the Yangtze River fishing ban, knife fish can reproduce for more than 5 generations, laying an average of 20,000 to 30,000 eggs per time, which can achieve population amplification well. The future results are worth looking forward to. Difficulties in the effect of
fishing ban: distinguishing between long-jawed horns and short-jawed horns and short-jawed horns and
knife fish are not isolated populations, but are distributed in Tonghai River, such as the Yangtze River, Yellow River, Qiantang River, , etc., forming a diverse geographical population. Among them, the Yangtze River has the highest yield of swordfish and is also the most well-known.
The scientific name of the Yangtze River Knife is long-jaw kelp (Coilia macrognathos Bleeker), but it is not easy to determine the species according to the appearance, because this fish is easily confused with short-jaw kelp (Coilia brachygnathus), lake kelp kelp (Coilia ectenes taihuenshinml2). On morphology , the general identification indicator is to look at the relative length of the jaw, that is, judged by the ratio of maxilla length/skull length (S/H). The S/H value of long jaw thorns is 1.012~1.524, short jaw thorns are 0.728~0.997, and lake jaws are 1.021~1.379.
The ratios of snails of different body lengths are also different, which increases the difficulty of identification. The ratio of jaw/head length of the three is highly similar. The lake and long-jaw snails are difficult to distinguish, and the upper limit of the short-jaw snails index 0.997 and the lower limit of the long-jaw snails 1.012 are also very close, and it is impossible to accurately distinguish with the naked eye alone.
It is also difficult to completely distinguish the relationship between the three based on ecological habits and distributed waters.
First of all, the easiest to distinguish is the lake savage, which represents the species Taihu Lake savage. Taihu is not directly connected to the main stream of the Yangtze River and is highly closed. The lake snail (also known as plum snail and wool fish) is completely adapted to the closed environment, with a yield of up to 720,000 to 50,000 tons of , which is small in size and low in price, and will also eat a lot during breeding.
long-jawed and short-jawed horns are difficult to distinguish. The two have similar body shapes and habits. The population has mixed habits and , and they all have ecological groups of migratory and settled horny horn8. However, it is generally believed that only migratory swordfish are the "Yangtze River swordfish" with the highest market price, but they do not know that there are both long-jawed and short-jawed swordfish. Similarly, not only short-jawed thorns settled in the lake, but some may also be long-jawed thorns.
Coilia macrognathos Bleeker
The difference between the two is that migratory long-jawed thorns live in the ocean and reproduce from February to September. They only cluster on a large scale when laying eggs along the river, and the parent fish do not eat. The "drinking without eating" recorded in ancient books is empirical. Short-jawed snails live in freshwater and reproduce from May to October, and there is no cluster phenomenon.
So, how can we accurately distinguish the real "Yangtze River Sword Fish"? Otolith detection provides new ideas. Scientists have found that the ratio of Sr/Ca elements in otolith is generally less than 3; in brackish environments, Sr/Ca is generally 3~7; in seawater environments, this ratio is generally 3~7; in seawater environments, this ratio is generally greater than 7.
(a) Long-jawed horn (b) Short-jawed horn (c) Lake-jawed horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn horn , then by detecting the Sr and Ca content ratio in the otoliths can be determined whether the knife fish has experienced the migration process from seawater to freshwater , and then combined with morphological characteristics , migratory long-jawed horn horn . Of course, if you only pay attention to taste and flavor and do not worry about species ownership, then the observation of migration is enough to identify the "high-value" swordfish.
Natural reproduction: the key to solving the "resource dilemma"
The recovery of knife fish population depends on natural reproduction. First, because artificial reproduction efficiency is low, the breeding cycle is long, and the technical cost is high, and the dilemma cannot be fundamentally solved; second, because knife fish are naturally delicate and die when they come out of water, and the survival rate of young and adult fish is difficult to guarantee; third, because it is difficult to simulate natural ecological changes in the artificial environment, such as: salinity changes during migration, and a slight carelessness may affect the reproduction effect.
Therefore, the secret of the natural reproduction of swordfish is the key to solving the "resource dilemma". Historically, from , the Yangtze River Estuary to Dongting Lake, Hunan, along the route, there are all places for the production of swordfish. With the improvement of the ecology, the spawning grounds in the lower and middle reaches of the Yangtze River have recovered steadily. I believe that there will be more and more good news in the future!
