There is an old principle in fishing that many anglers use. That means that small fish can continue to live, while we reel in only the older ones. We previously assumed that larger and older fish could no longer contribute much to the renewal of the fish population, but that is likely to be a mistake now. Researchers in Germany have recently found out some contradicting facts to that belief. Berlin scientists carried out numerous studies with colleagues from other countries and came to the opposite conclusion about large old fish, especially about older female fish, which we underestimated for a long time.
Therefore, the researchers advocate sparing fat old fish more in the future, because we can protect ecosystems more effectively and thus ensure a faster recovery as studies have shown that the number of eggs increases with the mass of a female fish. This is particularly evident in the case of fish such as cod and pike. Conversely, that means that when we fish older females, the population suffers as well. Fishing for large spawning fish hurts the total number of eggs released.
The authors published their new study in the journal proceedings of the US National Academy of Science. The deviation from the previous level of knowledge is astonishing. So far, scientists have assumed that the number of eggs increases with the weight of the fish. While that is correct in some cases, an essential factor is missing in the calculation because the number of eggs does not increase proportionally with weight but rather disproportionately. At the same time, experts have also overestimated the spawning potential of smaller fish to be much lower, especially in fish, whose fertility increases with size. According to the new study, the Pacific sardine is an excellent example of that.
During their study, the scientists examined a total of 32 species. They found that we have overestimated the spawning potential of small fish by 22 percent. The consequences of these misjudgments could have had dramatic damaging effects. After all, we base many catch quotas on these estimates, and it could be that many allowances have been set too high.
In their opinion, these percentile connections are essential to recognizing the weak links in ecosystems. Therefore, the researchers suggest that we should determine the number of eggs depending on the mass of the fish, which would make it easier to reclassify which fish types will need more protection in the future. Both nature conservation and the fishing industry could benefit from this new calculation method. Scientists are therefore increasingly recommending selective fishing strategies, so that fishers would not only spare the young but also some bigger fish. As a solution, protection zones and closed seasons for angling large fish can give them the retreat and safety they need. These new findings are essential for sustainable fishery, too. According to the World Food Organization, around a third of the world’s fish is regularly over-fished, as this type of marine life is the most important source of protein for around three billion people.