Truncation of sizes by fishery could leave the marine ecosystem in Chile without large Crabs

The FONDECYT project carried out from 2017 to 2020 includes a study on the effects of fishing on the reproduction of the Crab (known in the marketssuch as Cangrejo Real del Sur) and was born with the need to generate knowledge for the management of the fishery and propose improvements in the efforts ofmonitoring carried out in the Los Lagos and Aysén Region.

The article entitled “The impact of size truncation on the reproductive success of the
Crab” was prepared by Carlos Molinet, Rubén H. Roa-Ureta , Paulina Gebauer, Manuel
Diaz, Patricio A. Diaz, Thamara Matamala, Katherine Espinoza, Jorge Henriquez, Daniela
Uribe, Oscar de Lázaro, Andrés Olguínf, Kurt Paschke, José Valenzuela and Yohnatan Jaramillo. And published in the prestigious Fisheries Research magazine.

The spider crab (similar to the king crab that is caught in the United States) is a species of very
high economic value, which has traditionally been exploited in Magallanes, however, in
In 2010, the fishery in the Los Lagos and Aysén Region increased by at least 10 times.

Size truncation

Fisheries are generally selective, that is, they select the individuals most
large, in fact a minimum legal size is established because it seeks to protect the
small individuals to reproduce at least once or twice during their lives
before they are caught. In addition, in the case of these crustaceans, it is a fishery of
only males and females should be returned to the water, as well as specimens of
smaller size.

The females of the Centolla resource prefer to reproduce with larger males, for
which, when the large males decrease excessively, the larger females
(which are the most fecund) are less likely to reproduce.

Furthermore, if the males are very small, they cannot copulate with the females, and/or that they do not
can protect when they shed their shell, then the
reproductive capacity of these crustaceans.

“Our results show that there is a proportion of large females that do not have eggs, the hypothesis is that they do not have eggs because there are no large males that can fertilize them,” said the leader of the investigation, Carlos Molinet.

Due to the selection pressure exerted by the fishery, which removes the individuals that
grow faster and reach legal catch size, it is expected that it would be less and less
It is common to find large crabs, therefore, the fishery is dwarfed, that is why
called length truncation.

It is said that it is also a truncation of ages, because the sizes are related to the
ages, but since it is not known exactly how old they are, then they talk about
size truncation.

In terms of production for the future, the academic mentioned that “it is bad for the
fishery because it implies that in the medium long term, individuals take longer to
grow, what used to grow in five years, now grows in 6, 7, or more years, that is, it is
making an inefficient fishery”.

On the other hand, the researcher also mentioned that we are far behind
knowledge of biodiversity associated with this resource and the effects of the excessive removal of crabs from Patagonian ecosystems, “in Chile the knowledge about the
Biodiversity affected or related to fisheries is very superficial, we know so
little of how these species interact that we are well restricted in information
regarding the consequences of crab fishing on the ecosystem.

However, the results suggest that the King Crab population of the Los Lagos Region is very truncated in its sizes, which means that it could even be collapsed if compared with the results obtained in the Aysén Region. In this sense, the reproductive health indicators proposed in the research could be a good tool to contribute to the management of the fishery”.

Reduce and regulate the effort: a possible solution

Currently, for the spider crab in the Aysén and Los Lagos Region, there is a closed season,
that the researcher classifies as insufficient since it is between December and January, without
consider that crabs go up to depths of 15 to 20 meters and mate in
September or October, leaving them more vulnerable. Therefore, the ban should be from
October at least until February, (to protect females recently shed in January)
“We have legislation that is too lax for the fishery,” said the academic.

Carlos Molinet mentioned that the administrative measures for the fishery should include
escape rings (through which small crabs escape), traps with materials that
avoid ghost fishing (material that degrades when traps are lost) as
does in Argentina.

Finally, Molinet carried out an analysis regarding the great gap between the
research and the download to the users, “the users, who are the artisanal fishermen,
they are difficult to regulate on our shores. In addition, the management of the fishery in Chile has
been historically hierarchical, then all decisions have been made in a hierarchical way.
decentralized, which has made users feel neither responsible nor committed to the measures that come from the centralized power of the Undersecretary
fishing. The management plans contributed superficially to improve this situation, however, the state’s neglect of these plans results in a new wave of
mistrust and lack of credibility”