The models used to evaluate fisheries were designed on the premise that the environment was relatively stable. However, ocean warming and other environmental changes are modifying the productivity of marine species, so it is necessary to incorporate these variables into fisheries management, says Francisco Arreguín, senior professor at the National Polytechnic Institute (IPN) attached to the Interdisciplinary Center for Marine Sciences (Cicimar).
Arreguín is working on the development of models that incorporate environmental variables to separate the effects of fishing from the effects of the environment on marine populations. He is currently participating in projects to evaluate shrimp fisheries in the Mexican Pacific, resources of the Upper Gulf of California and nearly 200 species of coastal fleets in different regions of the country.
This interview has been edited for synthesis and better reading.
— Why do current fishing models face difficulties in explaining what is happening to many species?
The sea temperature trend from 1920 to 1980 was, with some variabilities, horizontal, which could be considered a stable environment. And it was during those years that population models associated with fishing were developed. The carrying capacity of ecosystems was considered practically constant and, based on that, it was calculated how much could be extracted without compromising the renewal of populations. The problem is that those conditions no longer exist.
— What has changed?
The temperature of the ocean has shown an increasing and continuous trend since the 1980s. In addition, ecosystems are constantly changing. Each species responds differently: short-lived species tend to recover faster, while long-lived species have less capacity to compensate for adverse environmental conditions.
— What are the implications of this for fishing?
We can no longer assume that the productivity of a population is fixed. If environmental conditions reduce biomass and fishing maintains the same level of extraction, both factors contribute to the decline of species. Therefore, fishing effort must be adjusted to the biomass available in the sea so as not to affect the renewal rate of each species.
— You propose adaptive fisheries management. What does it consist of?
The idea is to carry out adaptive fisheries management focused on dynamic sustainability, which means establishing a catch rate that supports populations at their maximum production capacity depending on the available biomass. If the population declines, extraction must also decrease; if it recovers, rates can be adjusted again. It has to be dynamic.
— What information is needed to do this?
It is necessary to know the available biomass, to understand what environmental variables are affecting each species and to estimate how they could influence the future. Monitoring would have to be carried out year after year to adjust fishing effort in a timely manner.
— Does the National Fisheries Charter of the National Aquaculture and Fisheries Commission (Conapesca) already incorporate this approach?
Not yet sufficiently because it continues to define the state of resource exploitation based on conventional approaches. Since 2018, notes have been included stating that some environmental variables may be affecting certain resources, but mentioning them is not enough. They need to be incorporated directly into evaluation models.
— Why is it important to separate the environmental effects of fishing vessels?
Because a decline in resources is often interpreted as if it were an exclusive consequence of fishing. Models can help distinguish which part of the change is due to the environment and which to fishing extraction. This allows for more precise decisions to be made.
— What advances are there to put this approach into practice?
We are currently working with the Mexican Institute for Research in Sustainable Fisheries and Aquaculture (IMIPAS) to evaluate shrimp fisheries in the Mexican Pacific, incorporating environmental variables. We also participate in projects in the Upper Gulf of California and in a national initiative to evaluate around 200 species of coastal fishing with the participation of about 20 institutions and 50 researchers.
— What is the ultimate goal?
Generate information that can be incorporated directly into the management instruments. For each evaluated species, we seek to prepare sheets compatible with the format of the Conapesca National Fishing Charter.
*This item is part of the #CuandoCambiaElMar series.
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