What else biodiversity changes could reveal about the effects of marine fisheries?

Biodiversity is essential for the adequate provision of various ecosystem services which we depend substantially upon for, among others, the development of fisheries, extractivism and agriculture. Our connection with nature in general and with biodiversity specifically is as old as our prehistoric hunter-gatherer origins, as humans have always observed and tried to understand the rhythm of nature in our quest for benefits that improve our welfare. There is nothing intrinsically wrong or very different from the behavior of so many other species in doing this. Our problems only began to emerge when profit and unnecessary consumption needs associated with population growth got into the equation and unbalanced the game between humans and the rest of nature.

At some point, we began to indulge excessively in nature provisions, as if they were permanent, secure, and unchanging, until one day, belatedly, we realized that something was not going well between us and the relationships we have with ecosystems. Such relationships are supposed to be as harmonious as possible, but there is unequivocal evidence that this has not been the case for a while. Whole populations of species are disappearing because of the constant disturbances we cause on them. There are countless fish species that have a smaller body size today than they had in the past, because we prefer to catch and eat the larger ones (which are also the most fertile individuals). These non-isolated facts are signs that we have been weakening the vital functions that nature provides us and we do that by affecting the biological interactions that keep them operating. 

A universal premise assumed by the typology of the tree of life is here generically summarized as "only from life can more life emerge". This could even be considered the first general law of biology, since all micro and macroscopic life forms depend on their precursors, to subsidize the rates of diversification in a region. This is how speciation happens. There are striking differences between the "types of life" (i.e., animal, plant...) that inhabit the planet, including the various types of attributes we use to differentiate and recognize them, which are products of selective forces that operate in the systems that harbor them. In these environments, innumerable natural factors constantly act to determine how much life can exist for short or long periods across geographical scales. 

In all terrestrial and aquatic biomes, thousands of life forms have diversified to form the exuberant biodiversity that pulsates everywhere, although at first this was done so that they could "adapt", colonizing territories and establishing their niches. Accidentally, they have made available all the resources that we benefit from today, from the air that is breathed into matter that decomposes. On the other hand, all human acts that disturb or alter biodiversity, produce countless consequences that affect the organization of many communities and the functioning of vast ecosystems, especially in the tropical region. 

This is worrying because as species signal the devastating effects of impacts, we remain unaware of how the pathways of biodiversity change, especially those caused by selective fishing pressures, resulting in the depletion of fish stocks, for example. Thus, the interactions between the factors (human-fishing-biodiversity) are relevant to be scientifically understood, since their relations can affect species that directly or indirectly promote the desired goals of fishing sustainability. It is essential to elucidate how these relationships take place over time and space, in order to identify which aspects of biodiversity respond more directly or strongly to the effects of fishing, and which remain indifferent or neutral to it in some hotspot, if any at all, given the current levels of depletion and of global changes. 

It is reasonable to assume that fishing acts differently on diverse parameters of diversity, including other dimensions beyond species level, such as evolutionary legacy, nest variability, and morphological heterogeneities, which, when dissociated, represent what we call, respectively, phylogenetic and functional diversity. These exercise complementary roles and, when observed together, are considered essential variables to estimate and understand the main aspects related to biodiversity (Schmeller et al., 2018), and can overcome preconceived ideas about the consequences of fishing-mediated declines on us and on ecosystems. 

Mechanistically, it is possible to classify the correlation of fishing with biodiversity as an essential connection, which the stronger and more positively imbricated, the more it favors us. Otherwise, these forces inevitably annihilate or seriously compromise each other, depending on how intense and stable the associations between them are. The performance of this union is presented in two main ways. One route ensures that nature replaces stocks free of charge, through the natural regulation of biomass, diversity and co-occurrence of all fish species in addition to those of fishing interest. The species we catch and consume may be more or less similar to each other, such as mullet, sea bass and marlin, because of their position in phylogenetic trees. Such positions inform us how long ago individuals have differed from each other and therefore, on how much evolutionary history we are currently putting pressure on. In this way, each species participates as a small part of the big machinery known as biodiversity. And in each place of such machinery, various forces of nature synchronize in the same way to form communities, assemblies or multi-specific aggregates of fish targeted by fisheries.

Local gains from fishing tend to directly reflect the conservation status of a region's biodiversity, since local natural processes ultimately determine the diversity of individuals that may be caught. By maximizing the development of attributes that ensure the survival and plasticity of responses to dominant conditions (ie, fitness = individuals most suited to the highest reproductive yields), organisms end up developing in parallel, and especially to human eyes, valuable attributes such as size. But to the extent that we "preferentially" fish these attributes (eg, heavier and larger fish), there is a negative repercussion on the evolutionary aspects of the groups that are exploited by the activity. Over time, fish diversity and quantity decrease, and both fishing and wild communities are hampered by processes triggered by loss of composition and reduction of biotic heterogeneity in stocks. On its turn, this increases pressure on certain groups.

The process described above, of the influence of fishing on biodiversity, is the second route, which is not generally positive, since it leads biodiversity to respond to the stressful removal of species with the best commercial attributes. Not coincidentally, these species tend to be ecologically peculiar and quite difficult to be replenished or compensated for. In part this is because the more peculiar the evolutionary position of a species in relation to the abundance of close relatives that occur in a certain place (ie, more or less branches), the more vulnerable they are to overfishing, and they leave us without potential substitutes.

The intensity of the fishing-biodiversity (positive or negative) relationship is dynamic and may suffer significant imbalances over time. Such imbalances can act as good indicators of the biodiversity status directly as a consequence of fishing. A contrast between functional vs. phylogenetic compositions can inform how much a coastal environment is susceptible to decline or loss of biodiversity. It is through this lens way that we intend to look at the health of the biodiversity of marine fish stocks in Brazil. We believe that assessing the relationships of fishing activity with descriptors of spatial and temporal coastal diversity may bring up important information. We believe that fishing is not likely to always work on the same types of attributes (e.g. habitat preference, reproductive or trophic guild) with the same artificial selective intensity. This could lead to interesting differences between the sets of species handled by fishing, whose causes and consequences may lead us to predict the main types of transformations that may occur due to the patterns of changes in the general and essential descriptors of biodiversity.

A lot of people believe that fish is all the same, a mistake not taken easily by the ichthyologists! However, it is important to note that the more similar the target species are, in terms of basic attributes such as food habits (which reflects on the taste of the fish) and body size, the more dangerous the effects of long-term fishing on them. This is so because fishing tends to focus on certain patterns that are difficult to find (fishers, depending on consumer demand, always want larger fish with specific tastes, but only a few species have all the desired characteristics). Therefore, finding out which combinations of traits best express the ways in which fishing acts on biodiversity is paramount in identifying changes in fish composition patterns that may be signaling the health of the ecosystems in which they operate. 

We have been developing a conceptual model to show the correlations we expect to observe between fishing and biodiversity. We expect biomass removed by fishing to affect positively or negatively the variability in the clades or traits of fished subsets.

In this sense, we believe that the measures of richness, divergence and phylogenetic (Tucker 2017) or functional integrity (Hatfield et al. 2018) represent some of the most important ways to evaluate how, when and how much biodiversity variability is related to fishing as a source of chronic disturbances (e.g., Teichert et al. 2018). These indicators should allow us to identify where the greatest and worst effects of fishing are, and to predict which routes are responsible for their magnitude in each place or time period (e.g., Worm et al. 2006).



These inferences will allow us to find out if there are plausible reasons to worry about the differences between the levels of diversity associated with fishing yields along the coastal gradients of Brazil, and whether significant losses can be detected within one or more facets of biodiversity (ie, taxonomic, functional or phylogenetic). In what direction and at what pace is all of this developing? What are the deficits we are generating for future communities? And, what can we do about it, other than standing and watching? 

All of this is important not only to identify the way the coastal fishery has affected biodiversity, but also to inform and invite the consumer society to consider: "if we fished less, how many different fish communities there would be in the seas?" The answer to this can be both disastrous and spectacular (e.g., Duffy et al. 2016), depending on the quality of the legacy we choose to leave in the oceans. In addition, it represents a fundamental issue relevant to the life quality of the species that support our survival. It is our way of seeing and living with the other species that determines the quality of our own life history. Since the moment we were born until well after we die, nature acts upon us, in such a way that to harass it, to attack it or to despise it are acts of carelessness and disrespect that hurt our very existence. In the ship of life, we are navigating along with all other evolutionary branches. Fortunately or not, it is only us who enjoy the privilege of having the helm to choose the destiny of all, with the caution and parsimony that should precede the forecasts that are based on the accumulation of observations. Welcome aboard the Anthropocene!

By Priscilla Ramos Cruz and Priscila F. M. Lopes

References

• Duffy, J. E., Lefcheck, J. S., Stuart-Smith, R. D., Navarrete, S. A., & Edgar, G. J. (2016). Biodiversity enhances reef fish biomass and resistance to climate change. Proceedings of the National Academy of Sciences, 113(22): 6230-6235.
• Hatfield, J. H., Harrison, M. L., & Banks-Leite, C. (2018). Functional diversity metrics: How they are affected by landscape change and how they represent ecosystem functioning in the tropics. Current Landscape Ecology Reports, 3:35–42.
• Schmeller, DS, Weatherdon, LV, Loyau, A., Bondeau, A., Brotons, L., Brummitt, N., ... & Mihoub, JB (2018). A suite of essential biodiversity variables for detecting critical biodiversity change. Biological Reviews, 93(1): 55-71.
• Teichert, N., Lepage, M., & Lobry, J. (2018). Beyond classic ecological assessment: The use of functional indices to indicate fish assemblages sensitivity to human disturbance in estuaries. Science of The Total Environment, 639: 465-475.
• Tucker, CM, Cadotte, MW, Carvalho, SB, Davies, TJ, Ferrier, S., Fritz, SA, & Pavoine, S. (2017). A guide to phylogenetic metrics for conservation, community ecology and macroecology. Biological Reviews, 92(2): 698-715.
• Worm, B., Barbier, E. B., Beaumont, N., Duffy, J. E., Folke, C., Halpern, B. S., ... & Sala, E. (2006). Impacts of biodiversity loss on ocean ecosystem services. science, 314(5800): 787-790.