Sustainable Yield in Fisheries

It is very difficult to achieve this goal. Typically, fisheries undergo stocks permanently at different temporal and spatial scales of exploitation that exceeds the biological capacity and ecological recovery of the species. On the other hand, the fishery always begins without further study of the population which will be exploted. When these studies exist, and these are more intensive, the population has already changed to another phase, ie, the response is delayed (Figure 1).

Figure 1. Evolution of changes in a fishery.

One factor that clearly shows these effects are average sizes of the populations subjected to exploitation. Body sizes of fish as well as the quality and quantity of their eggs, are subject to biological changes. Drastic natural events, and fishing pressure, can severely affect the exploited stocks (Figure 2). 

Figure 2. Some changes in a fish population during its inappropiate exploitation.

Generally, these changes can be observed after several years of inappropiate fishing pressure, but in some cases may occur over short periods due to a combination of several factors. Fisheries also have problems due to these changes, yields may decrease while the exploited population undergoes various changes (Figure 3). It is necessary to apply the ecosystem approach to fisheries management, through a comprehensive and multidisciplinary study taking in account all parts involved.

Wrong fisheries management decisions

In marine ecosystems there is an important connection between what happens in the surface layers of the sea and the dynamics of bottom-dwelling organisms. One of the key relationships identified for this relationship is called 'biological pump', which represents the exchange of matter and energy between the surface and bottom. 

On the other hand, it is important to consider that for many years has exerted strong pressure and human impact on the seabed and its ecological connections, one of those impacts identified is through the trawl fishery. This type of extractive activity removes most of the sediment surface and generates enormous disturbance on benthic communities at different scales of space.  Although in some parts of the world it is banned, this type of fishery is still practiced in some marine areas. This is critical particularly in countries with large fisheries associated with highly productive upwelling systems. The Peruvian marine ecosystem hosts a large population of fish (and other resources) of global economic importance, the main target species is the Peruvian anchovy, and therefore, its pelagic ecosystem has been a long time ago one of the most studied.  However, there are still some environmental aspects that have not been sufficiently addressed and that represent key issues for the comprehensive study and understanding of this ecosystem. It is also necessary to integrate this research in relation with the impact of the fishery on the Peruvian sea, which is generated at different scales of space and time.

Another major fisheries that also needs further research emphasis aims to Peruvian hake fishery (Merluccius gayi peruanus) This species has more than three decades of exploitation and the focus of study has pointed mainly to the study of the fishery, that is, fishing patterns, 'classical' population dynamics, among other issues arising from monitoring fishing only. However, this resource and other demersal species accompanying this vast habitat, have not undergone to thorough analysis on aspects of trophic ecology, community interactions, or determinations of its importance in the flow of matter and energy within the marine system.

Additionally, the northern coast of Peru, where is the hake fishery (Figure 1, mainly off Paita), is regularly affected by oceanographic fluctuations, especially the Cromwell Current, which conditions both biology and ecology of most organisms living in these waters.

 Figure 1.Port of Paita, Peru (click to enlarge)

This area also represents part of a biogeographical ecotone because it is an intersection point between the Panamanian province and the Peruvian province. However all this must be adequately protected for its continuity in time and their use by future generations. Special care should be given to trawling taking place in these marine areas. This method of fishing is, from a strictly scientific point of view, an inappropriate method for some marine populations and this should be strictly regulated. Although there is information, most people engaged in this fishery usually do not understand the consequences of their activity. On the contrary, it is common to ignore the recommendations of the scientists who warn of these dangers. This gets worse when there are misunderstandings about the fisheries data. One reason is the lack of criteria for fisheries ecology! When we limit the study of a exploited population to assess only fishing data, we have many problems, it is critical consider many other factors driving the patterns of distribution and concentration of marine resources. Conduct multidisciplinary approaches that allow more rigorous analysis, and conclusions more robust, is essential in fisheries management.

One of the most difficult things to do is "talk" to the fishery itself, and ensure that their members can understand the message. Understand the criteria and scientific decisions is one of the most difficult goals to achieve in fisheries management!  Normally, scientists are ridiculed because they simply do not say what industrial fishery want to hear (Figure 2); however, the fishery may be facing serious signals in exploited populations and their actual level of abundance and distribution, and be blind to this and still continue their activities and believe that everything stays the same or even better.  

 Figure 2. Perception of changes of fishing quotas (click to enlarge)

The misconception that the catch of some big fish in an exploited population of fish mean recovery of this population have long been demonstrated as misinterpretations of the real state of a fishery. Catch Per Unit Effort (CPUE) and the "false image" that gives this index about the real distribution and abundance (Figure 3) of the resource has also been observed in other cases such as the Atlantic cod fishery (Figure 4).

 Figure 3. Misinterpreting the reality of a fishery and its impact on fish stocks (click to enlarge).

 Figure 4. Collapse of Atlantic cod stock. (click to enlarge) Source: Millenium Ecosystems Assessment

Only considering an integrated management of our fisheries and being responsible with their full implementation and continuity, we get some 'sustainability' in exploited fish stocks...and remember to use the fisheries ecology please!