Extra-large preys: to shoot or not to shoot?

Like every year, also this winter a discussion about the big sea bass full of eggs will occur on several social networks…should we shoot or not? What is the right thing to do? We can read many comments and many theories, but few of these are based on scientific knowledge. Finally the spring will arrive, sea basses become less frequent and the topic will lose importance…at least until the following winter!

By a logic analysis of the topic, there is no reason why the capture of a large sea bass should generate a greater media impact than other species (for example, large white seabream, brown meagre or snappers full of eggs). The same argument is applicable to other vulnerable species during the breeding season. Furthermore, an extra-large fish remains a great spawner even after the breeding season. But probably the video of a big female of sea bass surrounded by males is much more striking. Nevertheless, this article doesn’t deal with the reproductive biology of our preys but analyzes the topic of catching a big fish from a different point of view: size selection. On the other hand, this argument does not concern only the breeding season but it is applicable to all extra-large preys targeted by any kind of fishery, including spearfishing.

As we all know, spearfishing is extremely selective, but this characteristic could play against our future catches. In fact, the selection of larger preys poses some problems. In some cases, current managing strategies impose limits for minimum sizes but not for maximum ones. There are only few exceptions such as the halibut in Canada.

Many studies have shown that an extreme size-selection on fish caused by professional or recreational fishing can strongly affect the population dynamics of our preys. One of these studies published in 2015 in the scientific journal Evolutionary Application [1] has shown that, if the largest individuals are systematically removed, in only 5 generations the average size of the population can be reduced and the behavior of the fish can be modified, making fish less prone to take risk (therefore less susceptible to be captured). The most interesting thing is that these traits can be hereditable and therefore remain present in the population even if the size selection is halted. This is an evidence of a real “evolutionary change induced by fishing”. Capturing a fish of extra-large size is a goal which we all have. Current scientific knowledge suggests that the systematic selection of larger fish reduces the average size of the population in future generations and makes fish less susceptible to capture. There are two reasons that could explain this process.

The first one is related to the fact that the systematic capture of larger animals selects individuals who have a higher growth rate (not all individuals of the same age grow at the same rate). For this reason, the fish that remains alive grow slower, reaching a smaller size. This type of changes, as evidenced by the experiments conducted in laboratory conditions [1], can be very fast. In fact only 5 generations can be enough to have a reduction in the average size. Although in a natural context the rate is probably slower than in laboratory experiments, however it could be tangible during spearfishers` life.

The second reason is due to the relationship that exists between the size of a fish and its behavior. Fish that reach a large size may have a type of behavior that allows them to get more food resources. They are for example more aggressive or bolder than others individuals. Thus, the systematic selection of size can, inadvertently, also select specific types of behavioral traits.

After fixing these ecological points let us analyze the issue as spearfishers. It would seem that the best thing to do is to stop capturing big fish. We are people who love the sea, especially in winter when there are nor boats neither too many people. We have all the rights to capture a big sea bass and to fully enjoy our recreational activity. Furthermore, recreational fishing trips also have considerable economic implications. In fact, in Europe marine recreational fishing generates around 5.9 billion euro every year [2]. If we put together the ecological dimension with the social one we get a very complex socio-ecological system with a series of reciprocal feedbacks.

The most interesting conclusion of this article is that systematically capturing big fish is against our fishing interests because fish will become smaller and less likely to be caught (maybe we will not even see them). What kind of behavior should the spearfisher adopt to limit the negative feedback of his/her actions while enjoying his/her activity?

Initially we suggest to:

  • Do not concentrate your fishing pressure always on the same spots.
  • If we know a hot spot for a specific fish species during its reproductive period, let’s try to manage it as a small personal reserve (it could really be). One or two visits during the breeding season could be enough to make a nice capture.
  • Do not practice just only one technique, such those aimed to capture sea bass. Once captured one or two big specimens during the breeding season it would be desirable to devote ourselves to other species, perhaps changing the technique or spot.
  • If we have already captured a big individual in the same area it would be desirable to select medium-sized ones or change the spot.

Each of us is obviously free to have his/her personal ethic. What really matters is to be aware that our actions may have a negative impact on fish and, indirectly, on our activity. Acting consciously will increase the likelihood of continuing the practice of our activity with success in the future.

In this article we focused on the potential impact of spearfishing. The omission of a comparison with commercial fishing derives from the fact that catches of professional fishing generate profit while catches of recreational fishing generate emotions for which we are willing to pay. This big difference means that the management of the two systems responds to totally different laws. We will deal with this specific difference in future articles.

To conclude we wish everyone a happy Christmas and if you do not know which gift to donate we recommend you the book by Paul Quinnett entitled “Darwin’s Bass: the evolutionary psychology of fishing man”. In this book the psychologist offers clinical advice for a longer, happier and healthier life based simply on going fishing as often as possible!!!

An example from which to take inspiration

An article published several years ago (2003) on Nature, a prestigious scientific journal, was entitled “Undesirable evolutionary consequences of trophy hunting” [3]. This article showed how over 30 years the population of sheep from the Rocky Mountains (Ovis canadensis) was affected by a clear reduction in body weight and size of the horns due to extremely selective hunting. People hunted only the largest sheep with the largest horns that were further displayed as trophies. Both the size of the individuals and the size of the horns are heritable characteristics of great importance in the sexual selection (the males use the horns in fights to contend the best females). The results of the study have shown that this type of selective hunting has produced a population of smaller sheep with smaller and lighter horns. This population doesn’t attract hunters and consequently the tourism sector dedicated to this type of activity has suffered serious economic damages. This is not an example of spearfishing, but highlights how the social system (tourism or fishing) is highly and intimately linked to the ecosystem management.

[1] Uusi-Heikkilä, S., Whiteley, A. R., Kuparinen, A., Matsumura, S., Venturelli, P. A., Wolter, C., Slate, J., Primmer, C. R., Meinelt, T., Killen, S. S., et al. (2015). The evolutionary legacy of size-selective harvesting extends from genes to populations. Evol. Appl. 8, 597-620.

[2] Hyder, K., Weltersbach, M. S., Armstrong, M., Ferter, K., Townhill, B., Ahvonen, A., Arlinghaus, R., Baikov, A., Bellanger, M., Birzaks, J., et al. Recreational sea fishing in Europe in a global context—Participation rates, fishing effort, expenditure, and implications for monitoring and assessment. Fish Fish. (in press)

[3] Coltman, D. W., O’donoghue, P., Jorgenson, J. T., Hogg, J. T., Strobeck, C. & Festa-Bianchet, M. (2003). Undesirable evolutionary consequences of trophy hunting. Nature. 426, 655-658.