Bioeconomics of the Allee effect in fisheries targeting sedentary resources

Abstract

The improvement of survival in some species due to the close coexistence between individuals is a concept that has caught the attention of scientists over the years. This behaviour has been documented in many taxa, including species which support commercial fisheries. In recent years, a better understanding of the mechanisms associated with the Allee effect has shown its importance in population dynamics and probably plays a more important role than previously thought. In this article, the Allee effect was analysed by means of a spatial bioeconomic model. The Allee effect component was the positive relationship between the mating probability and the density of spawners. A depensation function with an offset to the right side of the origin represented the fraction of females that mated based on density. When the model did not include the Allee effect, the fishery reached the bioeconomic equilibrium; however, when the Allee effect was considered, the fishery did not reach equilibrium, but the stock collapsed in 15 years. Fishing mortality altered the spatial distribution of the stock, causing depensation in recruits per spawner. These results may contribute to a better understanding of the Allee effect on sedentary resources and can be used to explore new models.

How does climate change affect a fishable resource? The case of the royal sea cucumber (Parastichopus regalis) in the central Mediterranean Sea

“…Since holothurians are gonochoric and sedentary, their reproductive success depends largely on their gregarious behavior and their chemical communication, and spawning synchrony. Therefore, a reduction in density can affect fertilization, causing a further decrease in population size (Hutchings, 2014;Kuparinen and Hutchings, 2014;Gonzaĺez-Durań et al, 2018). However, other factors such as biotic factors could affect variation in P. regalis abundance.…”

On the effects of temperature and pH on tropical and temperate holothurians

“… Projection of biochemical pathways and physiological responses into population. Adapted from Seijo et al (1994) , Pörtner et al (2004) , Pörtner & Langenbuch (2005 ), Dhaka et al (2006) , An and Seijo (2010 ), Takahashi et al (2011) , Kalyanaraman (2013) , ( Quijano et al (2016) and González-Durán et al (2018) . * Although indirect effects constitute an important source of impacts, for the simplicity of the figure they are not considered at this time.…”

“…Recruitment to the population depends basically on three factors: the amount of eggs spawned, the fertilization rate and the survival of larval stages (11). Furthermore, since the species have external fertilization, spawners’ density is incorporated as a depensatory function that occurs at low abundance (12) ( González-Durán et al, 2018 ). From this perspective, it is clear that the increase in natural or fishing mortality produces a reduction in abundance, which eventually affects the spawning biomass and reduces the success of recruitment.…”

“…Commonly, the incorporation of the Allee effect has been achieved through the addition of exponents in the parameters of the recruitment function ( Lierman & Hilborn, 2001 ); however, the disadvantage is that these exponents do not have a simple biological interpretation ( Lierman & Hilborn, 1997 ). Recently, a model developed for holothurians showed how external factors such as fishing could reduce the spawning stock biomass down to levels, under which reproductive fitness is no longer possible ( González-Durán et al, 2018 ). To include the Allee effect, the authors set the recruitment as a function of density and included an additional term to shift the origin (threshold) to the left; this point represents the moment when all recruitment ceased (12).…”

“…Their reproductive success depends largely on their gregarious behaviour, spawning synchrony and their chemical communication ( Fujiwara et al , 2010 ; Hamel & Mercier, 1996 , 1999 ; Zacarías-Soto et al , 2013 ). A reduction in density can affect fertilization and thus produce changes in the population intrinsic growth rate ( González-Durán et al , 2018 ; Hutchings, 2014 ; Kuparinen & Hutchings, 2014 ). From this perspective, we explore the responses that tropical and temperate sea cucumbers exhibit throughout their life cycle when exposed to variation in water temperature and pH.…”