Abstract
In the last century, the growing evidence that global fisheries are depleting natural resources much faster than they can recover has led to negative processes, like overfishing, being addressed with increasingly complex models and thus mitigating or regulating actions that aim to protect stocks. Said negative processes contain two components: (i) they can diminish the reproductive potential of fish stocks, called over exploitation by recruitment, and (ii) the effect of early capture prevents the full realization of the growth potential, called overfishing by growth. In this article, the structure of common sardine sizes is analyzed. Due to the precise moment in which pre-recruits are incorporated into the exploited phase of the stock is unknown, the estimation of a recruitment size is a hard problem. This problem is addressed by modeling the mean size via a stochastic process, applying models of structural change. A time series (2001–2015) was analyzed on a weekly time scale based on the size structure of the pelagic fishery landings in the central-southern zone of Chile (32∘10′–40∘14′ LS), from the V. to the XIV. Region. Specifically, the evolution of sizes according to macro-zones was studied for the conglomerates identified in two sub-zones, the V.–VIII. and IX.–XIV. Regions. In this context, the reference size for juveniles to cautiously allow the recruitment process of the common sardine from the central-southern zone of Chile was estimated, and the behavior of these sizes was spatially analyzed. Finally, a statistical inferential criterion was established that confirms the mean size of juveniles with a certain margin of error, which allows nonetheless later on to define a fraction that could be protected to avoid overfishing by growth.
Highlights
The recruitment process corresponds to the number of juveniles that are incorporated into the exploitable population of a fishing area each year through a growth process, i.e., an individual grown to a size suitable to be caught in the area [1]
The biological data derives from weekly routine sampling carried out by the Instituto de Fomento Pesquero (IFOP) as part of the Project “Monitoring of the Main Central-South Pelagic Fisheries” (32◦10 –40◦14 LS), from 2001 to 2015, in the ports of San Antonio
We considered Akaike’s information criterion (AIC) instead of BIC for model selection because BIC penalizes the log-likelihood function using sample size n
Summary
The recruitment process corresponds to the number of juveniles that are incorporated into the exploitable population of a fishing area each year through a growth process, i.e., an individual grown to a size suitable to be caught in the area [1]. This, is not directly applicable because the reproductive process of pelagic fish includes several spawning cycles over several months [6,7] This generates many juvenile cohorts that are difficult to quantify and require defining a spatio-temporal process through a reference size for recruits. This size has been estimated via methods that allow establishing the different sizes for purse seine (selectivity) [8]. See more details in [9] This reference length was further justified by previously established production criteria and coincides with a practical use measure deployed in reduction fishery. The insufficiency of statistically solid criteria for determining recruitment size has motivated this study to model time series of average weekly lengths based on trend breaks, which could find a unique recruitment size
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