Assessing the contribution to overfishing of small- and large-scale fisheries in two marine regions as determined by the weight of evidence approach

Abstract

Overfishing is taking place all over the world threatening marine ecosystems’ health and associated livelihoods. Correctly identifying the drivers of overexploitation are crucial to guide effective fishery measures. In the present study the distinct contribution to overfishing of large-scale fisheries (LSF) and small-scale fisheries (SSF) in the Gulf of California and in the Mediterranean Sea has been compared. To accomplish the task, a weight of evidence approach has been applied based on a thorough literature review documenting overfishing. Results showed that both SSF and LSF shared responsibilities in overfishing in the two geographical locations considered, albeit with different contributions. In the Gulf of California, the weight of evidence revealed that overfishing was mainly driven by fishers engaged in SSF whereas in the Mediterranean, overfishing was mainly driven by LSF. In the Mediterranean, bycatch by LSF played a greater role than in the Gulf of California where, instead, a higher number of endemic overfished species were recorded. In order to attain fisheries sustainability some recommendations are given. In the Mediterranean, selective fishing practices and fishery policies that include input controls and catch limits are highly desirable. In the Gulf of California, the presence of governmental agencies and their services together with participatory management schemes should be reinforced in the region.

Introduction

The use of aquatic natural resources by humans is a millennial activity, in some cases raising concerns over their overexploitation (Jackson et al., 2001; Myers and Worm, 2003). The extraction of fish at a higher speed than the needed for the resource to replenish itself, also called overfishing, has seen globally a large increase in the late-1970s and 1980s (FAO, 2020a). Overfishing effects go beyond the status of single-species fish populations to reach global food security, ecological extinction, and other cascading effects (Blanchard et al., 2017; Murawski, 2000; Jackson et al., 2001; Scheffer et al., 2005). A stock can be considered overfished or overexploited when its biomass is below the level that produce the Maximum Sustainable Yield (MSY), while overfishing refers to a fishing mortality above the level that gives the MSY (Froese and Proelss, 2012). Following Pauly et al. (1989), there are four different forms overfishing is occurring or a stock is considered to be overfished: (i) growth overfished, when fish are caught before they can fully grow; (ii) recruitment overfished, when the adults left in a exploited stock are not sufficient to avoid the reduction on the capacity of fish to reproduce; (iii) economic overfishing, when fishing mortality is higher than the level that affords the Maximum Economic Yield; and (iv) ecosystem overfishing, when the fishing effort is at a rate higher than the rate of the ecosystem to maintain all fished communities (Link and Watson, 2019).

Fisheries has been broadly classified into small and large scale (Chuenpagdee et al., 2006). Although a single categorization has not yet been reached, they can be broadly distinguished in terms of catch capacity (Sumaila et al., 2001). In this sense, while small-scale fisheries (SSF) have less catch capacity, generally using small boats (≤10–15m) or no boats, traveling shorter distances and having a small crew, large-scale fisheries (LSF) use large boats (>10–15m), and have high capital costs and sophisticated technology (Chuenpagdee et al., 2006). Yet, the classification can also contain sociocultural dimensions (e.g., ethnic group, religion, etc.) (Smith and Basurto, 2019). Starting in the 1950s, the progression from small to large in world fisheries promoted by nations has paid preferential attention to LSF in fishery management (Carvalho et al., 2011).

Different arguments have been used to explain overfishing. For instance, the Malthusian argument argues that overfishing is driven by the tendency of the fishing effort to increase until no further extraordinary profits are produced. In this line of thinking, Pauly (1990) argues that overfishing is the outcome of a tragedy of the commons in which the number of fishers increases unsustainably as no other alternative livelihoods can be found. Following the same line of thinking but using a different point of view, scholars such as Mansfield (2011) argue that the growth of industrial fishing since World War II, encouraged by government policies and international treaties, is the main cause of global overfishing. Following Mansfield's idea, industrialization, or the increase in fishing capacity of a higher number of big vessels and powerful fleets of LSF, are the main drivers of overfishing. The contribution to food security and the short-term dependency of the community on the fishing activity differs in the two scenarios, especially in developing countries (Béné, 2005), and therefore should differ the fishery management following FAO Code of Conduct for Responsible Fisheries and FAO (2009). Additionally, in order to effectively prevent overfishing, decisions need to be made on the basis of adequate information on which species are overexploited and who is responsible of the situation (Pauly et al., 2014).

Weight of evidence methods (hereafter WoE) evaluate the extent to which evidence supports possible answers to a scientific question (EFSA Scientific Committee, 2017). These methods have been widely used in ecological risk assessment as a valuable tool for the evaluation of multiple hypotheses when various types of data are considered (Suter, 2006). Although the application of WoE approaches in fisheries has been rather limited, it has proved to be an effective method to discriminate among multiple hypotheses (McAdam, 2015).

The main aim of the present study was to evaluate, through a literature review, the distinct contribution made by SSF and LSF to overall overfishing in two selected marine regions: The Gulf of California and the Mediterranean Sea. This study aims to compare responsibilities in the overall overfishing situation of the two major sectors of the fishing industry in the two marine regions considered. Two hypotheses, that apply for both regions, are presented: (i) overfishing is mainly driven by fishers engaged in SSF; or (ii) overfishing is mainly driven by the industrial fleet or large-scale fishery (LSF). To accomplish the task, a WoE approach has been applied on the literature recording overfishing in the two areas.