Article

Reconsidering the Consequences of Selective Fisheries

Commission on Ecosystem Management, International Union for Conservation of Nature (IUCN-CEM), Fisheries Expert Group, Brussels, Belgium.
Science (Impact Factor: 31.48). 03/2012; 335(6072):1045-7. DOI: 10.1126/science.1214594
Source: PubMed

ABSTRACT Balanced fishing across a range of species, stocks, and sizes could mitigate adverse effects and address food security better than increased selectivity.

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    • "Among others, minimum size limits have a long history as a widely used approach commonly implemented through mesh size regulations, which is usually set with reference to fish size at maturity (L m ) (Ricker, 1945; Beverton & Holt, 1957; Froese, 2004). More recently, there has been increasing interest in the concept of ''balanced harvest,'' whereby harvesting levels should be proportional to the productivity of different-sized organisms along the size spectrum of the ecosystem (e.g., Bundy et al., 2005; Garcia et al., 2012; Law et al., 2012; Rochet & Benoıˆt, 2012). In either approach, knowledge of gear selectivity is still essential in order to determine sizes vulnerable to fishing, determine fishing effort to maximize yield (the ultimate goal of both measures), and to monitor the size distribution of the fish stocks over time (Millar & Holst, 1997; Huse et al., 2000). "
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    ABSTRACT: We evaluated the statistical models that best describe the selectivity of common fishing gears used in Lake Koka for four freshwater species widely distributed in Ethiopia and elsewhere: tilapia Oreochromis niloticus (L.), catfish Clarias gariepinus (B.), common carp Cyprinus carpio (L.), and barb Labeobarbus intermedius (R.). Sampling was conducted from October 2012 to March 2013 using gillnets (60, 80, 100, and 120 mm stretched mesh), longlines (4/0, 6/0, and 8/0 hooks size), and a beach seine with covered codend. Size at maturity (L m) was determined for each species. The SELECT method was used to explore unimodal selectivity models for gillnet and longline gears, while the logistic function was used for beach seine. Results show that a log-normal model best described gillnet selectivity for all species, while a normal scale model best described longline selectivity for C. gariepinus. Gillnets with ≥100 mm mesh and longlines with >4/0 hooks could be safely used, as they allow target resources to attain L m before becoming vulnerable to fishing. The mesh size of the beach seine needs to be enlarged, as the estimated length of capture was much smaller than all L m values. The results have important management implications for protecting juveniles and mega-spawners of the studied species in Lake Koka and beyond.
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    • "In contrast to some recent studies in fisheries management (e.g. Law, 2007; Garcia et al., 2012), Froese et al. (2008, 2014) speak out for drastic increases in size selectivity. Indeed, it is argued that length at first catch, L c , should be raised to optimal length, L opt . "
    Fisheries Research 04/2015; 164. DOI:10.1016/j.fishres.2014.12.008 · 1.84 Impact Factor
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    • "Given that the large-bodied species are more vulnerable to fishing because of their slow life history strategy (Jennings, Greenstreet & Reynolds, 1999), it is clear that their selective harvesting is unsustainable and disrupts ecosystem structure and function, i.e., leading to ecosystem overfishing (Murawski, 2000). Balanced harvesting (moderate fishing mortality across a wide range of species, stocks, and sizes) would mitigate adverse ecological effects of fishing and support sustainable fisheries by maintaining size and species composition (Garcia et al., 2012). In addition, size-dependent fish prices may change optimal fishing mortalities leading to unsustainable resource utilization (Zimmermann, Steinshamn & Heino, 2011). "
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    ABSTRACT: The relationship between fish market price and body size has not been explored much in fisheries science. Here, the mean market prices and fish body size were collected in order to examine the hypothesis that large fish, both among- and within-species, are being selectively targeted by fisheries because they may yield greater profit. Trophic levels, vulnerability to fishing and global landings were also collected because these variables may also be related to the market fish price. These relationships were examined using generalized additive models (GAM), which showed that, among species, fish market price was positively dependent on maximum total length (P = 0.0024) and negatively on landings (P = 0.0006), whereas it was independent of trophic level (P > 0.05) and vulnerability to fishing (P > 0.05). When the fish price vs. size relationship was tested within-species, large individuals were consistently attaining higher market prices compared to their medium and small-sized counterparts. We conclude that the selective removal of the larger fish, which is driven by their market price and to a lesser extent by their availability, may contribute to their overfishing.
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