Cascading Effects of the Loss of Apex Predatory Sharks from a Coastal Ocean

Department of Biology, Dalhousie University, 1355 Oxford Street, Halifax, NS B3H 4J1, Canada.
Science (Impact Factor: 33.61). 03/2007; 315(5820):1846-50. DOI: 10.1126/science.1138657
Source: PubMed


Impacts of chronic overfishing are evident in population depletions worldwide, yet indirect ecosystem effects induced by predator removal from oceanic food webs remain unpredictable. As abundances of all 11 great sharks that consume other elasmobranchs (rays, skates, and small sharks) fell over the past 35 years, 12 of 14 of these prey species increased in coastal northwest Atlantic ecosystems. Effects of this community restructuring have cascaded downward from the cownose ray, whose enhanced predation on its bay scallop prey was sufficient to terminate a century-long scallop fishery. Analogous top-down effects may be a predictable consequence of eliminating entire functional groups of predators.

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    • "Trophic level decreases have been used to address overexploitation of resources in marine food webs (Pauly et al. 1998, Myers et al. 2007). Cortés (1999) estimated a trophic level for M. higmani of 3.6, which is slightly higher than the present estimation (3.3). "
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    ABSTRACT: Mustelus higmani is categorized as " least concern " according to the red list of the International Union for Conservation of Nature, but gaps in population trends occur in most of its distribution range. In Venezuela, this species has local importance because it is part of typical dishes. The aim of this work is to analyse the population structure, reproduction and feeding of M. higmani from Margarita Island's artisanal fishery landings for management purposes. Between 2006 and 2008, 2223 specimens were analysed: 1156 females (24.8-88.4 cm total length [TL]) and 1067 males (20-69.2 cm TL). Temporal variations in sex ratio and length class structure were detected. Changes in body size were detected throughout different years of sampling. A decrease in TL and an increase in immature specimens in the catch were observed in 2008. Mean length at maturity (L 50) was estimated at 46.7 cm TL for females and 47.6 cm TL for males. Female fecundity was 4±1.8 embryos (n=388). Length at birth was between 20 and 29 cm TL, and no differences in sex ratio were detected for embryos. Feeding analyses (n=266 stomachs) showed a diet mainly based on decapod crustaceans, small fish, stomatopods and cephalopods. The trophic level was 3.3, which shows feeding based on benthic and demersal species of the continental shelf, especially crustaceans.
    Scientia Marina 12/2015; 75(4):00. DOI:10.3989/scimar.04245.09A · 1.14 Impact Factor
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    • "Many large-bodied pelagic predators are highly-mobile, and regularly undertake migrations of hundreds to thousands of kilometres at annual and inter-annual timescales (Block et al., 2011). Despite their widespread distributions, mobile pelagic predators have declined in abundance due to overfishing (Baum & Worm, 2009), causing changes to open ocean food webs (Myers et al., 2007; Worm & Tittensor, 2011). Climate-induced distribution shifts are likely to alter the functioning of pelagic ecosystems already under pressure from anthropogenic stressors (Beaugrand et al., 2008; Hazen et al., 2012; Robinson et al., 2014). "
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    Global Change Biology 10/2015; DOI:10.1111/gcb.13129 · 8.04 Impact Factor
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    • "availability of resources) processes is a difficult one to definitively answer, with much evidence for both cases (Estes et al. 1998; Pace et al. 1999; Richardson and Schoeman 2004; Ware and Thomson 2005; Myers et al. 2007; Frank 2008). The abundance and diversity of coral reef fishes are often thought to be largely controlled from the top-down, in part because of a rich history of apex-predator induced trophic cascades (Myers et al. 2007; Baum and Worm 2009; Ferretti et al. 2010; Rizzari et al. 2014), and in part because of the importance of herbivorous fishes and invertebrates in controlling macroalgal growth and in maintaining a coral-dominated system (Hughes 1994; Bellwood et al. 2006; Mumby et al. 2006; Hughes et al. 2007). However, some members of the reef ecosystem are likely to be moderated by bottom-up processes, in particular, availability of food and benthic habitat for resource-specialists (Munday et al. 1997; Pratchett et al. 2006; Emslie et al. 2011). "
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    Marine and Freshwater Research 09/2015; DOI:10.1071/MF15012 · 1.47 Impact Factor
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