Loss of Large Predatory Sharks from the Mediterranean Sea

Authors

  • FRANCESCO FERRETTI,

    Corresponding author
    1. Department of Biology, Life Sciences Centre, 1355 Oxford Street, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada
      ‡ email ferretti@dal.ca
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  • RANSOM A. MYERS,

    Corresponding author
    1. Department of Biology, Life Sciences Centre, 1355 Oxford Street, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada
      §Ransom A. Myers died during the writing of this paper. We will greatly miss his unique personality, passion, and intelligence.
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  • FABRIZIO SERENA,

    1. ARPAT (Agenzia Regionale per la Protezione Ambientale della Toscana), Via Marradi 114, 57100 Livorno, Italy
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  • HEIKE K. LOTZE

    1. Department of Biology, Life Sciences Centre, 1355 Oxford Street, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada
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email ferretti@dal.ca

§Ransom A. Myers died during the writing of this paper. We will greatly miss his unique personality, passion, and intelligence.

Abstract

Abstract: Evidence for severe declines in large predatory fishes is increasing around the world. Because of its long history of intense fishing, the Mediterranean Sea offers a unique perspective on fish population declines over historical timescales. We used a diverse set of records dating back to the early 19th and mid 20th century to reconstruct long-term population trends of large predatory sharks in the northwestern Mediterranean Sea. We compiled 9 time series of abundance indices from commercial and recreational fishery landings, scientific surveys, and sighting records. Generalized linear models were used to extract instantaneous rates of change from each data set, and a meta-analysis was conducted to compare population trends. Only 5 of the 20 species we considered had sufficient records for analysis. Hammerhead (Sphyrna spp.), blue (Prionace glauca), mackerel (Isurus oxyrinchus and Lamna nasus), and thresher sharks (Alopias vulpinus) declined between 96 and 99.99% relative to their former abundance. According to World Conservation Union (IUCN) criteria, these species would be considered critically endangered. So far, the lack of quantitative population assessments has impeded shark conservation in the Mediterranean Sea. Our study fills this critical information gap, suggesting that current levels of exploitation put large sharks at risk of extinction in the Mediterranean Sea. Possible ecosystem effects of these losses involve a disruption of top-down control and a release of midlevel consumers.

Abstract

Resumen: La evidencia de declinaciones severas de peces depredadores grandes está incrementando alrededor del mundo. Debido a su larga historia de pesca intensiva, el Mar Mediterráneo ofrece una perspectiva única de las declinaciones de poblaciones de peces en escalas de tiempo histórico. Utilizamos un conjunto diverso de registros que datan de inicios del siglo XIX hasta mediados del siglo XX para reconstruir las tendencias poblacionales de largo plazo de tiburones depredadores en el noroeste del Mar Mediterráneo. Compilamos 9 series de tiempo de índices de abundancia de capturas comerciales y recreativas, muestreos científicos y registros visuales. Usamos modelos lineales generalizados para extraer tasas de cambio instantáneas de cada conjunto de datos, y realizamos un meta-análisis para comparar tendencias poblacionales. Solo 5 de las 20 especies consideradas tuvieron suficientes datos para el análisis. Sphyrna spp., Prionace glauca, Isurus oxyrinchus, Lamna nasu y Alopias vulpinus declinaron entre 96 y 99.99% en relación con su abundancia anterior. De acuerdo con criterios de la Unión Mundial de Conservación (IUCN), estas especies serían consideradas en peligro crítico. Hasta ahora, la falta de evaluaciones poblacionales cuantitativas ha impedido la conservación de tiburones en el Mar Mediterráneo. Nuestro estudio llena este vacío de información crítico, lo cual sugiere que los niveles actuales de explotación han puesto en riesgo de extinción a los tiburones grandes en el Mar Mediterráneo. Los posibles efectos de estas pérdidas a nivel ecosistema implican una interferencia del control arriba-abajo y la detonación de consumidores primarios.

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