Contributed Paper Population Trends in Pacific Oceanic Sharks and the Utility of Regulations on Shark Finning SHELLEY C. CLARKE, * SHELTON J. HARLEY, SIMON D. HOYLE, AND JOEL S. RICE Oceanic Fisheries Program, Secretariat of the Pacific Community, B.P. D5,98848, Noum´ ea CEDEX, New Caledonia Abstract: Accurate assessment of shark population status is essential for conservation but is often constrained by limited and unreliable data. To provide a basis for improved management of shark resources, we analyzed a long-term record of species-specific catches, sizes, and sexes of sharks collected by onboard observers in the western and central Pacific Ocean from 1995 to 2010. Using generalized linear models, we estimated population-status indicators on the basis of catch rate and biological indicators of fishing pressure on the basis of median size to identify trends for blue (Prionace glauca), mako (Isurus spp.), oceanic whitetip (Carcharhinus longimanus), and silky (Carcharhinus falciformis) sharks. Standardized catch rates of longline fleets declined significantly for blue sharks in the North Pacific (by 5% per year [CI 2% to 8%]), for mako sharks in the North Pacific (by 7% per year [CI 3% to 11%]), and for oceanic whitetip sharks in tropical waters (by 17% per year [CI 14% to 20%]). Median lengths of silky and oceanic whitetip sharks decreased significantly in their core habitat, and almost all sampled silky sharks were immature. Our results are consistent with results of analyses of similar data sets. Combined, these results and evidence of targeted fishing for sharks in some regional fisheries heighten concerns for sustainable utilization, particularly for oceanic whitetip and North Pacific blue sharks. Regional regulations that prohibit shark finning (removal of fins and discarding of the carcass) were enacted in 2007 and are in many cases the only form of control on shark catches. However, there is little evidence of a reduction of finning in longline fisheries. In addition, silky and oceanic whitetip sharks are more frequently retained than finned, which suggests that even full implementation of and adherence to a finning prohibition may not substantially reduce mortality rates for these species. We argue that finning prohibitions divert attention from assessing whether catch levels are sustainable and that the need for management of sharks should not be addressed by measures that are simple to implement but complex to enforce and evaluate. Keywords: indicator, mortality, sustainability Tendencias Poblacionales de Tiburones del Oc´ eano Pac´ ıfico y la Utilidad de Regulaciones sobre Cercenamiento de Aletas Resumen: La evaluaci´ on precisa del estatus de las poblaciones de tibur´ on es esencial para la conservaci´ on pero a menudo es constre˜ nida por datos limitados y poco confiables. Para proporcionar una base para un mejor manejo del recurso tibur´ on, analizamos un registro de largo plazo sobre la captura de especies, tama˜ nos y sexos de tibur´ on recolectados por observadores a bordo de embarcaciones en el Pac´ ıfico occidental y central de 1995 a 2010. Utilizando modelos lineales generalizados, estimamos indicadores del estatus de la poblaci´ on con base en la tasa de captura e indicadores biol´ ogicos de la presi´ on de pesca con base en tama˜ no medio para identificar tendencias para Prionace glauca, Isurus spp., Carcharhinus longimanus y Carcharhinus falciformis. Las tasas de captura estandarizadas declinaron significativamente para P. glauca en el Pac´ ıfico Norte (5% por a˜ no [IC 2% a 8%]), para I. spp. en el Pac´ ıfico Norte (7% por a˜ no [IC 3% a 11%] y para C. longimanus en aguas tropicales (17% por a˜ no [IC 14% a 20%]). Los tama˜ nos medios de C. falciformis y C. longimanus decrecieron significativamente en su h´ abitat n´ ucleo, y casi todos los individuos de C. falciformis eran inmaduros. Nuestros resultados son consistentes con los an´ alisis de conjuntos de datos similares. Combinados, estos resultados y evidencia de la pesca de tiburones en algunas pesquer´ ıas regionales ∗ email scc@sasama.info Paper submitted February 9, 2012; revised manuscript accepted July 3, 2012. 197 Conservation Biology, Volume 27, No. 1, 197–209 C  2012 Society for Conservation Biology DOI: 10.1111/j.1523-1739.2012.01943.x