Sexual segregation of pelagic sharks and the potential threat from fisheries

Mucientes, Gonzales R; Queiroz, Nuno; Sousa, Lara L.; Tarroso, Pedro; Sims, David

doi:10.1098/rsbl.2008.0761

Cited by 173 publications

(154 citation statements)

References 16 publications

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“…Strong segregation by size, sex and reproductive stage are well documented characteristics of most shark populations (Springer 1967;Sims 2005). Mucientes et al (2009), for example, reported strong sex segregation at large scales in the Pacific Ocean for shortfin mako (Isurus oxyrinchus) and suggested that differential exploitation of males was possible. Camhi et al (1998) also suggested selective take of males only as a potential management measure for sharks.…”

Section: Risk Mitigation Strategies In Multispecies Tropical Shark Fmentioning

confidence: 99%

Evaluating catch and mitigating risk in a multispecies, tropical, inshore shark fishery within the Great Barrier Reef World Heritage Area

Harry¹,

Tobin²,

Simpfendorfer³

et al. 2011

Mar. Freshwater Res.

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Abstract. Small-scale and artisanal fisheries for sharks exist in most inshore, tropical regions of the world. Although often important in terms of food security, their low value and inherent complexity provides an imposing hurdle to sustainable management. An observer survey of a small-scale commercial gill-net fishery operating within the Great Barrier Reef World Heritage area revealed at least 38 species of elasmobranch were present in the catch. Of the total elasmobranch catch, 95% was 25 species of Carcharhiniformes from the families Carcharhinidae, Hemigaleidae and Sphyrnidae. Individual species were captured in a variety of ways by the fishery, often with strongly biased sex ratios and in a variety of life stages (e.g. neonates, juveniles, adult). Despite this, the main carcharhiniform taxa captured could be qualitatively categorised into four groups based on similar catch characteristics, body size and similarities in life history: small coastal (,1000 mm); medium coastal (1000-2000 mm); large coastal/semi-pelagic (.2000 mm); and hammerheads. Such groupings can potentially be useful for simplifying management of complex multispecies fisheries. The idiosyncrasies of elasmobranch populations and how fisheries interact with them provide a challenge for management but, if properly understood, potentially offer underutilised options for designing management strategies.

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Section: Risk Mitigation Strategies In Multispecies Tropical Shark Fmentioning

confidence: 99%

Evaluating catch and mitigating risk in a multispecies, tropical, inshore shark fishery within the Great Barrier Reef World Heritage Area

Harry¹,

Tobin²,

Simpfendorfer³

et al. 2011

Mar. Freshwater Res.

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show abstract

“…Hence, the large-scale, trans-national area occupied by juvenile blue sharks within this 'nursery' further complicates any future management or conservation initiatives (Baum et al 2003), which would require internationally coordinated action. Moreover, while the pattern appears complex, there is evidence that blue sharks exhibit age and sexual segregation in different regions of the North Atlantic, indicating different components of the population may face differential risk from fisheries depending on which geographical regions they occupy at specific times (Mucientes et al 2009). This may act to accelerate declines further.…”

Section: Fisheries and Conservationmentioning

confidence: 99%

Short-term movements and diving behaviour of satellite-tracked blue sharks Prionace glauca in the northeastern Atlantic Ocean

Queiroz¹,

Humphries²,

Noble³

et al. 2010

Mar. Ecol. Prog. Ser.

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Shifts in the movement, activity or behaviour of individual animals in relation to changing environmental landscapes play an important role in determining re-distribution patterns of populations. Such spatial dynamics are poorly understood for pelagic sharks despite the decline of many species due to overfishing. Satellite-linked archival transmitters were used to record the movements of blue sharks Prionace glauca for the first time in the northeast Atlantic. A total of 256 tracking days were recorded, with sharks covering an estimated minimum distance of 11 432 km. Generally, blue sharks displayed wide-ranging southward movements away from the tagging areas (English Channel, southern Portugal and the Azores Islands), with juvenile sharks displaying less site fidelity than previously suggested from other methods. Vertical movements ranged from the surface to a maximum depth of 696 m, and water temperatures varied from 10.6 to 24.6°C. Shifts in both thermal and depth-use patterns were detected, with tracked sharks displaying behavioural variability correlated with the environment, both within and between individuals. Patterns of behaviour in coastal areas were generally linked to the thermal structure of the water column; sharks displayed some preference for surface layers in thermally stratified waters, but displayed less regular behaviour in wellmixed or weakly stratified waters. In offshore locations, sharks usually adopted either a surfaceoriented or a depth-oriented diving pattern, often switching between both in response to probable changes in prey distribution or prey type when in deeper water. Fishing-induced mortality of tracked sharks was approximately 10% during the period of 13 to 70 d post-tagging. Our results indicate a variety of short and longer range movements of juvenile and sub-adult blue sharks with respect to time and environment in the northeast Atlantic, which suggests complex spatial dynamics and population structuring in this exploited species.

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“…Although sexual segregation for most pelagic species is of little interest, sexual segregation for sharks has attracted great interest because of the potential impacts on fisheries population dynamics and management (Mucientes et al 2009). None of the 7 species examined in this study showed sexual segregation in vertical habitat, as there were no significant differences in vertical distributions between genders.…”

Section: Implication Of Differences/similarities In Vertical Distribumentioning

confidence: 99%

Comparative analysis of depth distribution for seventeen large pelagic fish species captured in a longline fishery in the central-eastern Pacific Ocean

Zhu¹,

Xu²,

Dai³

et al. 2011

Sci. Mar.

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SUMMARY: The objective of this study was to estimate depth distribution of pelagic species captured in a longline fishery and to evaluate the difference in depth distribution among species. We estimated depth distribution for 17 frequently captured species based on a Chinese longline fishing trip targeting bigeye tuna (Thunnus obesus) in the central-eastern Pacific Ocean in February-November 2006. The depth distributions of 13 bycatch species were significantly different from that of bigeye tuna. Although most of the bycatch species were found to be distributed in water depths shallower than bigeye tuna (i.e. increasing hook depths can decrease catch rates of these species), the rates of catch rates declined with increasing hook depths may be different. The depth distributions were found to be not significantly different between genders for 7 species. There was no significant correlation between fish sizes and capture depths. The information derived from this study can play an important role in reducing bycatch in pelagic tuna longline fisheries in the central-eastern Pacific Ocean.Keywords: pelagic fish, tuna, bycatch, vertical distribution, longline, Pacific Ocean. RESUMEN: Análisis comparativo de la distribución en profundidad de diecisiete especies de grandes pelági-cos, capturados en una pesquería de palangre en el océano Pacífico centro-oriental. -El objetivo de este estudio ha sido estimar la distribución en profundidad de especies pelágicas capturadas en una pesquería de palangre y evaluar la diferencia en la distribución en profundidad entre las especies. Se estimó la distribución en profundidad para 17 especies capturadas frecuentemente, sobre la base de los datos obtenidos en una marea de una pesquería de palangre china dirigida al patudo (Thunnus obesus) en el océano Pacífico centro-oriental, durante febrero-noviembre 2006. Las distribuciones en profundidad de 13 especies no objetivo de la pesquería fueron significativamente diferentes de la del patudo. Aunque la mayoría de estas 13 especies se encontraron a menor profundidad que el patudo, la medida en la que la captura acompañante disminuye puede ser diferente al situar los anzuelos a mayor profundidad. En 7 de las especies no se encontraron diferencias significativas entre sexos en relación a la distribución en profundidad. No hubo correlación significativa entre los tamaños de los peces y las profundidades de captura. La información derivada de este estudio puede jugar un rol importante en la reducción de la captura acompañante de pesquerías pelágicas con palangre dirigidas a captura de atunes en el océano Pací-fico centro-oriental.

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Sexual segregation of pelagic sharks and the potential threat from fisheries

Cited by 173 publications

References 16 publications

Evaluating catch and mitigating risk in a multispecies, tropical, inshore shark fishery within the Great Barrier Reef World Heritage Area

Evaluating catch and mitigating risk in a multispecies, tropical, inshore shark fishery within the Great Barrier Reef World Heritage Area

Short-term movements and diving behaviour of satellite-tracked blue sharks Prionace glauca in the northeastern Atlantic Ocean

Comparative analysis of depth distribution for seventeen large pelagic fish species captured in a longline fishery in the central-eastern Pacific Ocean

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