The Experts below are selected from a list of 3837 Experts worldwide ranked by ideXlab platform
Bryan Raveen Nelson - One of the best experts on this subject based on the ideXlab platform.
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carcinoscorpius rotundicauda latreille 1802 population status and Spawning behaviour at pendas coast peninsular malaysia
Global Ecology and Conservation, 2018Co-Authors: Nur Fairuzfozi, Behara Satyanarayana, Nurul Ashikin Mat Zauki, Aidy M Muslim, Mohdlokman Husain, Sulong Ibrahim, Bryan Raveen NelsonAbstract:Abstract The present study evaluates impacts from seasonal monsoons and lunar phases on the Spawning activity of the mangrove horseshoe crab, Carcinoscorpius rotundicauda at Pendas (Sites 1–3) in State Johor, Peninsular Malaysia. The biological (no. of crabs and nests/eggs) observations indicated that Pendas is an active Spawning Ground for C. rotundicauda throughout the year. Higher egg yield was observed for Southwest monsoon (2918 eggs in 55 nests), followed by Northeast (2331 eggs in 48 nests) and Inter-monsoon (1253 eggs in 20 nests) periods. In all seasons, the full moon conditions favoured more number of eggs than to the new moon. Besides the availability of adult crabs in all three sampling sites, the Spawning took place only at Site-1 due to its location (mini sandbar) being sheltered away from the impact of Johor Strait waters, underGround (domestic) discharge point and pioneer mangroves like Sonneratia and Avicennia spp. nearby. In contrast, Sites 2 and 3 are open to the seawater current and its surface sediment is covered by broken seashells/pebbles and/or dense A. alba pneumatophore roots. Among the environmental (water quality and sediment) parameters tested, except sand, silt and clay, the rest (e.g. temperature, pH, salinity, total organic carbon, etc.) didn't show any strong correlation with the Spawning behaviour of C. rotundicauda. The ongoing physical infrastructure developments on housing and property constructions in the vicinity are likely to pose a threat to the Spawning Ground of C. rotundicauda and thus requires a serious attention for its conservation and management.
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Carcinoscorpius rotundicauda (Latreille, 1802) population status and Spawning behaviour at Pendas coast, Peninsular Malaysia
'Elsevier BV', 2018Co-Authors: Nur Fairuz-fozi, Behara Satyanarayana, Nurul Ashikin Mat Zauki, Aidy M Muslim, Mohdlokman Husain, Sulong Ibrahim, Bryan Raveen NelsonAbstract:The present study evaluates impacts from seasonal monsoons and lunar phases on the Spawning activity of the mangrove horseshoe crab, Carcinoscorpius rotundicauda at Pendas (Sites 1–3) in State Johor, Peninsular Malaysia. The biological (no. of crabs and nests/eggs) observations indicated that Pendas is an active Spawning Ground for C. rotundicauda throughout the year. Higher egg yield was observed for Southwest monsoon (2918 eggs in 55 nests), followed by Northeast (2331 eggs in 48 nests) and Inter-monsoon (1253 eggs in 20 nests) periods. In all seasons, the full moon conditions favoured more number of eggs than to the new moon. Besides the availability of adult crabs in all three sampling sites, the Spawning took place only at Site-1 due to its location (mini sandbar) being sheltered away from the impact of Johor Strait waters, underGround (domestic) discharge point and pioneer mangroves like Sonneratia and Avicennia spp. nearby. In contrast, Sites 2 and 3 are open to the seawater current and its surface sediment is covered by broken seashells/pebbles and/or dense A. alba pneumatophore roots. Among the environmental (water quality and sediment) parameters tested, except sand, silt and clay, the rest (e.g. temperature, pH, salinity, total organic carbon, etc.) didn't show any strong correlation with the Spawning behaviour of C. rotundicauda. The ongoing physical infrastructure developments on housing and property constructions in the vicinity are likely to pose a threat to the Spawning Ground of C. rotundicauda and thus requires a serious attention for its conservation and management. Keywords: Mangrove horseshoe crab, Spawning ecology, Seasonal impact, Local topography, Johor strait, Malaysi
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the final Spawning Ground of tachypleus gigas muller 1785 on the east peninsular malaysia is at risk a call for action
PeerJ, 2016Co-Authors: Bryan Raveen Nelson, Behara Satyanarayana, Julia Hwei Zhong Moh, Mhd Ikhwanuddin, Anil Chatterji, Faizah ShaharomAbstract:Tanjung Selongor and Pantai Balok (State Pahang) are the only two places known for Spawning activity of the Malaysian horseshoe crab - Tachypleus gigas (Muller, 1785) on the east coast of Peninsular Malaysia. While the former beach has been disturbed by several anthropogenic activities that ultimately brought an end to the Spawning activity of T. gigas, the status of the latter remains uncertain. In the present study, the Spawning behavior of T. gigas at Pantai Balok (Sites I-III) was observed over a period of thirty six months, in three phases, between 2009 and 2013. Every year, the crab's nesting activity was found to be high during Southwest monsoon (May-September) followed by Northeast (November-March) and Inter monsoon (April and October) periods. In the meantime, the number of female T. gigas in 2009-2010 (Phase-1) was higher (38 crabs) than in 2010-2011 (Phase-2: 7 crabs) and 2012-2013 (Phase-3: 9 crabs) for which both increased overexploitation (for edible and fishmeal preparations) as well as anthropogenic disturbances in the vicinity (sand mining since 2009, land reclamation for wave breaker/parking lot constructions in 2011 and fishing jetty construction in 2013) are responsible. In this context, the physical infrastructure developments have altered the sediment close to nesting sites to be dominated by fine sand (2.5Xφ ) with moderately-well sorted (0.6-0.7σφ), very-coarse skewed (-2.4SKφ), and extremely leptokurtic (12.6Kφ) properties. Also, increased concentrations of Cadmium (from 4.2 to 13.6 mg kg(-1)) and Selenium (from 11.5 to 23.3 mg kg(-1)) in the sediment, and Sulphide (from 21 to 28 µg l(-1)) in the water were observed. In relation to the monsoonal changes affecting sheltered beach topography and sediment flux, the Spawning crabs have shown a seasonal nest shifting behaviour in-between Sites I-III during 2009-2011. However, in 2012-2013, the crabs were mostly restricted to the areas (i.e., Sites I and II) with high oxygen (5.5-8.0 mg l(-1)) and moisture depth (6.2-10.2 cm). In view of the sustained anthropogenic pressure on the coastal habitats on one hand and decreasing horseshoe crabs population on the other, it is crucial to implement both conservation and management measures for T. gigas at Pantai Balok. Failing that may lead to the loss of this final Spawning Ground on the east coast of P. Malaysia.
Jessica H Farley - One of the best experts on this subject based on the ideXlab platform.
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RESEARCH ARTICLE Spawning Dynamics and Size Related Trends in Reproductive Parameters of Southern
2016Co-Authors: Bluefin Tuna, Jessica H Farley, Tim L O Davis, Retno Andamari, Thunnus Maccoyii, Mark V. Bravington, R. DaviesAbstract:Knowledge of Spawning behaviour and fecundity of fish is important for estimating the repro-ductive potential of a stock and for constructing appropriate statistical models for assessing sustainable catch levels. Estimates of length-based reproductive parameters are particular-ly important for determining potential annual fecundity as a function of fish size, but they are often difficult to estimate reliably. Here we provide new information on the reproductive dynamics of southern bluefin tuna (SBT) Thunnus maccoyii through the analysis of fish size and ovary histology collected on the Spawning Ground in 1993–1995 and 1999–2002. These are used to refine previous parameter estimates of Spawning dynamics and investi-gate size related trends in these parameters. Our results suggest that the small SBT tend to arrive on the Spawning Ground slightly later and depart earlier in the Spawning season rela-tive to large fish. All females were mature and the majority were classed as Spawning capa-ble (actively Spawning or non-Spawning) with a very small proportion classed as regressing. The fraction of females Spawning per day decreased with fish size, but once females start a Spawning episode, they spawned daily irrespective of size. Mean batch fecundity was esti-mated directly at 6.5 million oocytes. Analysis of ovary histology and ovary weight data indicated that relative batch fecundity, and the duration of Spawning and non-Spawning epi-sodes, increased with fish size. These reproductive parameter estimates could be used with estimates of residency time on the Spawning Ground as a function of fish size (if known) and demographic data for the Spawning population to provide a time series of relative annu-al fecundity for SBT
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Spawning dynamics and size related trends in reproductive parameters of southern bluefin tuna thunnus maccoyii
PLOS ONE, 2015Co-Authors: Jessica H Farley, Tim L O Davis, Retno Andamari, Mark V. Bravington, Campbell R DaviesAbstract:Knowledge of Spawning behaviour and fecundity of fish is important for estimating the reproductive potential of a stock and for constructing appropriate statistical models for assessing sustainable catch levels. Estimates of length-based reproductive parameters are particularly important for determining potential annual fecundity as a function of fish size, but they are often difficult to estimate reliably. Here we provide new information on the reproductive dynamics of southern bluefin tuna (SBT) Thunnus maccoyii through the analysis of fish size and ovary histology collected on the Spawning Ground in 1993–1995 and 1999–2002. These are used to refine previous parameter estimates of Spawning dynamics and investigate size related trends in these parameters. Our results suggest that the small SBT tend to arrive on the Spawning Ground slightly later and depart earlier in the Spawning season relative to large fish. All females were mature and the majority were classed as Spawning capable (actively Spawning or non-Spawning) with a very small proportion classed as regressing. The fraction of females Spawning per day decreased with fish size, but once females start a Spawning episode, they spawned daily irrespective of size. Mean batch fecundity was estimated directly at 6.5 million oocytes. Analysis of ovary histology and ovary weight data indicated that relative batch fecundity, and the duration of Spawning and non-Spawning episodes, increased with fish size. These reproductive parameter estimates could be used with estimates of residency time on the Spawning Ground as a function of fish size (if known) and demographic data for the Spawning population to provide a time series of relative annual fecundity for SBT.
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demographic structure sex ratio and growth rates of southern bluefin tuna thunnus maccoyii on the Spawning Ground
PLOS ONE, 2014Co-Authors: Jessica H Farley, Paige J Eveson, Tim L O Davis, Retno Andamari, Craig H Proctor, Budi Nugraha, Campbell R DaviesAbstract:The demographics of the southern bluefin tuna (SBT) Thunnus maccoyii Spawning stock were examined through a large-scale monitoring program of the Indonesian longline catch on the Spawning Ground between 1995 and 2012. The size and age structure of the Spawning population has undergone significant changes since monitoring began. There has been a reduction in the relative abundance of larger/older SBT in the catch since the early 2000s, and a corresponding decrease in mean length and age, but there was no evidence of a significant truncation of the age distribution. Pulses of young SBT appear in the catches in the early- and mid-2000s and may be the first evidence of increased recruitment into the Spawning stock since 1995. Fish in these two recruitment pulses were spawned around 1991 and 1997. Size-related variations in sex ratio were also observed with female bias for fish less than 170 cm FL and male bias for fish greater than 170 cm FL. This trend of increasing proportion of males with size above 170 cm FL is likely to be related to sexual dimorphism in growth rates as male length-at-age is greater than that for females after age 10 years. Mean length-at-age of fish aged 8–10 years was greater for both males and females on the Spawning Ground than off the Spawning Ground, suggesting that size may be the dominant factor determining timing of maturation in SBT. In addition to these direct results, the data and samples from this program have been central to the assessment and management of this internationally harvested stock.
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demographic patterns of southern bluefin tuna thunnus maccoyii as inferred from direct age data
Fisheries Research, 2007Co-Authors: Jessica H Farley, Tim L O Davis, John S Gunn, Naomi P Clear, Ann L PreeceAbstract:Abstract Otolith-based age estimates were obtained for 2769 southern bluefin tuna (SBT) ( Thunnus maccoyii ) caught on feeding Grounds in the southern oceans and their Spawning Ground in the north-east Indian Ocean between 1985 and 1998. Ages ranged from 0 to 41 years, and males were on average larger at age than females after age 6 for fish sampled in the southern oceans. This sexual dimorphism in growth contributed to the sex ratio being biased toward males for length classes ≥170 cm FL. The estimated age composition of catches, derived from age-length keys applied to length frequency data, showed clear differences between fisheries and fishing Grounds that are consistent with seasonal and ontogenetic changes in migration patterns. Specific information that can be gained on the distribution and migration of juveniles from their relative abundance in catches is limited because of unknown targeting or discarding practices on some fishing Grounds. However, the occurrence of 2–4-year-old SBT on opposite sides of the Indian Ocean during the austral summer confirms that juveniles are not restricted to the southern coastal waters of Australia, and that a divergent migration path must exist possibly near the southern west coast of Australia. During the winter months, SBT aged 2–4 years were caught on all fishing Grounds south of the Spawning Ground, confirming that they are capable of extensive migrations. By age 5, SBT were rarely caught north of about 35°S, except in waters adjacent to Australia's west coast where adults were caught migrating to/from the Spawning Ground. The commercial catch of SBT in the southern oceans was dominated by juveniles and sub-adults on most fishing Grounds examined. Off north-east New Zealand, however, the majority of fish caught were of Spawning age (61% were >10-year old) suggesting that the Tasman Sea may form the eastern boundary for juvenile migration. SBT caught on the Spawning Ground ranged in age from 8 to 34 years with the majority being between 15- and 25-years old.
Campbell R Davies - One of the best experts on this subject based on the ideXlab platform.
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Spawning dynamics and size related trends in reproductive parameters of southern bluefin tuna thunnus maccoyii
PLOS ONE, 2015Co-Authors: Jessica H Farley, Tim L O Davis, Retno Andamari, Mark V. Bravington, Campbell R DaviesAbstract:Knowledge of Spawning behaviour and fecundity of fish is important for estimating the reproductive potential of a stock and for constructing appropriate statistical models for assessing sustainable catch levels. Estimates of length-based reproductive parameters are particularly important for determining potential annual fecundity as a function of fish size, but they are often difficult to estimate reliably. Here we provide new information on the reproductive dynamics of southern bluefin tuna (SBT) Thunnus maccoyii through the analysis of fish size and ovary histology collected on the Spawning Ground in 1993–1995 and 1999–2002. These are used to refine previous parameter estimates of Spawning dynamics and investigate size related trends in these parameters. Our results suggest that the small SBT tend to arrive on the Spawning Ground slightly later and depart earlier in the Spawning season relative to large fish. All females were mature and the majority were classed as Spawning capable (actively Spawning or non-Spawning) with a very small proportion classed as regressing. The fraction of females Spawning per day decreased with fish size, but once females start a Spawning episode, they spawned daily irrespective of size. Mean batch fecundity was estimated directly at 6.5 million oocytes. Analysis of ovary histology and ovary weight data indicated that relative batch fecundity, and the duration of Spawning and non-Spawning episodes, increased with fish size. These reproductive parameter estimates could be used with estimates of residency time on the Spawning Ground as a function of fish size (if known) and demographic data for the Spawning population to provide a time series of relative annual fecundity for SBT.
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demographic structure sex ratio and growth rates of southern bluefin tuna thunnus maccoyii on the Spawning Ground
PLOS ONE, 2014Co-Authors: Jessica H Farley, Paige J Eveson, Tim L O Davis, Retno Andamari, Craig H Proctor, Budi Nugraha, Campbell R DaviesAbstract:The demographics of the southern bluefin tuna (SBT) Thunnus maccoyii Spawning stock were examined through a large-scale monitoring program of the Indonesian longline catch on the Spawning Ground between 1995 and 2012. The size and age structure of the Spawning population has undergone significant changes since monitoring began. There has been a reduction in the relative abundance of larger/older SBT in the catch since the early 2000s, and a corresponding decrease in mean length and age, but there was no evidence of a significant truncation of the age distribution. Pulses of young SBT appear in the catches in the early- and mid-2000s and may be the first evidence of increased recruitment into the Spawning stock since 1995. Fish in these two recruitment pulses were spawned around 1991 and 1997. Size-related variations in sex ratio were also observed with female bias for fish less than 170 cm FL and male bias for fish greater than 170 cm FL. This trend of increasing proportion of males with size above 170 cm FL is likely to be related to sexual dimorphism in growth rates as male length-at-age is greater than that for females after age 10 years. Mean length-at-age of fish aged 8–10 years was greater for both males and females on the Spawning Ground than off the Spawning Ground, suggesting that size may be the dominant factor determining timing of maturation in SBT. In addition to these direct results, the data and samples from this program have been central to the assessment and management of this internationally harvested stock.
Behara Satyanarayana - One of the best experts on this subject based on the ideXlab platform.
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carcinoscorpius rotundicauda latreille 1802 population status and Spawning behaviour at pendas coast peninsular malaysia
Global Ecology and Conservation, 2018Co-Authors: Nur Fairuzfozi, Behara Satyanarayana, Nurul Ashikin Mat Zauki, Aidy M Muslim, Mohdlokman Husain, Sulong Ibrahim, Bryan Raveen NelsonAbstract:Abstract The present study evaluates impacts from seasonal monsoons and lunar phases on the Spawning activity of the mangrove horseshoe crab, Carcinoscorpius rotundicauda at Pendas (Sites 1–3) in State Johor, Peninsular Malaysia. The biological (no. of crabs and nests/eggs) observations indicated that Pendas is an active Spawning Ground for C. rotundicauda throughout the year. Higher egg yield was observed for Southwest monsoon (2918 eggs in 55 nests), followed by Northeast (2331 eggs in 48 nests) and Inter-monsoon (1253 eggs in 20 nests) periods. In all seasons, the full moon conditions favoured more number of eggs than to the new moon. Besides the availability of adult crabs in all three sampling sites, the Spawning took place only at Site-1 due to its location (mini sandbar) being sheltered away from the impact of Johor Strait waters, underGround (domestic) discharge point and pioneer mangroves like Sonneratia and Avicennia spp. nearby. In contrast, Sites 2 and 3 are open to the seawater current and its surface sediment is covered by broken seashells/pebbles and/or dense A. alba pneumatophore roots. Among the environmental (water quality and sediment) parameters tested, except sand, silt and clay, the rest (e.g. temperature, pH, salinity, total organic carbon, etc.) didn't show any strong correlation with the Spawning behaviour of C. rotundicauda. The ongoing physical infrastructure developments on housing and property constructions in the vicinity are likely to pose a threat to the Spawning Ground of C. rotundicauda and thus requires a serious attention for its conservation and management.
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Carcinoscorpius rotundicauda (Latreille, 1802) population status and Spawning behaviour at Pendas coast, Peninsular Malaysia
'Elsevier BV', 2018Co-Authors: Nur Fairuz-fozi, Behara Satyanarayana, Nurul Ashikin Mat Zauki, Aidy M Muslim, Mohdlokman Husain, Sulong Ibrahim, Bryan Raveen NelsonAbstract:The present study evaluates impacts from seasonal monsoons and lunar phases on the Spawning activity of the mangrove horseshoe crab, Carcinoscorpius rotundicauda at Pendas (Sites 1–3) in State Johor, Peninsular Malaysia. The biological (no. of crabs and nests/eggs) observations indicated that Pendas is an active Spawning Ground for C. rotundicauda throughout the year. Higher egg yield was observed for Southwest monsoon (2918 eggs in 55 nests), followed by Northeast (2331 eggs in 48 nests) and Inter-monsoon (1253 eggs in 20 nests) periods. In all seasons, the full moon conditions favoured more number of eggs than to the new moon. Besides the availability of adult crabs in all three sampling sites, the Spawning took place only at Site-1 due to its location (mini sandbar) being sheltered away from the impact of Johor Strait waters, underGround (domestic) discharge point and pioneer mangroves like Sonneratia and Avicennia spp. nearby. In contrast, Sites 2 and 3 are open to the seawater current and its surface sediment is covered by broken seashells/pebbles and/or dense A. alba pneumatophore roots. Among the environmental (water quality and sediment) parameters tested, except sand, silt and clay, the rest (e.g. temperature, pH, salinity, total organic carbon, etc.) didn't show any strong correlation with the Spawning behaviour of C. rotundicauda. The ongoing physical infrastructure developments on housing and property constructions in the vicinity are likely to pose a threat to the Spawning Ground of C. rotundicauda and thus requires a serious attention for its conservation and management. Keywords: Mangrove horseshoe crab, Spawning ecology, Seasonal impact, Local topography, Johor strait, Malaysi
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the final Spawning Ground of tachypleus gigas muller 1785 on the east peninsular malaysia is at risk a call for action
PeerJ, 2016Co-Authors: Bryan Raveen Nelson, Behara Satyanarayana, Julia Hwei Zhong Moh, Mhd Ikhwanuddin, Anil Chatterji, Faizah ShaharomAbstract:Tanjung Selongor and Pantai Balok (State Pahang) are the only two places known for Spawning activity of the Malaysian horseshoe crab - Tachypleus gigas (Muller, 1785) on the east coast of Peninsular Malaysia. While the former beach has been disturbed by several anthropogenic activities that ultimately brought an end to the Spawning activity of T. gigas, the status of the latter remains uncertain. In the present study, the Spawning behavior of T. gigas at Pantai Balok (Sites I-III) was observed over a period of thirty six months, in three phases, between 2009 and 2013. Every year, the crab's nesting activity was found to be high during Southwest monsoon (May-September) followed by Northeast (November-March) and Inter monsoon (April and October) periods. In the meantime, the number of female T. gigas in 2009-2010 (Phase-1) was higher (38 crabs) than in 2010-2011 (Phase-2: 7 crabs) and 2012-2013 (Phase-3: 9 crabs) for which both increased overexploitation (for edible and fishmeal preparations) as well as anthropogenic disturbances in the vicinity (sand mining since 2009, land reclamation for wave breaker/parking lot constructions in 2011 and fishing jetty construction in 2013) are responsible. In this context, the physical infrastructure developments have altered the sediment close to nesting sites to be dominated by fine sand (2.5Xφ ) with moderately-well sorted (0.6-0.7σφ), very-coarse skewed (-2.4SKφ), and extremely leptokurtic (12.6Kφ) properties. Also, increased concentrations of Cadmium (from 4.2 to 13.6 mg kg(-1)) and Selenium (from 11.5 to 23.3 mg kg(-1)) in the sediment, and Sulphide (from 21 to 28 µg l(-1)) in the water were observed. In relation to the monsoonal changes affecting sheltered beach topography and sediment flux, the Spawning crabs have shown a seasonal nest shifting behaviour in-between Sites I-III during 2009-2011. However, in 2012-2013, the crabs were mostly restricted to the areas (i.e., Sites I and II) with high oxygen (5.5-8.0 mg l(-1)) and moisture depth (6.2-10.2 cm). In view of the sustained anthropogenic pressure on the coastal habitats on one hand and decreasing horseshoe crabs population on the other, it is crucial to implement both conservation and management measures for T. gigas at Pantai Balok. Failing that may lead to the loss of this final Spawning Ground on the east coast of P. Malaysia.
Tim L O Davis - One of the best experts on this subject based on the ideXlab platform.
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RESEARCH ARTICLE Spawning Dynamics and Size Related Trends in Reproductive Parameters of Southern
2016Co-Authors: Bluefin Tuna, Jessica H Farley, Tim L O Davis, Retno Andamari, Thunnus Maccoyii, Mark V. Bravington, R. DaviesAbstract:Knowledge of Spawning behaviour and fecundity of fish is important for estimating the repro-ductive potential of a stock and for constructing appropriate statistical models for assessing sustainable catch levels. Estimates of length-based reproductive parameters are particular-ly important for determining potential annual fecundity as a function of fish size, but they are often difficult to estimate reliably. Here we provide new information on the reproductive dynamics of southern bluefin tuna (SBT) Thunnus maccoyii through the analysis of fish size and ovary histology collected on the Spawning Ground in 1993–1995 and 1999–2002. These are used to refine previous parameter estimates of Spawning dynamics and investi-gate size related trends in these parameters. Our results suggest that the small SBT tend to arrive on the Spawning Ground slightly later and depart earlier in the Spawning season rela-tive to large fish. All females were mature and the majority were classed as Spawning capa-ble (actively Spawning or non-Spawning) with a very small proportion classed as regressing. The fraction of females Spawning per day decreased with fish size, but once females start a Spawning episode, they spawned daily irrespective of size. Mean batch fecundity was esti-mated directly at 6.5 million oocytes. Analysis of ovary histology and ovary weight data indicated that relative batch fecundity, and the duration of Spawning and non-Spawning epi-sodes, increased with fish size. These reproductive parameter estimates could be used with estimates of residency time on the Spawning Ground as a function of fish size (if known) and demographic data for the Spawning population to provide a time series of relative annu-al fecundity for SBT
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Spawning dynamics and size related trends in reproductive parameters of southern bluefin tuna thunnus maccoyii
PLOS ONE, 2015Co-Authors: Jessica H Farley, Tim L O Davis, Retno Andamari, Mark V. Bravington, Campbell R DaviesAbstract:Knowledge of Spawning behaviour and fecundity of fish is important for estimating the reproductive potential of a stock and for constructing appropriate statistical models for assessing sustainable catch levels. Estimates of length-based reproductive parameters are particularly important for determining potential annual fecundity as a function of fish size, but they are often difficult to estimate reliably. Here we provide new information on the reproductive dynamics of southern bluefin tuna (SBT) Thunnus maccoyii through the analysis of fish size and ovary histology collected on the Spawning Ground in 1993–1995 and 1999–2002. These are used to refine previous parameter estimates of Spawning dynamics and investigate size related trends in these parameters. Our results suggest that the small SBT tend to arrive on the Spawning Ground slightly later and depart earlier in the Spawning season relative to large fish. All females were mature and the majority were classed as Spawning capable (actively Spawning or non-Spawning) with a very small proportion classed as regressing. The fraction of females Spawning per day decreased with fish size, but once females start a Spawning episode, they spawned daily irrespective of size. Mean batch fecundity was estimated directly at 6.5 million oocytes. Analysis of ovary histology and ovary weight data indicated that relative batch fecundity, and the duration of Spawning and non-Spawning episodes, increased with fish size. These reproductive parameter estimates could be used with estimates of residency time on the Spawning Ground as a function of fish size (if known) and demographic data for the Spawning population to provide a time series of relative annual fecundity for SBT.
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demographic structure sex ratio and growth rates of southern bluefin tuna thunnus maccoyii on the Spawning Ground
PLOS ONE, 2014Co-Authors: Jessica H Farley, Paige J Eveson, Tim L O Davis, Retno Andamari, Craig H Proctor, Budi Nugraha, Campbell R DaviesAbstract:The demographics of the southern bluefin tuna (SBT) Thunnus maccoyii Spawning stock were examined through a large-scale monitoring program of the Indonesian longline catch on the Spawning Ground between 1995 and 2012. The size and age structure of the Spawning population has undergone significant changes since monitoring began. There has been a reduction in the relative abundance of larger/older SBT in the catch since the early 2000s, and a corresponding decrease in mean length and age, but there was no evidence of a significant truncation of the age distribution. Pulses of young SBT appear in the catches in the early- and mid-2000s and may be the first evidence of increased recruitment into the Spawning stock since 1995. Fish in these two recruitment pulses were spawned around 1991 and 1997. Size-related variations in sex ratio were also observed with female bias for fish less than 170 cm FL and male bias for fish greater than 170 cm FL. This trend of increasing proportion of males with size above 170 cm FL is likely to be related to sexual dimorphism in growth rates as male length-at-age is greater than that for females after age 10 years. Mean length-at-age of fish aged 8–10 years was greater for both males and females on the Spawning Ground than off the Spawning Ground, suggesting that size may be the dominant factor determining timing of maturation in SBT. In addition to these direct results, the data and samples from this program have been central to the assessment and management of this internationally harvested stock.
-
demographic patterns of southern bluefin tuna thunnus maccoyii as inferred from direct age data
Fisheries Research, 2007Co-Authors: Jessica H Farley, Tim L O Davis, John S Gunn, Naomi P Clear, Ann L PreeceAbstract:Abstract Otolith-based age estimates were obtained for 2769 southern bluefin tuna (SBT) ( Thunnus maccoyii ) caught on feeding Grounds in the southern oceans and their Spawning Ground in the north-east Indian Ocean between 1985 and 1998. Ages ranged from 0 to 41 years, and males were on average larger at age than females after age 6 for fish sampled in the southern oceans. This sexual dimorphism in growth contributed to the sex ratio being biased toward males for length classes ≥170 cm FL. The estimated age composition of catches, derived from age-length keys applied to length frequency data, showed clear differences between fisheries and fishing Grounds that are consistent with seasonal and ontogenetic changes in migration patterns. Specific information that can be gained on the distribution and migration of juveniles from their relative abundance in catches is limited because of unknown targeting or discarding practices on some fishing Grounds. However, the occurrence of 2–4-year-old SBT on opposite sides of the Indian Ocean during the austral summer confirms that juveniles are not restricted to the southern coastal waters of Australia, and that a divergent migration path must exist possibly near the southern west coast of Australia. During the winter months, SBT aged 2–4 years were caught on all fishing Grounds south of the Spawning Ground, confirming that they are capable of extensive migrations. By age 5, SBT were rarely caught north of about 35°S, except in waters adjacent to Australia's west coast where adults were caught migrating to/from the Spawning Ground. The commercial catch of SBT in the southern oceans was dominated by juveniles and sub-adults on most fishing Grounds examined. Off north-east New Zealand, however, the majority of fish caught were of Spawning age (61% were >10-year old) suggesting that the Tasman Sea may form the eastern boundary for juvenile migration. SBT caught on the Spawning Ground ranged in age from 8 to 34 years with the majority being between 15- and 25-years old.