Postrelease survival, vertical and horizontal movements, and thermal habitats of five species of pelagic sharks in the central Pacific Ocean

From 2001 to 2006, 71 pop-up satellite archival tags (PSATs) were deployed on five species of pelagic shark (blue shark [Prionace glauca]; shortfin mako [Isurus oxyrinchus]; silky shark [Carcharhinus falciformis]; oceanic whitetip shark [C. longimanus]; and bigeye thresher [Alopias superciliosus]) in the central Pacific Ocean to determine species-specific movement patterns and survival rates after release from longline fishing gear. Only a single postrelease mortality could be unequivocally documented: a male blue shark which succumbed seven days after release. Meta-analysis of published reports and the current study (n=78 reporting PSATs) indicated that the summary effect of postrelease mortality for blue sharks was 15% (95% CI, 8.5–25.1%) and suggested that catch-and-release in longline fisheries can be a viable management tool to protect parental biomass in shark populations. Pelagic sharks displayed species-specific depth and temperature ranges, although with significant individual temporal and spatial variability in vertical movement patterns, which were also punctuated by stochastic events (e.g., El Niño-Southern Oscillation). Pelagic species can be separated into three broad groups based on daytime temperature preferences by using the unweighted pair-group method with arithmetic averaging clustering on a Kolmogorov-Smirnov Dmax distance matrix: 1) epipelagic species (silky and oceanic whitetip sharks), which spent >95% of their time at temperatures within 2°C of sea surface temperature; 2) mesopelagic-I species (blue sharks and shortfin makos, which spent 95% of their time at temperatures from 9.7° to 26.9°C and from 9.4° to 25.0°C, respectively; and 3) mesopelagic-II species (bigeye threshers), which spent 95% of their time at temperatures from 6.7° to 21.2°C. Distinct thermal niche partitioning based on body size and latitude was also evident within epipelagic species

Diving into the vertical dimension of elasmobranch movement ecology

Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements

Diving into the vertical dimension of elasmobranch movement ecology

Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements

Diving into the vertical dimension of elasmobranch movement ecology

Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements

Population genetics and zoogeography of australian freshwater golden perch, macquaria ambigua (Richardson 1845) (teleostei: Percichthyidae), and electrophoretic identification of a new species from the lake eyre basin

Populations of golden perch (Macquaria ambigua) were sampled from both sides of the Great Dividing Range (GDR): from the Murray-Darling drainage basin (Murray R., L. Keepit and Condamine R.), the L. Eyre internal drainage basin (Barcoo R. and Diamantina R.), and the internal drainage basin of the Bulloo R.-all to the west of the GDR-and from the Fitzroy drainage basin (Dawson R. and Nogoa R.) east of the GDR. Starch-gel and polyacrylamide electrophoresis of 12 enzyme systems plus two general muscle proteins was used to estimate the genetic variation within and between populations. Of the 18 presumed genetic loci examined, nine were either polymorphic at the P0.99 criterion level or exhibited fixed allelic differences between some of the populations. Within the Murray-Darling drainage basin, there was little indication of heterogeneity. Contingency Χ2 analyses of allelic distributions among drainage basins indicated significant levels of heterogeneity at six variable loci. The isolated L. Eyre population exhibited diagnostic alleles at four loci when compared with the Murray- Darling and Fitzroy populations. The genetic distance of the L. Eyre population (Nei's D=0.23) from these two populations indicates that the L. Eyre golden perch is most probably a previously unrecognized allopatric species. The level of divergence (0 = 0.06) between Fitzroy and Murray-Darling golden perch indicates differentiation at the subspecies level, with no fixed differences observed between these two populations. Finally, golden perch from the Bulloo R. represent either (i) an intermediate evolutionary unit between the presumed ancestral L. Eyre population and the derived Murray-Darling and Fitzroy populations or (ii) a complex hybrid between these populations. Average gene-flow statistics, FST = 0.760 and Nem=0.08, suggest that the populations in each of the four basins can be regarded as separate gene pools that have been isolated for different, and considerable, periods of time

Evidence for cryptic speciation in Australian freshwater eel-tailed catfish, Tandanus tandanus (Teleostei: Plotosidae)

Allopatric populations of Australian freshwater eel-tailed catfish, Tandanus tandanus, were compared morphologically and electrophoretically. Five populations from east of the Great Dividing Range and six from within the Murray-Darling basin, west of the Great Dividing Range, were sampled. An absence of morphological differentiation among all populations was in contrast to electrophoretic evidence in which fixed allelic differences revealed three discrete gene pools: (1) an undescribed species from the Bellinger River; (2) a second undescribed species from the Nymboida River; and (3) the remaining populations that were genetically similar to one another. Mean heterozygosity in all populations ranged from 0.000-0.011

Factors influencing mortality estimates in post-release survival studies

Campana et al. (2009; Mar Ecol Prog Ser 387:241-253) explored the survival Of blue sharks Prionace glauca captured and released from the North Atlantic commercial longline fishery. We think that their comments and comparisons do not accurately reflect a previous survival study of blue sharks in Hawaii (Moyes et al. 2006; Trans Am Fish Soc 135:1389-1397). The differences in mortality between the studies, similar to 5% in the Hawaii-based fishery and similar to 35% in the North Atlantic fishery, were suggested to be due to failure of Moyes et al. (2006) to accurately reflect commercial fishing conditions. Careful examination of the data, however, suggests that the mortality depends on fishery-specific features-hook type, soak time and handling of the bycatch during release-rather than the respective tagging protocols. Survival studies based on pop-up satellite archival tags (PSATs) are cost-prohibitive; alternative (e.g. biochemical) approaches to estimate stress and morbidity are needed to supplant PSAT studies and to increase sample sizes. Standardization of fishing methods and sampling protocol is needed for future survival studies, to reduce experimental bias and improve the cost:benefit relationship