Post‐release mortality estimates of loggerhead sea turtles (Caretta caretta) caught in pelagic longline fisheries based on satellite data and hooking location

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Using mixed stock analysis to assess source populations for at‐sea bycaught juvenile and adult loggerhead turtles (Caretta caretta) in the north‐west Atlantic

Assessments of fisheries by‐catch on marine megafauna are important for developing effective management strategies. For sea turtles, impacts may be evident in nesting population trends, but generally only after a lag, as turtles are slow to mature. We examined 850 loggerhead turtle (Caretta caretta) by‐catch samples collected over 14 years throughout the western North Atlantic to identify source nesting populations. We identified proportions of turtles from 19 distinct management units (MUs), using mitochondrial DNA and mixed stock analysis, considering population size. We found a significant split in the distribution of small versus large loggerheads to the north and south of Cape Hatteras, North Carolina (latitude 35°N). North of Cape Hatteras, large turtles came from south‐east Florida (SEFL; 44% ± 15%) and the northern United States (33% ± 16%) MUs, while south of Cape Hatteras, the major contributors were Central East Florida (52% ± 20%) and south‐east Florida (SEFL; 41% ± 20%). Small turtles in the north came from Central East Florida (64% ± 14%), and in the south, south‐east Florida had the highest representation (56% ± 25%). There was little contribution from Mediterranean and Cape Verde populations, indicating low risk from western North Atlantic by‐catch to MUs in the Mediterranean. Understanding where threats may impact source populations is important, particularly for larger size turtles, as these individuals have the highest reproductive value. These findings allow more informed threat assessments to be conducted for loggerhead turtles considering spatial and demographic structure.     

Post‐capture survival of whale sharks encircled in tuna purse‐seine nets: tagging and safe release methods

1. Whale shark, the world's largest fish, is believed to be particularly vulnerable owing to its biological characteristics (slow growth, late maturation, great longevity) and is listed as Vulnerable by IUCN and included in Appendix II of CITES. 2. Whale sharks are occasionally encircled in tropical tuna purse‐seine nets, throughout this global fishery. Although apparent immediate survival rates following encirclement and release have recently been assessed through scientific onboard observer programmes, a more rigorous methodology is still required for studying post‐released survival. 3. This work provides a method for applying pop‐up satellite tags and reports an enhanced release procedure for whale sharks. The first assessment of survival after release from purse‐seine nets involved six whale sharks tagged between May and September 2014 in the eastern tropical Atlantic Ocean. Five tags transmitted data: three popped up as programmed (after 30 days), while two surfaced prematurely (one after 21 and the other after 71 days (programmed to pop off after 30 and 90 days, respectively)) but showed no sign of unusual behaviour. 4. Overall, whale sharks survived at least 21 days (one at least 71 days) after release from purse‐seine nets. These observations based on five large individuals (total length > 8 m), suggest that whale sharks have a good chance of survival when released with the proposed method. 5. Additional tagging in this and other oceans, especially of juveniles which may be more sensitive to encirclement and release operations, is essential to further assess whale shark post‐release survival rates in tuna purse‐seine fisheries. Copyright © 2016 John Wiley & Sons, Ltd.     

Turtles on the edge: movement of loggerhead turtles (Caretta caretta) along oceanic fronts, spanning longline fishing grounds in the central North Pacific, 1997–1998

Nine juvenile loggerhead sea turtles tracked during 1997 and 1998 in the central North Pacific by satellite telemetry all travelled westward, against prevailing currents, along two convergent fronts identified by satellite remotely sensed data on sea surface temperature (SST), chlorophyll and geostrophic currents. These fronts are characterized by gradients in sea surface height that produce an eastward geostrophic current, with gradients in surface chlorophyll and SST. Six of the turtles were associated with a front characterized by 17°C SST, surface chlorophyll of about 0.2 mg m^–3, and eastward geostrophic current of about 4 cm s^–1, while the other three turtles were associated with a front with 20°C SST, surface chlorophyll of about 0.1 mg m^–3, and eastward geostrophic flow of about 7 cm s^–1. These results appear to explain why incidental catch rates of loggerheads in the Hawaii longline fishery are highest when gear is set at 17°C and 20°C, SST. Further, from the seasonal distribution of longline effort relative to these fronts, it appears that the surface longline fishing ground lies largely between these two fronts during the first quarter and well to the south of the 17°C front, but including the 20°C front, in the second quarter. These findings suggest seasonal or area closures of the longline fishery that could be tested to reduce incidental catches of loggerheads. Finally, these results illustrate the insights which can be achieved by combining data on movement of pelagic animals with concurrent remotely sensed environmental data.     

A geostatistical approach for the stock assessment of the edible sea urchin, Paracentrotus lividus, in four coastal zones of Southern and West Sardinia (SW Italy, Mediterranean Sea)

Quantitative surveys of the edible sea urchin, Paracentrotus lividus, were conducted in four fishing zones of Sardinia (Southern Italy, Mediterranean Sea), in Autumn 2007. A total of 120 stations were geo-located along a bathymetric gradient ranging from 0 to 10 m. A geostatistical method was used to evaluate spatial patterns in density and to estimate harvestable stocks. Variographic analyses showed that the isotropic Gaussian and spherical models successfully explained the spatial structure of sea urchin assemblages in these areas. Density maps obtained by punctual kriging showed that sea urchin populations tend to be patchy rather than uniform in their density distribution. A combination of mapping and size categories was used to generate diverse scenarios of harvestable stocks (specimens ≥50 mm in diameter) before the start of the current fishing season. We conclude that the geostatistical approach, which takes into consideration the spatial autocorrelation structure of the populations in small areas, seems to be a good estimator of P. lividus density and biomass and for the assessment of its harvestable stocks, and thus provides an initial step towards a scientific approach to the management of local sea urchin fisheries.     

New records of the distribution and conservation status of the endangered limpet Patella ferruginea in Sardinia (Italy,W Mediterranean)

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Behavioural characteristics of loggerhead turtles (Caretta caretta) in a submerged bag net of a setnet observed in a bycatch simulation and the development of a turtle releasing device

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Long‐term variation in the abundance of Pacific herring (Clupea pallasii) from the Yellow Sea in the western North Pacific and its relation to climate over the past 590 years

A qualitative understanding of the long‐term variation in the population dynamics of Yellow Sea (YS) herring is particularly important for clarifying the evolutionary processes and driving mechanisms of the YS large marine ecosystem. Unfortunately, because of a lack of long‐term, continuous, and simultaneous monitoring data, the specific driving processes and mechanisms of climate effects on the population dynamics of YS herring remain largely unknown. In response to this scientific issue, we preliminarily propose the idea of reconstructing long‐term changes in YS herring abundance over the past 590 years (AD 1417–2004) based on historical documents and attempt to explore the impacts of climate on the population. Our results show that YS herring abundance maintained at a relatively high level from AD 1417 to 1870 (during the Little Ice Age); in contrast, the population declined significantly from AD 1870 to 2004 at different rates. In addition, we also found that there were strong relationships between the population abundance of YS herring and the Pacific decadal oscillation (PDO) and drought/flood cycles. We suggest that the fluctuations in YS herring abundance may be influenced by ocean–climatic circulation shifts throughout the North Pacific, especially the PDO.     

Biological performance of Octopus vulgaris in ‘integrated aquaculture’ models: effect of two potential fresh diets,sex and sexual maturation during the grow‐out phase

Two fresh diets were tested on the biological performance of males and females of Octopus vulgaris under industrial rearing conditions in floating cages. The presence of females could potentially release paralarvae to the natural environment (‘integrated aquaculture’). Octopuses were fed on a single diet of bogue (aquaculture by‐product), and on a mixed diet (60–40% crab‐bogue), in two trials. In Trial 1 (918 ± 125 g), growth was higher in octopuses fed on the mixed diet (1.9–2.0%d^?1) than in those fed on the bogue diet (1.8–1.9%d^?1) irrespective of sex, and mortality was 3% regardless of sex and diet. In Trial 2 (1483 ± 269 g), growth was higher in males fed on the mixed diet (1.8%d^?1) than in males fed on the bogue diet (1.4%d^?1), both higher than females (1.1–1.3%d^?1), and mortality was 22–28% regardless of sex and diet. Best biological performance in trial 1 was related to the lack of functional maturation in females, evidence by the low average gonadosomatic index (2.0–3.6%) in comparison with trial 2 (8.8–11.4%), regardless of diet. No correlations between final weight and sexual maturity indices were found, so the length of the rearing period to maximize biomass increment or to release paralarvae depends on functional maturation in females.     

Fate and legacy of an invasion: extinct and extant populations of the soft‐shell clam (Mya arenaria) in Grays Harbor (Washington)

1. The soft‐shell clam, Mya arenaria, was intentionally introduced to Washington State during the mid‐1870s. Presently, extensive shell deposits cover parts of the intertidal flats of Grays Harbor, an estuarine ecosystem that has received much attention because of its role as nursery ground for Dungeness crab (Cancer magister), a commercially significant species. 2. Preliminary observations revealed that shells in the deposits belonged to clams that were much larger than extant conspecifics. Shell deposits and extant populations have spatially disjoint distributions; few individuals are found living within the deposits. The purpose of our study was to determine the cause of the different size characteristics between extinct and extant clams, when and how the deposits originated, and why the extant population does not prosper in what appears to be prime habitat. 3. We (i) surveyed extant populations and shell deposits, (ii) followed the extant population through periodic sampling over a 3‐year period, (iii) investigated growth and survival in extant and extinct populations, (iv) experimentally manipulated growth conditions, and (v) searched archival sources for information about the origin of the deposits. 4. We conclude that extinct clams grew faster and lived longer, apparently because they occupied the best habitats available. Archival records suggest that the population expanded rapidly during the period around 20 years after its introduction, but was decimated between 1895 and 1897 by a mass‐mortality episode that resulted in the formation of the deposits. The population since then has never rebounded in its prime habitat, in spite of potential settlers being regularly available. 5. Dungeness crab larvae settle preferentially in the shell deposits, where the abundance of 0+ age juveniles is orders of magnitude higher than in the adjacent flats. We hypothesize that predation by juvenile crabs limits clam recruitment. 6. The introduction of Mya to Grays Harbor during the 1870s has had long‐lasting effects, which persist a century after their once large populations were decimated by a mass‐mortality event. Copyright © 2000 John Wiley & Sons, Ltd.     

Substitution effect of Undaria pinnatifida with citrus (Citrus unshiu,Marcovitch) peel by‐product in feed on the growth,body composition and air exposure stressor of juvenile abalone (Haliotis discus,Reeve 1846)

Substitution effect of Undaria pinnatifida with citrus peel by‐product (CPB) on growth, body composition and air exposure stressor of abalone was determined. A total of 1,080 abalone were distributed into 18 net cages. Five formulated diets were prepared in triplicate. The CPB0 diet contained 200 g/kg U. pinnatifida. The 250, 500, 750 and 1,000 g/kg U. pinnatifida were substituted with the equal amount of CPB, referred to as the CPB250, CPB500, CPB750 and CPB1000 diets, respectively. Finally, dry U. pinnatifida was prepared. Abalone were fed for 16 weeks and then subjected to air exposure stressor for 24 hr. The cumulative mortality of abalone was monitored for the following 4 days after 24‐hr air exposure. Survival, weight gain and specific growth rate (SGR) of abalone fed all formulated diets were greater than those of abalone fed the U. pinnatifida. The greatest weight gain and SGR were achieved in abalone fed the CPB500 diet. The chemical composition of the soft body of abalone was not affected by the experimental diets. Higher cumulative mortality was observed in abalone fed the CPB0 and dry U. pinnatifida at 16 hr after 24‐hr air exposure compared to abalone fed all other diets. In conclusion, U. pinnatifida could be completely substituted with CPB in abalone feed.     

Impacts of an inter‐basin water transfer: distribution and abundance of Micronecta poweri (Insecta: Corixidae) in the River Wear,north‐east England

1. Micronecta poweri (Insecta: Corixidae) is potentially sensitive to changes in river flow. A field experiment was designed to assess the impact of an inter‐basin water transfer on the distribution and abundance of M. poweri in the receiving River Wear, north‐east England. 2. The transfer increased river discharge threefold for a period of 1 h; the transfer discharge was then reduced to a rate equivalent to double the receiving flow. Velocity changes were variable: some parts of the river channel were subjected to order of magnitude increases in near‐bed velocity, others suffered no perceptible change. Losses of fine particulate organic material were associated with the areas of greatest velocity increase. 3. Downstream of the transfer outlet, average total M. poweri abundance in replicate samples was reduced by approximately 50% during the transfer. Losses were variable within the 250 m reach monitored, with some areas gaining and some losing animals. Differences could not be explained simply as a function of proximity to the transfer outlet. 4. Results suggest that transfer impacts are location specific, varying greatly even over short (250 m) distances. For flow sensitive taxa, even relatively minor flow changes (increasing discharge to the 50 percentile flow value) may be considered as disturbance events when viewed at the patch or reach scales. 5. Despite the impacts identified for M. poweri, transfers are generally viewed as having a beneficial effect on the conservation of aquatic habitat in the River Wear. They ensure that water abstractions for potable and industrial supply can continue during the summer months without reducing the availability of suitable salmonid habitat. However, there remains a need to assess the possible transfer of biological material from the donor River Tyne to the receiving River Wear. Copyright © 2000 John Wiley & Sons, Ltd.