Time-dependent instantaneous mortality rates from multiple tagging experiments with exact times of release and recovery

Instantaneous natural mortality rates and a nonparametric hunting mortality function are estimated from a multiple-year tagging experiment with arbitrary, time-dependent fishing or hunting mortality. Our theory allows animals to be tagged over a range of times in each year, and to take time to mix into the population. Animals are recovered by hunting or fishing, and death events from natural causes occur but are not observed. We combine a long-standing approach based on yearly totals, described by Brownie et al. (1985, Statistical Inference from Band Recovery Data: A Handbook, Second edition, United States Fish and Wildlife Service, Washington, Resource Publication, 156), with an exact-time-of-recovery approach originated by Hearn, Sandland and Hampton (1987, Journal du Conseil International pour l'Exploration de la Mer, 43, 107-117), who modeled times at liberty without regard to time of tagging. Our model allows for exact times of release and recovery, incomplete reporting of recoveries, and potential tag shedding. We apply our methods to data on the heavily exploited southern bluefin tuna (Thunnus maccoyii).

A field investigation of a modified intravaginal progesterone releasing device and oestradiol benzoate based ovulation synchronisation protocol designed for fixed-time artificial insemination of Brahman heifers

Pregnancy rates (PR) to fixed-time AI (FTAI) in Brahman heifers were compared after treatment with a traditional oestradiol-based protocol (OPO-8) or a modified protocol (OPO-6) where the duration of intravaginal progesterone releasing device (IPRD) was reduced from 8 to 6 days, and the interval from IPRD removal to oestradiol benzoate (ODB) was increased from 24 to 36 h. Rising 2 yo heifers on Farm A: (n = 238 and n = 215; two consecutive days AI); B (n = 271); and C (n = 393) were allocated to OPO-8 or OPO-6. An IPRD was inserted and 1 mg ODB i.m. on Day 0 for OPO-8 heifers and Day 2 for OPO-6 heifers. On Day 8, the IPRD was removed and 500 μg cloprostenol i.m. At 24 h, for OPO-8 heifers, and 36 h, for OPO-6 heifers, post IPRD removal all heifers received 1 mg ODB i.m. FTAI was conducted at 54 and 72 h post IPRD removal for OPO-8 and OPO-6 heifers. At Farm A, OPO-6 heifers, AI on the second day, the PR was 52.4 to FTAI (P = 0.024) compared to 36.8 for OPO-8 heifers. However, no differences were found between OPO-8 and OPO-6 protocols at Farm A (first day of AI) (39.9 vs. 35.7), or Farms B (26.2 vs. 35.4) and C (43.2 vs. 40.3). Presence of a corpus luteum at IPRD insertion affected PR to FTAI (43.9 vs. 28.8; P < 0.001). This study has shown that the modified ovulation synchronisation protocol OPO-6 may be a viable alternative to the OPO-8 protocol for FTAI in B. indicus heifers.

A novel and effective technology for mitigating nitrous oxide emissions from land-applied manures

Land-applied manures produce nitrous oxide (N2O), a greenhouse gas (GHG). Land application can also result in ammonia (NH3) volatilisation, leading to indirect N2O emissions. Here, we summarise a glasshouse investigation into the potential for vermiculite, a clay with a high cation exchange capacity, to decrease N2O emissions from livestock manures (beef, pig, broiler, layer), as well as urea, applied to soils. Our hypothesis is that clays adsorb ammonium, thereby suppressing NH3 volatilisation and slowing N2O emission processes. We previously demonstrated the ability of clays to decrease emissions at the laboratory scale. In this glasshouse work, manure and urea application rates varied between 50 and 150 kg nitrogen (N)/ha. Clay : manure ratios ranged from 1 : 10 to 1 : 1 (dry weight basis). In the 1-year trial, the above-mentioned N sources were incorporated with vermiculite in 1 L pots containing Sodosol and Ferrosol growing a model pasture (Pennisetum clandestinum or kikuyu grass). Gas emissions were measured periodically by placing the pots in gas-tight bags connected to real-time continuous gas analysers. The vermiculite achieved significant (P ≤ 0.05) and substantial decreases in N2O emissions across all N sources (70% on average). We are currently testing the technology at the field scale; which is showing promising emission decreases (~50%) as well as increases (~20%) in dry matter yields. This technology clearly has merit as an effective GHG mitigation strategy, with potential associated agronomic benefits, although it needs to be verified by a cost–benefit analysis.