WIOMSA-CORDIO spawning book Full Doc 10 oct 13.pdf

anterior of the anus and below the lateral line. The incision was then closed using 2 non-absorbablepolynylon sutures. At the end of the surgical procedure, fish were transferred into a recovery tankand monitored until normal colour and behaviour returned. Fish were released in small groups atthe point of capture within 3 hours after being fished.Data analysesAll data files downloaded from the acoustic receivers were screened for false detections (foreignidentification codes) caused by code collisions (Heupel et al. 2006). Fish that were only detectedwithin the first 6 hours after tagging (n = 4) were excluded from analyses to increase the probabilitythat monitored fish were actively participating in spawning aggregations and not simply transitingthrough the sites at the time of tagging. Residency time was calculated based on the methodsof Ohta & Kakuma (2005) and was defined as the duration that an acoustically tagged fish wascontinuously detected by the acoustic array at one FSA site without day-scale (> 24 h) absences.If total residency time at a single FSA site represented more than 75% of the estimated tag batterylife, the fish was considered to be resident at that site and was subsequently removed from allfurther analyses as it was not possible to distinguish between transient spawning and non-spawningrelated behaviour. FSA site residency times occurring in the month of tagging are termed truncatedsince time of arrival of the fish at the site was unknown. However, both truncated and nontruncatedspawning residency times were used in the calculation of mean residency time at theFSA sites, as results from the plotting of survival curves (not shown) and the Wald statistic of theCox proportional hazards regression model (Cox 1972) showed that the two types of residencytimes were not significantly different from each other (p = 0.29, df = 1). Spawning residency timesare defined as those times that occur, at least partially, within the 7-day spawning aggregationperiod described by Robinson et al. (2011). This period comprises 3 days before the full moon,the day of the full moon and 3 days after the full moon, and accounts for inter-monthly variationin the timing of aggregation formation, duration and dispersal. Fidelity to a single FSA site or useof multiple FSA sites over the spawning aggregation season was based on the detections of taggedfish only within the 7-day spawning aggregation period. Due to the unavoidable constraint ofusing small tags with a maximum battery life less than the known duration of reproductive activity(approximately 10 months), fidelity to FSA sites could only be assessed for the active life of the tag(i.e. 93 days). The temporal dynamics of FSAs were assessed in relation to lunar and diel rhythmiccycles. The start and end of a residency time was taken as the time and day of arrival and departure.Lunar arrivals and departures were assessed in relation to the full moon with -1 and +1 being a daybefore and after the full moon, respectively. Diel arrivals and departures were assessed in relation tothe 24 hour clock with time of arrivals and departures being grouped in 1 hour time bins.ResultsLunar timing of arrivals and departuresPooling data across sites, the 7-day reproductive period accounted for 86.5% of arrivals at thespawning sites (Fig. 2a). The number of arrivals peaked 1 day before the full moon and were alsohigh 2 days before the full moon, on the full moon and 2 days after the full moon. Each of thesedays amounted to more than 10% of arrivals (Fig. 2a).48