Analysis of Tide Data at Dhigurah in Relation to Predicted Tide Data at Male

Abstract

As a tool for planning future whale shark fieldwork and sighting frequency correlations, the MWSRP utilising equipment donated by Valeport Ltd. aimed to conduct a detailed recording of the tidal cycle at Dhigurah island in South Ari atoll, Republic of Maldives and identify any correlation between the observed Dhigurah tides and the predicted tides at Malé, based on HW and LW events as calculated by two methods of prediction (Total Tide and University of Hawaii). Over a period of one month, a Valeport miniTIDE sensor was deployed in Dhigurah harbour to record actual tidal cycle at that location.

Analysis of data collected by the miniTIDE and comparison to the Total Tide & University of Hawaii predictions showed that on average HW & LW times arrived 23 minutes earlier than Malé. The only unusual or anomalous event recorded at Dhigurah was the absence of a second LW event in the 2 days following the three-quarter moon. The University of Hawaii predictions for Malé bear a closer resemblance to actual Dhigurah recordings than Total Tide. Given the low number and magnitude of imprecision’s in the data acquisition in relation to the calculated time offset, it is considered that either source of predictions may be used directly with a great degree of confidence.

Using these findings, the MWSRP intends to explore the numerous empirical hypotheses which exist suggesting that shark sightings are more common at particular states of the tide.  It is hoped that patterns in the MWSRP’s historical encounter database may be identified that may be attributed to this measurable and predictable external factor.