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Reef manta ray (Yards. alfredi) sightings and related hitchhiker types (1987–2019)

Reef manta ray (Yards. alfredi) sightings and related hitchhiker types (1987–2019)

Spatial adaptation from the exposure of the most extremely seem to seen hitchhiker types with Meters. alfredi (adult and you may juvenile E. naucrates) was basically investigated by the mapping the fresh percentage of sightings at every web site (labeled from the web site means) where in actuality the hitchhiker types is introduce (total number out-of sightings where hitchhikers was in fact seen / total number of sightings within webpages) for the ArcGIS ten.eight. One sites having all in all, nine or a lot fewer sightings (213 sites) had been excluded to reduce the brand new prejudice a decreased number of sightings possess towards the data.

Temporary variation regarding the presence away from mature and you can juvenile Age. naucrates which have Meters. alfredi try investigated using month-to-month big date collection. This show provided that point into the top quantity of sightings (2008–2019) to provide a suitable several months where in order to visualise styles (we.elizabeth., seasonality). The monthly final number off sightings have been fixed having questionnaire energy from the calculating the latest indicate month-to-month amount of manta light seen for each questionnaire (month-to-month total manta beam sightings / month-to-month final amount out-of surveys).

Generalised linear blended patterns.

Logistic generalised linear mixed models (GLMM) using R v4.0.0 were used to investigate relationships between the presence of the most frequently observed hitchhiker species (adult and juvenile E. naucrates, G. speciosus, and Lutjanus bohar) with M. alfredi and four explanatory variables: sex with pregnancy status, maturity status, site function (determined by the predominant behaviour observed at the site ), and seasonality (NE or SW Monsoon). Due to the low number of recorded associations between M. alfredi and most of the hitchhiker species, only those with sufficient data were included in the GLMM analysis. The same model was used for Remora remora (the most frequently observed hitchhiker species with M. birostris), but without site function, and sex was classified only Wiccan dating site as male or female as pregnancies were only observed during four sightings. Each GLMM was fitted with a logit link function to the binary response of hitchhiker species presence (1) and absence (0) using the ‘lme4′ R package . Each model contained the manta-ID as a random intercept to account for any temporal autocorrelation arising from individual rays being repeatedly observed . To compare the relative goodness-of-fit, GLMM models without random effects (GLM) were tested. To reliably estimate the parameters, categories of variables with levels observed equal to or less than five times were removed. For example, under the category behavioural activity, the level ‘breaching’ was observed on less than five occasions, so was removed from analysis. The most informative explanatory variables were identified by firstly testing GLMM models with all combinations of explanatory variables. The variance inflation factor (VIF) was used to test models for multicollinearity; the maximum VIF was <1.5. Model performance was assessed using corrected Akaike information criterion (AICc) test statistic using the ‘MuMin' R package , and the DHARMa R package was used to check the model residuals were normally distributed. The highest-ranking models (with the lowest AICc value, S1 Table) for each hitchhiker species were then interpreted in terms of odds ratios (ORs) (the likelihood of the presence of the hitchhiker species in comparison with the reference category). Any models with ?AICc <2 were considered in interpretation of the highest-ranking model . The significance of each explanatory variable was determined by the 95% confidence interval (CI) of OR, whereby a narrower CI indicates a more precise estimation while, in comparison, a wider CI which had a greater uncertainty. A CI that crossed one is considered non-significant. Any ORs with p > 0.05 are not reported.


All in all, 4901 Meters. alfredi had been directly identified [men = 2442 (50%), women = 2459 (50%)] during the a total of 72912 sightings, where 44071 (60%) was basically of women [mature = 25700 (58%), teenager = 18371 (42%)] and you may 28841 (40%) was in fact males [mature = 25968 (90%), subadult = 1443 (5%), juvenile = 1430 (5%)]. All of the sightings happened across 353 web sites, where 95 (27%) was indeed cleanup channels [sightings = 24034 (33%)], 53 (15%) was touring elements [sightings = 129 (0%)], and you can 205 (58%) feeding components [sightings = 48749 (67%)].


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