Reef manta ray (Meters. alfredi) sightings and you may related hitchhiker variety (1987–2019)

Spatial variation on presence really appear to seen hitchhiker kinds that have Yards. alfredi (mature and you can teenager Age. naucrates) were examined because of the mapping brand new percentage of sightings at each website (categorized by the webpages form) where in fact the hitchhiker varieties was introduce (total number away from sightings where hitchhikers have been noticed / total number away from sightings at the site) within the ArcGIS ten.7. People internet which have a total of nine otherwise fewer sightings (213 internet sites) was in fact omitted to reduce the fresh new prejudice a decreased quantity of sightings could have toward studies.

Temporary version regarding presence out of adult and teenager Elizabeth. naucrates with Yards. alfredi try investigated using monthly time show. That it show integrated the period to your best level of sightings (2008–2019) to include a suitable several months from which so you can visualise style (i.age., seasonality). The fresh monthly total number away from sightings had been corrected getting survey effort because of the figuring new imply monthly quantity of manta radiation noticed for every single questionnaire (month-to-month complete manta ray sightings / monthly final amount out of surveys).

Generalised linear mixed activities.

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 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 Rate My Date dating 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.

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All in all, 4901 Yards. alfredi had been in person known [male = 2442 (50%), lady = 2459 (50%)] while in the all in all, 72912 sightings, of which 44071 (60%) was of women [adult = 25700 (58%), teenager = 18371 (42%)] and you may 28841 (40%) were males [adult = 25968 (90%), subadult = 1443 (5%), juvenile = 1430 (5%)]. The sightings taken place all over 353 websites, where 95 (27%) have been clean channels [sightings = 24034 (33%)], 53 (15%) was driving section [sightings = 129 (0%)], and you may 205 (58%) feeding parts [sightings = 48749 (67%)].