Reef manta beam (Yards. alfredi) sightings and associated hitchhiker varieties (1987–2019)
Spatial version about presence of the very most frequently seen hitchhiker kinds having M. alfredi (adult and you can teenager E. naucrates) were examined by mapping the new percentage of sightings at each web site (grouped by the webpages means) where the hitchhiker variety is introduce (final amount regarding sightings where hitchhikers was basically noticed / final amount of sightings at webpages) inside the ArcGIS ten.seven. One websites which have a total of 9 otherwise fewer sightings (213 sites) was in fact excluded to minimize the new bias a minimal number of sightings possess to the studies.
Temporal type from the exposure of adult and you may juvenile Elizabeth. naucrates with Yards. alfredi was examined using month-to-month date series. It show provided that time for the most useful quantity of sightings (2008–2019) to include a suitable several months at which so you’re able to visualise trends (we.elizabeth., seasonality). This new monthly final number of sightings was in fact remedied getting survey energy of the figuring the fresh new suggest month-to-month level of manta light seen per questionnaire (monthly total manta beam sightings / monthly total number out of surveys).
Generalised linear blended designs.
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 real Threesome Sites singles dating site review 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 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.
Performance
A maximum of 4901 M. alfredi have been yourself recognized [male = 2442 (50%), lady = 2459 (50%)] during a total of 72912 sightings, where 44071 (60%) was in fact of women [mature = 25700 (58%), teenager = 18371 (42%)] and 28841 (40%) was basically males [adult = 25968 (90%), subadult = 1443 (5%), juvenile = 1430 (5%)]. Every sightings happened round the 353 web sites, from which 95 (27%) was cleanup stations [sightings = 24034 (33%)], 53 (15%) were driving section [sightings = 129 (0%)], and you will 205 (58%) feeding components [sightings = 48749 (67%)].
