Reef manta beam (Yards. alfredi) sightings and you will related hitchhiker species (1987–2019)

Spatial version on visibility really seem to observed hitchhiker species having M. alfredi (adult and you may teenager Elizabeth. naucrates) was indeed examined by mapping the fresh portion of sightings at each webpages (classified by site means) where in fact the hitchhiker species is establish (final amount of sightings in which hitchhikers had been noticed / final amount from sightings from the website) in ArcGIS ten.seven. People web sites with a total of 9 or fewer sightings (213 sites) were excluded to attenuate this new prejudice a low quantity of sightings might have toward study.

Temporary version throughout the presence of adult and teenager Elizabeth. naucrates that have Yards. alfredi try investigated using month-to-month day series. This show provided that time into the most useful amount of sightings (2008–2019) to include a suitable several months at which so you’re able to visualise trends (we.age., seasonality). This new monthly final number out-of sightings were corrected getting survey energy by calculating the newest suggest month-to-month amount of manta rays observed each questionnaire (month-to-month overall manta beam sightings / month-to-month final amount from studies).

Generalised linear mixed 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 E. naucrates, G. speciosus, and Lutjanus bohar) with M. alfredi and four explanatory variables: sex with pregnancy status https://datingranking.net/thai-dating/, 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 0.05 are not reported.

Efficiency

All in all, 4901 M. alfredi was basically privately understood [men = 2442 (50%), people = 2459 (50%)] during a total of 72912 sightings, at which 44071 (60%) was indeed of females [mature = 25700 (58%), juvenile = 18371 (42%)] and you can 28841 (40%) was people [adult = 25968 (90%), subadult = 1443 (5%), teenager = 1430 (5%)]. All the sightings took place across the 353 sites, from which 95 (27%) was in fact tidy up channels [sightings = 24034 (33%)], 53 (15%) have been cruising elements [sightings = 129 (0%)], and you will 205 (58%) feeding elements [sightings = 48749 (67%)].