Satellite tagging highlights the importance of productive Mozambican coastal waters to the ecology and conservation of whale sharks
- Published
- Accepted
- Subject Areas
- Aquaculture, Fisheries and Fish Science, Conservation Biology, Ecology, Marine Biology
- Keywords
- Rhincodon typus, Biotelemetry, Movement Ecology, Oceanography, Fishing Pressure
- Copyright
- © 2017 Rohner et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2017. Satellite tagging highlights the importance of productive Mozambican coastal waters to the ecology and conservation of whale sharks. PeerJ Preprints 5:e3029v2 https://doi.org/10.7287/peerj.preprints.3029v2
Abstract
The whale shark Rhincodon typus is an endangered, highly migratory species with a wide, albeit patchy, distribution through tropical oceans. Ten aerial survey flights along the southern Mozambican coast, conducted between 2004–2008, documented a relatively high density of whale sharks along a ~200 km stretch of the Inhambane Province, with a pronounced hotspot adjacent to Praia do Tofo. To examine the residency and movement of whale sharks in coastal areas around Praia do Tofo, where they may be more susceptible to gill net entanglement, we tagged 15 juveniles with SPOT5 satellite tags and tracked them for 2–88 days (mean = 27 days) as they dispersed from this area. Sharks travelled between 10 and 2,737 km (mean = 738 km) at a mean horizontal speed of 28 ± 17.1 SD km day-1. While several individuals left shelf waters and travelled across international boundaries, most sharks stayed in Mozambican coastal waters over the tracking period. We tested for whale shark habitat preferences, using sea surface temperature, chlorophyll-a concentration and water depth as variables, by computing 100 random model tracks for each real shark based on their empirical movement characteristics. Whale sharks spent significantly more time in cooler, shallower water with higher chlorophyll-a concentrations than model sharks, suggesting that feeding in productive coastal waters is an important driver of their movements. To investigate what this coastal habitat choice means for their conservation in Mozambique, we mapped gill nets during two dedicated aerial surveys along the Inhambane coast and counted gill nets in 1,323 boat-based surveys near Praia do Tofo. Our results show that, while whale sharks are capable of long-distance oceanic movements, they can spend a disproportionate amount of time in specific areas, such as along the southern Mozambique coast. The increasing use of large-mesh gill nets in this coastal hotspot for whale sharks is likely to be a threat to regional populations of this iconic species.
Author Comment
The pre-print has been updated following modifications of the initial manuscript based on reviewer comments in the peer reviewed version of this manuscript.
Supplemental Information
Data for MS Rohner et al. PeerJ
Data for MS Rohner et al. PeerJ
Direction and step lengths
Supplementary Figure 1: (a) Frequency of directions and (b) the step length frequency for tagged whale sharks.
Map of real track and its 100 random shark tracks
Supplementary Figure 2. An example of the track for whale shark MZ-241(red) and its 100 random model shark tracks (blue).