Distribution and ontogenetic habitat shifts of reefassociated shark species in the northeastern Caribbean

Understanding how reef-associated sharks utilise coastal reef habitats throughout their ontogeny is essential for their effective management. In this study, we assessed the distribution of sharks in the northern Caribbean Netherlands (Saba, Saba Bank and St Eustatius) and ontogenetic shifts in habitat and depth use of the 2 most observed species: Caribbean reef shark Carcharhinus perezi and nurse shark Ginglymostoma cirratum. We used stereo baited remote underwater video (stereo-BRUV) surveys at 376 sites. A total of 126 shark sightings (6 species) were recorded, with C. perezi (n = 72) and G. cirratum (n = 42) most frequently observed. The probability of recording at least 1 shark per deployment ranged from 0.19 to 0.37 and is comparable with shark occurrences in the small number of other stereo-BRUV studies in the Wider Caribbean Region. Habitat type was the most important factor driving reef-associated shark occurrences, with the highest probability of observing C. perezi and G. cirratum in soft-coral habitat. Additionally, occurrences of C. perezi were significantly influenced by the management zone, with highest probabilities of occurrence in no-fishing zones. Almost all observed reef-associated sharks (95.6%) were juveniles, indicating that the study area may be a nursery area. Overall, both species were observed in deeper waters with increasing size, indicating ontogenetic shifts in depth use. Our findings imply that protected areas should not be limited to a single habitat or depth, but focus on protecting a large area with the range of habitats and depths necessary for reef-associated sharks to complete their life cycle.

Distribution pattern and habitat shifts during ontogeny of the blue swimming crab, Portunus pelagicus (Linnaeus, 1758) (Brachyura, Portunidae)

This study determined the distribution and ontogenetic habitat shifts of Portunus pelagicus in coastal habitats in Thailand. Samples were collected by gill nets and traps, at six study sites during May 2013 and September 2014. It was found that, in the bay, the catches from both gears were significantly influenced by depth ( and ) but not by season (). For offshore, the catch was significantly influenced by season () but not by depth (). The catches of berried females in the bay and in the offshore area were not influenced either by depth, or by season (). In addition, it is proven by this study that a habitat shift during ontogeny occurs as young crabs or small-sized crabs inhabit shallow waters, and migrate to deeper water when they grow larger.