The movement patterns of animals examined in the context of their surroundings reveal central aspects of their life history and resource needs. Coral reef fish, in particular, live in highly heterogeneous environments, making diel movements between habitat types in order to balance predation risk, foraging benefits, and competition avoidance [1, 2]. The mosaic of habitats inhabited by a fish comprises their home range, an area regularly utilized for feeding and shelter . Analysis of reef fish movement patterns demonstrates direct connectivity across different habitat types for certain reef fish families , a life history strategy that promotes survival of the individual and influences overall productivity and reef health in visited areas .
Studies using visual surveys have shown that spatial distributions of fish can be predicted by underlying habitat type and condition . This type of assessment is limited, however, in that it is affected by observer presence, usually represents a single time point, and is difficult to link to other environmental variables such as temperature or tidal phase. For general long-term, coarse-scale movement patterns and space utilization analysis, passive acoustic telemetry is a well-suited method , which allows the tracking of many fish continuously over a long period of time [8, 9]. This technology can help identify important parameters of fish ecology and life history such as diel changes in space use [1, 4, 10, 11], habitat association [12, 13], site fidelity , residence time , and seasonal migrations .
Members of the coral-reef-associated fish family Lutjanidae have been shown to have high site fidelity and a relatively small home range [4, 12], so their movements should display a strong association with a small area within their home range. Lutjanid abundance is higher in specific edge habitats, such as areas with abundant patch reefs and large amounts of seagrass [6, 17], presumably because the proximity of usable resources signifies higher-quality habitat than structure alone . Lutjanids and Haemulids have been shown to predictably use multiple habitats within a day, performing diel movements between coral reefs, where they shelter during the day, and seagrasses, where they forage at night [1, 4, 19]. Therefore, an individual’s home range would be expected to contain a large proportion of each of these habitats, with daytime and nighttime activity spaces dominated by coral reef and seagrass habitats, respectively.
Mutton snapper, Lutjanus analis (Cuvier, 1828), are economically important to Caribbean fishers that target nearshore reef fish. In the northern US Virgin Islands, this species comprised an average of 18% by weight of commercial snapper landings between 2011 and 2017 (USVI Department of Planning and Natural Resources, unpublished data). The species is classified as “Near Threatened” by the International Union for Conservation of Nature due to trends of decreasing estimated population sizes throughout its range . This is due, at least in part, to their reproductive strategy of aggregating at predictable times and locations in large groups for spawning. These transient fish spawning aggregations occur after the full moon in March through July, during which the species is highly vulnerable to fishing [21, 22]. When not aggregating, individuals are solitary and territorial , and are found in a wide variety of habitats. This species undergoes ontogenetic shifts in primary habitat association, with juveniles being found mainly in nearshore seagrass beds and adults in coastal or offshore habitats over hard substrate . In the Dry Tortugas, Florida, adults are usually observed over hard bottom, swimming actively along reef edges , and are also often observed in these locations in St. Thomas (S. L. Heidmann, pers. obs.).
L. analis are generalist predators, opportunistically feeding mainly on arthropods such as crabs and shrimp, gastropods, and reef fish , with individual variability in foraging style to reduce intraspecific competition . It has been shown that L. analis have temporal diet variations based on prey availability [27, 28], and therefore the species is ecologically important for top-down control over prey populations. This species is known to be more mobile than some comparably sized benthic-associated grouper species, but retain high site fidelity .
With size-at-maturity estimates ranging from 28.0 cm to 52.0 cm [28, 29, 30], L. analis are likely to utilize a larger home range size than well-studied smaller species of snapper because of associated increased mobility and resource needs [31, 32], but previous studies of this species have been limited in acoustic receiver array continuity. A long-term tracking study by Farmer and Ault  obtained location data from a single mutton snapper for 168 days and estimated its home range size at 7.64 km2, but this estimate included two long-distance presumed spawning migrations which were unrepresentative of routine movements. Another study by Feeley et al.  identified home range areas, excluding observed spawning migrations, for 13 resident L. analis at a mean size of 2.5 km2. Both these studies had non-overlapping array coverage over a large area, which may inflate home range estimates. Additionally, these studies contained only a cursory description of home range characteristics and finer-scale movements, which are not currently well-understood in this species.
To quantitatively describe L. analis movement patterns, this study used passive acoustic telemetry and spatial analysis tools on an individual level to 1) determine home range characteristics and degree of site fidelity and 2) examine diel, daily, and seasonal changes in space use. Based on characteristics of other snapper species, we hypothesized that L. analis display high site fidelity to a home range that is smaller than previous estimates, and that each has a nighttime activity space comprising seagrass beds in which they forage, which is larger than and separate from a coral-reef-dominated daytime activity space.