Ontogenetic shifts in home range size of a top predatory reef-associated fish (Caranx ignobilis): implications for conservation

Abstract

De ning the home range of vulnerable species is critical for designing effective spatial management strategies. However, animal home ranges often change with ontogeny and quantifying the associated temporal and spatial changes is particularly challenging for mobile marine species. Here, we investigate how the space use of a top predatory reef-associated sh (Caranx ignobilis) scales with body size. We tagged 17 individuals, representing a wide range of sizes (40.5-120 cm fork length (FL)), with acoustic transmitters, and passively tracked them for over 3 years at a tropical island and atoll in the Republic of Seychelles, Western Indian Ocean. We found that a sheltered atoll environment was critical for juvenile sh (< 60 cm FL) that exhibited a shift in home range location and area as they matured into adults. Small (60-100 cm FL) and large (> 100 cm FL) adult sh appeared to favour shallow coral reefs and associated reef drop offs whilst sharing a similar core home range location. Large adult sh, however, utilized a greater diversity of habitat types and had signi cantly (p < 0.05) greater annual dispersal distances (mean = 35.29 km, max = 91.32 km) than small adults (mean = 13.72 km, max = 21.55 km). Additionally, the home range (represented by minimum convex polygons) of large adults (mean = 209.74 km 2) was signi cantly (p < 0.05) larger than that of juveniles (mean = 38.73 km 2) and small adults (77.32 km 2) and there was a signi cant (p = 0.02) relationship between sh length and home range size, with sh length accounting for 32% of the home range size variance. Furthermore, tagged sh took up to 34 months (mean = 18.54) to utilize the full extent of their home range. The habitat shift and expansion in home range size throughout ontogeny exhibited by C. ignobilis in this study should be taken into account when designing effective spatial management plans for the species.

Effects of human footprint and biophysical factors on the body‐size structure of fished marine species

“…The probability of occurrence of large fishes, however, displayed a weaker response to the effect of NTMR protection, a result that can be partly explained by the generally low number of individuals observed in the samples, as well as their potential larger home range size and mobility (Daly et al. 2021 ), which may not be captured adequately by small reserves (Claudet et al. 2010 ; Edgar et al.…”

“…Our assemblage-level model demonstrated that the network of NTMRs around Australia can enhance ecological benefits by boosting the relative abundance of individuals above the MLS across a broad array of species and ecosystem configurations. The probability of occurrence of large fishes, however, displayed a weaker response to the effect of NTMR protection, a result that can be partly explained by the generally low number of individuals observed in the samples, as well as their potential larger home range size and mobility (Daly et al 2021), which may not be captured adequately by small reserves (Claudet et al 2010;Edgar et al 2014). For instance, NTMRs had a strong effect on the probability of occurrence of large-bodied individuals of coral trout (Plectropomus spp.…”

PIT POP! Bursting the bubble on home-range bias with fine-scale PIT telemetry

“…Designing effective methods to observe fish movement is not a trivial task; the underwater world differs immensely from the terrestrial realm, and methods of visual surveillance, identification and tracking come with complex challenges for the fish biologist. Nonetheless, a proper understanding of spatial requirements of fish remains at the forefront of designing, implementing and evaluating effective conservation management strategies (Daly et al 2021).…”

“…Differences between these metrics, and those often described in batchmarking studies, are important; unable to monitor individual fish, batch-marking metrics are often derived from movement distances rather than the area over which a fish ranges. Individual tracking offers many benefits over traditional batch-marking designs; individual fish can be monitored, facilitating attribution of behaviours and spatial patterns to individual characteristics such as fish size, sex or previous locations (Pillans et al 2017;Daly et al 2021). As technology advances and transmitters become smaller and cheaper, more studies are able to implement this design rather than traditional batch-marking approaches .…”