Abstract
Knowledge of the movement patterns of the lemon shark Negaprion acutidens is poor in contrast to the allopatric N. brevirostis. Using acoustic telemetry, we investigated daily (diel and tidal) and seasonal patterns in residency, fidelity, home range, habitat preference, and migratory patterns along the Ningaloo coast, Australia. Thirty eight adult N. acutidens were monitored for up 6.1 years (mean 2.5 y) with 19 animals detected for more than 3 years and 5 for more than 5 y. Approximately 50% of the tagged animals remained within 10 km of their tagging location for more than 12 months (average core home range of 1.7 km2). Surprisingly, residency of adults was greater than juveniles in this known nursery area. Adults showed a strong preference for lagoon habitats and moved into shallow nearshore habitats at high tide and at night. During winter months, female sharks shifted their core home range 0.45 km further offshore into deeper lagoon areas, a shift which is likely due to behavioral thermoregulation. Space use by males and females within core areas was asynchronous indicating sexual segregation by resident sharks. Both resident and non-resident sharks were detected up to 140 km away. These highly directional (southerly) and rapid movements (140 km in 2 days) were largely correlated with the parturition and mating periods with males departing 1–2 months earlier than females. In females, periodicity of migrations was variable with evidence of annual and biannual patterns. Negaprion acutidens are highly susceptible to over-fishing and movement data are essential to quantify spatio-temporal overlap with fisheries and assist with developing spatially explicit stock assessment models.
Highlights
In order to mitigate anthropogenic impacts such as habitat modification or loss, fishing and long term changes to climate, we need to understand how animals use available space and how much space they require
The exception was the analysis of long-distance movements to the southern site groups (Point Cloates and Coral Bay); false detections would have been very rare at these locations, where 0.02 and 0.1% of detections were within 10 seconds of the previous detection respectively
Long-term (6 years) data from acoustic tagging revealed tidally influenced short term movements, regular seasonal shifts in the location of home ranges most likely related to temperature and regular seasonal patterns in long distance movements probably related to reproduction
Summary
In order to mitigate anthropogenic impacts such as habitat modification or loss, fishing and long term changes to climate, we need to understand how animals use available space and how much space they require. Data on how environmental factors such as tide (Pillans et al, 2009; Lyon et al, 2017), temperature (Bestley et al, 2013; Kessell et al, 2014), salinity (Pillans et al, 2020) as well biological factors such as food availability (Sims et al, 2006) and mating and reproduction (Mourier et al, 2013; Chapman et al, 2015; Heupel and Simpfendorfer, 2015) are required to understand how management can be tailored to maximize effectiveness It is well-established that the proportion of the population offered highest levels of protections is positively correlated with size of spatial closures and inversely correlated with species mobility (Kramer and Chapman, 1999; Gerber et al, 2002; Heupel and Simpfendorfer, 2005). Less is known about interindividual variation, especially for species which exhibit multiple types of movement patterns such as partial migration (Jonsson and Jonsson, 1993) and residence versus nomadism which will influence how much time is spent outside of the core area or protected area (Martin et al, 2007; Reyier et al, 2014; Runge et al, 2014)
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