Young-of-the-year (YOY) and juvenile-stage white sharks may use southern California nearshore beach habitats more extensively than previously known, within meters of some of the most heavily used beaches in the world. Such knowledge forms a critical component of species management and conservation plans, in addition to public safety and risk mitigation planning. We used data derived from a combination of satellite tag locations (13 animals over 3 years) and passive acoustic monitoring (34 animals over 8 years) to examine the occurrence, relative abundance, and residency patterns of YOY white sharks in southern California waters. Our results suggest that southern California contains spatiotemporally dynamic centers of primary nursery habitat. Tagged YOY white sharks formed loose aggregations at “hotspot” locations that were interannually variable, where individuals exhibited temporal fidelity, higher levels of residency, and spatially restricted movements, with multiple YOY individuals simultaneously displaying this behavior. While models of biotic and abiotic variables suggested relative abundance of tagged sharks may be predicted by sea surface temperature, salinity and productivity (chlorophyll-A), these predictors were not consistent across all years of the study. Thus, novel approaches that incorporate technologies to derive high resolution environmental data, paired with more comprehensive telemetry datasets are therefore required to better understand the extrinsic factors that drive habitat selection and residency patterns in juvenile white sharks.

Many terrestrial and aquatic taxa are known to form periodic aggregations, whether across life history or solely during specific life stages, that are generally governed by the availability and distribution of resources. Associations between individuals during such aggregation events are considered random and not driven by social attraction or underlying community structure. White sharks (Carcharodon carcharias) have been described as a species that exhibits resource-driven aggregative behaviors across ontogenetic stages and juvenile white sharks are known to form aggregations at specific nursery sites where individuals may remain for extended periods of time in the presence of other individuals. We hypothesized juvenile white sharks form distinct communities during these critical early phases of ontogeny and discuss how a tendency to co-occur across life stages may be seeded by the formation of these communities in early ontogeny. We present results from a series of social network analyses of 86 juvenile white sharks derived from 6 years of passive acoustic telemetry data in southern California, demonstrating the likelihood of association of tagged juvenile white sharks is greater when sharks are of similar size-classes. Individuals in observed networks exhibited behaviors that best approximated fission-fusion dynamics with spatiotemporally unstable group membership. These results provide evidence of possible non-resource driven co-occurrence and community structure in juvenile white sharks during early life stages.

1. Globally, one quarter of shark and ray species are threatened with extinction due to overfishing. Effective conservation and management can facilitate population recoveries. However, these efforts depend on robust data on movement patterns and stock structure, which are lacking for many threatened species, including the Critically Endangered soupfin shark Galeorhinus galeus, a circumglobal coastalpelagic species. 2. Using passive acoustic telemetry, we continuously tracked 34 mature female soupfin sharks, surgically implanted with coded acoustic transmitters, for 7 years via 337 underwater acoustic receivers stationed along the west coast of North America. These sharks and an additional six were also externally fitted with spaghetti identification tags. Our tagging site was a shallow rocky reef off La Jolla (San Diego County), California, USA, where adult females were observed to aggregate every summer. 3. Tagged soupfin sharks were highly migratory along the west coast of North America, between Washington, USA and Baja California Sur, Mexico. However, every 3 years, they returned to waters off La Jolla, California, where they underwent gestation. This is the first conclusive evidence of triennial migration and philopatry ('homeloving') in any animal, which is apparently driven by this species' unusual triennial reproductive cycle. Females of other shark and ray species with triennial reproductive cycles are also likely to exhibit triennial cycles of migration and philopatry. 4. At least six (15%) of our tagged soupfin sharks were killed in commercial gillnets in Mexico. 2 | Journal of Applied Ecology NOSAL et AL. 1 | INTRODUC TI ON Migration, the long-distance movement between distinct habitats for distinct purposes, is widespread among animal taxa (Dingle & Drake, 2007). In long-lived, iteroparous species (i.e. most vertebrates), loop and to-and-fro migrations are most common, involving recurring round-trip journeys between breeding and nonbreeding habitats in response to seasonal changes in the environment (Ramenofsky & Wingfield, 2007). Along these migratory circuits, many animals are philopatric ('home-loving'), returning to previously occupied 'bottleneck sites' for feeding, mating, parturition, molting or staging (Mayr, 1963). Such predictable site fidelity can be used to monitor individual animals via automated tracking and markrecapture methods, to study the long-term patterns of migration within an individual's lifetime. Understanding where, when and why animals move can improve management and conservation, by identifying essential habitat, migratory corridors and bottleneck sites, and enabling more targeted management actions that are flexible in space and time (Allen & Singh, 2016). Migration and other phenological events, such as reproduction, molting and hibernation, usually cycle with a period of 1 year, regulated by endogenous circannual rhythms that are entrained to seasonally varying environmental cues such as photoperiod, temperature and rainfall (Helm et al. 2013; Visser et al. 2010). Circa...

The giant sea bass Stereolepis gigas Ayres 1859 (GSB) is a critically endangered top marine predator in California. Since protection in 1982 and 1994, the population has appeared to increase, and individuals within a growing population may expand their ranges to new habitats to reduce intraspecific competition and increase foraging opportunities. In 2016-2018, two GSB tagged with acoustic transmitters were detected at artificial reefs for periods of up to 3 months during October-March, and one individual travelled 53 km from an offshore island to mainland California in 56 h. Artificial reefs may provide important foraging opportunities for these protected marine predators as they recover from exploitation. K E Y W O R D S acoustic telemetry, artificial reefs, giant sea bass, Stereolepis gigas, VPS, wastewater Giant sea bass Stereolepis gigas Ayres 1859 (GSB) are one of the few top predators resident to California kelp forest and rocky reef commu

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