Predicting feeding success in a migratory predator: integrating telemetry, environment, and modeling techniques

Abstract

Foraging theory predicts that mobile predators should target high profitability areas with plentiful resources and minimize time spent moving between these areas. This has led to a focus in recent literature on the identification of "hotspots" important for migratory marine predators, i.e., regions where predators spend disproportionate amounts of time ostensibly due to high prey abundance; and determination of the environmental features characteristic of such areas. We investigated factors predicting foraging success in southern bluefin tuna (SBT; Thunnus maccoyii), by integrating telemetry-based feeding and movement data (n = 19 fish, length to caudal fork [LCF] = 99 +/- 3 cm) with environmental data over the scale of their annual oceanic migrations during 1998-2000. We used widely available statistical modeling techniques, generalized linear models, and generalized linear mixed models, formulated to represent feeding as a Markov process. The results showed increased feeding and predictability of feeding occurs in the coastal waters of southern Australia, providing some evidence that this area represents a fixed foraging "hotspot" for juvenile tuna during the austral summer. However, in oceanic waters southern bluefin tuna did not fit the common model of migration, but rather showed a pattern of relatively high foraging success throughout their migratory range, especially during periods of continuous travel. Interestingly, foraging "coldspots" (prolonged low-feeding periods) as well as "hotspots" were apparent across individual tracks, predicted most strongly by warm ocean temperatures. These results provide a new perspective on the ecology of large-scale feeding migrations within the context of the heterogeneous ocean environment, where the continuous and opportunistic feeding of generalist predators may be more common, particularly in predatory large pelagic fishes, than is currently documented.

Area-restricted searching by manta rays and their response to spatial scale in lagoon habitats

“…For example, tortuous movement paths are more indicative of patch use, while straighter movements may suggest transiting between habitats (but see Bestley et al 2010). The fractal value (D) of a movement path is a measure of tortuosity and can range from 1 for a straight line to 2 for a path that is so tortuous it completely covers a 2-dimensional plane (Nams 1996, 2005, Doerr & Doerr 2004.…”

“…In some situations, emerging technologies can be used to directly infer specific behaviors (e.g. feeding, Bestley et al 2010), but in the majority of cases we are left with indirectly inferring as much as possible about their behavioral ecology from movement path structure.…”

Post release survival and movement patterns of roosterfish (Nematistius pectoralis) off the Central American coastline

“…The oscillatory behavior typically occurred within relatively confined areas (i.e., 100 to 200 m) of high prey density and proximal to complex topographical features (i.e., reefs and river mouths). Increased vertical activity has been shown to be associated with active foraging in several pelagic fishes (Sepulveda et al, 2004;Bestley et al, 2010;Nakamura et al, 2011), and crepuscular periods have been shown to be consistently important foraging times for many species (Holland et al, 1996). Although this work was not able to verify feeding activity, the observation of tagged roosterfish pursuing prey at the surface in as little as 9 h after release suggests that some of the behaviors recorded in this study are representative of foraging patterns.…”

Foraging strategy switch of a top marine predator according to seasonal resource differences

“…Model selection was made using the likelihood ratio test, based on maximum likelihood (ML). Terms were only retained if they improved the fit (p < 0.05; Zuur et al, 2009;Bestley et al, 2010). In all cases, models were ranked via Akaike Information Criterion (AIC) (Burnham and Anderson, 2002), to ensure the most parsimonious (i.e., lowest AIC value) model was selected.…”

“…Elephant seals are known to feed opportunistically even while in transit to winter forging grounds (Thums et al, 2011). Continuous foraging during transit has previously been reported in several other pelagic predators that feed over extensive regions, including wandering albatross Diomedea exulans (Weimerskirch et al, 2005), leatherback turtles Dermochelys coriacea (Hays et al, 2006), southern bluefin tuna Thunnus maccoyii (Bestley et al, 2010). This foraging strategy allows animals to efficiently locate highly dispersed prey items or isolated patches of prey while still making progress to know areas of higher prey abundance.…”