Behavior Webs of Piscivores at Subtropical Live-Bottom Reefs

Abstract

Direct visual and acoustic observations at subtropical reefs off the southeast united states and northeast Gulf of mexico revealed a complex web of behavioral interactions within and between mid-water and demersal guilds of piscivorous fishes. While mixed-species groups of mid-water and demersal piscivores stalked and attacked common prey species independently, facilitative behaviors between mid-water and demersal piscivores were common in each region. in the latter case, prey reduced nearest neighbor distances and retreated toward the seafloor during predatory attacks by mid-water fishes. Demersal fishes subsequently attacked and consumed prey in these ephemeral high density patches. aggregations of fishes in other trophic guilds, unassociated with predation events, modified movements of prey fishes and provided camouflage for piscivores that occurred within and along the periphery of those aggregations. Demersal piscivores often assumed the role of mid-water piscivores when the abundance of mid-water piscivores was low and when demersal piscivores were larger than mid-water species. Young-of-the-year great barracuda, Sphyraena barracuda (edwards, 1771), also assumed this role, generally when other piscivores were absent. such behavioral interactions appear to be common in these communities. if predator-prey relationships are regularly facilitated by these types of mixed-species interactions, such facilitative behaviors may be important in terms of population processes (e.g., yielding increases in prey consumption with resultant increases in growth rate, and fecundity). a framework for testing such predictions provides a pathway for assessing the population consequences of such interactions.

Use of High-Resolution DIDSON Sonar to Quantify Attributes of Predation at Ecologically Relevant Space and Time Scales

“…Such a time period, while long by traditional visual sampling approaches, covers normal day (or night) periods inclusive of crepuscular periods over much of the globe and can capture variability at particular sample sites. The metrics derived from DIDSON imaging support, in general, diver observations related to the range in numbers and sizes of predators, coordinated group behaviors, and patchy prey distribution localized to ledge features (Auster et al, 2009(Auster et al, , 2013.…”

“…Demersal piscivores include black sea bass Centropristis striata, bank sea bass Centropristis ocyurus, scamp Mycteroperca phenax and gag grouper Mycteroperca microlepis. Both groups prey upon highly abundant round scad Decapterus punctatus, mackerel scad Decapterus macarellus, and juvenile tomtate Haemulon aurolineatum (Auster et al, 2009(Auster et al, , 2013.…”

“…A shortage of prey refugia has also been shown to cause short-term density dependent mortality due to predation (Johnson, 2006). If prey use particular seafloor features for refuge, predators may then occur at a higher density around these features (Kracker et al, 2008;Auster et al, 2009Auster et al, , 2011Auster et al, , 2013. Cosner et al (1999) suggests that predation rates are therefore density dependent for both predator and prey as competition between predators increases.…”

“…The importance of intra-and interspecific interactions that facilitate predation, such as herding and confusing prey for other group members to attack or ambush (e.g., Hobson, 1968;Strand, 1988;Parrish, 1993;Auster et al, 2013), is unknown in most ecological settings in the ocean. However, where studies have been conducted, the act of facilitation between predator species (sensu Dill, 2003) appears to be common.…”

“…1997;Safina, 1990;Clua & Grosvalet, 2001;Robinson & Tetley, 2007). Auster et al (2013) observed predation by single and mixed-species groups of piscivores at subtropical reefs off the southeast United States and eastern Gulf of Mexico, where only 11% of 379 predation events involved only a single piscivore. All other events involved facilitation of predation by monospecific and mixed species groups of midwater and demersal predators.…”